In the anaerobic digestion (AD) process there are some difficulties in maintaining process stability due to the complexity of the system. The variability of the raw material coming to the facility, ...temperature fluctuations and pH changes as a result of microbial processes cause process instability and require continuous monitoring and control. Increasing continuous monitoring, and internet of things applications within the scope of Industry 4.0 in AD facilities can provide process stability control and early intervention. In this study, five different machine learning (ML) algorithms (RF, ANN, KNN, SVR, and XGBoost) were used to describe and predict the correlation between operational parameters and biogas production quantities collected from a real-scale anaerobic digestion plant. The KNN algorithm had the lowest accuracy in predicting total biogas production over time, while the RF model had the highest prediction accuracy of all prediction models. The RF method produced the best prediction, with an R2 of 0.9242, and it was followed by XGBoost, ANN, SVR, and KNN (with R2 values of 0.8960, 0.8703, 0.8655, 0.8326, respectively). Real-time process control will be provided and process stability will be maintained by preventing low-efficiency biogas production with the integration of ML applications into AD facilities.
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•Industrial Scale anaerobic digestion plant data were collected.•5 different ML algorithms were used to predict biogas production.•The best prediction was achieved with the RF algorithm (R2 = 0.9242).•The model with the lowest R2 value (0.8326) was the SVR algorithm.•Process stability could be maintained with ML applications in AD plants.
•Two TAD of food waste both had good performances at HRT 30 d in stable stage.•The VS destructions and methane yields of food waste in two TAD were comparable.•Two TAD recovered similar energy from ...the fed and destructed food waste.•Single stage TAD had higher energy recovery, rate and special rate of reaction for the four AD steps.•Two-stage TAD need to be adjusted its operational parameters to improve its AD efficiency.
The single-stage and two-stage thermophilic anaerobic digestion (TAD) in lab scale continuously stirred tank reactor systems fed semi-continuously with food waste (FW) were studied to compare their performance, energy balance and reaction processes. The experimental results showed the two TADs both had good performance at a sludge retention time (SRT) of 30 d. The VS destruction (83.22 ± 1.33%) of the single-stage TAD was comparable with the two-stage TAD (82.02 ± 1.25%) during the steady period. While the average biogas yield of the two-stage TAD (0.810 ± 0.13 L/g Added VS) was higher than that of single-stage TAD (0.775 ± 0.20 L/g Added VS) and the methane content of the former (59.1 ± 1.4%) was lower than that of the latter (61.6 ± 2.1%), the methane yields of the two TADs were similar. The single stage TAD had higher energy recovery, rate and specific rate of reaction for the four AD steps than the two-stage TAD. The two-stage TAD had to adjust its operational parameters to improve its AD efficiency.
As antibiotic resistance continues to spread globally, there is growing interest in the potential to limit the spread of antibiotic resistance genes (ARGs) from wastewater sources. In particular, ...operational conditions during sludge digestion may serve to discourage selection of resistant bacteria, reduce horizontal transfer of ARGs, and aid in hydrolysis of DNA. This study applied metagenomic analysis to examine the removal efficiency of ARGs through thermophilic and mesophilic anaerobic digestion using bench-scale reactors. Although the relative abundance of various ARGs shifted from influent to effluent sludge, there was no measureable change in the abundance of total ARGs or their diversity in either the thermophilic or mesophilic treatment. Among the 35 major ARG subtypes detected in feed sludge, substantial reductions (removal efficiency >90 %) of 8 and 13 ARGs were achieved by thermophilic and mesophilic digestion, respectively. However, resistance genes of aadA, macB, and sul1 were enriched during the thermophilic anaerobic digestion, while resistance genes of erythromycin esterase type I, sul1, and tetM were enriched during the mesophilic anaerobic digestion. Efflux pump remained to be the major antibiotic resistance mechanism in sludge samples, but the portion of ARGs encoding resistance via target modification increased in the anaerobically digested sludge relative to the feed. Metagenomic analysis provided insight into the potential for anaerobic digestion to mitigate a broad array of ARGs.
