Algal wastewater treatment integrated with carbon adsorption and ozonation for water reclamation: Multi-criteria comparison with conventional pathways

Our previous reports have documented a mixotrophic algal wastewater treatment (A-WWT) system integrated with downstream technologies for recovering net energy and fertilizers from domestic wastewater. In the current study, we explore the potential for reclaiming reuse-quality water via the A-WWT system by treating its effluent further by granular activated carbon (GAC) adsorption or/and ozonation (O3). Our study also includes a comparison of water reclamation capability of a pilot-scale A-WWT system against that of a full-scale conventional activated sludge (CAS) system, both fed with the same primary effluent and followed by GAC and O3. In this preliminary evaluation, aggregate chemical water quality data collected from the following 8 treatment trains are compared: T1) CAS + GAC; T2) CAS + O3; T3) CAS + GAC + O3; T4) CAS + O3 + GAC; T5) A-WWT + GAC; T6) A-WWT + O3; T7) A-WWT + GAC + O3; and T8) A-WWT + O3 + GAC. Based on aggregate water quality measures, ozonation followed by GAC adsorption achieved the lowest concentrations of organics (dissolved organic carbon, chemical oxygen demand, and UV absorbance) and nutrients (total nitrogen and total phosphorus), irrespective of the treatment provided by the CAS and A-WWT systems. Despite the higher footprint requirement, all four algal-based treatment trains (T5 to T8) ranked better than the CAS-based trains (T1 to T4) when compared on the basis of energy demand and energy recoverability. Following these findings, a multicriteria evaluation of the 8 treatment trains was performed considering 16 criteria spanning energy demand, energy recoverability, disinfection capability, emissions, areal footprint, and complexity. The multi-criteria evaluation ranked the A-WWT system integrated with ozonation and GAC adsorption (T8) highest among the eight treatment trains considered here. This preliminary evaluation adds further credence to the A-WWT system and warrants a detailed Water quality-based evaluation of its effluent and follow-up treatment to reclaim reusequality water.

Automated summary

The study investigates the potential of reclaiming reuse-quality water through the A-WWT system with further treatment by GAC and O3, finding that ozonation followed by GAC adsorption achieved the lowest concentrations of organics and nutrients. Algal-based treatment trains outperformed CAS-based trains in terms of energy demand and recoverability. A multi-criteria evaluation ranked the A-WWT system integrated with ozonation and GAC adsorption highest among the eight treatment trains considered.