IMPACT OF HEAVY METALS INHIBITION STUDY ON CHESTERFIELD COUNTY, VIRGINIA'S PRETREATMENT PROGRAM

Chesterfield County's industrial base has been increasing steadily at an approximate rate of ten percent (10%) per year, resulting in the increase of industrial wastewater flow to its treatment plants. In order to keep pace with its growth rate and ensure that the industries' pollutant loadings do not exceed the acceptable loadings at the plant, it was necessary to re-evaluate the site-specific local limits for various pollutants. Continuous plant data collected over the years made the above task relatively simple, and it appeared that the local limit could be evaluated based on just the influent, effluent and some intermediate plant data. However, the in depth analysis provided the information that local limits for different pollutants, with the exception of mercury, were determined by its inhibition criteria indicating that the site-specific inhibition data for the plant were critical. If the historical inhibition data were to be used, the local limits of various pollutants would be reduced to very low levels from the existing levels, simply because the same allowable loadings had to be shared by a larger industrial base. The consequence of lowering the local limits for the existing industries would result in costly treatment upgrades for various industries, and therefore, would only withstand the legal challenges if the limits were based on site-specific inhibition data, rather than historical data from EPA's guidance manual. Further, the data previously utilized from the EPA's guidance manual appeared to be not only very outdated, but did not address the current configuration of Chesterfield County's wastewater plants.A pilot scale study to generate site-specific inhibition data was thus undertaken, so that it would result in more realistic and justifiable local limits for the industrial users. The study also investigated the effect of dissolved metals on the plant performance, since metals in ionic forms are more bioavailable and, therefore, exhibit greater degree of toxicity than metals in non-ionic form. Further, the data collected from the pilot plant were analyzed to study the pollutant's removal efficiencies across the plant. The study indicated that establishing inhibition levels of various pollutants for the treatment plants resulted in much higher local limits, while meeting all the goals of the pretreatment program of protecting the plant, waterways and biosolids.