Advanced water treatment for water reuse in a hydroponic system – experiences from the first full-scale implementation in Germany

ABSTRACT This study examines the first full-scale implementation of a hydroponic greenhouse with water reuse in Germany, focusing on water quality parameters in the context of the EU Water Reuse Regulation. Class A standards were confirmed for the routine monitoring parameters BOD5, TSS, turbidity and Escherichia coli. The target reduction for validation required for Class A water quality for E. coli was achieved; however, achieving adequate log reductions for Clostridium perfringens spores and somatic bacteriophages was challenging due to low influent concentrations. C. perfringens spores had a concentration sufficient for a log 4 reduction in only 47 out of 52 samples, while somatic bacteriophages never reached sufficient levels for a log 6 reduction in the influent. These results highlight the difficulties in validating water reuse systems with intermittent indicator organisms. With regard to heavy metals and metalloids, the irrigation water is of drinking water quality. Some of the organic micropollutants could not be degraded by 80%, but their concentrations in the irrigation water are very low, making it highly unlikely that their accumulation in the plants will cause health and safety concerns according to the Threshold of Toxicological Concern.