1. Evaluation of the removal of heavy metals using the Biosand Filter
Lesly J. Mamani Paco
Laboratorios Analíticos del Sur, Peru
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2. Reason & Purpose for Study
The drinking water sources for the peri-urban communities surrounding Lima, Peru are contaminated with heavy metals from closed mines that had not been abandoned properly.
This study was undertaken to evaluate if the biosand filter*, with and without amendment, could remove these heavy metal contaminants from the drinking water.
* A sand filter sized for a household’s water needs
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3. CAWST Learning Exchange - June 2011
Objective
To evaluate the removal of heavy metals* from drinking water; using the Biosand filter (BSF) amended with copper-zinc granules and activated carbon.
* chromium (Cr), cadmium (Cd), lead (Pb) and iron (Fe)
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4. Experimental procedure
10 biosand filters for each metal studied (40 in total)
For 3 metals; Chromium (Cr), Cadmium (Cd) and Iron (Fe): 6 filters were amended with differing amounts of Cu-Zn and activated carbon (accessory) and 4 were not amended.
In the experiments for Lead (Pb); all 10 filters were amended.
Targeted 3 initial concentrations (Ci) of each metal:
Ci ≈ LMP; Ci ≈ 10 · LMP; Ci ≈ 100 · LMP
Where LMP is maximum allowable limit for drinking water; Cr = 50 µg/L; Cd = 3 µg/L; Pb = 10 µg/L; Fe = 300 µg/L (Peruvian Legislation)
LMP: límite máximo permitido (Maximum limit allowed)
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Chromium (Cr)
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6. Results: Percentage removal of Cr
Chromium average removal
(final concentration / initial concentration) in percent
Removal %
Ci (low): µg/L
Ci (intermediate): µg/L
Ci (high). 2,530 µg/L
-For an initial low chrome concentration (near to LMP), the removal percentage is between %. Maximum removal was obtained with the filter of 1000g of grains of Cu-Zn and 200 grams of activated carbon. The four filters without accessories have lower removals.
For intermediate initial concentrations ( of approximately 10 times the LMP) the removal % oscillates between 97 and 99 %. The highest removal is for filters with grains Cu-Zn of 1000g de Cu-Zn, but it is not observed the influence of active carbon. The removal is greater in a maximum of 3%, that in the case of filters without accessories.
-For high initial concentrations (100 times LMP), the % of removal is always higher than 99%.
It is observed that when initial concentration of chrome increases, the removal percentage of chrome also increases.
Filter
Activated carbon (g)
Cu-Zn granules (g)

7. Results: Percent removal with and without accessory
Chromium removal percentage - High initial conc. (Ci)
(final concentration/ initial concentration) in percent
Removal WITH accessory
Ci = 2,530 µg/L
Removal WITHOUT accessory
Ci = 1,545 µg/L
Removal %
Removal percentages for filters with accessories (grains of Cu-Zn) with initial high concentrations of chrome are always between 99,9 %
In the case of the same initial concentration condition but for filters without accessory, the removal percentages are above 99%.
Consequently, the difference between including or not accessory is 0,5% -1 % in Cr removal.
Filter
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Results for Chromium
Removal Effectiveness:
In all tests, with and without accessory, Cr concentrations were reduced by 85% %
Higher removals were found for higher initial concentrations
Improvement in removal WITH accessory versus WITHOUT accessory ranged from 1 -5% depending on initial concentration
Little benefit apparent from greater amounts of Cu-Zn granules
Output Concentration of Chromium:
No result exceeded the maximum allowed limit: 50 µg/L
pH Influence:
In general, initial pH has no influence in chromium removal
The increase of pH might be due to contact of water with the limestone in the filter bed. This is favorable for the removal process due to precipitation of chrome due to increase of pH.
The basis of chrome precipitation theory in aqueous solutions is based on the solubility curve where appears the theoretical performance of chrome (that presents a minimum solubility of approximately pH 8).
