Development of Treatment Systems for Nitrate Ester Wastewater to Meet Toxicity Based Effluent Limits
Dyno Nobel, Inc. (Dyno Nobel) operates a plant near Carthage, Missouri, which manufactures various explosives, including commercial dynamite. The plant produces nitrate esters, including primarily nitroglycerine (NG) and ethylene glycol dinitrate (EGDN), for use in explosive products, using continuous flow and batch nitrators. Diethylene glycol dinitrate (DEGDN) and metriol trinitrate (MTN) are also produced in limited quantities for certain products. The nitration processes use significant quantities of water to wash the products. In addition, water is used as a transport medium for these products. Process waters become contaminated with nitrate esters, which have significant solubility in water, as well as nitration and cleaning process byproducts including nitric and sulfuric acid, sodium carbonate, sodium nitrate, and sodium sulfate. In the past, treated process wastewaters and stormwater were discharged to Center Creek under a National Pollutant Discharge Elimination System (NPDES) permit issued by the Missouri Department of Natural Resources (MDNR). A subsequent permit revision imposed stringent water quality based effluent limitations (WQBELS) for NG and EGDN. Dyno Nobel appealed the renewed NPDES permit largely on the basis that the revised nitrate ester effluent limits were unachievable using current wastewater treatment technology. Dyno Nobel and MDNR negotiated a settlement of the permit appeal which contained a schedule of compliance requiring Dyno Nobel to evaluate, test, design and install improvements to the existing wastewater management system at the plant and ultimately achieve compliance with the final effluent limits by July 1, 1998.
In order to meet the requirements of the Settlement Agreement, Dyno Nobel retained Roy F. Weston, Inc. (WESTON®) to implement a multiphase wastewater compliance program. As part of this overall compliance program, Dyno Nobel investigated potential production process changes to reduce wastewater discharges from the plant. It was determined that recycle of prewash water combined with miscellaneous water use reduction efforts could significantly reduce the total volume of wastewater and the mass of nitrate esters discharged to the stream. The extent of reduction achievable would be determined by safety, operational and engineering considerations. For remaining nitrate ester wastewaters Dyno Nobel and WESTON conducted an extensive treatability program to identify, test and select technologies which could treat wastewater constituents to meet permit limits. In this paper, the results of Dyno Nobel’s treatability testing program and a discussion on the systems utilized to achieve compliance with the final effluent limits are presented.