Disposal Of Municipal Sewage Sludge Research Articles

Biochar from Co-Pyrolyzed Municipal Sewage Sludge (MSS): Part 2: Biochar Characterization and Application in the Remediation of Heavy Metal-Contaminated Soils

The disposal of municipal sewage sludge (MSS) from wastewater treatment plants poses a major environmental challenge due to the presence of inorganic and organic pollutants. Co-pyrolysis, in which MSS is thermally decomposed in combination with biomass feedstocks, has proven to be a promising method to immobilize inorganic pollutants, reduce the content of organic pollutants, reduce the toxicity of biochar and improve biochar’s physical and chemical properties. This part of the review systematically examines the effects of various co-substrates on the physical and chemical properties of MSS biochar. This review also addresses the effects of the pyrolysis conditions (temperature and mixing ratio) on the content and stability of the emerging pollutants in biochar. Finally, this review summarizes the results of recent studies to provide an overview of the current status of the application of MSS biochar from pyrolysis and co-pyrolysis for the remediation of HM-contaminated soils. This includes consideration of the soil and heavy metal types, experimental conditions, and the efficiency of HM immobilization. This review provides a comprehensive analysis of the potential of MSS biochar for environmental sustainability and offers insights into future research directions for optimizing biochar applications in soil remediation.

Thermal Characterization, Kinetic Analysis and Co-Combustion of Sewage Sludge Coupled with High Ash Ekibastuz Coal

Efficient utilization of natural resources and possible valorization of solid waste materials such as sewage sludge into secondary materials via thermal conversion and simultaneously recovering energy is vital for sustainable development. The continuous increase in metropolises leads to an enormous production of wet sewage sludge, which creates major environmental and technical issues. In this paper, the samples of sewage sludge from Astana’s waste water treatment plant are analyzed for their thermochemical properties, followed by thermogravimetric and kinetic analysis using the Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods. Overall, the calorific value of sewage sludge sample was 18.87 MJ/kg and was comparable to that of the bituminous coal samples. The activation energy varied from 140 to 410 kJ/mol with changing conversion from 0.1 to 0.7. Further, mono-combustion and co-combustion experiments of the sewage sludge with high ash bituminous coal were conducted using the laboratory scale bubbling fluidized bed rig, respectively. The difference in NOx emissions between mono-combustion of sewage sludge and co-combustion with coal were at around 150 ppm, while this value for SO2 was similar in average, but fluctuates between 150 and 350 ppm. Overall, the findings of this study will be useful in developing a co-combustion technology for a sustainable disposal of municipal sewage sludge.

Recycling reuse of municipal sewage sludge in sustainable structural materials: Preparation, properties, crystallization and microstructure analyses

As a common solid waste in daily life, the disposal of municipal sewage sludge has always been global hot issues concerned by the world environmentalists. The present study reported the fabrication of lightweight high-strength bricks as sustainable structural materials by using kaolin and recycled municipal sewage sludge waste, and systematically discussed the effect mechanism of sintering temperature on product technical properties from both phase composition and microstructure. It showed that after sintering at 1250–1400℃, the porosity, sintering shrinkage, bulk density, compressive and bending strength of lightweight high-strength bricks were 11.30–37.18%, 23.81–38.86%, 1.57–2.22 g/cm3, 35–105 MPa and 23–84 MPa, respectively. And the variation trend of sintering shrinkage, bulk density and mechanical strength was positively correlated with sintering temperature, but completely opposite to that of porosity. For the phase composition, the change of sintering temperature would not affect the crystallization phase types in bricks, which were all composed of aluminum iron phosphate (Al0.67Fe0.33PO4), cristobalite (tetragonal SiO2), hematite (Fe2O3), sillimanite (Al2O3·SiO2) and mullite (3Al2O3·2SiO2). For the microstructure, the melting and consolidation degrees of bricks were higher as the sintering temperature rose, and the structure became more dense and compact under the action of liquid glass phase, leading to a remarkable improvement and optimization of technical properties. Besides, the developed lightweight high-strength bricks presented strong competitiveness in structural materials, advancing a win–win for environment and development.

