Effect of ammonia on anaerobic degradation of amino acids

Abstract

Since amino acids are the main intermediates converted from protein and they produce ammonia which affects on the efficiency of anaerobic digestion, the effect of ammonia on anaerobic degradation of the amino acids should be evaluated. As the initial NH4+-N concentrations increased from 0 to 5,000 mg NH4+-N/L, deamination of the amino acids decreased from 100 to 55% implying that deamination was inhibited by the ammonia toxicity. Although the initial NH4+-N was absent, the produced ammonia from the amino acids inhibited methane production. VFAs produced through deamination accumulated and were not converted to methane due to the ammonia toxicity. Among all of the amino acids, only β-alanine was very sensitive to ammonia inhibition. Conclusively, concentration of ammonia both in wastewater and to be produced from amino acids should be investigated for better anaerobic digestion of wastewater having a high content of protein such as hydrolysed wastewater sludge.