APPLICATION OF LOW-TEMPERATURE THERMAL ARC PLASMA REACTOR FOR PETROLEUM INDUSTRY WASTEWATER SLUDGE TREATMENT

A large quantity of wastewater sludge is generated yearly. Traditional disposal methods are short of providing the much needed benign treatment. Thermal plasma is a promising treatment technique to address this problem. A 20 cm3 capacity laboratory-scale thermal-arc plasma reactor was developed using a 4.5 kW TIG welding torch and was used to treat wastewater sludge. The design was based on a DC transferred-arc torch with argon gas as plasma forming gas. The reactor was tested with wastewater sludge from the petroleum industry. The plasma arc temperature was in the range of 356 – 1694 oC at an arc current of 100 – 190 A. Two products, flue gas and a vitreous slag were obtained. A mass reduction of 36.87 – 91.40% of the sludge was achieved at an arc current 150 – 190 A, which correspond to a plasma temperature range of 539 – 1603 oC. The mass reduction increased with treatment duration from 2 – 8 min. The mass reduction also increased with increasing arc current from 150 – 190 A at an interval of 20 A. Reduction in total organic carbon (TOC) was between 74.03 – 75.83%. The metal elements in the wastewater sludge were enriched after the plasma treatment. The composition of the flue gas is H2, CO, O2, CO2, CH4 and C2 hydrocarbons. CO is the major component accounting for over 74%. The concentration of greenhouse gases (CH4 and CO2 combined) is less than unity. The system was able to gasify the organics in the wastewater sludge to combustible gases and vitrified the inorganics into a slag. Keyword: Thermal plasma, wastewater sludge, plasma temperature, mass reduction, TOC, carbon conversion