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[Display omitted] • The quantities of plastic debris in raw digestate were 415–3298 particles/kg-ww. • Depackaging food waste at source can reduce plastic debris in solid digestate. • Fiber was the dominant shape in raw and solid digestate. • There were 7–38 particles/L MPs in the liquid digestate. Plastic debris, including macroplastics (>5 mm) and microplastics (0.1–5 mm), has proven to be an emerging contaminant. Anaerobic digestion, coupled with energy recovery, can be an effective valorization technology for biogenic waste. But the use of the resulting digestate as a soil conditioner is a source for plastic debris release into the environment. The preprocess and postprocess used could influence the quantity of plastic debris found in the digestate, but the specifics of these effects are relatively unknown. Therefore, we measured the quantity of plastic debris in raw digestate under a variety of preprocessing scenarios. We also investigated the occurrence of plastic debris in solid and liquid digestates resulting from the dewatering of raw digestate. The quantity of plastic debris ranged from 41 to 3298 particles/kg (WW) for raw digestate, 319–3604 particles/kg (WW) for solid digestate and 7–38 particles/kg (WW) for liquid digestate. We observed that depackaging at source by citizens themselves (removing the package of biogenic waste when dropping it into bins), significantly reduced the quantities of plastic debris in raw digestate by an order of magnitude. Furthermore, the number of polymer types in raw digestate, where depackaging occurred at source, were lower than that where this rule was not in place. The average size of plastic debris in solid digestate was significantly smaller than that in raw digestate, which indicated that the process of mechanical dewatering could generate MPs. It is recommended to depackage for biogenic waste at source to reduce the quantities of MPs in digestate. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bioaugmentation was implemented with nondomesticated mixed microbial consortia. • Introduction of bioaugmentation culture significantly improved methane production. • The strategy works by regulating the relationship between syntrophs and methanogens. • Selection of consortium and the dosage were key to the bioaugmentation strategy. Bioaugmentation shows promise in mitigating ammonia-induced microbial inhibition in anaerobic digestion processes. However, the advanced technical requirements and high costs associated with pure strain cultivation, as well as the time-consuming and labor-intensive process of domesticating consortia, present challenges for industrial applications. Herein, the efficacy of bioaugmentation with nondomesticated mixed microbial consortia was evaluated, which resulted in a significant methane production improvement of 5.6%–11.7% and 10.3%–13.5% under total ammonia nitrogen concentrations of 2.0 and 4.9 g-N/L, respectively. Microbial analysis revealed that at high ammonium levels, the bioaugmented culture facilitated a transition in the methanogenic pathway from acetoclastic to hydrogenotrophic by regulating symbiotic relationships between propionate- and acetate-oxidizing bacteria and methanogens. Consortium type and dose applied were identified as crucial factors determining bioaugmentation effectiveness. Overall, nondomesticated mixed microbial consortia demonstrate potential as cost-effective bioaugmentation agents for mitigating ammonia-induced inhibition. [ABSTRACT FROM AUTHOR]

Acid crisis characterized by acid accumulation and/or low pH is a common reason for the failure of anaerobic digestion (AD), which is usually applied for wastewater and waste treatment. Acid-tolerant methanogens are rarely reported to be active in the artificial anaerobic digester. In this study, we observed that the thermophilic methanogenesis by a consortium in the form of flocs and not granules could still be recovered during long-term operation at acetate concentration of up to 104 mM and pH 5.5 by adjusting the pH gradually or directly to pH 5.5 or 5.0. The acclimation process involving the gradual decrease in pH could enhance the resistance of the consortium against extreme acidification. The stable isotopic signature analysis of biogas revealed that Methanosarcina , which produced methane through acetoclastic methanogenesis (AM) pathway, was the predominant methane producer when the pH was decreased gradually to 5.0. Meanwhile, the abundance of Coprothermobacter increased with a decrease in pH. Contrastingly, when directly subjected to an environment of pH 5.5 and 104 mM acetate (15.84-mM free acetic acid) after a 42-day lag phase, Methanothermobacter was the predominant methanogen. Methanothermobacter initiated methane production through the hydrogenotrophic pathway and formed syntrophic relationship/consortium with the potential acetate-oxidizing bacteria, Thermacetogenium and Coprothermobacter. Comparative metagenomic and metatranscriptomic analysis on this self-adapted and acid-tolerant consortium revealed that the genes, such as GroEL, DnaK, CheY, and flagellum-related genes (FlaA, FlgE, and FliC) from Anaerobaculum , Thermacetogenium , and Coprothermobacter were highly overexpressed in response to system acidification. Microbial self-adaptation patterns (community structure adjustment, methanogenesis pathway shift, and transcriptional regulation) of thermophilic methanogenic consortium to gradual and sudden acidification were evaluated by integrated stable isotopic signature and comparative meta-omic approaches. The study elucidated the acid-resistant mechanism of thermophilic methanogenic consortium and deepened our knowledge of the function, interaction, and microbial characteristics of Methanosarcina , Methanothermobacter , and Coprothermobacter under extreme acidic environment. [ABSTRACT FROM AUTHOR]

• Doubled microbial enrichment was found in mesophilic digesters with powdered biochar. • CH 4 production increased by 32.5% in granular biochar amended mesophilic digesters. • CH 4 production increased by 13.3% in powdered biochar amended thermophilic digesters. • Biochar relieved propionic acid accumulation in thermophilic digesters. Oil is a desirable substrate for anaerobic digestion (AD) for its high energy recovery potential. However, low solubility of oil and long-chain fatty acids (LCFAs) inhibition hinder microbial growth and further reduce the biogas production in most cases. Biochar is a cheap but reliable additive in AD. Its functions to enrich microbial enrichment and enhance biogas production were confirmed previously. In present study, effects of biochars with different particle sizes on oil AD were investigated under thermophilic and mesophilic conditions. Results from the quantification and space distribution of microbes indicate that powdered biochar (<5 μm) aggregated more microbes than granular biochar (0.5–1 mm). Especially in the mesophilic digesters, powdered biochar doubled the number of microbes in the whole digester, which was a satisfactory result of acclimation. In addition, powdered biochar was able to adjust the microbial communities and further increased CH 4 production by 13.3% in thermophilic digesters. Granular biochar enhanced the maximum CH 4 potential by 32.5% under mesophilic condition, which was most promising from the perspective of energy recovery. Biochar of both particle sizes relieved propionic acid accumulation in thermophilic digesters. Hence, biochar addition might be an ideal approach to elevate energy recovery efficiency by overcoming the barriers of anaerobic microbes to utilize LCFAs. [ABSTRACT FROM AUTHOR]

