South West Water (Cornborough WWTP) Automatic Sludge Age Control Benefits

South West Water's (SWW) Cornborough WWTP (UK) is a coastal wastewater treatment plant and sludge reception center serving the area around Bideford in Devon-UK. Black & Veatch Corp constructed Cornborough WWTP during 2001/2, subsequently going on line during the winter of 2002.Cornborough is located in an area subject to significant population increases during the summer months as tourists flock to the beaches and holiday resorts located along the south west coast of the UK. This situation leads to significant increases in both diurnal solids variations and short-term shock loading incidents at vacation time. The combined impact of a rapid but short-term growth in population and a steady reduction in rainfall during the summer months is a quadrupling of solids loading on Cornborough WWTP. The challenge for Cornborough was to maintain plant compliance at all times without recourse to additional manpower or unplanned capital expenditure. Stabilising F: M (food: mass) based on a strategy of maintaining a constant SRT (Sludge Retention Time) via automation of the solids wasting process and using continuously online total suspended solids as the primary control input provided a solution to the challenge.The ChallengeAny WWTP plant experiencing large changes in plant loadings would require an experienced and diligent team to operate the plant in such a way as to maintain compliance. This has proved both expensive and time consuming, with little leeway for error. Significant numbers of plants have traditionally used a strategy based on constant MLSS, as this is significantly easier for operators to understand and less open to human error effects. Unfortunately SWW Cornborough experiences significant loading variations rendering such a strategy ineffective. An alternative solution based upon automatic calculation of SRT linked to automatic wasting as the principle control philosophy for maintaining the plant's optimum SRT was investigated. Like most WWTP's, Cornborough's sludge holding facilities are not infinite, any automatic wasting control system would be required to work around and overcome any such limitations without the need for human intervention.Figure 1 summarizes how the switch-over from manual to automatic wasting resulted in the immediate control of SRT. This was achieved with the SRT controller steadfastly working towards the optimum SRT set point, despite plant loading increasing at the end of April 2003.