Immobilization of Azospira sp. strain I13 by gel entrapment for mitigation of NO from biological wastewater treatment plants: Biokinetic characterization and modeling.

Development of a strategy to mitigate nitrous oxide (NO) emitted from biological sources is important in the nexus of wastewater treatment and greenhouse gas emission. To this end, immobilization of NO-reducing bacteria as a biofilm has the potential to ameliorate oxygen (O) inhibition of the metabolic activity of the bacteria. We demonstrated the effectiveness of calcium alginate gel entrapment of the nosZ clade II type NO-reducing bacterium, Azospira sp. strain I13, in reducing levels of NO, irrespective of the presence of O. Azospira sp. strain I13 cells in the gel exhibited NO reduction up to a maximum dissolved oxygen concentration of 100 μM in the bulk liquid. The maximum apparent NO uptake rate, [Formula: see text] , by gel immobilization did not appreciably decrease, retaining 72% of the NO reduction rate of the cell suspension of Azospira sp. strain I13. Whereas gel immobilization increased the apparent half-saturation constant for NO, [Formula: see text] , and the apparent O inhibition constant, [Formula: see text] , representing the degree of O resistance, correspondingly increased. A mechanistic model introducing diffusion and the reactions of NO consumption was used to describe the experimental observations. Incorporating Thieles modulus into the model determined an appropriate gel size to achieve NO reduction even under aerobic conditions.

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