Occurrence, influence and removal strategies of mycotoxins, antibiotics and microplastics in anaerobic digestion treating food waste and co-digestive biosolids: A critical review

Evaluating micro-nano bubbles coupled with rice-crayfish co-culture systems: A field study promoting sustainable rice production intensification

Traditional rice-fish symbiosis systems efficiently use soil and water resources but the adverse effects of prolonged flooding on the stability of rice growth can be mitigated. The feasibility and efficacy of injecting micro-nano bubbles (MNBs) in rice-crayfish co-cultures was investigated in a 22-hectare field experiment conducted over five months. This injection significantly enhanced the growth of both rice and crayfish, and increased total nitrogen and phosphorus levels in the soil, thereby augmenting fertility. Analysis of dissolved oxygen (DO), water temperature and gene expression (rice and crayfish) clarified that micro-nano bubbles (MNBs) foster an optimal environment for rice root respiration, whereas rice establishes an optimal temperature for crayfish, thereby enhancing their activity and growth. Comparative analyses of gene expression profiles and metabolic pathway enrichment revealed that the injection of MNBs diversifies soil microbial communities and intensifies biological processes, such as plant hormone signal transduction. This was in marked contrast to the situation in our controls, rice monoculture (R) and micro-nano bubbles rice monoculture (MNB-R). The combination of rice-fish symbiosis with MNBs led to a 26.8 % increase in rice production and to an estimated 35 % improvement in economic efficiency. Overall, this research introduces an innovative and environmentally sustainable method to boost rice yields, thereby enhancing food security and providing additional income for farmers.

Evaluating the potential of different bioaugmented strains to enhance methane production during thermophilic anaerobic digestion of food waste

Bioaugmentation technology for improving the performance of thermophilic anaerobic digestion (TAD) of food waste (FW) treatment is gaining more attention. In this study, four thermophilic strains (Ureibacillus suwonensis E11, Clostridium thermopalmarium HK1, Bacillus thermoamylovorans Y25 and Caldibacillus thermoamylovorans QK5) were inoculated in the TAD of FW system, and the biochemical methane potential (BMP) batch study was conducted to assess the potential of different bioaugmented strains to enhance methane production. The results showed that the cumulative methane production in groups inoculated with E11, HK1, Y25 and QK5 improved by 2.05%, 14.54%, 19.79% and 9.17%, respectively, compared with the control group with no inoculation. Moreover, microbial community composition analysis indicated that the relative abundance of the main hydrolytic bacteria and/or methanogenic archaea was increased after bioaugmentation, and the four strains successfully became representative bacterial biomarkers in each group. The four strains enhanced methane production by strengthening starch, sucrose, galactose, pyruvate and methane metabolism functions. Further, the correlation networks demonstrated that the representative bacterial genera had positive correlations with the differential metabolic functions in each bioaugmentation group. This study provides new insights into the TAD of FW with bioaugmented strains.

Revealing How Polyvinyl Chloride Microplastic Physicochemically Affect the Anaerobic Digestion of Waste Activated Sludge

Recent studies have shown that the microplastics in waste activated sludge (WAS) can directly reduce the microbial activity and influence the performance of anaerobic digestion. Unfortunately, few studies paid attention on the interactions between WAS and MPs, since MPs could impact the contact between sludge flocs and microorganisms. We found that PVC-MP changed the interfacial energy properties of the WAS surface and affected methane production. Low concentration (40 mg/L) of PVC-MP changed the water affinity and greatly reduced the energy barrier of interfacial reaction. Simultaneously, WAS surface charge characteristics changed with increasing MPs concentration, which made the sludge difficult to contact with microorganisms. The change process of WAS surface functional groups also indicated that PVC-MP first cover the sludge surface to prevent from being utilized by microorganisms, and then affect the surface protein structure before toxic substances leaching. Our study provides new insights into how MPs affect anaerobic digestion.

