Optimizing media and substrate for efficient anaerobic biological ammonia synthesis: A response surface methodology approach

Abstract

Ammonia ranks among the most extensively produced natural and anthropogenic chemicals due to its immense applications, especially in agriculture as fertilizer. The global demand for ammonia has thus been projected to increase. Haber process, the conventional method of ammonia production is costly, energy intensive and responsible for ∼2% of CO₂ emission. The rumen Hyper Ammonia Producing Bacteria (HAB) has the potential to convert protein to ammonia. To develop an industrial feasible ammonia production alternative, this study aims to optimize soy-based media composition for biological ammonia using response surface methodology (RSM). A one-factor-at-a-time (OFAT) statistical design was used to determine the most important media components affecting biological ammonia production. Eight media components were screened, and results showed that K₂HPO₄, KH₂PO₄, Na₂SO₄ and soy meal protein isolate (SMPI) had the most significant impact on biological ammonia production. The four identified media components were further optimized using a central composite design (CCD). The RSM model equation for independent and response variables was computed and used to create the response surface and contour plots. Results showed a maximum biological ammonia experimental yield of ∼7,500 mg/L at 0.0492 g/100 mL K₂HPO₄, 0.0492 g/100 mL KH₂PO₄, 0.64 g/100 mL Na₂SO₄, and 10 % SMPI. The observed yield was ∼80 % higher than the biological ammonia production from previous studies.