Application of high rate nitrifying trickling filters for potable water treatment

The interference of ammonia with chlorination is a prevalent problem encountered by water treatment plants located throughout South East Asia. The efficacy of high rate, plastic-packed trickling filters as a pre-treatment process to remove low concentrations of ammonia from polluted surface water was investigated. This paper presents the findings from a series of pilot experiments, which were designed to investigate the effect of specific conditions—namely low ammonia feed concentrations (0.5–5.0 mg NH4-N L−1), variations in hydraulic surface load (72.5–145 m3 m−2 d−1) and high suspended solid loads (51 ± 25 mg L−1)—on filter nitrifying capacity. The distribution of nitrification activity throughout a trickling filter bed was also characterised. Results confirmed that high hydraulic rate trickling filters were able to operate successfully, under ammonia-N concentrations some 10- to 50-fold lower and at hydraulic loading rates 30–100 times greater than those of conventional wastewater applications. Mass transport limitations posed by low ammonia-N concentrations on overall filter performance were insignificant, where apparent nitrification rates (0.4–1.6 g NH4-N m−2 d−1), equivalent to that of wastewater filters were recorded. High inert suspended solid loadings had no adverse effect on nitrification. Results imply that implementation of high rate trickling filters at the front-end of a water treatment train would reduce the ammonia-related chlorine demand, thereby offering significant cost savings.