Remote Sensing Detection and Resource Utilisation of Urban Sewage Sludge Based on Mobile Edge Computing

Abstract Improper disposal of municipal sewage sludge poses a significant threat to effective environmental protection. With the continuous advancement of artificial intelligence technology and the Internet of Things (IoT), remote sensing detection technology is emerging as a promising research avenue to address this issue. However, the current state of real-time detection technology is inadequate, hindering comprehensive and stable monitoring operation. Additionally, the rational use of network resources remains suboptimal. To address this challenge, this study proposes a resource optimisation technology for the current insufficient intelligent monitoring system of urban sewage sludge. By leveraging IoT and wireless technology, water meter data can be collected with minimal earth construction compared to traditional PLC collection. This is followed by utilising Faster R-CNN to plan the network transmission of sewage remote sensing information resources. Finally, the architecture collection module’s scalability is enhanced by incorporating edge computing and reserving sensor ports to meet future plant expansion demands. The experiment demonstrates the significant potential of this technology in application and resource optimisation. In actual parameter tracking tests, the proposed method effectively monitors sewage sludge, providing policy guidance and measure optimisation for relevant authorities, ultimately contributing to pollution-free urban development.

Hydrodynamics of a reactor for thermocatalytic oxidation of sewage sludge

One of the promising methods for the disposal of municipal sewage sludge is its thermocatalytic oxidation in fluidized bed reactors. An important factor determining the stability of the operation of fluidized bed reactors is the uniform introduction of the air flow, which, on the one hand, fluidizes a bed of catalyst solid particles and solid sewage sludge, and, on the other hand, the oxygen of the air flow serves as an oxidizing agent in chemical reactions occurring in the reactor. A pilot plant for thermocatalytic oxidation, created according to the technology of the Boreskov Institute of Catalysis, is operated at JSC Omskvodokanal (Omsk, Russia). The plant's capacity is 50 thousand tons per year of mechanically dehydrated sludge with a water content of 70–80 wt%. The cross-sectional area of the sludge combustion zone is 3.8 m2. The heat flow from the incoming sludge (physical heat and heat of combustion) is 6527000 kcal/h. The air flow was introduced into the fluidized bed reactor with a sparger of 6 perforated pipes arranged horizontally and in parallel. The purpose of this work is to investigate the influence of inlet conditions on fluidized bed hydrodynamics. The results obtained showed that despite the uneven distribution of air flow through the holes of the sparger tubes, each pair of adjacent sparger tubes mutually compensate each other in terms of air flow per unit area of the cross section of the reactor. It is also shown that during the operation of the reactor, air cavities are formed under the sparger pipes, which are practically free of solid particles. The position of such air cavities and their approximate volume are stationary in time for a developed fluidized bed, and the volume of the cavities is approximately proportional to the dimensions of the respective sparger tubes. These air cavities periodically eject bubbles into the overlying portions of the fluidized bed. The dimensions of the bubbles are comparable to the transverse dimensions of the pipes.

Utilization of Indole Acetic Acid with Leucadendron rubrum and Rhododendron pulchrum for the Phytoremediation of Heavy Metals in the Artificial Soil Made of Municipal Sewage Sludge.

The development of phytoremediation by garden plants is an effective way to deal with the dilemma of municipal sewage sludge disposal. In this study, two ornamental plants were used as phytoremediation plants to rehabilitate heavy-metal-contaminated municipal sewage sludge in field experiments, and the role of exogenous phytohormone IAA was also tested. Ornamental plants Loropetalum chinense var. rubrum (L. rubrum) and Rhododendron pulchrum (R. pulchrum) adapted well to the artificial soil made of municipal sewage sludge, and the concentrations of Cu, Zn, Pb, and Ni were decreased by 7.29, 261, 20.2, and 11.9 mg kg−1, respectively, in the soil planted with L. rubrum, and 7.60, 308, 50.1, and 17.7 mg kg−1, respectively, in the soil planted with R. pulchrum, accounted for 11−37% of the total amounts and reached significant levels (p < 0.05), except Cd. The concentration of Pb in all parts of the two ornamental plants was increased, as well as most heavy metals in L. rubrum root. As a result, three months after transplant, the phyto-extraction amounts in L. rubrum were 397, 10.9, and 1330 μg for Ni, Cd, and Pb, respectively, increased by 233% to 279%. The phyto-extraction amount in R. pulchrum were 1510, 250, and 237 μg for Zn, Pb, and Cu, respectively, increased by 143% to 193%. These results indicated a potential to remediate heavy metals of the two ornamental plants, especially L. rubrum. The results of correlation analysis implied that the interaction of heavy metals in the plant itself played an important role in the uptake of heavy metals. This seemed to explain why applying IAA in the experiment had little effect on plant growth and phytoremediation of heavy metals. This study provided a green and feasible idea for the proper disposal of municipal sewage sludge.

