Feasibility of a semi-batch vertical-flow wetland for onsite residential graywater treatment

• Semi-batch vertical flow wetland provides low cost residential graywater treatment.
• Treated graywater quality suitable for above ground use achieved in about 3 h.
• Coconut coir soil substitute in wetland enabled high hydraulic loading.
• Semi-batch vertical flow wetland can handle detergent shock loads.

The technical feasibility of graywater treatment, via a semi-batch vertical flow wetland (SB-VFW), was evaluated at a single family home for aboveground water reuse. Graywater treatment was achieved to a quality level that was well within the regulatory compliance limits (e.g., with respect to biochemical oxygen demand (BOD), total suspended solids (TSS) and turbidity) for above ground reuse. System performance over the course of a five-month field study demonstrated that the necessary treatment time was typically ∼3 h for a 300 L batch. The SB-VFW operated in a stable manner owing to the use of a coconut soil substitute that has high hydraulic conductivity and also enabled avoidance of clogging due to excess biofilm growth. The latter was made possible through the use of a bio-based laundry (BBL) detergent which had a lower organic content relative to conventional laundry detergents. The system was able to return to normal operation even after detergent shock loads. Results of the present study are encouraging and suggest that residential level graywater treatment is technically feasible and can thus potentially expand the range of possible water reuse applications.