Performance evaluation and microbial community dynamics in a novel AnMBR for treating antibiotic solvent wastewater

Antibiotic resistance evolution driven synergistically by antibiotics and typical organic pollutants in antibiotic production wastewater

A major concern regarding the risk of antibiotic production wastewater (APW) for the transmission of antibiotic resistance (AR) stems from the residual antibiotics. However, APW also contains high concentrations of organic pollutants, many of which have severe biological toxicity and joint toxicity with antibiotics. The contribution of these organic pollutants to the development of AR in the APW treatment system is unknown. In this study, a wild-type Escherichia coli strain was exposed to six typical organic pollutants in APW individually and synergistically with the antibiotic ampicillin (AMP). Independent exposure to organic compounds had negligible effects on the evolution of AR, whereas they synergistically induced AR mutations and increased antibiotic persistence with AMP, especially the raw material d-p-hydroxyphenylglycine (DHPG), at relevant concentrations in APW. Combined exposure to 1-500 mg/L DHPG and 1 mg/L AMP synergistically increased the mutation frequencies against multiple antibiotics by up to 2928.9-fold in a dose-time pattern, and the combination index reached 445.7. Phenotypic and genotypic analyses revealed that the synergism between DHPG and AMP was associated with increased antibacterial activity, enhanced oxidative stress, and stimulation of efflux pump expression. Overall, our results highlight the elevated risk of AR induction caused by antibiotics and organic pollutants in APW.

Rapid start-up and excellent performance of anaerobic membrane bioreactor for treating poly (butylene adipate-co-terephthalate) wastewater by using one-step feeding mode

The traditional anaerobic treatment process for highly concentrated, toxic, and acidic poly (butylene adipate-co-terephthalate) (PBAT) wastewater faces challenges. In contrast, the anaerobic membrane bioreactor (AnMBR) offers the advantage of robust performance, but the influence of start-up modes has not been explored. This study investigated the impact of one-step and stepwise startup (gradual dilution of wastewater) strategies in AnMBR treating PBAT wastewater. The results indicated that the one-step startup group achieved COD removal efficiency of 91.2% ± 2.7% and methane conversion rate of 234.7 ± 8.5 mLCH4/gCOD, which were 21.7% and 81.8 mL CH4/gCOD respectively higher than those achieved by the stepwise start-up group. Furthermore, the one-step startup led to the reduction of startup time by 10 days and the decrease in the average membrane fouling cycle by 6.6 days. Compared to the stepwise start-up group, the one-step startup group exhibited a lower abundance of Bacteroidota (11.3%), and a higher abundance of Proteobacteria (27.1%), Chloroflexi (10.5%), and Actinobacteria (11.8%). The one-step startup strategy facilitated the rapid development of a toxicity-tolerant hydrogenotrophic methanogenic pathway. Consequently, the one-step startup method provided a promising approach for the rapid start-up and excellent performance of AnMBR in PBAT wastewater treatment.

Occurrence of antibiotics in wastewater: Potential ecological risk and removal through anaerobic-aerobic systems

Antibiotics are intensively used to improve public health, prevent diseases and enhance productivity in animal farms. Contrarily, when released, the antibiotics laden wastewater produced from pharmaceutical industries and their application sources poses a potential ecological risk to the environment. This study provides a discussion on the occurrence of various antibiotics in wastewater and their potential ecological risk in the environment. Further, a critical review of anaerobic-aerobic processes based on three major systems (such as constructed wetland, high-rate bioreactor, and integrated treatment technologies) applied for antibiotics removal from wastewater is performed. The review also explores microbial dynamics responsible for antibiotic biodegradation in anaerobic-aerobic systems and its economic feasibility at wider-scale applications. The operational problems and prospective modifications are discussed to define key future research directions. The appropriate selection of treatment processes, sources control, understanding of antibiotic fate, and adopting precise monitoring strategies could eliminate the potential ecological risks of antibiotics. Integrated bio-electrochemical systems exhibit antibiotics removal ≥95% by dominant Geobacter sp. at short HRT ∼4-10 h. Major process factors like organic loading rate, hydraulic loading rate (HRT), and solid retention time significantly affect the system performance. This review will be beneficial to the researchers by providing in-depth understanding of antibiotic pollution and its abatement via anaerobic-aerobic processes to develop sustainable wastewater treatment technology in the future.

