Effect of low levels of oxytetracycline on anaerobic digestion of cattle manure

Uncovering the mechanisms of ethanol stimulation on magnetite-enhanced anaerobic process treating oxytetracycline contained wastewater

Magnetite has been proved to facilitate direct interspecies electron transfer (DIET)-based syntrophys and might alleviate inhibitory effects of antibiotics in anaerobic digestion (AD), while feeding ethanol was an effective approach to enrich the DIET partners. However, most of the existing studies were conducted at fixed ethanol concentration, few attentions were paid on the effects of differential ethanol proportion on AD, the underlying roles and mechanisms of ethanol stimulation remains unclear. This study systematically investigated the impact of ethanol stimulation on anaerobic processes treating oxytetracycline (OTC)-contaminated wastewater at varying proportions (20%, 50%, and 80%, based on equivalent COD value). In the presence of magnetite, ethanol stimulation promoted the methane production from 244.9 mL/g COD to a maximum 434.2 mL/g COD, with the most pronounced enhancement observed at high ethanol proportions. In particular, the average methane production obtained at 50% and 80% ethanol was 328.5 and 297.7 mL/g COD, respectively, whereas the enhancement of 20% ethanol stimulation was relatively limited. Concurrently, more stable COD removal and OTC reduction was noted in the existence of both magnetite and high ethanol proportions. Microbial analysis revealed the pivotal roles of Methanosaeta, alongside the predominance of Methanobacterium, in regulating COD conversion and driving methanogenesis through the CO2 reduction pathway. Notably, high ethanol proportions fostered the enrichment of exoelectrogens (Geobacter, Desulfovibrio) in the magnetite-amended system, accompanied by the up-regulation of genes involved in organic metabolism pathways. Further investigation of functional genes highlighted the prevalence of pilA enrichment in the magnetite-amended system at low ethanol proportions, whereas omcS became more abundant at high ethanol proportions.

Unravelling the resilience of magnetite assisted granules to starvation and oxytetracycline stress

Starvation and antibiotics pollution are two frequent perturbations during breeding wastewater treatment process. Supplying magnetite into anaerobic system has been proved efficient to accelerate microbial aggregates and alleviate the adverse effect caused by process disturbance. Nevertheless, whether these magnetite-based granules are still superior over normal granules after a long-term starvation period remains unknown, the responsiveness of these granules to antibiotics stress is also ambiguous. In current study, we investigated the resilience of magnetite-based anaerobic granular sludge (AnGS) to starvation and oxytetracycline (OTC) stress, by unravelling the variations of reactor performance, sludge properties, ARGs dissemination and microbial community. Compared with the AnGS formed without magnetite, the magnetite assisted AnGS appeared more robust defense to starvation and OTC stress. With magnetite supplement, the average methane yield after starvation recovery, 50 mg/L and 200 mg/L OTC stress was enhanced by 48.95%, 115.87% and 488.41%, respectively, accompanied with less VFAs accumulation, improved tetracycline removal rate (76.3-86.6% vs. 51.0-53.5%) and higher ARGs reduction. Meanwhile, magnetite supplement effectively ameliorated the potential sludge breakage by triggering more large granules formation. Trichococcus was considered an important impetus in maintaining the stability of magnetite-based AnGS process. By inducing more syntrophic methanogenesis partnerships, especially for hydrogenotrophic methanogenesis, magnetite ensured the improved reactor performance and stronger resilience at stress conditions.

Combined effects of oxytetracycline concentration and organic loading rate on semi-continuous anaerobic digestion of swine wastewater

High concentrations of antibiotics in swine wastewater raises concerns about the potential adverse effects of anaerobic digestion (AD). Current studies mainly focused on the effects of various antibiotic concentrations. However, these studies didn't take into account the fluctuation of swine wastewater quality and the change of reactor operating conditions in practical engineering applications. In this study, it was found that in the operating systems with COD of 3300 mg/L and hydraulic retention time (HRT) of 4.4 days, the continuous addition of oxytetracycline for 30 days had no effect on the AD performance. Nevertheless, when COD and HRT were changed to 4950 mg/L and 1.5 days respectively, oxytetracycline at 2 and 8 mg/L increased the cumulative methane yield by 27% and 38% at the cost of destroying cell membrane, respectively, while oxytetracycline at 0.3 mg/L improved the performance and stability of AD. These results could be referred for practical engineering applications.

A comprehensive review on the advances of bioproducts from biomass towards meeting net zero carbon emissions (NZCE)

This review investigates the development of bioproducts from biomass and their contribution towards net zero carbon emissions. The promising future of biomasses conversion techniques to produce bioproducts was reviewed. The advances in anaerobic digestion as a biochemical conversion technique have been critically studied and contribute towards carbon emissions mitigation. Different applications of microalgae biomass towards carbon neutrality were comprehensively discussed, and several research findings have been tabulated in this review. The carbon footprints of wastewater treatment plants were studied, and bioenergy utilisation from sludge production was shown to mitigate carbon footprints. The carbon-sinking capability of microalgae has also been outlined. Furthermore, integrated conversion processes have shown to enhance bioproducts generation yield and quality. The anaerobic digestion/pyrolysis integrated process was promising, and potential substrates have been suggested for future research. Lastly, challenges and future perspectives of bioproducts were outlined for a contribution towards meeting carbon neutrality.

Effects of heavy metals and antibiotics on performances and mechanisms of anaerobic digestion

Anaerobic digestion (AD) is an efficacious technology to recover energy from organic wastes/wastewater, while the efficiency of AD could be limited by metals and antibiotics in substrates. It is of great significance to deeply understand the interaction mechanisms of metals and antibiotics with anaerobic microorganisms, as well as the combined effects of metals and antibiotics, which will help us break the inherent dysfunction of AD system and promote the efficient operation of AD. Therefore, this paper reviews the effects of metals, antibiotics and their combinations on AD performance, as well as the combined effects and interactional mechanisms of metals and antibiotics with anaerobic microorganisms. In addition, control strategies and future research needs are proposed. This review provides valuable information for the enhancement strategies and engineering applications of AD for organic wastes/wastewater containing metals and antibiotics.