Purifying River Water for Paper Board Manufacture

IGGESUND Paperboard uses some 22 megalitres of raw water per day in the manufacture of 260,000 tonnes of folding boxboard at its Workington plant in England. To ensure the continuity of a high quality water supply, Iggesund decided to manage the treatment on its own site, using Hydro International (UK)`s DynaSand® filtration plant to handle
automatically the large volumes within a very small footprint and requiring minimal supervision. Alan Brown, Contracts & Supply Manager at Iggesund explains: “The source of process water is the River Derwent, which is a typical spate river; at low flow levels it`s pretty clean but, in spate it carries high amounts of suspended solids. Our objective is to have water approaching potable quality all year round, and Hydro`s DynaSand® units and Lamella Plate Clarifier have consistently and successfully delivered that since their commissioning in the spring of 2006, with minimal maintenance requirements.
“The river water is extracted by a utilities company from the river and pumped to large underground reservoirs. It then flows under gravity to the mill where the underground pipeline passes close to our wastewater plant, so it made sense to locate the raw water treatment plant there. Although the project required major civil work including cutting back into the hill side, the vertical configuration of the DynaSand® enabled us to locate all 28 units plus the Hydro Lamella Plate Clarifier
and dosing equipment there.”
“The process takes the raw water, doses it with a PAC flocculant, which enables the DynaSand® units operating in parallel, to filter out the suspended solids. pH is corrected and small dose of hydrochlorite sterilises the water before it enters the board mill. The backwash water from the filter is passed through a lamella clarifier to remove the solids before this flow is returned and mixed with the raw water supply. This ensures that only a minimal amount of the water is wasted through the process. Apart from topping up the chemicals there is very little intervention. The plant is automatic/PLC controlled, and this enabled us to locate a remote control station in the existing control room for the waste water treatment operator.”
The DynaSand® units comprise a sand filter bed held within a hopper into which the water, pre-dosed with coagulant, is pumped via a manifold to deep within the sand. The water flows up through the sand bed, where solids are trapped on the grains of sand, into the open space above the sand, and the cleansed water exits via a weir at the top to a buffer tank.
The sand containing the entrapped solids is continuously air lifted from the bottom of the hopper, washed by a turbulent mixing action, and the clean sand allowed to return to the sand bed at the top to ensure a circular cleansing cycle.
The wash water with separated solids is discharged separately for treatment. The DynaSand® filtration plant is packaged with pumps, flowmeters and dosing equipment, in a compact installation.
The Hydro Lamella Plate Clarifier occupies an area as little as 10% of that required by an equivalent settling pond.
In it a gentle up flow over incline plates via a patented flow control system allows settled sludges to fall to the bottom of the separator and clarified water to leave at the top.