Importance of Methane Oxidation for Microbial Degradation of the Herbicide Bentazone in Drinking Water Production

Abstract

Bentazone is a herbicide, which is frequently detected in groundwater due to its mobility and persistence in aquifers. Groundwater is used as a drinking water source all over the world, and sustainable methods to remove pesticides at low concentrations are urgently needed since pesticide contaminations can adversely affect human health. The aim of this study was to investigate whether microbial bentazone degradation was associated with methane oxidation in full-scale drinking water treatment plants.To this end, we investigated bentazone biodegradation in microcosms with water and filter material from rapid sand filters, or biomass from aeration systems, and we investigated the statistical relation between the presence of methane and bentazone in groundwater abstraction wells. An array of evidence supported an association between bentazone degradation and methane oxidation in the biological treatment process. The biodegradation potential of bentazone was associated with the presence of methane in the raw water at 14 different water works. In contrast, no association was observed with any of the other investigated inorganic energy sources, e.g., ammonium. Addition of acetylene inhibited methane oxidation and the bentazone degradation in filter material from two investigated waterworks. Biomass from the aeration tanks degraded bentazone, but only while oxidizing methane. Bentazone removal rates and methane removal rates correlated significantly across all the experiments with biomass or filter material, with an overall transformation yield of 15 ± 1 × 10 −5 mole BTZ /mole CH4 . This demonstrated that the bentazone degradation was conducted by the same type of process in all the investigated communities, governed by methane oxidation. Furthermore, based on more than 10.000 water analyses from waterworks abstraction wells in Denmark, bentazone was detected significantly less frequent in wells with high methane concentrations (>1 mg/L) than in wells without methane. This suggests that biological treatment of bentazone contamination in drinking water may be achieved using methanotrophs.

Acidophilic methanotrophs: Occurrence, diversity, and possible bioremediation applications

“…sMMO is also able to oxidize several emerging contaminants, including methyl tertiary‐butyl ether (MTBE) (Hesselsoe et al, 2005 ; Steffan et al, 1997 ) and N ‐nitrosodimethylamine (NDMA) among others (Sharp et al, 2005 ). Pharmaceuticals such as sulfamethoxazole (Benner et al, 2015 ) and ibuprofen (Dawas‐Massalha et al, 2014 ), as well as a variety of pesticides including bentazone, dichlorprop, and chlorophenoxy herbicide (Hedegaard et al, 2020 ; Papadopoulou et al, 2019 ), are also degraded by sMMO. 1,4‐Dioxane, which is commonly used as a stabilizer for chlorinated solvents such as 1,1,1‐trichloroethane (TCA), was originally reported to be oxidized by sMMO (Mahendra & Alvarez‐Cohen, 2006 ).…”

Removal of phytotoxins in filter sand used for drinking water treatment

“…Organic trace contaminants can be degraded either by primary metabolism, where microorganisms utilize them as sources of carbon and possibly also nitrogen, phosphorus, or sulphur ( Alexander, 1999 ), or by co-metabolism where contaminants are transformed by enzymes without being used as an energy source ( Vickers, 2017 ). Other studies have shown that co-metabolism by methane oxidizing bacteria in rapid sand filters are relevant for degradation of the pesticide bentazone ( Hedegaard et al, 2020 ). Biological removal was only observed for gramine and sparteine and was primarily of importance at Regnemark waterworks.…”

“…Lab-scale investigations with filter sand have shown that microbiological degradation of pesticides such as bentazone led to complete mineralization ( Hedegaard et al, 2019 ). However, pesticide degradation can depend on certain groups of bacteria, such as methanotrophs ( Hedegaard et al, 2020 ). Since the microbial communities of rapid sand filters depends on inlet water chemistry and age ( Albers et al, 2015 ; Palomo et al, 2016 ), the removal potential of micropollutants might differ between waterworks.…”