New technologies or innovative treatment lines for reliable water treatment for P&P and minimization of waste production ppt

AquaFit4Use is co-financed by the European Union’s 7
th
Framework Programme




The project for sustainable water
use in chemical, paper, textile and
food industries














New technologies or innovative treatment lines for
reliable water treatment for P&P and minimization of
waste production

Authors : S. Mauchauffée, M P. Denieul (VEO)
B. Simstich, J. Rumpel, H. Jung, P. Hiermeier, G. Weinberger,
D. Pauly, S. Bierbaum, H J. Öller, C. Hentschke (PTS)
M. Engelhart, J.v. Düffel, M. Wozniak (ENV)
D. Hermosilla, N. Merayo, R. Ordoñez, L. Blanco, H. Barndok, L.
Cortijo, P. López, J. Tijero, C. Negro, A. Blanco (UCM)
A. Rodriguez (HOL)
M. Bromen, J. Vogt, J. Mielcke, (WED)

January 2012




New technologies or innovative treatment lines for reliable water treatment for
P&P and minimization of waste production
VEO,PTS, ENV, UCM, HOL, WED, January 2012


Page | 2

Executive summary

This report is a result of the project AquaFit4Use, a large-scale European research project co-
financed by the 7
th
framework program of the European Union on water treatment technologies
and processes.

In the Pulp&Paper industry a lot of effort is put into to water saving and closing water circuits, also

reducing substantially the environmental impact, both by process modelling and Kidney
technologies as internal process water treatment. However a number of problems around the
removal of substances are not solved yet and further closing of the water cycle causes other
problems. Challenges for water re-use in the Pulp&Paper industry are the following:
- The elimination of residual (soluble) COD and BOD which can both affect the production
process and the paper quality;
- The removal of sticky solids and suspended solids, which can induce plugging of pipes
and showers, deposit formation, abrasion, loss of tensile strength;
- The treatment of concentrate streams containing calcium, sulphate, chloride and organics
which can lead to salt accumulation in case of water loop closure, corrosion, scaling of
pipes and showers in the paper production process. The removal of calcium carbonate is
crucial in the last case.
Therefore there is a need to find new and reliable (combinations of) technologies to solve this
challenges to achieve the water quality target for water re-use and which are tailored to suit
product demands and standards.
The work described in this report concerned the laboratory and preliminary work for the
implementation of pilot trials on two industrial paper mills. The emphasis was on different
technologies as part of a global treatment line to solve the above challenges.

On the basis of waste water characterization and the defined water quality requirements for paper
mills, new treatment lines were defined to reach the water quality target including effectiveness,
reliability and minimization in waste and concentrate production. These new treatment lines are
focused on internal recycling.
The emphasis was on different key steps of the global treatment train:
- Biological treatment: anaerobic processes and MBR;
- Filtration processes: 3FM high speed technology and nanofiltration;
- Tertiary treatments to reduce hard COD: AOPs, coagulation/precipitation;
- Integration of processes (evapoconcentration, electrodialysis and softening) in the
treatment line:
o To treat the concentrate streams containing calcium, sulphate, chloride, organics;

o To minimize the waste production and enhance internal recycling.

Technologies were tested at lab scale on the waste waters from 3 different paper mills:
• Paper mill 1 (PM1), producing corrugated board and board;
• Paper mill 2 (PM2), producing high quality coated and uncoated board from recycled
paper;
• Paper mill 3 (PM3), producing standard newsprint, improved newsprint (higher brightness)
and light weight coated paper (for magazines).

On basis of the obtained results, the best treatment combinations to be implemented and tested
at pilot scale within WP5.1.4 were selected as summarized below for each type of paper mill:


New technologies or innovative treatment lines for reliable water treatment for
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VEO,PTS, ENV, UCM, HOL, WED, January 2012


Page | 3

a) Corrugated board paper mills (PM1 and PM2)
Most important findings are:
• Stable MBR operation is not possible at calcium concentrations > 400 mg/l due to scaling
problems. Softening upstream of the MBR is than absolutely necessary. Trials with a lime
softening stage showed a removal of 50 – 80 % of the Ca
2+
concentration in the feed
(600 – 1000 mg/l).
• Ozone trials with pre-filtered final effluent of both mills led to a COD reduction by about 20-
25%. Economical viable specific ozone dosages of 0.25 to 0.7 g O

3
/g COD
0
have been
used. Overall it is more costly and complex to achieve COD levels below ~50 mg/l. The
increased BOD
5
shows that a subsequent biological treatment can be promising for further
COD reduction. The water can be reused in the production process, especially because
the water after ozone treatment is visibly colour-free. Possible reuse processes are
showers at the paper machine were it can be used instead of fresh water. Calcium
concentrations may be a limiting factor for reuse.
• NF membranes with high retention capacity for monovalent ions (Dow Filmtec NF 90 and
Koch TFC ULP) are able to fulfil quality requirements for white grade paper reclamation
water (for PM1 and PM2).
• Intensive pre-treatment or conditioning is needed to obtain steady NF membrane
performance and high recovery rates due to the high scaling tendency (membrane
blocking) of aerobic effluents of both PMs. Reduction of pH to around pH 6.5 (HCl) and
dosing of anti-scalant was necessary to achieve recovery rates of 80%. Softening of
wastewater allowed higher recovery up to 93% and lower chemical consumption for
conditioning (no-use of hydrochloric acid).
In this view, the Multiflo
TM
softening technology (lime softening) is well adapted to remove
calcium carbonate.
Long term stability of membrane treatment (plateau formation, high system recovery)
needs to be evaluated on pilot scale continuously.
• 3FM technology showed good performances at lab scale regarding TSS removal and
turbidity reduction. These have to be confirmed at pilot scale.

Most important findings concerning the treatment of concentrates of PM1 and PM2 are:
• Evapoconcentration proved to be an adapted technology to treat NF concentrates in terms
of production of a colourless water with a quality fulfilling the water quality criteria of both
paper mills for re-use and to reduce the final volume of concentrates:
o Reduction of wastes as a global volumic concentration factor VCF up to 50 for
combined “NF+evapoconcentration” could be obtained at lab scale for PM2 and 25
for PM1.
These global VCFs should be increased at industrial scale to 60 without NF
membrane pre-treatment and up to 250 with 3FM/softening as pre-treatment
provided conversion rate on NF process and pre-treatment processes are the
same at pilot scale. Then the addition of evapoconcentration would lead to a final
concentrate to be disposed off representing respectively 1.7% to 0.4% in the last
case in volume of the waste water treated by the global treatment line.
o Pre-treatments before NF process have a positive impact on the global VCF which
could be reached at industrial scale leading to a very substantial reduction of the
volume of final waste to be disposed off down to 0.4% in the case of 3FM
combined with softening as pre-treatment.

New technologies or innovative treatment lines for reliable water treatment for
P&P and minimization of waste production
VEO,PTS, ENV, UCM, HOL, WED, January 2012


Page | 4

• AOP treatment: High conductivity and chloride concentrations > 4,000 mg/l prevented
biological degradation after AOP treatment. To reduce chloride intake to the wastewater,
softening before membrane processes is preferable to acidification with HCl.
• Re-injection of NF concentrates has a negative impact on anaerobic degradation rate in
pellet sludge reactors.

