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•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.
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.
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.
•The continuous bio-H2 and bio-CH4 production was sustainable in long term.•The optimized bio-H2 and bio-CH4 production parameters was obtained.•The methane production was supposed to through SAO-HM ...pathway.
Anaerobic digestion is a well-established technology for treating organic waste, but it is still under challenge for food waste due to process stability problems. In this work, continuous H2 and CH4 production from canteen food waste (FW) in a two-stage system were successfully established by optimizing process parameters. The optimal hydraulic retention time was 5d for H2 and 15d for CH4. Overall, around 59% of the total COD in FW was converted into H2 (4%) and into CH4 (55%). The fluctuations of FW characteristics did not significantly affect process performance. From the energy point view, the H2 reactor contributed much less than the methane reactor to total energy balance, but it played a key role in maintaining the stability of anaerobic treatment of food waste. Microbial characterization indicated that methane formation was through syntrophic acetate oxidation combined with hydrogenotrophic methanogenesis pathway.
•Thermophilic is more advantageous than the hyperthermophilic to pretreat FW.•Long-term and stable H2 production was established in thermophilic CSTR.•Process kinetics of both temperatures were ...obtained.•Rate-limiting step in pretreatments was determined.
High-temperature pretreatment plays a key role in the anaerobic digestion of food waste (FW). However, the suitable temperature is not yet determined. In this work, a long-term experiment was conducted to compare hydrolysis, acidogenesis, acetogenesis, and hydrogen production at 55°C and 70°C, using real FW in CSTR reactors. The results obtained indicated that acidification was the rate-limiting step at both temperatures with similar process kinetics characterizations. However, the thermophilic pretreatment was more advantageous than the hyperthermophilic with suspended solids solubilization of 47.7% and 29.5% and total VFA vs. soluble COD ratio of 15.2% and 4.9%, for thermophilic and hyperthermophilic treatment, respectively, with a hydrolytic reaction time (HRT) of 10days and an OLR of 14kgCOD/m3d. Moreover, stable hydrogen yield (70.7ml-H2/gVSin) and content in off gas (58.6%) was achieved at HRT 5days, pH 5.5, and temperature of 55°C, as opposed to 70°C.
•Lipids extraction increased CH4 yield by 4.5% and 24.5% at 35°C and 55°C.•Mixing sludge with FW enhanced stability of AD process.•Thermophilic process had higher CH4 yield and lower Rmax than ...mesophilic process.
Anaerobic digestion (AD) of FW shows instability due to both the presence of high lipids and accumulation of volatile fatty acids. In this study, AD of food waste (FW) was optimized by removing lipids (LRFW) and by co-digestion with sewage sludge (1:1w/w on dry matter). The results obtained showed that lipids extraction increased FW methane yield from 400 to 418mL-gVSadded−1 under mesophilic conditions (35°C) and from 426 to 531mL-gVSadded−1 in thermophilic conditions (55°C). Two degradation phases (k1 and k2) described FW and LRFW degradation. In the thermophilic, LRFW-k1 (0.1591d−1) was slightly higher than that of FW (k1 of 0.1543d−1) and in the second stage FW-k2 of 0.0552d−1 was higher than that of LRFW (k2 of 0.0117d−1). The majority of LRFW was degraded in the first stage. FW and sewage sludge co-digestion reduced VFA accumulation, preventing media acidification and improving process stability.
Anaerobic digestion is a well-established technology for treating organic waste, but it is still under challenge for food waste due to process stability problems. In this work, continuous H
and CH
...production from canteen food waste (FW) in a two-stage system were successfully established by optimizing process parameters. The optimal hydraulic retention time was 5d for H
and 15d for CH
. Overall, around 59% of the total COD in FW was converted into H
(4%) and into CH
(55%). The fluctuations of FW characteristics did not significantly affect process performance. From the energy point view, the H
reactor contributed much less than the methane reactor to total energy balance, but it played a key role in maintaining the stability of anaerobic treatment of food waste. Microbial characterization indicated that methane formation was through syntrophic acetate oxidation combined with hydrogenotrophic methanogenesis pathway.
