Mitigation of ammonia gas from animal house using microalgae
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We suggest a strong potential of algae to mitigate ammonia gas from animal house and to be used as a high-value animal feed. Ammonia gas emission from animal manure decomposition is a major concern in animal housing operations. Excessive ammonia gas volatilization will affect both animal and worker health and can also cause significant environmental concerns. Current ammonia gas mitigation methods are based on physical, chemical, biological, and dietary treatments, but the costs are high and the performances are not stable. In this project, we proposed an algae-based method for removing ammonia gas generated from animal housing operations while producing a biomass with high protein content which can be potentially used as high-value animal feed products. The green algae Scenedesmus dimorphus was used for evaluating its ability to mitigate ammonia gas in a gas-lift photobioreactor under continuous operational mode. Different conditions were tested for optimal algal biomass productivity: 0.05, 0.1, 0.2, and 0.3 day-1 of dilution rate; 17, 42, 60, and 72 ppm of ammonia gas concentration in inlet air; and pH 5, 6, 7, and 8. The nitrogen mass balance was calculated for each case and results showed that as high as 98.6 % of nitrogen was assimilated by algae biomass at optimal condition (60ppm, pH 7, and 0.1 day-1 of dilution rate). The amino acid profile of the biomass was also analyzed in application of algae as a source of animal feed. This experiment implies two benefits. One is economic benefit, i.e., cost down ammonia gas removal and algae growth, the other is a new algae market: animal feed.