Improving the ozone-activated peroxymonosulfate process for removal of trace organic contaminants in real waters through implementation of an optimized sequential ozone dosing strategy.

The ozone-activated peroxymonosulfate process (O/PMS) has received increasing attention for the removal of trace organic contaminants (e.g. pesticides and pharmaceuticals) from water bodies. However, the ozone dosing strategy has not yet been properly investigated, especially in real water matrices. Typically, one-step dosing is applied in literature. Nevertheless, optimal dosing is an important step for improving the process. This study investigates the effect of sequential ozone dosing on the PMS activation, atrazine (ATZ) removal, residual ozone concentration and radical exposure, and compares the results to those of a one-step ozone dosing approach. Experiments were performed in three water matrices with a different (in)organic content, i.e. secondary effluent, surface water and groundwater. In all matrices, the highest PMS activation was reached when applying three sequential ozone doses (3 × 5 mg O/L). This resulted in a 3 times higher ATZ removal efficiency (up to 46 %) in secondary effluent compared to that obtained with a one-step ozone dosing (15 mg O/L). In surface water and groundwater, similar ATZ removal (>90 %) was observed among the different ozone dosing strategies. However, the sulfate radical (SO) exposure increased after each ozone addition. After three ozone additions of 5 mg/L, SO contributed for 9 %, 26 % and 54 % to ATZ removal in respectively secondary effluent, surface water and groundwater. This high SO contribution compared to OH contribution is an advantage as the selectivity of SO gives rise to less radical scavenging by bulk organic matter and thus increases the (cost-)effectiveness of the O/PMS process.