CHEMICAL FREE PHOSPHOROUS ELIMINSTION P-UPTAKE PROCESS

Transcription

1 CHEMICAL FREE PHOSPHOROUS ELIMINSTION P-UPTAKE PROCESS 2013 Florida Water Resources Conference Albert Bock Panama City, Florida, (407) ,

2 1 Introduction: Today Bay County is successfully meeting effluent phosphorous compliance entirely without the use of chemical treatment. Bay County Utilities was looking for a process procedure that could eliminate the high phosphorous content side streams from the aerobic digesters without using expensive chemicals as well as an overall solution to meet effluent phosphorous permit levels together with lower operating and chemical costs. The procedure for phosphorous control was finally changed in May 2011 with positive and immediate results generating significant operational cost savings that exceeded the Utilities expectations by far. Mid 2011 Bay County Utilities adopted the use of the P-Uptake Process for effluent phosphorous and digester side stream control, which has completely eliminated the daily use of chemicals for P-control and additionally reduced the treatment plants power costs by over 20 %. The P-Uptake Process is a Digester Process Method that reduces the BNR Total Phosphorous Inventory to low concentrations, which automatically generates effluent phosphorous values below 0.5 mg/l. Chemicals for phosphorous control are kept on site and only used for backup in emergency conditions. Bay County AWTF enjoys the following advantages by using the P-Uptake Process: Significant Chemical Cost Savings 20 Percent Overall Power Cost Savings Zero Capital Start up Costs Reliable Process Stability Long Term Economic Benefits Increase in Operational and Process Knowledge State Wide Recognition for Outstanding and Efficient Plant Operation The Florida Department of Environmental Protection awarded Bay County Utilities the winner of the 2012 Operations Excellence Award for the State of Florida for using the P-Uptake Process. Bay County has also shared the knowledge of the process method with other treatment plants in our area. These plants are now experiencing the same positive results in chemical and power cost savings.

3 Since September 2012 Bay County Utilities has moved to full automation and monitoring of the P-Uptake Process. This automation was an in house project using our own resources for design, installation, and implementation. 2 Process Overview: The P-Uptake Process is a digester process method that operates the aerobic digesters in 3 alternating process cycles. This process utilizes a biochemical process technology that binds and fixes large amounts of phosphorous in the digested bio solids. The digested biosolids of the P-Uptake process removes greater amounts of phosphorous from the wastewater treatment plant BNR, than the influent flow delivers. This method reduces and maintains the treatment plant s total phosphorous inventory to very low concentrations. A low BNR total phosphorous inventory automatically reduces the effluent phosphorous concentration to less than 0.5 mg/l without using chemicals. Customized digester process cycles reduce the digester aeration time by over 80 % compared to a conventional aerobic digester process. Facilities using the P-Uptake Process experience major overall power cost savings of typically > 20%. 3 Digester Cycles of the P-Uptake Process: 3.1 Anaerobic Cycle Waste activated sludge is treated for periods of time under anaerobic conditions. In this cycle the volatile components of the biosolids are broken down to organic acids. Ammonia, phosphorous and calcium carbonates are ionized and released during the anaerobic digestion phase. 3.2 Aerobic Cycle Following the anaerobic cycle the bio solids are treated in an aerobic cycle. Under aerobic conditions the soluble organic acids and carbonates are striped out of the liquid sludge phase in the form of CO 2 gas, which is then released into the atmosphere. This step generates a positive ph shift in the sludge and catalyzes a biochemical reaction between the calcium and phosphates. Calcium, which previously was reacting with the air stripped carbonates, becomes available and reactive. The available reactive calcium now chemically reacts with the soluble phosphorous and forms Calcium Phosphates and Calcium Hydrogen Phosphates. These insoluble compounds then become part of the sludge structure. This reaction continues, as long as soluble calcium is available. The ortho phosphate concentration is reduced during the digester aeration cycle significantly from > 40 mg/l to < 2 mg/l.

4 Concentration mg/l Dewater Cycle Phosphorous Uptake during Aeration Cycle Aeration Time (h) The sludge dewatering cycle is initiated once the soluble phosphorous concentration of the digested sludge is less than 10 mg/l. Now over 98 percent of the digester s total phosphorous inventory is bound up in the sludge in the form of calcium phosphate and calcium hydrogen phosphate compounds. The biosolids are dewatered and disposed of to a land application site. The centrate from the dewatering facility contains total phosphorous concentrations of < 10mg/L and is returned to the wastewater treatment facility. Conventional aerobic digesters generate Phosphorous side streams of > 150 mg/l. These high loaded site streams cause overloads of the treatment plant system and require chemical phosphorous fixation to meet effluent permit compliance parameters.