Based on these results, following treatment trains have been selected to be tested on site at pilot
scale within WP5.1.4:

Impact of reinjection???
Water to be
re-used ?
Final waste
Water to be
re-used ?
Water to be
re-used ?
NF
PM2 Anaerobic
Multiflo
softening
AOP (O
3
)
AOP (O
3
)
Evapo
MBR
Water to be
re-used ?
Can be
recycled into
Anaerobic ???
Final waste

Water to be
re-used ?
NF
PM2 Anaerobic Aerobic
AOP (O
3
)
AOP (O
3
)
Evapo
3FM
Multiflo
softening
Water to be
re-used ?
Impact of reinjection???
Water to be
re-used ?
Final waste
Water to be
re-used ?
Water to be
re-used ?
NFNFNF
PM2PM2 AnaerobicAnaerobic
Multiflo
softening
Multiflo
softening

AOP (O
3
)AOP (O
3
)
AOP (O
3
)AOP (O
3
)
EvapoEvapo
MBRMBR
Water to be
re-used ?
Can be
recycled into
Anaerobic ???
Final waste
Water to be
re-used ?
NFNF
PM2PM2 AnaerobicAnaerobic AerobicAerobic
AOP (O
3
)
AOP (O
3
)AOP (O
3
)

EvapoEvapo
3FM3FM
Multiflo
softening
Multiflo
softening
Water to be
re-used ?



b) Newsprint paper mill (PM3)
Most important findings derived from PM3 effluent treatment are:
• Although AOP treatments are efficient for bio-recalcitrant organics removal, due to the
high amount of volatile fatty acids that are difficult to oxidize and consume high amounts of
OH·, in the effluent of PM3 a previous biological treatment is expected to be more reliable.
Despite this, colour removal was higher than 95% and COD removals vary between 20 to
40%. In addition, AOPs processes improve biodegradability of the treated effluent.
• Anaerobic pre-treatment showed very good performance treating a low organic load
wastewater as the effluent of a 100% recycled NP/LWC paper mill, and assisting the
aerobic stage on removing organics and sulphates; besides it produced enough biogas for
being considered as cost-effective.
• The biological treatments studied in the two pilot plants achieved a final COD, BOD
5
and
sulphates removal of 80-85%, 95-99% and 25-35%, respectively. Wastewater quality after
biological treatment resulted suitable to further perform a posterior membrane treatment

New technologies or innovative treatment lines for reliable water treatment for
P&P and minimization of waste production

VEO,PTS, ENV, UCM, HOL, WED, January 2012


Page | 5

• Membrane treatment by UF + RO is able to generate permeates of high water quality,
fulfilling all the requirements for being used in critical points of the paper machine that
require a very high water quality.
• 3FM filtration followed by acidification seemed to have a positive effect on membrane
treatment. A higher recovery rate was obtained and permeate with a very good quality was
obtained. These results would have to be confirmed at pilot scale as the RO process was
performed on a membrane test cell.
Most important findings derived from the application of evapoconcentration, coagulation /
softening / flocculation treatment and AOPs to the treatment of RO concentrates from PM3 are:
• Evapoconcentration proved to be an adapted technology to treat membrane concentrates
of both tested treatment trains (Anaerobic  Aerobic  3FM  RO and Anaerobic 
MBR  RO). In both cases the produced water (final VCF = 11.5-11.7) has a very good
quality respecting all PM3 requirements for re-use as fresh water.
Considering the VCF of the RO step, the addition of evapoconcentration would then lead
to a final waste to be disposed off representing respectively 2.8% and 7% in volume of the
waste water treated by the global treatment line.
• Coagulation eliminated more than 95% of coloured compounds with a high level of
resonance (A
500
), however, high coagulant doses were needed, making the process
economically unfeasible. Besides, PACl addition by itself increases conductivity.
• Lime-softening was a good alternative to reduce conductivity. Organic matter was
adsorbed on Mg(OH)
2
and CaCO

3
surface and, thus, additionally removed in the
precipitation process.
• Coagulating water with 2500 mg/L of PACl1 in the presence of lime and a PAM produces a
60% COD removal, independently of the pH and the dosage.
• Fenton and photo-Fenton processes were optimised by response surface methodology.
Low pH and high [H
2
O
2
] were optimum conditions for both methods. Low ferrous ion
concentration might achieve good COD removals with photo-Fenton process and Fenton
process need higher ferrous ion concentrations. More than 50% of COD removal may be
obtained at neutral pH.
• AOPs led to a high removal of COD at laboratory scale. Photo-Fenton obtained the best
COD removal (99%) followed by Fenton (90%) processes in comparison to the 40%
achieved by ozone processes.
• Photocatalysis at laboratory scale did not obtain so high COD and TOC removals from RO
reject, but the combination of photocatalysis treatment (10 g/L of TiO
2
) with biological
treatments got a total removal of COD from the wastewater.

Based on these results, following treatment trains have been selected to be tested on site at pilot
scale within WP5.1.4 in PM3:


New technologies or innovative treatment lines for reliable water treatment for
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VEO,PTS, ENV, UCM, HOL, WED, January 2012

Page | 6


SCREENER LAMELLA
C LARIFIER
PRE-ACIDIF ICATION
TANK
AN AEROBIC
REA CTOR
AEROBIC
REACT OR
LAMELLA
C LARIFIER
U LTRAF ILTRATION REVERSE
OSMOSIS
Sludge
Biogas
Nutrients
Backwash
NaOH/HCl
Permeate
Wastewater
from DAFs

Pilot plant 1.


SCREENER

ANAEROBIC
REACTOR
REVERS E OSMOSIS
Purge 

 Sludge
Biogas
Nutrients
Permeate
NaOH/HCl
Permeate
MEMBRANE BI OREACTO R
Purge
Wastewater
from DAFs
Antiscalant
Backwash
CONDITIONING
TANK

Pilot plant 2.



Important note: This final deliverable is a compilation of all lab scale results performed within
WP3.1, which have been reported in details in following internal results:
• I3.1.1.1 Proof of concept of aerobic water treatment technologies and separation
techniques on bench scale for Pulp & Paper
• I3.1.1.2 Proof of concept of anaerobic water treatment technologies and MBR techniques
on bench scale for Pulp & Paper

• I3.1.1.3 Assessment of technologies for the treatment of membrane retentate streams for
Pulp & Paper
• I3.1.1.4 Assessment of technologies for the elimination of inorganic compounds for Pulp &
Paper




New technologies or innovative treatment lines for reliable water treatment for
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Page | 7

Content

EXECUTIVE SUMMARY 2
CONTENT 7
1 INTRODUCTION 9
1.1

S
TATE OF THE ART
9

1.1.1

Waste water treatment in Paper industry (Jung and Pauly, 2011) 9

1.1.2

State-of-the-art of tested technologies within the study 14

1.2

O
BJECTIVES
35

2 METHODS 36
2.1

M
ETHODS
36

2.1.1

Paper mill 1 (PM1) 37

2.1.2

Paper mill 2 (PM2) 39

2.1.3

Paper mill 3 (PM3) 41

2.2

M
ATERIALS AND EQUIPMENT
43

2.2.1

MBR processes 43

2.2.2

3FM technology 44

2.2.3

Membrane technologies (UF, NF, RO) 46

2.2.4

AOP technologies 47

2.2.5

Evapoconcentration 50

2.2.6

Electrodialysis 51

2.2.7

Softening and controlled precipitation technologies 52

2.2.8

Biodegradability experiments (PM1, PM2 and PM3) 52

3 RESULTS AND ACHIEVEMENTS 55
3.1

M
AJOR RESULTS AND ACHIEVEMENTS
55

3.1.1

Corrugated paper mill (PM1 and PM2) 55

3.1.2

News print paper mill (PM3) 58

3.2

T
ECHNICAL PROGRESS OF THE WORK
60

3.2.1

Corrugated paper mill (PM1 and PM2) 60

3.2.2

Newsprint paper mill (PM3) 86

4 CONCLUSIONS 116
4.1

M
AJOR ACHIEVEMENTS
116

4.1.1

Corrugated board paper mills (PM1 and PM2) 116

4.1.2

Newsprint paper mill (PM3) 117

4.2

F
UTURE WORK
119

4.2.1

Within AquaFit4Use 119

4.2.2

General recommendations 120

5 LITERATURE 121
6 ANNEX 128
6.1

A
NNEX ON EVAPOCONCENTRATION
128

6.2

D
ETAILED RESULTS ON
PM1 129

6.3

D
ETAILED RESULTS ON
PM2 130

6.4

D
ETAILED RESULTS ON
PM3 132

6.5

3FM
FILTRATION TESTS ON
PM1
AND
PM2
ANAEROBIC EFFLUENT
133

6.6

NF90
APPLIED TO
3FM
FILTRATE OF
PM2

(O
SMONIC FILTRATION CELL
) 135


New technologies or innovative treatment lines for reliable water treatment for
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6.7