• The PBAT/PLA coated paper shows high methane yield under AD condition. • Plastic film residues remain after the digestion of PBAT/PLA coated paper. • The decrease of hydrophobicity for PBAT/PLA bags is due to the formation of PLA monomers. • The bacterial community shows difference between PBAT/PLA coated paper and bags. • Methanoculleus is enriched on the plastic surface under mesophilic AD. Poly (lactic acid) (PLA) and Poly(butylene adipate-co-terephthalate) (PBAT) are two of biodegradable plastics with the highest production capacities in 2021. Bioplastic waste management can be easily integrated with organic waste management, especially when bioplastics are used as food packaging material, since they are potentially biodegradable. The aim of this study was to assess the biodegradability of biodegradable polymer-coated paper (BPCP) and bioplastic bags made from PBAT/PLA blend during mesophilic and thermophilic anaerobic digestion (AD) and to reveal the changes in the physicochemical properties of the bioplastics. BPCP obtained 155 NmL-CH 4 /g VS and 307.3 NmL-CH 4 /g VS under mesophilic and thermophilic conditions, respectively, but left bioplastic film residues. The bioplastic bags did not exhibit significant biodegradation during the AD processes. 1H NMR results indicated that the ratio of PLA to PBAT decreased significantly after AD of the BPCP film and that PLA monomers were formed from the bioplastic bags, leading to a decrease in the hydrophobicity on the surfaces of the materials. Methanoculleus was found to be enriched on the bioplastic surface after mesophilic AD. From the perspective of coupling bioplastic waste management with the food waste management, the incorporation of BPCP into the AD reactor not only enhances system stability and methane production to a greater extent than biodegradable plastic bags but also raises concerns regarding the residual biofilm when utilizing the digestate for direct land applications. [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: Increasing the degradation ratio of organic matter is one of the key challenges for sludge anaerobic digestion. The conventional solution is by directly treating the raw sludge so as to enhance the sludge degradation. In contrast, the target of the present study was digested sludge enriching in refractory organic matter. The method proposed to improve the organic degradation of digested sludge uses ultrasound combined with linear alkylbenzene sulfonate (LAS) to control flocs re‐flocculation. RESULTS: Gas production of the sludge treated with the highest ultrasound energy (360 W, 20 min) was only 57.7 ± 0.3 mL‐CH4 g‐1‐VSadded, and the sludge treated with lower ultrasound energy (120 W, 20 min) with LAS had the highest gas production, up to 92.5 ± 8.5 mL‐CH4 g‐1‐VSadded. Meanwhile, the total VS degradation of 120 W, 20 min with LAS was up to 69.6 ± 5.2%. And the gas production of 360 W, 5 min with LAS was 27.1% higher than that of 360 W, 5 min without LAS. CONCLUSION: These results revealed that digested sludge treated by ultrasonication could be further degraded, and the addition of LAS could significantly improve the re‐digestion performance with less energy. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The effectiveness and optimization strategy of various pretreatment methods to enhance the anaerobic biodegradability and dewaterability of waste activated sludge are still inconclusive. In order to explore the intrinsic triggers determining the apparent biodegradability and dewaterability, sludges pretreated by freeze-thawing, acid, alkali, sonication, thermal autoclaving, and ultraviolet radiation were fractionized according to the cohesion of extracellular polymeric substances (EPS). The fractionized EPS and cells were characterized for microscopic properties by biochemical and elemental composition, Fourier transform infrared spectroscopy, and surface-enhanced Raman spectroscopy. Multivariate statistical analysis was used to mining the key microscopic factors affecting the apparent biodegradability or dewaterability of sludge. Results show that, solubilization degree significantly determined the dewaterability of the pretreated sludge, but did not affect the biodegradability. The properties of slime and lightly-bound EPS were different from other fractions, and inclined to be altered by various pretreatments. However, only the H content, H/C ratio and some functional groups of tightly-bound EPS have significant correlation with the ultimate methane production yield, while the N/C ratio of lightly-bound EPS was important for the initial methane production rate. Free-thawing improved sludge’s biodegradability and dewaterability through dehydration in micro-zones. Autoclaving and ultraviolet weakened sludge’s biodegradability and dewaterability by accelerating the denaturation of some collagen proteins in tightly-bound EPS, transforming it into a viscous gel-like network with higher water-holding capacity. Sonication acted similarly but at a micro-zone level. Acid and alkali pretreatments improved biodegradability by accelerating the release of cell endocytes including pigments carotene and carotenoids. [ABSTRACT FROM AUTHOR]

One-stage dry anaerobic digestion with solid-liquid-separated digestate recirculation was applied to treat synthetic organic solid waste at Digestion Time (DT) of 15, 25, 35 days for several cycles. The highest methane yield of 0.360 ± 0.045 m 3 /kg-VS add with lowest accumulation of hydrolytes was achieved under DT of 15 days. The analysis of intact lipid profiles, including phospholipid fatty acid for bacteria and phospholipid ether lipid for archaea, indicated that the inoculum breakdown occurred, mainly during the start of the process. A significant decline of hydrolytic bacteria was observed during the granular breakdown, which was likely related to the lower methane yield in subsequent cycles. In contrast, the amount of methanogens was still stable even after granular breakdown occurred. The accumulated ammonia in the liquid digestate was partially removed by solid-liquid separation before digestate recirculation, which relieved possible inhibition to some extent with minor microorganism loss. Hence the levels of ammonia, which was highly possible to be the inhibitor causing the decline of methane production, were lower in DT15 than in DT25 and DT35. In this case, it could be implied that the microorganism community reconstruction in DT15 may face less challenges comparing to the other two setups. [ABSTRACT FROM AUTHOR]

The addition of various amounts of biochar to anaerobic digestion of food wastes at different ratios of inoculum to substrate (ISR) was investigated to evaluate the effect of biochar as a functional additive and to optimize the additive dosage of biochar. The biochar treatments at ISR 2, 1, and 0.8 shortened the lag phase of digestion by −20.0%–10.9%, 43.3%–54.4%, and 36.3%–54.0%, and raised the maximum methane production rate by 100%–275%, 100%–133.3%, and 33.3%–100%, respectively, compared to control without biochar. Biochar also enhanced the degradation rate of dissolved organics and volatile fatty acids. Furthermore, the amount of biochar with best effectiveness at ISR = 2, 1, and 0.8 was 2.5, 0.625, and 0.5 g g−1-waste, respectively. Therefore, the effectiveness of biochar depended on the additive amount of biochar and at the same time the inoculum amount, implying a complementary role of abiotic biochar to biotic inoculum. [ABSTRACT FROM AUTHOR]

