Rainwater treatment system efficiency: Household slow sand filter combined with UVC lamp disinfection

Abstract

A household system to treat rainwater composed of a Household Slow Sand Filter (HSSF) and a commercial ultraviolet lamp reactor was evaluated. Rainwater was collected in the southeast of Brazil (São Carlos, São Paulo) and inoculated with Escherichia coli to simulate contamination. The system was evaluated for 100 consecutive days under real-scale conditions, aiming to remove microbiological and physical-chemical parameters. Results indicated that HSSF removed 1.10 ± 0.33 log of E. coli even with the schmutzdecke in slow formation due to the low concentration of organic matter concentration and scarcity and low diversity of microorganisms in the rainwater. On the other hand, the UV disinfection (UV dose of 30 mJ/cm2) presented an average removal of 4.60 ± 0.58 log, with 87.5 % of the samples presenting absence of microbiological risk. No significant improvement in physical-chemical water quality after the household treatment was observed due to the high quality of raw rainwater. Therefore, it was recognised that rainwater quality was not substantially improved by the HSSF (i.e., filtration could be dispensed) and only UVC lamp disinfection would be enough to produce drinking water. Recontamination was observed during the tests, as weather events and monitored parameters were capable of highlighting the importance of safe storage practices.