Research Paper Ripening of household slow sand filter by adding fish food Kalyl Gomes Calixto, Lyda Patricia Sabogal-Paz, Eloisa Pozzi and Luiza Cintra Campos ABSTRACT Vulnerable communities can improve their quality of life using point-of-use water treatment technologies. Among these technologies, household slow sand filters (HSSF), which are filters adapted to domestic operations, stand out as one of the most effective and sustainable alternatives. However, some technical issues are not fully understood, such as the ripening process, which may take a long time to take place. In this context, this research evaluated the performance of a HSSF, in real scale and operated in continuous flow when a source of nutrients ( fish food) was added to influent water, as a potential ripening agent. Physicochemical and microbiological parameters were evaluated to estimate the filter efficiency. According to the results, the HSSF reached a partial ripeness level in a short time with target parameter reduction in filtered water. Nevertheless, the instability observed in the filtered water quality reveals the significant health risks associated with human consumption when the HSSF is not yet ripened. Kalyl Gomes Calixto Lyda Patricia Sabogal-Paz (corresponding author) Eloisa Pozzi Department of Hydraulics and Sanitation, São Carlos School of Engineering, University of São Paulo, Avenida Trabalhador São-carlense 400, São Carlos, São Paulo, 13566-590, Brazil E-mail: lysaboga@sc.usp.br Luiza Cintra Campos Department of Civil, Environmental and Geomatic Engineering, University College London, Gower St, London, WC1E 6BT, England Key words | biological maturation, biosand filter, drinking water, slow sand filtration, tracer tests, treatment INTRODUCTION Despite the progress made in water and sanitation services over the last decades, deficiencies related to equality and accessibility persist, affecting populations all over the world. For instance, approximately 840 million people still lack access to basic drinking water services (WHO & UNICEF ). Ingestion of water contaminated by faecal matter causes almost four billion cases of diarrhoeal disease per year, of which 1.8 million are fatal (UNEP ). Further global data show the high level of exposition to inappropriate water sources and highlight the vulner- ability of low- and middle-income countries to waterborne disease (WHO ). While reliable, safe, and piped water is not accessible to every household, temporary actions, such as household water treatment and safe storage (HWTS), are needed to reduce waterborne diseases (WHO ). In this context, biosand filters (BSFs) or household slow sand filters (HSSF) stand out as one of the most promising alternatives due to their affordability, simplicity, and efficiency (Sobsey et al. ; Sabogal-Paz et al. ). The benefits derived from using these filters can be seen in studies in real-world implementations, where diarrhoea and other gastroenteritis symptoms have been drastically reduced (Stauber et al. ; Sisson et al. ). Some questions about this technology remain unclear, such as those related to the biological processes responsible for water purification (Haig et al. ) and those linked to the maturing process (Palmateer et al. ). Ripening of sand beds is a critical factor influencing particle and micro- organism removals in slow sand filters (SSF). A filter is 76 Research Paper © IWA Publishing 2020 Journal of Water, Sanitation and Hygiene for Development | 10.1 | 2020 doi: 10.2166/washdev.2020.143 Downloaded from http://iwaponline.com/washdev/article-pdf/10/1/76/723679/washdev0100076.pdf by guest on 28 September 2023