302928 UFO MBR – A NOVEL Potable Reuse and Nutrient Recovery System
UFO MBR – A NOVEL POTABLE REUSE AND NUTRIENT RECOVERY SYSTEM
R.W. Holloway1 and T.Y. Cath*1
1Colorado School of Mines, Golden, USA
*1500 Illinois Street, Golden, CO, 80401, (303) 273-3402, tcath@mines.edu
The importance of water reuse has been increasing over the last half century as urban populations have increased and fresh-water supplies have remained constant or declined. Potable reuse has not been widely implemented, but will likely be an important part of the water budget in these water stressed regions. The implementation of potable reuse will require treatment processes with multiple barriers (e.g., chemical, biological, and physical) to prevent microbial, nutrients, and other contaminants of concern (CECs) from entering the public water supply. The osmotic membrane bioreactor (OMBR) is an example of a multiple barrier process designed to produce high quality water from impaired water sources.
The OMBR is comprised of three treatment barriers: biological treatment for carbon and nutrient removal, forward osmosis (FO) membrane for suspended and dissolved solids separation, and reverse osmosis (RO) for brine reconcentration and high quality potable water production. The novel aspect of the OMBR compared to conventional membrane bioreactors (MBRs) is the utilization of FO membrane for water extraction as opposed to traditional porous microfiltration (MF) or ultrafiltration (UF) membranes. FO membranes are permeable mainly to water and exhibit superior rejection of suspended and dissolved organic matter, CECs, and almost all inorganic species.
In the current study, the OMBR is being used to treat municipal wastewater produced by a small student community in Golden, CO. The wastewater carbon and nutrients are removed in two biological treatment stages: first stage pre-anoxic (anoxic) and second stage post-aerobic (aerobic). In the anoxic stage, nitrate (NO3) circulated from the aerobic stage is mixed with the carbon-rich wastewater influent stream and reduced to nitrogen gas. Effluent from the anoxic stage feeds the aerobic stage where ammonia (NH4+) is oxidized to NO3.
An FO plate and frame membrane module (Hydration Technologies Inc. (HTI), Albany, OR) is submerged in the aerobic tank where it is continuously aerated to promote liquid flow between the plates and to mitigate membrane fouling. Water is drawn through the membrane from the aerobically treated wastewater into a concentrated sodium chloride (NaCl) draw solution. The driving force for water flux in FO is the difference in chemical potential between the low salinity wastewater and the high salinity draw solution (DS). The DS diluted in the FO process is re-concentrated and pristine permeate is produced using a fully automated RO system.
The current research being conducted on the OMBR is the second phase of a two-phase long-term study. At this time, the system has been in continuous operation for more than six months. The system is being fed continuously with a screened (2 mm drum screen) raw wastewater. The FO membrane cassette is HTI's third generation OMBR membrane with an active membrane area of approximately 1.2 m2. The water flux and DS stream temperature have been recorded continuously using the integrated control system. The carbon and nutrient concentrations (chemical oxygen (COD), NH4+, NO3, and total phosphorus (TP)) in the wastewater influent, anoxic tank, aerobic tank, DS, and RO permeate have been measured weekly over the duration of the study.
Preliminary results illustrate that the water flux has consistently been approximately 5 LMH and that changes in water flux have been correlated to changes in the activated sludge temperature. The steady flux is particularly significant considering that the FO membrane cassette has not been cleaned over the duration of the experiment. The COD, total nitrogen (TN), and TP removals from the wastewater influent to the RO permeate have been greater than 98%, 90%, and 99% for each constituent, respectively. Preliminary conclusions from this study are that the OMBR can be continuously and reliably operated to produce a pristine water supply that may be of direct potable reuse quality.