MIB and 2,4‐D Removal by Biofilters During Episodic Loading

Abstract

Episodic occurrences of trace organic contaminants may affect their removal by biofilters. Removal of the naturally occurring algal metabolite 2‐methylisoborneol (MIB) and the herbicide 2,4‐dichlorphenoxyacetic acid (2,4‐D) by seven biofilters with an average empty bed contact time (EBCT) of 8.7 min is presented under a range of intermittent exposure conditions with continuous presence of dissolved organic matter. An average 70% removal of both MIB and 2,4‐D was found under constant exposure conditions over seven months. With the use of a pseudo‐first‐order model, much of the variability in removal during this time could be explained by EBCT changes. Microorganisms in the biofilters retained the capacity to biodegrade MIB and 2,4‐D after non‐exposure periods of up to five months. However, after nine months of non‐exposure, the MIB and 2,4‐D removals were lower than with the control biofilter, although the biofilter began to quickly reacclimate to these contaminants.

From full-scale biofilters to bioreactors: Engineering biological metaldehyde removal

“…Studies have shown that biofilms can be quite resilient and, despite not being exposed to high concentrations of a pollutant for several months, they might be able to continue degrading that pollutant due to legacy of degraders within the biofilm and long-term redundancy for biocenosis by facultative degraders. Zearley and Summers (2015) reported that biofilters adapted to MIB and 2,4-D retained their ability to remove these pollutants after non-exposure periods of up to 5 months. This shows there may be potential to use a biological technology seasonally for metaldehyde removal.…”

“…These limits include metaldehyde, a widely used molluscicide first identified in drinking water in 2008 (Water UK, 2008). Despite accounting for just 1-2% of all pesticides applied in the UK (FERA, 2013), metaldehyde was responsible for over 90% of the total DWD failures for pesticides in England in and 2015(DWI, 2017. Metaldehyde is uncharged, highly soluble and has a low molecular weight, which make it highly mobile in the environment.…”

North American biofiltration practices

“…In addition to removal of particles and pathogens, biofilters naturally biodegrade organic carbon, thereby reducing formation of disinfection byproducts, reducing regrowth and improving disinfectant stability in distribution systems (Chowdhury et al, ; Emelko, Huck, Coffey, & Smith, ; Evans, Opitz, Daniel, & Schulz, ; Evans et al, ; Wert, Neemann, Rexing, & Zegers, ). Inorganic compounds, such as iron, manganese, ammonia, and nitrate (Bouwer & Crowe, ; Kohl & Dixon, ; Lauderdale et al, ; Lauderdale, Brown, Chadik, & Kirisits, ), and trace organic contaminants, such as algal toxins, tastes and odors, and some contaminants of emerging concern (Evans et al, ; Lauderdale et al, ; Wunder, ; Zearley & Summers, ), are also biodegradable. Key biofilter design factors, which may optimize biodegradation of these contaminants, include water quality, process criteria, operational procedures, and backwashing methods.…”