S
OFTENING TESTS ON
PM2
WASTE WATER
137

6.7.1

Softening on Aerobic effluent 137

6.7.2

Multiflo
TM
Softening on 3FM filtrate 138

6.8

E
VAPOCONCENTRATION APPLIED TO
NF
CONCENTRATES FROM
PM1
AND
PM2 139

6.9

E
LECTRODIALYSIS ON
RO
CONCENTRATES FROM
PM2
AND
PM3 140

6.10

3FM
FILTRATION APPLIED TO
PM3
ANAEROBIC
/
AEROBIC EFFLUENT
141

6.11

NF/RO
SCREENING ON
3FM
FILTRATE FROM
PM3

(O
SMONIC FILTRATION CELL
) 142

6.12

E
VAPOCONCENTRATION ON
RO
CONCENTRATES FROM
PM3 144

6.12.1

RO concentrates from “PM3 waste water

Anaerobic

Aerobic

3FM

RO” 144

6.12.2

RO concentrates from “PM3 waste water

Anaerobic

MBR

RO” 145

6.13

C
OAGULATION
/
SOFTENING
/
FLOCCULATION OF
RO
CONCENTRATES FROM
PM3 146




New technologies or innovative treatment lines for reliable water treatment for
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1 Introduction

This report is a result of the project AquaFit4Use, a large-scale European research project co-
financed by the 7
th
framework programme of the European Union on water treatment technologies
and processes.

The research objectives of AquaFit4Use are the development of new, reliable cost-effective
technologies, tools and methods for sustainable water supply use and discharge in the main water
using industries in Europe in order to reduce fresh water needs, mitigate environmental impact,
produce and use water of a quality in accordance with the industries specifications (fit-for-use),
leading to a further closure of water cycle.

This report corresponds to the Task 3.1.1 “Evaluation of tailor-made water treatment concepts for
different water qualities, sustainable water reuse and more reliable technologies connected with
Pulp&Paper” of WP3.1 in SP3.
For more information on AquaFit4Use, please visit the project website: www.aquafit4use.eu.


In the Pulp&Paper industry a lot of effort is used to water saving and closing water circuits, and to
reducing substantially the environmental impact, also by process modelling and Kidney
technologies as internal process water treatment. However a number of problems around the
removal of substances are not solved yet and further closing of the water cycle causes other
problems. Challenges for water re-use in the Pulp&Paper industry are the following (Negro et al.
1995):
- The elimination of residual (soluble) COD and BOD which can both affect the production
process and the paper quality;
- The removal of sticky solids and suspended solids, which can induce plugging of pipes
and showers, deposit formation, abrasion, loss of tensile strength;
- The treatment of concentrate streams containing calcium, sulphate chloride organics
which can lead to salt accumulation in case of case of water loop closure, corrosion,
scaling of pipes and showers in the paper production process. The removal of calcium
carbonate is crucial in the last case.
Therefore there is a need to find new and reliable (combinations of) technologies to solve this
challenges to achieve the water quality target for water re-use and which are tailored to suit
product demands and standards.
The work described in this report concerned the laboratory and preliminary work for the

implementation of pilot trials on two industrial paper mills. Focus was done on different
technologies as part of a global treatment line to solve the above challenges. Comparison was
done to select the best treatment combinations to be implemented at pilot scale.


1.1 State of the art
1.1.1 Waste water treatment in Paper industry (Jung and Pauly, 2011)
1.1.1.1 Preliminary mechanical treatment - Mechanical processes for solids removal
Effluents from pulp and paper mills contain solids and dissolved matter. Principal methods used to
remove solids from pulp and paper mills effluents are screening, settling/clarification and flotation.
The method chosen depends on the characteristics of the solid matter to be removed and the
requirements placed on the purity of the treated water.

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The separation of solids from the effluents is accomplished with help of screens, grid chambers
and settling tanks. Screens are units which operate according to the sieving/filtration process. The
function of the screens is to remove coarse, bulky and fibrous components from the effluents. If
necessary, fractionated particle separation can be achieved by graduating the gap width (bar
screen, fine screen, inlet screen, ultra-fine screen).

For reasons of operating reliability of waste water treatment plants, it is also necessary to
separate the grit transported with the effluents and other mineral materials from the degradable
organic material. Grit separation from effluents can prevent operational troubles such as grit
sedimentation, increased wear and clogging. The grit separating systems currently in use are

subdivided into longitudinal grit traps, circular grit traps and vortex grit traps, depending on their
design and process layout.

Sedimentation technology is the simplest and most economical method of separating solid
substances from the liquid phase. High efficiency is achieved in subsequent effluent treatment
processes when the solid substances suspended in the effluents settle in a sedimentation tank as
completely as possible, and settled sludge is removed from the sedimentation tank.
Sedimentation tanks must be appropriately designed and operated. Alternative sedimentation
equipment with sets of lamella-shaped passages, are employed in the paper industry, especially
for effluents with high fibre concentrations.

Mechanical effluent treatment alone, however, is not sufficient to keep lakes and rivers clean,
since it is incapable of removing colloidal suspended and dissolved substances.

1.1.1.2 Biological treatment
Biological waste water treatment is designed to degrade pollutants dissolved in effluents by the
action of micro-organisms. The micro-organisms utilize these substances to live and reproduce.
Pollutants are used as nutrients. Prerequisite for such degradation activity, however, is that the
pollutants are soluble in water and non-toxic. Degradation process can take place either in the
presence of oxygen (aerobic treatment) or in the absence of oxygen (anaerobic treatment). Both
naturally occurring principles of effluent treatment principles give rise to fundamental differences in
the technical and economic processes involved (Table 1).
Table 1: Advantages and disadvantages of anaerobic and aerobic waste water treatment
(Chernicharo, 2007)
Anaerobic treatment Aerobic treatment
Usually needed COD > 1000 mg/l High amount of excess sludge
Tolerance of high organic loads High energy demand
Low production of excess sludge 3 to 5
times less than in aerobic processes
Higher tolerance to toxic substances

Energy generation by use of biogas High required space
Low energy demand Fully biological degradation
Low required space Higher tolerance to variations in the effluent
Sensitive against high sulphate and
calcium concentrations

No fully biological degradation

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Possibility of preservation of the biomass
with no reactor feeding for several
months

Low nutrient consumption
Application in small and large scale

The paper industry uses a variety of effluent treatment systems. The preferred process
combination for each individual case depends on the grade-specific quality of the effluent that is
going to be treated. Experience shows that multi-stage processes based on an aerobic-aerobic or
anaerobic-aerobic processing principle enables significantly more reliable operation of the plant.
The same effect can be achieved through a cascade system which allows a graduation of the
loading conditions. Among the German pulp and paper mills with on-site waste water treatment
plants, 60 % have only aerobic treatment (operated as one- or two-stage processes) for their
effluents, whereas 40 % have an additional anaerobic stage (Jung et al., 2009).

a) Anaerobic treatment
Anaerobic processes are employed for treatment of more highly polluted effluents such as
effluents from recovered paper converting mills (Hamm, 2006). Anaerobic micro-organisms
conduct their metabolism only in the absence of oxygen. Anaerobic processes are characterized
by a small amount of excess sludge produced and low energy requirements. As biogas is
produced during the degradation process, anaerobic processes produce an excess of energy.
Biogas is a mixture of its principal components methane and carbon dioxide with traces of
hydrogen sulfide, nitrogen and oxygen. Biogas is energetically utilized mainly in internal
combustion engines or boilers. In its function as a regenerative energy carrier, biogas replaces
fossil fuels in generation of process steam, heat and electricity. Composition and quality of biogas
depends on both effluent properties and process conditions such as temperature, retention time
and volume load.

Before discharge into surface waters, anaerobically treated effluents have to undergo aerobic
post-treatment, because – according to the current state of the art – fully biological degradation of
paper mill effluents is not feasible (Möbius, 2002).

