Ammonia, iron and manganese removal from potable water using trickling filters

The presence of ammonia in potable water supplies is often accompanied by the presence of iron and manganese in concentrations above the permitted limits. Nitrogenous compounds are very important in water management due to the potentially detrimental impact on the environment and human health. Also iron and manganese, cause serious impairment of water quality, like reddish or brown-black colour, metallic taste and bad odor. Biological removal of pollutants has certain advantages over physico-chemical removal systems. Attached growth systems like trickling filters provide a support medium for biofilm growth, thus allowing the possibility of maintaining bacteria at high hydraulic loadings. Three pilot-scale nitrifying trickling filters were used for ammonia removal, using three different gravel sizes. The mean size of the gravel or the specific surface area was found to be critical for optimal nitrification performance. It was found that there was a range of the gravel size for which maximum nitrification rate was observed while for higher or smaller gravel sizes, filters performance was reduced, due to different effects in each case. Steady state and dynamic models of previous works were used to predict filters' performance for various operating conditions and different support material. Models were very accurate for the range of gravel size where the maximum nitrification rates were observed. Using these models the operating diagram of the system was constructed, and the range of operating conditions resulting in safe and complete nitrification was determined. The effect of the operational conditions on the physico-chemical and combined physicochemical and biological iron oxidation in potable water was studied using another pilot scale trickling filter. The extent of each oxidation type was assessed and mathematical models were developed for each type of oxidation. First order kinetic was used to describe the physico-chemical iron oxidation while Monod type kinetic was used to describe the net biological iron oxidation. Another filter was used to study biological manganese removal from potable water. Similar experiments were performed while Monod type kinetic was used to describe biological manganese oxidation. Many series of experiments were also performed to investigate filter performance for various operational conditions and the interactions between the three pollutants when simultaneously present in a biological filter.