Influence of sand depth and pause period on microbial removal in traditional and modified biosand filters.

Three different-sized biosand filters (i.e., the center for Affordable Water and Sanitation Technology v10 concrete filter, a 5-gal bucket filter, and a 2-gal bucket filter with fine sand depths of 54, 15, and 10 cm, respectively), configured with and without the addition of iron nails to the diffuser basin, were evaluated for removal of bacteria, protozoa, and viruses over pause periods ranging from 1 to 72 hrs. Biosand filtration proved effective at all pause periods tested, and log10 removal of bacteria and protozoan cysts for all filter sizes and configurations ranged from 3 to 4. The addition of nails resulted in significantly better (p<0.05) bacteria removal for all filter sizes and significantly better (p<0.02) protozoan removal for the bucket-sized filters. Log10 virus removal for all filter types and sizes ranged from <1 to 6. Both the pause period and filter type (size/configuration) influenced virus removal, and the addition of nails to the filter improved virus removal at the shorter pause periods. Scaled-down biosand filters provide a viable household water treatment option for some of the millions of people that still lack access to an improved water source.

Evaluation of consistent use, barriers to use, and microbiological effectiveness of three prototype household water treatment technologies in Haiti, Kenya, and Nicaragua.

Household water treatment (HWT) can improve drinking water quality and reduce diarrheal disease. New HWT technologies are typically evaluated under ideal conditions; however, health gains depend on consistent, effective household use, which is less often evaluated. We conducted four evaluations of three prototype HWT technologies: two filters and one electrochlorinator. Evaluations consisted of a baseline survey, HWT distribution to households (ranging from 60 to 82), and four visits (ranging from 1 week-14 months after distribution). Each visit included a survey, observation of treated water presence (confirmed use), and microbiological analysis of treated and untreated samples for E. coli. Consistent use was defined as the proportion of total visits with confirmed use. Overall, confirmed use declined 2.54% per month on average, and 2-72% of households demonstrated 100% consistent use. Consistent use was positively associated with baseline HWT knowledge and practice and belief that drinking water was unsafe, and negatively associated with technological problems. Reported barriers to use were behavioral, such as forgetting or when outside the home, and technological failures. Technologies demonstrated 68-96% E. coli reductions, with 18-70% of treated samples having detectable E. coli. Results highlight the importance of household use evaluations within prototype HWT technology design cycles, the need for standard evaluation metrics, and difficulties in achieving both consistent use and microbiological effectiveness with HWT technologies.

Effect of Sand Bed Depth and Medium Age on Escherichia coli and Turbidity Removal in Biosand Filters.

The main objective of this study was to build several full-scale biosand filters (BSFs) and assess the long-term (9 month) efficacy for particulate and Escherichia coli removal under simulated real-world usage. Four replicates of three different filter designs were built: the traditional concrete BSF and two scaled-down versions that use a 5 or 2 gal bucket as the casing material. The smaller sand bed depths in the bucket-sized filters did not impact filter performance with respect to (i) turbidity and E. coli removal or (ii) effluent levels of turbidity and E. coli. All filters produced effluents with a mean turbidity of <0.6 nephelometric turbidity unit. In addition, 78, 74, and 72% of effluent samples for the concrete, 5 gal, and 2 gal filters, respectively, had E. coli concentrations of <1 colony-forming unit/100 mL. The bucket-sized filters were found to be a potential alternative to the concrete BSFs for the removal of E. coli and turbidity from drinking water. Because smaller BSFs must be filled more frequently than larger BSFs to produce comparable water volumes, the effect of shorter pause periods on BSF performance should be investigated.

Transport effects on hydraulic loading rate and microbial removal performance in biosand filters.

Biosand filters (BSFs) are increasingly designed using smaller and/or lighter casing material in an effort to reduce logistical requirements and implementation costs. The increased portability of a smaller, lighter design presents a potential negative consequence: the ability to move the installed/operational filter by the homeowner and potentially disturb the system. This study investigated the effects of moving and agitation on filter performance, using mature BSFs which had been in use for over nine months prior to the move. Data were analyzed for four replicate filters of three different filter types: the traditional concrete BSF and two plastic bucket (5-gal and 2-gal, respectively; 5-gal bucket = 18.9-L bucket, 2-gal bucket = 7.6-L bucket) BSFs. Filters were moved approximately 1 km and monitored for hydraulic loading rates (HLRs) and Escherichia coli removal for 8 weeks following the move. Moving the filters resulted in reduced HLRs, likely due to sand compaction, but E. coli removal remained high (log10 removal ≥2.8 for all sizes) and increased significantly as compared to data collected prior to the move. The resulting operational implications of moving BSFs are discussed.

Effect of production variables on microbiological removal in locally-produced ceramic filters for household water treatment.

Diarrhoeal diseases cause an estimated 1.87 million child deaths per year. Point-of-use filtration using locally made ceramic filters improves microbiological quality of stored drinking water and prevents diarrhoeal disease. Scaling-up ceramic filtration is inhibited by lack of universal quality control standards. We investigated filter production variables to determine their affect on microbiological removal during 5-6 weeks of simulated normal use. Decreases in the clay:sawdust ratio and changes in the burnable decreased effectiveness of the filter. Method of silver application and shape of filter did not impact filter effectiveness. A maximum flow rate of 1.7 l(-hr) was established as a potential quality control measure for one particular filter to ensure 99% (2- log(10)) removal of total coliforms. Further research is indicated to determine additional production variables associated with filter effectiveness and develop standardized filter production procedures prior to scaling-up.