Toxicity variability of urban road stormwater during storage processes in Shenzhen, China: Identification of primary toxicity contributors and implications for reuse safety

Abstract

Urban road stormwater reuse is one of the most important ways to mitigate water resource shortage. Generally, stormwater is stored prior to reuse or further treatment. This study explored the stormwater toxicity variability during two types of storages, closed and open storages using Chinese hamster ovary cells (CHO), which are mammalian cells. The toxicity test by CHO cells can indirectly represent the risk related to human health. Both rainfall (without reaching ground surfaces) and urban road stormwater were collected to undertake laboratory-scaled storage experiments and basic water quality parameters (pH and dissolved oxygen), microorganisms (E.coli and total bacteria), total organic carbon and heavy metals (copper, Cu, zinc, Zn, nickel, Ni, chromium, Cr, cadmium, Cd and lead, Pb) were also investigated during storage processes. The outcomes showed that rainfall has a better water quality with lower toxicity than urban road stormwater (EC50 values of rainfall were generally twice higher than road stormwater). Additionally, it is found that storing road stormwater for a certain period would reduce the toxicity and hence improve their reuse safety (EC50 values in Day 1 were 10.30 mL and 8.46 mL for closed and open storage respectively while they were 14.3 mL and 13.0 mL in Day 7). Organic matters and Cu are important contributors of toxicity during both closed and open storages while bacteria is also essential in toxicity contribution in open storage. The research results implied that storing stormwater for a certain period has a benefit for reuse safety. This is related to cost-effectiveness in terms of treatment system design to avoid over engineering. Additionally, it is suggested that for reducing toxicity, the stormwater treatment designed before/after storage devices should focus on removal of organic matters and heavy metals (specially Cu) as well as restraining bacteria growth.