Background
The Horsham wastewater treatment plant treats domestic sewage from the nearby town of Horsham and surrounding villages in West Sussex. The plant comprises preliminary treatment (screens, grit removal), primary settlement followed by secondary biological trickling filters and tertiary treatment to polish the effluent comprising sand filters.
The Overall Objective
The existing treatment works struggles to deal with fine solids from the tertiary treatment process. The fines solids which collect on the sand particles during filtration are scoured and backwashed from the sand particles before being returned to the head of the works. These solids are difficult to remove via conventional settlement and can give rise to high turbidity in the final effluent.
Solution
Siltbuster initially tested the backwash water from the sand filters in our in-house laboratory and found that Dissolved Air Floatation (DAF) treatment worked well in removing the fine solids (70% removal efficiency); Solid’s removal was increased further to 90% when Ferric Chloride is dosed as a pre-treatment in a mixing stage prior to DAF. The DAF plant can process flows upwards of 100 m3/hr (27 l/s) and feed solids concentration up to 1,000 mg/l.
