Enhanced medium-chain fatty acids production from Cephalosporin C antibiotic fermentation residues by ionizing radiation pretreatment

Deciphering the reduction of antibiotic resistance genes (ARGs) during medium-chain fatty acids production from waste activated sludge: Driven by inhibition of ARGs transmission and shift of microbial community

Medium-chain fatty acids (MCFAs) production from waste activated sludge (WAS) by chain extension (CE) is a promising technology. However, the effects and mechanisms of CE process on the fate of antibiotic resistance genes (ARGs) remain unclear. In this study, the results showed that the removal efficiency of ARGs was 81.15 % in CE process, suggesting its efficacy in reducing environmental risks. Further, the observed decrease in mobile genetic elements (MGEs) indicated that CE process restricted the horizontal gene transfer (HGT). Complementing this, the increase in soluble organic matters and extracellular 16 S rDNA confirmed that MCFAs production caused bacterial damage. Decreased intracellular ARGs and increased extracellular ARGs further revealed that MCFAs production impaired ARGs hosts, thereby limiting the vertical gene transfer (VGT) of ARGs. Shift of microbial community combined with co-occurrence network analysis demonstrated that functional bacteria without host potential for ARGs were enriched, but potential ARGs and MGEs hosts decreased, showing the role of functional bacterial phylogeny and selection pressure of MCFAs in reducing ARGs. Finally, partial least squares path model was used to systematic verify the mechanism of ARGs removal in CE process, which was attributed to the inhibition of ARGs transmission (HGT and VGT) and shift of microbial community.

Comprehensive review of microbial production of medium-chain fatty acids from waste activated sludge and enhancement strategy

Microbial production of versatile applicability medium-chain fatty acids (MCFAs) (C6-C10) from waste activated sludge (WAS) provides a pioneering approach for wastewater treatment plants (WWTPs) to achieve carbon recovery. Mounting studies emerged endeavored to promote the MCFAs production from WAS while struggling with limited MCFAs production and selectivity. Herein, this review covers comprehensive introduction of the transformation process from WAS to MCFAs and elaborates the mechanisms for unsatisfactory MCFAs production. The enhancement strategies for biotransformation of WAS to MCFAs was presented. Especially, the robust performance of iron-based materials is highlighted. Furthermore, knowledge gaps are identified to outline future research directions. Recycling MCFAs from WAS presents a promising option for future WAS treatment, with iron-based materials emerging as a key regulatory strategy in advancing the application of WAS-to-MCFAs biotechnology. This review will advance the understanding of MCFAs recovery from WAS and promote sustainable resource management in WWTPs.

Enhanced medium-chain fatty acid production from sewage sludge by combined electro-fermentation and anaerobic fermentation

Electro-fermentation (EF) was combined with anaerobic fermentation (AF) to promote medium-chain fatty acid (MCFA) from sewage sludge. Results showed that EF at acidification process significantly increased short-chain fatty acid (SCFA) production of by 0.5 times (82.4 mmol C/L). AF facilitated the chain elongation (CE) process by enhancing the SCFA conversion. Combined EF at acidification and AF at CE (EF-AF) achieved the highest MCFA production of 27.9 mmol C/L, which was 20 %-866 % higher than the other groups. Electrochemical analyses showed that enhanced SCFA and MCFA production was accompanied with good electrochemical performance at acidification and CE. Microbial analyses showed that EF-AF promoted MCFA production by enriching electrochemically active bacteria (EAB, Bacillus sp.). Enzyme analyses indicated that EF-AF promoted MCFA production by enriching the functional enzymes involved in Acetyl-CoA formation and the fatty acid biosynthesis (FAB) pathway. This study provided new insights into the production of MCFA from enhanced sewage sludge.

Influence of adding strategy of biochar on medium-chain fatty acids production from sewage sludge

Production of medium-chain fatty acids (MCFAs) from sewage sludge has dual effects on valuable sludge disposal and renewable energy generation, while low efficiency limits its application. Biochar addition is considered an effective method to improve MCFAs production. In this study, the influence of biochar adding strategies (i.e., adding biochar in acidification or chain elongation (CE) processes) on MCFAs production was explored. Results showed that by adding biochar in the acidification process, MCFAs accumulation increased by over 114%, accompanied by the highest carbon conversion efficiency (134.66%) and electron transfer efficiency of MCFAs (94.22%) by the terminal CE. Adding biochar before the acidification process better enriched CE bacteria (e.g., Paraclostridium) and strengthened the dominant metabolic pathway. In contrast, the biochar added before the CE process priorly enriched the bacteria capable of degrading organics, like unclassified_f__Dysgonomonadaceae, norank_f__norank_o__OPB41, and Acetobacterium. The differences in excessive ethanol oxidation and short-chain fatty acids accumulation induced by varied adding strategies might be responsible for this.

