Microcystis aeruginosa and microcystin-LR removal by household slow sand filters operating in continuous and intermittent flows

Abstract

A household slow sand filter (HSSF) is a widely used water treatment technology recognized as one of the most effective and sustainable in reducing waterborne diseases. However, there is a lack of knowledge concerning its behaviour in the presence of cyanobacteria and cyanotoxins. In this context, the study aimed to evaluate HSSF ability to remove Microcystis aeruginosa cells (stain BB005) and microcystin-LR from water, among other parameters, when operated under continuous (C-HSSF) and intermittent (I-HSSF) flows. CHSSF was operated at a constant filtration rate (1.22 m3 m-2 day-1), while I-HSSF was operated at a variable filtration rate (starting at 2.95 m3 m-2 day-1 and finishing at zero). Each filter produced 60 L day-1. The influence of the pause period was also tested in the I-HSSF. The water from the study was prepared by inoculating M.aeruginosa culture in water from a well to a final cell density of ± 1 × 105 cells mL-1. M.aeruginosa removal rates were 2.39 ± 0.34 log and 2.01 ± 0.43 log by CHSSF and I-HSSF, respectively. Microcystin-LR concentration in studied water was 5.55 μg L-1, and both filters produced filtered water with microcystin concentrations below 1.0 μg L-1, the maximum value recommended by the World Health Organization (WHO), for most of the samples. Turbidity and apparent colour were also within WHO guidelines. Filters operating with different flow regimes and distinct residence times did not statistically influence treatment efficiencies. Both filters showed promising results in the M.aeruginosa and microcystin-LR removals from water; nevertheless, more research is needed to understand the mechanisms involved in the reduction of both cyanobacteria and cyanotoxin through household slow sand filtration.