Extraction and separation of lipids from municipal sewage sludge for biodiesel production: Kinetics and thermodynamics modeling

Safe disposal of municipal sewage sludge is a severe environmental issue in the wastewater treatment plan worldwide due to its enormous volume of generation and containing hazardous substances. The purpose of the present study is to appraise the possibility of utilizing the municipal sewage sludge as a lipids feedstock for biodiesel production. Lipids from the municipal sewage sludge were extracted via the soxhlet extraction method using methanol as a solvent. The soxhlet extraction of lipids was conducted with varying temperature (40–80 °C), treatment time (2–12 h), and sewage sludge to solvent (S/L) rato (1: 05–1:10). The maximum lipids extraction obtained about 27% from municipal sewage sludge using methanol as a solvent at S/L ratio of 1: 10, the temperature of 70 °C, and a treatment time of 8 h. Thermodynamics and kinetics behavior of the soxhlet extraction of lipids were determined using Eyring theory and a second-order rate equation, respectively. Approximately 84% of biodiesel was synthesized from soxhlet extracted lipids using the alkaline transesterification method at a catalyst loading of 5 wt%, temperature of 60 °C, an oil and methanol molar ratio of 1:9, and reaction time of 4 h. The physicochemical characterization of biodiesel showed that the biodiesel properties complied with the American Society for Testing and Materials standards of D6751 (ASTM D6751) and European Nationals standards of 14214 (EN 14214). The finding of the present study showed that the municipal sewage sludge could be consumed as an impending feedstock for biodiesel production.

Promoting the sustainable fabrication of bricks from municipal sewage sludge through modifying calcination: Microstructure and performance characterization

The disposal of municipal sewage sludge (MSS) has long been a huge burden for metropolis. It has been proved that the MSS can be recycled in fired brick manufacture, but the influence mechanism of calcination procedure is still worth to be investigated deeply. And the shift from natural clay resources to rich shale and sludge resources is urgently needed in brick industry. In this study, 15% of MSS was used as pore-forming agent and mixed with 85% of shale for preparing the green body. The influence of calcination procedure (firing temperature and heating rate) on the overall performance, involving the volume stability, compressive strength and durability, was analyzed systematically. Results showed that 900 °C was the optimal firing temperature at which the compressive strength of bricks reached up to 34.4 MPa, the thermal conductivity was lower than 0.50 W/(m·K), and the water absorption and strength loss after freezing-thawing attack were both below 20%. Rising the temperature too quickly tended to form a highly heterogeneous structure characterized by the appearance and phase gradient distribution outside in. The quantitative microstructure determination and mechanism analysis further confirmed that amorphous phase content and porosity were the crucial factors affecting the brick performance. The leaching analysis confirmed that incorporating MSS in brick preparation achieved a safe disposal of heavy metals. The fundamental study would lay a solid foundation for the firing optimization and recycling sludge more efficient, and provide date support for complete usage of shale and MSS in fire brick manufacture.

Sewage sludge ditch for recovering heavy metals can improve crop yield and soil environmental quality

The treatment and disposal of municipal sewage sludge (MSS) is an urgent problem to be resolved in many countries. Safely using the nutrients within MSS to increase crop yield and enhance the fertility of poor soil could contribute to achieving sustainable development. An indirect use of MSS in ditches alongside Pennisetum hybridum plants was studied in field plots for 30 months and the contents of heavy metals and macronutrients were monitored in soil, sludge and plant samples. We found that the yield of P. hybridum was significantly increased by 2.39 to 2.80 times and the treated plants had higher N content compared with no sludge. In addition, the organic matter (OM) and N contents in the planted soil increased significantly compared with the initial soil. The OM content in the planted soil of the MSS treatment was 2.9 to 5.2 times higher than that with no sludge, and N increased by 2.0 to 3.8 times. However, MSS had no significant effect on the N, P and K contents in the soil at the bottom of the MSS ditch, and the content of heavy metals (Cd, Pb, Cu and Zn) were also within the safe range. Moreover, the moisture content and phytotoxicity of MSS after this indirect use were reduced and the heavy metal contents changed little, which is favorable to the further disposal of recovered MSS. Therefore, this indirect use of MSS is beneficial to agricultural production, soil quality and environmental sustainability.