When introducing anaerobic technology into the pulp and paper industry, operational problems
and their possible consequences shown in Table 2 must be taken into account:
Table 2: Operational problems and possible consequences on anaerobic treatment in the pulp
and paper industry
Operational problem Possible consequences
High concentrations of suspended solids in
the feed flow
Displacement of biomass
Loss of pellets
High sulfate concentrations Displacement of methane bacteria
Inhibiting or toxic effects of sulfide
Performance losses
High calcium concentrations Precipitation of CaCO

3

Displacement of biomass

New technologies or innovative treatment lines for reliable water treatment for
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Additives used in production (especially
biocides and detergents)
Inhibiting/toxic influences
Poorer degradation performance
Decomposition/wash-out of pellets
Insufficient supply of nitrogen and
phosphorus
Unstable operation
Performance losses
Loss of pellets
Temperature variations Unstable operation
Performance losses
Fluctuating organics loads (e.g. shock loads)

Excessive production of organic acids
Methanation disturbed

b) Aerobic treatment
Aerobic micro-organisms require oxygen to support their metabolic activity. In effluent treatment,

oxygen is supplied to the effluent in the form of air by special aeration equipment. Bacteria use
dissolved oxygen to convert organic components into carbon dioxide and biomass. In addition,
aerobic micro-organisms convert ammonified organic nitrogen compounds and oxidize
ammonium and nitrite to form nitrate (nitrification). The key factors for the success of an aerobic
process are an adequate amount of nutrients in relation to the amount of biomass, certain
temperature and pH regime and the absence of toxic substances (Hynninen, 2000). Aerobic
processes are characterized by high volumes of excess sludge and higher energy demands
compared to anaerobic processes. Furthermore, these reactors typically have large space
requirements.

Aerobic treatment allows fully biological degradation of paper mill effluents. The BOD5 efficiency
achievable with well operated activated sludge processes is typically within the range of 90-98 %
(Hamm, 2006). The drawbacks of aerobic treatment technology are the relatively high operating
costs due to the aeration of the effluent. On the other hand, aerobically operated plants exhibit
higher plant stability and are less sensitive to fluctuations in effluent and plant parameters.

Among different types of aerobic treatment technologies, activated sludge processes are currently
the most frequently used treatment technologies in the German pulp and paper industry and have
achieved a share of three quarters of the operating reactors. Both Moving Bed Bio Reactors
(MBBR) and biofilters represent another 10 % of the reactors used (Jung et al., 2009).
c) Secondary clarification
Secondary clarification is intended to separate the biomass (activated sludge) formed in biological
reactors and is therefore a key element in all processes employed in the final stage of a treatment
plant. The quality of the separation process is just as crucial for the final effluent quality as is
biological treatment itself.

As far as activated sludge process is concerned, secondary clarification determines the bioreactor
performance. Separation and thickening of the recirculated sludge is crucial for sludge volumes in
biological treatment and also for the potential sludge loading. Correct dimensioning of secondary
clarification is therefore of maximum importance for overall plant performance.

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1.1.1.3 Advanced and tertiary treatment
Tertiary and/or advanced waste water treatment is used to remove specific waste water
constituents that cannot be removed by secondary treatment. Different treatment processes are
necessary to remove nitrogen, phosphorus, additional suspended solids, refractory organics or
dissolved solids. Sometimes it is referred to as tertiary treatment because advanced treatment
usually follows high-rate secondary treatment. However, advanced treatment processes are
sometimes combined with primary or secondary treatment (e.g., chemical addition to primary
clarifiers or aeration basins to remove phosphorus) or used in place of secondary treatment (e.g.
overland flow treatment of primary effluent). Reasons for advanced effluent treatment are:
• Reduction in costs (discharge fee);
• Compliance with limit values;
• Increase in production.

Table 3: Treatment aims of different advanced treatment methods
Treatment method Aim of treatment
Biofiltration Reduction in COD and BOD concentration
Removal of suspended solids
Ozone treatment Elimination of residual COD
Decoloration
Membrane treatment Elimination of residual COD
Elimination of suspended solids
Demineralization

Decoloration
Filtration processes Removal of suspended solids
De-nitrification and phosphate precipitation Nitrogen and phosphate elimination

Advanced waste water treatment in the pulp and paper industry is focused mainly on additional
biological membrane reactors, ozone treatment and membrane filtration techniques such as
micro-, ultra- or nanofiltration and reverse osmosis. Due to relatively little full-scale experience,
relatively high costs and greater complexity of water treatment, there have been only few full-
scale applications of tertiary treatment of mill effluents up to now.

The method that is ultimately chosen depends on the treatment aim and economic efficiency of
the method in a given application.

1.1.1.4 Water circuits and quality demands in paper production
In the history of papermaking, the water circuit was created as a result of the invention of the
paper machine and with it the advent of endless papermaking. As industrial papermaking evolved
and developed, so did the importance and scope of water circuits as well. Factors that have
shaped and influenced this development are:
• A reduction in the specific water volume: As the specific water volume is reduced, the
demands on the contaminant removal efficiency of the installed circulation water treatment
rise, since the water must be used several times and fresh water is also replaced by

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circulation water at critical locations. This means that more water must be treated and higher

requirements are placed on the treated water.
• Development of production capacities: The increased productivity, which in some cases is
considerable, makes it necessary to hydraulically adapt the elements of the water circuit.
• Increased product quality and greater use of recovered paper: High requirements on water
quality make it necessary to separate heavily loaded and slightly loaded water and the
removal of components detrimental to the product. The greater use of recovered paper
significantly aggravates the above-mentioned conditions even more.
• Greater raw material efficiency: This requires the collection and recirculation of all partial
flows containing solids. Only clarified water is discharged. A system that is integrated into the
water system must take over solids management.
The requirements mentioned above result in practice in the construction of complex water
circulation systems. Their appearance, the mode of operation of the elements contained in them
and possibilities for system closure were investigated in the SP1. In the related reports an in-
depth analysis of the water quality requirements can be found.

On the basis of waste water characterization and the defined water quality requirements in SP1
for paper mills, WP3.1 aimed at defining new treatment lines to reach the water quality target
including effectiveness, reliability and minimization in waste and concentrate production. These
new treatment lines should be focused on internal recycling.
Therefore a focus has been done on different key steps of the global treatment train:
- Biological treatment: anaerobic processes and MBR;
- Filtration processes: 3FM high speed technology and nanofiltration;
- Tertiary treatments to reduce hard COD: AOPs, coagulation/precipitation;
- Integration of processes (evapoconcentration, electrodialysis and softening) in the
treatment line to:
o treat the concentrate streams containing calcium, sulphate, chloride, organics
which can lead to salt accumulation in case of water loop closure, corrosion,
scaling of pipes and showers in the production process. The removal of CaCO
3
is

crucial in the last case
o minimize the waste production and enhance internal recycling.

A state-of-the art of each of these technologies is done in following chapter.

1.1.2 State-of-the-art of tested technologies within the study
1.1.2.1 Anaerobic technology
Since the early 1980s, anaerobic treatment of industrial effluents has found widespread
application in the pulp and paper industry. Several hundreds of installations are treating a large
variety of different pulp and paper mill effluents. Of 205 operating anaerobic installations for the
treatment of industrial wastewater in e.g. Germany around 75 plants are located in the pulp and
paper industry.
Most of the reactors rely on granulation of biomass (sludge pellets, sludge granules). Granulation
allows for effective separation of hydraulic and solids retention times. Pelletized biomass forms
the so called anaerobic sludge bed which is flowed through in upward direction by the wastewater
fed to the reactor bottom using an inlet distribution system. Treated effluent is discharged at the
reactor top after separation of biogas and sludge pellets in a three phase separator. Some
effluent may be recirculated to the inlet distribution system to adjust hydraulic upflow velocity in

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the reactor compartment. Consequently these reactors are named UASB reactors (upflow
anaerobic sludge bed). EGSB reactors (expanded granular sludge bed) are a further development
of the UASB type. The main difference is that EGSB type reactors are operated at much higher
upward velocities (5 – 10 m/h compared to 0.5 – 1.5 m/h) and therefore higher recirculation rates.

