The Treatment Process
The treatment process at Farlington Water Treatment Works is outlined in the diagram below:
Spring water is collected at Havant and Bedhampton, dosed with chlorine to begin the disinfection process and pumped by High Lift Pumps to Farlington Water Treatment Works.
Partially treated water enters the Splitter Weir Chamber where, if necessary, alum is added to aid the filtration process. Here the flow is split with one third of the flow going to Stream 1 and two thirds to Stream 2.
The partially treated water passes to the Flash Mixer where the alum, a coagulation aid, starts to bind together the small particles which cause turbidity.
The coagulated water is then divided equally between five Rapid Gravity Filters in Stream 1 and eight Filters in Stream 2. Here the water is filtered through a graded sand and gravel bed, approximately one metre deep, before being discharged to the filtered water channel below.
To provide an effective barrier against Cryptosporidium, the filtered water is then passed through a membrane filtration system.
The membrane system consists of submerged microfiltration modules designed to treat 84 Ml/d.
The microfiltration plant consists of 6 cells, each incorporating 396 microfiltration modules containing PVDF (Polyvinylidene Fluoride) hollow fibre membranes with a pore size of 0.2 microns (1 micron = one thousandth of a millimetre). Feed water passes through the walls of the hollow fibres to the centre of the fibres producing a filtrate virtually free of suspended solids which accumulate on the outer surface of the membranes.
Following the membrane filtration process, the filtered water is dosed with chlorine solution and orthophosphoric acid solution, before the treated water enters the Contact Tank.
Chlorine disinfects the water by killing bacteria and viruses.
Orthophosphoric acid reacts with any lead pipes in customers' individual service connections and coats the inside of the pipe with lead phosphate. This inhibits the dissolution of lead pipe and reduces the lead content of drinking water at the customer's tap.
After a minimum of ten minutes contact with the chlorine dose, a number of monitoring checks are conducted for Water Quality purposes before the treated water is transferred from the Treatment Works to the nearby underground service reservoirs, see picture below.