Co-incineration costs less, but on the other hand monoincineration provides the option of phosphorus recovery. Another factor in favour of incineration is the fact that it allows to recover the amount of energy consumed for sludge transport, dewatering and drying. It is an innovative concept of decentralised sludge utilisation by generation and use of thermal and electrical energy.The plant on WWTP Straubing is designed for 200,000 PE and presently treats about 35,000 m3 wastewater per day. After anaerobic sludge treatment and dewatering by means of centrifuges this is an annual volume of almost 9,000 t sludge dewatered to on average 28-29 % DR. The thermal energy content of dried sludge is a substantial value for the creation of an energy balance. The thermal value of dried sludge with 65% dry residue is comparable with brown coal and provides 1,020 kWh of energy. With according boiler efficiency, about 800 kWh of thermal energy can be generated. After deduction of further thermal losses in the micro gas turbine about 700 kWh of thermal energy effectively remain for the drying process. With a thermal energy consumption of about 565 kWh for the drying process there is even a surplus of energy available.
IWA Search Theme: Resources Recovery and Reuse
Use of biogas for cogeneration of heat and electricity for local application: performance evaluation of an engine power generator and a sludge thermal dryer
A small unit of cogeneration of energy and heat was tested at the Centre for Research and Training on Sanitation UFMG/COPASA – CePTS, located at the Arrudas Sewage Treatment Plant, in Belo Horizonte, Minas Gerais, Brazil. The unit consisted of an engine power generator adapted to run on biogas, a thermal dryer prototype and other peripherals (compressor, biogas storage tank, air blower, etc.). The heat from engine power generator exhaust gases was directed towards the thermal dryer prototype to dry the sludge and disinfect it. The results showed that the experimental apparatus is self-sufficient in electricity, even producing a surplus, available for other uses. The tests of drying and disinfection of sludge lasted 7 h, leading to an increase in solids content from 4 to 8% (50% reduction in sludge volume). Although the drying of sludge was not possible (only thickening was achieved), the disinfection process proved very effective, enabling the complete inactivation of helminth eggs.