Diverse Microbial Community Profiles of Propionate-Degrading Cultures Derived from Different Sludge Sources of Anaerobic Wastewater Treatment Plants

Anaerobic digestion (AD) has been used for wastewater treatment and production of renewable energy or biogas. Propionate accumulation is one of the important problems leading to an unstable system and low methane production. Revealing propionate-degrading microbiome is necessary to gain a better knowledge for alleviation of the problem. Herein, we systematically investigated the propionate-degrading cultures enriched from various anaerobic sludge sources of agro-industrial wastewater treatment plants using 16S rRNA gene sequencing. Different microbial profiles were shown even though the methanogenic activities of all cultures were similar. Interestingly, non-classical propionate-degrading key players Smithella, Syntrophomonas, and Methanosaeta were observed as common prevalent taxa in our enriched cultures. Moreover, different hydrogenotrophic methanogens were found specifically to the different sludge sources. The enriched culture of high salinity sludge showed a distinct microbial profile compared to the others, containing mainly Thermovirga, Anaerolinaceae, Methanosaeta, Syntrophobactor, and Methanospirillum. Our microbiome analysis revealed different propionate-degrading community profiles via mainly the Smithella pathway and offers inside information for microbiome manipulation in AD systems to increase biogas production corresponding to their specific microbial communities.

Polytetrafluoroethylene (PTFE) hollow fiber AnMBR performance in the treatment of organic wastewater with varying salinity and membrane cleaning behavior

PTFE hollow fiber anaerobic membrane bio-reactor (AnMBR) performance was investigated in the treatment of organic wastewater, with varying salinity and PTFE membrane cleaning behavior. The AnMBR was operated for 226 days, with a total and biological COD removal efficiency of 97.2% and 89.9% respectively, at a NaCl concentration of 35 g L^-1. A high number of Proteobacteria (38.2%) and Bacteroidetes (25.9%) were present in the system, with an increase in membrane fouling rate from 1.88 × 10¹¹ to 2.63 × 10¹¹ m^-1 d^-1 with higher salinity. The effects of soluble microbial products (SMP), extracellular polymeric substances (EPS), low molecular-weight (LMW) carbohydrates, sludge particle size and inorganic element accumulation, were evaluated on membrane fouling. Flux recovery of fouled PTFE membranes reached 91.6% with offline cleaning. Overall, results indicate that PTFE hollow fiber AnMBR provides a promising method for the treatment of saline organic wastewater.

Acclimation of acid-tolerant methanogenic propionate-utilizing culture and microbial community dissecting

The acid-tolerant methanogenic propionate degradation culture was acclimated in a propionate-fed semi-continuous bioreactor by daily adjusting the digestate pH. The performance of propionate fermentation, the respond of microbial community structure to the acidic environment, and the microbial network for propionate degradation in the acid-tolerant culture was investigated. The results demonstrated that after long term of acclimation to low pH, the digester could produce methane from propionate at pH 4.8-5.5 with 0.3-0.4 L g^-1 propionic acid (HPr) d^-1 of the volatile solids (VS) methane production. The predominant methanogens shifted from acetoclastic methanogens (∼87%) to hydrogenotrophic methanogens (∼67%) in the bioreactor with the dropping pH, indicating that hydrogenotrophic methanogens were more acid-tolerant than acetoclastic methanogens. Smithella (∼11%), Syntrophobacter (∼7%) and Pelotomaculum (∼3%) were the main propionate oxidizers in the acid-tolerant propionate-utilizing culture. Methanothrix dominant acetoclastic methanogens, while Methanolinea and Methanospirillum were the major H₂ scavengers to support Syntrophobacter and Pelotomaculum syntrophic propionate degradation.