Thermal swing intermittently-operated biological activated carbon filtration for rapid, non-sewered treatment of psychrophilic black water

Abstract

On-site treatment of wastewater requires robust processes that can handle a range of organic loads, start up and shut down quickly, and have limited energy consumption. Cold climates present a particular challenge for small-scale wastewater treatment given the potential for psychrophilic water temperatures (e.g., <15 °C) that reduce treatment kinetics. On-site treatment systems are critical in remote and underserved communities in cold regions, and better technology solutions are needed. Thermal-swing intermittently-operated biological activated carbon (TS-IOBAC) filtration is a two-step heterogeneous treatment process that overcomes these challenges and achieves organics removal across influent temperatures with minimal energy input. In the loading step, contaminants are primarily removed by adsorption to the GAC media. In the subsequent bioregeneration step, the filter is drained and selectively heated to temperatures that facilitate biodegradation of the adsorbed contaminants, thereby restoring adsorptive capacity to the filter. The present study assessed the thermal swing phenomenon for the first time, demonstrating enhanced bioregeneration performance when heating the filter media to 28 °C or 35 °C, without heating the cold influent water. For a synthetic influent with 1250 mg L⁻¹ COD, an IOBAC control without thermal swing achieved COD removals of 53% in cool water (10 °C), whereas thermal swing (TS-IOBAC) improved COD removal to 68%. Compared to the alternate approach of heating the bulk water to achieve an optimal biodegradation rate, the TS-IOBAC approach could reduce energy requirements by almost 97% for the temperature conditions tested. The results of this study support further development of TS-IOBAC as a robust and energy-efficient biological process concept for on-site wastewater treatment in cold climates.