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A Low-Energy Wastewater Treatment Process for Producing High Quality Reuse Water – Phase 2

Project: 10-06 (Phase 2)
Type: Report

Program: Principal
Funding Partner: Bureau of Reclamation
Total Budget: $202,373.84 (Cash: $152,373.84, In-Kind cash and service: $50,000)

Principal Investigator: Eric A. Marchand, Ph.D., P.E., University of Nevada, Reno

Background

The high costs associated with aeration in activated sludge wastewater treatment plants have been documents by numerous sources. While there can be some economies of scale associated with larger treatment plants, it has been report that U.S. facilities have an average energy cost of 1,200 kWh/MG of wastewater treated. This number can be as high as 2/200 kWh/MG for smaller facilities (~1 MGD) with up to 60% of the energy attributed to aeration. It is clear that this is a model that cannot be sustained in light of increasing energy costs and other economic pressures. While improving aeration equipment (e.g., blowers, aeration diffusers, increased maintenance) and control systems (e.g., automated control of aeration to meet instantaneous oxygen demand) can have a positive influence, the ultimate solution most likely involves shifting from aerobic to anaerobic technology to achieve waste degradation. However, anaerobic bioprocesses alone are not a complete solution since they have a limited range of applicability and do not effectively remove nutrients.

Goals and Objectives

The project will evaluate an innovative wastewater treatment process to include membrane contractor processes (forward osmosis (FO) and membrane distillation (MD)) to produce potable-quality water while relying on energy efficient biological processes to treat contaminants, followed by a resource recovery unit to produce struvite. Preliminary modeling has revealed that this process scheme holds promise for lowering treatment costs while producing high-quality water. This will be done through performing laboratory and pilot scale studies to assess the feasibility of an innovative process scheme for wastewater reuse with minimal energy consumption while operating with a high removal efficiency and small footprint.

Research Approach

The research will be completed in four tasks:

  • Coupled FO and MD Bench-Scale Investigation: Develop a coupled FO + MD process in three steps: selection of FO membrane, MD membrane, and draw solution. The FO + MD target level of performance and efficiency will be assessed in terms of water flux, reverse salt flux, and process recovery.
  • Anaerobic MBR bench-scale Investigation: Develop and characterize a bench-scale anaerobic membrane bioreactor for treating concentrated wastewater from the forward osmosis system. The data will be useful for interpreting results when the pilot-scale system is brought online and representative municipal wastewater FO concentrate is fed into the pilot-scale anaerobic membrane bioreactor system.
  • Pilot-scale System Retrofit: Retrofit a pressure retarded osmosis (PRO)-RO pilot-scale system. The PRO-RO system membranes will be replaced by FO membranes and process flow lines will be re-plumbed as needed.
  • Testing of the FO and AnMBR Pilot-Scale System: Test the FO + AnMBR system. The FO portion of the sytem will be monitored for parameters such as water flux, reverse salt flux, contaminant rejection, water recovery, and energy requirements. Biochemical experimental variables associated with AnMBR performance will include dissolved organic carbon, chemical oxygen demand, ammonia-nitrogen, pH, methane yield, and biomass.

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