Enhancement of Biogas Production from Anaerobic Digestion of Disintegrated Sludge: A Techno-Economic Assessment for Sludge Management of Wastewater Treatment Plants in Vietnam

Currently, in Vietnam 35 urban WWTPs had been constructed with a total capacity of 850,000 m³/day. Some 40 new WWTPs are in the design or construction phase with a capacity of 1,600,000 m³/day. During operation, a lot of excess sludge must be wasted out of the system. It is well recognized that sludge disposal is one of the most critical issues for WWTPs as the cost of the excess sludge treatment and disposal can account for 50–60% of the operating cost. In Vietnam, sludge discharged from wastewater treatment plants were mostly disposed by the conventional method such as landfill. Therefore, reduction of sludge volume before disposal is very important for sludge transportation and management. In this study, the sludge was disintegrated by alkalis to enhance the sludge biodegradability before adding to the anaerobic digestion. As a result, MLSS reduced from 6600 mg/L down to about 4800 mg/L when alkalis dosage was increased from 1 to 1.8 g/L. Soluble COD was increased from less than 100 mg/L to over 1800 mg/L. The sludge biodegradability enhancement is linearly correlated to COD solubilization. The biogas production of the disintegrated sludge was higher compared to the sludge without the alkali disintegration (358 and 245 mL biogas/g sludge added), representing a 46% increase in the biogas production. The cost of chemical consumption for sludge disintegration was about 0.36 US $/kg TSS. The alkali sludge disintegration combined with anaerobic digestion process could be considered as a potential approach for sludge management of wastewater treatment plants in Vietnam.