Removing sulfates from waste water is conducive to the health of babies, who are made particularly ill by drinking contaminated groundwater.
Sulfates and heavy metals from waste water leach into groundwater, resulting in potentially disastrous effects. Sulfate-contaminated groundwater results in diarrhea and intestinal pain, dehydration, and a decrease in stomach acidity. Heavy metals, such as lead, copper, cadmium, and mercury, can damage the brain and central nervous system. Current procedures for waste water filtering can remove both sulfates and heavy metals from waste water with, advantageously, a low amount of leftover solid waste.
Instructions
1. Add hydrated lime to the waste water, to precipitate sulfate in the form of gypsum. Precipitation forces sulfate to take a solid form, which can easily be filtered out of solution. Mix the lime with the waste water, in a large tank, for 40 to 60 minutes. Afterwards, remove the gypsum by filtering; since you have precipitated pure gypsum, no special handling procedures for the gypsum disposal are necessary. This step reduces water sulfate concentrations to between 4000 and 5000 mg/L.
2. Add more hydrated lime to the waste water, after filtering, until pH (measured by a pH meter) reaches 10.5. Continuously mix for 40 to 60 minutes, once again. The higher pH causes metals to precipitate, in the form of sludge containing hydroxides. This step also precipitates more sulfates as gypsum. In total, about 45 pounds of gypsum and hydroxide waste sludge should precipitate per 1000 gallons of treated waste water.
3. Separate the gypsum and metals precipitated in Step 2 individually, to avoid the possibility of contaminating pure gypsum with metal sludge. As in Step 1, remove gypsum by filtering. Remove metal sludge by dewatering in a filter press, which uses pressure to separate solid waste from runny waste water.
4. Conduct a final sulfate precipitation. Increase pH again, using hydrated lime, to 11.5. The hydrated lime will react with sulfate to form a precipitate of ettringite, into which metals from the waste water may be incorporated. Remove the ettringite using a filter press.
5. Reduce the waste water pH, by adding carbon dioxide, to prevent it from depositing carbonates on surfaces and to meet disposal standards.
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