Changes in content of microbially available phosphorus, assimilable organic carbon and microbial growth potential during drinking water treatment processes

There are regions where microbial growth in drinking water is limited by phosphorus instead of organic carbon. In phosphorus limited waters small changes in phosphorus concentration significantly affect microbial growth. We studied how water treatment processes in waterworks affect the availability of microbial nutrients and microbial growth potential in drinking water. The nutrients studied were assimilable organic carbon (AOC potential) and microbially available phosphorus (MAP) which both were quantified by bioassays. Chemical coagulation, commonly used in surfacewater works, effectively removed AOC potential and MAP. In contrast to activated carbon filtration, ozonation increased the concentrations of AOC potential and MAP, and also microbial growth potential. In most of the drinking waters, microbial growth was limited by phosphorus, and microbial growth potential correlated with the MAP concentration. Microbial growth potential was lowest in drinking waters produced from surface waters with efficient treatment technique and highest in less treated ground waters.