Drinking water biofiltration: Assessing key factors and improving process evaluation

Biodegradable organic matter (BOM) removal in drinking water biofilters can be affected by several factors. The factors investigated in this research were non-biological particles/coagulant in the influent, chlorine in the backwash water, air scour during backwashing, anthracite/sand vs. GAC/sand media, and low (5°C)/high (20°C) temperature operation. Other investigations included: impact of biomass accumulation within a filter run; impact of empty contact time (EBCT); and impact of step increases in BOM concentration and hydraulic loading rate, and filter shutdown on biofilter performance. The research also included the evaluation of biomass respiration potential (BRP) as an alternative biomass measurement, the development of a simple experimentally-based approach for estimation of key bio-kinetic parameters, and the modeling of BOM removal in drinking water biofilters.; Fractional factorial design experiments in blocks I and II (phases I and II) showed that the three main factors (chlorine in backwash, temperature and media type) and their two or three-factor interactions were significant in most cases.; Further investigation of factors affecting drinking water biofiltration in phase III suggested that air scour, particle and coagulant effects were generally negligible although an air scour effect should be considered under unfavourable operating conditions (low temperature, chlorine, anthracite).; The concept of bed utilization (the ratio of the bed depth required for substantial BOM removal to the entire bed depth) was introduced in the study.; The amount of biomass on the filter media was evaluated by BRP (biomass respiration potential) and the phospholipid method in parallel. A good linear relationship was found between BRP and phospholipid biomass.; The key bio-kinetic parameters (k and K_s) were estimated in a dedicated experiment in which the biomass from the filter media and the BOM from the filter influent were used.; Three biofilter models, based on the simplified biofilm model, Suidan and Wang's semi-empirical equation, and Sáez and Rittmann's revised solution, respectively, were applied to the modeling of acetate removal performance in biofilters in this study. The modeling results indicated that these three models are all applicable to the modeling of drinking water biofilter performance and they all provided a good prediction for acetate removal in biofilters for the conditions evaluated.; A revised S_min (minimum substrate concentration that can maintain a single layer biofilm in biofilters) and critical dimensionless contact time X*_critical (beyond X*_critical , little further removal is obtained) were proposed and evaluated in this study. (Abstract shortened by UMI.)...