From the Editor

News and Opinions

The Citizens Petition Regarding Land Application of Biosolids Review and Commentary

ELIOT EPSTEIN, Ph.D.

Feature

EU Strategy and Practice for Sludge Utilization in Agriculture, Disposal and Landfilling

LUDOVICO SPINOSA

Review

Biological Aerosol Emission, Fate, and Transport from Municipal and Animal Wastes

JOHN P. BROOKS, CHARLES P. GERBA and IAN L. PEPPER

Research

Suitability of Fresh and Aged Paper Mill Sludge as Soil Amendments

G. K. EVANYLO, W. L. DANIELS and S. NAGLE

Development of a Laboratory Protocol to Measure Network Strength of Sludges

Using Torque Rheometry

BANU ÖRMECI, KIDON CHO and MOHAMMAD ABU-ORF

Conditioning and Dewatering of Digested Waste Activated Sludges

JOHN T. NOVAK, CHUL PARK and MOHAMMAD M. ABU-ORF

Total and Leachable Extractable Metal Content of South African Sewage Sludge

HEIDI G. SNYMAN and GRAEME KASSELMAN

Factors Affecting Heavy Metals Enrichment in Fly Ash from Sludge Incineration

by a Rotating Drum Furnace

C. M. BRAGUGLIA, D. MARANI and G. MININNI

Treatment of Sludge with Peracetic Acid to Reduce the Microbial Content

J. A. BARRIOS, B. JIMENEZ, and C. MAYA

ARTICLE ABSTRACTS (January 2004, Volume 1/Number 1)

EU Strategy and Practice for Sludge Utilization in Agriculture, Disposal and Landfilling

LUDOVICO SPINOSA

ABSTRACT: The shape of sludge regulation in Europe is undergoing a period of great evolution in which the economical and social implications connected to waste minimization, reuse, and utilization of its material and energy content are also taken into consideration together with the general objective of environmental protection. In this paper the management options for biodegradable wastes, i.e., biological treatments, land application and landfilling, are discussed in relation to the present European legislation in view of its implementation. Activities carried out at European level for the development of standardized testing methods and procedures for sludge characterization are also outlined.

Biological Aerosol Emission, Fate, and Transport from Municipal and Animal Wastes

JOHN P. BROOKS, CHARLES P. GERBA and IAN L. PEPPER

ABSTRACT: This review concerns the generation and fate of aerosols generated from the treatment of wastewater, composting plants, and during handling and land application of wastewater and biosolids. Though many aerosol studies have been conducted on composting and wastewater treatment plants, few studies have been conducted on land-applied biosolids. Wastewater treatment and composting plants generate almost a constant source of aerosols during plant operation, but these aerosols tend to be contained within the plants and pose the greatest risk towards the workers themselves. Land application sites; whether wastewater application or biosolids application, are of concern as communities are beginning to interface with rural areas where land application occurs. However, the majority of the available data suggests that land application operations pose little risk towards the general public with respect to infection from aerosols. Aerosolized microorganisms generated by any of these land application operations appear to be inactivated relatively quickly as many are already in stressed physiological states, and the aerosol environment is also a harsh environment. Inactivation can occur via environmental desiccation, ultra violet light, and oxygen radicals. In the Dowd et al., paper (2000) "worst case" scenarios during land application of biosolids predicted a risk of infection of 1.00 (100%). However an incorrect infectivity constant (r) was used in this calculation. Using the correct (r) value and more realistic values of phage: human virus ratios, the predicted risk is 5 orders of magnitude less than 1.00. In recent years biosolid treatment has improved resulting in lower pathogen concentrations, and even less potential for aerosolization. Risk that does exist can be reduced for waste-treatment workers through the use of hygienic practices, and towards the general public via the implementation of appropriate buffer zones. Overall, the risk of infection via aerosols generated during land application of biosolid is low.

Suitability of Fresh and Aged Paper Mill Sludge as Soil Amendments

G. K. EVANYLO, W. L. DANIELS and S. NAGLE

ABSTRACT: Nutrient availability and the stability of organic matter in pulp and paper mill sludges are key variables that determine the value of such residuals as soil amendments. The effects of fresh and aged dewatered, combined primary and secondary wastewater treatment paper mill sludge on soil properties and plant growth were determined in greenhouse and field studies to clarify how maturity affects their beneficial use. Corn growth was depressed by the fresh paper mill sludge and increased by the aged sludge in comparison to the unamended control soil in the greenhouse. Phytotoxicity, rather than N or P immobilization, appeared to be the cause of the fresh sludge growth suppression in the greenhouse. Corn yields in the field increased with sludge treatment in the order: control<fresh<aged and with sludge rate. Nitrogen availability did not appear to be limited by sludge application despite lower early season soil inorganic N concentrations in the sludge-amended soils. The aged sludge increased soil C more than the same rates of fresh sludge despite the higher concentration of total C in the fresh sludge, possibly due to a more stable form of C in the aged than in the fresh material. Fresh paper mill sludge is a potentially valuable soil amendment due to its nutrient composition and organic C content, but its use may be limited by phytotoxic properties due to inadequate decomposition.

Development of a Laboratory Protocol to Measure Network Strength of Sludges Using Torque Rheometry

BANU ÖRMECI, KIDON CHO and MOHAMMAD ABU-ORF

ABSTRACT: This study aims to develop a laboratory protocol necessary to measure the network strength of water and wastewater sludges using torque rheometry. Previous research has shown that the area under a torque-time rheogram (termed totalized torque) represents the total energy dissipation rate in a suspension, and can be used to estimate the network strength of wastewater sludges [1]. Use of network strength for comparison of sludge samples provides several advantages over using parameters such as peak of the rheogram, yield stress, yield point, and apparent viscosity which do not identify the fundamental changes in the sludge properties during conditioning prior to dewatering. In this study, several aspects of rheogram generation were investigated in order to develop a protocol for network strength measurement. These include reproducibility of the produced rheograms, the impact of impeller speed on measured torque and totalized torque values, and the effect of shear application time on network strength calculations. Several residuals from different treatment facilities including alum, waste activated, aerobically and anaerobically digested sludges were used in developing and testing the protocol. The reproducibility of all rheological measurements was very good which was attributed to the large sample volumes required for measurements with the torque rheometer. The optimum impeller speed was the lowest impeller speed that produced a significant signal output. Higher impeller speeds decreased the sensitivity of the impeller, and decreased the accuracy and precision of the measurements due to the increased turbulence in the beaker. The results also indicated that peaks formed in the first part of the rheograms may provide some information on the characteristics of suspensions and the degree of flocculation, but they are heavily influenced by operational parameters, design of the impeller, and initial turbulence created in the beaker and may not be reliable.

