Feasibility of Onsite Residential Graywater Recycling Using a Semi-Batch Vertical Flow Wetland for Non-Potable Water Reuse
[Thesis]
Yu, Zita Lai Ting
Stenstrom, Michael K.; Cohen, Yoram
UCLA
2015
UCLA
2015
Water sustainability has become a critical issue in various regions around the world given rapid population rise and the impact of climate change on water resources. In this regard, onsite treatment and reuse of graywater (defined as wastewater is not originated from toilets or urinals), for non-potable applications, can be an important element of the approach to water sustainability. Treatment of graywater prior to reuse is essential in order to enable effective product water reuse and storage without creating nuisance, as well as comply with local regulatory requirements. In order to encourage adoption of graywater treatment, low-cost graywater treatment systems suitable for onsite residential deployment must be made available. The goal of the present research was to develop a low-cost, compact graywater treatment system using a semi-batch vertical flow wetland (SB-VFW) approach for residential graywater reuse for recycling. In order to assess the treatment performance and to elucidate the treatment mechanism and the removal kinetics, a SB-VFW system was developed and evaluated in a 13-month field study in a single-family home in Los Angeles. The SB-VFW consisted of a coconut coir dust layer (soil) and a cross flow media layer (CFM) was demonstrated to be effective for treatment of bathroom and laundry graywater. The treatment system was able to attain California Title 22 water reclamation requirements in ~3 hours for a 300-liter batch. The soil was found to be important for the removal of organics, turbidity, and suspended solids; while the use of CFM media enhanced aeration in the SB-VFW system. Organics removal in the SB-VFW was evaluated using a first-order kinetic model and found that graywater with lower organic removal rate constants stimulated more biomass growth and could lead to excess biomass accumulation when treatment time was short. Economic feasibility of onsite graywater treatment and reuse using SB-VFW systems were evaluated and found that a less-than-two-year return-on-investment could be achievable. Besides water-savings, energy required for graywater treatment using the SB-VFW approach was lower than the energy needed for potable water importation and centralized wastewater treatment. The present research demonstrated that onsite residential graywater treatment and reuse is both technically and economically feasible.