BUET- A NWA R ISPA T 1st Ba ng la d e sh C ivil Eng ine e ring SUM MIT 2 0 1 6 BUET, Dhaka, Bangladesh www.cesummitbd.com Assessing the Energy Values of Sewage Sludge from Pagla Sewage Treatment Plant S.A.A. Rafie* 1 , N. Haider 2 , N. Islam 3 and A. B. M. Badruzzaman 4 1,2,3 Department of Civil Engineering, BUET, Dhaka, saad.abdarrafie@gmail.com , nafis04107@gmail.com , nayeems4087@gmail.com . 4 Professor, Department of Civil Engineering, BUET, Dhaka, borhan61@yahoo.com *Corresponding Author ABSTRACT The wastewater treatment process gives sewage sludge as a byproduct. The traditional practice of Sludge management utilizes the method of landfilling.According to the Dhaka Structure Plan 2016- 2035 by RAJUK, DWASA operates only one Sewage treatment plant at Pagla (PSTP), about 8 km from the city, onan area of 110.5 ha. It was originally constructed in 1978.The plant provides treatment of thewastewater collected by the central sewerage system. PSTP has design capacity of 120 MLD (peak flow rate)while the current sewage generated within the catchment served by the centralized seweragesystem is approximately 250-300 MLD and is expected to be 500 MLD in the near future. This makes landfilling only a temporary expensive solution since finding the space to dispose of such large amounts of sludge from PSTP along with the other proposed STP projects in or around Dhaka city is an impossible task. Thus, the approach of energy generation from sewage sludge through thermal combustion may provide a viable option providing the opportunity for dual benefits, namely, energy generation as well as sludge management. In this paper, experimental as well as theoretical methods along with an extensive study of literature have been used to estimate the energy value of the sewage sludge generated at PSTP. ASTM D2015 method using bomb calorimeter to determine the energy value of excreta has been followed.Energy content measurements indicate that the energy value of the sewage sludge generated at the PSTP found to be 2.1MJ/kg,which is far too low for it to be used as fuel alone. However, there may be scope for increased level of energy generation through co-combustion of sludge with coal. KEYWORDS: Sludge Management; Energy; Alternative Fuel; Sewage Treatment; Pagla Sewage Treatment Plant;Waste Management; Dhaka INTRODUCTION: Treated wastewater and sludge are formed when wastewater is subjected to physical, chemical and biological operations to achieve removal of settleable solids, organic forms of carbon, nitrogen and phosphorus. The sewage sludge is essentially made up of solids and bio-solids, resulting from the wastewater treatment operations and processes, usually in the form of a liquid or semisolid liquid depending upon the operations and processes applied (Tchobanoglous et al, 1991).Evidently, the process applied to wastewater during treatment determines the characteristics of the sludge (Sanin, Clarkson, and Vesilind, 2011).Together with energetically desirable components sewage sludge also contains organic, inorganic and biological impurities in soluble, insoluble and colloidal forms.The organic fraction of sewage sludge comprises mostly of carbon.Theinorganic fraction of sewage sludge includes constituents such as calcium, magnesium, iron, potassium and sodium as well as toxic heavy metals such as cadmium, chromium, copper, lead, mercury and so on (Lester et al, 2006). As a result, it can be said that uncontrolled disposal of sewage sludge to the environment increases the risk faced by environmental and public health. The content of organic components is normally in the range of 45-60% in a sewage sludge sample. Organic components identified in sewage sludge includes- polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides, dioxins, furans, adsorbed and extracted “chloro-” derivatives, phenols, phthalates, etc. These organic compounds are identified by using Gas Chromatography-Mass Spectrometry (GC-MS) (Werle, 2014).Inorganic components identified in sewage sludge include- major elements (carbon, hydrogen, oxygen, nitrogen, sulfur, chlorine, fluorine), mineral elements (magnesium, calcium), alkaline metals (sodium, potassium), phosphorous, heavy metals (zinc, lead, nickel, mercury, copper, chromium, cadmium, selenium, arsenic) etc.Sewage sludge contains a significant number of microbial pathogens (bacteria, virus, protozoa, fungi, etc.) which mainly come from human feces.The amount and characteristics of the impurities in