Bio-H2 and bio-CH4 production from food waste in a two-stage temperature phased system were investigated to determine the effects of digestate recirculation on energy efficiency and process ...stability. Different recirculation ratios (RR), i.e. 0.3, 0.5, and 1.0, were tested. Maximum H2 production of 3 L-H2 L−1d−1 and yield of 135 L-H2 kg−1VSin were achieved for an RR of 0.3 at HRT 5 d and OLR of 18 kg-VS m−³d−1. The RR of 0.3 was also the best for producing CH4 and gave results of 2.9 L-CH4 L−1 d−1, i.e. 510 L-CH4 kg−1VSin at HRT 9 d and OLR of 5.7 kg-VS m−³ d−1. The energy recovered from the recirculation process increased the H2 production by 8% and decreased the CH4 production by 3%; the total energy production did not change. Digestate recirculation in comparison with a no-recirculation system reduced the need for alkali addition to maintain pH in the H2-reactor by 54%.
•Two-stage AD process was positive for food waste digestion.•Digestate recirculation in the first stage reduced alkaline addition by 54%.•Optimal recirculation ratio was 0.3•The hydrogen energy obtained from FW was improved by 8% with recirculation.•Digestate recycling did not increase the overall energy yield.
Efficient treatment of swine wastewater at a high rate would facilitate the development of a sustainable pig industry. In this study, to investigate methane fermentation and membrane filtration ...performance, an anaerobic membrane bioreactor was operated under mesophilic conditions for 207 days during four stages, with a hydraulic retention time (HRT) decreasing from 5 to 3, 2, and 1 day, and a changing of solid retention time/hydraulic retention time (SRT/HRT) ratio from 18,18 to 8 and 3.2. The results showed that a higher volumetric methane production of 1.63 L/(L·d) and a lower VFAs concentration (<200 mg/L at stable stage) could achieved when the HRT was 1 day and SRT/HRT ratio was only 3.2. The specific methanogenic activity slightly decreased under the shorter HRT, and with SRT/HRT shortening, hydrogenotrophic Methanocorpusculum tended to dominate in bulk sludge while acetoclastic Methanosaeta dominated in the biofilm. Membrane fouling was observed after 4 months with a flux decline and a significant increase in trans-membrane pressure. A serial cleaning test indicated that organic pollutants contributed highly to the membrane fouling.
Display omitted
•HRT was successfully reduced to 1 day in the AnMBR.•The specific methanogenic activity decreased during the shortening of the HRT.•The biofilm attached to the membrane had higher acetoclastic methanogens.•Membrane fouling was almost completely removed by sodium hypochlorite.
Anaerobic digestion is a promising technology for the treatment of chicken manure but its application has limitations due to the inhibition induced by high concentration of ammonium nitrogen. In this ...study, the methane yield and methanogenic pathway of high solid anaerobic digestion of chicken manure, and their response to total ammonium nitrogen (TAN) variations with and without ammonia stripping were investigated through 194 days' continuously fed experiment. The results obtained show a 20% reduction in the TAN and a 30% reduction of volatile fatty acids by a moderate in-situ ammonia stripping. Methane yield increased by 34% and the enhanced acetoclastic and hydrogenotrophic methanogenic activities were significant. Firmicutes, Bacteroidetes, and Cloacimonetes were dominant at a TAN range of 5.8–6.8 g/L. Methanosarcina sp. was the dominant archaea and its relative abundance increased with in-situ ammonia stripping. The shifts of methanogenic pathway with and without stripping was quantified by 2–13C stable isotope probing and was consistent with the microbial community's changes. The positive effects achieved by in-situ ammonia stripping set the foundation for its use in the anaerobic digestion process of nitrogen-rich and high solid materials during treatment management.
•Moderate in situ stripping reduced TAN by 20% and VFAs by 30%.•Stripping increased both methane yield and methanogenic activities.•The microbial communities were identified by high throughout sequencing.•The methanogenic pathway was quantified by 2–13C isotope probing.
•Process performance with shortening HRTs was simulated by kinetic model.•Microorganisms were washed out at HRT of 3 days.•Acidogenesis and methanogenesis became the rate limiting step.•VS removal ...correlated with the methanogenic communities.
