Iwa international Specialist Conference

48.

Investigation and Assessment of Sludge Pre-treatment Processes

Johannes A. Müller

Institute of Sanitary Engineering and Institute of Mechanical Process Engineering,
Post Box 3329,Technical University of Braunschweig, D-38023 Braunschweig, Germany,
Tel. [phone], Fax [phone], E-mail: [e-mail]
Key-Words: sewage sludge, pre-treatment, disintegration, economic efficiency

Pre-treatment methods are extensively investigated in order to improve subsequent processes of wastewater or sludge treatment. The results presented in this paper will summarize the work of several investigations in lab and full scale quantifying positive as well as negative effects of pre-treatment processes. Based on these results the main focus of this contribution is an assessment of technical and economical pros and cons.

Various methods have been used for pre-treating sludge like heat-treatment, chemicals, mechanical disintegration, advanced oxidation processes, enzymes and others. As much as these processes differ from each other in their mode of operation as much they do in their impact and the costs they are causing.
The following positive effects could be detected in subsequent process steps of wastewater and sludge treatment:

• 
  Shortened stabilisation time and increased degree of degradation
  
• 
  Reduction of the amount of sludge that has to be disposed
  
• 
  Reduction of Pathogens
  
• 
  Improved sedimentation
  
• 
  Reduction of foaming in aeration tanks, settlers and digesters.
  
• 
  Higher solids content of the dewatered sludge and reduced amount of conditioning agent
  
• 
  Substitution of external carbon-sources for the denitrification process
  
• 
  Improvement of processes for nitrogen and phosphorous recycling
  

Apart from the positive effects there are also negative secondary influences as well as the cost of operating the devices and equipment, that have to be considered.

Applying disintegration methods as pre-treatment step, negative secondary influences on the sludge- and wastewater-treatment have to be taken into account as well, such as:

• 
  Increase in sludge water pollution
  
• 
  Increase in flocculent amount needed for conditioning
  
• 
  Reduction in solids content after dewatering
  
• 
  Increase in effluent pollution of WWTP
  

The extent of these problems could be quantified depending on the application and the disintegration method used.

Technical and Economical Assessment: The pre-treatment is an additional step in the chain of sewage sludge treatment. This results in extra costs for build-up and operation of the machines. Main factors are:

• 
  Investment costs
  
• 
  Energy consumption
  
• 
  Personnel costs for operation
  
• 
  Maintenance costs
  
• 
  Costs caused by secondary effects
  

All of the applications mentioned above have been investigated in the presented research work. Positive as well as negative effects could be quantified. The most important results will be presented focussing on investigations in full scale operation, especially in the field of stabilisation processes. Based on these results the cost effectiveness has been assessed taking into account different conditions (Size of WWTP, cost for disposal etc.). From these considerations recommendations are derived, if operational and/or cost advantages by application of pre-treatment processes can be expected.

Literature:

J. Müller (2001). Prospects and Problems of Sludge Pre-Treatment Processes, Water, Science and Technology, 44(2001)10, IWA-Publishing, 121-128 and IWA - Sludge Management Conference, Taiwan, March 2001

Lee, D. J. and Müller, J. A. (2001). Preliminary Treatments in: Sludge into Biosolids – Processing, Disposal, Utilization. Editors: L. Spinosa, A. Vesilind, IWA Publishing, July 2001, ISBN 1-900222-08-6

Further informations at www.tu-bs.de/~jom

49.

Experimental Assessment of Factors Influencing Dewatering Properties of Thermophilically Digested Biosolids
Jianpeng Zhou*, Donald S. Mavinic, Harlan G. Kelly, and William D. Ramey

*Environmental Engineering Program, Department of Civil Engineering, University of British Columbia, Vancouver, BC, Canada.

