White Water Recovery – the Benefits Go Beyond Just Saving Water
Corporate sustainability statements often emphasize water reduction as a goal associated with minimizing a company’s environmental footprint and impact on the community. Being a “good neighbor” by optimizing the use of water and reducing water costs are the two most obvious benefits. What many people do not realize is the cost to purchase and dispose of mill process water typically represents less than one-third of the potential savings. Additional benefits include energy savings from reduced freshwater heating, increased fiber recovery, and reduced landfill or sewer charges.
The typical savings for each area is shown in the table below. The savings potential can be significant and will likely vary depending on the mill’s operating environment and practices. With many variables to consider, the first step in any water recovery project should be to audit the water system and understand the economics.
Estimated Annual Savings Associated with Reducing Mill Water Consumption 100 GPM
Area Of Savings
|Water consumption||River or well water, $0.30/1000 GPM||$15,120||10.9%||$151,200||36.0%|
|High (Municipal Purchase/Treatment) $3/1000 gallons|
|Water heating||Average ($4.0 BTU Cost Per Million)||$92,474||66.5%||$138,711||33.0%|
|High ($6.0 BTU Cost Per Million)|
|Fiber recovery(recover 500 PPM)||Recycle Corrugated - $250/Ton||$26,271||18.9%||$84,067||20.0%|
|Market Pulp - $800/Ton|
|Landfill avoidance(500 PPM)||Low $50/Ton||$ 5,254||3.8%||$46,237||11.0%|
|High - Municipal Sewer $440/Ton|
|Note: Estimated savings are based on 350 operating days per year.|
The actual cost of water can vary significantly depending on the source. Water purchased from a municipality is typically well defined and tends to be more expensive compared to that from a river or well. However, with river or well water, the distance the water must be pumped as well as maintenance of the raw water purification system and the permits associated with using the water are important cost considerations. In some areas of the world, “free” water from a well or river may actually be very expensive to use!
The largest dollar savings potential is typically found with energy savings. The major factors that affect energy include the heating fuel cost, the temperature difference between the paper machine wet end and the incoming freshwater, and heat recovery equipment installed in the mill. The calculations in the table use a 55°F increase in temperature to determine the savings. In cold climates where 32°F river water must be heated to 120°F (88°F increase) the economic impact would be larger.
Fiber recovery can have a positive impact on multiple mill budgets. For example, fiber lost to the sewer has been purchased as a raw material and processed through the mill stock preparation system using mill resources. At the end of the pipe, the mill is also paying disposal costs. Depending on the grade of paper and the fiber source, the savings could range from $200-$800 per ton. In many instances, the fiber can be recovered and put directly back into the mill stock chest. In this case, an additional $50-$440 per ton in reduced landfill or sewer costs could be achieved. The total potential savings could range from $250 to more than $1,200 per ton.
Treatment of the mill discharge is almost always calculated separate from the purchase price. Municipal water treatment plants typically base their fees on both volume and the total suspended solids in the wastewater. Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) may also be key factors in the calculation. Ignoring BOD and COD means at least three different rate reductions are possible if there is a decrease in sewer volume, solids, or both. Many mills have on-site waste treatment plants with fixed operating costs representing a high percentage of the plant budget. Each situation must be examined closely to determine the total economic impact of a reduction inflow. Mills operating at 100 percent capacity can easily justify white water reuse projects when faced with the alternative of expanding the wastewater treatment plant. On the other hand, if the plant is operating well under capacity the savings may be small, but the end result will still align with the corporate sustainability vision.
Learn more about the RotoFlex™ resource recovery strainer.