High concentrations of soluble calcium in industrial wastewater present problems due to the calcification of downstream processing. The current trend towards circuit closure and increased water re-use will escalate this problem. We investigated ureolytic microbial carbonate precipitation as a novel process for removing excess calcium from industrial effluents. Two laboratory-scale reactors, both with a hydraulic retention time of 8 h, were fed with 1.8 dm 3 of anaerobic effluent (about 11 mM Ca 2+ ) from a paper recycling plant. Both reactors were inoculated with pre-cultivated calcareous sludge and the treatment reactor was additionally dosed with urea to a final concentration of 8.3 mM. Even though the anaerobic wastewater was saturated as such with respect to CaCO 3 , urea addition and hydrolysis was shown to be a pre-requisite for precipitation. Almost all (85-90% w/v) of the soluble calcium was precipitated as CaCO 3 and removed through sedimentation in the treatment reactor. This bio-catalytic process presents an uncomplicated and efficient method for the removal of calcium from industrial wastewater.

To obtain a sustainable water catchment in the dune area of the Flemish west coast, the integration of treated domestic wastewater in the existing potable water production process is planned. The hygienic hazards associated with the introduction of treated domestic wastewater into the water cycle are well recognised. Therefore, the concept of HACCP (Hazard Analysis and Critical Control Points) was used to guarantee hygienically safe drinking water production. Taking into account the literature data on the removal efficiencies of the proposed advanced treatment steps with regard to enteric viruses and protozoa and after setting high quality limits based on the recent progress in quantitative risk assessment, the critical control points (CCPs) and points of attention (POAs) were identified. Based on the HACCP analysis a specific monitoring strategy was developed which focused on the control of these CCPs and POAs.

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