Incineration has been used as a disposal method for wastewater treatment biosolids for over sixty years. The first multiple hearth furnace for biosolids incineration was built in 1935 in Dearborn, MI. From that time through the late sixties, the multiple hearth was the thermal technique of choice for biosolids disposal. Today there are still some 150-175 aging multiple hearths in operation in North America.In the seventies, the fluid bed furnace became the preferred thermal technique for biosolids disposal, primarily due to tighter emission regulation and to increasing cost of auxiliary fuel. The first municipal fluid bed was installed in the USA at the Lynnwood, WA wastewater treatment plant in 1962. There have been over 125 fluid bed incinerators installed since then in North America.Since 1988 there have been 43 new municipal fluid bed systems installed. Among these new fluid bed installations, 11 replaced existing multiple hearths.The dominance of fluid bed over multiple hearth for the last three decades can be explained by the advantages of the fluid bed, which derive from the basic design differences between the two technologies. These fundamental differences which result in lower emission, reduced auxiliary fuel use and reduced operating and maintenance costs are developed in this paper.In recent years, to deal with tighter emission regulations, some multiple hearths have been retrofitted with afterburners to increase their exhaust gas temperatures. Different alternatives of refurbishment are discussed in this paper. A graphical method is developed and presented to determine the fuel requirement in the afterburner. This is a useful tool in the evaluation of the rehabilitation of a multiple hearth. While the organic and carbon monoxide releases from the multiple hearth can be reduced with the use of an afterburner, the penalty is higher fuel usage and higher nitrogen oxides generation.When life cycle costs are considered, including capital, labor, fuel and maintenance, it is often more economical to install a new fluid bed system than to rehabilitate an existing multiple hearth.

Emissions of major air pollutants including carbon monoxide (CO), nitrogen oxides (NOx) and mercury (Hg) were studied at two sewage sludge fluidized bed combustion (FBC) plants. Both the North West Bergen (NWB) County Utility Authority and the Little Miami (LM) plants have air pollution control systems (APCS) that are of the wet type. Various operating conditions such as temperature, excess air, fuel and feed properties, concentration of calcium chloride, and the method of operating were investigated to determine their effect on the emissions.Results of the study reveal that NOx increase with increased bed temperatures and excess air. CO is lower at higher freeboard temperatures.Both CO and NOx emissions are strongly dependent on the feed characteristics. CO and NOx fluctuate more with higher sludge solid content (TS). They increase not only with TS, but also with the sludge volatile solids (VS) and its heat content. NOx increase with the ratio of sludge oxygen over sludge nitrogen concentration. They are also higher with fuel oil than with natural gas when selected as the auxiliary fuel source.CO and NOx emissions are also higher and fluctuate more when the operation is not run consistently; when the feed quality is inconsistent, or when the feeding is intermittent or interrupted, or when the roof sprays are activated. It is believed that the feed characteristics and mode of operating affect the flame temperature and the excess air surrounding the combusting materials, which in turn have an impact on CO and NOx emissions.While some of the mercury (Hg) vapor is removed by condensation due to flue gas cooling, the addition of calcium chloride to the feed has shown a clear reduction in both emissions of NOx and Hg. It is believed that calcium chloride can generate strong oxidants, promoting the oxidation of both elemental mercury and NOx into more soluble forms, which can then be separated from the exhaust gas in a wet scrubber.

Soaring energy costs have made it imperative to reduce consumption of traditional fossil fuels. This has resulted in demand for alternative sources of energy from sustainable localized sources that are considered renewable in nature. Increasingly, the use of biogas from anaerobic digesters to generate process heat and in some case electricity using cogeneration mechanisms have made anaerobic digestion an attractive treatment choice for many small to medium size facilities.Delhi Charter Township Wastewater Treatment Plant (WWTP) located in Ingham County, Michigan has established the states first integrated biomass-to-energy digester system. The plant upgrade included the implementation of a two-phase anaerobic digestion system with a fully integrated state-of-the-art microturbine based cogeneration system. The two-phase anaerobic digestion system is designed to treat primary solids and waste activated sludge to produce Class A biosolids and the microturbine system to capture, treat and utilize biogas to produce heat and electricity.This integrated biomass-to-energy digestion and cogeneration system was designed to help reduce energy consumption in two folds, first, by reducing the volume of sludge to be hauled to the final disposal location by minimizing fuel associated with the transporting of biosolids and second, by minimizing the use of natural gas and electricity usage by locally generating heat for process heating and electricity for electrical operation.At current capacity, the facility is able to reduce electricity consumption by over 40 percent and close to 100 percent of the process heat. This essentially sustains the operation of the solids handing system. The plant demonstrates that wastewater treatment facilities can be designed to significantly reduce consumption of traditional fuels and offset carbon footprint while producing numerous usable bi-products such as Class A biosolids, electricity and process heat. The WWTP is projected to be fully energy independent when the solids treatment facility reaches design capacity.

Thermal processes used in sludge disposal have become more attractive as process improvements have been introduced, such as power generation and efficient heat recovery. More and more utilities and agencies are reevaluating their sludge management practices to ensure that they are providing sustainable management solutions for their clients. The thermal process design approach to the disposal of sludge is not only designed to achieve stricter emission limits but also is more energy efficient compared to its predecessors. Increasing numbers of new plants are being built every year with more energy efficient heat recovery features such as air preheating and cogeneration with steam and electricity production. This paper presents an overview of fluid bed incineration in North America and its evolution over the last decades. Case studies of the last three newest and largest plants in North America are presented, including the Lakeview Plant, Duffin Creek Plant, both in Ontario, Canada and the Southerly Plant in Cleveland, Ohio, USA.

Soaring energy costs have made it imperative to reduce consumption of traditional fossil fuels. This has resulted in demand for alternative sources of energy from sustainable localized sources that are considered renewable in nature. Increasingly, the use of biogas from anaerobic digesters to generate process heat and in some case electricity using cogeneration mechanisms have made anaerobic digestion an attractive treatment choice for many small to medium size facilities. Delhi Charter Township Wastewater Treatment Plant (WWTP) located in Ingham County, Michigan has established the states first integrated biomass-to-energy digester system. The plant upgrade included the implementation of a two-phase anaerobic digestion system with a fully integrated state-of-the-art microturbine based cogeneration system. The two-phase anaerobic digestion system is designed to treat primary solids and waste activated sludge to produce Class A biosolids and the microturbine system to capture, treat and utilize biogas to produce heat and electricity. This integrated biomass-to-energy digestion and cogeneration system was designed to help reduce energy consumption in two folds, first, by reducing the volume of sludge to be hauled to the final disposal location by minimizing fuel associated with the transporting of biosolids and second, by minimizing the use of natural gas and electricity usage by locally generating heat for process heating and electricity for electrical operation. At current capacity, the facility is able to reduce electricity consumption by over 40 percent and close to 100 percent of the process heat. This essentially sustains the operation of the solids handing system. The plant demonstrates that wastewater treatment facilities can be designed to significantly reduce consumption of traditional fuels and offset carbon footprint while producing numerous usable bi-products such as Class A biosolids, electricity and process heat. The WWTP is projected to be fully energy independent when the solids treatment facility reaches design capacity.