The effect of disinfectants and antiseptics on co- and cross-selection of resistance to antibiotics in aquatic environments and wastewater treatment plants.

The outbreak of the SARS-CoV-2 pandemic led to increased use of disinfectants and antiseptics (DAs), resulting in higher concentrations of these compounds in wastewaters, wastewater treatment plant (WWTP) effluents and receiving water bodies. Their constant presence in water bodies may lead to development and acquisition of resistance against the DAs. In addition, they may also promote antibiotic resistance (AR) due to cross- and co-selection of AR among bacteria that are exposed to the DAs, which is a highly important issue with regards to human and environmental health. This review addresses this issue and provides an overview of DAs structure together with their modes of action against microorganisms. Relevant examples of the most effective treatment techniques to increase the DAs removal efficiency from wastewater are discussed. Moreover, insight on the resistance mechanisms to DAs and the mechanism of DAs enhancement of cross- and co-selection of ARs are presented. Furthermore, this review discusses the impact of DAs on resistance against antibiotics, the occurrence of DAs in aquatic systems, and DA removal mechanisms in WWTPs, which in principle serve as the final barrier before releasing these compounds into the receiving environment. By recognition of important research gaps, research needs to determine the impact of the majority of DAs in WWTPs and the consequences of their presence and spread of antibiotic resistance were identified.

Effect of low temperature and municipal wastewater organic loading on anaerobic granule reactor performance.

Biogas production and municipal wastewater COD removal at low temperatures by granulated anaerobic biomass were investigated. Two anaerobic granule reactors were operated continuously for 1025 days by stepwise increase of organic loading from 1.3 to 15.2 g CODdissolved·l-1·d-1 at 25, 16, 12, 8.5, 5.5, and 2.5 °C. The sustained reactor performance was evaluated by COD removal efficiency, methane production, and microbial community analysis. Stable COD removal of 50-70% were achieved at 25-8.5 °C and up to 15 g CODdissolved·l-1·d-1, and no significant temperature effect was observed on specific methane production rate and yield. Below 8.5 °C, COD removal and methane yields reduced, but still significant methane formation was observed even at 2.5 °C. More than 90% of COD removed was converted to methane. Methanogenic archaea communities showed that temperature changes affected the major methane formation pathways, which explains temperature adaptability of the granules.

A Review on Occurrence and Spread of Antibiotic Resistance in Wastewaters and in Wastewater Treatment Plants: Mechanisms and Perspectives.

This paper reviews current knowledge on sources, spread and removal mechanisms of antibiotic resistance genes (ARGs) in microbial communities of wastewaters, treatment plants and downstream recipients. Antibiotic is the most important tool to cure bacterial infections in humans and animals. The over- and misuse of antibiotics have played a major role in the development, spread, and prevalence of antibiotic resistance (AR) in the microbiomes of humans and animals, and microbial ecosystems worldwide. AR can be transferred and spread amongst bacteria via intra- and interspecies horizontal gene transfer (HGT). Wastewater treatment plants (WWTPs) receive wastewater containing an enormous variety of pollutants, including antibiotics, and chemicals from different sources. They contain large and diverse communities of microorganisms and provide a favorable environment for the spread and reproduction of AR. Existing WWTPs are not designed to remove micropollutants, antibiotic resistant bacteria (ARB) and ARGs, which therefore remain present in the effluent. Studies have shown that raw and treated wastewaters carry a higher amount of ARB in comparison to surface water, and such reports have led to further studies on more advanced treatment processes. This review summarizes what is known about AR removal efficiencies of different wastewater treatment methods, and it shows the variations among different methods. Results vary, but the trend is that conventional activated sludge treatment, with aerobic and/or anaerobic reactors alone or in series, followed by advanced post treatment methods like UV, ozonation, and oxidation removes considerably more ARGs and ARB than activated sludge treatment alone. In addition to AR levels in treated wastewater, it examines AR levels in biosolids, settled by-product from wastewater treatment, and discusses AR removal efficiency of different biosolids treatment procedures. Finally, it puts forward key-points and suggestions for dealing with and preventing further increase of AR in WWTPs and other aquatic environments, together with a discussion on the use of mathematical models to quantify and simulate the spread of ARGs in WWTPs. Mathematical models already play a role in the analysis and development of WWTPs, but they do not consider AR and challenges remain before models can be used to reliably study the dynamics and reduction of AR in such systems.

