Wastewater nutrient changes lead to savings for mill owners
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.
Wastewater Microorganisms & Nutrition
Microorganisms are the backbone of biological treatment processes and require specific micro- and macronutrients to efficiently and cost-effectively treat wastewater. Under the right conditions, microorganisms consume and digest contaminants, usually converting them to small amounts of water and harmless gasses such as carbon dioxide and methane (process dependent). A stable microbial ecosystem requires specific macronutrients (nitrogen, phosphorous, sulfur, potassium, etc.) and micronutrients (zinc, manganese, molybdenum, etc.), as well as a carbon source in order for microorganisms to survive, replicate and consume/treat wastes. Each vitamin and mineral is essential to microbial growth and metabolism and has a unique and specific function to perform. Signs of nutrient deficiency include sludge bulking, foaming, poor settleability, inefficient removal of suspended solids, odor, excess sludge accumulation and inefficient removal of BOD or COD. For example, many foaming and sludge-bulking issues are due to excessive filamentous bacteria that thrive in nutrient-deficient environments and prevent settling. Bioavailable nutrients can improve the treatment process while reducing the overall volume of essential chemical nutrients used. This facilitates the growth of healthy microorganisms, which in turn leads to more stable and efficient wastewater treatment processes.
More stable processes allow for desirable higher microbial life-form development, such as amoebas, ciliates, rotifers, etc. These higher life forms are necessary for efficient wastewater treatment, as they feed mainly on loose bacterial cells. Lack of these higher life forms leads to sludge buildup and inefficient and costly mill operations.
Super Phos, a Probiotic Solutions product, is a tech-grade white phosphoric acid and monoammonium phosphate source that is pre-complexed with Micro Carbon Technology (MCT), a proprietary process that converts a soft, humic material into extremely small oxygen-rich carbon molecules. The MCT process results in a carbon source that is an ultra-efficient carrier—due to the micro-carbon molecule’s low molecular weight, greater specific surface area and higher cation exchange capacity—to deliver readily bioavailable nutrients to microorganisms.
Mill #1 has the capacity to produce 1,800,000 metric tons of pulp and 3,100,000 metric tons of paper a year. Its wastewater system consists of four parallel sequencing batch reactors (SBR), followed by an aeration system that treats 50,000 cu m per day and meets all national and local standards.
For this study, Tank 3 and Tank 4 were selected, while Tank 1 and Tank 2 were maintained under normal operations. Tank 3 was used to test the replacement of typical liquid phosphoric acid with Super Phos, and Tank 4 was the control. Testing occurred over seven days. Super Phos incrementally replaced the typical phosphoric acid over the course of three days to a final reduced ratio of 1:4 to minimize any potential impacts to Tank 3.
The COD removal rates, average MLSS and average SV30 were monitored for both tanks during the test. It was found that both tanks were statistically equivalent in all three metrics, with Tank 3 having a COD removal rate that was 3% better with 75% less phosphorus added (see Table 1).
Cost savings are found when systems run efficiently. Bioavailable phosphorus is absolutely necessary to develop and maintain a healthy microbial population leading to an efficient wastewater treatment system. Utilizing a bioavailable phosphorus source such as Super Phos with Micro Carbon Technology improves system performance while greatly reducing the volume of phosphorus required and lowering effluent phosphorus levels. This leads to cost savings that mill owners are looking for while maintaining the treatment system’s operational effectiveness.