A review of chemical and microbial contamination in food: What are the threats to a circular food system?

Enhanced mitigation of antibiotic resistance genes in anaerobic digestion of food waste using biochar-supported nanoscale zero-valent iron.

Composition and contamination of source separated food waste from different sources and regulatory environments

Managing food waste is key to tackling climate change

Antibiotic resistance genes (ARGs) have emerged as a significant global health threat, contributing to fatalities worldwide. Wastewater treatment plants (WWTPs) and livestock farms serve as primary reservoirs for these genes due to the limited efficacy of existing treatment methods and microbial adaptation to environmental stressors. Anaerobic digestion (AD) stands as a prevalent biological treatment for managing sewage sludge and manure in these settings. Given the agricultural utility of AD digestate as biofertilizers, understanding ARGs’ fate within AD processes is essential to devise effective mitigation strategies. However, understanding the impact of various factors on ARGs occurrence, dissemination, and fate remains limited. This review article explores various AD treatment parameters and correlates to various resistance mechanisms and hotspots of ARGs in the environment. It further evaluates the dissemination and occurrence of ARGs in AD feedstocks and provides a comprehensive understanding of the fate of ARGs in AD systems. This review explores the influence of key AD parameters such as feedstock properties, pretreatments, additives, and operational strategies on ARGs. Results show that properties such as high solid content and optimum co-digestion ratios can enhance ARG removal, while the presence of heavy metals, microplastics, and antibiotics could elevate ARG abundance. Also, operational enhancements, such as employing two-stage digestion, have shown promise in improving ARG removal. However, certain pretreatment methods, like thermal hydrolysis, may exhibit a rebounding effect on ARG levels. Overall, this review systematically addresses current challenges and offers future perspectives associated with the fate of ARGs in AD systems.Graphical

Does lipid stress affect performance, fate of antibiotic resistance genes and microbial dynamics during anaerobic digestion of food waste?

Edible insects recycle food waste, which can help feed a hungrier planet by making food systems more circular and diversifying protein production. The potential for entomophagy (i.e., insect cuisine) to contribute to waste recycling and lower input food production is only beginning to be explored in the U.S., although insects have been consumed by people for millennia in a wide range of cultures. In this perspective piece, we consider as a case study the potential for university foodservice programs in New England to serve as incubators for circular entomophagous food systems. Students are likely early adopters of entomophagy because they increasingly demand sustainable non-meat protein options. University foodservices meanwhile purchase large amounts of food wholesale from local producers, utilize standardized pre-processing, and generate consistent waste streams which may be valuable feed for local insect farmers. Current Farm to Institution approaches strengthen regional food systems by connecting small farmers with university foodservices; we argue that a similar model (Farm to Institution to Farm) could support establishment of local insect farms, introduce edible insects to a relatively receptive base of university student customers, and provide a more sustainable mechanism for repurposing university food waste as insect feed. But to enable this type of food system, additional requirements include: (1) research on domestication of native insect species; (2) investment in processing capacity, ensuring new insect farmers have reliable markets for raw insect products; (3) infrastructure to recirculate waste streams within existing food systems; and (4) creation of recipes that entice new insect consumers.

Anaerobic co-digestion of food waste (FW) and sewage sludge (SS) has shown superior performance over anaerobic mono-digestion. However, the fate of antibiotic resistance genes (ARGs) under various co-digestion ratios has been rarely reported to date. Thus, this study investigates the effects of FW:SS ratios on the digester's performance and the fate of ARGs at different FW:SS ratios. The results demonstrated that at a 50:50 FW:SS ratio, 738mL.g-1 VS of biogas and 393mL.g-1 VS of methane were produced in the system on day 18. Response surface methodology (RSM) was also used for optimization, showing 42.5% FW is the optimal FW content for maximum biogas and minimum H2S production. The distribution of select ARGs (qnrS, tetA, emrB, blaTEM, ampR) was tracked in the liquid and solid fraction of the digestate. Results illustrated a decrease (83-99% reduction) in the overall abundance of the ARGs in the solid fraction after AD. A similar trend was observed for the ARGs in the liquid fractions (65-99% reduction), except for ermB which became 1.74-10.6-fold higher in the final digestate. Also, at 50% FW, the abundance of intl1 increased in the liquid and solid fraction of digestate, indicating increased potential of ARG dissemination via horizontal gene transfer.