Selecting sustainable technologies for disposal of municipal sewage sludge using a multi-criterion decision-making method: A case study from China

With rapid economic development and urbanization, there has been an increased generation and discharge of municipal sewage in China, ultimately increasing the amount of sewage sludge entering the treatment facilities. Given this rising problem, finding environmentally friendly, cost-effective, and socially acceptable disposal options for the municipal sewage sludge is crucial for sustainable development. This study evaluated various sludge disposal and treatment technologies for their environmental, economic, and social sustainability and developed an assessment model using multi-criteria decision-making methods. A combined Analytic Hierarchy Process and Vlsekriterijumska Optimizacija I Kompromisno Resenje approach was used for sequencing of the alternatives and evaluation of the most sustainable disposal system based on a set of sustainability indicators. The model results were validated using the Technique for Order Performance by Similarity to Ideal Solution method. Six typical municipal sewage sludge disposal technologies in China were selected for evaluation. The results showed that municipal sewage sludge disposal through land application revealed the best performance (Q = 0.000), and proved to be the ideal choice for sustainable sludge treatment. This was followed by building materials application (Q = 0.207) and disposal through pyrolysis (Q = 0.362), while landfill showed the highest environmental impact and least overall benefit (Q = 1.000). Then, a sensitivity analysis showed that the results obtained are robust and effective, and weight changes of more than 80% indicated land application to have the best performance. Finally, the predicaments and suggestions of municipal sewage sludge land application was analyzed in China from the aspects of standard and sludge quality.

Study on the current situation of municipal sewage sludge disposal and disposal process

In the process of urbanization, each city should actively respond to the call of the country and regard sustainable development as the core of development. Based on this, cities should pay attention to urban environment and ecological benefits. In cities, urban sewage plants should pay more attention to sludge treatment and disposal. Through strict sludge treatment, the impact of heavy metals and pathogens in the sludge on the urban environment will be reduced. Based on the continuous updating of sludge treatment technology and processing equipment in China, urban sewage plants must strengthen the rational disposal of sludge. In order to improve the efficiency of sludge disposal and avoid pollution to the environment, it is particularly important to do a good job in sludge treatment status and technology research. Briefly analyse the source and nature of sludge in urban sewage treatment and the status of sludge treatment and disposal, and focus on the relevant sludge treatment technology to provide reference for better application of sludge treatment technology.

One-step preparation of ZVI-sludge derived biochar without external source of iron and its application on persulfate activation

Zero Valent Iron (ZVI) is an important and widely employed environmental remediation material in brownfield. However, the instability of fine size ZVI and the strong aggregation of nanoscale-ZVI limited its further application. To overcome these drawbacks, ZVI-Sludge Derived Biochar (SDBC) was prepared without external iron source through the one-step process of pyrolysis. The characterization results including SEM-EDX, XRD and XPS confirmed the successful loading of Fe0 on the surface of SDBC. The activation efficiency of persulfate (PS) in in-situ chemical oxidation system was studied. The environmental remediation properties of ZVI-SDBC/PS system were evaluated employing acid orange (AO7) and landfill leachate as target pollutants. ZVI-SDBC/PS system was highly efficient as that 99.0% of AO7 (0.06 mM) was removed by 0.925 mM of PS and 0.5 g L−1 of ZVI-SDBC. In addition, total organic carbon (TOC) and ammonia in leachate were removed by 62.8% and 99.8%, respectively. The removal efficiency of AO7 was nearly independent on initial pH as that 89.1% and 99.1% of AO7 were removed at pH of 9.08 and 2.13 respectively. Hydroxyl radicals dominated in the reaction under neutral and alkaline conditions with contribution rates of 71.9% and 86.1% respectively. Noticeably, not only free radicals but also non-radical species such as singlet oxygen contributed to the degradation, which favored the pH-independent performance. The reuse performance of ZVI-SDBC was higher than these of previously reported ZVI-based catalysts as that the first-order rate constant of AO7 removal decreased not much from 0.0718 to 0.0502 min−1 after the three-cycle reuse assays. In summary, ZVI-SDBC showed advantages such as the facile and chemical-saving preparation method, reliable disposal of municipal sewage sludge, remarkable efficiency and stability. These advantages proved ZVI-SDBC/PS system as an effective strategy of controlling waste by waste, and implicated its potential application in full-scale for environmental remediation in brownfield.

