Design and trial of an alternative option for suburban sewerage pump stations

Abstract

[Abstract]: Collection and pumping of waste water represents a significant cost for urban communities in Australia. The flows in a sewerage system are not constant. In residential areas flows will be at a maximum in the morning and evening. Additionally during rain periods there is an increase of flow into the pump stations due to faults in the gravity sewers allowing inflows and infiltration. It is common for multiple pump stations to feed into the same pressure main. This causes the pressure in the common pressure main to change depending on how many and which pumps are operating at any given time. Consequently the pump stations feeding into the common pressure main will operate at various flows. A given pump station will operate against maximum pressure during wet weather when all other pump stations are also operating, resulting in a decrease in the flow rate produced by the pump station. This is not desirable as the largest flow outputs are needed during wet weather conditions. The purpose of this project is to devise an alternative pump configuration. The configuration will enable pumps to operate within their recommended operating range for normal and wet weather operating conditions. The design must comply with the current standards required by the waste water industry. It must also be cost competitive compared with current pump station designs, and be able to be operated and maintained effectively in a similar manner to existing designs. The selected pump configuration consisted of three identical pumps. For normal dry weather operation each pump operates as a stand alone unit (i.e., duty / standby / standby). The pumps are equipped with piping and valving to enable two pumps to operate in series to deliver the higher pressures needed during wet weather operation. (i.e., duty / duty / standby). A prototype of this series pump configuration was designed and built. The prototype was run in a test tank to compare measured and theoretical pump performance. The tests undertaken in the test tank indicated that the pump configuration performed as predicted and it was therefore suitable for installation in an operating sewerage pump station. The prototype pumps were installed in an existing sewerage pump station in July 2007. Monitoring of the performance showed that the pumps successfully operated within their recommended operating range for normal dry weather operation and for simulated wet weather operation. There has been no evidence of increased susceptibility to blockage with this pump configuration. The proposed series pump arrangement appears to meet the goal of providing a cost effective alternative that uses identical fixed speed pumps. Each pump operates within the recommended range above and below the best efficiency point under all flow conditions. Longer term field testing is needed to demonstrate satisfactory reliability and performance of the pumps over an extended period.