UK Experiences of Full Scale Activated Sludge Real Time Control Systems

In recent years both power and chemical costs have increased at hyper inflation rates. In the UK, commercial power costs have increased from 7p/kWh to 9/kWh within a year and future power cost inflation is expected to be at least 11% per annum excluding any climate change levies. The water industry is a major commercial power consumer. This power consumption is constantly increasing to meet ever more stringent discharge consents within smaller site footprints. Many sites in the UK have gone from low energy and simple percolating filter works to energy intensive activated sludge processes (ASP), driven by tighter carbonaceous and ammonium discharge standards and new and tightened standards for Total Nitrogen. Recognising this trend, MWH and Hach Lange developed Real Time Control (RTC) for activated sludge processes. Following successful trials conducted by MWH and Hach Lange at a 250,000 population equivalent ASP on the south coast of the UK which showed RTC for both aeration and methanol dosing control could significantly reduce aeration costs by 20 % and methanol cost by 50 % whilst still delivering the required effluent quality. The technology has been widely used on activated sludge plants with populations ranging from 50k to 250k. Real Time Control has also benefited clients by avoiding expensive capital expenditure due to tightening Total Nitrogen consents and has increased compliance with discharge consents.