Abstract
A study was conducted at a water treatment plant to optimize parallel rapid gravity biofilters for dissolved organic matter (DOM) removal. The biofilters treat urban and agriculturally impacted river water using a commercial non-adsorptive, expanded-clay filter medium. The study aimed to locate the optimal operating conditions via experimental manipulation of the biofilter empty bed contact time (EBCT) during full-scale operation at the plant. During a two-month experiment, contact times in four parallel biofilters were switched to and maintained at 15, 30, 50, and 80 min by manipulating the hydraulic loading on each filter. The removal efficiency of organic matter fractions increased with EBCT for dissolved organic carbon (DOC) and microbial humic-like (F290/420) and protein-like (F280/340) fluorescent organic matter. Other DOM fractions were largely unaffected by biofiltration, or at slightly higher concentrations in the effluent. Protein-like fluorescence is associated with labile organic matter fractions, which are known to be removed poorly by drinking water treatment barriers apart from biological filters. The results suggest that long contact times (>30 min) have advantages for the operation of some biological filters, especially if placed ahead of barriers that are sensitive to biofouling, e.g., membranes.
Highlights
Drinking waters around the world are produced from raw waters that contain natural organic matter, i.e., organic chemicals derived from living and dead organisms.[1]
This study examined the role of the empty bed contact time (EBCT) on the dissolved organic matter (DOM) removal performance by Filtralite biofilters at full scale
Over 2 months, rapid gravity biofilters operating in parallel at a full-scale treatment plant were manipulated to allow a direct comparison of removal efficiency at different EBCTs and hydraulic loadings when treating the same raw water under actual operating conditions
Summary
Drinking waters around the world are produced from raw waters that contain natural organic matter, i.e., organic chemicals derived from living and dead organisms.[1]. Biological filtration is an efficient treatment technology for removing biodegradable DOM compounds. “Direct” biofilters are mostly used to remove turbidity, particles, and biological organic matter before membrane filtration. First-stage biofilters receiving coagulated water accumulate more flocs and particles during a filtration cycle.[5,6] In all biofilters, DOM adsorbs onto a naturally occurring biofilm or is biodegraded by microbes living within the biofilm. These biofilm microbes utilize the biodegradable fraction of DOM as a carbon source for their growth, metabolism, and reproduction, yielding effective DOM removal.[7]
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