Simultaneous TOC and Ammonia Removal in Drinking-Water Biofilters: Influence of pH and Alkalinity

A bench-scale biofiltration study was conducted to investigate the potential benefits of adjusting water pH and alkalinity as a simple water quality control on biofilter efficacy in terms of organic carbon removal, ammonia removal, and head loss development. Two biofilter columns were tested at pH values between 6.0 and 10.0 with low and high alkalinity levels of 25-50 and180-220 mg CaCO3/L, respectively. Total organic carbon (TOC) removal was 67% at the lower pH range tested (6.0-7.5), and then decreased as the pH increased to an observed low of 31% removal at pH 10. Ammonia removal demonstrated the opposite trend, with a low of 13% removal at pH 6.0, 48% at pH 7.5, and greater than 90% at pH 9-10. An assessment of the available dissolved oxygen (DO) indicated it may have been a limiting factor in complete ammonia removal. Changes in alkalinity demonstrated a modest impact on biofilter activity, i.e., TOC, ammonia removals, and adenosine triphosphate (ATP) levels. Overall, pH 7.5 demonstrated an optimum condition for water quality and head loss control with 67% and 48% removal in terms of TOC and ammonia, respectively, and with the lowest head loss development. (c) 2020 American Society of Civil Engineers.