Photolytic Destruction of Halogenated Pyridines in Wastewaters

The degradation of 2-chloropyridine, ▪ and 2-fluoropyridine, ▪, compounds typically found in effluents of pharmaceutical processing, was studied by means of ultraviolet irradiation. Experiments were conducted at temperatures of 293, 303, 313 and 323 K for 2-chloropydine and 313 K for 2-fluoropyridine. Liquid volumes of 0.25, 0.40 and 0.55 L and initial substrate concentrations of 0.3 g L −1 and 0.5 g L −1 have been used in a flow reactor with internal recycle. Both compounds were readily susceptible to photolytic degradation with complete conversion being achieved within 2–4 h of reaction depending on the operating conditions employed. During that period, mineralization was generally low with the extent of organic carbon not exceeding 20%. However, complete mineralization was achieved after approximately 10–50 h of irradiation depending on the conditions employed. At 313 K, 2-fluoropyridine was more readily degradable than 2-chloropyridine. Degradation was found to follow pseudo-first order kinetics in regard with substrate concentration with the rate increasing with increasing temperature and decreasing liquid volume and initial concentration. 2-pyridinol was identified as one of the intermediate degradation compounds produced at the early stages of irradiation.