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Solid reductions and nutrient flows in biological phosporus sludge using thermophilic aerobic digestion Cross, Elizabeth


This study was on autothermal thermophilic aerobic digestion (ATAD) of "Biological Nutrient Removal" (BNR) sludge. Solids and nutrient balances were performed using 2 bench scale thermophilic aerobic digesters operated in series. In total there were 4 reactors; 2 series running in parallel. The digesters were fed waste activated sludge from a biological phosphorous removal treatment plant located in Penticton, B.C. Four experiments were completed, each under different aeration conditions and different hydraulic retention times i.e. a 2x2 factorial design. The aeration conditions were defined by a combination of airflow, oxidation reduction potential and dissolved oxygen measurements. The hydraulic retention times that were investigated were 24 hours and 48 hours and the aeration rates used in conjunction with them were 0.5 L/min and 1.5 L/min. The overall findings were that this type of treatment was extremely successful in decreasing chemical oxygen demands (COD) and solids levels. In the low air flow experiments the decrease in COD and solids values were, 35.5% and 45% respectively, and in the high air flow experiments they were 26.5% and 33% respectively. Orthophosphates were noted to increase significantly (+8%) in the low air flow experiments when compared to the high air flow experiments (-12.5%) i.e. therefore there was absorption of the orthophosphates happening in the high air experiments. The total kjeldahl nitrogen (TKN) values were found to decrease by 30% in the low air experiments and 27.5% in the high air flow experiments. The liquid phase nitrogen increased by 134% in the low air experiment and by 124% in high air flow experiments.

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