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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]

Abstract Digestate from biogas plants managing municipal solid waste needs to be stabilized prior to final utilization or disposal. Based on the concept of urban mining, aged refuse from a closed landfill was used to treat landfill leachate, but nitrogen removal by biological denitrification was limited. The aim of this study was to use a digestate layer in bioreactors containing aged refuse to enhance the biological denitrification capacity of the aged refuse, stabilize digestate, and mitigate the ammonia emissions from digestate leaching with leachate recirculation. Six identical landfill columns filled with 0% (R0), 5% (R5), and 15% (R15) of solid digestate above aged refuse (ratios based on Total Solids) were setup and nitrified leachate was periodically fed and recirculated to the columns. The nitrate removal rate in R5 and R15 was 3.4 and 10 times higher relative to the control (no digestate added). A 31.5–35.9% increase of solid digestate biostability was confirmed by tests performed under both aerobic and anaerobic conditions. The results showed that instead of land use, the solid fraction of digestate could be utilized as an inexpensive functional layer embedded in an old landfill site to enhance the denitrification capacity and achieve digestate stabilization with minimal ammonia leaching from digestate. Graphical abstract A combined approach to manage digestate and landfill leachate treatment. Image 1 Highlights • Bioreactors packed with aged refuse and digestate were used to treat landfill leachate. • Digestate addition enhanced the denitrification capacity of aged landfill waste tenfold. • The aged refuse mitigated the amount of ammonia leaching from the solid digestate by 67.2%–84.8%. • N removal of old landfill leachate was jointly gained with digestate stabilization. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co-digestion improved methane yield 31.3%-68.0% at thermophilic temperature. • Co-digestion improved methane yield 83.0%-136.5% at mesophilic temperature. • The highest methane yield of anaerobic co-digestion obtained at P/S = 2:1. • NCST and TS of sediment increased with increasing initial TS of substrate. • NCST has a strong negative correlation with the water removal efficiency. The objective of this study is to assess the effects of the mixing ratio on the methane production and digestate dewaterability of co-digestion of pig manure (P) and sludge (S). Batch experiments were carried out at five different P/S mixing ratios at mesophilic and thermophilic temperatures. Compared to sludge anaerobic digestion, co-digestion of pig manure with sludge increased methane yield 83.0%-136.5% at mesophilic temperature and 31.3%-68.0% at thermophilic temperature. The normalized capillary suction time (NCST) and total solids (TS) of sediment (centrifugal dewatering) increased when pig manure proportion of substrate increased. The NCST at thermophilic temperatures (4.87–17.58 s g−1-TSS) was higher than that at mesophilic temperatures (1.89–10.95 s g−1-TSS). However, the TS of sediment was close at thermophilic and mesophilic temperatures. The results indicated that anaerobic co-digestion of pig manure and sludge at a proper mixing ratio (P/S = 2:1) provides a good choice for energy recovery and land utilization. [ABSTRACT FROM AUTHOR]