The removal of dinitrotoluene from wastewater via zero-valent iron reduction and enzyme-catalyzed oxidative polymerization with Arthromyces ramosus peroxidase

Dinitrotoluenes are versatile chemical species being employed in a variety of manufacturing processes. With their widespread use, dinitrotoluenes are of some concern as they have been linked to a number of diseases and are listed as priority pollutants by the US EPA. In the interest of public health and with more stringent antipollution legislation, the release of dinitrotoluenes in wastewater effluent is unacceptable and the search for new and better treatment methods is ongoing.; Enzyme-catalyzed polymerization and precipitation processes have been suggested as an alternative means for treating wastewater containing phenolic and anilino species. In biological processes, enzymes operate under mild conditions and have a limited environmental impact. Enzymes have several advantages over conventional biological processes including: action on, or in the presence of, chemicals which are toxic to microbes; operation on a broad range of compounds; operation over a variety of reaction conditions; operation at both high and low concentrations of contaminants; reduced sludge volume; and no shock loading effect or delays due to the acclimatization of microbes.; This study presents a two-step treatment process for 2,4-dinitrotoluene and 2,6-dinitrotoluene. The first step involves reduction of dinitrotoluene to diaminotoluene using iron. This is a necessary first-step as nitroaromatics are not substrates of the enzyme. The second step is the enzyme-catalyzed polymerization of the diaminotoluene generated. The focus of the first step is on the effect pH has on the reduction of dinitrotoluene. Aspects of interest with regards to the enzyme-catalyzed polymerization step include the optimal operating conditions, the effect of polyethylene glycol as additive and the rates of substrate consumption and of enzyme inactivation.; A number of different methods for the removal of enzymatically-generated polymeric products were also probed. These methods included the flocculation with polyvalent metal cation salts, flocculation with polyelectrolytes, both with and without a flocculant aid and adsorptive micellar flocculation using sodium lauryl sulphate and alum. Preliminary product analysis studies were also conducted to help explain observed differences in the polymeric products of the two isomers studied. A combined treatment regime for dinitrotoluene was then proposed based on the experimental data.