Investigating the impact of multi-day residence periods on intermittently operated slow sand filters
Authors: Young-Rojanschi, C, C Madramootoo
Description: Intermittently operated slow sand filters (IOSF) are among the most promising household drinking water treatment systems for developing world applications, with approximately 200 000 in use in over 70 countries as of 2009. Existing guidelines require users to run the filters with a residence time of 12 to 48 hours. Research to date has examined the impact of shorter residence periods (e.g. 6, 12, 24, and 36 hours) with no studies in the peer-reviewed literature reviewed found to have exceeded 36 hours. The present study looks at the impact of extended residence periods. Nine sand columns were constructed with sand properties and depth matching that recommended for field IOSFs. The columns were randomly distributed to be operated with one of the three residence periods (24, 48, or 72 hours). The columns were operated for 84 days from November 2011 to February 2012. Columns were fed with lake water supplemented with E.coli B (ATCC# 11303). Influent, effluent, and control samples were tested for a range of parameters including E.coli colony forming units, turbidity, pH, electroconductivity, dissolved oxygen, N-NH4, N-NO3, N-NO2, and total carbon. Hydraulic conductivity and dissolved oxygen of pore water were measured for different sand depths within the beds every six days. Preliminary results will be presented. Household operation of technologies is rarely optimal. It is critical to have a strong understanding of the consequences of non-optimal operation before distribution to users, especially if it may unintentionally expose users to pathogens.
Keywords: slow sand filter, water treatment, biosand filter, biologically active filtration
Technical field: technical_fields_app3
Session name: Ecological engineering