Integration of the energy recovery step in municipal wastewater treatment chain: a case study of Moshi municipality, Tanzania

A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Master's of Environmental Science and Engineering of the Nelson Mandela African Institution of Science and Technology (NM-AIST)The energy demand which is expected to increase more worldwide has sparked the interest of researchers to find sustainable and inexpensive sources of energy. This study aims to integrate energy recovering step into municipal wastewater treatment plants (MWWTPS) through anaerobic digestion. The anaerobic digestion of municipal wastewater (MWW) and then co-digestion with sugar cane molasses (SCM) to improve its organic content was conducted at 25 oC and 37 oC. The results showed substrate mixture containing 6% of SCM and total solids (TS) of 7.52% yielded higher amount of biogas (9.73 L/L of modified substrate). However, chemical oxygen demand (COD) of the resulting digestate was high (10.1 g/L) and pH was not stable hence needed careful adjustment using 2M of NaOH solution. This study recommends substrate mixture containing SCM (2%) and TS (4.34%) having biogas production (4.97 L/L of modified substrate) for energy recovering from MWWTPS, since is found to have more stable pH and low COD residue (1.8 g/L) which will not hold back the MWW treatment process. The annual generation of modified substrate (662 973 m3 ) is anticipated to generate about 16 241 m3 of methane which produce up to 1.8 GWh and 8193 GJ per annum. The study concluded that biogas is among of the future fuel if the modern technology on anaerobic digestion is functional. Also the use of combined heat and power (CHP) engine for the conversion of biogas to heat and electrical energy increases the energy value of the wastewater. (Keywords: Anaerobic digestion, Biogas, Municipal wastewater, Sugarcane molasses