With the increasing use of municipal solid waste incineration (MSWI) and more stringent limits on landfilling of organic waste, more MSWI bottom ash is being landfilled, and the proportion of inorganic wastes in landfills is increasing, causing the increased Ca concentrations in landfill leachate. In this research, the inhibition effect of Ca concentration on the anaerobic treatment of landfill leachate was studied using a biochemical methane potential experiment. Slight inhibition of methane production occurred when the addition of Ca concentration was less than 2000 mg/L. When the addition of Ca concentration was between 6000 and 8000 mg/L, methane production was significantly reduced (to 29.4-34.8 % of that produced by the BLK reactor), and the lag phase was increased from 8.55 to 16.32 d. Moreover, when the dosage of Ca concentration increased from zero to 8000 mg/L, reductions in solution Ca concentration increased from 929 to 2611 mg/L, and the proportion of Ca in the residual sludge increased from 22.58 to 46.87 %. Based on the results, when the dosage of Ca concentration was less than 4000 mg/L, the formation of Ca precipitates on the surface of sludge appeared to prevent mass transfer and was the dominant reason for the reduction in methane production and sludge biomass. At higher Ca concentrations (6000-8000 mg/L), the severe inhibition of methane production appeared to be caused by the toxic effect of highly concentrated Ca on sludge as well as mass transfer blockage. [ABSTRACT FROM AUTHOR]

This investigation evaluated the effectiveness of biochar of different particle sizes in alleviating ammonium (NH 4 + ) inhibition (up to 7 g-N/L) during anaerobic digestion of 6 g/L glucose. Compared to the control treatment without biochar addition, treatments that included biochar particles 2–5 mm, 0.5–1 mm and 75–150 μm in size reduced the methanization lag phase by 23.9%, 23.8% and 5.9%, respectively, and increased the maximum methane production rate by 47.1%, 23.5% and 44.1%, respectively. These results confirmed that biochar accelerated the initiation of methanization during anaerobic digestion under double inhibition risk from both ammonium and acids. Furthermore, fine biochar significantly promoted the production of volatile fatty acids (VFAs). Comparative analysis on the archaeal and bacterial diversity at the early and later stages of digestion, and in the suspended, biochar loosely bound, and biochar tightly bound fractions suggested that, in suspended fractions, hydrogenotrophic Methanobacterium was actively resistant to ammonium. However, acetoclastic Methanosaeta can survive at VFAs concentrations up to 60–80 mmol-C/L by improved affinity to conductive biochar, resulting in the accelerated initiation of acetate degradation. Improved methanogenesis was followed by the colonization of the biochar tightly bound fractions by Methanosarcina . The selection of appropriate biochar particles sizes was important in facilitating the initial colonization of microbial cells. [ABSTRACT FROM AUTHOR]

Ammonia inhibition represents a major operational issue for anaerobic digestion. In order to refine our understanding of the terminal catabolic steps in thermophilic anaerobic digestion under ammonia stress, we studied batch thermophilic acetate fed experiments at low (0.26 g L −1 ) and high (7.00 g L −1 ) Total Ammonia Nitrogen concentrations (TAN). Although methane production started immediately for all incubations and resulted in methane yields close to stoichiometric expectations, a 62–72% decrease of methanogenic rate was observed throughout the incubation at 7.00 g L −1 of TAN compared to 0.26 g L −1 . Stable Isotope Probing analysis of active microbial communities in 13 C-acetate fed experiments coupled to automated ribosomal intergenic spacer analysis and 16S rDNA pyrotag sequencing confirmed that microbial communities were similar for both TAN conditions. At both TAN levels, the 13 C-labeled bacterial community was mainly affiliated to Clostridia -relatives, with OPB54 bacteria being the most abundant sequence in the heavy DNA 16S rDNA pyrotag library. Sequences closely related to Methanosarcina thermophila were also abundantly retrieved in the heavy DNA fractions, showing that this methanogen was still actively assimilating labeled carbon from acetate at free ammonia nitrogen concentrations up to 916 mg L −1 . Stable isotopic signature analysis of biogas, measured in unlabeled acetate fed experiments that were conducted in parallel, confirmed that acetoclastic methanogenic pathway was dominant at both ammonia concentrations. Our work demonstrates that, besides the syntrophic acetate oxidation pathway, acetoclastic methanogenesis catalyzed by Methanosarcina can also play a major role in methane production at high ammonia levels. [ABSTRACT FROM AUTHOR]

The addition of 0.5–1 mm biostable biochar (10 g/L) to mesophilic anaerobic digesters inoculated with crushed granules (1 g-VS/L) and fed with 4, 6 and 8 g/L glucose shortened the methanogenic lag phase by 11.4%, 30.3% and 21.6% and raised the maximum methane production rate by 86.6%, 21.4% and 5.2%, respectively, compared with the controls without biochar. 75 μm biochar further shortened the lag phase by 38.0% and increased the methane production rate by 70.6% at 6 g/L glucose loading. Biochar also simultaneously enhanced the production and degradation of intermediate acids. The fingerprint and sequencing analysis used to examine the spatial distribution and temporal evolution of communities revealed that proportion of Archaea was higher in the biochar-added treatments and in the tightly-bound fractions. Methanosarcina located in the tightly-bound fractions on the biochar surface, and was most abundant in the larger 2–5 mm biochar particles. Methanosaeta was enriched in the loosely-bound fractions by all-size biochar particles and within the tightly-bound fractions by small biochar particles. Because biochar is cost-effective and can remain in digestate for direct use as soil amendment without separation, eco-compatible biochar may serve as a good substrate for highly-loaded digestion by inducing selective colonization of functional microbes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Metabolomics provides a potential strategy for monitoring AD stability. • Alkanes and aromatic compounds are the main components of mVOCs in AD. • Trichococcus is positively related to most metabolites. • HS-SPME and LL totally extracted 218 metabolites classified in 14 categories. • AD stage shift could be differentiated by mVOCs. It has been a challenge to recognize appropriate compounds as indicators for monitoring and early-warning of the anaerobic digestion process. A strategy was initiated to explore the evolution of the panorama profile of volatile and semi-volatile metabolites. Non-target analysis using high-resolution gas chromatography coupled with Orbitrap mass spectrometry was applied to construct a time-series molecular fingerprint of 218 metabolites classified in 14 categories. Alkanes accounted for the main part in early and late stages of methanization and aromatic compounds were the major in middle stage. Spearman correlation analysis and partial least squares analysis unwind that Trichococcus (1.49%-83.96%) was positively related to most of metabolites at early and middle stages, while Brevundimonas (0%-24.04%) was positively related to acylamide at late stage. This indicated that microbial volatile organic compounds were possible to serve as biochemical indicators for anaerobic digestion performance and to build nexus of "what" (metabolites), "who" (microorganism), and "how" (kinetics). [ABSTRACT FROM AUTHOR]

