The Submerged Biofilm Process as a Pre-Treatment for Polluted Raw Water for Tap Water Supply

The submerged biofilm process is a promising system for polluted raw water pre-treatment systems. General treatment performance and factors affecting treatment efficiency were investigated through pilot plant scale experiments using water from four different lakes. Regarding the quality of the raw waters, BOD was generally below 10 mg/l and the ammonium nitrogen (NH₄-N) concentration was below 0.4 mg/l. The efficiency of removal of NH₄-N was about 80% under complete mixing conditions and when the raw water quality did not fluctuate rapidly. Under the adverse conditions of the low water temperatures which occurred in winter and spring, the removal of NH₄-N was 60 to 80%. The critical NH₄-N concentration was observed to be approximately 0.01 to 0.02 mg/l, and a moderate decrease in E₂₆₀ was also observed in the experiments. Overall treatment performance of the submerged biofilm process was superior in those systems with carriers which were not likely to become clogged.