Effect of Sulphate on Fermentative Sludge Hydrolysis Cum Biodegradation of Waste Activated Sludge

Abstract

The waste activated sludge (WAS) from the activated sludge process needs an appropriate sustainable sludge treatment and management. The sludge treatment and the management cost around 60% of the capital cost and 50–60% of the operating cost of a wastewater treatment plant. Anaerobic digestion is the dominant process for the sludge reduction and/or stabilization of WAS. Though many physico-chemical techniques are developed as a pre-treatment to enhance the hydrolysis of sludge prior to biomethanation, most of the techniques are very expensive and therefore not practical to apply in the field scale. This work shows the effect of fermentative sludge hydrolysis cum biodegradation of WAS in the presence and in the absence of sulphate. Sequencing batch reactor (SBR) operation at room temperature (31–33 °C) in an orbital shaker at 120 ± 2 rpm with cycle time of 7 days was adopted to compare the performance of fermentation in the presence and in the absence of sulphate. The fermentation in the absence of sulphate was conducted in the presence of externally added COD (sucrose) varied as 500, 1000, 1500 and 2000 (in mg/L). The sulphidogenesis reactors were maintained at a COD/SO42− ratio of 1.0 and varied the concentration of both sulphate and COD as 500, 1000, 1500 and 2000 (in mg/L). An abiotic control was also maintained to evaluate the processes. The percentage sludge reduction varied between 27 and 98%, where the maximum reduction of about 96% was observed in the fermentative reactor in the presence of 500 mg/L of COD, whereas 98% solid reduction was observed in the sulphidogenesis reactor at 2000 mg/L of COD and sulphate. The other parameters such as pH, oxidation–reduction potential (ORP), VFA, alkalinity, soluble and total COD, and turbidity were analysed, and the results are discussed in the paper.