Nutrients are required in wastewater treatment systems to ensure the bacteria are healthy, able to reproduce and can convert soluble chemicals into biosolids, which are removed via settling, filtration, clarification, or other solids removal process. Many paper mills are deficient in the two macronutrients nitrogen and phosphorus and therefore require the supplemental addition of these nutrients to provide the bacterial population the proper ratio they need to function efficiently.
Nutrient evaluations, utilizing plant data, help one ensure the bacterial population of the wastewater system receives the proper ratio of supplemental nitrogen to phosphorus necessary based on background quantities readily available and daily BOD loading to the system. With proper nutrient feed rates based on loading data, a plant can maintain environmental compliance and save money by not overfeeding.
Maintaining proper nutrient feed rates is done by developing a nutrient worksheet based on current loading, nutrient requirements, and the blended nutrient supplement currently fed at the plant and correlating it with a surrogate for BOD5 (typically BOD1, COD or TOC) and actual BOD5 data. This worksheet can then be used to calculate and adjust the feed rates as needed, preventing the plant from feeding too much nitrogen and/or phosphorus to the system. By maintaining the optimum nitrogen and phosphorus concentrations, maximum efficiency during normal operation and in upset conditions can be achieved.
EBS is the largest supplier of nutrient to the paper industry and conducts in-depth nutrient evaluations of wastewater treatment systems on a regular basis. Data on the pond and a sample point upstream of nutrient addition are reviewed for flow, BOD5, BOD1, COD, TOC, TSS, pH, and nutrient residuals. A three-year period of data is ideal for the evaluation, but a BOD surrogate possibly can be estimated with less data.
During the nutrient analysis, data is graphed with spikes or oddities analyzed. EBS then determines if a correlation exists between a possible surrogate (BOD1, COD, or TOC) and BOD5. From here, a worksheet is created to predict the BOD5 value of the wastewater influent. EBS calculates the nutrient need of the wastewater system using a mass balance formula and uses this to calculate an N:P ratio and feed rate required to meet this need. The worksheet can be updated daily by plant personnel and is used to determine the nutrient feed dosage for that day and over time whether the ratio of N:P in the nutrient fed needs to be adjusted. A nutrient evaluation and BOD5 surrogate gives the plant better control of the nutrient usage and better control means reduced cost.