The increased upward flow permits partial expansion of the sludge bed, improved mass transfer
between wastewater and biomass as well as some wash-out of inert influent suspended particles
(provided different settling velocities of biomass granules and suspended matter). Higher upward
velocities lead to taller reactors (approx. 15 – 25 m) compared to conventional UASB systems (5 –
8 m). For example there are 22 UASB-type installations and altogether 42 EGSB-type reactors of
different manufacturers (DWA IG 5.1, 2009) in German Pulp&Paper industry. In recent years
EGSB-type reactors are almost exclusively built for the treatment of pulp and paper effluent.

Anaerobic treatment is most commonly used for effluents originating from recycle paper mills,
especially during production of containerboard. Moreover wastewater of mechanical pulping
(peroxide bleached), semi-chemical pulping and sulphite and kraft evaporator condensates may
be treated. The advantages of anaerobic pre-treatment are (1) net production of renewable
energy (biogas), (2) minimized bio-solids production leading to reduced disposal of excess
sludge, (3) minimal footprint because of high volumetric loading rate and (4) reduced emission of
greenhouse gases (Habets and Driessen, 2007). Via in-line application of anaerobic treatment in
closed circuits (paper kidney technology) further savings on cost of fresh water intake and effluent
discharge levies may be generated.
Some major prerequisites have to be fulfilled for successful application of anaerobic treatment
technology in pulp and paper industry (see also chapter 1.1.1.2 above):
• Elevated temperature: In most cases the temperature optimum of mesophilic
microorganisms (30°C - 37°C) is adjusted in anaerobic reactors. Thermophilic conditions
(50°C – 55°C) have been also applied in P&P sector and may be successfully used at
existing elevated temperature of effluents (van Lier, 1996).
• Optimum pH: The pH in anaerobic reactors has to be kept at 6.5 ≤ pH ≤ 7.5 in the
optimum range for methanogenic bacteria. Fermentative bacteria my also proliferate at
lower pH e.g. in hydrolysis reactors or equalisation tanks.
• Reduced suspended solids (SS) concentrations: High concentrations of suspended solids
(SS) have to be removed before modern high rate anaerobic reactors, because SS may
accumulate in the reactor and replace active biomass or prevent successful granulation
respectively. The acceptable solids load in the influent varies depending on reactor system

and nature of solids (e.g. fibre, inorganic solids). COD of organic SS should not exceed
around 10 % of the total COD load (DWA IG 5.1, 2002).
• Sulphate toxicity: Effluents of P&P production are often rich in sulphates. Reduction of
sulphate will predominantly lead to generation of H
2
S, which is toxic for anaerobic bacteria
at certain concentrations, depending on reactor pH. As reduction of sulphate also is
energetically more favourable than methanogenesis, high sulphate concentrations in the
influent to the anaerobic reactors will limit methane production. COD/S ratio is the major
governing factor. At COD/S > 100 limitations are not to be expected, at COD/S < 50
inhibition may occur.
• Precipitation products: Inorganic precipitates: - especially CaCO
3
- will influence reactor
performance. Because of pH-shift in the anaerobic reactor precipitation will occur starting
at around 100 mg Ca
2+
/L. As Ca
2+
concentration in effluents of containerboard production
may easily exceed 1000 mgCa
2+
/L heavy precipitation of CaCO
3
has to be expected, which
will lead to clogging and calcification of sludge pellets. Selective removal of precipitates in-
or outside the anaerobic reactor has to be accomplished. There are some technologies for
softening available, relying on precipitation of CaCO
3
through pH-shift and oversaturation.

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Softened water may be recycled to the anaerobic treatment in order to dilute Ca2+
concentrations.
• Nutrient balance: Nutrient (N, P) and trace element concentrations (e.g. Fe, Co, Ni, Se, W,
Mg) for anaerobic processes have to be controlled regularly. P&P wastewater usually is
deficient in nutrients and trace elements. Nutrient balance COD:N:P:S should be
maintained at around COD:N:P:S ≈ 800-500:5:1:0.5 (DWA IG 5.1, 2002).

1.1.2.2 MBR processes
There is currently growing interest in the MBR (membrane bioreactor) process in municipal and
industrial wastewater treatment.
A membrane bioreactor employs ultrafiltration (pore size 0.01 - 0.05 microns) to retain solids and
micro-organisms in the aeration tanks of the biological treatment stage. The ultrafiltration module
thus replaces the final clarification stage.
The first generations of the MBR were developed in 1960. They are based on side stream
configuration, which is usually designed with tubular membrane. They are operated under cross-
flow conditions with a very high liquid velocity. In this concept, the activated sludge is pumped into
the membrane modules placed on the side of the biological tank resulting in high performances
and high fluxes, but at significant energy consumption and a larger footprint. Therefore this
technology is preferred for difficult wastewaters and small-scale high strengths water application.


Biological tank

Sludge in excess
Mixed liquor recirculation Waste water
MF/UF
module
Treated

water

Figure 1: Side stream configuration
Submerged bioreactors (MBRs) have been developed in the middle of 1980s in order to simplify
the use of these systems and to reduce operating costs. In this configuration the membranes are
immersed in a tank containing the biological sludge and the permeate water is extracted. Air
coarse bubbles are used to promote proper turbulences and circulation around the membrane
modules. They are designed with hollow fibres or flat sheet membranes.
MBRs exist in two configurations. In the inside configuration, membrane modules are immersed
directly into the bioreactor. In the outside configuration, membrane modules are placed outside
the bioreactor. A pump circulates the mixed liquor from the bioreactor to the membrane module or
back at a flow rate of 100 to 500 % of the influent flow. Advantages associated with the outside
submerged MBR implementation are among others easier maintenance and cleaning, and higher
operational flexibility. This probably explains why outside submerged MBRs quickly became the
favoured MBR design for municipal plants in Europe. However, the inside configuration is strongly
preferred for smaller plants, for flat sheet membrane applications.




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Treated
water
Biological tank
Effluent
Sludge in excess
Treated
water
Biological tank
Effluent
Sludge in excess

Figure 2: Inside Submerged membrane bioreactor
Biological tank
Sludge in excess
Mixed liquor recirculationEffluent
MF/UF
Module
Treated
water
Biological tank
Sludge in excess
Mixed liquor recirculationEffluent
MF/UF
Module
Treated
water

Figure 3: Outside Submerged membrane bioreactor
There is currently growing interest in the MBR (membrane bioreactor) process in municipal and
industrial wastewater treatment. In the year 2007, Germany already boasted about 70 - 80 MBR
facilities, 17 of which were in municipal wastewater treatment plants (Pinnekamp, 2007). Since
2007, three German paper mills have invested in this technology too, putting MBR plants into
service. Added up, this means that at the European level paper mills are currently operating at
least nine MBR plants (Simstich and Öller, 2010). Generally speaking, the operating costs of the
MBR process are still higher compared to the conventional version with a final clarifier (Möbius
and Helble, 2007). If the costs are higher than those of conventional systems, what speaks in
favour of this technology? The advantages for a use in the paper industry can be narrowed down
to the following three points (Judd, 2011):
• Sedimentation becomes a thing of the past: this means not only smaller space
requirements but also the end to problems caused by bulking or floating sludge or sludge
overflow in general.
• Better effluent quality: solids and micro-organisms are retained, only dissolved substances
and salts can pass through the membrane.
• Higher sludge age and MLSS (mixed liquor suspended solids) concentration: this results in
a more compact construction and shorter hydraulic retention times being possible.
MBR is used in the paper industry as end-of-pipe technology as well as process integrated
measure for the reduction of the concentration of detrimental substances in the water circuit. A
typical problem of the membrane filtration of paper industry wastewaters is calcium scaling.
Calcium carbonate is used in paper production as filler and coating pigment. Due to the common
use of recovered paper as raw material, high concentrations of calcium can occur in the water
circuit. Especially mills producing board or corrugated paper typically have a nearly closed water
circuit with low specific effluent volumes of << 5 l/kg paper. This combination of dissolved calcium
from the raw material and high process water reuse rates leads to high water hardness and
problems with scaling and precipitation. As filtration processes are susceptible to scaling
problems, measures have to be studied to enable the successful use of membrane technologies
in the paper industry.
Despite the challenge of the water hardness, the MBR technology was chosen in the project as it

is a feasible and reliable process to reach a further reduction in water use in the paper industry.
Especially in terms of effluent quality and economical aspects a MBR is a sustainable technology

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for the industrial wastewater treatment. But, however, precondition for a more common use is
research on fouling and scaling if an application in the paper sector is considered.

