Search

The role of total solids (TS) content on sludge mesophilic anaerobic digestion (AD) was investigated in batch reactors. A range of TS below 10% was evaluated with two replicates. The volumetric biogas production rate (VBPR) increased with increasing initial TS. On day 5, VBPR increased from 133.2 ± 11.2 mL L −1 d −1 at TS 2% to 1111.7 ± 58.1 mL L −1 d −1 at TS 10%. The ultimate biogas yield ( P ) firstly increased and then decreased with the increasing TS. The greatest P was 246.8 mL g −1 -VS added at TS 8%. The corresponding free ammonia nitrogen (FAN) and total ammonia nitrogen (TAN) were 84.0 ± 16.1 and 1163.0 ± 108.6 mg L −1 , respectively. Normalized capillary suction time (NCST) and solid content of thickened sludge obtained by centrifuging sludge increased with increasing TS. On day 49, NCST were 1.2 ± 0.2 (TS = 2%) and 13.2 ± 1.1 (TS = 10%) s g −1 -TS. Meanwhile, solid content of thickened sludge was 7.5 ± 0.5 (TS = 2%) and 15.4 ± 0.0% (TS = 10%). In summary, high VBPR and dewatering effects were obtained after TS content optimization. [ABSTRACT FROM AUTHOR]

The role of total solids content on sludge thermophilic anaerobic digestion was investigated in batch reactors. A range of total solids content from 2% to 10% was evaluated with two replicates. The lowest inhibitory concentration for free ammonia and total ammonia of sludge thermophilic anaerobic digestion was 110.9–171.4 mg/L and 1313.1–1806.7 mg/L, respectively. The volumetric biogas production rate increased with increasing of total solids content, but the corresponding biogas yield per gram volatile solid decreased. The result of normalized capillary suction time indicated that the dewaterability of digested sludge at high total solids content was poor, while solid content of sediment obtained by centrifuging sludge at 2000 g for 10 min increased with increasing of total solids content of sludge. The results suggest that thickened sludge mixed with dewatered sludge at an appropriate ratio could get high organic loading rate, high biogas yield and adequate dewatering effort. [ABSTRACT FROM AUTHOR]

Enrichment of the microbial mass is critical to enhance the performance of anaerobic digestion, especially under adverse conditions. In this study, microbial electrolysis cells combined with anaerobic digesters were used for anaerobic digestion of ammonia rich synthetic substrates and sludge. For the synthetic substrate, with the increasing of applied voltage, the methane yield presented earlier increase and later decrease trend. The methane yield was the highest at an applied voltage of 0.7 V. For the sludge, the amounts of ammonia nitrogen and free ammonia nitrogen at an applied voltage of 0.7 V were higher than that at 0 V, and the maximum methane yield at voltages of 0 V and 0.7 V were 52.6 and 97.8 mL g−1-VSS added , respectively. Methanosarcina and Methanothermobacter were the predominant archaea. Archaea species at an applied voltage of 0.7 V were more diverse than those at an applied voltage of 0 V. The results indicated that microbial electrolysis cells could increase the number and mass of microbial species in the thermophilic anaerobic digesters under ammonia inhibition. This study might provide a feasible method to operate sludge thermophilic anaerobic digestion at higher organic loading rates. [Display omitted] • The performance of thermophilic AD-MEC were affected by applied voltage. • AD-MEC (0.7 V) improved the sludge hydrolysis and biofilm biomass. • AD-MEC (0.7 V) enriched the diversity bacteria and archaea. • AD-MEC (0.7 V) enhanced the methane yield at higher ammonia and FAN. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]