Requirement of a long hydraulic retention time (HRT) for efficient degradation restrains the anaerobic digestion of hydrothermal pretreated sludge. Shortening the HRT can increase the treatment capacity of a plant but may also induce digester instability. This study investigated the impact of HRT on process performance and microbial community by consecutively operating a reactor for 145 days. The HRT was gradually decreased from 20 to 10, 5, and 3 days. The methane yield declined from 0.28 to 0.12 L/g-VSin with this shortening, and acetate concentration increased from 38 to 376 mg/L. Methanoculleus (58%) dominated methanogens at a 20 days HRT. However, the methanogenic structure shifted toward an increased level of Methanospirillum, representing 95% of the total archaea at a 3 days HRT. Microorganisms were almost washed out at the end of experiment. Conclusively, shortening HRTs is a feasible strategy to increase treatment capacity and produce more biogas at existing plants.
Illustrations of the methanogenic pathways indicated by carbon isotope (δ13C) analysis under mesophilic and thermophilic conditions.
Display omitted
•The Methanogenesis pathway was quantitatively ...determined by 2–13C isotope.•SAO-HM account for 41% and 50% of methane formation at 37 °C and 55 °C.•The thermophilic digester had 15% lower methane yield rates.•Stable processes were achieved at free ammonia of 31 and 145 mg/L, respectively.
The impact of temperature on the anaerobic digestion of chicken manure was investigated by studying the process performance and pathway for continuously-fed digesters under mesophilic and thermophilic conditions. The mesophilic digester obtained a 15% higher methane yield compared with the thermophilic digester. Mesophilic and thermophilic digester had free ammonia of 31 and 145 mg/L, respectively. The stable carbon isotope analysis indicated that 41% and 50% of acetate was converted to methane through the syntrophic acetate oxidation and hydrogenotrophic methanogenesis (SAO-HM) pathway under mesophilic and thermophilic conditions, respectively. The genus Pseudomonas represented 10% and 16% under mesophilic and thermophilic conditions, respectively. A high abundance of the methanogens genus Methanoculleus (94% of total methanogens) in mesophilic and the genus Methanothermobacter (96%) in thermophilic digesters indicated they were the main hydrogenotrophic partners in SAO. The present study therefore illustrated that methanogenic pathway shifting, induced by free ammonia, closely correlated to the process performance.
•Effects of HRT (20-5d) on AD of biological hydrolyzed sludge was investigated.•An ‘inhibited steady state’ of methane production was observed at shorter HRT.•HRTs mediated a remarkable variation in ...microbial community profiles.•Sporosarcina and Methnosarcina correlated to VS removal and methane yield.
Hyperthermophilic biological hydrolysis of sewage sludge was applied before long-term anaerobic digestion to investigate how shortening hydraulic retention times (HRT, 20-5d) affected methanogenic performances and microbial dynamics. Results indicated that although the three different HRTs provided a stable process with a steady-state of methane production, both methane yield (161 L kg-VSin−1, 25% higher) and volatile solids removal (VS, 50%, 2-fold higher) increased during longer HRTs. Redundancy analysis results indicated that Sporosarcina and Methnosarcina positively correlated to VS removal and methane yield, and negatively correlated to volatile fatty acids (VFAs) accumulation. The relative abundance of Coprothermobacter (>60%), syntrophic acetate oxidation bacteria (SAOB), and Methanospirillum (8–15%), increased during shorter HRTs. A slight shift to two-stage acetate conversion was observed during shorter HRTs. The results demonstrated that HRTs played a key role in shaping microbial structure, leading to a new steady-state of microbial community profiles and process performances at variable HRTs.
Display omitted
•A hybrid AnMBR was developed to treat food waste with anti-fouling function.•About 21% of biomass attached on the carriers in the hybrid AnMBR.•Membrane fouling was largely ...alleviated in the hybrid AnMBR.•Thermophilic AD of food waste can maintain stability at high OLR.
The thermophilic anaerobic digestion of food waste was a long-term challenge for maintaining process stability. A hybrid submerged anaerobic membrane bioreactor (AnMBR), integrating 27%(v/v) polyurethane sponge as fixed carriers were therefore investigated at (50 ± 2) °C. The organics removal efficiencies, COD mass balance, and membrane filtration performance were investigated in a 75-days continuously operated experiment. The results showed that methane production reached 0.31 L/(kg·COD) under an organic loading rate of 7.3 kg·COD/(m3·d). The low concentration of total volatile fatty acids of 247 ~ 274 mg/L and a high proportion of Methanosarcina (>97%) represented the high stability of the thermophilic process. Approximately 21% of biomass grew on the carriers in the hybrid AnMBR and induced a much lower suspended solids concentration and viscosity of bulk sludge. Noticeable lower trans-membrane pressure was consequently observed. The affecting factors identified by PCA analysis proved the advantages of the hybrid AnMBR for alleviating membrane fouling formation.
