Microbial pesticide removal in rapid sand filters for drinking water treatment – Potential and kinetics

Abstract

Filter sand samples, taken from aerobic rapid sand filters used for treating groundwater at three Danish waterworks, were investigated for their pesticide removal potential and to assess the kinetics of the removal process. Microcosms were set up with filter sand, treated water, and the pesticides or metabolites mecoprop (MCPP), bentazone, glyphosate and p-nitrophenol were applied in initial concentrations of 0.03-2.4 μg/L. In all the investigated waterworks the concentration of pesticides in the water decreased - MCPP decreased to 42-85%, bentazone to 15-35%, glyphosate to 7-14% and p-nitrophenol 1-3% - from the initial concentration over a period of 6-13 days. Mineralisation of three out of four investigated pesticides was observed at Sjælsø waterworks Plant II - up to 43% of the initial glyphosate was mineralised within six days. At Sjælsø waterworks Plant II the removal kinetics of bentazone revealed that less than 30 min was needed to remove 50% of the bentazone at all the tested initial concentrations (0.1-2.4 μg/L). Increased oxygen availability led to greater and faster removal of bentazone in the microcosms. After 1 h, bentazone removal (an initial bentazone concentration of 0.1 μg/L) increased from 0.21%/g filter sand to 0.75%/g filter sand, when oxygen availability was increased from 0.28 mg O2/g filter sand to 1.09 mg O2/g filter sand. Bentazone was initially cleaved in the removal process. A metabolite, which contained the carbonyl group, was removed rapidly from the water phase and slowly mineralised after 24 h, while a metabolite which contained the benzene-ring was still present in the water phase. However, the microbial removal of this metabolite was initiated over seven days.

Mecoprop (MCPP) removal in full-scale rapid sand filters at a groundwater-based waterworks

“…However, an adaptation phase of more than 16 days is required before MCPP degradation is initiated in aquifer material (Agertved et al, 1992;Tuxen et al, 2000;Janniche et al, 2010). Filter sand that has not previously been exposed to pesticides is able to remove pesticides without an adaptation phase (Hedegaard and Albrechtsen, 2014) and in the current laboratory experiments degradation of MCPP was also initiated immediately ( Figure 7). However, the secondary filters at Kerteminde Waterworks had been exposed to concentrations of MCPP for at least nine years prior to these investigations (Figure 1).…”

“…The complete removal in Filter line 1 might simply be due to a longer reaction time in the filter; otherwise, the longer contact time could cause greater biomass and thereby the increased microbial degradation of MCPP in the filter. Other research has also indicated that longer contact time has a positive effect on the removal of micro pollutants in rapid sand filters (Hedegaard and Albrechtsen, 2014;Zuehlke et al, 2007).…”

“…Though lab-scale studies have shown a biological removal potential of pharmaceuticals and pesticides (Zearley and Summers, 2012;Hedegaard and Albrechtsen, 2014), it is still uncertain whether there is a similar removal potential in full-scale rapid sand filters and the biological chemical processes involved remain unknown (Benner et al, 2013).…”

Clean Water for Developing Countries

“…Apart from bacterial contamination, pesticides in water are also a major concern. In a recent study, Hedegaard et al (40) investigated the effect of rapid sand filters for treating contaminated groundwater at three Danish waterworks. They found that the filters could effectively remove pesticides such as bentazone, glyphosate, and p-nitrophenol.…”

Using an Attapulgite-Activated Carbon Composite Ceramisite Biofilter to Remove Dibutyl Phthalate from Source Water

“…A biofilter with granular filter materials has been considered as a viable option for drinking water treatment, allowing for microorganisms in the source water to attach to the media surface [13]. It had been reported that various kinds of emerging organic pollutants could be removed in biofilters, including geosmin [14], 17β-estradiol [15], mecoprop, bentazone, glyphosate, p-nitrophenolat [16], dimethylamine [17], and carbofuran [18], etc. Although granular activated carbon (GAC) has been widely used as filter media [14][15], its high cost and potential loss during backwashing are hurdles for its direct application in a rapid filter.…”