Triclosan in contact with activated sludge and its impact on phosphate removal and microbial community

Modeling and optimization of triclosan biodegradation by the newly isolated Bacillus sp. DL4: kinetics and pathway speculation

Triclosan is a widely used antibacterial agent and disinfectant, and its overuse endangered ecological safety and human health. Therefore, reducing residual TCS concentrations in the environment is an urgent issue. Bacillus sp. DL4, an aerobic bacterium with TCS biodegradability, was isolated from pharmaceutical wastewater samples. Response surface methodology (RSM) and artificial neural network (ANN) were carried out to optimize and verify the different condition variables, and the optimal growth conditions of strain DL4 were obtained (35 °C, initial pH 7.31, and 5% v/v). After 48 h of cultivation under the optimal conditions, the removal efficiency of strain DL4 on TCS was 95.89 ± 0.68%, which was consistent with the predicted values from RSM and ANN models. In addition, higher R2 value and lower MSE and ADD values indicated that the ANN model had a stronger predictive capability than the RSM model. Whole genome sequencing results showed that many functional genes were annotated in metabolic pathways related to TCS degradation (e.g., amino acid metabolism, xenobiotics biodegradation and metabolism, carbohydrate metabolism). Main intermediate metabolites were identified during the biodegradation process by liquid chromatography-mass spectrometry (LC-MS), and a possible pathway was hypothesized based on the metabolites. Overall, this study provides a theoretical foundation for the characterization and mechanism of TCS biodegradation in the environment by Bacillus sp. DL4.

Performance of an anaerobic-oxic-anoxic (AOA) system in the simultaneous removal of nutrients and triclosan and bacterial community

The constant presence of triclosan (TCS) in surface water and wastewater has been verified due to its application in several pharmaceutical and personal care products. Thus, removing this emerging contaminant is essential to minimize the contamination of water bodies. The anaerobic-aerobic-anoxic (AOA) system is an innovative alternative that combines the removal of nutrients and triclosan. This study focuses on the simultaneous removal of carbonaceous matter, nitrogen, phosphorus, and triclosan in a continuous pilot-scale AOA system from synthetic wastewater. The upflow system, in series, was operated at hydraulic retention time (HRT) of 8 h and a flowrate of 2.40 L h-1. Glucose (190 mg L-1) was added to the anoxic reactor as the external carbon source. Besides that, bacterial community structure was investigated using 16S rRNA sequencing in each reactor. The system achieved average removal efficiencies of 96% (14.03 g d-1) for Chemical Oxygen Demand (COD), 85% (2.64 g d-1) for Total Kjeldahl Nitrogen (TKN), 88% (1.40 g d-1) for Total Ammonia Nitrogen (TAN), 20% (0.12 g d-1) for Total Phosphorus (TP), and 93% (1.87 μg d-1) for Triclosan (TCS). The phyla Proteobacteria, Firmicutes, Bacteroidetes, and Chloroflexi were found in greater abundance. The main genera identified were Anaeromusa, Aeromonas, Azospira, Clostridium, and Lactococcus. The organisms related to phylum and genus corroborate the involved processes and the removal performance achieved. In addition, Lactococcus, Thermomonas, Ferruginibacter, and Dechloromonas were involved in triclosan biodegradation. The anaerobic-oxic-anoxic system successfully removed carbonaceous, nitrogenous matter, and triclosan, with glucose increasing the denitrifying activity.