Highlights: [•] Fluorescence peaks of tyrosine were appropriate for protein evaluation during AD. [•] SUVA254 and Ex/Em of 230/436nm were suitable for evaluating humidification degree. [•] E 4/E 6 and Ex/Em of 350/436nm were unsuitable for evaluating humidification degree. [•] Fluorescence peaks of tryptophan were inconsistent with dissolved protein content. [Copyright &y& Elsevier]

Biogas recirculation was conducted to improve the performance of two thermophilic anaerobic sequenced batch reactors (ASBRs), in which high concentrations of volatile fatty acids (VFAs) were accumulated. To accelerate degradation of VFAs, facilitating acetate consumption via syntrophic acetate oxidation coupled with hydrogenotrophic methanogenesis (SAO-HM) was expected to be effective. Hence, to promote the SAO-HM pathway, hydrogen was removed to create low hydrogen partial pressure (pH2) in reactor RH, yet in reactor RB, hydrogen was not treated. The performance of RB and RH on VFAs degradation and methane production processes was compared at steady stage; the VFAs and soluble microbial products (SMP) in the effluents were monitored. The results showed that lowpH2intensified the SAO reaction, thereby accelerating conversion of acetate to methane, as well as acetate production from glucose and VFAs. Glucose fermentation type was also influenced. VFAs and SMP in the effluents were reduced after the introduction of biogas mixing, which proceeded much faster in RH with lowpH2. Recirculation of low hydrogen biogas with SAO-HM pathway being promoted should be more effective to alleviate high acid level stress and to improve the reactor performance. [ABSTRACT FROM AUTHOR]

Highlights: [•] High concentrated bicarbonate promoted hydrogenotrophic methanogenesis. [•] High concentrated bicarbonate promoted acid production, lowered acid methanization. [•] Higher concentration of organics led to a larger carbon isotope fractionation effect. [•] The boundary concentration of bicarbonate serving as buffer was 0.15mol/L. [ABSTRACT FROM AUTHOR]

Abstract: Combined effects of acids and ammonium on functional pathway and microbial structure during organics methanization were investigated by stable isotopic method and quantitative PCR. The results showed that the stress from acids and ammonium was synergetic, resulted in different inhibition for acetoclastic and hydrogenotrophic methanogenesis and syntrophic acetate oxidation, leading to pathway shift. Methane production from acetate was affected more by acetate than by ammonium until the ammonium concentration reached 6–7 g-N/L. When the ammonium concentration exceeded 6 g-N/L, ammonium inhibition was strengthened by the increased concentration of acetate. At a low acetate concentration (50 mmol/L), acetoclastic methanogenesis dominated, regardless of ammonium concentration. At higher acetate concentrations (150 and 250 mmol/L) and at low-medium ammonium levels (1–4 g-N/L), acetate was mainly degraded by acetoclastic methanogenesis, while residual acetate was degraded by a combination of acetoclastic methanogenesis and the syntrophic reaction of syntrophic acetate oxidization and hydrogenotrophic methanogenesis with the latter dominating at 250 mmol/L acetate. At high ammonium levels (6–7 g-N/L), the degradation of acetate in the 150 mmol/L treatment was firstly through a combination of acetoclastic methanogenesis and the syntrophic pathway and then gradually shifted to the syntrophic pathway, while the degradation of acetate in the 250 mmol/L treatment was completely by the syntrophic pathway. [Copyright &y& Elsevier]

Abstract: With the goal of starting-up the methanogenesis of easily biodegradable waste with minimum inoculum, the present work evaluated different inoculum-to-substrate ratios (r I/S) in completely mixed systems and in the systems with spatial separation of inoculum and waste. It was found difficult to initiate methanogenesis in the completely mixed systems, even at high r I/S 1.105 on a volatile solid basis. Fermentation efficiencies were independent of r I/S. In the spatial-separation systems with a low total r I/S 0.053, the ultimate methane yield (35°C, 1atm) reached 445mL/g-VS added for the inoculum-waste initially completely separated system. The yields decreased to 285, 181, and 34mL/g-VS added, respectively, for partially separated systems with the ratios controlled at 1.105, 0.254, and 0.113 in the inoculum-containing reactors. This demonstrates the importance of setting spatial separation between inoculum and waste when inoculation is employed. An appropriate inoculation method would initiate methanogenesis rapidly even at low inoculum-to-substrate ratios. [Copyright &y& Elsevier]

Anaerobic digestion (AD) is a matured technology for waste (water) remediation/stabilization and bioenergy generation in the form of biogas. AD technology has several inherent benefits ranging from generating renewable energy, remediating waste (water), and reducing greenhouse gas emission to improving health/hygiene and the overall socio-economic status of rural communities in developing nations. In recent years, there has been a paradigm shift in applications of AD technology beyond biogas. This special issue (SI) entitled, " Anaerobic Digestion Beyond Biogas (ADBB-2021)," was conceptualized to incorporate some of the recent advances in AD in which the emphasis is beyond biogas, such as anaerobic biorefinery, chain elongation, treatment of micropollutants, toxicity and system stability, digestate as biofertilizer, bio-electrochemical systems, innovative bioreactors, carbon sequestration, biogas upgrading, microbiomes, waste (water) remediation, residues/waste pre-treatment, promoter addition, and modeling, process control, and automation, among others. This VSI: ADBB-2021 contains 53 manuscripts (14 critical reviews and 39 research). The key findings of each manuscript are briefly summarized here, which can serve as a valuable resource for AD researchers to learn of major advances in AD technology and identify future research directions. [ABSTRACT FROM AUTHOR]

Abstract: This work reveals that, at pH 5–9, a lactate level of up to 30gl−1 retarded hydrolysis rates in polysaccharide-rich potato samples. Lactate substantially limited carbohydrate hydrolysis and enhanced the hydrolysis of proteins. Statistical analysis identified the significance of numerous process factors in substrate hydrolysis. At fixed pH, dissociated lactate affected hydrolysis rates more strongly than its molecular counterpart. At a fixed lactate level, an alkaline environment favors carbohydrate hydrolysis; the effect of pH is secondary. Significant effects of lactate on substrate hydrolysis may be evident in fermenting organic substrates with high carbohydrate content. [Copyright &y& Elsevier]

pH and volatile fatty acids both might affect the further hydrolysis of particulate solid waste, which is the limiting-step of anaerobic digestion. To clarify the individual effects of pH and volatile fatty acids, batch experiments were conducted at fixed pH value (pH 5–9) with or without acetate (20 g/L). The hydrolysis efficiencies of carbohydrate and protein were evaluated by carbon and nitrogen content of solids, amylase activity and proteinase activity. The trend of carbohydrate hydrolysis with pH was not affected by the addition of acetate, following the sequence of pH 7>pH 8>pH 9>pH 6>pH 5; but the inhibition of acetate (20 g/L) was obvious by 10%–60%. The evolution of residual nitrogen showed that the effect of pH on protein hydrolysis was minor, while the acetate was seriously inhibitory especially at alkali condition by 45%–100%. The relationship between the factors (pH and acetate) and the response variables was evaluated by partial least square modeling (PLS). The PLS analysis demonstrated that the hydrolysis of carbohydrate was both affected by pH and acetate, with pH the more important factor. Therefore, the inhibition by acetate on carbohydrate hydrolysis was mainly due to the corresponding decline of pH, but the presence of acetate species, while the acetate species was the absolutely important factor for the hydrolysis of protein. [ABSTRACT FROM AUTHOR]