Conditioning and Dewatering of Digested Waste Activated Sludges

JOHN T. NOVAK, CHUL PARK and MOHAMMAD M. ABU-ORF

ABSTRACT: Laboratory digestion studies were carried out in order to better understand the effect of digestion on conditioning and dewatering of waste activated sludges. Changes in biopolymer content, dewatering rate as measured by both capillary suction time (CST) and specific resistance to filtration (SRF), and conditioning requirements were measured. It was found that when waste activated sludge (WAS) was anaerobically digested, substantial quantities of protein were released into solution, increasing conditioning chemical requirements and the specific resistance to filtration (SRF). For aerobically digested sludges, both proteins and polysaccharides were released and together, they accounted for the increased conditioning demand and SRF. For both anaerobically and aerobically digested sludges, the degree of deterioration in dewatering and conditioning requirements were related to the degree of volatile solids (VS) destruction.

Total and Leachable Extractable Metal Content of South African Sewage Sludge

HEIDI G. SNYMAN and GRAEME KASSELMAN

ABSTRACT: This paper reports on a survey of the metal content of South African sewage sludge. Sludge samples were extracted using two total and one leachable extraction method and analyzed for Cd, Co, Cr, Cu, Hg, Mo, Ni, Pb, Zn, Se and B. The study showed that less than 1.75% of the total amount of metal was leached and that none of the sludge analyzed exceeded the South African Sludge Guidelines leachable limit values. The metal content (with the exception of B) was higher in sludge from plants that receive industrial effluent compared to the sludge from plants receiving mainly domestic effluent. The survey indicated that Ni and Zn are the metals of concern in South Africa. Despite this, the majority of the sludge analyzed could still be applied to agricultural soil on a limited sliding scale according to South African Guidelines.

Factors Affecting Heavy Metals Enrichment in Fly Ash from Sludge Incineration by a Rotating Drum Furnace

C. M. BRAGUGLIA, D. MARANI and G. MININNI

ABSTRACT: Incineration tests were performed using sewage sludge as is or spiked with chlorinated organic compounds. Cd, Cr, Cu, Mn, Ni, Pb, and Zn behaviour was studied by assessing their partitioning among bottom, cyclone, and filter ash. Only Cd, Pb, and Zn undergo significant enrichment in the filter ash. Cd and Pb enrichment is enhanced by high chlorine concentrations in the feed-stream. With exception of zinc, the experimental results may be satisfactorily predicted by a thermodynamic model of the combustion chamber. The unpredicted volatilisation of Zn at low chlorine input is attributed to incomplete mixing conditions in the furnace (pyrolysis pockets).

Treatment of Sludge with Peracetic Acid to Reduce the Microbial Content

J. A. BARRIOS, B. JIMENEZ and C. MAYA

ABSTRACT: Land application of biosolids is a practice that represents a beneficial reuse of a wastewater treatment by-product. However, health related problems are reducing the acceptance of this recycling practice, especially when pathogens are present in high concentrations. New processes, or modifications of existing ones, are being studied to achieve better pathogen removal to reduce the potential of spreading diseases. In this study, 550 ppm of peracetic acid were applied to physicochemical sludge showing a reduction of up to 6.9, 6.5 and 1.9 logs of fecal coliforms, Salmonella spp. and helminth ova, respectively, demonstrating the applicability of the process to produce biosolids.

From the Editor

News and Opinions

Pathogens in Sludge: A Case of Sufficient Challenge

AARNE VESILIND

Feature

Innovative Technologies to Reduce Water Content of Dewatered

Municipal Residuals

MOHAMMAD ABU-ORF, CHRISTOPHER D. MULLER, CHUL PARK, and JOHN T. NOVAK

Review

State of the Art in Treatment and Survival of Pathogens in Biosolids

ROBERT S. REIMERS, KARI B. FITZMORRIS, JAMES E. SMITH, GLEN R. BOYD, and

DWIGHT D. BOWMAN

Research

Organic Contaminants of Emerging Concern in Land-Applied Sewage Sludge (Biosolids)

MARK J. LA GUARDIA, ROBERT C. HALE, ELLEN HARVEY, ELIZABETH O. BUSH,

T. MATTESON MAINOR, and MICHAEL O. GAYLOR

Developing Protocols for Measuring Biosolids Stability

MICHAEL S. SWITZENBAUM, ALBERT B. PINCINCE, JOHN F. DONOVAN, ELIOT EPSTEIN,

and JOSEPH B. FARRELL

An Investigation of Activated Sludge Floc Structure in Relation to Solids Retention Time

MOHAMED LAMIN SESAY and F. DILEK SANIN

Energy Recovery in Sludge Management Processes

D. J. LEE and J. H. TAY

ARTICLE ABSTRACTS (April 2004, Volume 1/Number 2)

Innovative Technologies to Reduce Water Content of Dewatered Municipal Residuals

MOHAMMAD ABU-ORF, CHRISTOPHER D. MULLER, CHUL PARK, and JOHN T. NOVAK

ABSTRACT: A large number of dewatering devices, process modifications, physical treatment technologies, and additives are available to enhance water and wastewater residuals dewatering. A combination of two or more of these technologies might be used to further enhance dewatering. These technologies are likely to be limited to particular sites where dryer cake, consistent throughput, or a high quality product is required. On the other hand, if a nearby landfill will accept residuals with low solids at a low cost, dewatering optimization might not be desirable. This paper reports on results from recent research conducted by the Veolia Water North American Technology Center (NATC) in collaboration with several academic institutions to improve dewatering of residuals. The researched areas for improving dewatering are: (1) evaluating an innovative dewatering/drying device; (2) opportunity for modifying upstream residuals characteristics through addition of aluminum ion; (3) evaluating physical pre-treatment through electromagnetic fields; (4) and finally introducing an aeration-processing step prior to dewatering. Results from this research verify the feasibility of several options and technologies for increased water removal from the dewatering processes. An evaluation of these methods and technologies in terms of their technical feasibility is important; however, economic feasibility may reveal opportunities to combine more than one enhancement technology at one site. More importantly, the improvement in dewatering should be economically feasible. Ultimately, these technologies must be evaluated by each specific dewatering facility to determine if dryer cakes are worth the expense.

