Assessing an intermittently operated household scale slow sand filter paired with household bleach for the removal of endocrine disrupting compounds. J Environ Sci Health A Tox Hazard Subst Environ Eng. 2013;48(7):753-9. doi: 10.1080/10934529.2013.744616.

Kennedy TJ, Anderson TA, Hernandez EA, Morse AN. Department of Civil and Environmental Engineering , Texas Tech University , Lubbock , Texas , USA.

Endocrine disrupting compounds (EDCs) are a contaminant of emerging concern throughout the world, including developing countries where centralized water and wastewater treatment plants are not common. In developing countries, household scale water treatment technologies such as the biosand filter (BSF) are used to improve drinking water quality. No studies currently exist on the ability of the BSF to remove EDCs.

In this experiment, the BSF was evaluated for the removal of three EDCs, estrone (E1), estriol (E3), and 17α-ethinyl estradiol (EE2). Removal results were compared to the slow sand filter (SSF) from the literature, which is similar to the BSF in principal but comparisons have revealed differences in removal of other water quality parameters between SSF and BSF.

In general, the BSF minimally removed the compounds from spiked lake water as removal was less than 15% for all three compounds, though mass removal much higher than other studies in which the SSF was used. Household bleach was added to the rate was BSF effluent as suggested in order to achieve different Cl- concentrations (0.67, 2.0, 5.0, and 10.0 mg/L) and subsequent removal of EDCs by oxidation was examined.

Concentrations were reduced > 98% for all compounds when the Cl- concentration was greater than 5 mg/L. Removal efficiency was > 50% at the 0.67 mg/L Cl- concentration, while almost 70% removal was observed for all compounds at the 2.0 mg/L Cl- concentration.

J Appl Microbiol. 2012 Jul 26. doi: 10.1111/j.1365-2672.2012.05411.x.

Investigation of Quaternary Ammonium Silane (QAS)-coated Sand Filter for the Removal of Bacteria and Viruses from Drinking Water.

Torkelson AA, da Silva AK, Love DC, Kim JY, Alper JP, Coox B, Dahm J, Kozodoy P, Maboudian R, Nelson KL.
Source

Department of Civil and Environmental Engineering, University of California, Berkeley, Berkeley, California, 94720-1710.

AIMS: Develop an antimicrobial filter media using an attached quaternary ammonium compound (QAC) and evaluate its performance under conditions relevant to household drinking water treatment in developing countries.

METHODS AND RESULTS: Silica sand was coated with dimethyloctadecyl [3-(trimethoxysilyl) propyl] ammonium chloride via covalent silane chemistry. Filter columns packed with coated media were challenged with microorganisms under different water quality conditions. The antibacterial properties were investigated by visualizing Escherichia coli (E. coli) attachment to coated media under fluorescence microscopy combined with a live/dead stain. 9-cm columns with a filtration velocity of 18 m/h achieved log(10) removals of 1.7 for E. coli, 1.8 for MS2 coliphage, 1.9 for Poliovirus type 3, and 0.36 for Adenovirus type 2, compared to 0.1-0.3 log(10) removals of E. coli and MS2 by uncoated sand. Removal scaled linearly with column length, and decreased with increasing ionic strength, flow velocity, filtration time, and humic acid presence. E. coli attached to QAC-coated sand were observed to be membrane-permeable, providing evidence of inactivation.

CONCLUSIONS: Filtration with QAC-coated sand provided higher removal of bacteria and viruses than filtration with uncoated sand. However, major limitations included rapid fouling by microorganisms and natural organic matter and low removal of viruses PRD1 and Adenovirus 2.

SIGNIFICANCE AND IMPACT OF STUDY: QAC-coated media may be promising for household water treatment. However, more research is needed on long-term performance, options to reduce fouling, and inactivation mechanisms.

Household Water Treatment: Slow Sand Filtration, 2011. CDC.