Revealing mechanisms of triclosan on the removal and distribution of nitrogen and phosphorus in microalgal-bacterial symbiosis system

Microalgal-bacterial symbiosis (MABS) system performs synergistic effect on the reduction of nutrients and carbon emissions in the water treatment process. However, antimicrobial agents are frequently detected in water, which influence the performance of MABS system. In this study, triclosan (TCS) was selected to reveal the effects and mechanisms of antimicrobial agents on MABS system. Results showed that the removal efficiencies of chemical oxygen demand, NH4+-N and total phosphorus decreased by 3.0%, 24.0% and 14.3% under TCS stress. In contrast, there were no significant decrease on the removal effect of total nitrogen. Mechanism analysis showed that both the growth rate of microorganisms and the nutrients retention capacity of extracellular polymeric substances were decreased. The intracellular accumulation for nitrogen and phosphorus was promoted due to the increased cytomembrane permeability caused by lipid peroxidation. Moreover, microalgae were dominant in MABS system with ratio between microalgae and bacteria of more than 5.49. The main genus was Parachlorella, with abundance of more than 90%. Parachlorella was highly tolerant to TCS, which might be conductive to maintain its survival. This study revealed the nutrients pathways of MABS system under TCS stress, and helped to optimize the operation of MABS system.

Advanced simultaneous nitrogen and phosphorus removal for non-sterile wastewater through a novel coupled yeast-sludge system: Performance, microbial interaction, and mechanism

A novel coupled yeast-sludge system (CYSS) was constructed by the yeast Candida sp. PNY integrated with activated sludge to treat non-sterile mainstream wastewater. After 240-day cultivation, compared with single activated sludge, simultaneous removal efficiency of total organic carbon (TOC), nitrogen and phosphorus increased by 19.5% (176.34 mg TOC g^-1 d^-1), 21.3% (11.25 mg TN g^-1 d^-1) and 15.0% (6.95 mg TP g^-1 d^-1), respectively, while the amount of sludge reduced by 50%. Amplicon sequencing analysis showed that the abundance of Nitrosomonas, Nitrospira, Zoogloea, Dechloromonas, and Candidatus Accumulibacter significantly decreased to 0% on Day 200. Abundance of nirS and nirK for denitrification significantly decreased in CYSS by quantitative PCR (qPCR), and the copies of nirS and nirK were 3.37-fold and 1.71-fold decrease from Day 0 to Day 240, respectively. The results of Fluorescence in situ hybridization and co-occurrence network showed that Candida sp. PNY predominated its distribution in CYSS, and strongly connected with environmental variables based on network analysis. Furthermore, this study reconstructed the carbon, nitrogen and phosphorus metabolic pathways of the CYSS based on metagenomics.

Degradation of Triclosan in the Water Environment by Microorganisms: A Review

Triclosan (TCS), a kind of pharmaceuticals and personal care products (PPCPs), is widely used and has had a large production over years. It is an emerging pollutant in the water environment that has attracted global attention due to its toxic effects on organisms and aquatic ecosystems, and its concentrations in the water environment are expected to increase since the COVID-19 pandemic outbreak. Some researchers found that microbial degradation of TCS is an environmentally sustainable technique that results in the mineralization of large amounts of organic pollutants without toxic by-products. In this review, we focus on the fate of TCS in the water environment, the diversity of TCS-degrading microorganisms, biodegradation pathways and molecular mechanisms, in order to provide a reference for the efficient degradation of TCS and other PPCPs by microorganisms.

Coagulants put phosphate-accumulating organisms at a competitive disadvantage with glycogen-accumulating organisms in enhanced biological phosphorus removal system

Enhanced biological phosphorus removal (EBPR) process is susceptible to the changed operation condition, which results in an unstable treatment performance. In this work, long-term effect of coagulants addition, aluminum salt for the reactor R₁ and iron salt for the reactor R₂, on EBPR systems was comprehensively evaluated. Results showed that during the initial 30 days' coagulant addition, effluent chemical oxygen demand and phosphorus can be reduced below 25 and 0.5 mg·L^-1, respectively. Further supply of metal salts would stimulate microbial extracellular polymeric substance excretion and induce reactive oxygen species accumulation, which destroyed the cell membrane integrity and deteriorated the phosphorus removal performance. Moreover, coagulants would decrease the relative abundance of Candidatus Accumulibacter while increase the relative abundance of Candidatus Competibacter, leading phosphors accumulating organisms in a disadvantage position. The results of this work might be valuable for the operation of chemical assisted biological phosphorus removal bioreactor.