Your web browser is out of date.

Update your browser for better security, speed and to get the best experience on this website.

Update your browser
Advert

Have you got the energy? − Operational efficiency in MBRs

Posted on
Simon Judd
Simon Judd

Professor Simon Judd has over 30 years’ post-doctorate experience in all aspects of water and wastewater treatment technology, both in academic and industrial R&D. He has (co-)authored six book titles and over 200 peer-reviewed publications in water and wastewater treatment.

In his capacity as director of Judd Water & Wastewater Consultants, Simon is co-owner of The MBR Site.com, as well as of our sister website SludgeProcessing.com. He is Professor in Membrane Technology at the Cranfield Water Science Institute at Cranfield University in the UK where he has been a staff member since 1992. Simon was also a Research Chair at Qatar University in the Middle East for six years until September 2018.

High operational costs, and energy costs in particular, are seen as being the Achilles heel of MBRs. There is naturally a great emphasis on energy efficiency and, given that most of the energy demand from operating MBRs relates to blowing air, aeration energy efficiency has attracted the most attention.

For biotreatment, the aeration demand is dependent on the loading of biodegradable organics. Increasing aeration energy efficiency is therefore achieved through increasing oxygen transfer at the lowest energy demand possible. This has led to the exploration and development of high shear aeration devices to generate small air bubbles with enhanced mixing.

For air scouring of the membrane in immersed MBRs the object is also to create shear, but at the membrane surface itself. This is generally achieved with coarse bubble aerators generating relatively large bubbles which scour the membrane surface directly (as for flat sheet systems) and/or cause lateral movement of the membrane (as in the case of hollow fibres).

So, how much air is actually needed? The low end for the specific energy demand for membrane scouring is now at around 0.1 kWh/m3 permeate for some existing optimised installations (like Brescia and Olu Pandan). It appears now that this figure may be revised downwards with more recent developments in intense intermittent scouring, combined with improvements in membrane module design. Sludge pumping and permeate extraction will always add at least another 0.1 kWh/m3 (at least, for HF systems), but the total of ~0.2 kWh/m3 is impressively frugal.

In fact, there’s now talk of MBRs being lower in carbon footprint than conventional activated sludge processes even without the polishing step to create parity of treated effluent quality. There are still challenges with the technology, but maybe the energy penalty one is abating.

Comments

All comments are moderated and may be edited or deleted at any time. You must not post anything that is defamatory, illegal, offensive or which contravenes our privacy policy guidelines. Email addresses are only used for comments purposes. Contact info@thembrsite.com to remove or edit a comment.

About this page

This page was last updated on 08 June 2021

Disclaimer

Information on this page may have been supplied by third parties. You are reminded to contact any third parties to confirm information is accurate, up to date and complete before acting upon it. TheMBRSite.com accepts no liability for information provided by third parties, actions taken on the basis of this information or information held on third-party websites.