Organic Contaminants of Emerging Concern in Land-Applied Sewage Sludge (Biosolids)

MARK J. LA GUARDIA, ROBERT C. HALE, ELLEN HARVEY, ELIZABETH O. BUSH, T. MATTESON MAINOR and MICHAEL O. GAYLOR

ABSTRACT: Modern wastewater treatment greatly ameliorates the release to the aquatic environment of pollutants present in industrial and residential discharges. However, the recycling of sewage sludge (also known as "biosolids") as a soil amendment presents additional challenges to the wastewater industry, as they must now also assure these complex materials do not adversely effect the environment. Concerns not only include contaminants historically tracked (e.g. heavy metals, petroleum products, PCBs and pesticides), but also those newly discovered in discharges. We recently detected four classes of emerging contaminants (polybrominated diphenyl ethers, alkylphenols and their associated ethoxylates, polycyclic musks, and triclosan) in 12 biosolid samples collected from around the U.S. These findings support the 2002 National Academy of Science conclusion that contaminants of potential toxicological concern, not previously investigated during development of the EPA Part 503-risk assessment, are present in modern biosolids and that a new National Sewage Sludge Survey and updated risk assessment need to be conducted.

Developing Protocols for Measuring Biosolids Stability

MICHAEL S. SWITZENBAUM, ALBERT B. PINCINCE, JOHN F. DONOVAN, ELIOT EPSTEIN and

JOSEPH B. FARRELL

ABSTRACT: A study was conducted to validate test protocols that are commonly used to assess the stability of various biosolids products and to specify a standard for each test method. A comprehensive and coordinated effort involving a literature review, a selected survey of practicing facilities, and a sampling and analysis program were performed. Information concerning stability testing protocols and data for each of the biosolids stabilization technologies evaluated (aerobic digestion and anaerobic digestion, alkaline stabilization, and composting) and testing methods (specific oxygen uptake rate, volatile solids reduction and additional volatile solids reduction; pH and changes in pH, and carbon dioxide evolution) were collected and evaluated. Specific protocols for each of the five testing methods are recommended. For each of the specific protocols, intrinsic precision data (that is related to the test) are presented. In addition, data are presented from facilities using each protocol to evaluate the collective degree of variability associated with each stabilization process. Using split sample testing, interlaboratory data (variability among different laboratories) are presented. Issues associated with variability, sources of error, shortcomings and numerical criteria values are discussed for each method.

An Investigation of Activated Sludge Floc Structure in Relation to Solids Retention Time

MOHAMED LAMIN SESAY and F. DILEK SANIN

ABSTRACT: In this research solids retention time (SRT) is investigated as a factor influencing activated sludge floc character. Replicate semi-continuous reactors with mixed culture microorganisms are operated at SRT values of 4, 8, 14 and 20 days. Once the reactors are confirmed to be at steady state, bioflocculation capability of sludge is examined by measuring the total extracellular polymer quantity and polymer composition. In addition, surface hydrophobicity is measured as a potential parameter to influence bioflocculation and hence sludge properties. Physical properties of sludge including settleability, filterability and rheology are analyzed for each of the SRT values studied. Results indicate that with the increase of SRT, increased total extracellular polymers (ECP) are produced, along with an increasing ratio of proteins to carbohydrates in the ECP as well as an increase in the hydrophobicity of the flocs. From the physical properties, filterability, settleability and viscosity of sludge increase as the SRT values increase, indicating that sludge at higher SRT values become easier to dewater and settle but harder to pump and transport.

Energy Recovery in Sludge Management Processes

D. J. LEE and J. H. TAY

ABSTRACT: This work presented a preliminary analysis of the energy recovery efficiency of sludge management. Using literature data, this work compares energy recovery potential from several thermal processes, including incineration (with electricity production or sludge pre-drying), supercritical wet air oxidation, pyrolysis, and digestion.

News and Opinions

Dioxins—Why EPA Decided Not to Regulate Dioxin in Sewage Sludge

ROBERT K. BASTIAN

Feature

Freeze-Thaw Conditioning of Activated Sludge: Effect of Monovalent, Divalent, and Trivalent Cations

BANU ÖRMECI

Review

Legislative and Legal Actions Related to Land Application of Biosolids in the United States

ELIOT EPSTEIN

Research

Assessment of Heavy Metals Leachability in Clay-Amended Sewage Sludge Stabilized with Cement for Use as Fill Material

T. T. LIM, J. CHU and M. H. GOI

Improvement of Sludge Quality by Iron-Reducing Bacteria

V. IVANOV, J.-Y.WANG, V. STABNIKOV, XING ZIKUN and J.-H. TAY

Modeling Thermally Pyrolyzed Sludge as a Continuous Mixture

R. M. WU, D. J. LEE, C. Y. CHANG

Heavy Metals Removal from Sewage Sludge—Is Practical Application a Feasible Option?

M .M .MARCHIORETTO, W. H. RULKENS and H. BRUNING

Pathogen Inactivation in Sludge and Two-Phase Anaerobic Digestion

B. PUCHAJDA, J. OLESZKIEWICZ and D. BOWMAN

Minimization of Bio-sludge Production on Anaerobic-Aerobic Treatment of Industrial Wastewater

G.-H. HE, K.-Y. SHOW, Y.-G. YAN, J.-L. LIU and Q.-G. ZHENG

Book Review

Sludge into Biosolids—Processing, Disposal and Utilization

UTA KROGMANN

ARTICLE ABSTRACTS (July 2004, Volume 1/Number 3)

Freeze-Thaw Conditioning of Activated Sludge: Effect of Monovalent, Divalent, and Trivalent Cations

BANU ÖRMECI

ABSTRACT: This study investigates the effect of monovalent (Na+ and K+), divalent (Ca⁺² and Mg⁺²), and trivalent (Al⁺³ and Fe⁺³) cations on freeze-thaw conditioning of activated sludge. Effects of cations on sludge characteristics and bioflocculation have been studied heavily, but few studies have investigated the effect of cations on freeze-thaw conditioning of sludges. This study evaluated the changes in the dewaterability, settleability, turbidity, and solids content of freeze-thawed activated sludge aggregates after the addition of NaCl, KCl,CaCl₂,MgCl₂, FeCl₃, andAlCl₃. The results showed that addition of cations does not improve the freeze-thaw conditioning of activated sludge. The improvement in the dewaterability and settleability of activated sludge after freeze-thaw conditioning decreases with increasing concentrations of cations, and the type of cation seems to be a factor in determining the overall effectiveness of freeze-thaw conditioning.