Incomplete degradation of aromatic-aliphatic copolymer leads to proliferation of microplastics and antibiotic resistance genes

Biodegradable plastics (BDPs) have attracted extensive attention as an alternative to conventional plastics. BDPs could be mineralized by composting, while the quality of compost affected by the presence of BDPs and the residual microplastics (MPs) has not been well evaluated. This study aimed to explore the MPs release potential and environmental implications of commercial BDPs (aromatic-aliphatic copolymer) films in uncontrolled composting. Results showed that the molecular weight of BDPs decreased by >60% within 60 d. However, the non-extracted organic matter and wet-sieving measurements indicated that MPs continuously released and accumulated during regular composting. The average MPs release potential (0.1-5 mm) was 134.6 ± 18.1 particles/mg (BDPs), which resulted in 103-104 particles/g dw in compost. The plastisphere of MPs showed a significantly higher (0.95-16.76 times) abundance of antibiotic resistance genes (ARGs), which resulted in the rising (1.34-2.24 times) of ARGs in compost heaps, in comparison to the control groups. Overall, BDPs promote the spread of ARGs through the selective enrichment of bacteria and horizontal transfer from released MPs. These findings confirmed that BDPs could enhance the release potential of MPs and the dissemination of ARGs, which would promote the holistic understanding and environmental risk of BDPs.

A comprehensive review on food waste anaerobic co-digestion: Research progress and tendencies

Food waste (FW) anaerobic digestion systems are prone to imbalance during long-term operation, and the imbalance mechanism is complex. Anaerobic co-digestion (AcoD) of FW and other substrates can overcome the performance limitations of single digestion, allowing for the mutual use of multiple wastes and resource recovery. Research on the AcoD of FW has been widely conducted and successfully applied to a practical engineering scale. Therefore, this review describes the research progress of AcoD of FW with other substrates. By analyzing the problems and challenges faced by AcoD of FW, the synergistic effects and influencing factors of different biomass wastes are discussed, and improvement strategies to improve the performance of AcoD of FW are summarized from different reaction stages of anaerobic digestion. By combing the research progress of AcoD of FW, it provides a reference for the optimization and improvement of the performance of the co-digestion system.

Differential effects of petroleum-based and bio-based microplastics on anaerobic digestion: A review

The number of plastics is increasing owing to the rapid development of the plastics industry. Microplastics (MPs) are formed during the use of both petroleum-based plastics and newly developed bio-based plastics. These MPs are inevitably released into the environment and are enriched in wastewater treatment plant sludge. Anaerobic digestion is a popular sludge stabilization method for wastewater treatment plants. Understanding the potential impacts of different MPs on anaerobic digestion is critical. This paper provides a comprehensive review of the mechanisms of petroleum-based MPs and bio-based MPs in anaerobic digestion methane production and compares their potential effects on biochemical pathways, key enzyme activities, and microbial communities. Finally, it identifies problems that must be solved in the future, proposes the focus of future research, and predicts the future development direction of the plastics industry.

Microplastics in Sewage Sludge: A review

Microplastics (MPs) represent a serious problem for the environment and for this reason they have been studied in many articles, especially their presence in aquatic environments and soils. MPs have been found in wastewater and sewage sludge from municipal wastewater treatment plants (WWTPs). Most part of the published works have focused on the detection and elimination of MPs in the water line and several reviews have been published in the last years. In addition, the application of sewage sludge produced from WWTPs for agricultural use is known to be a primary source of MPs in soils. However, in the scientific literature less attention has been paid to the sludge and little is known about MPs fate when it is applied in agriculture. This work aims to give a global revision on the most used techniques to identify and detect MPs in sludges, their characteristics and incidence, their effect on sludge treatments and their impact on the environment. As far as we know, there are no standardized protocols for MPs extraction from soil and the possible repercussions on the cultivation of plants are not known. This review evidences that more studies are necessary to stablished standardized protocols and decipher the main mechanisms and the effects of MPs from sewage sludge in the environment.