Improving antibiotic removal and anaerobic digestion performance of discarded cefradine pellets through thermo-alkaline pretreatment

Discarded cefradine pellets (DCP) as the hazardous wastes contain lots of bioavailable sucrose. Anaerobic digestion (AD) may be a promising technology for treating DCP, achieving dual goals of waste treatment and resource recovery. However, high concentration of cefradine will inhibit the AD process. This study applied thermo-alkaline pretreatment (TAP) to remove cefradine and improve the AD performance of DCP. Around 95% cefradine could be degraded to different intermediate degradation products (TPs) in TAP at optimal condition, and hydrolysis and hydrogenation were the main degradation pathways. Quantitative structure-activity relationship analysis indicated that the main TPs exhibited lower toxicity than cefradine, and DCP residues after TAP were almost not toxic to E. coli K12 and B. subtilis growth by antibacterial activity analysis. Therefore, TAP promoted the biomethane yield in AD of DCP residues (274.74 mL/g COD), which was 1.91 times that of control group. Besides, compared to control group, final cefradine concentrations in liquids and sludge were significantly decreased in AD system with TAP, lowering environmental risk and indicating stronger prospect for process application. Microbiological analysis revealed that acidogens (Macellibacteroides, Bacteroides), syntrophs (Syntrophobacter, Syntrophorhabdus), and acetoclastic Methanosaeta were enriched in AD system with TAP, which contributed to improving AD performance of DCP.

Volatile fatty acids recovery and antibiotic degradation from erythromycin fermentation residues by combined thermal pretreatment and anaerobic fermentation: Insights into microbial communities and metabolic pathways

High resistance of erythromycin has been the key factor restricting the disposal of erythromycin fermentation residues (EFR). Considering the high sensitivity of erythromycin to acidic conditions, anaerobic fermentation may be a good approach for EFR treatment, through which pH decreases along with the volatile fatty acids (VFA) accumulation. This study firstly explored the EFR treatment by combined thermal pretreatment and anaerobic fermentation. Results showed that thermal pretreatment and anaerobic fermentation exhibited a synergistic effect on erythromycin removal. Erythromycin concentration decreased to 20.0 mg/L with the maximum removal rate of 60.0%, which was 140% and 71.4% higher than erythromycin removal by sole thermal pretreatment and anaerobic fermentation. Thermal pretreatment induced the increased VFA production by 22.3% with the highest VFA concentration of 5325.4 mg/L. Microbial analysis shows that thermal pretreatment stimulated erythromycin degradation and VFA production by increasing the microbial diversity and enriching the functional enzymes involved in acetate-producing pathways.

Production of medium chain fatty acids from fermentation of antibiotic residuals: Fate of antibiotic resistance genes

The potential of antibiotic resistance genes (ARGs) amplification restricts the biological recovery of antibiotic fermentation residues (AFRs) through two-stage anaerobic fermentation. This study explored the fate of ARGs during the fermentation of AFRs that comprising of acidification and chain elongation (CE). Results showed that with the alteration of fermentation process from acidification to CE, microbial richness was significantly increased, total abundance of ARGs was slightly decreased by 1.84%, and the significant negative correlations between ARGs and microbes were increased, implied the inhibitory effect of CE microbes to ARGs amplification. However, the total abundance of mobile genetic elements (MGEs) was increased by 24.5%, indicating that the potential of gene horizontal transfer of ARGs increased. This work suggested that two-stage anaerobic fermentation could effectively restrict the ARGs amplification, but more concerns are needed for the long-term dissemination of ARGs.

Production of medium chain fatty acids from antibiotic fermentation residuals pretreated by ionizing radiation: Elimination of antibiotic resistance genes

The propagation of antibiotic resistance genes (ARGs) restricts the application of antibiotic fermentation residues (AFRs). This study investigated medium chain fatty acids (MCFA) production from AFRs, focusing on the effect of ionizing radiation pretreatment on the fates of ARGs. The results indicated that ionizing radiation pretreatment not only stimulated the MCFA production, but also inhibited the proliferation of ARGs. Radiation at 10-50 kGy decreased ARGs abundances by 0.6-21.1% at the end of fermentation process. Mobile genetic elements (MGEs) exhibited higher resistance to ionizing radiation, radiation over 30 kGy was required to suppress the proliferation of MGEs. Radiation at 50 kGy achieved an adequate inhibition to MGEs, and the degradation efficiency was 17.8-74.5% for different kinds of MGEs. This work suggested that ionizing radiation pretreatment could be a good option to ensure the safer application of AFRs by eliminating the ARGs and preventing the horizontal gene transfer of ARGs.