5 Annual Chemical Costs ($) Annual Power Costs ($) 4 Bay County Cost Savings: 4.1 Annual Power Cost Savings The controlled digester aeration cycles reduced the treatment plant facility s overall annual power costs by approximately 20 % from $300,000 to $225, Annual Power Cost Savings Without P-Uptake With P-Uptake 4.2 Annual Chemical Cost Savings The AWT has entirely eliminated the daily use of chemicals for effluent phosphorous control. A small quantity of aluminum sulfate is stored on site for emergency treatment only. The overall annual cost savings for chemicals average over $40, ,000 45,000 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 Annual Chemical Cost Savings Without P-Uptake With P-Uptake

6 4.3 Overall Annual Process Cost Savings The Bay County Military Point AWTF s annual cost savings average > $115,000 due to the operation of the P-Uptake Process. The process method was implemented with zero capital investment costs by using existing on site equipment and digester tanks. 5 Automation of the P-Uptake Process: Operating the P-Uptake Process required monitoring, sampling, and hourly evaluations by the treatment plant staff during the length of the aeration cycle. Onsite process training by the Plant Supervisor followed by written SOP instructions that guide the operators through the process steps and are guarantors for successful operation. Bay County Utilities automated the monitoring of the P-Uptake process to achieve an even higher productivity and efficiency of the process. The utility staff designed a continuous flow monitoring vessel that monitors the digester tanks during the aeration phase. The sampling vessel is equipped with a phosphorous analyzer which transmits the readings to the SCADA system where the data is processed and analyzed. The automated monitoring system of the P-Uptake Process consists of: 5.1 Sample Tank The sample tank is connected to each of the four digesters and fed by gravity force. Isolation valves on each digester tank enable the operator to feed the sample tank from the digester that is in the aeration cycle for continuous monitoring. The tank is also equipped with a return pump, which maintains a constant tank level and returns the sludge sample from the sampling vessel to the digester. The sample tank includes an overflow pipe which leads directly into the sanitary sewer drain to prevent possible spills. An alarm will be initiated on the SCADA system if the return pump fails, or the sludge level reaches the high float ball level.

7 5.2 Return Pump The Return pump maintains a constant sample tank level and pumps the sludge back into the digester that feeds the sample tank. The return pump is controlled by float balls. A portion of the return flow is recycled back into the sample vessel to keep the sludge sample continuously suspended. 5.3 Phosphorous analyzer The sample tank is equipped with a phosphorous analyzer that measures the phosphorous uptake during the aeration cycle. The readings are send to the Scada System for evaluation and monitoring by the utility staff. The phosphorous analyzer consists of three units: - a self cleaning sample membrane that prepares and filters the sludge sample, - a phosphorous measuring unit that analyzes the sample, and - a digital controller that displays the measuring results locally and transmits a 4-20 ma signal to the PLC.

8 5.4 SCADA Control The digital controller sends a 4-20 ma signal to the PLC, which is connected to the SCADA system. The Phosphorous concentration data is displayed on the SCADA system in the form of a data table and a digital trend chart. The in house engineered control logic of the SCADA system analyses the Phosphorous data continuously during the aeration cycle. The program is designed so that possible sample errors of the analyzer are identified and invalidated. The control logic s logarithm also determines the completion of the aeration cycle and initiates an alarm for the operator to start the dewatering cycle. High level tank alarms and possible pump failures are also monitored by the SCADA system. 6 SUMMARY: The automated monitoring system of the P-Uptake Process was completed in September Bay County Utilities now operates a digester program that generates high power cost savings and eliminates the chemicals typically required to meet Effluent Phosphorous Permit Compliance. The carbon footprint of the AWT Military Point has reduced significantly and changed the treatment plant to a cleaner and more effective operation. Resultant from this the plant now demonstrates its inherent long term stability and sustainable economic benefits. The P-Uptake Process has been reviewed, evaluated and validated by technical engineers and the process method is now being taught at operator short schools and wastewater conventions.

9 MPAWTF Operator Taking P-Uptake Readings

10 MPAWTF Operator Monitoring P-Uptake Process Performance through SCADA

11 MPAWTF Operator Conducting Phosphorous Test

12 MPAWTF Operator Initiating Aeration Cycle of P-Uptake Process