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Cadmium (Cd)
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10. Results : Percentage removal of Cadmium
Cadmium average removal
(final concentration / initial concentration) in percent
Removal %
Ci (low): 4.1 µg/L
Ci (intermediate): 31µg/L
Ci (high) µg/L
-For an initial low concentration of cadmio (next to LMP) the removal percentage is %. No significant influence of Cu-Zn grains is noted. The same for activated carbon.
For intermediate initial concentrations (of approximately 10 times LMP), the removal % is over 99 %. No significant influence is appreciated from Cu-Zn grains nor of activated carbon.
For high initial concentrations (100 times LMP), removal % is always over 99,9%. No significant influence is appreciated from Cu-Zn grains nor of activated carbon.
It is noted that as the initial concentration of cadmio increases, the percentage of cadmio removal also increase; in all the filters (independently that they have accessories or not) there are removal % higher than 90%
Filter
Activated carbon (g)
Cu-Zn granules (g)
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11. Results: Cadmium removal with and without accessory
Cadmium removal percentage (High Ci)
(final concentration/ initial concentration) in percent
AVERAGE WITH accessory
Ci = 280 µg/L
AVERAGE WITHOUT accessory
Ci = 253 µg/L
Removal %
It can be observed how the filters with and without accessories have no significant differences in the removal percentage
Filter
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Results for Cadmium
Removal Effectiveness:
In all tests, with and without accessory, Cd concentrations were reduced by 88% %
Higher removals were found for higher Ci
No improvement in removal WITH accessory versus WITHOUT accessory is apparent at any initial concentrations
No benefit from any amount of Cu-Zn or activated carbon
Output Concentration of Cadmium:
No result exceeded the maximum allowed limit: 3 µg/L
pH Influence:
In general, initial pH has no influence in chromium removal
The increase of pH might be due to contact of water with the limestone in the filter bed. This is favorable for the removal process due to precipitation of chrome due to increase of pH.
The basis of chrome precipitation theory in aqueous solutions is based on the solubility curve where appears the theoretical performance of chrome (that presents a minimum solubility of approximately pH 8).
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Lead (Pb)
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14. Results: Percent Removal of Lead
Lead average removal
Ci (low): 21.5 µg/L
Ci (intermediate): µg/L
Ci (high) µg/L
Removal %
In this case all the filters had accessories.
-For an initial low concentration of lead (next to LMP), the removal percentage is between %. Apparently there is no influence of activated carbon and the highest removals are obtained with 750 and 1000 g of Cu – Zn grains.
For intermediate initial concentrations (of approximately 10 times the LMP), the removal % is over 75 %. The higher removal is observed for 1000 g of Cu-Zn grains and 200 g of activated carbon.
For initial high concentrations (100 times LMP), the removal % is always over 98%. No significant influence is noted from the Cu-Zn grains or activated carbon.
It is observed that as the initial lead concentration increases, the lead removal percentage also increases.
The difference in lead removal percentages might be explained by the affinity of some microorganisms for various heavy metals, included lead.
Filter
Activated carbon (g)
Cu-Zn granules (g)
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15. Results: Lead removal with and without accessory
Lead removal percentage (High Ci)
(final concentration/ initial concentration) in percent
AVERAGE WITH accessory
Ci = 890 µg/L
AVERAGE WITHOUT accessory
Ci = 879 µg/L
Removal %
Studies of filters without accessories were made to study their influence
It can be observed how the filters with accessories have removal percentages slightly higher than the filters without accessories (between 0,3-1,6 %). Even though, in all the cases, the removal percentage is 97% or higher.
Filter
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Results for Lead
Removal Effectiveness:
20 – 40% removal for Low Ci (21.5 µg/L)
70 – 90% for Intermediate Ci (104.5 µg/L)
97 – 99% for High Ci (890.2 µg/L)
No apparent change from differing amounts of Cu-Zn or activated carbon
Output Concentration of Lead:
Some results exceeded the maximum allowed limit of 10 µg/L especially at the higher Ci
pH Influence:
In general, initial pH has no influence in lead removal
The increase of pH might be due to contact of water with the limestone in the filter bed. This is favorable for the removal process due to precipitation of chrome due to increase of pH.