[Display omitted] • The production and recovery of valuable products in AD are reviewed. • Closed-loop application of the recovered products in AD is proposed. • More long-term and pilot-scale separation studies are needed in field application. • Future opportunities lie in achievement of industrial stable in-situ extraction. Anaerobic digestion, as an eco-friendly waste treatment technology, is facing the problem of low stability and low product value. Harvesting value-added products beyond methane and removing the inhibitory compounds will unleash new vitality of anaerobic digestion, which need to be achieved by selective separation of certain compounds. Various methods are reviewed in this study for separating valuable products (volatile fatty acids, medium-chain carboxylic acids, lactic acid) and inhibitory substance (ammonia) from the liquid fraction of digestate, including their performance, applicability, corresponding limitations and roadmaps for improvement. In-situ extraction that allows simultaneous production and extraction is seen as promising approach which carries good potential to overcome the barriers for continuous production. The prospects and challenges of the future development are further analyzed based on in-situ extraction and economics. [ABSTRACT FROM AUTHOR]

Poly(butylene adipate-co-terephthalate) (PBAT) is a biodegradable plastic that is difficult to degrade under both mesophilic and thermophilic anaerobic conditions. In this study, the impact of the thermo-alkaline pretreatment (48 h, 70 °C, 1 % w/v NaOH) on the anaerobic degradation (AD) of PBAT, poly(lactic acid) (PLA) and PBAT/PLA blended plastics was investigated. Under mesophilic conditions, pretreatment only improved the methane yield of PBAT/PLA/starch plastic (100 days, 51 and 34 NmL/g VS add for the treated and original plastics, respectively). Under thermophilic conditions, the pretreatment increased the methanogenic rate of PLA, PBAT and PBAT/PLA/starch plastic at the beginning stage (22 days, 35 and 79 NmL/g VS add for original and treated PBAT, respectively), but did not change the methane yield at the end of the incubation (100 days, 91 NmL/g VS add for original and treated PBAT). The reduction in the molecular weight and the formation of pore structures on the plastic surface accelerated the utilization of plastics by microorganisms. Furthermore, the pretreated plastics tend to form microplastics (MPs) with size predominantly below 500 µm (>90 %). The numbers of MPs dynamically changed with the degradation time. Several genera of bacteria showed specific degradation of biodegradable plastics under thermophilic conditions, including Desulfitibacter , Coprothermobacter , Tepidimicrobium , c_ D8A-2 and Thermacetogenium. The results suggest that more attention should be paid to the problem of MPs arising from the thermo-alkaline pretreatment. [Display omitted] • Thermo-alkaline pretreatment improved methane yield of PBAT under thermophilic AD. • PLA and aliphatic component in PBAT were preferentially degraded. • The molecular weight was reduced and pore structure was formed of treated plastics. • The pretreated plastics are more likely to form MPs with size less than 500 µm. [ABSTRACT FROM AUTHOR]

• Composting & anaerobic digestion are efficient ways for attenuating ARGs in biowastes. • Factors, i.e. substrate property, pretreatment, additive and operating condition affect ARGs fate. • ARGs hosts should be identified by combining in situ analysis with culture method. Antibiotic resistance genes (ARGs) in biowaste, such as livestock manure and excess activated sludge, pose potential threat to human and ecological health when applied to agricultural fields. Biological treatment approaches, such as thermophilic composting/vermicomposting and anaerobic digestion, widely adopted to stabilize biowaste have demonstrated significant effects on the fate of ARGs. However, the influence of these biological treatments on ARGs is not known. This review summarizes the occurrence of ARGs in biowaste and the impact of thermophilic composting, vermicomposting, and anaerobic digestion on the fate of ARGs with discussion on factors, including substrate properties, pretreatments, additives, and operational parameters, associated with ARGs during biological treatment of biowaste. Finally, this review explores the research implications and proposes new avenues in the field of biological treatment of organic waste. [ABSTRACT FROM AUTHOR]

• Rheological parameters can be used to optimize HSAD digestate dewatering and conditioning. • Integrated solutions for HSAD digestate were reviewed. • Nitrogen emission from the integrated systems could be a big environmental concern. Digestate management for anaerobic digestion (AD) is becoming a bottleneck of the sustainability of AD plants when the use of digestate for agricultural application is restricted due to nutrient surplus and low market acceptance. Digestate quality and treatment in high solid anaerobic digestion (HSAD) can be better than conventional low-solid system. The rheological behavior of digestate in high solid anaerobic digestion (HSAD) can have a great impact on the energy consumption of digestate management. After post-conditioning guided by rheological parameters, the solid digestate can be further treated based on the integrated solutions to enhance the energy efficiency or nutrients recovery. The environmental impacts for some core parts of those integrated systems were also evaluated in this study. This article presented a critical review of recent investigations of digestate management for HSAD, especially focusing on the rheology of HSAD digestate, integrated solutions and their environmental performances. [ABSTRACT FROM AUTHOR]

Process monitoring is an essential measure to achieve efficient and stable performance in anaerobic digestion, thus requiring identification of effective early warning indicators. However, the application of early warning indicators to full-scale dry anaerobic engineering biogas plant still remains elusive. This study evaluated the effectiveness of common early warning indicators (including CH 4 , CO 2 , H 2 S, volatile fatty acids (VFAs), alkalinity (ALK), total ammonia concentration (TAN) and free ammonia concentration (FAN)) in monitoring the instability of anaerobic digestion process at a practical engineering plant. The results showed that the individual indicators could not provide a sufficient early warning time before the digester fell into failure collapse. In comparison, the coupling indicators (the ratio of CH 4 /CO 2 , CH 4 /pH, and CH 4 /H 2 S) had sensitive response to perturbation, which could regard as a potential early warning indicator, with the early warning time of 6, 7 and 10 days, respectively. Moreover, the VFA/ALK could be used as auxiliary indicators due to the limitation of complex detection methods. In addition, the result also indicated that the application of some warning indicators needs to be further verified, when transferring the result of laboratory scale to the practice application scenarios. This study provides insight into the stable operation of dry anaerobic engineering. [Display omitted] • The commissioning process of a full-scale biogas plant was investigated. • Household kitchen waste was digested at dry thermophilic condition. • The digester was inhibited and failed when the OLR increased to 15 kgVS/(m³·d). • The digester instability was primarily caused by the over-acidification. • The ratio of CH 4 /H 2 S and CH 4 /pH were selected as early warning indicators. [ABSTRACT FROM AUTHOR]

