Remediation of suspended solids and turbidity by improved settling tank design in a small-scale, free-standing toilet system using recycled blackwater.

Our research is focused on the development of decentralized waste water treatment technologies enabling onsite water reuse. Accumulation of solids with recycling of treated blackwater increases the energy required for disinfection with an electrochemical process. We hypothesized that improving the preprocess settling of blackwater by increasing the tortuosity of the liquid flow path would reduce this energy demand by reducing particle-associated chemical oxygen demand (COD). This approach successfully reduced the total suspended solids and turbidity in the process liquid accumulated per user-day equivalent. A modest reduction in the apparent steady-state accumulation of COD was also observed, likely because of the retention of COD associated with larger particles in the settling tanks. Interestingly, these improvements did not improve the energy efficiency of the electrochemical disinfection process, as predicted. These observations suggest that improving the energy efficiency of electrochemical disinfection will require remediation of dissolved COD.