Destruction of Mycotoxins in Poultry Waste under Anaerobic Conditions within Methanogenesis Catalyzed by Artificial Microbial Consortia

To reduce the toxicity of modern feeds polluted by mycotoxins, various sorbents are added to them when feeding animals. A part of the mycotoxins is excreted from the body of animals with these sorbents and remains in the manure. As a result, bulk animal wastes containing mixtures of mycotoxins are formed. It is known that it is partially possible to decrease the initial concentration of mycotoxins in the process of anaerobic digestion (AD) of contaminated methanogenic substrates. The aim of this review was to analyze the recent results in destruction of mycotoxins under the action of enzymes present in cells of anaerobic consortia catalyzing methanogenesis of wastes. The possible improvement of the functioning of the anaerobic artificial consortia during detoxification of mycotoxins in the bird droppings is discussed. Particular attention was paid to the possibility of effective functioning of microbial enzymes that catalyze the detoxification of mycotoxins, both at the stage of preparation of poultry manure for methanogenesis and directly in the anaerobic process itself. The sorbents with mycotoxins which appeared in the poultry wastes composed one of the topics of interest in this review. The preliminary alkaline treatment of poultry excreta before processing in AD was considered from the standpoint of effectively reducing the concentrations of mycotoxins in the waste.

Removal performance and inhibitory effects of combined tetracycline, oxytetracycline, sulfadiazine, and norfloxacin on anaerobic digestion process treating swine manure

Combined veterinary antibiotics (CVAs) belonging to different antibiotics classes could cause exacerbated impacts on the anaerobic digestion (AD) process of swine manure. Four different antibiotics "two tetracyclines: tetracycline (TC) and oxytetracycline (OTC), one fluoroquinolones: norfloxacin (Norf), and one sulfonamides: sulfadiazine (SDZ)" were combined to evaluate their removal performances and its inhibition effects on AD. Results indicated that CVAs removal decreased from 84.3 to 63.7 %, with an increase in the initial concentration from 12.5 to 50 mg L^-1, where the removal of CVAs occurring in the order OTC > TC > Norf > SDZ. An average of 9.5, 7.5, 9.5, and 32.1 % of the spiked TC, OTC, SDZ, and Norf were remained in the sludge, respectively. With 50 mg L^-1 of CVAs, a competitive adsorption phenomenon was found to have a notable impact on biodegradation microorganisms' activity leading a 73.1 % decrease in CH₄ production. CVAs caused a temporal inhibition to the acidogenic activity followed by partial inhibition to methanogenic by 66.8 %, and IC₅₀ was 38.5 mg L^-1. Moreover, CVAs resulted in acetate accumulation, while 26 % and 48 % lower in TS and COD removal, respectively, were observed. A significant reduction in the relative abundance of bacteria and archaeal genera was also mentioned. The findings of this research would provide a more in-depth understanding of AD's performance in treating swine manure contaminated with combined antibiotics.

A review on the effect of micro- and nano-plastics pollution on the emergence of antimicrobial resistance

The recent upsurge in the studies on micro/nano plastics and antimicrobial resistance genes has proven their deleterious effects on the environmental and human health. Till-date, there is a scarcity of studies on the interactions of these two factors and their combined influence. The interaction of microplastics has led to the formation of new plastics namely plastiglomerates, pyroplastics. and anthropoquinas. It has long been ignored that the occurrence of microplastics has become a breeding ground for the emergence of antimicrobial resistance genes. Evidently microplastics are also associated with the occurrence of other pollutants such as polyaromatic hydrocarbons and pesticides. The increased use of antibiotics (after Covid breakout) has further elevated the detrimental effects on human health. Therefore, this study highlights the relation of microplastics with antibiotic resistance generation. The factors such as uncontrolled use of antibiotics and negligent plastic consumption has been evaluated. Furthermore, the future research prospective was provided that can be helpful in correctly identifying the seriousness of the environmental occurrence of these pollutants.

A critical review on retaining antibiotics in liquid digestate: Potential risk and removal technologies

Substantial levels of antibiotics remain in liquid digestate, posing a significant threat to human safety and the environment. A comprehensive assessment of residual antibiotics in liquid digestate and related removal technologies is required. To this end, this review first evaluates the potential risks of the residual antibiotics in liquid digestate by describing various anaerobic digestion processes and their half-lives in the environment. Next, emerging technologies for removing antibiotics in liquid digestate are summarized and discussed, including membrane separation, adsorption, and advanced oxidation processes. Finally, this study comprehensively and critically discusses these emerging technologies' prospects and challenges, including techno-economic feasibility and environmental impacts.