Characteristics of Liquid Products in Supercritical Water Gasification of Municipal Sewage Sludge by Continuous Flow Tubular Reactor

Sewage sludge is a by-product of wastewater treatment, containing high water and organic content. Supercritical water gasification provides sustainable treatment for biomass sources such as sewage sludge. In this study, the effects of operating conditions (temperature, solid matter content and catalyst) and raw material properties on the resulting liquid products were determined in order to exhibit the success of this innovative technology for treatment and disposal of municipal sewage sludge using a continuous flow pilot-scale tubular reactor for the first time in Turkey. As a result of the study, it was determined that the higher the temperature, the higher the quality of the liquid product. TOC removal efficiencies increased from 84.4% to 99% with increasing the temperature from 450 to 650 °C, for 1% solid matter content. The pollutant concentrations in the liquid products increased by increasing the solid matter content of the raw sludge from 1 to 2%. This situation has been eliminated by the catalyst (KOH) addition, resulting in a very transparent liquid product. Additionally, TOC removal of 99.8% was obtained after addition of 2% catalyst. Thus, supercritical water gasification (SCWG) has been considered as a notable technology for the treatment and disposal of sewage sludge without the need of additional pre- or post-treatment.

Sustainable management of sewage sludge

The structure of municipal sewage sludge management in Poland, along with the change in legal regulations, has changed radically. The management of sewage sludge is of key importance for environmental pollution and limiting the negative impact on human health. This article presents current legal policies in Poland, methods of commonly used sewage sludge management in European countries, discusses the selection of an appropriate method for the disposal of municipal sewage sludge and an analysis of the current state of sewage sludge management in Poland. In addition, the difficulties associated with the adaptation of sewage sludge management for the requirements of sustainable development are discussed. The article contains foundations, challenges and concerns related to the thermal transformation of municipal sediments. Also forecast and directions of activities in sewage sludge management in Poland are presented.

Effect of agricultural application of municipal sewage sludge on plant-soil system: A review

Currently, reasonable disposal of municipal sewage sludge is one of the important issues in the field of resources and environmental science. Sludge is rich in large amounts of organic matter and available nutrients, promoting soil fertility, soil physical structure and biological properties. However, sludge contains a variety of heavy metals, organic contaminants and other hazardous substance, especially heavy metals, which are the bottlenecks of agricultural application of sludge. To improve the sewage sludge utilization efficiency and decrease the effect on soil, this essay made a summary on domestic and foreign studies on plant-soil interaction ecosystem with sewage sludge to provide a theoretical basis and scientific guidance for advancing sewage sludge utilization efficiency.

Enhanced photodegradation of pentachlorophenol in a soil washing system under solar irradiation with TiO2 nanorods combined with municipal sewage sludge

A novel remediation method for soil contaminated with hydrophobic chlorinated aromatic pollutants (HCAPs) was developed using TiO2 nanorods combined with municipal sewage sludge in surfactant solution. The target contaminant washed into surfactant solution from polluted soil can be rapidly removed under natural sunlight irradiation. The photocatalyst synthesized by TiO2 combined with municipal sewage sludge by a hydrothermal process shows excellent ability in this situation. The TiO2 nanorods appear on the surface of municipal sewage sludge, which offers a new way of solving waste municipal sewage sludge disposal problem and of producing high-activity photocatalyst. The nanocomposite was characterized by SEM, X-ray diffraction, and UV–Vis DRS. Results showed that the new nanocomposite was better than the original TiO2 catalyst. Using the proposed method in this study, the target contaminant can be removed by up to 97% after 30min of irradiation in natural sunlight, whereas the surfactant loss was only 27%.

Soil microbial functional and fungal diversity as influenced by municipal sewage sludge accumulation.

Safe disposal of municipal sewage sludge is a challenging global environmental concern. The aim of this study was to assess the response of soil microbial functional diversity to the accumulation of municipal sewage sludge during landfill storage. Soil samples of a municipal sewage sludge (SS) and from a sewage sludge landfill that was 3 m from a SS landfill (SS3) were analyzed relative to an undisturbed reference soil. Biolog EcoPlatesTM were inoculated with a soil suspension, and the Average Well Color Development (AWCD), Richness (R) and Shannon-Weaver index (H) were calculated to interpret the results. The fungi isolated from the sewage sludge were identified using comparative rDNA sequencing of the LSU D2 region. The MicroSEQ® ID software was used to assess the raw sequence files, perform sequence matching to the MicroSEQ® ID-validated reference database and create Neighbor-Joining trees. Moreover, the genera of fungi isolated from the soil were identified using microscopic methods. Municipal sewage sludge can serve as a habitat for plant pathogens and as a source of pathogen strains for biotechnological applications.

