China has seen a signifıcant expansion in the number of wastewater treatment plants constructed over recent years, and the fırst sludge drying plant in Beijing is currently under construction. As more operators worldwide consider options for sludge treatment, a leading company in the fıeld examines the benefıts of sludge drying. Fluidized bed drying: A necessary step for sludge usage by Klaus Stanke, Juergen Geyer and Yan Xu .,. ---=--! An important consideration for operators of wastewater treatment plants 0f'N'(TPs) is how to handle the disposal of the residual sludge in a reliable, sustainable, legal and economical way. This by-product of wastewater treatment contains abundant organic material, including many kinds of bacteria. it also levels ofphosphorus and other nutrients. However, there are a number of concerns about this route induding: .,_-,--- contains heavy metals and its composition is generally unknown. Although reliability and flexibility are important factors in the operation ofa WWTP. the choice ofthe optimal solution for sludge disposal has to take account ofa number of factors such as legislation, government guidelines, the cost and possible applications for the dried sludge. This means thatthere is no universal solution to the problem of sludge disposal for ali plants. The benefits of drying sludge can be seen in two main treatment options: t use of the dewatered sludge as a fertilizer or in fertilizer blends t incineration with energy recovery. Use as a fertilizer This option takes advantage of the high organic content (40%-70%) of the dewatered sludge and its high t the chemical composition of the sludge ( e.g. heavy metals, hormones and other pharmaceutical residues) t pathogen risk (e.g. salmonella, Escherichia coli, prionic proteins, ete.) t potential accumulation of heavy metals and other chemicals in the soil. To prevent a build-up of heavy metals and other contaminants in the soil, there are restrictions on the amount that can be applied per area. in addition, fertilizer use is not necessary on a particular field every season but sludge is produced daily from WWTPs receiving a continuous flow of domestic sewage and other wastewaters. Sludge can be applied as a fertilizer in three forms: t liquid sludge t wet cake blended into compost t dried granules. Thermally dried sludge in granular form reduces the pathogen risk and provides flexibility as it can be stored until needed. Energy recovery This option takes advantage ofthe energy available in the sludge's organic content. Drying the sludge reduces its water content, thus increasing its calorific value and making it easier to combust. it also reduces odours and improves handling, with lower transport and storage costs. Sludge from WWTPs is typically combusted in: t cement kilns t coal-fıred power plants t mono-incinerators, i.e. plants burning refuse-derived fuel ora single waste stream t mixed waste incinerators, e.g. municipal waste incinerator. 1 ENERJi OÜNYASI _§UBAT 2007 ♦ - 6 ,-- 4-+------'�----===========- "EnerjideSürdürülebili�ik ve Küreselleşme: Vemılilik, Emisyonlar,Yeni Piyasaotuşmılan"
RkJQdWJsaXNoZXIy MTcyMTY=