Antibiotics in anaerobic digestion: Investigative studies on digester performance and microbial diversity

The ever-increasing consumption of antibiotics in both humans and animals has increased their load in municipal and pharmaceutical industry waste and may cause serious damage to the environment. Impact of antibiotics on the performance of commercially used anaerobic digesters in terms of bioenergy output, antibiotics' removal and COD removal have been compared critically with a few studies indicating >90% removal of antibiotics. AnMBR performed the best in terms of antibiotic removal, COD removal and methane yield. Most of the antibiotics investigated have adverse effects on microbiome associated with different stages and methane generation pathways of AD which has been assessed using high throughput technologies like metatranscriptomics, metaproteomics and flow cytometry. Perspectives have been given for understanding the fate and elimination of antibiotics from AD. The challenge of optimization and process improvement needs to be addressed to increase efficiency of the anaerobic digesters.

Spatial distribution and risk assessment of certain antibiotics in 51 urban wastewater treatment plants in the transition zone between North and South China

The release of antibiotics from WWTPs into the environment has raised increasing concern worldwide. The monitoring of antibiotics in WWTPs throughout a region is crucial for emerging pollutant management. A large-scale survey of the occurrence, distribution, and ecological risk of seven antibiotics in 51 WWTPs was conducted in Shaanxi Province, China. Norfloxacin and ofloxacin had the highest detection concentrations of 474.2 and 656.18 ng L^-1, respectively. Antibiotic residues in effluents were decreased by 5.88-94.16 % after different treatment processes. In particular, A²O or mixed processes performed well in removing target antibiotic compounds simultaneously. The ecological risk posed by antibiotic compounds detected in effluents was calculated using the risk quotient (RQ). Norfloxacin, ofloxacin, tetracycline, and roxithromycin posed different levels of potential ecotoxicological risk (RQ = 0.02-7.59). Based on the sum of the RQ values of individual antibiotic compounds, each investigated WWTP showed potential ecological risk. WWTPs with high risk levels were mainly found in the central region, while those in the southern region exhibited low risk levels, and those in the northern region showed risk levels between medium and high. This comprehensive investigation provides promising results to support the safe use and control of antibiotics in the study area.

Motivation of reactive oxygen and nitrogen species by a novel non-thermal plasma coupled with calcium peroxide system for synergistic removal of sulfamethoxazole in waste activated sludge

Large amounts of antibiotics are concentrated in waste activated sludge (WAS) and released into the environment. It is thus critical to develop advanced sludge treatment technology to remove these antibiotics. Dielectric barrier discharge (DBD) combined with calcium peroxide (CaO₂), as an innovative technology to attenuate sulfamethoxazole (SMX) in sludge, was investigated. Evident synergistic effects between DBD and CaO₂ were observed on the SMX degradation with a synergistic factor of 2.02. Moreover, the energy consumption of DBD/CaO₂ was significantly lower than that of DBD alone. At a typical CaO₂ dosage of 0.1 g/g TS and discharge power of 64.5 W, the highest SMX removal of 96% was achieved within 50 min. The synergistic effects of DBD/CaO₂ could be associated with the base catalysis of H₂O₂ and O₃, UV-base-photolysis, peroxone oxidation, and photocatalytic H₂O₂. DBD/CaO₂ generated various reactive oxygen species (ROS) and nitrogen species (RNS) that participated in SMX removal. The contributions of these reactive species followed the sequence of e^- > •OH > •O₂^- > ¹O₂ > ONOO^-. Based on the detected transformation by-products and their variations during treatment, a plausible SMX degradation pathway in sludge was proposed. Besides, DBD/CaO₂ also promoted sludge disintegration, dewatering, heavy metal removal, sludge reduction, sludge solubilization, and acetate-enriched volatile fatty acid (VFA) production. Therefore, DBD/CaO₂ exhibited great potential for controlling antibiotic, as well as promoting sludge reduction, decontamination, and resourcization.

