Backwash as a simple operational alternative for small-scale slow sand filters: From conception to the current state of the art

Abstract Slow sand filtration is one of the oldest water treatment technologies and it is still in use and development. Slow sand filters are simple and capable of removing suspended solids, protozoa cysts, bacteria, and virus. With the emerging concern about trace contaminants, this technology has been studied for their removal, sometimes with some improvements such as activated carbon. The most discussed operational aspect in slow sand filtration is filter cleaning, usually scraping, that can be laborious and inhibit the technology application. Backwash cleaning has been proposed by many studies as an operational improvement for small-scale filters, especially for the applicability of slow sand filters in rural areas or small municipalities. This review paper compiles and discusses the findings from these studies. Furthermore, it presents how backwashed slow sand filters have been used and improved to the model proposed in the most recent research and applications. Research showed that ∼4 min backwash simplifies filter cleaning without impairing water quality according to many water quality parameters such as turbidity ( 80 %). Overall, other contaminants such as protozoa cysts (>2 Log), cyanobacteria (>88 %), agrochemicals (11–64%) and total iron (67–92 %) were also removed with no significant differences from scraped filters. So, it is concluded that backwash slow sand filters can be operated in a simple way, being a good alternative for small-scale systems. Furthermore, a broader communication and application would help spreading this promising technology.