Role of lime treatment in the removal of bacteria, enteric viruses, and coliphages in a wastewater reclamation plant.

Lime flocculation/sedimentation in the first process unit of a 4,500-m3/day wastewater reclamation plant reduced numbers of microorganisms extensively when operated at pH 11.2. The efficiency was much less at lower pH values, and some bacteria even multiplied at pH 9.6. Data on reduction in the number of microorganisms in the lime treatment and subsequent units indicate that inactivation by hydroxide alkalinity plays an important role in the efficiency of lime treatment. Reductions in the numbers of enteric viruses were higher than those of coliphages, enterococci, and total plate and coliform bacteria, which indicate that lime treatment can be monitored by means of coliphage and conventional bacteriological tests. This paper illustrates the valuable role of high-pH lime treatment in reducing the load of pathogenic microorganisms on subsequent units, including ultimate disinfection processes, which is important in the multiple safety barrier concept of wastewater reclamation processes.