The pulp and papermaking industry is very water-intensive and ranks third in the world in terms of freshwater withdrawal—as much as 60 cu m of water per ton of paper produced. As pulp and paper mills strive to survive in increasingly difficult economic times, many mills attempt to improve and expand their production processes. Consequently, this generates larger volumes of contaminated wastewater and increased use of chemicals to deal with that contamination. The treatment systems can easily become unbalanced or insufficient to meet the increased loadings.
The plant operator for a city in Wisconsin noticed a buildup of sludge in the treatment plant lagoons and wanted to prevent the need for future dredging, as the costs for dredging were cost prohibitive to the city. With the onset of cold winter weather there was also a need to increase the microbial population to help manage BODs and increase sludge reduction.
Assessing the Situation
The existing wastewater treatment system of a pulp and paper facility in China uses 600 kg per day of diammonium phosphate (DAP) to provide the needed phosphorus concentration to maintain a healthy microbial population to treat wastewater. These microorganisms break down the organic matter being discharged from the paper processing facility. Without the correct concentration of available phosphorus, the microorganisms are unable to grow and reproduce. The facility’s effluent has a chemical oxygen demand (COD) of 200mg/L.