Abstract: Beneficial land application of processed wastewater sludges (biosolids) is a cost effective, and environmentally sustainable option for the final disposal of sludges, because nutrients and organic matters in the sludge are recovered and reused as a resource. Such a disposal method reduces the need for landfills and incinerations of sludges. The quality of biosolids has a significant impact on whether or not a land application program can be implemented with the support and acceptance of the public, and whether or not biosolids can be successfully marketed as a valuable resource. Thermophilic digestion is an innovative process that digests sludge at high temperatures (50-70^oC), and produces Class A biosolids that are essentially pathogen free, meet metal concentrations, and vector attraction reduction requirements, and can be beneficially reused without any restrictions.
Recent experience from the operation of full-scale thermophilic sludge digestion facilities in Canada and United States, revealed that, although when thermophilic biosolids were adequately conditioned, higher cake dryness and satisfactory solids recovery could be obtained, dewatering thermophilically digested biosolids required 3-10 times (up to 44 to 50 kg polymer/dry-ton solids) more polymers to condition than mesophilically digested biosolids. Therefore, the costs to dewater thermophilically digested sludge are substantially increased.
The current knowledge and understandings on dewatering properties of thermophilically digested biosolids are limited and incomplete. Full-scale application of thermophilic digestion of wastewater sludges had a relatively short history in North America (about 10 years since early 90’). European thermophilic digestion facilities mostly apply biosolids to land directly without dewatering. Reported efforts to reduce polymer consumptions in full-scale included the use of inorganic chemicals (e.g. ferrous or ferric chloride) as the conditioner; to store and to aerate thermophilically digested sludges at ambient temperatures for 25 days. The limitations of these work included: the mass quantities of inorganic chemicals added into biosolids were greater (up to 5 times); additional handling and storage facilities are needed for the corrosive inorganic chemicals; storage and extended aeration required additional tankage and increased power consumptions, therefore, compromised the cost-effectiveness of thermophilic digestion.
The proposed paper is to report a laboratory study that investigated factors having significant impacts on dewatering properties of digested biosolids, and assessed the relationship among digestion, dewatering properties, and characteristics of thermophilically digested biosolids.
The experimental work used batch operated, bench-scale aerobic sludge digesters (5 L each). Duplicate digesters were placed in a waterbath and were operated at 40^oC, 50^oC, 55^oC, 60^oC, or 70^oC, while the third digester was operated at ambient room temperatures of about 22^oC. Feed sludge was thickened secondary sludge (waste activated sludge), and primary sludge from a local secondary wastewater treatment plant. Collected sludge contained approximately 4.5% total solids (TS), and was diluted with tap water to about 2.5% TS as the feed to the digesters. Dewaterability was measured as Capillary Suction Time (CST), and was reported as specific CST (S-CST is CST normalized by TS, high S-CST indicates poor dewaterability). Samples were centrifuged at 10,000g for 20 minutes, and then were filtered through Fisher G-6 filter papers for further analysis of soluble inorganics and cellular biopolymers. Biopolymers were measured as proteins using the Lowry assay (with bovine serum albumin as the standard), and as polysaccharides using the Dubois assay (with glucose as the standard). Other parameters such as pH, conductivity were measured according to Standard Methods. The morphology of thermophilically digested biosolids was examined using a scanning electron microscope. The studied operational factors included feed sludge composition, digestion time, digestion temperature, and shear effects. The characteristics of the thermophilic sludge were assessed for reduction in total solids and volatile solids, the production of ammonia, release of phosphate, the release and formation of cellular biopolymers (proteins and polysaccharides), and the digestion effects on conductivity, pH, particle sizes, and surface charges (Zeta potential) of the digested sludge.
The study found that feed sludge composition significantly affected dewatering properties of both undigested sludge and digested biosolids. When the feed sludge contained higher percentage of the secondary sludge, deterioration in dewaterability of digested biosolids was more significant. The effect of thermophilic temperatures on dewaterabilty is rapid, occurred within 3-hour of digestion (a similar effect was not observed with the mesophilic digestion). The rapid effect in thermophilic digestion appears to be due to “heat shock”, rather than due to growth of a new microbial community. When excessive shear was applied to the sludge in digesters, the shear resulted in a significant deterioration in dewaterability in both of thermophilically and mesophilically digested biosolids.
The accelerated reduction in volatile solids due to thermophilic digestion is not a cause for the excessive poor dewaterability of thermophilically digested biosolids. Increased levels of ammonia and phosphate in the sludge had a slight effect on dewaterability, but the effect was not significant. Thermophilic digestion resulted in smaller particle sizes, but not much change in charges of sludge particles. Thermophilic digestion resulted in a substantial increase in concentrations of cellular biopolymers (proteins and polysaccharides). It appears there is a strong correlation between dewaterability (S-CST) and cellular biopolymers. Protease treatment of the soluble portion of thermophilic digested biosolids resulted in up to 19% reduction in S-CST, which confirmed that cellular biopolymers play a role in dewatering properties of thermophilic biosolids. Similar treatment, using several polysaccharide enzymes, resulted in only a slight reduction in S-CST, which suggested the complex nature of biopolymers’ effect on dewaterability. Such effects might be due to protein-polysaccharides interactions, hydrogen bonding, or hydrophilic and hydrophobic interactions.
Findings from this study presented new information on factors that are most important in affecting dewaterability of thermophilically digested biosolids. Such new information will benefit further efforts in the search of practical solutions to improve the dewatering properties of thermophilically digested biosolids.

