Fixed- and real-time dairy manure treatment and experiments on digestion and phosphorus recovery

A combined approach of biological treatment, solids digestion and nutrient recovery was tested on dairy manure. A total of three different sequencing batch reactors (SBRs) were studied. The first one, that employed mechanical mixing, was operated in three modes, in order to optimize nutrient (nitrogen and phosphorus) removals. The highest average removal efficiencies of 91% for NH₄-N, 59% for P0₄-P and 80% for total COD were achieved. Staining experiments suggested the coexistence of glycogen and phosphorus accumulating organisms. Anaerobic digestion of biosolids wasted from this reactor was able to produce a P0₄-P concentration of 70 mg/L in the supernatant. The second SBR employed gas-mixing, where the contents of the SBR were kept mixed by anoxic recirculation and air circulation in the anoxic and aerobic stages, respectively. The reactor showed interesting results, suggesting a relationship between nitrification and oxidation reduction potential (ORP). Little to no nitrification was observed when low ORP values of about -250 mV to -280 mV were encountered in the aerobic phase. The deterioration and re-establishment of nitrification appeared to be in relation to the ORP values being below or above ORP values, in the order of 0 mV. The third pilot-scale SBR used real-time control strategies for controlling cycle times. It was designed to detect the end of nitrification, which coincides with the disappearance of ammonical-nitrogen (NH₄-N) from the mixed liquor of the reactor. It was found that the reactor gave> 99% NH₄-N treatment efficiency for most of the study period, even when the operating conditions were not steady. The reactor, however, gave high (80-90%) orthophosphate-phosphorus (P0₄-P) removals only when the feed conditions reached a relatively steady state. A pilot scale experiment, designed to recover phosphorus (as struvite, magnesium ammonium phosphate) in the supernatant obtained from acetate treatment ofbiosolids wasted from this SBR, was able to remove 82% of soluble P0₄-P.Applied Science, Faculty ofCivil Engineering, Department ofGraduat