Assessment of Heavy Metals Leachability in Clay-Amended Sewage Sludge Stabilized with Cement for Use as Fill Material

T. T. LIM, J. CHU and M. H. GOI

ABSTRACT: Potential fate and impact of various significant heavy metals, namely, Pb, Zn,Cu, Ni andCr, in the cement-stabilized sewage sludge products with and without clay amendment were examined using sequential extraction technique, toxicity characteristic leaching procedure (TCLP), and NEN 7341 availability test. It was found that the heavymetal fractionation among various phases in the sludge changed as a result of cement stabilization and clay amendment. While leaching of the heavy metals remained lower than their TCLP limits, the highly alkaline condition introduced by the cement may have the potential to mobilize certain heavy metals, for example, Cu and Cr, due to the dissolution of organic matter in the sludge and the formation of dissolved organo-metals. Amending the sludge with the waste clay could reduce leachability of the heavy metals and enhance the mechanical properties of the resulted sludge product. The mobility of the five heavy metals in the untreated sludge followed the order Zn>>Ni>Cu>Pb>>Cr. However, the order changed to Cu>Zn>Ni>Cr>Pb in the cement-stabilized sludge products.

Improvement of Sludge Quality by Iron-Reducing Bacteria

V. IVANOV, J.-Y. WANG, V. STABNIKOV, XING ZIKUN and J.-H. TAY

ABSTRACT: Sewage sludge can be used in agriculture as organic fertilizer. However, one of the obstacles for this use is the high concentration of heavy metals and the presence of sulphides (acidifying soil or compost). The aim of this research was to develop the biotechnology for improving the quality of sewage sludge that would be used as organic fertilizer. Microbial reduction of inexpensive sources of Fe(III) in anaerobic digester is proposed as a means of preventing the accumulation of sulphide and of enhancing the accumulation of phosphate in sewage sludge. Industrial grade iron hydroxide can serve as a suitable source of Fe(III) The results show that almost all dissolved phosphate is recovered by the reaction with Fe²⁺. Additionally, the activity of iron-reducing bacteria inhibits the production of sulphide by sulphate-reducing bacteria and the growth of these bacteria in anaerobic digesters.

Modeling Thermally Pyrolyzed Sludge as a Continuous Mixture

R. M. WU, D. J. LEE and C. Y. CHANG

ABSTRACT: This work had modeled the pyrolyzed sludge as a continuous mixture, and proposed a general kinetic scheme for interpreting the data of thermogravimetric analysis (TGA) based on Arrhenius-type correlation. The Arrhenius-type of chemical kinetic model is widely employed for interpretation of thermal pyrolysis data of organic compounds. According to the Arrhenius-type kinetic model, the correlation with experimental data is good.

Heavy Metals Removal from Sewage Sludge—Is Practical Application a Feasible Option?

M. M. MARCHIORETTO, W. H. RULKENS and H. BRUNING

ABSTRACT: The present work evaluates some new developments concerning research into the removal of heavy metals from sewage sludge and discusses the significance for practical application. As such, the complete process of sludge treatment as an integral part of a sludge management process is considered. Two conceptual designs of a treatment process that may be applied in practice for heavy metals removal from sewage sludge are discussed. One refers to a physical-chemical treatment and the other to a biological-physical-chemical treatment. In the physical-chemical treatment, the solubilization of heavy metals is achieved by acidification with HCl (pH around 1) with a previous oxidative pre-treatment (in the same reactor) either by aeration or by hydrogen peroxide. In the biological-physical-chemical treatment, the approach is to use a heavy metal mobilization technique, which is mediated by acidophilic bacteria (Thiobacillus) able to produce sulfuric acid. This system consists of an anaerobic bioreactor fed with elemental sulfur as a reduced sulfur source component, which is oxidized by Thiobacillus and converted into sulfuric acid. In this system, a biological sulfate-reducing step, where sulfate is converted into sulfur, is included and, thus, a closed sulfur cycle can be achieved. Based on a brief qualitative evaluation, the feasibility of both treatment systems is accessed. The biological-physical-chemical process seems to be more attractive than the physical-chemical process.

Pathogen Inactivation in Sludge and Two-Phase Anaerobic Digestion

B. PUCHAJDA, J. OLESZKIEWICZ and D. BOWMAN

ABSTRACT: The goal of this study was to examine the ability of the two-phase anaerobic digestion system (thermophilic-mesophilic) to reduce pathogen densities in sewage sludge. Comparisons with single-stage digesters operated at thermophilic and mesophilic temperatures were made. Pathogens tested included fecal coliforms, Ascaris suum eggs, and Clostridium perfringens. The single thermophilic reactor and two-phase system achieved Class A biosolids standards with respect to fecal coliforms and Ascaris eggs destruction at all SRTs tested. The single mesophilic reactor often failed to produce Class B biosolids when fecal coliforms were used as an indicator organism. Very low destruction of Ascaris eggs was observed in mesophilic conditions. None of the systems achieved 1-log reduction of Clostridium perfringens. Based on results from this experiment, the minimum (batch) time to achieve Class A biosolids standards was 1 day at 55°C.

Minimization of Bio-sludge Production on Anaerobic-Aerobic Treatment of Industrial Wastewater

G.-H. HE, K.-Y. SHOW, Y.-G. YAN, J.-L. LIU and Q.-G. ZHENG

ABSTRACT: A biological wastewater treatment plant usually produces large amount of bio-sludge, which incurs high disposal cost. Typically it generates 0.30~0.60 kgVSS/kgCOD_removed. This paper describes a case study that is able tomaintain an overall yield of 0.02 kgVSS/kgCOD_removed using anaerobic and aerobic processes in an industrial wastewater treatment plant. Four steps have been used to minimize the bio-sludge production: 1) optimising the process to enhance expanded granular sludge bed (EGSB) anaerobic reactor to remove 90% of the organics; 2) applying extended aeration to digest bio-sludge at the aerobic process; 3) recycling the filtrate from belt press to anaerobic influent to further digest bio-sludge anaerobically; 4) using sludge dryer to dry the bio-sludge to 90% dry solids. This industrial wastewater treatment plant using anaerobic-aerobic process to treat approximate 10,000 kgCOD/day, but only produces 233 kg of bio-sludge (90%DS by gross weight) every day. The impressive results demonstrate that well-designed and innovative modification can minimize the bio-sludge production from industrial wastewater treatment.

Opinion

Do Bioaerosols Generated During Composting and Land Application of Biosolids Present a Public Health Risk?

