EVALUATION OF CLINOPTILOLITE FOR USE AS A SORPTIVE MICROBIAL CARRIER IN CONSTRUCTED WETLAND TREATMENT SYSTEMS DESIGNED TO TREAT AMMONIA

Sorptive materials may be used to remove dissolved ammonia from water. Transfer from the aqueous phase to binding sites may enhance performance in constructed wetland treatment systems (CWTSs) by concentrating ammonia where nitrifying bacteria (Nitrosomonas spp. and Nitrobacter spp.) may be active. The zeolite clinoptilolite was selected as a sorptive medium for use in CWTSs based on its affinity for ammonia and high surface area for growth and attachment of periphytic biofilms. The objective of this research was to determine the effects of clinoptilolite on ammonia treatment performance in pilot-scale CWTSs. A serial batch sorption experiment was performed to determine the ammonia sorptive capacity of clinoptilolite. Data from the serial batch sorption experiment were used to predict ammonia removal in response to clinoptilolite added (1000g and 500g) to a pair of pilot-scale CWTSs containing sandy sediment. After 50 days, nitrifying bacterial activity reactivity tests (n-BARTs) were used to detect the presence of nitrifying bacteria in the added clinoptilolite and sandy sediment. Results indicate that clinoptilolite has an affinity for ammonia described by the Freundlich equation Q=0.72C_e^0.57 for equilibrium ammonia-N concentrations from 0.07 to 30.1 mg/L. The addition of 1000g clinoptilolite to a CWTS operating on 2-day hydraulic retention time (HRT) and containing Schoenoplectus californicus produced a measurable decrease in the effluent concentration of ammonia-N when compared with a system containing no clinoptilolite (2.0 vs 5.6 mg/L) during a 10-day sampling period. The addition of 500g clinoptilolite to a CWTS operating on 4-day HRT and containing Typha latifolia produced no discernable difference in the effluent concentration of ammonia compared with a system containing no clinoptilolite. n-BARTs indicated similar levels of activity in both the sediment and clinoptilolite in the Schoenoplectus system. No activity was detected in either the sediment or clinoptilolite in the Typha system. The difference in performance between the Schoenoplectus and Typha systems is attributed to factors including dissolved oxygen and equilibrium ammonia concentrations. This work has demonstrated that clinoptilolite can be effective in increasing ammonia removal and nitrifying activity in CWTSs.