M. Tomar, T. H. Abdullah
Dec 1, 1994
Abstract The effect of hydrogen peroxide, sodium/calcium hypochlorite and ferrous/ferric salts on hydrogen sulfide dissolved in waste water were investigated to establish an effective odour control system for Kuwait Sewage Networks. The waste water samples were collected from the inlet structure of main pumping station with pressure pipelines and analyzed for dissolved sulfide and pH before and after addition of chemicals individually and in combination under controlled laboratory conditions. The waste water contained dissolved sulfide in the range of 18 to 25 mg/l and pH ranged between 7.2 and 7.8. Various concentrations of above mentioned chemicals were tried to determine the accurate chemical requirement for oxidation or precipitation of dissolved sulfide in waste water. The reaction temperature was maintained at 35°C (±2°C), the normal temperature of waste water in Kuwait during summer. To oxidize 1 g of sulfide 1.25, 2.0 and 1.8 g hydrogen peroxide, sodium hypochlorite and calcium hypochlorite were required respectively. To remove 1 g of sulfide by precipitation with ferrous sulfate and ferric salt solution, 8 g and 4 g ferrous and ferric salt were required respectively under laboratory investigations. A combination of sodium hydroxide and sodium hypochlorite was also studied to control malodorous hydrogen sulfide in waste water. The addition of sodium hydroxide with sodium hypochlorite in waste water reduced the demand of hypochlorite 50%. This procedure was found to be cost effective and best suited for the warm climate of Kuwait and was implemented in the field at a screw conveyor type lifting station with gravity sewer pipelines. When sodium hypochlorite was injected without shock loadings of sodium hydroxide 46% reduction of dissolved sulfides was recorded and it was increased to 57% with shock loadings of sodium hydroxide, though the quantity of sodium hypochlorite was reduced to half than the former case. Similarly, 45 and 70% reduction in the emission of gaseous hydrogen sulfide was recorded with NaOCl injection without and with NaOH shock loading respectively. The cost comparison of all the chemicals when applied in field is also presented.