Improved Filtration Technology for Pathogen Reduction in Rural Water Supplies
Abstract
:1. Introduction
1.1. Background
- The flow rate through the sand decreases with usage, and this limit to water availability may lead to the application of excessive flows or use of other (untreated) sources of water.
1.2. Research Objectives
- Increase in sand grain size. The greater pore size would be expected to increase initial flow rates and, possibly, flow rates even as the bio-layer develops.
2. Materials and Methods
2.1. Filter Characteristics
Filter Configuration | Filter Media (see Figure 1) | 1ES or D10 |
---|---|---|
F1 | River sand | 0.3 mm |
F2 | Crushed granite gravel | 0.15 mm |
F3 | River sand + ZVI (0.5 kg) | 0.3 mm |
2.2. Filter Construction and Design
2.3. Media and Filter Preparation
Zero-Valent Iron (ZVI)
2.4. Experimental Design
2.5. Sample Collection
2.6. Odor Management
2.7. Microbial Analysis of Water Samples
2.8. Physico-Chemical Analysis of Water Samples
2.9. Data Analysis
3. Results and Discussion
3.1. Microbial Reduction
Concentration of Pathogen indicators (Colony Forming Units per 100 mL) | ||||
---|---|---|---|---|
Pathogens | Week 2 | |||
Raw Water | F1 | F2 | F3 | |
TC | >100 | >100 | 10 | 0 |
FC | >100 | >100 | 10 | 0 |
FS | 100 | 80 | 10 | 0 |
Week 4 | ||||
TC | >100 | 100 | 3 | 0 |
FC | >100 | 100 | 3 | 0 |
FS | 100 | 50 | 0 | 0 |
Week 9 | ||||
TC | >100 | 80 | 0 | 0 |
FC | >100 | 80 | 0 | 0 |
FS | 100 | 30 | 0 | 0 |
3.1.1. Total and Fecal Coliforms
3.1.2. Fecal Streptococci
Time (days) | Percent Reduction of Total Coliform (%) | ||||||
---|---|---|---|---|---|---|---|
F1 | F2 | F3 | |||||
14 | 0 | 98.88 | 99 | ||||
29 | 0 | 98.97 | 99 | ||||
62 | 95 | 99 | 99 | ||||
Average | 31.7 | 98.9 | 99 |
Time (days) | Percent (%) Reduction of Fecal Coliform | ||||||||
---|---|---|---|---|---|---|---|---|---|
F1 | F2 | F3 | |||||||
14 | 0 | 98.88 | 99 | ||||||
29 | 0 | 98.97 | 99 | ||||||
62 | 95 | 99 | 99 | ||||||
Average | 31.7 | 98.9 | 99 |
Time (days) | Percent (%) Reduction Of Fecal Streptococci | ||
---|---|---|---|
F1 | F2 | F3 | |
14 | 95 | 98.88 | 99 |
29 | 98 | 99 | 99 |
62 | 98.57 | 99 | 99 |
Average | 97.2 | 99 | 99 |
Traditional BSF (F2) | Improved BSF (F3) | |||
---|---|---|---|---|
Days | Factor | Pathogen indicatorremoval | Factor | Pathogen indicator removal |
<14 | -Straining -Capture efficiency | <98.88% | -ZVI biocidal effects -Capture efficiency -Straining | 99% |
>14 | -All factors for < 14 days -Biofilm | 98–99% | -All factors for <14 days -Biofilm | 99% |
3.2. Natural Organic Matter
NOM (mg/L) | |||||
---|---|---|---|---|---|
Days | Raw Water | F1 | F2 | F3 | AFNOR/WHO Limits |
Day 14 | 2.9 | 1.6 | 0.9 | 0.6 | <5 |
Day 28 | 2.5 | 2.9 | 6.2 | 3.3 | <5 |
Day 62 | 2.3 | 2.4 | 3.2 | 1.8 | <5 |
3.3. Some Impacts on Water Chemistry
Days | 14 | 28 | 62 | Limit |
---|---|---|---|---|
F3 | 0.4 | 0.0 | 0.0 | <0.2 mg/L |
3.4. Head-Loss Development over BSF Operating Time