50.

Pilot Study of a Fluidized-Pellet-Bed Technique for Simultaneous Solid/Liquid Separation and Sludge Thickening in a Sewage Treatment Plant

X.C. Wang*¹, P.K. Jin*, H.L. Yuan*, E.R. Wang**, N. Tambo***

* School of Environmental and Municipal Engineering, Xi’an University of Architecture and Technology, No 13 Yanta Road, Xi’an 710055, China.

** Beishiqiao Wastewater Purification Center, No 368 Kunming Road, Xi’an 710003, China

*** The University of the Air, 2-11, Wakaba, Mihama-Ku, Chiba 264-8586, Japan

A fluidized-pellet-bed separator was applied in pilot scale at Beishiqiao Wastewater Purification Center, Xi’an, China, for the separation and thickening of activated sludge from an oxidation ditch which performs biological degradation of domestic wastewater. The principle of solid/liquid separation by fluidized pellet bed operation was based on the theory of one-by-one attachment of small particles onto grown particles under rational dosing of polymer flocculant and mechanical agitation as was previously proposed by Tambo and coworkers. The pilot plant for this study was with a capacity of 1.5-2.0 m³/hr. The fluidized pellet bed was formed within a cylindrical column of 700 mm inner diameter and 1450 mm effective height. Mechanical agitation was provided by a number of propellers mounted on a vertical shaft. At the bottom entrance of the bed, polymer flocculant was injected to the inflow suspension that was pumped from the oxidation ditch. Under a stable condition, solid/liquid separation and sludge thickening were performed simultaneously within the fluidized pellet bed – the separated liquid (supernatant) flowed out through the top weir while granular sludge with comparatively low moisture content was collected from the side windows of the cylindrical column by mesh containers where the pellet-like or granular sludge particles were easily screened.

Under the condition of suspension SS around 4000 mg/L, polymer (CJX103, cationic, MW 5x10⁶) dose at a dry solid ratio of 0.003 and upward flow velocity at 5.4 m/hr (volume flow rate of 1.5 m³/hr), the fluidized pellet bed performed solid/liquid separation and sludge thickening well. The SS concentration of the separated liquid was about 5 mg/L on average and the moisture content of the separated sludge was less than 94% which is much lower than that after conventional settling and thickening (about 97% at Beishiqiao Wastewater Purification Center) and easy to be finally disposed. At higher upward flow velocity of 7.2 m/hr (volume flow rate of 2.0 m³/hr), similar results could also be obtained but higher polymer dose (solid ratio of 0.004) was required.

The morphological characteristics and density-size relationship of the granular particles formed in the fluidized pellet bed were also investigated by image analysis and settling velocity measurement of individual particles. On the two dimensional basis, there exists a linear relation between the maximum length and the projected area of the particle on a log-log coordinates, and the fractal dimension was evaluated to be 1.65-1.78, showing a good quasi-spherical morphology of the granular sludge particles. The density-size relation of the particles follows a linear relationship on the log-log coordinates and could be expressed as _e = d^–k, where  = 0.03-0.07, k = 0.7-1.2, showing a much higher density of the granular sludge than the conventional activated sludge.

It is considered that in the fluidized pellet bed, the sludge particles undergo a self thickening process as a result of the mechanical agitation in the high concentration fluidized layer. The polymer flocculant molecules act as bridging agent between individual small particles, bringing about strong resistance of the grown granular particles against the mechanical shear force. On the other hand, under the mechanical shear force any random growth of a particle can be effectively prevented, and a quasi-spherical structure is eventually formed because such structure is believed to be stronger to resist mechanical or hydraulic shearing. With spherical structure, the interstitial water between the granular particles can easily flow out during a simple process such as screening. This explains why the granular sludge has much lower moisture content than the thickened sludge by conventional processes.

The results of the pilot study indicate a possible way to innovate the conventional secondary settling and gravitational thickening processes for solid/liquid separation and sludge handling, especially for small scale wastewater treatment plants to reach the goal of space saving and higher treatment efficiency.

