Intensifying the biogas production from food waste using ultrasound: Understanding into effect of operating...

The present work depicts the novel approach of using ultrasound (US) induced cavitation for feedstock pretreatment with an objective of improving the anaerobic digestion (AD) process for biogas production. Initially the critical analysis of literature based on US for improving the biogas production has been presented briefly followed by study on use of US in pretreatment of food waste (FW) as well as during AD to quantify the intensification in the biogas production. Effect of different operating parameters for pretreatment such as irradiation time (over the range 2-14 min), power density (0.2-1 W/mL), duty cycle (20-80%) and substrate loading (3-11%w/v) has been investigated. Highest increase in soluble chemical oxygen demand (sCOD) with final value as 18500 mg/L (±20) (increase of 61.5%) was obtained at optimum treatment conditions of 10 min as irradiation time, 0.4 W/mL as power density, 60% as duty cycle and 7% w/v as the substrate loading. Pretreated FW was further subjected to low intensity US assisted AD process. Parameters optimized for biogas production were power (over the range of 100-200 W), irradiation time (5-15 min) and duty cycle (10-60%). Increased biogas production (almost two times) with 80% sCOD removal after 15 days was obtained at best conditions of 200 W as the US power (0.04 W/mL as power density), 5 min as the US irradiation time and 10% of US duty cycle while AD process without US resulted in only 48% sCOD removal within same time period. The work demonstrated the effective application of US in the pretreatment of feedstock and subsequent AD process giving much higher yield of biogas in shorter time.