ELIOT EPSTEIN

Feature

Bilevel Thresholding of Sliced Image and Construction of Three-Dimensional Model of Sludge Floc

C. P. CHU, D. J. LEE and P. J. HE

Review

Regulations for Biosolids Land Application in U.S. and European Union

R. IRANPOUR, H. H. J. COX, R. J. KEARNEY, J. H. CLARK, A. B. PINCINCE and G. T. DAIGGER

Research

Fate of Selected Heavy Metals during Gasification of Municipal Biosolids

N. CICEK, Q. ZHANG, S. ZUBRISKI and C. EVANS

Comparative Rheology and Particle Size Analysis of Various Types of Bacillus Thuringiensis Fermented Sludges

S. K. BRAR, M. VERMA, R. D. TYAGI, J. R. VALERO, R. Y. SURAMPALLI and S. K. BANERJI

Effects of Storage on Stability and Pathogen Reduction in Biosolids

AMANDA FOX, MOHAMED F. DAHAB, RAO Y. SURAMPALLI and JAMES SMITH

Understanding the Mechanics of Desiccation Cracking of Alum Sludge: Model Development

BANU ÖRMECI, P. AARNE VESILIND and LI-CHUNG CHUANG

Hyperion Plant Biosolids Land Application and Effect on Groundwater Quality

R. IRANPOUR, F. ALATRISTE-MONDRAGON, H. H. J. COX and R. J. KEARNEY

An Application of Winery Sludge to Artistic Clay Productions

D. F. LIN, H. L. LUO and R. Y. LEE

ARTICLE ABSTRACTS (October 2004, Volume 1/Number 4)

Bilevel Thresholding of Sliced Image and Construction of Three-Dimensional Model of Sludge Floc

C. P. CHU, D. J. LEE and P. J. HE

ABSTRACT: This work examined the feasibility of employing various thresholding algorithms to determining the optimal bilevel thresholding value for estimating the geometric parameters of sludge flocs from the confocal laser scanning microscope (CLSM) images. Morphological information extracted from images depends on the bilevel thresholding value. Otsu's method estimated the floc porosity, and the maximum convex perimeter method probed the shapes and spatial distribution of the pores among the biomass granules in the floc. The three-dimensional interior structural model of the sludge floc could be established, based on which the intraflow processes could be simulated.

Regulations for Biosolids Land Application in U.S. and European Union

R. IRANPOUR, H. H. J. COX, R. J. KEARNEY, J. H. CLARK, A. B. PINCINCE and G. T. DAIGGER

ABSTRACT: Land application of biosolids allows the nutritional value of treated sewage sludge to be used beneficially in agriculture. Biosolids are also useful as amendments in soil reclamation projects. Wastewater treatment plants in the U.S. and European Union (EU), however, are facing increasing public opposition to land application due to concerns about human and animal health and the environment from the presence of pollutants and pathogenic organisms in biosolids. This review discusses how present and proposed legislation on biosolids land application in the U.S. and Europe will affect land application as a management option for biosolids. Understanding the regulations is necessary as they guide biosolids research recently in progress at many wastewater treatment plants and institutions. Regulations in the U.S. and EU share the same objective of controlling pathogens and pollutants in biosolids, although differences exist in specific requirements. Future regulations on both continents are likely tobecomemore stringent and more similar to each other. The presence of persistent pollutants in biosolids is of particular concern because: i) concentration limits for pollutants in biosolids are likely to be reduced; ii) newly introduced chemicals may find their way to wastewater treatment plants and accumulate in biosolids; and iii) current metal concentrations in biosolids seem to be the lowest attainable with current pretreatment technologies. These factors as well as future pathogen reduction requirements will put more pressure on wastewater treatment plants seeking to ensure that land application will remain a viable option for biosolids management. In addition, critical studies of the U.S. EPA 40 CFR Part 503 regulations and a Congressional hearing have questioned the scientific basis of this rule as well as policy decisions and monitoring by the U.S. EPA. Odor emissions, emergent pathogens, radio nuclides, and certain pharmaceutical products such as antibiotics and endocrine disruptors are perceived as the main issues that may eventually revise the Part 503 rule. Despite these concerns, no scientific evidence exists that the current practice of biosolids land application would be harmful either to human health or to the environment.

Fate of Selected Heavy Metals during Gasification of Municipal Biosolids

N. CICEK, Q. ZHANG, S. ZUBRISKI and C. EVANS

ABSTRACT: An industrial-scale downdraft gasification system was evaluated for the destruction and conversion of dried municipal biosolids mixed with saw-dust. The producer gas was incinerated in a thermal oxidizer and stack analysis was performed on the emissions. Results on the thermal incinerator emissions indicated that the concentration of total particulate matter exceeded the current provincial (Manitoba) limit for combustion sources, and that further cleaning of the product gas was necessary prior to combustion. All measured heavy metals were found in trace concentrations in the thermal incinerator emissions, with the majority in non-volatile particulate form. The total mercury concentration in the emission (0.019 mg/m3) were below the Canada-wide standard for mercury emissions from sewage sludge incineration (0.070 mg/m3). A mass balance of heavy metals revealed that barium, cobalt, chromium, copper, nickel, and selenium were predominantly captured in the residual ash, while silver, lead, mercury, zinc, and cadmium were predominantly discharged to the atmosphere in particulate form. EPA leachate tests showed that the residual ash was well below the limits where hazardous waste disposal would become necessary.

Comparative Rheology and Particle Size Analysis of Various Types of Bacillus Thuringiensis Fermented Sludges

S. K. BRAR, M. VERMA, R. D. TYAGI, J. R. VALERO, R. Y. SURAMPALLI and S. K. BANERJI

ABSTRACT: Studies have been carried out on variations in the rheological parameters of raw and fermented primary, secondary andmixed type of sludges in the concentration range 10–40 g/l at three different stages—raw, hydrolysed fermented and raw fermented. A rheological study (viscosity and particle size) to ascertain their behaviour was also performed. The impacts of rheology on fermentation of Bacillus thuringiensis var. kurstaki (Btk) to produce a biopesticide were also examined. The sludges were found to be pseudoplastic, thixotropic and, in general, non-Newtonian. The viscosity values increased from 9 to 361 cP; 3 to 156 cP and 4.5 to 72 cP for primary, secondary andmixed sludges respectively at total solids concentration of 10, 15, 20, 30 and 40 g/l. However, the correlation of particle size could not be drawn directly, except for primary sludges where the particle size increased proportionately with increase in viscosity and solids concentration (50–70 mm) in comparison to secondary (42–55 mm) and mixed sludges (27–32 mm). The contribution to non-Newtonian behaviour was a cumulative effect of viscosity and particle size which were further influenced by the treatment processes, namely, sterilisation, hydrolysis and fermentation.

Effects of Storage on Stability and Pathogen Reduction in Biosolids

AMANDA FOX, MOHAMED F. DAHAB, RAO Y. SURAMPALLI and JAMES SMITH

ABSTRACT: Storage can be an effective means of stabilizing small quantities of wastewater sludge. This paper summarized the performance of two pilot-scale storage units operated in the laboratory as well as that of four storage tanks sampled at four different treatment facilities in eastern Nebraska. The degree to which these systems reduced volatile solids (vector reduction) and pathogenic organisms was measured. The pilot-scale storage units consisted of one aerated and one non-aerated storage tank; both of which were intermittently mixed and stored for a period of six-months. Only the non-aerated unit achieved Class A pathogen reduction requirements in terms of fecal coliform reduction and adequate VSS reduction. Three of the four sampled storage tanks at the treatment facilities achieved Class B pathogen reduction requirements and one plant nearly achieved Class A requirements. With increased detention times, these sludge storage tanks may be able to produce a more stabilized end product, which meets Class A requirements.

