Fig. 3. Mineralization of aqueous TNT (0.22 mM) in dark-Fenton reactions comparing abiotic with coupled abiotic–biotic treatments at high and low biomass (waste-activated sludge [WAS] or 2,4-dinitrophenol [DNP] biomass) concentrations: (A) pH 3, WAS biomass; (B) pH 3, DNP biomass; (C) pH 7, WAS biomass; (D) pH 7, DNP biomass. Abiotic reaction (•); high biomass concentration, either 467 mg WAS L^-1 or 333 mg DNP L^-1 (); low biomass concentration, either 93 mg WAS L^-1 or 67 mg DNP L^-1 (). Abiotic, pH 7, reactions conducted with Fe³⁺ to nitrilotriaceticacid (NTA) ratio = 1:1. Biotic reactions for (A) and (B) were conducted after solution neutralization. Error bars on symbols indicate standard error of means (n = 3, P 0.05); where absent, bars fall within symbols.