Figure: Granular sludge particles collected from the side window of the fluidized pellet bed

1. 
   flow velocity 5.4 m/hr, polymer dose 0.003 (dry solid ratio);
   
2. 
   flow velocity 5.4 m/hr, polymer dose 0.004;
   
3. 
   flow velocity 7.2 m/hr, polymer dose 0.003;
   
4. 
   flow velocity 7.2 m/hr, polymer dose 0.004.
   

51.

Sludge drying, an overview.
Jon Alsaker

Managing Director, Stord Bartz Biosystems AS, Norway

Abstract.
Drying of the sludge arising from waste water treatment plants has become an increasingly used method of sludge disposal.

Despite of this, sludge drier installations have not been without problems, since they became a real part of the sludge disposal in the early 1980’s.

Factors influencing the choice of drying plant will mainly be :

1. 
   Drying sludge, part drying (scalping) or full drying.
   
2. 
   Sludge characteristics in respect of the drying process.
   
3. 
   The economy of drying, based on the use of energy.
   
4. 
   The economy of drying, other considerations.
   
5. 
   Fire and explosion considerations.
   
6. 
   Drying of sludge and odour abatement.
   
7. 
   Various sludge drier types.
   

In this lecture, an overview is given in respect of :

1. 
   Classifying the drying process :
   

• 
  Part drying, (“Scalping”, drying to 35 – 50 % ts) : Technologies used. Specific heat value of sludge, depending on sludge moisture.
  
• 
  Full drying to 85 – 95 % ts, technologies used.
  

2. 
   Sludge characteristics in respect of drying.
   

• 
  The “glue zone”
  
• 
  Glue characteristics, relating to wastewater treatment method.
  
• 
  Granulation characteristics, relating to sludge drying methods.
  
• 
  Survival of pathogenic bacterias.
  

3. 
   Drying economy in respect of drying method.
   

• 
  Direct fire drying, of hot air drying.
  
• 
  Indirect drying.
  
• 
  Friction drying.
  

4. 
   Drying economy, other considerations.
   

• 
  Cost of drying plant.
  
• 
  Size of the drying plant
  
• 
  Final treatment of dried sludge.
  

5. 
   Fire and explosion considerations.
   

• 
  Self ignition
  
• 
  Critical temperatures.
  
• 
  Critical volumes.
  
• 
  Risk and HAZOP analysis.
  

6. 
   Drying of sludge and odour abatement.
   

• 
  Principles.
  
• 
  Odour abatement methods.
  
• 
  Odour abatement and various drying methods.
  

7. Finally an overview of some of the most popular drying types are being described, such as :

• 
  Direct fired and hot air rotary driers.
  
• 
  Indirect driers, disc, tubes, thin film.
  
• 
  Band driers.
  
• 
  Friction driers.
  

Closing comments.

Disposing of wet, untreated sludge on to landfills will by law cease within the EC area in 2005. Methods at the sludge owner’s disposal will then be limited to a few handful, of which drying in many cases will be the preferred method.

52.

Sludge incineration: good practice and environmental aspects

G. Mininni*, D. Marani* & V. Lotito**

Cnr – Istituto di Ricerca sulle Acque

*Via Reno, 1 – 00198 Roma; **via F. De Blasio 5 – 70123 Bari

The paper presents the results of pilot plant experiments carried out at the Water Research Institute by a fluidised bed and a rotary kiln furnaces on sewage sludge spiked with chlorinated hydrocarbons at different dosages and in different operating conditions. The organic chlorine content in the feed stream was as high as 5 %. On the basis of the experimental results, sludge incineration technologies and relevant best practices are discussed, outlining the criteria for proper selection of the incineration process considering capital and operating costs and environmental constraints.

Test conditions

Main units of the pilot plant are an indirect dryer, a completely circulated fluidised bed furnace (FBF), a rotary kiln furnace (RKF) (it could operate both co- and counter-current mode), an afterburning chamber, a heat recovery system and a flue gas cleaning system (bag filter and wet scrubber). The throughput of the plant was about 250 kg/h of sewage sludge at 20 % solids concentration (60 % volatile) or 160 kg/h of dried sludge at 75 % solids. Either tetrachloroethylene (C₂Cl₄) or a Surrogate Organic Mixture (SOM) consisting of 55 % of tetrachloroethylene (C₂Cl₄), 25 % of chlorobenzene (C₆H₅Cl) and 20 % of toluene (C₆H₅CH₃) were used for spiking sewage sludge on line just before the furnace. In some tests a solution of copper (II) nitrate was added (about 0.25 % of copper, dry basis), to enhance de-novo synthesis of PCDD/F. The two furnaces operated alternatively.