Sludge is a major by-product and the final reservoir of antibiotic resistance genes (ARGs) in wastewater treatment plants (WWTPs). Temperature-phased anaerobic digestion (TPAD), consisting of ...thermophilic anaerobic digestion (AD) (55 °C) and mesophilic AD processes (37 °C), has been implemented in WWTPs for sludge reduction while improving the biomethane production. However, the impact of TPAD on the ARGs' fate is still undiscovered in lab-scale experiments and full-scale WWTPs. This study, for the first time, investigated the fate of ARGs during the TPAD process across three seasons in a full-size WWTP. Ten typical ARGs and one integrase gene of class 1 integron (intI1) involving ARGs horizontal gene transfer were examined in sludge before and after each step of the TPAD process. TPAD reduced aac(6′)-Ib-cr, blaTEM, drfA1, sul1, sul2, ermb, mefA, tetA, tetB and tetX by 87.3–100.0 %. TPAD reduced the overall average absolute abundance of targeted ARGs and intI1 by 92.39 % and 92.50 %, respectively. The abundance of targeted ARGs in sludge was higher in winter than in summer and autumn before and after TPAD. During the TPAD processes, thermophilic AD played a major role in the removal of ARGs, contributing to >60 % removal of ARGs, while the subsequent mesophilic AD contributed to a further 31 % removal of ARGs. The microbial community analysis revealed that thermophilic AD reduced the absolute abundance of ARGs hosts, antibiotic resistant bacteria. In addition, thermophilic AD reduced the abundance of the intI1, while the intI1 did not reproduce during the mesophilic AD, also contributing to a decline in the absolute abundance of ARGs in TPAD. This study demonstrates that TPAD can effectively reduce the abundance of ARGs in sludge, which will suppress the transmission of ARGs from sludge into the natural environment and deliver environmental and health benefits to our society.
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•TPAD reduced the average absolute abundance of targeted ARGs and intI1.•Thermophilic AD plays a major role in the ARGs and intI1 removals.•The removal of ARGs is related to the decreased abundance of ARB and intI1.•The abundance of targeted ARGs was higher in winter than in summer and autumn.
The policies and technological drivers to manage food waste in Asia have been shaped by the increasing awareness of the countries to this issue, their commitment to national and international ...development goals, their socio-economic constraints, and their recognition of the potency to recover nutrients and energy from food waste. The concept of reduce, reuse and recycle (the 3R principles) streamline the existing food waste management policies, and scrutinising the gaps and challenges led to a conclusion that most of the countries emphasise food waste segregation and treatment instead of prevention at source itself. Furthermore, a qualitative SWOT analysis of five prevailing treatment options led to a conclusion that animal feeding, incineration, and landfilling are unsustainable since they pose various health and environmental hazard risks. It was further concluded that anaerobic digestion was the preferred option than aerobic digestion (composting) considering the characteristics of the available food waste in Asia as well as the underlying environmental and economic benefits. Moreover, decentralised, community-scale, anaerobic digestion system has been gaining traction over centralised, large-scale system because of their lower energy footprint, ease of operation, need for lesser resources, lower operation and maintenance costs, and higher chances of public acceptance. It was also observed that the policy to gain energy from segregated food waste is a larger driving force for the efforts to promote anaerobic digestion and thereby manage food waste sustainably.
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•Policies and technological drivers to manage food waste in Asia have been reviewed.•Food waste reduction is not adequately prioritised in most Asian countries.•Community-scale systems are gaining traction for food waste management.•Policies, rather than technologies, are driving food waste management efforts in Asia.
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•Improvement of the organic substrate biodegradation was associated to H2 injections.•Non-dominant hydrogenotrophic methanogens became predominant with H2 injections.•CH4 production ...was similar regardless of initial microbial activity levels.•CH4 production from organic matter increased of a least 626 NmL with H2 injections.
