Enhanced mesophilic bio-hydrogen production of raw rice straw and activated sewage sludge by co-digestion

Abstract

Abstract:In this study, batch biohydrogen production by co-digestion of raw rice straw and activated sewage sludge was investigated with different inoculum heat treatment, pH, S/X ratio (based on VS) and substrate sizes under mesophilic condition. In order to achieve a high bio-hydrogen yield and methanogens activity inhibition, heat treatment of inoculum was optimized at different exposure times (30, 45 & 60 min) and temperature ranges (80, 90 and 100 °C) prior to dark fermentation process. Collected data was analysed using response surface methodology (RSM).The heat treatment of inoculum at 100 °C for 60 minutes produced the highest bio-hydrogen yield of 14.22 NmL H2/g VS at concentration of 70.97 % and Production of 0.073 NmLCH4/gVS at 0.17% concentration in total produced biogas. The raw rice straw was also co-digested with heat-treated inoculum at different ratios of volatile solids (2:1, 4:1 and 6:1) and initial pH (4, 4.75 and 5.5) as numerical variables and 4 categories of substrate size ( (250-500 µm], (500 µm-2mm], (2-20mm), [20-30mm]) . The highest bio-hydrogen yield of 14.70 NmL/g VS was recognized at the optimum initial pH of 5.01 and S/X ratio of 4.54:1 using 2-20 mm rice straw.

Biochemical methane potential (BMP) from anaerobic co-digestion of sewage sludge and decanter cake

“…The quantity of hydrogen (H2), methane (CH4) and carbon dioxide (CO2) in 1 mL of gas samples were calculated using Equation 1, 2 and 3 [17].…”

“…In the next step, percentage of each individual gas in biogas was calculated using Equation 4, 5 and 6 [17]. Using the calculated percentage and the amount of accumulated biogas in the syringe, total quantity of each gas was measured.…”

“…The characteristic of sewage sludge was reported as; TS, VS and pH were 2.60 g/L, 12.60 g/L and 6.64, respectively. Alemahdi et al (2015) reported that the characteristic of the sewage sludge of TS, VS and pH are 5.182 g/L, 3.734 g/L and 6.20 respectively. The characteristic of sewage sludge obtained were almost similar as compared to previous study by Alemahdi et al (2015).…”

“…Alemahdi et al (2015) reported that the characteristic of the sewage sludge of TS, VS and pH are 5.182 g/L, 3.734 g/L and 6.20 respectively. The characteristic of sewage sludge obtained were almost similar as compared to previous study by Alemahdi et al (2015). The characteristic of decanter cake was based on TS and VS were 19.40 g/L and 16.70 g/L, respectively.…”

“…In contrast, agro-wastes contain a high percentage of carbon and a low percentage of nitrogen (high C/N ratio). Different types of agro-wastes can be used in admixture with sewage sludge, such as rice straw [17], wheat straw [15] and municipal solid wastes [8]. Co-digestion of sewage sludge and decanter cake is considered the best solution for enhancing methane yield.…”