27 tests were performed by FBF and 13 by RKF.

Environmental aspects

PAHs were typically detected in the emissions at levels several orders of magnitude lower than the Italian limit of 10 μg/m³ (Lotito et al. 2001). Lab experiments (Mascolo et al. 2001) suggested that high PAHs emissions are principally due to up-set conditions. Random dioxin concentrations at the stack above the European limit of 0.1 ng/m³ (ITEQ) were found in very few tests, unrelated with the feed characteristics (level of chlorine and type of spiking agent) or with the afterburning temperature. On the contrary the concentrations of PAHs and PCDD/F in the untreated flue gas may be correlated with the temperature of the afterburning chamber. Temperatures in the range of 900-950 °C seem to be high enough to keep the concentration of organic micropollutants at reasonable low levels, even when sewage sludge was spiked with high dosage of chlorinated hydrocarbons (Mininni et al. 2002, a and b). The experimental tests carried out using the rotary kiln furnace showed emissions of organic micropollutant much lower than those relevant to the fluidised bed furnace. This is probably due to the large difference in the gas residence time in the furnace: 6-10 s in the rotary kiln versus 1-1.5 s in the fluidised bed furnace.

As far as the potential emission of heavy metals is concerned, the pilot plant tests showed that metal enrichment in the fly ashes is strictly dependent on the combustion temperature, metal type, chlorine concentration in the feed stream, and on the type of furnace (Braguglia et al. 2001). In the tests by rotary kiln furnace Cd, Pb, Sn and Zn enriched up to 20 times in the fly ashes with respect to the inert fraction of the feed, while Cr, Cu, Mn and Ni showed a refractory behaviour. When the fluidised bed furnace was used, only Cd and Pb showed a significant enrichment in the tests with high chlorine input.
Heat recovery aspects

Sewage sludge is typically a poor fuel with a low heat value (3,100-6,300 kJ/kg) due to the high moisture content (60-80 %) still present after mechanical dewatering. Even though sludge dewatering by filter press may yield solids concentration up to 40 %, usually sewage treatment plants are equipped with centrifuges and belt-presses reaching solids concentrations up to 25-30 %. As a result, sludge incineration is quite expensive due to the high fuel consumption. The optimisation of energy recovery is therefore of paramount importance for minimising operating costs (including amortization) of a sludge incineration plant, in order to make this disposal option attractive.

Typical design approach for energy recovery in sludge incineration performed by fluidised bed furnace implies the use of a sludge drying system. Usually an indirect dryer is utilised, recovering the heat content of steam produced in a boiler downstream the furnace. Dryer, furnace, and boiler design is still uncertain due to the different variables to be optimised, including solids concentration after drying and temperature of exhaust gases after boiler. In this work enthalpy and mass balances are discussed for an assessment of practical and feasible alternatives of energy recovery.

Assuming that steam produced in the boiler is completely used for sludge drying, Fig. 1 (Mininni, 2000) shows that critical concentration of 45.9 %, needed for an autothermal combustion, is obtainable when cake concentration to the dryer is 21.2 %. It must be considered that for disk dryers it is advisable to avoid running the dryer in the critical range of solids concentration between 40 and 60 %, where the sludge becomes sticky and causes clogging problems. Recycling dried cake to the feed sludge and bypassing part of the sludge can prevent these problems.

Electricity production can be estimated in 1.76 MW for a plant of 1 million inhabitants when cake concentration after mechanical dewatering is 40 %. This corresponds to 30-40 % of total energy requirement of the wastewater treatment plant. The percentage drops to 20-25 when cake solid concentration is equal to 30 %.

