STRATEGIES TO SHOW COMPLIANCE WITH VECTOR ATTRACTION REDUCTION REQUIREMENTS WITH AEROBIC DIGESTION

The purpose of the paper is to present the data collected over an eight (8) year period that evaluated methods for demonstrating compliance with vector attraction reduction (VAR) requirements in a wastewater treatment plant (WWTP) that employs aerobic digestion. Many WWTPs in the northern states experience periods during the winter when they either can't meet VAR or are unable to show that they meet VAR. The methods available to show compliance with VAR for aerobic digestion are: volatile solids reduction over the digestion process, bench scale testing, or the specific oxygen utilization rate (SOUR) test. Each method can present some problems for the operator.The data collected by the Annville Township Authority Wastewater Treatment Plant (AWWTP) staff was necessitated by passage of 40 CFR Part 503. During the first year after 503 was published, the AWWTP staff chose to conduct the Bench Scale test several times in order to become proficient. While conducting these initial bench-scale tests, they discovered that they did not meet VAR over the winter months (for biosolids tested in the spring). Because the biosolids did not meet VAR requirements, surface applications of biosolids in the spring, without incorporation, were not permitted under the regulations. Because the bench-scale test takes 30 days to complete, scheduling biosolids applications with the farmers was problematic. AWWTP staff made several operational changes to meet VAR in the spring. The staff calculated the percent volatile solids reduction for the bench scale test using mass balance and Van Kleeck, as a matter of interest. They found that in most cases, either method could be used to calculate the percent volatile solids reduction as both methods generated similar results, ie, passing or failing the test.The AWWTP staff also analyzed the volatile solids content of their biosolids used in the bench-scale testing. They found that they could use the volatile solids content of the digester solids to predict the outcome of the bench scale test. The significance being that volatile solids content can be conducted in one day verses 30 days for the bench scale test. They also looked for a relationship between the bench scale test results and the SOUR test, using undiluted and diluted samples. However, additional data is needed before any relationship can be established. The data they collected over the past 8 years is interesting and should provide insight to other WWTPs that employ aerobic digestion.The AWWTP currently operates a biosolids management program that relies entirely on land application of liquid biosolids. The treatment plant is small and generates only 130 dry tons of biosolids each year. Aerobic digestion is employed for stabilization of the wastewater solids.