Sodium Ferrate (Ⅳ) and Sodium Hypochlorite in Disinfection of Biologically Treated Effluents. Ammonium Nitrogen Protection against THMs and HAAs

摘要

The work described in this paper presents an evaluation of disinfection by-products generation in four different biological treatment plant effluents, making use of sodium hypochlorite and sodium ferrate (IV) at varying concentration and reaction time. Correlations between pH, chemical oxygen demand, total organic carbon, ammonium nitrogen, combined chlorine and trihalomethanes (THMs) and haloacetic acids (HAAs) were carried out. Disinfection by-products generation presented a direct relation with concentration and sodium hypochlorite reaction time. For the highest hypochlorite concentration employed (20 mg L~(-1)) and highest reaction time (168 h), the THMs total did not exceed 312.96 μg L~(-1), a value that lies below the Brazilian emission standard for treated effluents (1 mg L~(-1) of chloroform). The THMs presented an inverse correlation with ammonium nitrogen, when inverse (R~2 = 0.646; P < 0.001) and exponential (R~2 = 0.707; P < 0.001) function were used. As per HAAs this same relation was observed for logarithmic (R~2 = 0.0397 P < 0.001) and exponential (R~2 = 0.508; P < 0.001) functions. The more nitrified the effluent, the bigger the chlorinated disinfection by-product generation. The disinfectant sodium ferrate (Ⅳ) does not lead to halogenated by-product formation.