Fig. 1 Cake concentration after thermal drying vs. cake concentration before drying (total utilisation of steam produced in incineration of dried cake)

Conclusions

From the above results it may be concluded that:

1. 
   Rotary kiln furnace appears very effective in destruction of organic micropollutants. In comparison, fluidised bed furnace may cause higher but still limited emissions of organic micropollutants but it produces fly ash with lower heavy metals content;
   
2. 
   Afterburning chamber may be a useful system for controlling organic emissions which are mainly caused by up-set conditions;
   
3. 
   Optimal design of an incineration process requires a minimisation of fuel consumption and of exhaust gas production. This can be easily obtained by a proper integration of the furnace with the thermal drying unit, in order to produce a dried cake with the minimum solid concentration, which guarantees a self-sustaining operation. Feeding the furnace with a too concentrated cake implies the use of bigger dryer and boiler, without any practical advantage from the energy point of view.
   

Bibliography

Braguglia C.M., Marani D. & Mininni G. (2001): “Comportamento e destino dei metalli pesanti nel processo d’incenerimento”, atti del Convegno “Processi termici con recupero di energia per lo smaltimento di fanghi e di rifiuti speciali anche pericolosi” Quad. Ist. Ric. Acque, n. 115, 93-123.

Lotito V., Mininni G., Spinosa L. & Antonacci R. (2001): “Valutazione delle emissioni prodotte nelle prove sull’impianto dimostrativo di essiccamento e di incenerimento di fanghi”, atti del Convegno “Processi termici con recupero di energia per lo smaltimento di fanghi e di rifiuti speciali anche pericolosi” Quad. Ist. Ric. Acque, n. 115, 14-59.

Mascolo G., Mininni G., Bagnuolo G., Lotito V. & Spinosa L. (2001): “Distruzione e formazione di microinquinanti organici nel processo di incenerimento”, atti del Convegno “Processi termici con recupero di energia per lo smaltimento di fanghi e di rifiuti speciali anche pericolosi” Quad. Ist. Ric. Acque, n. 115, 124-159.

Mininni G. (2000): “Ottimizzazione del recupero di energia nell’incenerimento dei fanghi di depurazione con forno a letto fluido” RICICLA 2000, Rimini fiera, 8-11 novembre 2000, 340-345.

Mininni G., Sbrilli A., Guerriero E. & Rotatori M. (2002): “Dioxins and furans in sludge incineration by fluidized bed and rotary kiln furnace”, accepted for publication on Chemosphere.

Mininni G., Sbrilli A., Guerriero E. & Rotatori M. (2002): “Polycyclic aromatic hydrocarbons formation in sludge incineration by fluidised bed and rotary kiln furnace”, submitted for publication on Water, Air & Soil Pollution, 12 pp.

53.

Abstract for the IWA International Specialist Conference

Biosolids 2003 – Wastewater Sludge as a Resource

Norwegian University of Science and Technology (NTNU)
Kinetic measurements during an acid thermal hydrolysis
Michael Recktenwald, Kemira Kemi AB, Sweden

Sewage sludge is a complex system composed of organic and inorganic compounds. In the KREPRO-process by KEMIRA, sludge volumes are reduced by an acid thermal hydrolysis. Both organic and inorganic compounds are transferred from the solid phase into a soluble form which decreases sludge volumes considerably by 80 %, compared to a conventionally dewatered digested sewage sludge. At the same time, the KREPRO-process makes valuable compounds accessible for recycling and recovery. The valuable compounds are e.g. precipitants and phosphates on the inorganic side, and organic compounds that create a carbon source for reuse in the sewage treatment plant on the organic side.

The inorganic compounds are simply dissolved by the impact of the acid in the aqueous system. Organic compounds undergo a different procedure. They are degenerated, hydrolysed and decomposed by the heat treatment.

Studies were made on the dissolution of organic and inorganic matter during the thermal hydrolysis. The variables were temperature, added amount of acid, dry solids content and residence time. Starting from these variables, a model can be formed for the description of the way of the individual compounds through the process.

For a later process design or an adaptation for a new customer, predictions can be made on the distribution of the compounds between the phases and on the benefits of the recovery and the reuse of the matter.

The studies showed that the choice of the starting variables had a decisive impact on the resulting volume reduction, on the yields and the recovery of the valuable compounds and thus on the process design.

The findings can form the base for an individually tailored process for any sewage treatment plant, depending on their preferences and needs for e.g. the recovery of coagulant or for the production of a carbon source.

Michael Recktenwald

Kemira Kemi AB

Box 902

SE – 252 34 Helsingborg
Tel.: [phone]

Fax: [phone]

E-Mail: [e-mail]
54.

Sludge thermal oxidation processes. Energy and material recovery.

Eric Guibelin. OTV S.A., France