• Full-text

A slow sand filter is a sand filter adapted for household use. Please note that although commonly referred to as the BioSand Filter, the BioSand Filter terminology is trademarked to one particular design, and this fact sheet encompasses all slow sand filters. The version most widely implemented consists of layers of sand and gravel in a concrete or plastic container approximately 0.9 meters tall and 0.3 meters square. The water level is maintained to 5-6 cm above the sand layer by setting the height of the outlet pipe. This shallow water layer allows a bioactive layer to grow on top of the sand, which contributes to the reduction of disease-causing organisms. A diffuser plate is used to prevent disruption of the biolayer when water is added. To use the filter, users simply pour water into the top, and collect finished water out of the outlet pipe into a bucket. Over time, especially if source water is turbid, the flow rate can decrease. Users can maintain flow rate by cleaning the filter through agitating the top level of sand, or by pre-treating turbid water before filtration.

WASHplus Weekly: 10 2011 Studies on HWTS

Feb 3, 2012 – This WASHplus Weekly contains 10 household water treatment and safe storage studies published in 2011. A number of HWTS technologies are reviewed, including studies on the technical performance of slow sand filtration, Moringa seeds, and Biosand filters. Studies from Bolivia, Malawi, and Rwanda investigate the behavioral and cultural aspects that influence the adoption and use of HWTS by communities. In addition to the 10 studies, links to two previous Weekly issues on HWTS and a listing of HWTS-related websites are included.

• Link

Water Res. 2011 Nov 15;45(18):6227-39.

Bacterial, viral and turbidity removal by intermittent slow sand filtration for household use in developing countries: experimental investigation and modeling.

Jenkins MW, Tiwari SK, Darby J. Department of Civil & Environmental Engineering, University of California, Davis, One Shields Ave., Davis, CA 95616, USA. mwjenkins@ucdavis.edu

A two-factor three-block experimental design was developed to permit rigorous evaluation and modeling of the main effects and interactions of sand size (d(10) of 0.17 and 0.52 mm) and hydraulic head (10, 20, and 30 cm) on removal of fecal coliform (FC) bacteria, MS2 bacteriophage virus, and turbidity, under two batch operating modes (‘long’ and ‘short’) in intermittent slow sand filters (ISSFs). Long operation involved an overnight pause time between feeding of two successive 20 L batches (16 h average batch residence time (RT)). Short operation involved no pause between two 20 L batch feeds (5h average batch RT). Conditions tested were representative of those encountered in developing country field settings.

Over a ten week period, the 18 experimental filters were fed river water augmented with wastewater (influent turbidity of 5.4-58.6 NTU) and maintained with the wet harrowing method. Linear mixed modeling allowed systematic estimates of the independent marginal effects of each independent variable on each performance outcome of interest while controlling for the effects of variations in a batch’s actual residence time, days since maintenance, and influent turbidity.

This is the first study in which simultaneous measurement of bacteria, viruses and turbidity removal at the batch level over an extended duration has been undertaken with a large number of replicate units to permit rigorous modeling of ISSF performance variability within and across a range of likely filter design configurations and operating conditions. On average, the experimental filters removed 1.40 log fecal coliform CFU (SD 0.40 log, N=249), 0.54 log MS2 PFU (SD 0.42 log, N=245) and 89.0 percent turbidity (SD 6.9 percent, N=263). Effluent turbidity averaged 1.24 NTU (SD 0.53 NTU, N=263) and always remained below 3 NTU. Under the best performing design configuration and operating mode (fine sand, 10 cm head, long operation, initial HLR of 0.01-0.03 m/h), mean 1.82 log removal of bacteria (98.5%) and mean 0.94 log removal of MS2 viruses (88.5%) were achieved.

Results point to new recommendations regarding filter design, manufacture, and operation for implementing ISSFs in local settings in developing countries. Sand size emerged as a critical design factor on performance. A single layer of river sand used in this investigation demonstrated removals comparable to those reported for 2 layers of crushed sand. Pause time and increased residence time each emerged as highly beneficial for improving removal performance on all four outcomes. A relatively large and significant negative effect of influent turbidity on MS2 viral removal in the ISSF was measured in parallel with a much smaller weaker positive effect of influent turbidity on FC bacterial removal. Disturbance of the schmutzdecke by wet harrowing showed no effect on virus removal and a modest reductive effect on the bacterial and turbidity removal as measured 7 days or more after the disturbance. For existing coarse sand ISSFs, this research indicates that a reduction in batch feed volume, effectively reducing the operating head and increasing the pore:batch volume ratio, could improve their removal performance by increasing batch residence time.