Removal of Hydrogen Sulphide from Water

Problem statement: The concentration of H₂S in groundwater is a significant problem in various areas across Canada. Hydrogen sulphide dissolves in ground water imparting undesirable taste and irritating rotten egg smell which makes it unpalatable. Ingestion of sulphides through drinking water can result in stomach discomfort, nausea and vomiting. Humans exposed to high concentrations of H₂S for prolonged periods show symptoms of gastro-intestinal upset, anorexia, nausea, somnolence, amnesia, loss of consciousness, delirium, hallucinations, difficulty in swallowing, low blood pressure, slowing of heart rate, double vision and epileptiform convulsions. Hydrogen sulphide in blood is rapidly oxidized by molecular oxygen and thus reduces the oxidation power of haemoglobin. Unoxidized hydrogen sulphide can act upon the central nervous system and cause either paralysis or respiratory failure. It is therefore, necessary to have a very low concentration of H₂S in the water. Approach: An automatic system for the addition of KMnO₄ and removal of hydrogen sulphide from ground water was developed and tested. The system consisted of a freshwater tank, a pump, a chemical storage tank, a solenoid valve, a photocell and electronic circuit, a drainage tank, a filter and a set of valves. It was possible to use a photocell to detect the presence of excess KMnO₄ in the system and to control the addition of KMnO₄ into the system. Results: The system accomplished complete removal of hydrogen sulphide in the range of 1-30 ppm. The present system utilizes on/off control for the addition of the chemical. The amount of KMnO₄ needed as a percentage of the amount used was in the range of 5-28%. Conclusion: The photocell and circuit could be used to add an amount of chemical that is constantly proportional to the amount of hydrogen sulphide in the water. The control of a positive displacement chemical feed pump would be an ideal application for this system. The speed of the pump could be controlled in such a manner that would allow a very small excess amount of potassium permanganate to be maintained in the system.