Chesapeake Bay nutrient pollution: Contribution from the land application of sewage sludge in Virginia

Human health concerns and the dissemination of anthropogenic substances with unknown consequences are the reasons most often given why disposal of municipal sewage sludge in landfills or using the organic waste as biofuel is preferable to land application. But no “fertilizer” causes more nitrogen pollution than sludge when applied according to Virginia law. Poultry litter is the only other “fertilizer” that causes more phosphorus pollution than sludge. Cost savings by the few farmers in Virginia who use sludge are far less than the costs of the nitrogen pollution they cause. A ban on the land application of all forms of animal waste is very cost-effective and would reduce Chesapeake Bay nutrient pollution by 25%.

Treatment and Disposal of Municipal Sewage Sludge and it’s Resources Utilization as Construction Material

During the process of sewage treatment, some by-products are generated and among them, the sludge stands out, because of the largest volume and mass generated, and for containing heavy metals in its composition. Sludge is generally disposed of through land filling and spreading on reclaimed land. It has resulted in seriously contamination. It is necessary to improve the method of the disposal of sludge. Balanced with the environmental and economic benefit, the disposal of sludge, the economy and the environment can be optimized so as to realize the sludge stabilization, sludge reduction and sludge reutilization.

Replacement of a multiple hearth by a fluid bed incinerator the Greensboro case history

The incinerator at the T.Z. Osborne Plant in Greensboro, North Carolina burns sludge from its own waste water treatment plant and sludge pumped from the nearby North Buffalo plant. The two plants have a combined capacity of 36 million gallons per day of wastewater. Because of the age of and increasing high maintenance on the existing multiple hearth incinerator, and the need to increase treatment capacity, the Osborne plant concluded a study in 1992 evaluating its options for future municipal sewage sludge disposal. Options which were evaluated during the study included; (i) rehabilitation of the existing eight-year old multiple hearth unit; (ii) addition of a new multiple hearth; (iii) addition of a new fluid bed system; (iv) drying, composting, or land application. The chosen option, based on both economic and environmental considerations, was a new fluid bed system with a capacity of 2.55 tons per hour, approximately double that of the existing multiple hearth. Design of the new fluid bed system began in December 1994 and equipment delivery for the incineration system was begun in April 1995. Initial operation occurred in August 1996. Primary and secondary sludge, dewatered to 28% dry solids by centrifuge, is delivered by piston pumps to the twenty-foot freeboard ID incinerator. A shell and tube heat exchanger recuperates heat from the exhaust gas and preheats the combustion air to 1250°F, resulting in minimal auxiliary fuel use. The air pollution control device is a high-energy Tandem Nozzle® scrubber. Greensboro was the initial installation of this scrubber design on a fluid bed incinerator and its characteristics and performance are discussed. Ash is dewatered in an ash thickener/belt press system prior to disposal to landfill. The system includes a state of the art Programmable Logic Controller (PLC) system for computer control of the operation. The unit was commissioned in August 1996 and has been in continuous operation since that time except for a one week inspection and maintenance shutdown in February 1999. The plant operates 24 h/day, 7 days per week. The initial performance test showed the system to readily meet federal and state air emission standards. Particulate released was 0.002 grains per dry standard cubic foot, carbon monoxide was 22.5 parts per million volumetric (ppmv) and opacity was 0.4%. These results show a significant emission reduction with the fluid bed when compared to the multiple hearth. Annual tests conducted since then and continuous emission monitoring have shown the unit to be in consistent compliance. Since the fluid bed system became operational, the old multiple hearth system has been maintained on standby as a backup, but its use has not been required. Operational experience is discussed, the most interesting of which is the relatively trouble-free operation. The minor problems which occurred and their solutions are detailed. Also included is a comparison of operation and maintenance experience of the fluid bed and the multiple hearth. Current sludge disposal actual cost data are also provided including the average cost per ton of dry solids treated. The almost three years of operational experience to date has shown that the decision to install a new fluid bed system was the correct one on both an environmental and economic basis. It has provided benefits to all interested parties — the wastewater treatment plant, the regulators, the taxpayers, and the surrounding community.