Enhancing biogas production with combined ultrasound and enzymatic hydrolysis treatment

Abstract

One of the aims of the “END-O-SLUDG” EU FP7 project focuses on the pre-treatment of sludge to enhance biogas production in anaerobic digestion. Different pre-treatments were studied within this context. This paper presents the results of applying ultrasound cell disruption (24 kHz, 3500 – 20000 kJ/kg TS) and Enzymatic Hydrolysis (42°C, 48 hours) as single treatments and in combination. Tests were performed on primary, secondary and combined sludge from two wastewater treatment plants. Each pre-treatment was followed by 24 hours of fermentation at 37°C to monitor the short-term improvement in performance. The results are discussed in terms of the variations in soluble chemical oxygen demand (sCOD) and ammonia. An increase in sCOD is interpreted as enhanced conversion of the organic load and hence greater energy recovery since the sCOD provides the carbon source for the microorganisms that produce biogas. As this parameter increases the level of recalcitrant compounds is also reduced accordingly as a consequence of the pre-treatments prior to sludge digestion. Ammonia is another parameter considered an indicator of biomass degradation, particularly of proteins.