Advanced Treatment Process for Papermaking Wastewater by Composite Photoelectrocatalysis and Heterogeneous Photocatalysis of Nano-TiO2 Colloid and its Pilot-scale System

It is difficult for papermaking wastewater to reach the discharge standard with only a sequencing batch reactor activated sludge process (SBR). This study developed an advanced wastewater treatment system with nano-TiO2 colloid photoelectrocatalysis and heterogeneous photocatalysis (PEPC). First, the performances of different flocculation processes and their influences on the subsequent PEPC process were studied. The recycling of the nano-TiO2 colloid photocatalyst was further investigated. The results showed that the ternary composite flocculation process using both the inorganic flocculant and the nano-TiO2 colloid (1 x 10(-3) wt%) had the best flocculation effect with a suspended solid (SS) removal rate of 93.5% and a chemical oxygen demand (COD) removal rate of 66.9%. It also achieved the best PEPC treatment performance with a COD removal rate of 93.6% in 90 min with the 0.05 wt% dosage of the nano-TiO2 colloid photocatalyst. Moreover, the COD removal rate reached 88.5% after four recyclings of the nano-TiO2 colloid photocatalyst, which demonstrated the excellent reusability of the nano-TiO2 colloid photocatalyst. Finally, based on the PEPC process, an automatic and continuous pilot-scale system was established. Its successful operation suggests the feasibility of operating PEPC technology at an industrial scale.