EFFECT OF SLUDGE MANAGEMENT STRATEGIES ON MINIMIZING GLOBAL WARMING POTENTIAL AT A MUNICIPAL WASTEWATER TREATMENT PLANT OF A METROPOLITAN CITY

摘要

In this paper, improvement in biogas production and its total energy equivalence were evaluated in the case of kitchen waste (KW) integration, and results were compared with the current situation (without KW integration) at a municipal wastewater treatment plant (WWTP) located in one of the metropolitan cities in Turkey. Moreover, the effect of different sludge disposal alternatives (e.g. co-combustion, composting, etc.) was discussed from the aspects including energy consumption/ production and the greenhouse gases (GHGs) emission, while comparing the results with the current sludge disposal via uncontrolled landfilling. In the current situation, about 18% of the annual electricity requirement of the WWTP could be provided from the produced biogas by mesophilic digestion, whereas more than half of the annual electricity requirement could be provided with KW integration when the operational temperature of the anaerobic digestion is shifted to thermophilic condition. At the same time, all heat requirements could be supplied with the produced biogas for each case. Moreover, substantial excess heat (i.e. 3 times more in the case of thermophilic digestion and KW integration) is obtained which can be utilized elsewhere in the premises of the WWTP. When global warming potential (GWP) of the WWTP is evaluated in terms of current sludge disposal method; results indicated ca. 416, 604 and 509 kg CO_2-eq/person/year emission factors without and with KW integration at mesophilic and with KW integration at thermophilic digestion, respectively. Moreover, in terms of composting (for both land use and peat substitution) and co-combustion alternatives for each option, minimum GWP is found when sludge is disposed of via co-combustion after mesophilic digestion with ca. -267 kg CO_2-eq/person/year. Hence, the WWTPs should be operated and/or upgraded regarding not only energy saving but also GHGs emission decrease that is worldwide concern from the point of global warming.