1.1.2.3 3FM technology
Tertiary treatment of secondary treated wastewater is the easiest way to improve first step in the
direct reuse of water. The filtration of water and wastewater plays indeed an important role within
industrial water treatment lines and the removal of particles and sticky solids can be a major
problem to implement a membrane process after a biological treatment, when speaking of
recycling water. The purpose of water filtration is to remove particles and colloids which either
disturb the industrial process, deteriorate the quality of the final product or support bacteria and
viruses that are a danger for human health.

The conventional treatment generally consists of coagulation, flocculation, sedimentation and
sand filtration. One of the main disadvantages of this process combining sedimentation and sand
filtration is the rather long residence time, mostly due to the flocculation and sedimentation
phases. Sand filters are as well used but though a good removal efficiency of particle including
colloids, they need relatively low filtration velocities thus requiring a large installation area.
Although applied at full scale for pre-treatment before a following nano-filtration or reverse
osmosis step, the performances of these pre-treatments is not as effective as that of MF and UF
(Vedavyasan, 2007). Another disadvantage of the conventional pre-treatments is their relatively

low filtration velocity (maximum velocity of 20 m/h).

A high rate fibre filter was then developed by Veolia Water STI and its high efficacy for the tertiary
treatment of waste waters was proved in terms of high filtration velocity and good removal of
particulate matter (Ben Aim et al. 2004). The 3FM
®
system (Flexible Fibre Filter Module) is a new
high speed filtration device that can be substituted for conventional solid-liquid separation process
such as coagulation, settling and sand filtration (Jeanmaire et al. 2007; Lee et al. 2008).
Compared with existing rapid sand filters, the 3FM filtration system has a velocity more than 10
times faster at 120 m/hr and has a smaller footprint, requiring up to 1/10
th
the space of sand
filters. Suspended solids are filtrated by flexible fibres in polyamide in a module, which have
softness, elasticity and a degree of surface roughness. These fibres have a three branch star
shape and are not porous (Figure 4).



Figure 4: 3FM fibres
The filter is packed with bundles of fibres along the module length and influent flow is introduced
to the bottom of 3FM. Utilising all of the filter area through deep bed filtration suspended solids
particles are captured (Figure 5). The optimum operating parameters are managed according to
the influent characteristics desired quality of the treated water.


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AIR
(FOR BACKWASH)
REJECT
(SLUDGE)
FILTRATED
WATER
SERVICE
WATER
AIR
(FOR BACKWASH)
REJECT
(SLUDGE)
FILTRATED
WATER
SERVICE
WATER





3FM fibers3FM fibers


Princip

le
of

3FM filtration
s
ystem
:

Alternation of filtration periods and backwash

o
Filtration process (+):
Service water is
fed through the
inlet pipe of the lower
part of the
apparatus and introduced
uniformly into fibro
us filter layer. During
the
filtration process, SS are removed by
the fibers and clean effluent water is
discharged to upper part.

o
Backwash process (++):
When
inner pressure reaches predetermined
value of pressure switch
due to SS clogged

in the filtering process
or time reaches
predetermined
value on the timer, the
backwash
process is initiated. SS clogged
in the
filter are remove in a short time by
introduction of air which shake the

fibers
.


Figure 5: 3FM
®
technology and its principle
Although an innovative process, 3FM
®
operation is easy as a sand filter. Head-loss increases
during the filtration cycle and the filtration capacity is recovered by periodic backwashing with a
small amount of influent waste water and scouring air (Figure 5). Backwash is generally operated
every 3 hrs approximately (depending of inlet specifications) and needs less than 1% of the
maximum treated water. Main impact of 3FM is on TSS content in the water and thus on turbidity
as well. A cut size of ~5-10 µm is obtained.
Applicable fields are SS removal from sewage/WTTP, from industrial and agricultural water,
water re-use, algae removal from river and reservoir, preliminary treatment of drinking water
(Korea, China).This technology is currently used at industrial scale on several WWTP in Korea for
obtaining treated water of high quality (Ben Aim et al. 2004) and has been applied as well as pre-
treatment to minimize the organic fouling of SWRO membranes used for desalination (Lee et al.

2009; Lee et al. 2010). Until now 3FM technology has never been applied as tertiary treatment to
P&P waste waters.
For more details regarding this technology and its industrial operation, refer to the report “D6.1.1
Knowledge and technological portfolio” and as well to internal report “I3.1.1.1 Proof of concept of
aerobic water treatment technologies and separation techniques on bench scale for Pulp &
Paper”.

1.1.2.4 Membrane technologies (UF, NF, RO)
Membrane treatment in P&P-industry serves to optimize loop closure and therefore helps to
reduce fresh water intake as well as wastewater treatment. Other purposes of membrane
processes are: improved product quality because of lowered pollution of loop water, re-use of
treated effluent in production, recovery of valuable substances e.g. coating pigments and
minimizing environmental impact because of improved effluent quality (Simstich and Öller, 2007).

Different types of modules have been use for NF in pulp and paper industry. A wide range of
spiral wound modules is commercially available, but also cross-rotational or vibratory shear
enhanced modules were tested. The latter two are basically circular flat sheet arrangements,
where high shear or cross-flow is created through rotation or vibration (Nyström et al., 2005).
These module configurations are used for cleaning of internal circuits, when a lot of fiber and

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suspended matter has to be expected. Spiral-wound modules are mostly installed in typical post-
treatment configurations, when suspended and colloidal matter has been reduced down to very
low concentrations in preceding treatment steps.

Full scale membrane filtration of Pulp & Paper effluents has been already installed in some mills.
Nanofiltration treatment of total effluent was installed in a newsprint paper mill several years ago
(Lien et al., 1995). Since no biological treatment had been installed, effluent was treated by
physico-chemical pretreatment and several pre-filtration steps before NF in order to reduce fouling
and clogging tendencies. In a Finnish paper mill paper machine clear filtrate is treated with
ultrafiltration using CR-filters (Metso Paper Chem Oy) and subsequent NF with spiral wound
modules (Sutela, T., 2001). Nanofiltration with spiral-wound modules has been used for full-scale
tertiary effluent treatment in one German mill producing newspaper from 100 % recovered paper.
NF was chosen in order to reduce residual COD, AOX, colour and salinity for direct discharge or
partial loop closure (Schirm et al., 2002). Another full-scale installation in Germany has been
started up recently (2008) in the production of cardboard and packaging paper featuring a
membrane bioreactor and reverse osmosis for the production of around 27 m³/h reclamation
water for reuse in the mill (90 % recovery).

The advantage of NF in the recovery of water for recirculation is mainly that the clean water can
be used even in the most demanding places in the paper mill. With NF, the COD reduction is
70 % – 90 %, the AOX reduction between 60 % and 97 %, most multivalent metals are reduced
by more than 90 % and colour is reduced for more than 90 % (Nyström et al., 2005, Schirm et al.,
2002). A combination of UF-NF-RO was even used in a pilot system to produce reclamation water
for the irrigation of crops in Australia (Cox et al., 2008). Drawbacks in the use of commercially
available NF modules are the need for heavy pretreatment e.g. the addition of chemicals for water
conditioning, clarification and filtration for removal of suspended solids (sand, screen or bag
filters, Mänttäri et al., 2006). In case of the German newspaper mill using NF two stages and
filtration is used for pre-treatment. MBR technology serves as modern alternative because of
superior quality of UF filtrate. A combination of MBR + NF / RO therefore seems promising for
water recycling in pulp & paper industry, but there is lacking experience to name it a proven
technology Recovery rates of up to 90 % – 93 % (volume concentration factor 10 – 15) have
been reported for the NF treatment of biologically pre-treated effluents depending on wastewater
load and membrane type (Mänttäri et al., 2006). Still the combination of membrane technology

and high inorganic content - which remains present in pre-treated effluents of paper board mills -
needs to be addressed in detail, since recovery rates and treatment costs are interconnected
closely.