Anaerobic digestion is a sustainable biotechnology for treating food waste (FW) with biogas production driven by microorganisms. Generation of FW increased greatly in China, which are mainly treated with anaerobic digestion technology. A survey into nine full-scale mesophilic anaerobic FW digesters was conducted, together with four sewage sludge digesters as a comparison, to investigate the specific physicochemical features and the resulted microbiota. Results showed that FW digesters were characterized with high salt, volatile fatty acid and ammonia concentrations. A unique "core" microbial community indigenous inside FW digesters was identified, including 70 bacterial and 4 archaeal genus-level taxa, which was quite different from that in sludge digesters. Stable carbon isotope signature of biogas revealed that, hydrogenotrophic methanogenesis (HM) played a significant role in methane generation. The hydrogenotrophic Methanobacterium demonstrated strong positive correlations with the syntrophic acetate oxidizing bacteria (SAOB) Syntrophaceticus and other SAOB candidates (Aminobacterium , Gelria , DTU014, Alkaliphilus), forming a unique SAO-HM functional guild which particularly prevailed in digesters receiving household FW. Feedstock composition was the essential factor influencing microbial structure, followed by salinity, ammonia, and VFAs. The high ammonia concentration and prominent contribution of diverse SAO-HM players indicate that, tailored management strategy needs to be developed for treating household FW. [Display omitted] •Full-scale anaerobic digesters treating household food waste was studied. •A unique core microbial community identified for FW digesters included 74 genera. •Hydrogenotrophic methanogenesis is a key pathway identified with isotope signature. •Acetate-oxidizing syntrophs of known and candidate members were abundant. •Special FW features, high salinity and ammonia shaped the community structure. [ABSTRACT FROM AUTHOR]

Highlights: [•] Successfully operating decentralized on-site treatments for 6 month. [•] Source-separated collection was successfully applied in rural areas. [•] The products of the mini-scaled on-site treatment were safe and stable. [•] The waste treatment had no impact to nearby communities. [•] The appropriate scale of on-site treatment facility was discussed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Anaerobic degradation parameters of nut waste were different from other food waste. [•] Paper should be subdivided into degradable paper and refractory paper. [•] Garden waste should be divided into grass and leaves, and branches. [•] Wood should not be subdivided according to CSF. [ABSTRACT FROM AUTHOR]

With the implementation of municipal solid waste source segregation, the enormous sorted biogenic waste has become an issue that needs to be seriously considered. Anaerobic digestion, which can produce biogas and extract floating oil for biodiesel production, is the most prevalent treatment in China for waste management and greenhouse gas (GHG) emissions reduction, in accordance with Sustainable Development Goal 13 of the United Nations. Herein, a large-scale biogas plant with a capacity of 1000 tonnes of biogenic waste (400 tonnes of restaurant biogenic waste and 600 tonnes of kitchen biogenic waste) per day was investigated onsite using material flow analysis, and the parts of the biogas plant were thoroughly analyzed, especially the pretreatment system for biogenic waste impurity removal and homogenization. The results indicated that the loss of the total biodegradable organic matter was 41.8% (w/w) of daily feedstock and the loss of biogas potential was 18.8% (v/v) of daily feedstock. Life cycle assessment revealed that the 100-year GHG emissions were −61.2 kgCO 2 -eq per tonne biogenic waste. According to the sensitivity analysis, pretreatment efficiency, including biodegradable organic matter recovery and floating oil extraction, considerably affected carbon reduction potential. However, when the pretreatment efficiency deteriorated, GHG benefits of waste source segregation and the subsequent biogenic waste anaerobic digestion would be reduced. [Display omitted] • A 1000 tonne/day plant handled biogenic waste, emphasizing efficient pretreatment. • Source segregation effectively improved the purity of biogenic waste up to 97.6%. • Pretreatment suffered losses: 41.8% organic and 18.8% biogas potential. • Efficient pretreatment was crucial for maintaining greenhouse gas benefits. [ABSTRACT FROM AUTHOR]

[Display omitted] • The database thoroughly reflects and organizes BMP testing content with precision. • Context and key variables for each data group are provided for clarity. • The dynamic information of batch experiments is visualized. • The database isn't static, but dynamic with growing data collected from literature. • Comparing data is simplified through substrate type and research aim distinctions. Diverse factors influence biogas production, such as material properties, testing conditions, reporting methods and other additional processing techniques. This complexity makes it difficult to compare biochemical methane potential (BMP) data, replicate experiments' results, and improve efficiencies associated with engineering applications. This study has taken preliminary attempts to build a sliced and structured BMP database, but optimizing the organization of data information and collecting more comprehensive and manually checked data information to cope with the increasing richness of the BMP test content. The first-generation BMP database contains 746 sets of data, covering 7 major substrate categories, including 187 key indicators and 26 supplementary indicators. It offers functions including data screening, comparing, uploading, and visual display of BMP data. The application of the database in comparing different types of substrates and additives is shown. In the future, the BMP database will be regularly upgraded to become more comprehensive. [ABSTRACT FROM AUTHOR]

Biochar addition is recognized as a promising way to increase the potential of anaerobic digestion. However, few studies have investigated the interaction between biochar leaching in complex, practical anaerobic digestion systems and the negative effects that biochar leachate may have on the anaerobic digestion process. The traditional measurement methods are relatively simple, but may underestimate the complexity of dissolved organic matter in biochar leachate. In this study, the leaching behaviors of biochar and the influence of biochar leachate on anaerobic digestion were studied at the molecular level by applying ultra-performance liquid chromatography online coupled with a hybrid quadrupole orbitrap mass spectrometer (UPLC Orbitrap MS/MS) test analysis and various molecular information-based analytical methods such as van Krevelen diagrams and by conducting a series of anaerobic digestion experiments. Dissolved organic matter leaching was higher in buffered saline solution and methanol than in ultrapure water and the dissolved organic matter mainly consisted of lipids and proteins. In the lactic acid solution, a large amount of dissolved organic matter was leached from the biochar, dominated by low molecular weight dissolved organic matter such as CHO and CHON, and the lower the pH, the more was leached, suggesting that lactic acid may have an inhibitory effect on anaerobic digestion. The maximum methane production amount and microbial abundance especially key methanogenic archaea such as Methanosaeta in the sample with biochar leachate addition were lower than those for the other samples. This meant that the dissolved organic matter in the biochar leachate might inhibit the growth of microorganisms and adversely affect the acetic acid methanogenesis process. The results from this study showed that a greater number of substances with more complex structures were leached out than had been detected in previous studies. When applying biochar to anaerobic digestion in the future, it is recommended that biochar is leached first to remove toxic and detrimental substances to prevent possible inhibitory effects. [Display omitted] • Leaching behaviors of biochar in anaerobic digestion three phases were firstly explored. • The number of compounds in the lactic acid leachate of biochar was up to 2207. • The lower the pH of the acid accumulation, the more compounds were precipitated from the biochar. • Leachable dissolved organic matters in biochar had obvious inhibitory effects on methanogen Methanosaeta. [ABSTRACT FROM AUTHOR]

