Pesticides wastewater treatment by coagulation-flocculation: Evaluation and optimization of operational parameters

Effluents from the pesticide industry have a high toxicity associated with its high organic load, elevated levels of turbidity, suspended solids and color. The effluent used contains the pesticides ametrine, atrazine, imidacloprid and tebuthiuron, provided by a pesticide factory. The coagulation-flocculation-decantation processes were evaluated as an alternative of wastewater treatment. First, the influence of the coagulant ion (Fe(NO3)3 and Al(NO3)3) and concentration (ranging from 2 to 32 mmol L-1) was evaluated in natural pH (4.9). The best results in terms of turbidity and color removal were obtained using Fe(NO3)3 and high concentrations of this salt were requested to reach almost complete color and turbidity removal (Figure 1). After this treatment, the pH decreases between 3.8 and 2.1 for the different concentrations of Fe3+ due the hydrolysis reactions mediated by Fe3+. Second, in order to reduce the solubility of this ion and increase the efficiency of the process, the pH was adjusted to 4.0 and new analyses were performed. Under these conditions, the use of 8 mmol L-1 Fe(NO3)3 resulted in 99% color and turbidity removal. In addition, a partial removal of the pesticides (between 43 and 78%) and 20% of total organic carbon was reached. However, no significant removal on toxicity was obtained, since the EC50 changed from 0.4 to 4.5 (% v/v), being extremely toxic. The coupling with photo-Fenton process is being evaluated as an additional stage to the effective treatment of this type of effluent.