Methane fermentation is an attractive practice in waste processing, which enables one to both control pollution and recover energy. This kind of anaerobic digestion is exposed to inhibitors, which can retard the process and cause failure. The mechanism causing toxicity of these substances and their impact on the efficiency of the process are already known, but there is still not much information about their influence on methane fermentation microorganisms' activity and the composition of microbiota. In this review, based on 168 articles, we present a summary of the up‐to‐date research on the inhibition of anaerobic processes by some specific toxicants: ammonia, sulfides, ions of light metals, heavy metals, antibiotics, ethylene and acetylene, chlorophenols, halogen aliphatic hydrocarbons, aliphatic nitro compounds, and long‐chain fatty acids. This review principally focuses on the impact of these inhibitors on the microorganisms involved in the process. More accurate recognition of methane fermentation inhibition mechanisms, with particular emphasis on the microbiological aspect, can help to improve the efficiency of the process.

Over the past few decades, due to the excessive consumption of drugs in human and veterinary medicine, the antimicrobial resistance (AR) of microorganisms has risen considerably across the world, and this trend is predicted to intensify. Many worrying research results indicate the occurrence of pools of AR, both directly related to human activity and environmental factors. The increase of AR in the natural environment is mainly associated with the anthropogenic activity. The dissemination of AR is significantly stimulated by the operation of municipal facilities, such as wastewater treatment plants (WWTPs) or landfills, as well as biogas plants, agriculture and farming practices, including animal production and land application of manure. These activities entail a risk to public health by spreading bacteria resistant to antimicrobial products (ARB) and antibiotic resistance genes (ARGs). Furthermore, subinhibitory concentrations of antimicrobial substances additionally predispose microbial consortia and resistomes to changes in particular environments that are permeated by these micropollutants. The current state of knowledge on the fate of ARGs, their dissemination and the complexity of the AR phenomenon in relation to anthropogenic activity is inadequate. This review summarizes the state-of-the-art knowledge on AR in the environment, in particular focusing on AR spread in an anthropogenically altered environment and related environmental consequences.

Global population growth generates problems relating to increasing demand for sustainable energy and waste treatment. Proper solid waste management promotes material reuse, maximizes recovery and reduces anthropological pressure on natural resources. Anaerobic digestion (AD) is an alternative method of stabilizing organic substrates and generating biogas as a source of environmentally friendly energy. In addition, digestate is not only a waste product of that process but also a renewable resource with many potential applications. The circular economy concept encourages the use of digestate as a source of nutrients that promotes plant growth and improves soil properties. However, the stabilized substrates often contain various contaminants, including heavy metals (HMs) and antibiotics that are also detected in digestate. Therefore, the agricultural use of digestate obtained by AD could increase the pool of these pollutants in soil and water environments and contribute to their circulation in these ecosystems. Moreover, digestate may also increase the co-selection of genes determining resistance to HMs and antibiotics in environmental microorganisms. This article comprehensively reviews published data on the residues of various HMs and antimicrobial substances in different digestates around the world and maps the scope of the problem. Moreover, the potential risk of residual levels of these contaminants in digestate has also been evaluated. The review highlights the lack of legal standards regulating the concentrations of drugs introduced into the soil with digestate. The results of the ecological risk assessment indicate that the presence of medically important antimicrobials in digestate products, especially those used in agriculture, should be limited.

This study explored the effect of eight antimicrobials on the efficiency of biogas production in the anaerobic digestion (AD) process of cattle manure. The microbiome involved in AD, presence and number of genes mcrA, MSC and MST specific for Archaea, and antibiotic resistance genes (ARGs) concentration in digestate (_D) were examined. Supplementation of antibiotics to substrate significantly lowered biogas production. Amoxicillin caused a 75% decrease in CH₄ production in comparison with the control samples. Enrofloxacin, tetracycline, oxytetracycline, and chlortetracycline reduced the amount of biogas produced by 36, 39, 45 and 53%, respectively. High-throughput sequencing of 16S rRNA results revealed that bacteria dominated the Archaea microorganisms in all samples. Moreover, antibiotics led to a decrease in the abundance of the genes mcrA, MSC, MST, and induced an increase in the number of tetracyclines resistance genes. Antibiotics decreased the efficiency of the AD process and lowered the quantity of CH₄ obtained, while stimulating an increase in the number of ARGs in _D. This work reveals how antimicrobials affect the cattle manure AD process and changes in microbial biodiversity, number of functional genes and ARGs in the digestate due to drugs exposure. It also, provides useful, practical information about the AD process.

The conversion of cattle manure into biogas in anaerobic digestion (AD) processes has been gaining attention in recent years. However, antibiotic consumption continues to increase worldwide, which is why antimicrobial concentrations can be expected to rise in cattle manure and in digestate. This study examined the long-term synergistic effects of antimicrobials on the anaerobic digestion of cattle manure. The prevalence of antibiotic resistance genes (ARGs) and changes in microbial biodiversity under exposure to the tested drugs was investigated using a metagenomic approach. Methane production was analyzed in lab-scale anaerobic bioreactors. Bacteroidetes, Firmicutes, and Actinobacteria were the most abundant bacteria in the samples. The domain Archaea was represented mainly by methanogenic genera Methanothrix and Methanosarcina and the order Methanomassiliicoccales. Exposure to antibiotics inhibited the growth and development of methanogenic microorganisms in the substrate. Antibiotics also influenced the abundance and prevalence of ARGs in samples. Seventeen types of ARGs were identified and classified. Genes encoding resistance to tetracyclines, macrolide–lincosamide–streptogramin antibiotics, and aminoglycosides, as well as multi-drug resistance genes, were most abundant. Antibiotics affected homoacetogenic bacteria and methanogens, and decreased the production of CH₄. However, the antibiotic-induced decrease in CH₄ production was minimized in the presence of highly drug-resistant microorganisms in AD bioreactors.

Environmentally-friendly management of landfill leachate (LL) poses a challenge, and LL is usually co-treated with municipal wastewater in wastewater treatment plants (WWTPs). The extent to which the co-treatment of LL and municipal wastewater influences the spread of antibiotic resistance (AR) in the environment has not been examined to date. Two WWTPs with similar wastewater composition and technology were studied. Landfill leachate was co-treated with wastewater in one of the studied WWTPs. Landfill leachate, untreated and treated wastewater from both WWTPs, and river water sampled upstream and downstream from the wastewater discharge point were analyzed. Physicochemical parameters, microbial diversity, and antibiotic resistance genes (ARGs) abundance were investigated to determine the impact of LL co-treatment on chemical and microbiological contamination in the environment. Landfill leachate increased pollutant concentrations in untreated wastewater and river water. Cotreatment of LL and wastewater could affect the abundance and diversity of microbial communities and the interactions between microbial species. Co-treatment also decreased the stability of microbial co-occurrence networks in the examined samples. The mexF gene was identified as a potential marker of environmental pollution with LL. This is the first study to explore the impact of LL on the occurrence of AR determinants in wastewater and rivers receiving effluents.