Co-immobilization of nitrifying bacteria and clinoptilolite

Kurt Templeton Preston, Purdue University

Abstract

Ammonia control and removal remains a challenge for both environmental engineers and aquaculturalists. In wastewater treatment, increasingly tighter controls are being placed on wastewater treatment plant operators in regard to nitrogenous discharge. Similarly, aquaculturalists are being challenged to control ammonia in closed-loop fish farming in an attempt to maintain profitability. Currently, ammonia removal options focus on biological fixed-film or flocculating systems. The primary organisms responsible for the oxidation of ammonia in wastewater treatment, Nitrosomonas and Nitrobacter, are notoriously slow growing, often suppressed by heterotrophic competition, and difficult to maintain within a biological reactor. The goal of this research is to develop a new method of biological ammonia removal which combines the control of ion exchange and the economy of nitrification. This is attempted by the co-immobilization of an enriched culture of nitrifying bacteria and clinoptilolite, a naturally occurring mineral which preferentially exchanges the ammonium ion, NH$\sb4\sp+.$ The experiments were divided into the following four groups: (1) Matrix Experiments; (2) Five Day Continuous-flow Reactor Experiments; (3) Sequenced Column Experiments, and (4) Shelf Life Experiments. The results of the matrix experiments indicate that barium alginate was the simplest, most durable, and least disruptive of the combinations attempted for the co-immobilization of nitrifying bacteria. Barium alginate with silica improved durability, but at the price of simplicity. Barium alginate with silica and clinoptilolite was the superior matrix of those tested for the co-immobilization of nitrifying biomass and clinoptilolite. The five day continuous-flow reactor experiments appeared to suggest that clinoptilolite co-immobilization did not significantly improve substrate utilization in the continuous reactor. The sequenced column experiments were perhaps the most interesting. It was apparent that the nitrifier/clinoptilolite system will take up ammonia as an ion-exchange column and hold it for biological recharge during a subsequent aeration cycle. It was demonstrated that the co-immobilized bed will remain active through numerous cycles. Finally, the shelf life experiments indicated that nitrifying biomass co-immobilized with clinoptilolite would remain viable for periods of at least three months when stored at a temperature of 4$\sp\circ$C. Once allowed to temperature equilibrate (2 hrs.), these co-immobilized, stored beads resumed their oxidation of ammonia. Overall conclusions. The immobilization of nitrifying bacteria in alginate gels with clinoptilolite provides a new and interesting variation for ammonia removal and oxidation. Much work remains to be performed, but the initial avenues for development are established.

Degree

Ph.D.

Advisors

Alleman, Purdue University.

Subject Area

Civil engineering|Sanitation|Environmental science

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