NAMS 2002 Workshop - ICOM 2008

Osmotically Driven Membrane Processes – 4
Tuesday July 15, 10:30 AM-11:00 AM, O’ahu/Waialua
Osmotic Membrane Bioreactor and Pressure Retarded Osmotic Membrane
Bioreactor for Wastewater Treatment and Water Desalination
A. Achilli (Speaker), University of Nevada, Reno, Reno, Nevada, USA, aachilli@unr.edu
T. Cath, Colorado School of Mines, Golden, CO, USA
E. Marchand, University of Nevada, Reno, Reno, Nevada, USA
A. Childress, University of Nevada, Reno, Reno, Nevada, USA
More stringent regulations and the ability to produce high quality effluent make
membrane bioreactors (MBRs) an attractive process for domestic and industrial
wastewater treatment. In a conventional MBR, microfiltration (MF) or ultrafiltration
(UF) membranes are utilized and water is commonly filtered through the
membranes using pressure. Suspended solids are completely rejected and
substantial removal of organic carbon and nutrients can be achieved [1]. MBRs
replace two pivotal stages of conventional activated sludge systems
(biotreatment and clarification) with a single, integrated process. MBR effluent
may be suitable for use as irrigation water, process water, or a source of potable
water. For potable reuse (e.g., indirect reuse through aquifer recharge),
advanced treatment such as reverse osmosis (RO), nanofiltration (NF), or
chemical oxidation is necessary after the MBR [2]. The advantages of MBRs over
conventional treatment have been thoroughly reviewed and include product
consistency, reduced footprint, reduced sludge production due to a high biomass
concentration in the bioreactor, and complete suspended solids removal from the
effluent [3].
A novel MBR system that utilizes a submerged forward osmosis (FO) membrane
in the bioreactor is investigated in the current study. In forward osmosis, water
diffuses across a selectively permeable membrane from a solution of higher
water chemical potential (lower osmotic pressure) to a solution of lower water
chemical potential (higher osmotic pressure); in this application, water diffuses
from the bioreactor into a controlled draw solution (DS). The FO membrane acts
as a barrier to solute transport and provides high rejection of contaminants
present in the wastewater stream. The diluted DS is reconcentrated using RO or
distillation, and being reused in the FO process; the permeate is a high-quality
product water. Thus, in most wastewater treatment applications, FO is not the
ultimate process but rather a high-level pretreatment step before an ultimate
reconcentration/desalination process.
Compared to the MF or UF process in a conventional MBR, the FO process in
the osmotic membrane bioreactor (OMBR) offers the advantages of much higher
rejection (semi-permeable membrane versus microporous membrane) without