Evaluation of nitrogen fate from land-application wastewater treatment for cheese making and vegetable processing facilities

Abstract

Cheese making and vegetable processing are vital industries worldwide, but their operations generate billions of liters of wastewater annually that must be managed in an environmentally safe yet cost-effective manner. For small to medium sized facilities or those without access to wastewater treatment plants, land application systems are commonly utilized. These systems rely primarily on plant uptake and denitrification to remove nitrogen (N) from the effluent. Quantification of soil denitrification is difficult because of the challenges in differentiating between the N₂ produced by microbial soil action and atmospheric N. At the behest of industry and regulators, we developed a full N mass balance for six industry facilities to evaluate their systems effectiveness in protecting local water resources. A fully automated acetylene inhibition technique (AIT) soil gas collection system was deployed at each site over two years. These data combined with effluent parameters, lysimeter and plant uptake data and continuously collected soil parameter data allowed mass balance calculation. A laboratory-based soil incubation study provided correction factors for known AIT limitations and evaluation over a greater temperature range. Lab study results indicate that the AIT underestimates system denitrification by 12.4× in the wetland-like cheese making treatment systems and 4.4× in the managed grassland vegetable processing treatment systems. While the wide variability between system performance limits method application at a single facility for short time periods, average values are indicative of general system design performance and utility in wastewater treatment when highly engineered options are unavailable or cost prohibitive.