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Enhanced Biogas Production and Dewaterability from Sewage Sludge with Alkaline Pretreatment at Mesophilic and Thermophilic Temperatures

Wang, Tianfeng, Xu, Bingqing, Zhang, Xinyun, Yang, Qiyong, Xu, Bingjie, Yang, Pinghua
Water, air, and soil pollution 2018 v.229 no.3 pp. 57
alkali treatment, anaerobic digestion, biogas, heat treatment, hydrolysis, pH, sewage sludge, sodium, temperature, total suspended solids
This study investigated the biogas production and dewaterability of sewage sludge with alkaline pretreatment at mesophilic and thermophilic temperatures. The total suspended solids (TSS) and volatile suspended solids (VSS) of raw sludges were 21.1 ± 2.3 and 16.2 ± 1.5 g L⁻¹, respectively. Raw sludges were pretreated at uncontrolled, pH 8, pH 10, and pH 12 under mesophilic (Mu, M8, M10, and M12) and thermophilic (Tu, T8, T10, and T12) conditions, respectively. All the pretreatments last 6 days. The pH of pretreated sludges was adjusted to the pH 7.0 prior to inoculating with mesophilic anaerobic digested sludge and undergoing 60 days of anaerobic digestion. The ultimate biogas yield of Mu, M8, M10, M12, Tu, T8, T10, and T12 was 296.8, 384.8, 339.9, 323.1, 376.6, 322.4, 271.5, and 258.1 mL g⁻¹-VSₐddₑd, respectively. Both the pH of alkali treatment and temperature of thermal treatment affect the performance of anaerobic digestion. High hydrolysis pH (pH 10 and pH 12) resulted in high Na⁺ concentration (over 4000 mg L⁻¹), and Na⁺ inhibitory effect reduced the ultimate biogas yield. The normalized capillary suction time (NCST) found in the treatments of M8 and Tu were 11.8 ± 1.1 to 23.4 ± 1.7 and 27.9 ± 5.4 to 111.8 ± 1.7 s g⁻¹-TSS, respectively. The results suggest that both the pH of alkali treatment and temperatures of mild thermal treatment affect the performance of anaerobic digestion and sludge pretreated at pH 8.0 under mesophilic conditions could achieve high biogas yield and adequate dewaterability of digested sludge.