Sequential coagulation treatment and processes based on ozone (O3, O3/UV, O3/UV/H2O2) for remediation of agro-food industrial wastewater

Cassava wastewater is a liquid resulting from the processing of cassava in the production of flour and extraction and purification of starch. Conventional treatment processes are inefficient for this kind of effluent; therefore the objective of this study was to evaluate coagulation followed by O3, O3/UV, and O3/UV/H2O2 reactions for degradation of cassava wastewater. Coagulation achieved reductions of about 70% in COD (chemical oxygen demand), which increases the practicability of sequential use of ozonation and its combinations. The use of ozone reduced the absorbance of samples at 393 nm in the course of processes, and among the evaluated systems, combination O3/UV/H2O2 was the most favorable in reducing effluent absorbance (74%), besides providing the highest kinetic degradation constant (2,236 × 10–3 min–1). The turbidity and COD were reduced by 95% and 30%, respectively, after combined coagulation and ozonation processes. Toxicity tests indicated the structural modification of organic components of cassava wastewater, due to lower effluent toxicity after evaluated treatments. Thus, the potential of ozone-based reactions for degradation of organic matter, especially of the compounds that provide color and turbidity to the effluent, was verified through evaluation of absorption spectra and their kinetics.