Is our food safe and free of the crisis of antibiotics and antibiotic resistance (AR)? And will the derived food waste (FW) impose AR risk to the environment after biological treatment? This study used restaurant FW leachates flowing through a 200 tons-waste/day biological treatment plant as a window to investigate the fate of antibiotics and antibiotic-resistance genes (ARGs) during the acceptance and treatment of FW. Sulfonamides (sulfamethazine, sulfamethoxazole) and quinolones (ciprofloxacin, enrofloxacin, ofloxacin) were detected during FW treatment, while tetracyclines, macrolides and chloramphenicols were not observable. ARGs encoding resistance to sulfonamides, tetracyclines and macrolides emerged in FW leachates. Material flow analysis illustrated that the total amount of antibiotics (except sulfamethazine) and ARGs were constant during FW treatment processes. Both the concentration and total amount of most antibiotics and ARGs fluctuated during treatment, physical processes (screening, centrifugation, solid–liquid and oil–water separation) did not decrease antibiotic or ARGs concentrations or total levels permanently; the affiliated wastewater treatment plant appeared to remove sulfonamides and most ARGs concentrations and total amount. Heavy metals Ni, Co and Cu were important for disseminating antibiotics concentrations and MGEs for distributing ARGs concentrations. Humic substances (fulvic acids, hydrophilic fractions), C-associated and N-associated contents were essential for the distribution of the total amounts of antibiotics and ARGs. Overall, this study implied that human food might not be free of antibiotics and ARGs, and FW was an underestimated AR pool with various determinants. Nonetheless, derived hazards of FW could be mitigated through biological treatment with well-planned daily operations. Unlabelled Image [ABSTRACT FROM AUTHOR]

The wide application of anaerobic digestion (AD) technology is limited by process fluctuations. Thus, process monitoring based on screening state parameters as early warning indicators (EWI) is a top priority for AD facilities. However, predicting anaerobic digester stability based on such indicators is difficult, and their threshold values are uncertain, case-specific, and sometimes produce conflicting results. Thus, new EWI should be proposed to integrate microbial and metabolic information. These microbial volatile organic compounds (mVOCs) including alkanes, alkenes, alkynes, aromatic compounds are produced by microorganisms (bacteria, archaea and fungi), which might serve as a promising diagnostic tool for environmental monitoring. Moreover, mVOCs diffuse in both gas and liquid phases and are considered the language of intra kingdom microbial interactions. Herein, we highlight the potential of mVOCs as EWI for AD process instability, including discussions regarding characteristics and sources of mVOCs as well as sampling and determination methods. Furthermore, existing challenges must be addressed, before mVOCs profiling can be used as an early warning system for diagnosing AD process instability, such as mVOCs sampling, analysis and identification. Finally, we discuss the potential biotechnology applications of mVOCs and approaches to overcome the challenges regarding their application. • mVOCs are considered the language of intra-kingdom microbial interactions. • mVOCs in both gas and water phases may act as infochemicals. • mVOCs production is highly dependent on microbial function. • mVOCs may act as early warning signals of AD instability. • mVOCs analysis, sampling and identification challenge must be addressed. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) is frequently restricted with the long lag phase and low methane (CH 4 ) production rate. Laboratory batch experiments were conducted to investigate the impact of different supplements on the performance of food waste AD, including AC-Ni, AC, and Ni. Results showed that the lag phase of AD was reduced with the addition of those supplementations. Compared with the control group without any supplementation, the AC-Ni could shorten the lag phase by 67% and increase the maximum CH 4 production rate by 50%, respectively. The speciation analysis indicated that the environmental risks of the AC-Ni was reduced by 30% after digestion. Microbial community structure analysis revealed that the AC-Ni promoted the evolution and activity of the hydrolytic-fermentative bacteria (e.g. Firmicutes and Bacteroidetes ) and methanogens (e.g. Methanobacterium, Methanoregula and Methanomassiliicoccus ). This study suggested that the AC-Ni waste could be feasible to be applied to enhance the performance of AD. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) of food waste (FW) has been widely used in China and shows great potential in both recovering renewable energy and reducing carbon emissions. Unfortunately, many digesters suffer from unexpected perturbations and low biogas production due to the specific characteristics of food waste. Modeling of AD is crucial to better understand the process and improve efficiency. In this study, five machine learning (ML) algorithms were used to build models to predict biogas production in an industrial-scale biogas plant treating FW. Three categories of routine monitoring indicators (feed amount, feedstock properties, and digester properties), individually or collectively, were used as the input variables. The results showed that the random forest (RF) model achieved the best performance with an average R2 of 0.74 when all the indicators were contained in the dataset. Feature importance analysis revealed that the significance descended in the order of feed amount (45.9%), digester properties (38.6%), and feedstock properties (15.4%). The performance of the predictive models degraded with lag time except for the RF model, which showed the potential to predict biogas production of the next day (R2 = 0.73). The study verified the feasibility of ML models in predicting biogas yield using routine monitoring data from industrial-scale biogas plants treating FW and suggested that the monitoring indicators and frequency be redesigned to build smarter ML predictive models and improve system efficiency. [Display omitted] • Different indicators were explored as input variables of machine learning models. • The random forest model outcompeted the others in predictive performance. • Feed amount was identified to be the most significant input variable. • Performance of the predictive models degraded with the increasing lag time. • Machine learning models were able to predict biogas yield of food waste biogas plant. [ABSTRACT FROM AUTHOR]

