The pesticide mineralization capacity in sand filter units of drinking water treatment plants (DWTP): Consistency in time and relationship with intake water and sand filter characteristics.

Sand filters (SFs) are commonly applied in drinking water treatment plants (DWTPs) for removal of iron and manganese but also show potential for microbial degradation of pesticide residues. The latter is advantageous in case the intake water contains pesticide residues. However, whether this involves mineralization suggesting no generation of harmful transformation products, its consistency over time, and how this ability relates to physicochemical and biological characteristics of the DWTP intake water and the SFs is unknown. The capacity to mineralize the herbicides bentazon and 2-methyl-4-chlorophenoxyacetic acid (MCPA) was examined in SF samples from 11 DWTPs differing in operation, intake water composition and pesticide contamination level. MCPA was mineralized in all biologically active SFs while mineralization of bentazon occurred rarely. Mineralization of both compounds was consistent in time and across samples taken from different SF units of the same DWTP. Kinetic modelling of mineralization curves suggested the occurrence of growth linked bentazon and MCPA mineralization in several SF samples. Multivariate analysis correlating intake water/SF characteristics with pesticide mineralization indicated that pesticide mineralization capacity depended on a range of intake water characteristics, but was not necessarily explained by the presence of the pesticide in the intake water and hence the in situ exposure of the SF community to the pesticide. This was supported by testing a sample from DWTP Kluizen for its capacity to mineralize 5 other pesticides including pesticides not present or occasionally present in the intake water. All of those pesticides were mineralized as well.

Biocarriers Improve Bioaugmentation Efficiency of a Rapid Sand Filter for the Treatment of 2,6-Dichlorobenzamide-Contaminated Drinking Water.

Aminobacter sp. MSH1 immobilized in an alginate matrix in porous stones was tested in a pilot system as an alternative inoculation strategy to the use of free suspended cells for biological removal of micropollutant concentrations of 2,6-dichlorobenzamide (BAM) in drinking water treatment plants (DWTPs). BAM removal rates and MSH1 cell numbers were recorded during operation and assessed with specific BAM degradation rates obtained in lab conditions using either freshly grown cells or starved cells to explain reactor performance. Both reactors inoculated with either suspended or immobilized cells showed immediate BAM removal under the threshold of 0.1 µg/L, but the duration of sufficient BAM removal was 2-fold (44 days) longer for immobilized cells. The longer sufficient BAM removal in case of immobilized cells compared to suspended cells was mainly explained by a lower initial loss of MSH1 cells at operational start due to volume replacement and shear. Overall loss of activity in the reactors though was due to starvation, and final removal rates did not differ between reactors inoculated with immobilized and suspended cells. Management of assimilable organic carbon, in addition to cell immobilization, appears crucial for guaranteeing long-term BAM degradation activity of MSH1 in DWTP units.

Mineralization of the Common Groundwater Pollutant 2,6-Dichlorobenzamide (BAM) and its Metabolite 2,6-Dichlorobenzoic Acid (2,6-DCBA) in Sand Filter Units of Drinking Water Treatment Plants.

The intrinsic capacity to mineralize the groundwater pollutant 2,6-dichlorobenzamide (BAM) and its metabolite 2,6-dichlorobenzoic acid (2,6-DCBA) was evaluated in samples from sand filters (SFs) of drinking water treatment plants (DWTPs). Whereas BAM mineralization occurred rarely and only in SFs exposed to BAM, 2,6-DCBA mineralization was common in SFs, including those treating uncontaminated water. Nevertheless, SFs treating BAM contaminated water showed the highest 2,6-DCBA mineralization rates. For comparison, 2,6-DCBA and BAM mineralization were determined in various topsoil samples. As in SF samples, BAM mineralization was rare, whereas 2,6-DCBA mineralization capacity appeared widespread, with high mineralization rates found especially in forest soils. Multivariate analysis showed that in both SF and soil samples, high 2,6-DCBA mineralization correlated with high organic carbon content. Adding a 2,6-DCBA degradation deficient mutant of the BAM mineralizing Aminobacter sp. MSH1 confirmed that 2,6-DCBA produced from BAM is rapidly mineralized by the endogenous microbial community in SFs showing intrinsic 2,6-DCBA mineralization. This study demonstrates that (i) 2,6-DCBA mineralization is widely established in SFs of DWTPs, allowing the mineralization of 2,6-DCBA produced during BAM degradation and (ii) the first metabolic step in BAM mineralization is rare in microbial communities, rather than its further degradation beyond 2,6-DCBA.