Understanding the Mechanics of Desiccation Cracking of Alum Sludge: Model Development

BANU ÖRMECI, P. AARNE VESILIND and LI-CHUNG CHUANG

ABSTRACT: Open-air sludge drying is one of the most commonly used methods of sludge dewatering in water treatment plants. It has been well known that formation of cracks increases the drying performance, but the mechanics of desiccation cracking of sludge has not been understood. The main goal of this research was to develop a mathematical model that can describe the mechanics of desiccation cracking of alum sludge on sand drying beds. The model can predict the total strain created on the surface of the drying sludge and the critical water concentration at which cracks start to form. The proposed model is composed of two parts, free shrinkage and the strain caused by the induced stress. Free shrinkage is mainly controlled by the difference in the water content of alum sludge before and after desiccation and the coefficient of shrinkage of alum sludge. The parameters that affect the strain caused by the induced stress are the tensile strength and Young's modulus of elasticity. If the mechanism of sludge cracking is understood, it will be possible to manipulate the drying process and engineer the formation of cracks by adding chemicals or changing the drying conditions.

Hyperion Plant Biosolids Land Application and Effect on Groundwater Quality

R. IRANPOUR, F. ALATRISTE-MONDRAGON, H. H. J. COX and R. J. KEARNEY

ABSTRACT: From 1994, the City of Los Angeles applied Class B biosolids from the Hyperion Treatment Plant (HTP) at its Green Acres Farm in Kern County, California. In response to local regulations, since October 2002 HTP has produced Exceptional Quality (EQ) biosolids by thermophilic anaerobic digestion. EQ biosolids comply with the most stringent limits in the U.S. EPA 40 CFR Part 503 Rule for pollutants (503.13), pathogen reduction (503.32) and vector attraction reduction (503.33) and are considered to be as safe as any other fertilizer. In a further effort to protect the public and the environment, the City of Los Angeles conducted an evaluation of the potential impact of biosolids land application on the groundwater quality. A literature review of the fate and mobility in soil of biosolids constituents indicated a potential for the leaching of nitrate from biosolids. However, this potential is minimal because of the Part 503 Biosolids Rule requirement of land application of biosolids at nitrogen-based agronomic rates. Leaching of other biosolids constituents to groundwater is relatively insignificant because of immobilization in soil (phosphorus, heavy metals, some organic pollutants), biodegradation or volatilization to the atmosphere (some organic pollutants), or inactivation (pathogens). This was confirmed by a review of ground water monitoring data from several land application sites in the USA with over 10 years of biosolids application. Elevated nitrate concentrations in groundwater were sometimes observed, however, an unequivocal correlation between nitrate in groundwater and the land application of biosolids could not be established. The presence of other biosolids constituents in groundwater has never been reported. Groundwater monitoring at the Green Acres Farm in Kern County over 1990–2002 did not indicate any effect of biosolids land application on the groundwater quality. This can possibly be attributed to a combination of two factors: a) low concentrations of pollutants in HTP biosolids; b) limitation of the biosolids application rate to the agronomic rate as calculated from the nitrogen needs of the crops cultured on the Green Acres Farm. Overall, this study confirms the findings of the 2002 reviews of the Part 503 Biosolids Rule by the National Research Council that there is no scientific evidence that the Part 503 Biosolids Rule has failed to protect public health or the environment. However, additional scientific work has been recommended.

An Application of Winery Sludge to Artistic Clay Productions

D. F. LIN, H. L. LUO and R. Y. LEE

ABSTRACT: The objective of this study is to extent the utilization of reclamation of winery sludge. The ceramic clay was replaced by 5% of winery sludge ash to make artistic productions and test tile specimens, which are then fired at four different temperatures, 1050°C, 1100°C, 1150°C, and 1200°C in a furnace. In order to investigate the influence of sludge ash on the productions, properties such as shrinkage, weight loss on ignition, water absorption, and bending resistance were examined. Then EDS and SEM were performed on the specimens. Results show that the addition of winery sludge ash to the ceramic productions lowers the firing temperature, densifies the bodies of productions, reduces the water absorption, and increase the bending resistance. However, the shrinkage increased with rising firing temperatures. The study suggests that it is feasible to apply winery sludge to manufacture artistic ceramic clay productions.

  VOLUME 2, 2005

  Contents and Abstracts

Commentary

Review

Agricultural Reuse of Foundry Sand

BILLIE J. LINDSAY and TERRY J. LOGAN

Feature

Recycling of Water Treatment Plant Sludge via Land Application: Assessment of Risk

PRADEEP JAIN, YONG-CHUL JANG, THABET TOLAYMAT, MICKAL WITWER and

TIMOTHY TOWNSEND

Research

Biodegradation of Sewage Sludge and Food Waste by a Mixed Culture

XIAO-GE CHEN, OLENA STABNIKOVA, JOO-HWA TAY, JING-YUAN WANG and

STEPHEN TIONG-LEE TAY

Presence of Pharmaceuticals and Personal Care Products (PPCPs) in Biosolids and Degradation during Composting

F. BÜYÜKSÖNMEZ and S. SEKEROGLU

Sewage Sludge Rheological Properties Evaluation by Extrusion Tests

VINCENZO LOTITO and GIUSEPPE MININNI

Survival, Growth, and Regrowth of Enteric Indicator and Pathogenic Bacteria in Biosolids, Compost, Soil, and Land Applied Biosolids

KATHLEEN J. ZALESKI, KAREN L. JOSEPHSON, CHARLES P. GERBA, and IAN L. PEPPER

Index Volume 1, 2004

ARTICLE ABSTRACTS (January 2005, Volume 2/Number 1)

Agricultural Reuse of Foundry Sand

BILLIE J. LINDSAY and TERRY J. LOGAN

ABSTRACT: Foundries continually generate large quantities of excess sand that has the potential to be beneficially reused outside of the foundry industry with only about 10% of the total reused primarily for construction purposes. Potential agricultural applications reviewed are as an in situ addition to agricultural soils, use in greenhouse potting or container mixes, as an ingredient in topsoil blends used for landscaping or reclamation purposes, or in rooting zones for sports turf applications. Several studies focused on risk assessment and regulatory guidelines. Use of foundry sand was compared to more commonly used materials like native soil, and composted yard waste.

