By Kirsten Nelson
Glatfelter operates an integrated de-inking and papermaking facility in Neenah, WI. The facility uses a combination of screening, flotation and sedimentation to recover excess fiber, as well as other wastes and water, which are lost during the de-inking and papermaking process. Part of this process water is re-used, with the majority being sent through the mill's wastewater treatment plant (WWTP) for further processing prior to discharge into the receiving water. Recycling as much water as possible helps reduce the amount of fresh water used and saves the company money.
At the mill's WWTP, primary treatment is used to remove more than 95 percent of the solid material from the process water, after which the water goes through secondary treatment to biologically remove waste organic material. The resulting byproduct, a combination of the solids removed in the primary clarifier and the waste biological solids from the secondary clarifier, is then de-watered and sent to an independent glass aggregate plant.
Glatfelter processes more than 4 mgd of wastewater at its Neenah facility, using a modified two-stage activated sludge treatment system that consists of aeration followed by clarification in each stage. The facility has been biologically treating wastewater since 1976.
Eight years ago, Glatfelter's Neenah facility was experiencing problems with its two-stage biological wastewater treatment system. Frequent upsets in the first stage of the system caused overloading in the second stage, which resulted in lower effluent quality and, at times, production curtailments. These interruptions to the production area translated into lost revenue.
Glatfelter is a very environmentally conscious company. Its Neenah facility was the first pulp and paper mill to become ISO 14001 certified in Wisconsin, and it recently received the Business Friend of the Environment Award for its pollution control efforts. Therefore, whichever treatment solution the facility adopted had to provide an effective means of enhancing the quality of the biologically treated wastewater prior to its discharge into the environment.
After consulting with USFilter Envirex Products, Glatfelter's environmental personnel decided to retrofit the mill's existing dissolved air flotation (DAF) thickener with a Folded Flow® DAF separator. The Folded Flow separator's unique hydraulic design allows the mill to treat the total flow that passes through its WWTP whereas the original DAF system only treated the flow of waste activated sludge from the secondary clarifiers. This is nearly an 8-fold increase with regard to hydraulic loading. The unit is installed so that it can treat the effluent from either of the second stage clarifiers, allowing Glatfelter greater operational flexibility than before.
The separator's high hydraulic loading capacity and effluent quality make it ideal to use in fiber recovery applications in the pulp and paper industry. Even with its small footprint, the Folded Flow separator remains on par with its conventional counterparts, in terms of maintaining superior float solids concentrations and energy efficiency.
Wanting to reduce the high solids loading to the secondary aeration basin and also to ensure high-quality effluent, USFilter converted the basin from a thickening process to a high-rate clarification process by custom-designing various DAF components. Such components included baffling for hydraulic efficiency, a feed header for optimum flow distribution, a three-shaft bottom sludge collector, a two-shaft surface skimmer and beach for floated solids removal and thickening, and an air dissolution recycle system.
In addition to the DAF separator, USFilter Envirex Products also provided a performance warranty, system startup services and post-warranty performance testing and optimization, said Ken Clusman, mill manager of the Neenah facility.
"The fact that they were willing to offer these additional services and understood the importance of this project was very important to us," he said
Since retrofitting the facility's original biological treatment system with the DAF separator and implementing some operational process changes, the WWTP rarely experiences upsets. However, when upsets do occur, the separator is there to protect the second stage and ensure the quality of the effluent to the river. The separator allows the facility to process on average 3,000 gpm and as much as 4,500 gpm. In addition, it is capable of treating influent with a total suspended solids (TSS) concentration of more than 2,500 parts per million (ppm), producing effluent solids concentrations of only a few ppm.
"In fact," said Bill Hartman, environment and safety director at Glatfelter's Neenah facility, "since installing the Folded Flow® DAF separator, the amount of solids in our discharged effluent is lower than that in Lake Winnebago, our process water intake source."
The separator typically removes between 90 percent and 95 percent of the solids that it encounters at the Neenah mill, although the performance of the unit exceeds this at times while experiencing hydraulic loadings in excess of 6 gpm/ft2.
"Installing the DAF separator significantly increased the facility's hydraulic throughput without taking up additional floor space," Hartman said. "This was very important to us because available space was limited.
"We also know that the separator will handle any upsets that may come our way, allowing us to focus on addressing the cause of the upset," he said.
And, according to Hartman, the separator recovers very quickly from overloading with high levels of solids, is completely automatic and self-cleaning, and requires minimal maintenance.
"In addition to saving us labor resources, the Folded Flow® DAF separator retrofit has also saved us time and money," Clusman said. "Along with operational changes that were implemented around the time that the DAF was retrofitted, the unit has helped save our facility thousands of dollars annually because of the flexibility it offers our environmental personnel.
"We have not experienced any production curtailments because of WWTP concerns since the unit started up."
The separator retrofit has also helped the Neenah facility consistently stay well below state and federal pollution prevention standards and conserve scarce water supplies. Moreover, Hartman says the mill is producing the highest quality effluent ever. The facility is currently discharging water that has TSS concentrations that are less than five percent of its permitted levels.
"Modifying the facility's two-stage biological wastewater treatment process has helped our company live up to its environmental commitments of compliance with laws and regulations, pollution prevention and continuous environmental improvement," Hartman said.
About the Author: Kirsten Nelson is the DAF/API product manager at USFilter Envirex Products, located in Waukesha, WI. Nelson joined USFilter five years ago. She has a bachelor's degree in Biology from Rockford College (Rockford, IL) and a BS degree in Civil Engineering from the University of Wisconsin-Milwaukee.