[Display omitted] • K+, NH 4 +, and Cl− were components with higher migration priority during ED. • Percentage removal of salt ions reached over 90% • ED recovered 35–70% N and P and extracted 70% VFAs from liquid digestate. • Organic molecules with benzene rings and carboxyls were easier to foul the membrane. • Agriculture application and VFAs products showed economic benefits about 20 USD/t-digestate. With the wider application of anaerobic digestion in food waste treatment, the digestate management becomes the bottleneck either from economic or carbon mitigating point. The high salt content in food waste digestate hinders the mass agriculture application. In this study, electrodialysis was performed to assess the performance of desalting from mature and fresh liquid digestate as well as the migration patterns of nutrients and value-added products. K+, NH 4 +, and Cl− were found to be the components with higher migration priority. Current efficiency (CE) for desalination scenario was about 35–50% while NH 4 + in mature digestate (MD) contributed about 50–55% of the cationic CE and volatile fatty acids (VFAs) in fresh digestate (FD) contributed about 20–25% of the anionic CE. Organic carbon in MD was well retained, whereas 49%-63% organic carbon in FD experienced migration, which is more obvious at neutral pH. Electrodialysis removed over 90% salts and recovered 35–70% N and P from both mature and fresh liquid digestate, and extracted 70% VFAs from FD. This is expected to save the cost in wastewater treatment of 19.46 USD/t-digestate or obtain a benefit of 17.36USD/t-digestate from VFAs product. But the membrane fouling brought great uncertainty to the operating costs. Compared with cation exchange membrane, more severe membrane fouling was found in anion exchange membrane, whose performance decreased to half of the original by the end of the experiment. Organic molecules with benzene rings and carboxyls were mainly responsible for the membrane fouling. [ABSTRACT FROM AUTHOR]

Near-infrared spectroscopy (NIRS) and hyperspectral imaging (HSI) techniques combined with chemometric method are emerging techniques and have been studied and applied to address current challenges in anaerobic digestion (AD) plants, such as the heterogeneity of feedstocks, low methane yield, process instability and digestate management. Prior to the AD process, the rapid and accurate measurement of the feedstocks' chemical composition can predict the biochemical methane potential and discern the potential microorganism inhibitors. During the AD process, monitoring the intermediate products in the AD digesters by using NIRS or HSI techniques allows for process optimization and avoids potential AD failure. Regarding digestate management, the NIRS or HSI can be applied to determine the biological stability and evaluate the digestate quality. In this review, we summarize recent research advances in monitoring AD process parameters and quality of feeding substrate and digestate using NIRS and HSI combined with machine learning techniques. This review highlights the application of NIRS and HSI technology in the AD of organic wastes with particular emphasis on the application drawbacks and possible enhancement solutions. In general, the existing machine learning augmented NIRS can obtain satisfactory quantification results. Future researches on characterization of high-moisture heterogeneous substrate and real-time monitoring AD by HSI combined deep learning are still in demand. [Display omitted] • NIR and HSI can be used for substrate classification, process monitoring and digestate identification in an AD plant. • NIR-HSI is a promising technique to analyze non-homogeneous samples from co-digestion AD systems. • The pretreatment of high moisture samples from AD is essential prior to NIR or NIR-HIS analysis. [ABSTRACT FROM AUTHOR]

Long-distance transportation of municipal biowaste can influence its physio-chemical characteristics and the subsequent anaerobic digestion (AD) performance. However, the effect of whole transportation processes on the characteristics of municipal biowaste from upstream source separation/collection to downstream storage remains poorly documented. To this end, this study presented the relevant work by sampling in practical conditions. Results showed that transportation led to a high hydrolysis rate of 33.4%–35.5%, and an acidification rate of 15.8%–17.3%. Simultaneously, lactic acid was produced to a concentration of 18.1 g/L, occupying approximately 20% of dissolved organic carbon. Furthermore, the highest cumulative CH 4 production was observed at the samples of source separation/collection (398 ± 52–519 ± 117 mL/gVS for FW, 276 ± 51–332 ± 41 mL/gVS for KW), and then accompanied by a decrease (299 ± 31 mL/gVS for FW and 285 ± 39 mL/gVS for KW) after downstream storage. The results indicated that the subsequent anaerobic digestion would be inclined to appear perturbation caused by the lactic acidification of the initial feed and it is imperative to avoid further conversion of lactic acid to propionic acid, which could provide vital guideline reference for the optimization of biogas production process. Moreover, the lactic acid-rich property also highlights other value-added pathways for the resource recovery of municipal biowaste. [Display omitted] • Practical transportation of municipal biowaste was investigated. • The hydrolysis process of biowaste primarily occurred during transportation. • Transportation and storage of biowaste promoted lactic acid production. • Lactic acid severely accumulated and occupied approximately 20% of DOC. • The CH 4 production decreased along with the prolonging of transportation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Filler enhance conversion rates of sludge digestion. [•] Pre-incubated filler improve dewaterability of digested sludge. [•] Filler alone do not improve dewaterability of digested sludge. [Copyright &y& Elsevier]

[Display omitted] • ADLD from dry and wet AD processes had regular differences in DOM indicators. • The effect of the process factor was more significant than the food waste type. • sCOD and pH were the drivers of molecular distribution of ADLD common compounds. • Compounds relating to plant hormones, nutrients and xenobiotics were identified. The treatment and valorization of liquid digestate (ADLD) after anaerobic digestion of biogenic waste are challenging. This study used ultra-high resolution mass spectrometry to determine the molecular characteristics of ADLD collected from different full-scale plants for food waste treatment. The results indicated that there were regular differences in the dissolved organic matter (DOM) indicators among the samples from dry and wet anaerobic processes. ADLD DOM had higher H/C and O/C, and contained more easily degradable proteins. In addition, sCOD and pH were the drivers of the molecular distribution of ADLD common compounds. The same common compounds were present in the ADLD from different anaerobic digestion plants. They had a significant correlation with physicochemical characteristics. The compounds relating to plant hormones and nutrients as well as xenobiotics were both identified, suggesting that comprehensive considerations should be taken into account for the land application of ADLD. [ABSTRACT FROM AUTHOR]

[Display omitted] • A PBAT/PLA blend is tested for anaerobic co-digestion with high-solid contents. • No biogas improvement is achieved after a long residential time of AD. • Food waste co-digestion greatly deteriorates the polymer hydrophobicity. • Polymer after 55℃ AD shows better biodegradability in aerobic post-treatment. • Polymer cracking at 55℃ may form microplastics and deteriorate digestate quality. Degradation of bioplastics in food-waste-treating anaerobic digestion (AD) plants is becoming an increasingly concerning issue as they are inevitably mixed with food waste during the waste collection process. The aim of this study was to assess the degradation of PBAT/PLA based biopolymer bags during mesophilic and thermophilic AD, co-digested with food waste, and subsequent aerobic post-treatment. After the AD process, no discernable biological degradation was observed for all of the PBAT/PLA polymers. The comparison of FTIR, XRD, TG analysis and contact angle analysis between raw and degraded PBAT/PLA polymer revealed structural changes after anaerobic incubation. Subsequent aerobic treatment facilitated the degradation of the PBAT/PLA polymers from thermophilic AD, which was attributed to the polymer-degrading microorganisms Brevundimonas and Sphingobacterium. Physical disintegration of the PBAT/PLA polymer was observed under thermophilic conditions. Those undegraded polymer fragments could affect digestate quality and increase the risk of releasing microplastics into the environment. [ABSTRACT FROM AUTHOR]