Recycling of Water Treatment Plant Sludge via Land Application: Assessment of Risk

PRADEEP JAIN, YONG-CHUL JANG, THABET TOLAYMAT, MICKAL WITWER and TIMOTHY TOWNSEND

ABSTRACT: Water treatment sludges (WTS) offer potential benefits when applied to soil and recycling of the waste stream via land application has been proposed as a management option. Recycling of WTS to the land helps conserve landfill disposal capacity and natural resources, but potential environmental and human health risks must be properly evaluated. In this study, alum, ferric and lime WTS samples were collected from 34 water treatment facilities in Florida, US. The concentrations of several inorganic and organic pollutants were analyzed. The results were compared to risk-based soil contaminant thresholds to assess possible human health risk. Leached concentrations were compared to water quality thresholds to examine the potential for groundwater contamination. Although As concentrations did exceed contaminant thresholds in some lime WTS samples, as a whole the land application of lime WTS was found to pose minimal risk. Several elements in the ferric and alum WTS samples exceeded the soil and groundwater thresholds. These include the Fe and Al from the chemical coagulants themselves, as well as trace elements such as As and V. Coagulant analysis suggested that a major source of the As and V in the alum and ferric WTS could be the treatment chemical itself. Other factors are recommended for consideration when evaluating the risk posed by ferric and alum WTS land application, including the rates of application (and thus the final concentration of the amended soil) and the elemental content of existing soil amendments that the WTS might replace or supplement.

Biodegradation of Sewage Sludge and Food Waste by a Mixed Culture

XIAO-GE CHEN, OLENA STABNIKOVA, JOO-HWA TAY, JING-YUAN WANG and STEPHEN TIONG-LEE TAY

ABSTRACT: Conversion of sewage sludge and food waste into fertilizer can offer the combined benefits of reducing the amount of wastes to be disposed of and recycling valuable nutrients for agricultural use. However, sewage sludge and food waste must be stabilized before they are applied in agriculture. In-vessel aerobic thermophilic digestion (ATD) process is an efficient approach for stabilization. To further enhance the ATD process, it is possible to use the active bacteria, which can efficiently degrade food waste and sludge, as a starter culture. In the present study, a mixed culture was developed by using two dominant and active thermophilic bacteria, namely Bacillus stearothermophilus SD 13 and Bacillus coagulans FW 04, isolated from sewage sludge and food waste, respectively. To test the biodegradation capability of the mixed culture on sewage sludge and food waste, the culture was inoculated into the sludge and food waste slurry medium and subsequently incubated at 60°C for 10 days. In the course of the process, total solids, volatile solids, pH, CO₂ evolution and VFA concentration were monitored. The results showed that the mixed culture was effective in degrading sewage sludge and food waste, as indicated by the significantly higher levels of total solids weight loss, volatile solids reduction and CO₂ evolution in comparison with the control in which no bacterial culture was added. The mixed culture inoculated process also exhibited a significantly different pattern in the changes of pH and VFA concentration when compared with the control process. Therefore, this mixed culture could be potentially useful for enhancing the bioconversion of sewage sludge and food waste into fertilizer.

Presence of Pharmaceuticals and Personal Care Products (PPCPs) in Biosolids and Their Degradation during Composting

F. BÜYÜKSÖNMEZ and S. SEKEROGLU

ABSTRACT: The presence of pharmaceuticals and personal care product (PPCPs) in biosolids generated during municipal wastewater treatment (WWTP) was monitored weekly for 19 weeks. Biosolids samples obtained from a local WWTP were subjected to extraction with Soxhlet® apparatus for 24 hours. The extracts were concentrated and analyzed with a gas chromatograph-mass spectrometer. Therewere 18 compounds representing a wide range of origins identified in biosolids including phthalate esters, ibuprofen and galaxolide. Phthalate esters were the most frequently detected compounds; and 4-nonyl phenol was the most concentrated chemical at 210 mg/kg-dry weight basis. The efficacy of the composting process to degrade the 10 of the PPCP compounds was also investigated with and without spiking biosolids. Biosolids were amended with straw, and composted for up to 45 days using a laboratory-scale composting system. The lowest degradation rate was observed for 50.11% for octyl-4-methoxy cinnamate (OM) and the highest was 99.73% for butylated hydroxyl toluene (BHT). For all tested compounds except for unspiked OM, degradation efficiencies surpassed 85% at the end of the 45 days of composting study. The results of this study confirm the presence of various organic contaminants originated from personal care products in biosolids, and suggest that composting could be an effective treatment alternative for biosolids.

Sewage Sludge Rheological Properties Evaluation by Extrusion Tests

VINCENZO LOTITO and GIUSEPPE MININNI

ABSTRACT: Rheological properties have a great importance in sludge management, as they have been successfully used for predicting performance of several sludge treatment processes. Sewage sludge is non-Newtonian fluid, because shear stress is not linearly proportional to shear rate or velocity gradient. Among different equations describing non-Newtonian fluids, the Bingham equation seems to better account physical behavior, i.e. the presence of an initial yield stress until deformation occurs. Rotating viscometers are generally used for measuring rheological properties, but they are costly and difficult to operate in the field. Therefore, research has been carried out to try and measure such properties by adopting simple and applicable field procedures. Several sewage sludges at different solids concentrations were tested using an extrusion apparatus (Kasumeter). Values of rheological parameters were estimated and compared to those measured by a viscometer. Results showed that yield stresses and apparent viscosity can be easily evaluated by Kasumeter and their values are well correlated with those by viscometer. For sludge samples of the same type and origin yield stress appeared strictly correlated to solids concentration, being relationships dependent on sludge type, thus evidencing that other physical, chemical and biological characteristics influence sewage sludge rheology.

Survival, Growth, and Regrowth of Enteric Indicator and Pathogenic Bacteria in Biosolids, Compost, Soil, and Land Applied Biosolids

KATHLEEN J. ZALESKI, KAREN L. JOSEPHSON, CHARLES P. GERBA and IAN L. PEPPER

ABSTRACT: In the U.S. approximately 60% of all biosolids are currently land applied. Although it is known that bacteria in biosolids normally decrease to low or non-detectable levels following treatment, a major concern is that regrowth of pathogens may occur. Specifically the question arises: "Does regrowth occur following reintroduction or recolonization of pathogens after land application or during storage under favorable conditions?" The following paper reviews available information on survival and potential regrowth of pathogenic and indicator bacteria in biosolids, compost, soil, and land applied biosolids. Based on the literature, a conceptual framework is provided to explain the phenomenon of "regrowth."

