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ABSTRACT: Ammonia is discharged at significant concentrations in coke-plant effluents and can adversely impact freshwater-receiving streams. This article reports on the removal of ammonia from such wastewaters by using synthetic zeolites. Factors affecting the ammonium exchange capacity included the contact time, the concentration of ammonia in the solution, the particle size of the zeolites, the loading flow rates, and the number of regenerations of zeolite. The 13x molecular sieve has also been tested for its capacity to remove ammonia from coke-plant secondary wastewater.
Results indicate that the ammonium adsorption rate increases with an increase in the contact time of zeolite with ammonia solution. Smaller particle size of the zeolite, increase in ammonium concentration, and lower loading flow rate elevate ammonium exchange capacity for the zeolite. Regeneration of the zeolite with NaCl solution reactivates the zeolite column, and repeated column regeneration is possible without loss of ammonium uptake capacity. Water Environ. Res., 69, 157 (1997). KEYWORDS: adsorption, ammonia, coke plant, treatment, zeolite.
Ammonia that is discharged by coke plants at high concentration in effluents can adversely impact freshwater-receiving streams. Because it is highly water soluble, ammonia will exert deleterious effects on receiving streams if it is not removed before discharge of wastewater. The maximum allowable concentration of ammonia in industrial wastewaters discharged into inland surface waters is 50 mg/L according to Indian Standards: 2490 (Indian Standards, 1981).
The available techniques (Prasad and Singh,1991a) for ammonia removal include the following: (1) recovering ammonia by concentrating it (ion exchange, reverse osmosis, or chemical precipitation), (2) stripping it as ammonia gas (air or steam stripping), and (3) destroying it by converting into nitrogen (breakpoint chlorination or biological nitrification-denitrification). Ion exchange is a well-known technique for purification of wastewater. Ion exchange may be done with ion-exchange resins, synthetic polymeric materials, natural zeolites, or synthetic zeolites. By using these ion exchangers, a selective ion-exchange process can be developed as the most useful ammonia-removal process. The advantage of this process is that it facilitates either recovery of ammonia or conversion of it into nitrogen gas by oxidation. This ion-exchange process has the following added advantages: (1) good performance of ammonia removal under low temperature and (2) compact size and easy maintenance of the full-scale plant. Materials and Methods
The synthetic zeolites...