The NSAF cells in the Bollfilter filtration system use a biological oxidation process to remove microscopic particles. These NSAF cells contain a biomass with microbes which purify the wastewater by feeding on ammonia and other contaminants when ozygen is pumped through.
The Bollfilter filtration system comprises an automatic self-cleaning filter with a manual filter on the bypass line and is designed to protect small pipework in the NSAF plant from risk of damage or blockages from particulates. As Cranleigh is low-lying, the Bollfilter system features a Hidrostal backflush assist pump to ensure efficient performance under the low pressure conditions.
Julian Dempster, Black & Veatch M&E coordinator said: “The NSAF plant is a continual process. If particulates enter the system they can foul the NSAF media and can cause blockages. The Boll system, which operates continually with an automatic backflushing cycle, removes the need for manual cleaning and prevents plant downtime.”
The Cranleigh Plant also has another Boll 6.18 automatic filter fitted on the washwater system to protect nozzles on the inlet works plant from blocking.