Effects of swine manure storage time on solid-liquid separation and biogas production: A life-cycle assessment approach

In the present study was evaluated and compared the effects of swine manure storage on a low-cost solid-liquid separation approach. We also determined the consequences of these stages on further treatment for energy recovery and environmental impact reduction. Different hydraulic retention times were studied in the solid-liquid separation techniques to determine the best pre-treatment conditions and apply these conditions in anaerobic digestion. This evaluation highlighted the possibility and advantages of applying solid-liquid separation using a settling pre-treatment in the swine chain. Storage time significantly affected the efficiency of screening which was reduced by 80 ± 0.5% after 5 d compared to fresh manure screening. This directly reflected the sludge volume generated in the following stages, with sludge increments of 51 ± 0.1% for settling. The waste solid-liquid separation provided better energy production results when the manure storage time was less than 5 d, resulting in improved power generation capacity of the system (up to 4.5 kWh of electricity for each m3 of raw manure). We observed the positive contribution of adequate manure management in swine sustainability through the life-cycle assessment of the swine chain during manure storage, solid-liquid separation, and anaerobic digestion. It promoted low greenhouse gas emissions, resulted in a carbon-neutral chain, and maximized energy production and recovery. The results highlighted the importance of previous solid-liquid separation in anaerobic digestion and the relevance of proper effluent management because more than 5 d of storage time compromised subsequent processes. This was also observed during the life-cycle assessment.