Removal of trace organic contaminants from wastewater by superfine powdered activated carbon (SPAC) is neither affected by SPAC dispersal nor coagulation.

Powdered activated carbon (PAC) is increasingly used as tertiary treatment for the removal of trace organic contaminants (TrOCs) from wastewater (WW). To enhance the sorption kinetics and capacity, the PAC particles can be milled down to superfine powdered activated carbon (SPAC). However, the small-grained SPAC particles are prone to aggregation, which may impact their treatment performance. In this study we examined the effect of SPAC dispersion and aggregation on TrOC removal kinetics and sorption capacity. Specifically, we assessed how two interventions that modulate the apparent size of SPAC - ultrasonication and coagulation - affect the uptake of TrOCs in secondary WW effluent. We quantified the removal of fourteen TrOCs, of which twelve are indicator substances for micropollutant removal in WWTPs as designated by the Swiss Water Protection Ordinance. We determined that at high SPAC doses (> 1.6 mgSPAC/mg Dissolved Organic Carbon [DOC]), the TrOC removal kinetics were fast even for aggregated SPAC, such that SPAC dispersal by ultrasonication yielded no benefit. At low SPAC doses (< 1.6 mgSPAC/mgDOC) and contact times (< 2 minutes) ultrasonication was beneficial, in particular if the SPAC particles reached complete dispersion prior to exposure to TrOCs. However, the energy consumption of such an ultrasonication step should be carefully weighed against the additional energy requirement associated with using a higher SPAC dose. Finally, a coagulant to mitigate membrane fouling can be added simultaneously with the SPAC without compromising the TrOC removal efficiency. We conclude that under realistic SPAC application scenarios in WWTPs, interventions that disperse SPAC during TrOC sorption are not necessary, and processes that aggregate SPAC are acceptable.

Super-fine powdered activated carbon (SPAC) for efficient removal of micropollutants from wastewater treatment plant effluent.

In an effort to mitigate the discharge of micropollutants to surface waters, adsorption of micropollutants onto powdered activated carbon (PAC) after conventional wastewater treatment has been identified as a promising technology for enhanced removal of pharmaceuticals and pesticides from wastewater. We investigated the effectiveness of super-fine powdered activated carbon, SPAC, (ca. 1 µm mean particle diameter) in comparison to regular-sized PAC (17-37 µm mean diameter) for the optimization of micropollutant removal from wastewater. Adsorption isotherms and batch kinetic experiments were performed for 10 representative micropollutants (bezafibrate, benzotriazole, carbamazepine, diclofenac, gabapentin, mecoprop, metoprolol, ofloxacin, sulfamethoxazole and trimethoprim) onto three commercial PACs and their super-fine variants in carbonate buffer and in wastewater effluent. SPAC showed substantially faster adsorption kinetics of all micropollutants than conventional PAC, regardless of the micropollutant adsorption affinity and the solution matrix. The total adsorptive capacities of SPAC were similar to those of PAC for two of the three tested carbon materials, in all tested waters. However, in effluent wastewater, the presence of effluent organic matter adversely affected micropollutant removal, resulting in lower removal efficiencies especially for micropollutants with low affinity for adsorbent particles in comparison to pure water. In comparison to PAC, SPAC application resulted in up to two-fold enhanced dissolved organic carbon (DOC) removal from effluent wastewater. The more efficient adsorption process using SPAC translates into a reduction of contact time and contact tank size as well as reduced carbon dosing for a targeted micropollutant removal. In the tested effluent wastewater (5 mg/L DOC), the necessary dose to achieve 80% average removal of indicator micropollutants (benzotriazole, diclofenac, carbamazepine, mecoprop and sulfamethoxazole) ranged between 13 and 15 mg/L. These promising results warrant pilot-scale tests using super-fine PAC as an alternative to PAC for more efficient micropollutant removal.