Enhancement of Biogas Production from Swine Wastewater Using Electrochemical Pretreatment and Anaerobic Co-digestion with Rice Straw

Co-digestion and pretreatment approaches were tested using batch tests for the enhancement of anaerobic digestion (AD) of swine wastewater (SW). AD was evaluated in mesophilic conditions to understand the effects of the addition of rice straw (RS) to the medium. The results showed that an increase in the SW/RS ratio led to higher cumulative methane production until 30 wt.% RS. The cumulative methane productions for SW/RS 70:30 and 50:50 were 903.66 ± 111.0 mL, and 625.55 ± 55.1 mL, respectively, which represented an increase of 41.3% and 17.8% compared with the control (525.78 ± 18.77 mL). Kinetic modeling translated well to methane production in the different treatments. The hydrolysis constant and maximum methane production were higher in the 70:30 SW/RS ratio, while the addition of higher quantities of RS increased the duration of the lag-phase. Electrochemical pretreatment was performed to increase the bioavailability of suspended particulate matter in SW at 10 mA cm⁻² and two temperatures (30 °C and 45 °C). Final methane production increased by 8% and 19% in the two pretreatments, respectively, when compared to the control. The pretreatment at 10 mA cm⁻² and 45 °C showed the best performance but delayed the time for stable methane production. Kinetic modeling confirmed these results as the parameters obtained for the second pretreatment group were better than the control. These findings support the potential of both enhancement approaches to enhance energy recovery via AD in swine farms.