Valorization of Field-Spent Granular Activated Carbon as Heterogeneous Ozonation Catalyst for Water Treatment.

Developing sustainable cost-effective strategies for valorization of field-spent granular activated carbon (s-GAC) from industrial water treatment has gained much interest. Here, we report a cost-effective strategy for the regeneration of s-GAC as an adsorbent in a large-scale drinking water treatment plant and used as an efficient and durable ozonation catalyst in water. To achieve this, a series of samples is prepared by subjecting s-GAC to thermally controlled combustion treatments with and without pyrolysis. The catalytic performance of the optimized sample is evaluated for oxalic acid degradation as the model pollutant under batch (>15 h) and continuous flow operations (>200 h). The partially deactivated catalyst upon reuse is restored by thermal treatment. Electron paramagnetic resonance and selective quenching experiments show the formation of singlet oxygen (1O2) during catalytic ozonation. The GAC-ozonation catalyst is efficient to minimize the formation of chlorinated disinfection by-products like trihalomethanes and haloacetic acids in an urban wastewater effluent.

Impact of chlorination and pre-ozonation on disinfection by-products formation from aqueous suspensions of cyanobacteria: Microcystis aeruginosa, Anabaena aequalis and Oscillatoria tenuis.

The influence of the pre-ozonization on the formation of disinfection by-products (DBPs) upon chlorination for fresh waters containing three common cyanobacteria, namely Microcystis aeruginosa, Anabaena aequalis and Oscillatoria tenuis at 10,000 cells/mL is reported. Specifically, the formation carbonaceous-DBPs (C-DBPs) (trihalomethanes (THMs), haloacetic acids (HAAs) and haloketones (HKs)) and nitrogenous-DBPs (N-DBP) (haloacetonitriles (HAN) and trichloronitromethane (TCNM)) has been determined as a function of the pH (6.5 or 8.0 and bromide ion concentration (300 µg/L). The main C-DBPs were THMs and HAAs with negligible formation of HKs accompanied by minor amounts of HANs in the absence of TCNM. Pre-ozonation of the aqueous cyanobacteria suspensions does not allow a control over all the DBPs. In fact, pre-ozonation increases THM formation and generates TCNM, has low influence on HAAs and only decreases the formation of HANs. The overall conclusion of this work is that pre-ozonation of waters containing a relatively low concentration of common fresh water cyanobacteria is not an appropriate process to decrease DBP formation from chlorine. Cyanobacteria removal from raw water before chlorination or ozonation should reduce DBP formation.