Thermal plasma treatment of stormwater sediments: comparison between DC non-transferred and partially transferred arc plasma

Abstract

The disposal of enormous amount of stormwater sediments becomes an emerging worldwide problem. Stormwater sediments are contaminated by heavy metals, phosphorus, trace organic and hydrocarbons, and cannot be disposed without treatment. Thermal plasma decontamination technology offers a high decomposition rate in a wide range of toxic organic compound and immobilization of heavy metal. In this study, we compared the treatment results between two different modes of thermal plasma: (1) a non-transferred direct current (DC) mode and (2) a partial DC-transferred mode. The reductions of total organic carbon (TOC) were, respectively, 25% and 80% for non-transferred and partially transferred plasma, respectively. Most of the toxic organic compounds were converted majorly to CxHy. In the gaseous emission, the accumulated CxHy, CO, NO and H2S were significantly higher in partially transferred mode than in non-transferred mode. The solid analysis demonstrated that the concentrations of Ca and Fe were enriched by 500% and 40%, respectively. New chemical compositions such as KAlSi3O8, Fe3O4, NaCl and CaSO4 were formed after treatment in partially DC-transferred mode. The power inputs were 1 and 10 kW, respectively, for non-transferred DC mode and a partially DC-transferred mode. With a lower energy input, non-transferred plasma treatment can be used for decontamination of sediments with low TOC and metal concentration. Meanwhile, partially transferred thermal plasma with higher energy input is suitable for treating sediments with high TOC percentage and volatile metal concentration. The organic compounds are converted into valuable gaseous products which can be recycled as an energy source.

Thermal Plasma Treatment of Medical Waste

“…However, high temperature also means more heavy metals will volatilize to the gas phase. A number of studies have reported the volatilization of heavy metals in plasma treatment of various waste streams [ 40 , 108 – 110 ]. Although the percentage of metals in medical waste may be lower, it can not be neglected.…”

Thermal Plasma Treatment and Co-processing of Sludge for Utilization of Energy and Material

“…The crucible furnace (or only the part that contacts the material) must be conductive in a transferred arc plasma reactor. Brass, graphite, ,− ,,,, conductive refractories (10% carbon), and tungsten , may be selected as anode material. The cathode may consist of tungsten ,,, and graphite. ,, A copper sleeve electrically connects to the negative terminal of a DC power supply as well as the plasma gas supply.…”

“…Plasma gas, such as argon, passes through the sleeve and cathode and takes away the heat from the cathode and insulator. The plasma gases that have been used in the transferred arc plasma system for treating sludge include argon, ,,,,,, air, N 2 , , H 2 , Ar mixed with other gases, , and CO 2 . The ceramic insulator is used to isolate undesirable electrical arcs and keeps the plasma torch stable.…”

“…As shown in Figure b, a typical DC non-transferred arc plasma torch for treating sludge consists of a water-cooled tube and an electrode placed in the center of the tube as the cathode. The anode may be made of graphite, copper, ,, etc. The cathode may consist of tungsten, , graphite, etc.…”

“…The cathode may consist of tungsten, , graphite, etc. In various studies of non-transferred arc plasma treatment of sludges, H 2 O 10 , air, argon, ,,, CO 2 , Ar–H 2 , H 2 , and N 2 , were ever used as plasma gas. The plasma gas passes through a constricting nozzle (anode), being ionized to plasma, and exits the nozzle from a small orifice at a high speed as a result of the Venturi effect .…”