Household slow sand filters in intermittent and continuous flow for a long-term surface water treatment: Efficiencies assessment and operational challenges

The Household Slow Sand Filter (HSSF) is a Point-Of-Use technology that has several technical, constructive, and operational advantages, which allows users to improve the quality of their own drinking water at home. This paper aims to provide results concerning the real possibility of treating surface water using HSSF with two feeding strategies, covering more than one year of operation (430 days), including seasons with different inputs on surface water. To do this, we compared the intermittent (HSSF-I) and the continuous (HSSF-C) feeding strategies in quantitative terms (filtered water quality and treatment efficiency) and qualitative terms (con-struction, cost, and operational challenges). Overall, both HSSF models were efficient and improved the water quality, but HSSF-C produced better quality filtered water in terms of turbidity (73 ( +/- 20)% versus 69 ( +/- 18)%), Escherichia coli (2.06 ( +/- 0.60) log versus 1.65 ( +/- 0.78) log), Giardia cysts (>3 log versus 2.89 ( +/- 0.32) log), and Cryptosporidium oocysts (1.22 ( +/- 0.10) log versus 0.95 ( +/- 0.45) log) than HSSF-I. In addition, HSSF-C was able to remain more stable throughout the entire operation, without major impacts caused by influent water variations and maintenance activities. On the other hand, HSSF-I was cheaper, took up less space in the house, had a simple and easy operation, and did not require as much maintenance as the continuous one. Results indicated that HSSF-C may be a more viable model for treating surface water, but it still needs to improve its transfer requirements and assess its user acceptability from field experiences.