Chronic effect of erythromycin on substrate biodegradation kinetics of activated sludge

Effects of antibiotics on anaerobic digestion of sewage sludge: Performance of anaerobic digestion and structure of the microbial community

As a common biological engineering technology, anaerobic digestion can stabilize sewage sludge and convert the carbon compounds into renewable energy (i.e., methane). However, anaerobic digestion of sewage sludge is severely affected by antibiotics. This review summarizes the effects of different antibiotics on anaerobic digestion of sewage sludge, including production of methane and volatile fatty acids (VFAs), and discusses the impact of antibiotics on biotransformation processes (solubilization, hydrolysis, acidification, acetogenesis and methanogenesis). Moreover, the effects of different antibiotics on microbial community structure (bacteria and archaea) were determined. Most of the research results showed that antibiotics at environmentally relevant concentrations can reduce biogas production mainly by inhibiting methanogenic processes, that is, methanogenic archaea activity, while a few antibiotics can improve biogas production. Moreover, the combination of multiple environmental concentrations of antibiotics inhibited the efficiency of methane production from sludge anaerobic digestion. In addition, some lab-scale pretreatment methods (e.g., ozone, ultrasonic combined ozone, zero-valent iron, Fe³⁺ and magnetite) can promote the performance of anaerobic digestion of sewage sludge inhibited by antibiotics.

Antibiotics in anaerobic digestion: Investigative studies on digester performance and microbial diversity

The ever-increasing consumption of antibiotics in both humans and animals has increased their load in municipal and pharmaceutical industry waste and may cause serious damage to the environment. Impact of antibiotics on the performance of commercially used anaerobic digesters in terms of bioenergy output, antibiotics' removal and COD removal have been compared critically with a few studies indicating >90% removal of antibiotics. AnMBR performed the best in terms of antibiotic removal, COD removal and methane yield. Most of the antibiotics investigated have adverse effects on microbiome associated with different stages and methane generation pathways of AD which has been assessed using high throughput technologies like metatranscriptomics, metaproteomics and flow cytometry. Perspectives have been given for understanding the fate and elimination of antibiotics from AD. The challenge of optimization and process improvement needs to be addressed to increase efficiency of the anaerobic digesters.

Phyto-mediated photocatalysis: a critical review of in-depth base to reactive radical generation for erythromycin degradation

Erythromycin (ERY), designated as a risk-prioritized macrolide antibiotic on the 2015 European Union watch list, is the third most commonly used antibiotic, most likely due to its ability to inhibit the protein. ERY has revealed record-high aquatic concentrations threatening the entire ecosystem and hence demands priority remedial measures. The inefficiency of various conventional ERY degradation methodologies opened up a gateway to advanced technologies. The conventional approach comprising of a chemically formulated, single photocatalyst has a major drawback of creating multiple environmental stresses. In this context, photocatalysis is grabbing tremendous attention as an efficient and cost-effective antibiotic treatment approach. Several studies have ascertained that ZnO, TiO₂, Fe₃O₄, and rGO nanoparticles possess remarkable pollution minimizing operational capabilities. Additionally, composites are found much more effective in antibiotic removal than single nanoparticles. In this review, an attempt has been made to provide a comprehensive baseline for efficient reactive radical production by a phyto-mediated composite kept under a certain source of irradiation. Considerable efforts have been directed towards the in-depth investigation of rGO-embedded, phyto-mediated ZnO/TiO₂/Fe₃O₄ photocatalyst fabrication for efficient ERY degradation, undergoing green photocatalysis. This detailed review provides photocatalytic nanocomposite individualities along with a hypothetical ERY degradation mechanism. It is assumed that derived information presented here will provoke innovative ideas for water purification incorporating green photocatalysis, initiating the construction of high-performance biogenic hierarchical nanocatalysts.

