Chemical wastewater treatment is a commonly used and highly effective process. Chemicals can be dosed at a series of different points during the full treatment process. As addition directly to the biological system, or 'co-precipitation', becomes increasingly popular, the direct effect of the chemicals on the biomass becomes of interest. The two major reasons for dosing chemicals in this manner are for phosphorus removal and the prevention of sludge bulking/foaming. Another possible use for chemicals at this point is for enhancement of biological treatment via micronutrient addition. This paper demonstrates the effectiveness of the use of chemicals for these three functions as well as exploring their effect on the biomass. The possibility of chemical dosing to achieve good phosphorus removal, sludge bulking control and biological treatment enhancement is also considered. Certain vitamins and trace metals were found to benefit aerobic biological treatment and other advantages of their use were improved sludge bulking control and alternative sludge disposal routes. However, some toxic effects have been reported if overdosed and the required concentration is difficult to determine. Chemicals used for phosphorus removal during co-precipitation have been found to control sludge bulking problems, increase BOD and suspended solids removal and enhance the removal of trace metals amongst other benefits. Drawbacks included nitrification/denitrification inhibition and increased sludge volume. Beneficial effects of chemicals used primarily for sludge bulking control included phosphorus removal, increased BOD and suspended solids removal and biological treatment enhancement. Detrimental effects included increased sludge production and increased costs.