Engineered methanotrophic syntrophy in photogranule communities removes dissolved methane.

The anaerobic treatment of wastewater leads to the loss of dissolved methane in the effluent of the treatment plant, especially when operated at low temperatures. The emission of this greenhouse gas may reduce or even offset the environmental gain from energy recovery through anaerobic treatment. We demonstrate here the removal and elimination of these comparably small methane concentrations using an ecologically engineered methanotrophic community harbored in oxygenic photogranules. We constructed a syntrophy between methanotrophs enriched from activated sludge and cyanobacteria residing in photogranules and maintained it over a two-month period in a continuously operated reactor. The novel community removed dissolved methane during stable reactor operation by on average 84.8±7.4% (±standard deviation) with an average effluent concentration of dissolved methane of 4.9±3.7 mg CH4∙l-1. The average methane removal rate was 26 mg CH4∙l-1∙d-1, with an observed combined biomass yield of 2.4 g VSS∙g CH4 -1. The overall COD balance closed at around 91%. Small photogranules removed methane more efficiently than larger photogranule, likely because of a more favorable surface to volume ratio of the biomass. MiSeq amplicon sequencing of 16S and 23S rRNA revealed a potential syntrophic chain between methanotrophs, non-methanotrophic methylotrophs and filamentous cyanobacteria. The community composition between individual photogranules varied considerably, suggesting cross-feeding between photogranules of different community composition. Methanotrophic photogranules may be a viable option for dissolved methane removal as anaerobic effluent post-treatment.

Wastewater characterisation by combining size fractionation, chemical composition and biodegradability.

The potential for resource recovery from wastewater can be evaluated based on a detailed characterisation of wastewater. In this paper, results from fractionation and characterisation of two distinct wastewaters are reported. Using tangential flow filtration, the wastewater was fractionated into 10 size fractions ranging from 1 kDa to 1 mm, wherein the chemical composition and biodegradability were determined. Carbohydrates were dominant in particulate size fractions larger than 100 µm, indicating a potential of cellulose recovery from these fractions. While the particulate size fractions between 0.65 and 100 µm show a potential as a source for biofuel production due to an abundance of saturated C16 and C18 lipids. Both wastewaters were dominated by particulate (>0.65 µm), and oligo- and monomeric (<1 kDa) COD. Polymeric (1-1000 kDa) and colloidal (1000 kDa-0.65 µm) fractions had a low COD content, expected due to degradation in the sewer system upstream of the wastewater treatment plant. Biodegradation rates of particulate fractions increase with decreasing size. However, this was not seen in polymeric fractions where degradation rate was governed by chemical composition. Analytical validation of molecular weight and particle size distribution showed below filter cut-off retention of particles and polymers close to nominal cut-off, shifting the actual size distribution.

Starch degradation and intermediate dynamics in flocculated and dispersed microcosms.

A large fraction of the organic substrate in municipal wastewater is particulate. Prior to uptake, particles have to be degraded through potentially a range of intermediates. However, research on intermediate dynamics during particle hydrolysis is limited. In this paper, batch experiments on flocculated and dispersed biomass microcosms using starch as particulate substrate are reported. Overall hydrolysis rate was not significantly different between the two systems. Particle colonization, and increased particle porosity in combination with particle breakup, led to increased substrate availability over time. Particle breakup was more important for flocculated biomass, while increased particle porosity and particle colonization played a larger role for dispersed biomass. During particle degradation intermediates were formed; however, all intermediate polymer sizes were not formed to the same extent. This can be explained by non-random enzymatic degradation, where some products are preferred over others. Intermediates' dynamics also depend on the biomass structure, and in a floc-based system, diffusion limitations allow glucose to accumulate in the system.

Protein phosphatase 2A holoenzyme is targeted to peroxisomes by piggybacking and positively affects peroxisomal ß-oxidation.

