Full Description

Many reverse osmosis plants treat groundwater containing dissolved hydrogen sulfide. In the membrane process, hydrogen sulfide is not significantly rejected by the membrane and is found in both the permeate and concentrate streams. The EPA has determined that sulfides are toxic to certain living organisms in surface waters and limit the concentration of sulfides in the discharge stream. The rules require that sulfides be limited to 0.2 mg/l if a successful biotoxicity test is conducted on the concentrate stream, otherwise, a limit of .002 mg/l is imposed. Permit conditions require that the dissolved oxygen in the discharge stream be greater than 5.0 mg/l. When sulfides exist in the concentrate the dissolved oxygen (DO) concentration will be very low or zero. Conventional methods of removing hydrogen sulfide from RO concentrate use a forced draft packed tower aerator (PTA) similar to the degasifiers used on the permeate streams. The packed tower aerator usually requires an odor control scrubber downstream of the PTA. The disadvantages of the PTA include high initial cost, high operating costs associated with the odor control system chemicals and additional pumping costs. Fouling with sulfur slime and odor problems are often found with the conventional methods. An alternative to the PTA method is the in-line oxidation system which mixes air and chlorine directly into the stream of concentrate to oxidize the H2S and increase the DO. A novel pressurized In-line Oxidation System was pilot tested and a full size system installed at the Indian River County, Florida, North Beach RO plant in 1992. This paper presents the process and mechanical design of the in-line system; the operating results from the pilot test and actual full size system; a discussion of the biotoxicity screening test; a present worth analysis showing the construction and operating costs of both the conventional PTA/Odor control method and the In-line Oxidation System.

Product Details

Published: 01/01/1993 ISBN(s): 0898677076 Number of Pages: 7File Size: 1 file , 210 KB