Nutrient recovery from anaerobically-digested dairy manure by struvite formation and its effect on gas releases

Manure management practices such as anaerobic digestion and lagoon storage have become important issues for large dairy farms partially due to water quality and air quality concerns caused by excess nitrogen and phosphorus. Prior research efforts have proven that struvite formation is an effective method for nutrients recovery from both municipal and agricultural wastewaters. However, little is known about nutrient recovery through struvite formation from anaerobically-digested dairy manure effluents.The effects of struvite precipitation on the releases of gases such as NH3, H2S, and CO2 are also unclear. In this thesis, both bench-scale tests and pilot-scale storage tests were conducted to investigate the factors that influence nitrogen and phosphorus recovery by struvite formation from anaerobically-digested dairy manure and the effects of this process on the releases of ammonia (NH3), nitrous oxide (N2O), methane (CH4), carbon dioxide (CO2) and hydrogen sulfide (H2S) during storage. The results of the bench-scale tests showed that over 98% as phosphate removal rate and over 97% as ammonium removal rate were achieved by struvite formation. Component molar ratio and pH were identified as the most sensitive parameters that affect the performance of struvite precipitation. The optimum pH and initial Mg2+:PO43-:NH4+ molar ratio were found to be 8.5 and 1.3:1.3:1, respectively. The results of the pilot-scale storage test suggested that struvite formation significantly reduced the releases of NH3, N2O and CH4. However, the influence of struvite crystallization on the releases of CO2 and H2S were less obvious