Economic assessment of NF treatment of ground wood mill effluent water has shown, that
depending on flux and pre-treatment associated cost for reclaimed NF permeate varied from
around 0.9 €/m³ - 1.4 €/m³. Schrader (2006) estimates around 0.2 €/m³ - 0.6 €/m³ for the
reclamation of NF permeate from municipal wastewater effluent, which is lower than for NF
treatment of P&P effluents. Cost for NF concentrate handling through incineration or hazardous
waste disposal (subsequent to evapoconcentration and drying) varied from 5 €/m³ to 38 €/m³
(total cost referring to permeate volume at around 83 % recovery of permeate). Governing factor
for economic feasibility of reclamation of NF permeate therefore are concentrate handling costs.
Consequently Schrader (2006) stated the need for a tailored concentrate treatment, which will
also be assessed during pilot trials in this project.


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1.1.2.5 Ozone/AOP technologies
Today Ozone and UV are well known and proven in the field of water and waste water treatment –
ozone as multifunctional powerful oxidant and UV as best available technique for disinfection
regarding treatment results, plant design and cost (Ried, 2009).
Nowadays so called advanced oxidation process (AOP) combining Ozone, UV and H
2
O

2
or other
techniques (e.g. Fe/H
2
O
2
, TiO
2
/UV) are more in the focus of public interest and are studied for a
broader potential use (Sievers, 2011).
The main goal of these combined processes is to enhance the oxidation potential. The reason for
this enhancement is the increased generation of hydroxyl radicals, which have a higher oxidation
potential (Glaze, 1987). It is known that hydroxyl radicals are almost twice as reactive as chlorine
and its oxidation potential is close to that of fluorine (E = 2.32 V/NHE at pH=7) (Bigda, 1995) and
they react very quickly with nearly all organic compounds. Therefore this enhanced reaction leads
to better treatment results regarding advanced degradation and faster kinetics.

Figure 6 gives an overview of possible pathways to generate hydroxyl radicals. There are 4 main
ways of using Ozone, UV, H
2
O
2
and their combinations.


ozone (O
3
)
•
OH

radical
UV - h
•
γ
γγ
γ , λ
λλ
λ
= 254 nm
,
ε
εε
ε

= 19
M
-1
cm
-1
Water compounds
OH
-
, Fe , TOC
Initiation
Promotion
O
1
2

•

OH

H
2
O
2

H
2
O
2


HO
2
-
UV
h
•
γ
γγ
γ
λ
λλ
λ
= 254 nm
,
ε
εε

ε
= 3.300
M
-1

cm
-1
H
2
O
2
+

h
•
γ
γγ
γ
O
3
+
HO
2
-
O
3
+
HO
2
-

O
1
+
H
2
O
+
H
2
O
2
a)
a)
b)
b)
c)
c)
+
H
2
O
2
4
4
3
3
2
21
1

Figure 6: O
3
/ UV / H
2
O
2
- possible pathways (1- 4) for OH-radical formation

Possible pathways for hydroxyl radical formation:
1. Typical water compounds, e.g. hydroxyl anions, iron ions or organic compounds can
initiate/promote a decomposition of dissolved Ozone and generate hydroxyl radicals.
Consequently a part of Ozone reactions in waste water goes with generation of hydroxyl
radicals without using any additional enhancement. These highly reactive hydroxyl radicals
usually initiate the oxidative destruction of organic substances (R) present in wastewater by
OH


addition reaction or hydrogen atom abstraction (Huang, 1993). Organic free radicals (R

)
are formed as transient intermediates and are further oxidized by other intermediates to form
stable, oxidized products (Huang, 1993).
2. Different oxidized species will be generated during the UV radiation of Ozone molecules in
water. The typical wavelength for this process is 254 nm. The molar extinction coefficient,
which describes the amount of absorbed photons by the ozone molecule, is 3300 mol-1 cm-1.

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Depending on the generated intermediates, e.g. excited oxygen atoms (O), hydrogen
peroxide (H
2
O
2
) or the conjugated base of H
2
O
2
(HO
2
-
), there are different further pathways
(a-c) for hydroxyl radical generation. In practice there are more than these three mentioned
pathways. So the Ozone/UV process is very complex. It is not really possible to describe
exactly all chemical reaction details or the kinetics and the hydroxyl radical yield.
3. In the presence of hydrogen peroxide Ozone reacts with the conjugated base of H
2
O
2
to form
hydroxyl radicals.
4. The UV radiation of H
2
O
2
leads directly to the formation of hydroxyl radicals. From the

stoichiometric yield (1 mol H
2
O
2
→ 2 mol OH


radicals) this process is the most efficient. But
the molar extinction coefficient for the wavelength 254 nm is only 19 mol
-1
cm
-1
. For a given
UV-radiation this low coefficient leads to a much lower OH-radical yield than the Ozone/ UV
process (20 times higher). One way for compensation is to use high concentrations of H
2
O
2

(> 10 mg/l). Moreover it is possible to work with wavelengths in the range of 200 to 250 nm to
improve the molar extinction coefficient. Therefore, typically, a medium pressure UV-lamp is
used. But, in that case the required energy input becomes the limiting factor compared with
other AOP`s.

Applying advanced oxidation processes AOPs
Combined chemical (AOP) and biological oxidation processes have a well-known potential for
removing recalcitrant and anthropogenic substances from wastewater. e.g., Scott and Ollis, 1995,
reviewed 58 publications – mostly based on lab scale studies – and identified four different types
of wastewater contaminants which can benefit from combined processes:
1) Process streams containing high concentrations of recalcitrant compounds;

2) Biodegradable wastewaters with small amounts of recalcitrant compounds;
3) Inhibitory compounds;
4) Intermediate dead-end products.
Additionally the decolourisation with ozone has already been established as an application of
polishing of biological treated effluents.

The positively synergistic effect of process combination is based on the enhancement of the
biodegradability of such compounds by chemical oxidation (ad 1, 3, 4) and the need of polishing
of biologically treated effluents (ad 2). (i.e.: Balcioglu, 2007; Bijan, 2008; Chang, 2004; Mounteer,
2007).
Complete oxidation of organic compounds is usually not economically feasible because large
amounts of energy and chemicals are necessary. Direct oxidation and the enhancement of COD
degradability compared to the untreated sample are crucial for total COD elimination (Simstich,
2010).
In general the following items are important when using AOPs:
- the potential yield of hydroxyl radicals;
- amount of radical scavengers;
- the required energy input;
- plant design;
- investment and operational cost.
Consequently, the application of AOPs for the treatment of retentates coming out from membrane
treatments of pulp and paper industries must mainly take into account i) the influence of
wastewater composition (these waters are usually high organic loaded and they have high values
of alkalinity and chlorides that could reduce the efficiency (De Laat, 2004)), ii) the efficiency of the
process and iii) as well as the economic study.

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In practice a high amount of so called scavengers, e.g. carbonates might quench hydroxyl
radicals. So the generated radicals are not available for the treatment process itself. In real waste
waters further possible pathways exist for radicals to react without increasing the treatment result
significantly. Due to this complexity of real waste waters in practice pilot trials have to prove the
best technique (Acero and Gunten, 2001; Ternes et. al., 2001).

What do we know so far?
a) Ozone based oxidation
Ozone can oxidize other compounds in two different ways: directly reacting with dissolved
compounds, or indirectly via hydroxyl radicals produced in its decomposition (Esplugas, 2002).
Due to the short half-life of ozone, continuous ozonation is required to keep the process going on.
This is one of the major drawbacks of the treatment, considering the cost of ozone generation
(Catalkaya, 2007; Kreetachat, 2007; Ried, 2009). Furthermore, reactivity of ozone is also affected
by the presence of salts, pH and temperature (Catalkaya, 2007); and the process efficiency is
highly dependent on efficient gas-liquid mass transfer.

