Examining relationships between total silver concentration and Sil silver resistance genes in domestic wastewater treatment plants.

AIMS: The overarching aims of this study were to determine if microbes found in wastewater treatment plants (WWTPs) carry silver resistance genes and ascertain whether a relationship exists between silver loading and sil silver resistance gene copy numbers. METHODS AND RESULTS: Activated sludge samples were collected from 17 WWTPs across the United States and characterized for chemical oxygen demand (COD) and total silver concentration. Gene copy numbers were quantified using qPCR for four common silver resistance genes (silC, silP, silR and silS). Spearman correlation analyses were performed to examine associations between three WWTP characteristics (i.e. size, COD and total silver concentration) and sil gene copy numbers. sil genes were found in all activated sludge samples, however the quantity of gene copy numbers was inconsistent. Of the sil genes screened, silS was the most abundant, followed by silR. Gene copy numbers for silC and silP were generally similar and overall lower than silS and silR. CONCLUSIONS: Neither individual or combined sil gene copy numbers correlated significantly with total silver concentration, suggesting either the presence of alternate mechanisms of silver resistance or that a critical silver concentration threshold within WWTPs was not met that would require specific resistance against silver. SIGNIFICANCE AND IMPACT OF THIS STUDY: To the authors' knowledge, this is one of the first studies to measure the prevalence of sil genes in engineered systems. Results from this study suggest that at least four silver resistance genes are commonly found within WWTP-activated sludge, however it is unclear if these genes are being expressed under current total silver loadings.

Evaluating the role of total organic carbon in predicting the treatment efficacy of biosand filters for the removal of Vibrio cholerae in drinking water during startup.

AIMS: In biosand filters (BSF), treatment is largely driven by the development of a biolayer (schmutzdecke) which establishes itself during the startup phase. In this study, the effect of changing influent total organic carbon (TOC) loading on the removal efficiency of Vibrio cholerae in laboratory-operated BSFs was quantified. METHODS AND RESULTS: BSFs were charged with high, medium or low TOC influents and removal efficacy and schmutzdecke composition was monitored over 2 months. The highest V. cholerae removal efficiencies were observed in the BSF receiving the lowest TOC. Schmutzdecke composition was found to be influenced by influent TOC, in terms of microbial community structure and amount of extracellular polymeric substance (EPS). CONCLUSIONS: Physical/chemical attachment was shown to be important during startup. The BSF receiving influent water with lower TOC had a higher attachment coefficient than the BSF receiving high TOC water, suggesting more physical/chemical treatment in the lower TOC BSF. The high TOC BSF had more EPS than did the biofilm from the low-TOC BSF, suggesting that schmutzdecke effects may be more significant at high TOC. SIGNIFICANCE AND IMPACT OF THE STUDY: Overall, this study confirms that influent water characteristics will affect BSF treatment efficacy of V. cholerae especially during the startup phase.

Evaluating the impacts of triclosan on wastewater treatment performance during startup and acclimation.

Triclosan (TCS) is a broad range antimicrobial agent used in many personal care products, which is commonly discharged to wastewater treatment facilities (WWTFs). This study examined the impact of TCS on wastewater treatment performance using laboratory bench-scale sequencing batch reactors (SBRs) coupled with anaerobic digesters. The SBRs were continuously fed synthetic wastewater amended with or without 0.68 µM TCS, with the aim of determining the effect of chronic TCS exposure as opposed to a pulse TCS addition as previously studied. Overall, the present study suggests inhibition of nitrogen removal during reactor startup. However, NH4+ removal fully rebounded after 63 days, suggesting acclimation of the associated microbial communities to TCS. An initial decrease in microbial community diversity was observed in the SBRs fed TCS as compared to the control SBRs, followed by an increase in community diversity, which coincided with the increase in NH4+ removal. Elevated levels of NO3- and NO2- were found in the reactor effluent after day 58, however, suggesting ammonia oxidizing bacteria rebounding more rapidly than nitrogen oxidizing bacteria. Similar effects on treatment efficiencies at actual WWTFs have not been widely observed, suggesting that continuous addition of TCS in their influent may have selected for TCS-resistant nitrogen oxidizing bacteria.

Determining the ecological impacts of organic contaminants in biosolids using a high-throughput colorimetric denitrification assay: a case study with antimicrobial agents.

Land application accounts for ∼ 50% of wastewater solid disposal in the United States. Still, little is known regarding the ecological impacts of nonregulated contaminants found in biosolids. Because of the myriad of contaminants, there is a need for a rapid, high-throughput method to evaluate their ecotoxicity. Herein, we developed a novel assay that measures denitrification inhibition in a model denitrifier, Paracoccus denitrificans Pd1222. Two common (triclosan and triclocarban) and four emerging (2,4,5 trichlorophenol, 2-benzyl-4-chlorophenol, 2-chloro-4-phenylphenol, and bis(5-chloro-2-hydroxyphenyl)methane) antimicrobial agents found in biosolids were analyzed. Overall, the assay was reproducible and measured impacts on denitrification over 3 orders of magnitude exposure. The lowest observable adverse effect concentrations (LOAECs) were 1.04 µM for triclosan, 3.17 µM for triclocarban, 0.372 µM for bis-(5-chloro-2-hydroxyphenyl)methane, 4.89 µM for 2-chloro-4-phenyl phenol, 45.7 µM for 2-benzyl-4-chorophenol, and 50.6 µM for 2,4,5-trichlorophenol. Compared with gene expression and cell viability based methods, the denitrification assay was more sensitive and resulted in lower LOAECs. The increased sensitivity, low cost, and high-throughput adaptability make this method an attractive alternative for meeting the initial testing regulatory framework for the Federal Insecticide, Fungicide, and Rodenticide Act, and recommended for the Toxic Substances Control Act, in determining the ecotoxicity of biosolids-derived emerging contaminants.

A New Perspective on Sustainable Soil Remediation-Case Study Suggests Novel Fungal Genera Could Facilitate in situ Biodegradation of Hazardous Contaminants.

Deciding upon a cost effective and sustainable method to address soil pollution is a challenge for many remedial project managers. High pressure to quickly achieve cleanup goals pushes for energy-intensive remedies that rapidly address the contaminants of concern with established technologies, often leaving little room for research and development especially for slower treatment technologies, such as bioremediation, for the more heavily polluted sites. In the present case study, new genomic approaches have been leveraged to assess fungal biostimulation potential in soils polluted with particularly persistent hydrophobic contaminants. This new approach provides insights into the genetic functions available at a given site in a way never before possible. In particular, this article presents a case study where next generation sequencing (NGS) has been used to categorize fungi in soils from the Atlantic Wood Industries Superfund site in Portsmouth, Virginia. Data suggest that original attempts to harness fungi for bioremediation may have focused on fungal genera poorly suited to survive under heavily polluted site conditions, and that more targeted approaches relying on native indigenous fungi which are better equipped to survive under site specific conditions may be more appropriate.