The effects of advanced treatment on the biological activity of recycled water

Abstract

The world’s growing population is causing an ever increasing demand for clean safe drinking water. In some countries suitable sources of drinking water are becoming scarce and will not be able to satisfy future demand. Consequently, there is a need to find alternative sources of water that can be used for potable supply or to augment current sources. Advanced water treatment methods are now being examined to investigate whether treated domestic sewage effluent can be treated to drinking water standards and discharged upstream of a drinking water abstraction point; a process known as Indirect Potable Reuse (IPR). The aim of this project was to investigate biological activity associated with developmental exposure to IPR water at the various stages of treatment using zebrafish embryos. Embryos reared in water at different stages of the treatment process were observed for developmental abnormalities, and differences in gene expression (compared to an aquarium water control) were used to establish both the nature and persistence of these effects along the treatment process. In addition to the embryo assays, passive sampling devices, Pharmaceutical Polar Organic Integrative Sampler (Pharm-POCIS) were deployed over eight, four week periods to collect composite concentrated samples of some of the contaminants present in the effluent. These concentrated extracts were then used in an in vitro assay; an Enzyme Immunoassay (EIA) to measure the inhibition of prostaglandins (an indirect measure of inhibitors of cyclooxygenase activity). We compared our results of the bioassays with the large body of chemical analysis data recorded over a number of years from each of the treatments. The developmental exposures highlighted a low frequency of consistent abnormalities to the heart and spine, and also a lack of pigmentation. Gene expression analysis demonstrates the developmental stage of the embryo to have the greatest influence on global gene expression as opposed to the treatment. Single genes of interest included the two cytochrome P450s (cyp1a and cyp1b1) and somatolactin beta. Some of the pathways disrupted included steroid synthesis, retinol metabolism, tryptophan metabolism and melanogenesis. The latter was consistent with observations of some embryos devoid of pigment. Along the treatment process reverse osmosis seemed to cause the largest change to the gene expression. The extracts from less treated effluent inhibited prostaglandin production, however following reverse osmosis prostaglandin inhibition was greatly reduced. The chemical contaminantion is greatly reduced as the effluent progresses along the IPR treatment process, this is evident from both the chemical data and the biological assays. Reverse osmosis seems to have the greatest influence on the gene expression. The results have highlighted the importance of an appropriate control, to remove background noise.