Evaluating Traditional and Innovative Concentrate Treatment and Disposal Methods for Water Recycling at Big Bear Valley, California

The Big Bear Area Regional Wastewater Agency (BBARWA) recently completed a study of advanced water reclamation as a means to augment existing potable water supplies for the residents and visitors of Big Bear Valley. Potable water is provided by local groundwater (GW); during periods of drought or prolonged dry weather water demand can exceed supply. The use of recycled water, treated to a high quality via an advanced treatment process and artificially recharged, has been identified as the best means of supplementing the native GW supply. The advanced treatment proposed at the BBARWA Facility consists of microfiltration (MF), reverse osmosis (RO), followed by ultraviolet disinfection (UV) with advanced oxidation. While backwash waste produced from MF/UF facility can be recycled back to the headworks of the BBARWA wastewater treatment facility, the concentrate (reject) flow from the RO needs to be properly disposed. In this paper, seven different treatment methods were evaluated to dispose of concentrate from a future 1.2-mgd recycled water facility: constructed wetlands, electrodialysis reversal (EDR), enhanced RO treatment, mechanical and solar evaporation, Vibratory Shear Enhanced Process (VSEP) and wastewater effluent blending. All treatments were evaluated on a paper study basis, except VSEP, which was tested on-site using concentrate from the MF/RO pilot system. The study included siting solar evaporation and constructed wetlands facilities in Lucerne Valley 25 miles from BBV, where BBARWA currently land applies their wastewater effluent. LV was selected in this evaluation, because it minimizes public perception issues (i.e., mosquito, vector issues), reduces evaporation and wetland sizes due to higher evaporation/evapotranspiration rates in this lower altitude region and leaves space in WWTP for future plant expansion. Study results showed the most cost effective approach is to combine RO concentrate volume reduction using VSEP or EDR with evaporation ponds or constructed wetlands in the LV. VSEP is preferred over EDR due to the ability to produce a high quality permeate that can be blended with BBARWA effluent and some fraction of RO concentrate while still meeting land application guidelines. Constructed wetlands offer the potential to better management wildlife issues associated with elevated concentrations of selenium but have not been demonstrated to be sustainable using a zero liquid discharge approach.