Commentary

AARON A. JENNINGS

Special Issue

Editors Note to Special Issue

AARNE VESILIND

Municipal Wastewater and Sludge Management in Turkey

F. DILEK SANIN

Review

Legislative Comparision of Turkey and the European Union on Sludge Management

GÜNAY KOCASOY and ÖZLEM DURMUS

Research

Current Status of Filtration Theory

HANDE YÜKSELER, ÜLKÜ YETIS and ISMAIL TOSUN

Carbonization and Reuse Possibilities of Domestic and Industrial Sewage Sludge

SERDAR AYDIN, SINAN GUNEYSU and SEMIHA ARAYICI

Nitrogen Removal from Municipal Sewage Sludge Liquor through Struvite Precipitation for Application in a Mobile Plant

D. ANTAKYALI, S. SCHMITZ, J. KRAMPE and U. ROTT

Thermochemical Hydrolysis of Waste Activated Sludge

SEVGI FERSIZ, MUSTAFA TÜRKER and SEVIL VELI

Modern Rheometric Characterization of Sludges

STEVEN K. DENTEL, AZIZE AYOL and AYSE FILIBELI

Legislative Comparison of Turkey and the European Union on Sludge Management

GÜNAY KOCASOY and ÖZLEM DURMUS

ABSTRACT: In this study, the European Union Environmental Directives and Turkish Environmental Regulations on sludge management were analyzed and compared for their scopes and contents in order to find out how sludge management is regulated in National and Community level. Since the main focus is at urban sewage sludge in both Turkish and EU Legislations, a comparative case study is conducted for Sewage Sludge Directive (86/278/EEC) and its implementation in Turkey as well as in member states. Results were assessed within the context of Turkey's future EU accession, in terms of legislative compliance and compatibility.

Current Status of Filtration Theory

HANDE YÜKSELER, ÜLKÜ YETIS and ISMAIL TOSUN

ABSTRACT: Sludge dewatering is a difficult process in water and wastewater treatment. The purpose of sludge dewatering is to remove as much of the liquid portion of the sludge so that its transport and disposal becomes possible and feasible. The extent of the performance of the filtration operation is highly influenced by the characteristics of the sludge; such as its solids concentration, bound water content, organic content, cellulose content, pH, electrical charge of particles and other sludge specific parameters. To assess the filterability and dewaterability of sludges, parameters like specific cake resistance, capillary suction time and Buchner funnel filtration time are used. The most commonly used parameter is the average specific cake resistance evaluated by the parabolic filtration equation which was developed by Ruth in 1933 employing a heuristic analogy with Ohm's Law. However, it is noted that the average specific cake resistance is not a correct parameter to characterize the filtration characteristics of many types of sludges. Because operational parameters such as, filtration area, pore size of the filter medium, applied vacuum pressure and mode of filtration operation are reported to affect the average specific cake resistance. Besides the conventional filtration theory, in literature three major theories are proposed to define filtration. However, all these three approaches are not practically applicable to characterize the filterability and dewaterability of sludges. This study is a brief review of the current status of the filtration theory.

Carbonization and Reuse Possibilities of Domestic and Industrial Sewage Sludge

SERDAR AYDIN, SINAN GUNEYSU and SEMIHA ARAYICI

ABSTRACT: Sewage sludge disposing methods in Turkey are generally sanitary landfill, land farming and incineration. The increasing numbers of wastewater treatment plants depends on industrialization the increasing amounts of sewage sludge problems. On this occasion, working on reusing of sewage sludge becomes more popular in European Community [1] with limited usage on farming. Pyrolysis is one of the developing technologies applied to make an usable materials from sewage sludge. For this reason, potential of adsorbent production from raw material was investigated in this study. Pyrolysed coke having 814.48 m²/g BET surface area was produced by the thermal process carried out at 500°C, heating rate of 10°C/min, and 2 hours soaking time, with the addition of 2.0 M ZnCl₂ solution. Adsorption capacity of the material was measured with different chemicals and its applicability on activated sludge system was studied.

Nitrogen Removal from Municipal Sewage Sludge Liquor Through Struvite Precipitation for Application in a Mobile Plant

D. ANTAKYALI, S. SCHMITZ, J. KRAMPE and U. ROTT

ABSTRACT: This study presents work done for optimizing the struvite formation in sludge liquors, aiming at the removal of surplus ammonium (NH⁺⁴). The project consists of lab-scale experiments and the transfer of these results onto a mobile experiment unit. The experiments were conducted through addition of external magnesium (Mg²⁺) and phosphate(PO₄^3-)compounds to real and synthetic sludge liquor. Variables such as molar ratio of the components, temperature and pH of the reaction mixture, magnesium and phosphate sources etc. were tested. The results led to the design of a pilot plant and preliminary findings from this plant are also reported.

Thermochemical Hydrolysis of Waste Activated Sludge

SEVGI FERSIZ MUSTAFA TÜRKER and SEVIL VELI

ABSTRACT: In this study, thermochemical hydrolysis of the waste activated sludge collected from the biological treatment plant of a food industry has been investigated. Thermochemical hydrolysis was used as a pretreatment method to reduce the production of waste activated sludge. In the tests, the effects of pH, temperature and reaction time on thermochemical hydrolysis of waste treatment sludge have been examined. It is observed that hydrolysis increases with the increasing temperature and hydrolysis time at extreme pH values. The nitrogen content in sludge dissolves in parallel with COD. The COD solubility in biomass has reached 18–85%. Furthermore, hydrolysis kinetics of sludge is developed at constant temperature and pH. The results are fitted to first order reaction kinetics.

Modern Rheometric Characterization of Sludges

STEVEN K. DENTEL, AZIZE AYOL and AYSE FILIBELI

ABSTRACT: Historically, sludge was one of the first materials for which non-Newtonian behavior was recognized and quantified, due to the engineering challenge of properly pumping this material. Rheology is now employed in many fields, and over recent decades, more sophisticated rheometric techniques have been developed for a range of applications. This paper reviews some of these newer techniques and demonstrates their use in the characterization of sludge. The conventional technique of controlled shear rate (CSR) is used on a waste activated sludge with and without chemical conditioning. The "stress overshoot" phenomenon is observed and discussed, as it complicates the conventional interpretation of such test results. Newer methods are also applied for comparison: a creep test, which uses a constant applied stress while deformation is measured over time, and a strain amplitude sweep test. Neither of these methods experienced the type of difficulties seen with the CSR test. The creep test provides the critical stress level and, with sufficient data, the four parameters defining the Burgers model of deformation. The strain amplitude test provides the yield stress without model assumptions or reliance on data beyond the yield point.

 
  VOLUME 3, 2006
 

CONTENTS (January 2006, Volume 3/Number 1)

Opinion