The basis of chrome precipitation theory in aqueous solutions is based on the solubility curve where appears the theoretical performance of chrome (that presents a minimum solubility of approximately pH 8).
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Iron (Fe)
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18. Results: Average % of Iron removal
Iron removal; average percentage
Ci (low) =
315.3 µg/L
Ci (intermediate) =
553.1 µg/L
Ci (high) =
3146 µg/L
Removal %
-For an initial low concentration of iron (next to LMP) the removal percentage is between 77-89%. Apparently there is no direct influence of the accessory on the removal % as F39 had the best results lacking it of accessories.
For intermediate initial concentrations (of approximately 20 times LMP) the removal % is between 93-97%. Once again it is not observed the influence of the accessory in the iron removal.
For initial high concentrations (100 times LMP) the removal % is always over 98%. No significant influences is noted from Cu –ZN grains nor of activated carbon.
It is observed that as the initial iron concentration increase the removal percentage also increase.
The absence of influence of accessories in the removal or iron might be due to oxidation and later precipitation of ions soluble in iron II as hydroxides. -
Filter
Activated carbon (g)
Cu-Zn granules (g)
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19. Results: Iron removal with and without accessory
Iron removal percentage (High Ci)
(final concentration/ initial concentration) in percent
AVERAGE WITH accessory
Ci = 3,146 µg/L
AVERAGE WITHOUT accessory
Ci = 3,712 µg/L
Removal %
The comparative analysis of the results with or without accessory are not conclusive. In general, no influence of the accessory in the removal of iron can be observed; it might be due to the precipitation process and not to the presence of accessory.
Filter
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Results for Iron
Removal Effectiveness:
75 – 90% removal for Low Ci (315 µg/L)
90 – 97% for Intermediate Ci (553 µg/L)
98 – 99% for High Ci (3146 µg/L)
No improvement in removal WITH accessory versus WITHOUT accessory is apparent at any initial concentrations
No apparent change from differing amounts of Cu-Zn or activated carbon
Output Concentration of Lead:
No results exceeded the maximum allowed limit of 300 µg/L
pH Influence:
In general, initial pH has no influence in iron removal
The increase of pH might be due to contact of water with the limestone in the filter bed. This is favorable for the removal process due to precipitation of chrome due to increase of pH.
The basis of chrome precipitation theory in aqueous solutions is based on the solubility curve where appears the theoretical performance of chrome (that presents a minimum solubility of approximately pH 8).
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21. Conclusions (Laboratory)
Based on the results from these experiments, the biosand filter demonstrated good removal effectiveness with and without the use of Cu- Zn granules and activated carbon.
Removal effectiveness increased with higher initial concentrations for all metals.
No influence of the accessory, Cu-Zn granules and activated carbon, was observed in the cadmium and iron removal. For the case of chromium, the presence of the accessory improved removal a maximum of 5%.
pH input had no influence in the removal effectiveness. pH increased in the effluent in all cases as a result of the water contacting the calcium carbonate in the concrete body of the filter.
For all the metals (except the lead) all the output samples were under the guidelines determined by WHO.
Conclusion of study:
Conclusions that can be obtained from the study are as follows:
Additional analysis should be made on this theme.
BSF seems to be quite efficient in the removal of metals studied.
The presence of accessories (Cu-Zn grains and activated carbon) do not improve removal results.
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22. CAWST Learning Exchange - June 2011
Research Issues
This study was short-term (approx. 2 months) with limited repeated sampling. Additional long-term testing is needed to determine if the removal effectiveness decreases with time.
Detailed information regarding the filters (sand size, ripening time, daily throughput) was not available.
The source water chemistry was not characterized. Further testing with different water sources is necessary to determine if the results are applicable generally.
The biosand filter did remarkably well in removing these heavy metal contaminants. Further research of this topic is recommended to validate the results and address the research issues.
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