Recovering the Energy in Municipal Wastewater with Membrane Centered Processes

Principal Investigator - Hongde Zhou, Professor, and Industrial Research Chair, University of Guelph, 2011 - 2014

Challenge

Sustainable wastewater treatment, with reduced energy consumption and resource recovery, is an increasingly important goal of many municipalities operating wastewater treatment plants.  The municipal wastewater treatment plant is often the largest consumer of energy for many communities.

A recent paradigm shift considers municipal wastewater as a potentially valuable source of energy, nutrients and other components. Previous studies have concluded that municipal wastewater contains approximately 10 times the energy needed to treat it. As energy costs rise and mineral phosphorus becomes increasingly scarce, the recovery and renewability of these resources is becoming more attractive.

This project, led by Dr. Hongde Zhou, addresses the increasing demand from many municipalities to develop membrane centered treatment processes that can recover energy efficiently and cost effectively, while providing opportunities to reuse water and recover other valuable resources. The project aims to develop a series of technical innovations to facilitate the adoption of energy-sustainable technologies in constructing and upgrading municipal wastewater treatment and reclamation facilities.

Project

The project team will explore the use of a membrane bioreactor operated at extremely short sludge residence times, (sludge treatment is a process for treating sewage and wastewaters using air and a biological floc composed of bacteria and protozoa).  This method is being tested to discover whether it will maximize the conversion of organic matter into recoverable biomass while minimizing the oxygen demand required for biological oxidation.  The low-pressure membrane filtration will also overcome a key barrier – poor settling of sludge generated at short sludge residence times – thus enabling separation of the biomass from the treated effluent.  A pilot study for this process will be installed at the City of Guelph Wastewater Treatment Plant.

More than 90 percent of the energy contained in wastewater ends up in sludge, which is generally digested anaerobically to generate biosolids – but the methane produced is usually not optimized or captured.  The team will examine an anaerobic membrane bioreactor with pre-treatment to improve methane production while concentrating the biosolids products (sludge digestion) and examining the use of the membrane permeate for potential nutrient recovery and water reuse.

In parallel with the membrane bioreactor tests, the fouling mechanisms and microbiological dynamics will be examined in both systems of membrane bioreactors.  As well, the use of process models will be integrated throughout the research program to assist with the design of experiments, facilitate analysis of the experimental data, and to assist in cost estimation through comparison of energy consumption and treatment costs.

Pilot tests of the Short SRT (solids retention time) MBR (membrane bioreactor) tests to evaluate membrane fouling, treatment performance, sludge production and sludge settleability.  The results showed high organics removal and near complete nitrification at all SRTs used.

In parallel with Short SRT MBR tests, membrane fouling was examined by monitoring transmembrane pressure.  The results showed that short SRT could result in very severe membrane fouling.  To provide an in-depth understanding of fouling mechanisms, extensive laboratory tests have been completed.  Based on these results, a different filtration model has been developed.

Outputs

This project has helped to develop new technologies, protocols, models, and equipment:

• All the required testing apparatuses have been designed and installed in order to accomplish the proposed research objectives.
  • Three aerobic ZeeWeed 10 MBR pilot plants for short SRT MBR tests
  • Three new AnMBR for sludge digestion provided by GE Water & Process Technologies.
  • Various water quality analysis, sludge characterization and membrane fouling measurement protocols have been established.
  • Model Development.  The collected data have been used to calibrate an integrated process model built on IWA Activated Sludge models.

The following academic publications have been a result of this project:

Lee, H.-S. and Yeo, H.  2013.  The effect of solids retention time (SRT) on dissolved methane concentration in anaerobic membrane bioreactors.  Environmental Technology, 34: 2105-2112.

Yeo H; Lee, H.S. (2013) Fates of dissolved methane in anaerobic membrane bioreactors (AnMBRs).  submitted to Bioresource Technology.

Chang, S., Jamal, S., Chen, H., Zhou, H., Hong, Y. and Adams, N. 2013. A novel approach to analysing concentration polarization of polysaccharide solutions”, submitted to Water Science & Technology.

Jamal, S., Chang, S. and Zhou, H. 2013.  Filtration behaviour and fouling mechanisms of polysaccharides, in preparation

Snider-Nevin, J., Adams, N., Suresh, K. and Zhou, H.  2013.  Evaluation of membrane bioreactors with short solids retention times on performance, biomass characteristics and membrane fouling. Accepted for oral presentation

Outcomes

• This project is expected to fill a critical knowledge gap on optimal membrane bioreactor (MBR) processes.  This process will help to optimize biomass or methane production, as well as reduce the membrane fouling potential of sludge generated in low sludge residence time MBRs and anaerobic digesters.
• Potential changes in practice as this knowledge may be applied to enable municipalities to recover the energy contained in their wastewater.
• The process model analysis approach developed for energy benchmarking analysis can also be adapted by decision-makers when assessing other alternative treatment technologies and operating conditions for different wastewater treatment plants.