The combination of ozone with hydrogen peroxide (O
3
/H
2
O
2
) is considered a promising alternative
to remove refractory organic chemicals from wastewaters (Masten, 1994). HO
2
−
(conjugate base

of H
2
O
2
) at millimolar concentrations can initiate the decomposition of ozone into hydroxyl radicals
much more rapidly than the hydroxide ion (Catalkaya, 2007), therefore the addition of hydrogen
peroxide produces a faster ozone degradation (Gogate, 2004a; Mounteer, 2007, Ried, 2005).

Ozonation is a successful method to oxidize chemicals present in wastewaters from pulp and
paper mills, such as eugenol, cathecol, phenol, trichlorophenol and cinnamic acid derivatives. The
double and triple bonds of lignin compounds that produce the colour of paper industry wastewater
are easily oxidized by ozone (i.e.: Kreetachat, 2007; Öller, 2009). Moreover, ozonation usually
increases biodegradability of paper mill effluents by toxic compound degradation and changes in
molecular weight fractions from HMW to LMW (Amat, 2005; Balcioglu, 2007). Two large-scale
ozone plants are operating successfully in paper mills in Germany and Austria (Schmidt et al.,
2000; Kaindl, 2009) for the tertiary treatment of wastewater.

Conducting systematic laboratory tests is recommended with the scope of meeting the envisage
target values in each case, as the structure of the organic compounds present in the effluents is
very important in terms of oxidation by ozone or other AOPs. Oxidation by ozone as a standalone
technology is considered as impractical for pulp and paper mill effluents and may not offer
sufficient removal and mineralization of organics (Bijan, 2008). However using ozone oxidation to
get partial oxidation of organics and enhance its biodegradability is more feasible (Bijan, 2008;
Tuhkanen 2002). An interesting possibility is to use a biological or membrane treatment to
separate the HMW fraction, avoiding the unnecessary oxidation of the LMW organic fraction
(Bijan, 2008).
b) Fenton method
Fenton method is one of the most common and efficient AOPs for wastewater treatment.
Moreover, it usually implies a lower capital cost than other AOPs (Esplugas, 2002; Tang, 1996;
Krichevskaya, 2010). It is based on the electron transfer between H

2
O
2
and Fe
2+
, which acts as a
homogenous catalyst to yield hydroxyl radicals (OH·) that can degrade organic compounds
(Harber, 1934), as it can be expressed by:
Fe
2+
+ H
2
O
2
→ Fe
3+
+ OH
-
+ OH

K
1
= 70.0 M
-1
•s
-1
(3)

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Typically, Fenton treatment is performed in the following four stages (Bigda, 1995): pH
adjustment, oxidation reaction, neutralization-coagulation, and precipitation (centrifugation);
whereas organic substances are removed by both oxidation and coagulation. pH is one of the
major factors limiting the performance of the Fenton process. It is optimum between pH 2.5-3 due
to a higher solubility of iron and a higher stability of hydrogen peroxide (Hermosilla, 2009a).
Moreover, the effectiveness of the Fenton method is directly related to the amount of hydroxyl
radicals formed, which is function to the concentration of hydrogen peroxide and the amount of
ferrous ion available.

Fenton treatment has two important drawbacks: the acid pH and the production of iron sludge,
which requires ultimate disposal (Pignatello, 2006). In order to diminishing the production of iron
sludge, the modification of the conventional Fenton process by the combined application of UV-
light has been suggested.
The photo-Fenton process has two major features: (a) the reduction of ferric to ferrous iron,
producing additional hydroxyl radicals via photolysis (Kavitha, 2004), i.e.:
Fe(III)OH
2+
+ hν → Fe
2+
+ OH

(4)
and (b) the photo-decarboxylation of ferric carboxylates (Kavitha, 2004), namely:
Fe(III)(RCO
2

)
2+
+ hν → Fe
2+
+ CO
2
+ R
.

(5)
R


+ O
2
→ RO


2
→ Products (6)
As shown above, the amount of catalytic iron required, and consequently the volume of sludge
produced, could be strongly reduced and, moreover, some additional organic compounds
(carboxylates) may also be effectively treated (Hermosilla, 2009a).
c) Photocatalysis using a catalyst semiconductor (TiO
2
)
New tendencies are focused in the UV assisted AOPs with reusable catalysts, such as TiO
2
(Yeber, 2000). These treatments imply the irradiation of a semiconductor (e.g. TiO
2

, ZnO) with UV
light at a wavelength shorter than 390 nm (Yeber, 2000). Heterogeneous photocatalysis
employing TiO
2
and UV light has demonstrated its efficiency in degrading a wide range of
ambiguous refractory organics via creating an electron-hole pair, whereas photogenerated “holes”
may react directly with organics and charge carriers might migrate to the surface where they react
with adsorbed water and oxygen to produce radical species that attack any adsorbed organic
molecule and can, ultimately, lead to complete decomposition into CO
2
and H
2
O (Ahmed, 2009).
Pérez (2001) reported that the heterogeneous photocatalytic process catalyzed by titanium
dioxide (UV/TiO
2
) efficiently removes colour and dissolved organic carbon (DOC) from ECF
bleaching effluents and lignin containing solutions. A rapid decrease of toxicity in different
solutions was also reported by different authors (Catalkaya, 2008; Perez, 2001; Yeber, 2000) and
the enhancement of biodegradability shows that photocatalytic systems may be an interesting
pre-oxidation step preceding biological treatment (Yeber, 2000).

1.1.2.6 Advanced flocculation
Colloidal material is stable in dispersion because of its high specific area, which allows it to
interact with the solvent. Therefore, removing this material by filtration, sedimentation or flotation
in an economic viable way is difficult. Chemical flocculation process is crucial because promotes
the aggregation of particles after being destabilized by a chemical agent. As a result, many
environmental technologies comprehend a flocculation stage: treatment of domestic and industrial
wastewater and removal of soil contaminants are some examples, as well as water softening,
fermentation processes, mineral separation by selective flocculation and papermaking.

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In pulp and paper industry, flocculation is involved in different parts of the process: it is essential
to form the paper sheet in the forming wire, determining retention, drainage rate and the
formation, and it is also used in the wastewater treatment to separate the colloidal material and in
the sludge thickening.
Factors, that affect the flocculation process and that are related to the flocculent, are nature,
structure, molecular weight and charge density of flocculent. However, flocculent dosage and
polymer chain conformation are also critical factors (Ordoñez, 2009). In addition, many different
chemical aids can be used to induce flocculation process. In this project, different polyaluminium
chlorides (PACs) and FeCl
3
have been used as coagulants; and combinations of a PAC with an
anionic and a cationic polyacrylamide (aPAM and cPAM) have been used as dual systems to
induce the flocculation of colloidal material.

The study and control of the flocculation or coagulation process is carried out by monitoring the
evolution of the particles chord size distribution on real time, which is obtained by a Focused
Beam Reflectance Measurement technique (FBRM) and contains information about the size and
concentration of the particles in the dispersion, whose variation is the image of the flocculation
process for all the flocculation mechanisms (Blanco, 2002).
The FBRM technique implies the use of commercial Mettler Toledo equipment with a probe, which
is entered into the suspension or into the pipe, and an electronic box with a detector (Figure 1). A
computer system controls the equipment and receives the data. This equipment has a laser diode

which emits a laser beam divided in different parallel rays that are focused on a focal point on the
external sapphire probe window (sited in the extreme of the probe that is introduced in the
suspension) through a rotating lens. The focal point describes a circular path at high speed
because of the rotation of the rotating lens. When a particle intercepts with the focal point path,
the light is reflected and conduced to the detector, which receives light impulses, whose duration
is proportional to the chord length of the particle that has intercepted the focal point path (Figure
1).The equipment can measure thousands of particles per second and thus, obtain a chord length
distribution that represents the particle population.


Figure 7: How the FBRM probe works.
This technology is applicable to study any flocculation process, independently of the aggregation
mechanism or the suspension nature. The traditional methodologies, based on the measurement
of the surface charge of the particle, are appropriate to study the aggregation process only when
it implies the modification of these properties, but not when the flocculation is carried out by other
mechanisms, as bridging with neutral polymers, for example (Blanco, 1996; Blanco, 2002).