Biogas plants have been widely used to both reclaim bio-energy from agricultural waste and to treat waste; however, the efficiency of these biogas plants has yet to be determined. In this study, the ...performance of five full scale biogas plants treating chicken manure (CM), pig manure (PM), a mixture of chicken and pig manure (MM), dairy manure (DM), and maize straw (MS) were investigated. The results showed that CM had the highest total energy (16.4 KJ/g-TS) and the MM had the highest bio-available energy (10.2 g-COD/g-TS). The CM plant adopted a suitable hydraulic retention time (HRT) but the other plants used a much longer HRT than necessary. The methane production from CM, PM, MM, and DM was improved by 12%, 22%, 32% and 25% with the addition of trace metals, and this also resulted in an increment in the methanogenic activity for CM, PG, MM and MS. The pH stability of all the biogas plants was maintained at an acceptable level; nevertheless, the high pH and ammonium in the CM digester negatively affected the methanogenic activity. The results, therefore, conclusively indicated that the operation of the biogas plants could be more effective.
•Performance of full scale biogas plants treating agricultural wastes was investigated.•Bio-energy availability of each agricultural substrate was obtained.•Chicken manure had the highest total energy of 16.4 KJ/g-TS.•Considerable room for improvement in the full scale biogas plants exists.
This study evaluated the influence of hyper-thermophilic pre-hydrolysis stage (70 °C) on methane recovery of sewage sludge at 35 °C. In this configuration, the process performance in both ...temperatures were estimated and the microbial communities were characterized by full-length16S rRNA genes and/or microbial activities. In addition, the appropriate solubilization reaction time was assessed. The results revealed that the higher hydrolysis and acidogenesis activities were achieved with longer reaction time of pretreatment (5 days) and thus higher organic nitrogen conversion and alkalinity were attained. Under appropriate pretreatment reaction time, pretreated sludge was characterized by 65% higher organic matters solubilization and 1.4-fold higher volatile fatty acids (VFAs) concentration compared to raw sludge. The overall methane yield produced under this scenario was 179 L CH4. KgVSin, with 15% of the absolute yield was produced in hydrolysis reactor. 50% reduction in bacteria belong to Firmicurtes was observed at mesophilic reactor and meanwhile the relative abundance of Bacteroidetes and Cloacimonetes were enhanced. The predominant methanogens in both stages did not change implying adaptation of Methanothermobacter (>62%) to mesophilic condition. However, increasing acetoclastic methanogens up to 30% in mesophilic reactor indicating methane was produced from pretreated sludge mainly through H2– mediated CO2 reduction and partially from acetate cleavage. The results highlight the key role of hyper-thermophilic pre-hydrolysis stage for better stabilization of sewage sludge without further investments in current biogas plants.
Display omitted
•Methane recovery of sewage sludge was enhanced by pre-hydrolysis stage at 70 °C.•Two-step conversion process was mainly taken place at hyper-thermophilic condition.•Hydrolysis and acidogenesis was stimulated at longer reaction time of pretreatment.•The methane was mainly produced by hydrogenotrophic methanogens.•Methanothermobacter was the dominant methanogens regardless process temperature.
An anaerobic membrane reactor (AnMBR) was investigated and compared with a continuously stirred tank reactor (CSTR) in order to treat thermal hydrolyzed sludge. Long term experiments were carried out ...by shortening the hydraulic retention time (HRT) from 30 d to 3 d under mesophilic conditions. The results obtained show that at each HRT the AnMBR had higher removal efficiencies for total solids and volatile solids, and higher specific methanogenic activities. Comparable process stability was obtained for the two reactors. A flat sheet membrane could work with the high solid system but the trans-membrane pressure appeared sensitive to total solid concentrations. Foaming occurred in the AnMBR at a HRT of 3 d, and an organic loading rate of 8.84 kg-COD/(m3·d) further deteriorated the membrane filtration. Hydrogentropic methanogens, in particular Methanospirillum, dominated the archaea community in both the AnMBR and the CSTR at a HRT of 3 d (i.e. 85% in the AnMBR and 95% in the CSTR). An obligate acetoclastic methanogen, Methanosaeta, was found at a very low level during all the HRTs. As a whole, the efficiency of methanogenesis in the AnMBR to treat thermal hydrolyzed sludge was proved to be better than in the CSTR during short HRTs.
•The efficiency of methanogenesis in the AnMBR was better than in the CSTR.•Hydrogentrophic methanogens dominate the two reactors at short HRT.•The trans-membrane pressure appeared sensitive to total solid concentrations.•Foaming occurred in AnMBR deteriorated the membrane filtration.
