Wastewater treatment and elimination of pathogens: new prospects for an old problem.

Although the development of wastewater treatment technology is more than one hundred years old, most wastewater treatment plants existing today do not eliminate pathogens satisfactorily. Even in highly developed nations, receiving waters, serving in many cases as drinking water resources, are contaminated with pathogens. Surface waters also contain large concentration of phosphate due to long lasting wastewater discharges. Cyanobacteria and algal overgrowth is the consequence. Present drinking water technology only partially overcomes the pollution; it can not be ruled out that drinking water originating from polluted resources contains pathogens. This situation frequently goes on unnoticed because current indicator organisms are not representative for all pathogens. As studies have shown that small concentrations of pathogens also pose a risk for the consumer health, this state of affairs is a matter of concern. Microfiltration technology is able to significantly eliminate bacteria and protists from wastewater. Viruses, although smaller than the pore size of the filters, are reduced too because, in wastewater, they are frequently bound to larger particles. If the microfiltration of wastewater is preceded by the addition of coagulants for the precipitation of phosphate, the precipitate will be retained by the filter. The effluent obtained contains very low concentrations of phosphate. As viruses also adsorb to the precipitate, the amount of viruses eliminated increases and with increasing amounts of coagulant they become undetectable.