Effect of Antibiotics on the Microbial Efficiency of Anaerobic Digestion of Wastewater: A Review

Recycling waste into new materials and energy is becoming a major challenge in the context of the future circular economy, calling for advanced methods of waste treatment. For instance, microbially-mediated anaerobic digestion is widely used for conversion of sewage sludge into biomethane, fertilizers and other products, yet the efficiency of microbial digestion is limited by the occurrence of antibiotics in sludges, originating from drug consumption for human and animal health. Here we present antibiotic levels in Chinese wastewater, then we review the effects of antibiotics on hydrolysis, acidogenesis and methanogenesis, with focus on macrolides, tetracyclines, β-lactams and antibiotic mixtures. We detail effects of antibiotics on fermentative bacteria and methanogenic archaea. Most results display adverse effects of antibiotics on anaerobic digestion, yet some antibiotics promote hydrolysis, acidogenesis and methanogenesis.

Responses of antibiotics, antibiotic resistance genes, and mobile genetic elements in sewage sludge to thermal hydrolysis pre-treatment and various anaerobic digestion conditions

Sewage sludge from wastewater treatment plants (WWTPs) harbours large amounts of antibiotics, antibiotic resistance genes (ARGs), and mobile genetic elements (MGEs), the variation and fate of these emerging pollutants during sludge treatment processes must be thoroughly studied to reduce their potential risks to human health. In this study, 7 pilot-scale CSTR anaerobic digesters were established with the same seed sludge and fed with the same thermal hydrolysis pre-treated sewage sludge, while operating under different conditions. High-throughput quantitative PCR, UPLC-MS/MS and Illumina Hiseq-sequencing were used to systematically evaluate the responses of antibiotics, ARGs, and MGEs in sewage sludge to thermal hydrolysis pre-treatment and various anaerobic digestion (AD) conditions. The results showed that thermal hydrolysis effectively reduced the abundance (>94%) of almost all subtypes of ARGs and MGEs, and it was a powerful technology for reducing tetracyclines, macrolides, and lincosamides. Besides, the abundance of ARGs and MGEs in thermophilic digesters was lower than that in mesophilic digesters, suggesting that thermophilic digesters could be used to avoid the ARGs rebounding. In addition, the thermophilic system further reduced the concentrations of quinolones. For the digesters operated under the mesophilic conditions, a longer hydraulic retention time (HRT) facilitated the removal of antibiotics, ARGs, and MGEs. Furthermore, the microbial community and MGEs had important effects on the persistence and proliferation of ARGs in AD process. The findings of this study provide effective clues for controlling the spread of antibiotic resistance and suggest the optimal operating conditions of digesters.

Response of Anammox biofilm to antibiotics in trace concentration: Microbial activity, diversity and antibiotic resistance genes

Long-term impacts of two antibiotics-norfloxacin (NOR) and erythromycin (ERY) in trace concentration (1ug L^-1) on Anammox biofilm were investigated. The specific Anammox activity (SAA) and dehydrogenase activity (DHA) of Anammox biofilm were detected by batch experiments, the microbial diversity was analyzed using high-throughput sequencing technology and the antibiotic resistance genes (ARGs) were measured by qPCR. Results showed that long-term NOR feeding decreased 30% SAA and 39.6% DHA, and also decreased the abundance of the OTUs related to autotrophic nitrogen removal, while ERY had slight impact on Anammox. Only two ARGs targeted to ERY (ermB, mphA) were detected in the two Anammox systems while those targeted to NOR (qnrA, qnrB, qnrD, and qnrS) were not detected. The relative expression of ermB to 16S rRNA increased from 2.08±0.32×10^-4 to 3.53±1.18×10^-4, and that of mphA increased to 5.00±0.48×10^-4 from 4.48±1.32×10^-5. The induced ARGs in the Anammox system help it resist the ERY shock.

