Organic matter hydrolysis prior to anaerobic digestion has been shown to improve biogas production (30–50%) and reduce solids (20–60%) by ultrasound, chemical, conventional heating, and microwave pretreatments. Numerous studies have been performed to determine the extent of digestion improvement but few focus on financial feasibility of these processes. A comprehensive model was created using Microsoft Excel and its Visual Basic Assistant to evaluate pretreatment permutations for conventional wastewater treatment plants. The four above-mentioned processes were evaluated for energetic and financial demands. Well-established energy equations and wastewater characteristics, both average and high, were used. Average and high flows were 460 and 750 × 103 m3/d, respectively. Net costs per influent flow for ultrasound, chemical, conventional heating, and microwave were 0.0166, 0.0217, 0.0124, 0.0119 $/m3 and 0.0264, 0.0357, 0.0187, and 0.0162 $/m3 for average and high conditions, respectively. The average cost increase from results excluding pretreatment use for all processes was 0.003 and 0.0055 $/m3 for average and high conditions, respectively. No matter the permutation, pretreatments requiring more energy to achieve required hydrolysis levels were costlier. If energetic recoveries are substantial, dewaterability is positively affected, and solids meet environmental constraints to be handled and disposed at lower costs, pretreatments can be viable.
Keywords: chemical, digestion, microwave, pretreatment, thermal, ultrasound