Ashridge Engineering

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Combined Sewer Overflow Measurement and Alarm


Combined sewer systems are sewers that are designed to collect rainwater runoff, domestic sewage, and industrial wastewater in the same pipe. Most of the time, combined sewer systems transport all of their wastewater to a sewage treatment plant, where it is treated and then discharged to a water body. During periods of heavy rainfall , however, the wastewater volume in a combined sewer system can exceed the capacity of the sewer system or treatment plant. For this reason, combined sewer systems are designed to overflow occasionally and discharge excess wastewater directly to nearby streams, rivers, or other water bodies. These overflows, called combined sewer overflows (CSOs), contain not only stormwater but also untreated human and industrial waste, toxic materials, and debris. They are a major water pollution concern for the UK which has a large number of combined sewer systems.

One of the most effective means of monitoring and controlling CSO’s is by measuring the level in a CSO to see when and how frequently it spills. The Ashridge CSO systems accurately record’s CSO levels and will send automatic alarms in the event of an impending spill event.