Inland Empire Paper Company (IEP), located in Millwood, WA specializes in the production of newsprint paper using a combination of mechanical pulp and recycled newspaper pulp. IEP produces an average of 525 tons per day of newsprint and specialty paper products in 20 to 40 pound weight paper. Waste wood chips collected from local sawmills are processed to produce up to 475 tons of thermo-mechanical pulp (TMP) per day. IEP also recycles newspapers collected from around the country for the production of up to 350 tons of recycled newspaper fiber per day. The recycled newspapers undergo a deinking process and are blended with the TMP prior to the bleaching process. IEP then dilutes the bleached pulp with water to lower its consistency to approximately 1 % solids for introduction to the paper machine. Water is removed via a press and dryer process to produce paper with approx. 8 % final moisture content.
IEP generates wastewater flows averaging 3 MGD (473 m³/hr), loaded with high strength BOD₅. The wastewater is deficient in nitrogen and phosphorus, so ammonia and phosphorous are added to the system as essential nutrients for the activated sludge system.
IEP also has a series of production campaigns for High Bright Paper runs that lead to higher organic loading and sludge bulking. The High Bright Paper campaigns run for a period of two days during which the wastewater treatment plant can see influent MLSS levels over 5,000 mg/L.
The challenge for IEP was to meet the stringent effluent discharge limitations set forth by the Washington State Department of Ecology for direct discharge to the Spokane River. This was achieved in part by retrofitting an existing Stock Tank into a Headworks BIO™ Inc. ActiveCell® moving bed biofilm reactor (MBBR) capable of reducing the BOD5 load by 44 % prior to an existing orbal oxidation ditch treatment system. The goals of the project were to off-load the oxidation ditch, minimize or eliminate the growth of filamentous bacteria and provide IEP the capability for future growth in newsprint paper production. IEP also was planning for modular expansion in treatment capacity to meet more stringent effluent discharge limits and mill production increases in the future.
Inland Empire Paper treated wastewater from its paper making process with an existing wastewater treatment system consisting of three major components: 462,000 gallon primary clarifier, 3-channel 2.1 million gallon Orbal ditch aeration basin, and a 705,000 gallon secondary clarifier. The current wastewater treatment plant required relief from intermittent hydraulic and BOD₅ surges. During the summer months, the Orbal ditch experienced filamentous bacteria growth that negatively impacted settling rates in the secondary clarifier.
IEP conducted a four month pilot study using Headworks BIO ActiveCell₄₅₀ media that demonstrated the overall performance of the system along with the BOD5 loading and removal rates. The biological wastewater treatment system was designed using a combination of actual data from the pilot study and the MediaPro™ computer modeling program.
The ActiveCell bioreactor was sized and designed to remove BOD₅ at a nominal rate of 7.15 kg BOD₅ per cubic meter of media per day, approximately a 44 % reduction of influent BOD5 load. The bioreactor was sized to fit within an existing 25 foot diameter by 38.5 foot high stock tank. The tank provides approximately 120,000 gallons of working capacity by operating at a nominal side wall depth (SWD) of 34.5 feet (approximately 4 feet of freeboard).
The existing stock tank was constructed of chemical and abrasion resistant tile-lined concrete furnished with a heeled bottom. This tank happened to be one of the oldest tanks at the mill site, having been constructed in 1911.
