High-solids thermophilic anaerobic digestion of sewage sludge: effect of ammonia concentration
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ORIGINAL ARTICLE
High‑solids thermophilic anaerobic digestion of sewage sludge: effect of ammonia concentration M. Takashima1 · J. Yaguchi2 Received: 3 March 2020 / Accepted: 11 September 2020 © Springer Japan KK, part of Springer Nature 2020
Abstract High-solids thermophilic anaerobic digestion fed with sewage sludge of 7–8% and 9–10% total solids was investigated at the hydraulic retention time of 20 days in this lab-scale study. The anaerobic digester fed with 7–8% sewage sludge was successfully operated, resulting in volatile solids (VS) destruction of 57.8% and methane production of 0.327 L/gVS (at standard temperature and pressure). When fed with 9–10% sewage sludge, the control digester was upset after about 80 days of operation. Total ammonia nitrogen (TAN) of 2500 mgN/L or more caused inhibition to anaerobic microorganisms. Another digester combined with weekly batch ammonia stripping of digested sludge in a side-stream configuration (80 °C, 2 h, initial pH of 9 with NaOH and return ratio of 70%), was maintained at the average TAN of 1720 mgN/L, and was able to continue without ammonia inhibition. TAN was a better indicator on inhibition of ammonia than free ammonia nitrogen (FAN). Microbial analysis revealed poor microbial diversity of digested sludge, that is, Class Clostridia for Bacteria and Geneus Methanothermobacter and Methanosarcina for Archaea were predominated. In conclusion, high-solids thermophilic anaerobic digestion can accommodate the influent sewage sludge up to 10%, as far as TAN is properly controlled in digester. Keywords Ammonia inhibition · Ammonia stripping · High-solids anaerobic digestion · Sewage sludge · Thermophilic anaerobic digestion
Introduction Anaerobic digestion is a widely employed method for sewage sludge treatment. It can reduce the amount of sewage sludge that needs to be disposed, and produce biogas, a source of renewable energy. Conventional sludge anaerobic digestion has been fed sewage sludge of 3–4% total solids (TS) in Japan and operated at mesophilic temperature. Improvement of the anaerobic digestion process has been found in thermophilic digestion, high-solids digestion, pretreatment of particulate solids, etc. [1]. Thermophilic digestion can accelerate the rate of anaerobic microbial reactions, and reduce pathogens and weed * M. Takashima takasima@fukui‑ut.ac.jp 1
Department of Architecture and Civil Engineering, Fukui University of Technology, 3‑6‑1 Gakuen, Fukui 910‑8505, Japan
Department of Industrial Systems Engineering, National Institute of Technology, Hachinohe College, 16‑1 Uwanotai, Tamonoki, Hachinohe 039‑1192, Japan
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seeds, thus producing superior biosolids. High-solids digestion can improve its cost-performance, as digester volume and operating costs are reduced [1]. In addition, transportation cost is lowered, when sludges are centralized and then treated. Therefore, high-solids anaerobic digestion can be generally advantageous in sludge processing and disposal [2]. At higher influent concentrations, however, the metabolites, partic
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