Kinetic and microbial response of activated sludge community to acute and chronic exposure to tetracycline

Current study aimed to discover both kinetic and microbial response of activated sludge biomass to continuous exposure to tetracycline, one of the most frequently detected antibiotics in wastewaters. Respirometric analysis and model evaluation of the oxygen utilization rate profiles generated at critical phases of the experimental period showed that, continuous exposure to tetracycline caused complete suppression of substrate storage aside from mild inhibition on the growth kinetics and it exerted a significant binding action with available organic carbon, leading to less oxygen consumption. Additionally, increase in endogenous decay rates by 1.5 fold was associated with maintenance energy dictated by the presence and production of antibiotic resistance genes, as demonstrated by resistance gene profile. High-throughput sequencing results showed that continuously exposure to tetracycline caused a significant shift in the community structure at species level so that tetracycline resistant bacteria like Arthrobacter sp and Diaphorobacter sp dominated the bacterial community.

Analysis of aerobic granules under the toxic effect of ampicillin in sequencing batch reactors: Performance and microbial community

To study the change of the aerobic granules' microbial community in the present of antibiotics, ampicillin (AMP) was selected as a model component. With acetate as carbon source, different concentrations of AMP (5, 10 and 15 mg L^-1) were applied to the inflow intermittently and the results showed that the stability of the aerobic granules was maintained below 10 mg L^-1 AMP. Simultaneously, under exposure to 5 and 10 mg L^-1 AMP, the COD removal efficiency in the batch reactors remained at 86% and AMP was degraded almost completely with a removal efficiency of 97%. However, the EPS concentration and dehydrogenase activity decreased constantly with increasing AMP dosage. High-throughput sequencing analysis revealed that Proteobacteria was the most prominent phylum in the whole experiment and contributed to the degradation of AMP. The percentages of Azoarcus and Mycoplana increased at 10 mg L^-1 AMP. In addition, Hydrogenophaga and Enterococcus played a key role in the microbial metabolism.

Is the chronic impact of sulfamethoxazole different for slow growing culture? The effect of culture history

The study evaluated impact of sulfamethoxazole on acetate utilization kinetics and microbial community structure using respirometric analysis and pyrosequencing. A fill and draw reactor fed with acetate was sustained at a sludge age of 10 days. Acute impact was assessed by modeling of respirometric data in batch reactors started with sulfamethoxazole doses in the range of 25-200 mg/L. Fill and draw operation resumed with continuous sulfamethoxazole dosing of 50 mg/L and the chronic impact was evaluated with acclimated biomass after 20 days. Acute impact revealed higher maintenance energy requirements, activity reduction and slight substrate binding. Chronic impact resulted in retardation of substrate storage. A fraction of acetate was utilized at a much lower rate with partial biodegradation of sulfamethoxazole by the acclimated biomass. Pyrosequencing indicated that Amaricoccus sp. and an unclassified Bacteroidetes sp., possibly with the ability to co-metabolize sulfamethoxazole, dominated the community.

Biodegradation and reversible inhibitory impact of sulfamethoxazole on the utilization of volatile fatty acids during anaerobic treatment of pharmaceutical industry wastewater

This study evaluated the chronic impact and biodegradability of sulfamethoxazole under anaerobic conditions. For this purpose, a lab-scale anaerobic sequencing batch reactor was operated in a sequence of different phases with gradually increasing sulfamethoxazole doses of 1 to 45 mg/L. Conventional parameters, such as COD, VFA, and methane generation, were monitored with corresponding antimicrobial concentrations in the reactor and the methanogenic activity of the sludge. The results revealed that anaerobic treatment was suitable for pharmaceutical industry wastewater with concentrations of up to 40 mg/L of sulfamethoxazole. Higher levels exerted toxic effects on the microbial community under anaerobic conditions, causing the inhibition of substrate/COD utilization and biogas generation and leading to a total collapse of the reactor. The adverse long-term impact was quite variable for fermentative bacteria and methanogenic achaea fractions of the microbial community based on changes inflicted on the composition of the residual organic substrate and mRNA expression of the key enzymes.