The eukaryotic, highly conserved serine (Ser)/threonine-specific protein phosphatase 2A (PP2A) functions as a heterotrimeric complex composed of a catalytic (C), scaffolding (A), and regulatory (B) subunit. In Arabidopsis (Arabidopsis thaliana), five, three, and 17 genes encode different C, A, and B subunits, respectively. We previously found that a B subunit, B'θ, localized to peroxisomes due to its C-terminal targeting signal Ser-Ser-leucine. This work shows that PP2A C2, C5, andA2 subunits interact and colocalize with B'θ in peroxisomes. C and A subunits lack peroxisomal targeting signals, and their peroxisomal import depends on B'θ and appears to occur by piggybacking transport. B'θ knockout mutants were impaired in peroxisomal ß-oxidation as shown by developmental arrest of seedlings germinated without sucrose, accumulation of eicosenoic acid, and resistance to protoauxins indole-butyric acid and 2,4-dichlorophenoxybutyric acid. All of these observations strongly substantiate that a full PP2A complex is present in peroxisomes and positively affects ß-oxidation of fatty acids and protoauxins.

Naphthalene biodegradation in temperate and arctic marine microcosms.

Naphthalene, the smallest polycyclic aromatic hydrocarbon (PAH), is found in abundance in crude oil, its major source in marine environments. PAH removal occurs via biodegradation, a key process determining their fate in the sea. Adequate estimation of PAH biodegradation rates is essential for environmental risk assessment and response planning using numerical models such as the oil spill contingency and response (OSCAR) model. Using naphthalene as a model compound, biodegradation rate, temperature response and bacterial community composition of seawaters from two climatically different areas (North Sea and Arctic Ocean) were studied and compared. Naphthalene degradation was followed by measuring oxygen consumption in closed bottles using the OxiTop(®) system. Microbial communities of untreated and naphthalene exposed samples were analysed by polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) and pyrosequencing. Three times higher naphthalene degradation rate coefficients were observed in arctic seawater samples compared to temperate, at all incubation temperatures. Rate coefficients at in situ temperatures were however, similar (0.048 day(-1) for temperate and 0.068 day(-1) for arctic). Naphthalene biodegradation rates decreased with similar Q10 ratios (3.3 and 3.5) in both seawaters. Using the temperature compensation method implemented in the OSCAR model, Q10 = 2, biodegradation in arctic seawater was underestimated when calculated from the measured temperate k1 value, showing that temperature difference alone could not predict biodegradation rates adequately. Temperate and arctic untreated seawater communities were different as revealed by pyrosequencing. Geographic origin of seawater affected the community composition of exposed samples.

Estimation of hydrocarbon biodegradation rates in marine environments: a critical review of the Q10 approach.

Offshore oil & gas industry is moving exploration and production activities into Arctic and deep water regions. Governmental regulations require environmental impact assessments before operations to evaluate the possible effects of accidental oil releases. These are often performed by numerical fate models, like the Oil Spill Contingency and Response (OSCAR) model, which has become an industry standard in Norway. In this model, biodegradation rates are adjusted to local conditions by temperature compensation according to a Q10 approach. Q10 is the multiplier by which rates of enzymatic reactions increase at a 10 °C temperature rise. Herein, this Q10 approach implemented in the OSCAR model is investigated based on published data and novel obtained results. Overall, biodegradation rate predictions calculated by temperature compensation are found to be questionable, and choosing one universal Q10 value is considered not feasible. The high variation in Q10 values is herein attributed to indirect effects of temperature.

Effects of initial molecular weight on removal rate of dextran in biofilms.

Degradation kinetics of different size dextrans in a biofilm reactor were evaluated. Degradation rates of dextran standards, measured as time series of oxygen utilisation rates, decreased with increasing initial molecular weight. Removal of bulk phase total organic carbon with time was highly correlated (R2>0.99) and could be modelled with variable half-order degradation rate expressions. A power correlation between initial molecular weight and the variable half-order degradation rate coefficient was found for polymers in the range 6-500 kDa. Degradation of dextran in the colloid size range (MW>1 Mda) did not follow the same kinetics. Reductions in the observed removal rate with polymer size can be explained by the effect of reduced diffusivities of the substrate, without assuming reaction rate effects.