During in situ biomethanation, microbial communities can convert complex Organic Matter (OM) and H2 into CH4. OM biodegradation was compared between Anaerobic Digestion (AD) and in situ biomethanation, in semi-continuous processes, using two inocula from the digester (D) and the post-digester (PoD) of an AD plant. The impact of H2 on OM degradation was assessed using a fractionation method. Operational parameters included 20 days of hydraulic retention time and 1.5 gVS.L−1.d−1 of organic loading rate. During in situ biomethanation, 485 NmL of H2 were injected for each feeding (3 times a week). Maximum organic COD removal was 0.6 gCOD in AD control and at least 1.6 gCOD for in situ biomethanation. Therefore, COD removal was 2.5 times higher with H2 injections. These results bring out the potential of H2 injections during AD, not only for CO2 consumption but also for better OM degradation.
Considerable amounts of organic waste materials are disposed of in landfills or by incineration, creating the potential for environmental problems and missing opportunities for energy and material ...applications. The more digestible, valuable, and edible components (e.g. starch, lipids, edible fibers, and essential proteins for human health) are generally extracted first from biomass feedstocks, leaving the more recalcitrant, less beneficial, and unpleasant components. Due to higher-cost extractions, immature conversion techniques, and lower market demand, lignin and protein can become enriched in these biomass wastes: agricultural residues, dedicated (biofuel) plants, distillers' grains, seed cakes, forestry residues, food wastes, municipal solid wastes, sewage sludges, and digestate solids. These protein-rich lignocellulosic wastes still contain abundant fibrous polysaccharides (e.g. cellulose and hemicellulose) that have the potential for (further) conversion. In this review, each waste feedstock is evaluated for valorization by hydrolysis + fermentation, and anaerobic digestion, based on biomass composition, biomass degradation mechanisms, and yield/quality of the end products. Agricultural residues, dedicated plants, and distillers’ grains have the highest bioethanol yields compared to the other feedstocks. Stillage, sewage sludge, municipal solid waste, de-oiled seed cakes, and food wastes show higher activities in anaerobic digestion and produce greater biogas yields. Integration of hydrolysis + fermentation and anaerobic digestion may maximize the bioenergy recovery, and minimize residue generation, from most types of protein-rich lignocellulosic wastes. Screening wastes for different conversion methods enables greater chances for profitability while mitigating environmental risks within agricultural, industrial, and municipal sectors.
•Agricultural residues, dedicated plants, and DDGS favor ethanol production.•Stillage, sewage sludge, seedcakes, and food wastes favor methane production.•Serial integration of conversion methods maximizes feedstock utilization value.
Livestock waste is a known reservoir of Escherichia coli (E. coli) carrying clinically important CTX-M-type extended-spectrum β-lactamase genes (blaCTX-M), however, the occurrence and transfer ...characteristics of blaCTX-M genes during anaerobic digestion (AD) remain unclear. Herein, four full-scale and two parallel lab-scale AD systems treating swine waste under ambient and mesophilic conditions were investigated by both molecular- and culture-based methods to reveal the occurrence and transfer behaviors of blaCTX-M genes during AD. Real-time TaqMan polymerase chain reaction revealed 1.3 × 104–6.8 × 105 and 3.0 × 104–7.0 × 105 copies/mL of blaCTX-M groups 1 and 9 in all feeding substrates. While AD reduced the absolute abundance of groups 1 and 9 by 0.63–2.24 and 0.08–1.30 log (P < 0.05), 5.0 × 102–4.1 × 103 and 1.1 × 104–3.5 × 104 copies/mL of groups 1 and 9 remained in the anaerobic effluent, respectively. In total, 141 blaCTX-M-carrying E. coli isolates resistant to cefotaxime were obtained from the AD reactors. Whole-genome sequencing showed that blaCTX-M-65 mainly carried by E. coli ST155 was the most frequently detected group 9 subtype in the feeding substrate; whereas blaCTX-M-14 associated with the dominant clones E. coli ST6802 and ST155 became the major subtype in AD effluent. Furthermore, blaCTX-M-14 was flanked by ΔIS26 upstream and ΔIS903B downstream. The ΔIS26-blaCTX-M-14-ΔIS903B element was mainly located on the IncHI2 plasmid in E. coli ST48 and ST6802 and also the IncFIB plasmid in ST155 in anaerobic effluent. Conjugation assays showed that the plasmids harboring blaCTX-M-14 could be successfully transferred at a frequency of 10−3–10−2 cells per recipient cell. This study revealed that blaCTX-M genes remained in both the full-scale and lab-scale AD effluents of swine waste. Thus, additional efforts should be implemented to block the discharge and spread of antibiotic resistance genes to the environment.