The fate of antibiotic resistance genes (ARGs) in full-scale anaerobic digestion (AD) of food waste (FW) and in the soil applied with biogas slurry has not been fully understood. In this study, 12 targeted ARGs and intI1 in FW, intermediate product, and biogas slurry from three full-scale ADwere analyzed. The results showed that subcritical water pretreatment was aneffective method for ARG attenuation, by which the absolute abundance of total targeted ARGs was removed by 99.69%. The predominant ARGs (ermB, tetM, and tetW) in FW were removed more than 99% after subcritical water pretreatment. The result of field experiments with biogas slurry as fertilizer showed that the absolute abundance of several ARGs (sul2, tetM, blaOXA-1, blaTEM) and intI1 accumulated significantly compared to the control group (CK) during three consecutive growth stages of the rice. The detected abundance of ARGs in paddy field soil increased from 190.50 (CK) to 8.87 × 104 copies/g (wet weight) (soil) during tillering stage, and increased from 4102.65 (CK) to 4.38 × 104 copies/g (wet weight) (soil) during heading time. Biogas slurry improved the soil nutrients (TN, AN, TP, and AP); meanwhile, the concentrations of total salt and Cl- increased. Network analysis indicated that 28 genera were the possible hosts of ARGs; variation partitioning analysis (VPA) indicated that microbial communities (contribution 59.30%) were the main factors that affected the fate of ARGs and intI1.

Metagenomic approach reveals the fate of antibiotic resistance genes in a temperature-raising anaerobic digester treating municipal sewage sludge

Enzymatic pretreatment mitigates the dissemination of antibiotic resistance genes via regulating microbial populations and gene expressions during food waste fermentation

Zero valent iron improved methane production and specifically reduced aminoglycoside and tetracycline resistance genes in anaerobic digestion.

Many important diseases are showing resistance to commonly used antibiotics, and the resistance is potentially caused by widespread use of antibiotics for maintaining human health and improving food production. Antibiotic resistance genes (ARGs) and antibiotic-resistant bacteria (ARB) are associated with this increase, and their fate in water resource recovery facilities is an important, emerging area of research. This literature review summarizes current findings of worldwide research on the fate of ARB and ARGs in various types of treatment plants. Twenty-five published studies were reviewed which contained 215 observations in activated sludge, membrane bioreactors, anaerobic digestion, constructed wetlands, coagulation-filtration, and three types of disinfection. We found 70% decreased observations, 18% increased observations, and 12% unchanged observations of all observations in all treatment processes. Resistance genes to tetracycline were most often observed, but more studies are needed in other antibiotic resistance genes. The causes for increased abundance of ARGs and ARB are not well understood, and further studies are warranted. PRACTITIONER POINTS: Antibiotic resistance is increasing with concern that treatment plants may acclimate bacteria to antibiotics. A literature survey found 215 resistance observations with 70% decreased, 18% increased, 12% unchanged after treatment. The type of treatment process is important with activated sludge showing the greatest reductions.

This study investigated the effect of ultrasonic (US) pretreatment at three different contact times (30, 45, and 60 min) with a power of 240 W and frequency of 40 kHz on the fate of antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and enteric pathogens during anaerobic digestion (AD) of sludge. By using real time-qPCR, three MGEs (int1, int2, and tnpA) and seven ARGs (sul1, sul2, tetW, tetA, tetO, ermF, and aac(6')-lb) were quantified that have serious human health impacts and represent the most widely used antibiotics (tetracycline, sulfonamide, macrolide, and aminoglycoside). Results indicated that US pretreatment under different contact times improved the removal of ARGs and MGEs. Compared to 30 and 45 min of US pretreatment, 60 min of US pretreatment resulted in a higher reduction of ARGs with total ARG reduction of 41.70 ± 1.13%. Furthermore, the relative abundance of ARGs and MGEs after US pretreatment was reduced more effectively in anaerobic reactors than in a control AD without US pretreatment. The total ARGs and MGEs removal efficiency of control AD was 44.07 ± 0.72% and 63.69 ± 1.43%, and if US pretreatment at different times were applied, the total ARGs and MGEs removal efficiency of the whole pretreatment AD process improved to 59.71 ± 2.76-68.54 ± 1.58% and 69.82 ± 2.15-76.84 ± 0.22%. The highest removal of total ARGs (68.54 ± 1.58%) and MGEs (76.84 ± 0.22%) was achieved after AD with US pretreatment at 45 min. However, US pretreatment and AD with US pretreatment were not effective in inactivation of enteric pathogens (total coliforms and E. coli), suggesting that posttreatment is needed prior to land application of sludge to reduce the level of enteric pathogens. There was no detection of the studied ARGs and MGEs in the enteric pathogens after US pretreatment in subsequent AD. According to this study, long contact times of US pretreatment can mitigate ARGs and MGEs in AD processes, offering valuable insight into improving environmental safety and sustainable waste management. Additionally, the study highlights the need to investigate posttreatment techniques for reducing enteric pathogens in AD effluent, a crucial consideration for agricultural use and environmental protection.

Reducing our waste size

The role of pretreatments in handling antibiotic resistance genes in anaerobic sludge digestion – A review