EVALUATION OF BIOLOGICAL PHOSPHOROUS REMOVAL VERSUS CHEMICAL PHOSPHOROUS REMOVAL AT A POTATO PROCESSING FACILITY

Wastewater from a potato processing facility is treated using an existing Upflow Anaerobic Sludge Blanket (UASB) treatment system followed by an activated sludge system with biological phosphorous removal. The operation of the biological phosphorous removal system required that the plant by-pass most of the wastewater around the UASB system thereby reducing the anaerobic biogas production, increasing activated sludge production and increasing aeration costs.The effects of the following modifications on the wastewater treatment system were evaluated as part of this study:Changing the production schedule of the plant from five days production followed by two days of shutdown to a ten day production, four day shutdown scheduleReducing the UASB bypass from 60% to 15%, to provide additional biogas productionDetailed wastewater treatment system operating data was gathered over a three year period and was used to calibrate a dynamic model of the anaerobic and activated sludge treatment processes. The treatment processes were simulated using the Activated Sludge Model No. 2d model, an extension of the IAWPRC Activated Sludge Model No. 1, as implemented using the commercially available GPS-X™ simulation software (Hydromantis Inc.). The calibrated model was used to study the dynamic effects on discharge parameters of the proposed modifications.The dynamic simulation was performed over 5 operational cycles under the new production schedule to ensure the model demonstrated consistent performance. The results of the simulation indicate the facility will remain in compliance with most required discharge parameters when the changes to the production schedule are made. A spike in effluent phosphorous concentrations were observed once the feed to the wastewater treatment system stopped at the end of the 10 day production schedule. The model estimated that the time to recover phosphorous levels to compliance targets was three to four days. In order to remain in compliance, the facility will have to add chemical (ferric chloride or aluminum sulfate) to remove phosphorous.Since the facility would require a chemical phosphorous removal system to meet discharge parameters approximately three days out of 14, the benefits of increasing flow to the anaerobic system and eliminating the biological phosphorous system entirely were evaluated using the dynamic model developed for the new production schedule. The effluent phosphorous results generated by the model were used to calculate ferric chloride volumes required to meet discharge parameters.Capital costs associated with reducing the bypass and using ferric chloride to remove phosphorous was estimated to be 171,000.The operating cost savings account for a reduction in aeration costs, an increase in chemical costs, an increase in revenue generated by anaerobic sludge and substantial biogas utilization cost benefits. The increased flow to the UASBs resulted in a net savings of 103,200 over one year. The associated payback was estimated at 1.17 years.Although previous evaluations of the UASB and activated sludge biological phosphorous removal system indicated that biological phosphorous removal was less costly than chemical phosphorous removal, this study indicated that at a facility where the facility can utilize the biogas, chemical phosphorous removal was more cost effective.