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•blaCTX-M groups 1 and 9 remained in swine waste effluent after anaerobic digestion.•Cefotaxime resistant E. coli was present in effluent after anaerobic digestion.•blaCTX-M-14 became the dominant group 9 subtype in E. coli in anaerobic effluent.•ΔIS26-blaCTX-M-14-ΔIS903B transferred among different E. coli clones and plasmids.•High conjugation frequency of IncHI2 plasmid favored blaCTX-M-14 propagation.
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•Syntrophic associations were enriched to relieve acid accumulation.•Fatty acid-oxidizing syntrophs and H2/formate-utilizing methanogens were enriched.•Enriched syntrophic ...associations favored degradation of propionate and butyrate.•The interspecies formate/hydrogen transfer was enhanced with microbial enrichment.
Aiming at relieving acid accumulation in anaerobic digestion (AD), syntrophic associations of syntrophic fatty acid-oxidation bacteria and H2/formate-scavenging methanogens were enriched by feeding propionate, butyrate and formate in an up-flow anaerobic sludge blanket (UASB) reactor. Results showed that methane yield increased by 50% with increasing formate concentration (0–2000 mg COD/L). In addition, the abundance and quantity of SFOB (Syntrophobacter, Smithella and Syntrophomonas) and H2/formate-scavenging methanogens (Methanobacteriales and Methanomicrobiales) were increased after microbial acclimation. The enriched syntrophic associations showed higher propionate and butyrate removal efficiencies of 98.48 ± 1.14% and 99.71 ± 0.71%, respectively. Furthermore, encoding genes of formate dehydrogenase and hydrogenases presented higher abundances after microbial enrichment, which suggested that the enhancements of interspecies formate transfer and interspecies hydrogen transfer between syntrophic associations benefited volatile fatty acids (VFAs) conversion. This research provided an effective strategy to relieve acid accumulation.
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•Recycling effluents boosts AD performance of lignocellulosic biomass. An 87 % improvement in specific biogas yield achieved by effluents recycled.•Methanol from pectin hydrolyzation ...involved into the methylotrophic methanogenesis.•Biogenic amine pathway contributed to methylamines production.
Effluents recycling proves to be an effective method for enhancing the performance of anaerobic digestion system for lignocellulosic-like biomass. However, a limited understanding exists regarding the regulation mechanisms of methanogens. This study aims to systematically assess the dynamic interactions between process parameters, microbial communities, and methanogenic activity throughout the AD process of corn stover with effluents recycling. The results show a significant increase in the specific biogas yields of corn stover to 369 ± 115 mL/g VS with effluents recycling, an 87 % improvement compared to the control system. Effluents recycling can recover nitrogen and selectively enrich the abundances of microorganisms such as Herbinix hemicellulosilytica, Bacteroides paurosaccharolyticus and Methanosarcina mazei, etc. Correspondingly, the strategy improves the abundance of CAZymes, enhancing the efficient depolymerization of cellulose, glucuronoarabinoxylan, xyloglucan and pectin. Methanol and methylamines originating from enhanced pectin hydrolyzation and the biogenic amine pathway boost methylotrophic methanogenesis. This study addresses knowledge gaps in producing-pathways of precursors for methylotrophic methanogenesis and elucidates the mechanism to boost methanogenesis process of lignocellulosic-like biomass with effluents recycling.
