Biofilters are finding increasing use in drinking water treatment. Among the substances they remove are ozonation by-products such as low molecular weight aldehydes and carboxylic acids. Because a number of these compounds also participate in or are produced by major bacterial metabolic pathways, their behaviour in biofilters may be complex. This pilot scale study investigated biodegradation relationships between methylglyoxal and pyruvate. A second objective was to determine the impact of mass transfer on removals.
The formation of pyruvate was observed when methylglyoxal was the sole easily biodegradable compound fed in the filter influent. The removal rates of formaldehyde and methylglyoxal were found to be comparable when each was the sole easily biodegradable compound fed. When fed alone, complete removals of methylglyoxal were obtained under steady-state conditions. When fed alone, the removal rate of pyruvate was more than twice than that of either formaldehyde or methylglyoxal. The removal rate of pyruvate was reduced by more than 50% when it was fed together with methylglyoxal. The reduced rate was probably due both to competition and to the formation of pyruvate from methylglyoxal. Backwashing was shown to have essentially no effect on removals of the compounds investigated.
The mass transfer investigations showed that neither external nor internal mass transfer was limiting. Therefore removals were governed by biodegradation rates. The lack of importance of mass transfer is significant because it simplifies modelling for the removal of easily biodegradable substances in drinking water biofilters.