Microplastic-associated pathogens and antimicrobial resistance in environment

The ubiquitous use of microplastics and their release into the environment especially the water bodies by anthropogenic/industrial activities are the major resources for microplastic contamination. The widespread and often injudicious use of antimicrobial drugs or antibiotics in various sectors including human health and hygiene, agriculture, animal husbandry and food industries are leading to the release of antibiotics into the wastewater/sewage and other water bodies, particularly in urban setups and thus leads to the antimicrobial resistance (AMR) in the microbes. Microplastics are emerging as the hubs as well as effective carriers of these microbial pathogens beside their AMR-genes (ARGs) in marine, freshwater, sewage/wastewater, and urban river ecosystems. These drug resistant bacteria interact with microplastics forming synthetic plastispheres, the ideal niche for biofilm formations which in turn facilitates the transfer of ARGs via horizontal gene transfer and further escalates the occurrence and levels of AMR. Microplastic-associated AMR is an emerging threat for human health and healthcare besides being a challenge for the research community for effective management/address of this menace. In this review, we encompass the increasing prevalence of microplastics in environment, emphasizing mainly on water environments, how they act as centers and vectors of microbial pathogens with their associated bacterial assemblage compositions and ultimately lead to AMR. It further discusses the mechanistic insights on how microplastics act as hosts of biofilms (creating the plastisphere). We have also presented the modern toolbox used for microplastic-biofilm analyses. A review on potential strategies for addressing microplastic-associated AMR is given with recent success stories, challenges and future prospects.

Mass Spectrometry Imaging Disclosed Spatial Distribution of Defense-Related Metabolites in Triticum spp

Fusarium Head Blight is the most common fungal disease that strongly affects Triticum spp., reducing crop yield and leading to the accumulation of toxic metabolites. Several studies have investigated the plant metabolic response to counteract mycotoxins accumulation. However, information on the precise location where the defense mechanism is taking place is scarce. Therefore, this study aimed to investigate the specific tissue distribution of defense metabolites in two Triticum species and use this information to postulate on the metabolites' functional role, unlocking the "location-to-function" paradigm. To address this challenge, transversal cross-sections were obtained from the middle of the grains. They were analyzed using an atmospheric-pressure (AP) SMALDI MSI source (AP-SMALDI5 AF, TransMIT GmbH, Giessen, Germany) coupled to a Q Exactive HF (Thermo Fisher Scientific GmbH, Bremen, Germany) orbital trapping mass spectrometer. Our result revealed the capability of (AP)-SMALDI MSI instrumentation to finely investigate the spatial distribution of wheat defense metabolites, such as hydroxycinnamic acid amides, oxylipins, linoleic and α-linoleic acids, galactolipids, and glycerolipids.

Biochar for agronomy, animal farming, anaerobic digestion, composting, water treatment, soil remediation, construction, energy storage, and carbon sequestration: a review

In the context of climate change and the circular economy, biochar has recently found many applications in various sectors as a versatile and recycled material. Here, we review application of biochar-based for carbon sink, covering agronomy, animal farming, anaerobic digestion, composting, environmental remediation, construction, and energy storage. The ultimate storage reservoirs for biochar are soils, civil infrastructure, and landfills. Biochar-based fertilisers, which combine traditional fertilisers with biochar as a nutrient carrier, are promising in agronomy. The use of biochar as a feed additive for animals shows benefits in terms of animal growth, gut microbiota, reduced enteric methane production, egg yield, and endo-toxicant mitigation. Biochar enhances anaerobic digestion operations, primarily for biogas generation and upgrading, performance and sustainability, and the mitigation of inhibitory impurities. In composts, biochar controls the release of greenhouse gases and enhances microbial activity. Co-composted biochar improves soil properties and enhances crop productivity. Pristine and engineered biochar can also be employed for water and soil remediation to remove pollutants. In construction, biochar can be added to cement or asphalt, thus conferring structural and functional advantages. Incorporating biochar in biocomposites improves insulation, electromagnetic radiation protection and moisture control. Finally, synthesising biochar-based materials for energy storage applications requires additional functionalisation.

Anaerobic digestion beyond biogas

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.