Post-hydrolysis ammonia stripping as a new approach to enhance the two-stage anaerobic digestion of poultry manure: Optimization and statistical modelling

Abstract

Post-hydrolysis ammonia stripping was investigated as a new approach to enhance the methane potential of high ammonia substrates, such as poultry manure. The objective of the proposed approach is to address some of the noticeable disadvantages in the existing ammonia-stripping techniques i.e., treatment of raw samples and side-stream stripping. Poultry manure (PM) and a co-substrate (mixed wastes from a cheese factory and a coffee house, referred to as MS) characterized by a high carbon-to-nitrogen ratio were mixed at five different ratios: PM:MS of 100:0, 75:25, 50:50, 25:75, and 0:100. Samples were hydrolyzed for six days to promote ammonia conversion from organic nitrogen and then the samples with higher ammonia levels (>2000 mg NH3–N/L) were stripped with air at initial pH values of 9 and 10 and temperatures of 40 and 55 °C. Biochemical methane potential (BMP) test results showed that post-hydrolysis ammonia stripping had alleviated ammonia inhibition and improved methane potential up to 200% when compared with untreated samples. The ammonia removal efficiency was mostly affected by pH. On the other hand, methane potential was highest in the samples treated at a higher temperature as their biodegradability was enhanced when compared with the samples treated at lower temperatures. Post-BMP characterization showed that the proposed approach had also limited the increase of ammonia in the digestate which ensured proper growth of methanogenic microorganisms.