Acute impact of tetracycline on the utilization of acetate by activated sludge sustained under different growth conditions

The study evaluated acute impact of tetracycline on the biodegradation of acetate by microbial cultures acclimated to different growth conditions. Two fill/draw reactors were operated to obtain acclimated cultures at sludge ages of 2 and 10 days. Acclimated biomass seeding was used in two series of batch experiments. The first run served as control and others were started with tetracycline doses of 100mg/L and 400mg/L. Parallel batch reactors were also operated for oxygen uptake rate (OUR) measurements. Acute impact was evaluated by model calibration of OUR, chemical oxygen demand (COD) and intracellular storage profiles. Exposure to tetracycline did not impair COD removal but induced a shift in acetate utilization toward polyhydroxybutyrate (PHB) storage. This shift was more pronounced for fast growing biomass; it identified itself both in related process kinetics and the modified stoichiometry between the magnitude of acetate directly used for microbial growth and converted to PHB.

Influence of an aniline supplement on the stability of aerobic granular sludge

In order to evaluate the stability of aerobic granules in a toxic environment, this study discussed the influence of an aniline supplement on the properties and microbial community of aerobic granules. In the early stages of sequencing batch reactor (SBR) operation, an aniline supplement slightly affected the properties of the aerobic granules (strength, growth rate, SVI and so on). This effect was thereafter removed because of a change in the microbial community and the structure of aerobic granules: with the present of aniline, microbes with biodegradation ability appeared and gathered in the aerobic granules and the aerobic granules densified and settled faster as their SVI decreased to 35 mL/g and settling velocity increased to 41.56 m/h. When a synthetic waste water containing acetate as carbon source was used as influent, aniline (10-500 mg/L) could be degraded in 6 h, at a rate as high as 37.5 mg aniline/(L·h), with a removal rate in excess of 90%, while the effluent COD fell below 100 mg/L from the initial about 2000 mg/L. The aerobic granules cultured by acetate were compact, stable and resistant to aniline.

Acute effect of erythromycin on metabolic transformations of volatile fatty acid mixture under anaerobic conditions

The study explored the acute inhibitory impact of erythromycin on the methanogenic activity of acclimated biomass fed with a volatile fatty acid mixture and acetate alone. Parallel batch reactors were operated for six days, with increasing erythromycin dosing in the range of 1-1000 mg L(-1). Substrate removal was monitored by means of soluble COD and volatile fatty acid (VFA) measurements together with parallel observations on biogas and methane generation. The inhibitory impact was variable with the initial erythromycin dose: At lower doses, the VFA mixture was completely removed but partially utilized, leading to reduced biogas and methane generation, suggesting the analogy of uncompetitive inhibition. At higher doses, propionate utilization was totally impaired and butyrate removal was reduced, but acetate was still fully removed. Remaining VFAs were partly converted to new VFA compound through isomerization and polymerization reactions. High erythromycin doses induced total inactivation of microbial metabolism with negligible methane generation.

Chronic impact of sulfamethoxazole on acetate utilization kinetics and population dynamics of fast growing microbial culture

The study evaluated the chronic impact of sulfamethoxazole on metabolic activities of fast growing microbial culture. It focused on changes induced on utilization kinetics of acetate and composition of the microbial community. The experiments involved a fill and draw reactor, fed with acetate and continuous sulfamethoxazole dosing of 50 mg/L. The evaluation relied on model evaluation of the oxygen uptake rate profiles, with parallel assessment of microbial community structure by 454-pyrosequencing. Continuous sulfamethoxazole dosing inflicted a retardation effect on acetate utilization in a way commonly interpreted as competitive inhibition, blocked substrate storage and accelerated endogenous respiration. A fraction of acetate was utilized at a much lower rate with partial biodegradation of sulfamethoxazole. Results of pyrosequencing with a replacement mechanism within a richer more diversified microbial culture, through inactivation of vulnerable fractions in favor of species resistant to antibiotic, which made them capable of surviving and competing even with a slower metabolic response.