In a preliminary study, field stormwater samples were stored at three different temperatures (i) room temperature (18 oC), (ii) fridge (5 oC) and (iii) freezer (-18 oC) for up to a period of one month to identify if, and if so how, various physico-chemical parameters changed over time.
The results of the study showed that pH, turbidity, total organic carbon (TOC) and dissolved organic carbon (DOC), total, dissolved and truly dissolved fraction of metals varied in relation to storage temperature and duration. In contrast, electrical conductivity (EC), total suspended solids (TSS), and chloride (Cl-) concentrations were unaffected by storage conditions and holding time. One freeze-thaw cycle altered the stormwater quality for selected parameters compared to both room temperature and fridge stored samples.
For example, turbidity levels decreased two-fold in the frozen samples while TOC and DOC in frozen samples was unaffected. Samples stored at room temperature reported changes in pH, TOC, DOC, dissolved and truly dissolved fractions of metals over time. Fridge temperature storage of stormwater resulted in minimal changes in its quality across most parameters, with only minimal decreases in TOC and DOC identified. Therefore, fridge temperature is more suitable for stormwater storage.
The stormwater used in this preliminary study was moderately polluted and further assessment with stormwater carrying different pollution loads will be undertaken to observe changes in stormwater quality and to support identification of storage options based on pollutants concentration ranges.