Pilkington Glass saves on water bills
Glass cutting produces a great deal of washwater which can be recycled using a fairly simple treatment system. Pilkington now uses a continuous batch process at its Leeds factory.One of the main lines at Pilkington's works in Leeds is decicated to finishing both bullet-proof and fire-resistant glass. The cutting of these specialist products involves three diamond cutting lines which are constantly lubricated with water as they make their way through sheets up to 60mm thick. Once the glass has been cut it needs hosing down to remove the debris and splash marks from the cutting process.
Until a wastewater treatment plant was installed, all the wastewater (3,600m3/yr) was sent to a simple settlement tank system prior to discharge to sewer. The settlement tank needed cleaning monthly. Even with this small treatment plant, a considerable saving in wastewater and settlement tank cleaning charges was achieved by recycling water within the cutting plant area.
The treatment plant had originally been installed at another Pilkington factory, where it was only being used twice a day. Now it is performing a treatment cycle every 30mins, 24hrs a day. At the moment the system recycles around 50% of the water. The clean water feeds the saws and hose-down equipment, while the dirty water is collected in a 4,500l holding tank and treated as a continuous batch process.
The Mini Sentinel treatment system, with a capacity of 750l, works as a continuous batch process. The clean treated water is returned to the 3,000l clean water tank, which is topped up to make up for that lost to sewer. Because the Mini Sentinel is not large enough to treat all the dirty water used by the cutting machines, some 1,800m3/yr is still discharged to the original settlement tanks. Simon Bailey, engineering manager at Pilkington Leeds, said: "We are making savings, but we would like a larger Sentinel, purpose built for this plant so that we could treat all the water." The wastewater has most impurities (soda lime glass, water glass and various organic binders) removed by the addition of a Fuller's earth compound. The sludge is removed once a week and sent off-site for disposal.