Benefits of paper mill white water recovery using backwash filtration system

While large quantities of white water are commonly reused in the pulping process, a significant portion of the white water (the clear/super-clear effluent from the save-all filter) is taken out of process circulation because it is not clean enough for reuse in the process. Clear/super-clear white water can still contain significant quantities of suspended material, such as pulp fibres, fillers and other suspended solids. Portions of this stream are typically discharged to a water processing plant, and replaced with fresh make-up water, which must be heated to process temperature for use in various applications. This practice comes at a price, namely the cost associated with fresh water usage and treatment, as well as the energy cost for heating the water. The use of backwash filtration system for recovery of clear/super-clear white water coming from the save-all is a novel approach using existing, proven backwash technology (1). It allows the recovery of a larger portion of white water for use as warm process water, and thus provides measurable environmental benefits: reduction of fresh water usage and treatment costs, reduction of steam usage, and reduction of waste water treatment costs. The reduction of steam usage can be significant and translates into a reduction of fuel required for steam generation. In this work, the author discusses how clear white water recovery through backwash filtration system contributes to environmental protection, including reduction in industrial water use and heating requirement, wastewater treatment costs, steam and fuel reduction.