Flow rates (L/m) | |||
---|---|---|---|
Time (days) | F1 | F2 | F3 |
1 | 2.1 | 1.2 | 1.9 |
14 | 2 | 1.1 | 1.8 |
22 | 1.95 | 0.9 | 1.8 |
28 | 1.9 | 0.8 | 1.7 |
32 | 1.8 | 0.8 | 1.5 |
48 | 1.8 | 0.7 | 1.5 |
54 | 1.8 | 0.6 | 1.5 |
62 | 1.75 | 0.5 | 1.45 |
Average | 1.8875 | 0.825 | 1.64375 |
3.5. Turbidity Removal
Time (Days) | Turbidity Removal (%) | ||
---|---|---|---|
F1 | F2 | F3 | |
8 | 50 | 83.3 | 91.5 |
25 | 51 | 95 | 95.1 |
62 | 70 | 98 | 98 |
3.6. Taste and Odor Removal
3.7. Effect of Sand Size on Bio-sand Filtration
Filter | Effective size of sand (mm) | Average percent reduction (%) | Average Turbidity removal (%) | Average flow rate (L/m) | Average NOM (%) | ||
---|---|---|---|---|---|---|---|
TC | FC | FS | |||||
F2 | 0.15 | 97.2 | 97.2 | 99 | 98 | 0.82 | 53.97 |
F1 | 0.3 | 31.7 | 31.7 | 98.9 | 70 | 1.88 | 47.64 |
4. Conclusions
Recommendations
- Since viruses are far smaller than bacteria and protozoan cysts, they can travel further into the sand bed of the BSF, thus making BSF less effective in removing viruses. Further research under well controlled conditions is needed to characterize viral removal by the improved BSF.
- Although this study indicates that the improved BSF can provide significant benefits, the capacity and limitations of ZVI use should be better understood, such as its long term performance and the quantity required in the BSF.
- Further research is needed to better understand the mechanisms of adsorption and inactivation of microbial organisms and of the removal of NOM by ZVI.
List of Acronyms and Abbreviations
AFNOR | Standard Association Francaise pour la Normalisation (French National Standards Institute) |
BSF | Bio-sand Filter |
CAWST | Center for Affordable Water and Sanitation Technology |
DBPs | Disinfectant by-products |
FC | Fecal Coliform |
FS | Fecal Streptococci |
Geosmin | Trans-1, 10-dimethyl-trans-9-decalol |
MIB | 2-methylisoborneol |
MS-2 | A type of bacteriophage |
NOM | Natural Organic Matter |
NTU | Nephelometric Turbidity Unit |
ØX174 | A type of bacteriophage |
SSF | Slow Sand Filter |
TC | Total Coliform |
U.S. EPA | United States Environmental Protection Agency |
UDaily archive | University of Delaware Daily archive |
UN | United Nations |
WEDC | Water Engineering Development Center |
WHO | World Health Organization |
ZVI | Zero-valent iron |
Acknowledgements
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Tellen, V.; Nkeng, G.; Dentel, S. Improved Filtration Technology for Pathogen Reduction in Rural Water Supplies. Water 2010, 2, 285-306. https://doi.org/10.3390/w2020285
Tellen V, Nkeng G, Dentel S. Improved Filtration Technology for Pathogen Reduction in Rural Water Supplies. Water. 2010; 2(2):285-306. https://doi.org/10.3390/w2020285
Chicago/Turabian StyleTellen, Valentine, George Nkeng, and Steven Dentel. 2010. "Improved Filtration Technology for Pathogen Reduction in Rural Water Supplies" Water 2, no. 2: 285-306. https://doi.org/10.3390/w2020285