Membrane bioreactors – A review on recent developments in energy reduction, fouling control, novel configurations, LCA and market prospects

TL;DR: In this article, a review of the recent work on membrane bioreactor (MBR) technology is presented, which discusses the overall life cycle of MBRs and the market prospects for MBR technology.

About: This article is published in Journal of Membrane Science.The article was published on 2017-04-01 and is currently open access. It has received 333 citations till now.

Summary

1. Introduction

• Membrane bioreactor (MBR) technology is considered a well-established, mature technology with many full-scale plants around the world treating municipal and industrial wastewater.
• Recent developments often resulting in novel configurations or focused on aspects related to energy reduction has attracted little attention.
• To this end, the purpose of this review is to address the recent R&D advances in MBR technology with regard to energy demand reduction and membrane fouling mitigation, both being the technology key challenges and important aspects of MBR functioning.
• Novel configurations are also discussed, based on the recent literature on the subject in order to improve the understanding of the recent advances in MBRs.
• This review starts with an update on the current technology status and discussion on the cases where MBR makes sense to be applied.

2. Current status and application potential of MBRs

• Overall the last years, several MBR plants having a design capacity much higher than that of Nordkanal have been developed and are operating.
• MBRs are able to effectively remove a wide spectrum of organic micropollutants including compounds that are resistant to activated sludge processes [43, 44].
• Concluding, MBRs have become an accepted option to consider for applications requiring a high quality of treated effluent, small footprint, particularly in situations with stringent suspended solids, nutrient and microbiological limits or when water reuse is required [33, 49].

3. Fouling and fouling control

• Membrane fouling remains the most important operational problem, hindering their universal and wide scale application.
• The control and mitigation of membrane fouling is essential in MBR systems in order to ensure a cost effective and long-term operation.
• Chemical cleaning is particularly effective for combating irremovable fouling, which cannot be removed during the normal operation of the MBR.
• Zeolite and activated carbon are adsorbents which have been added into the mixed liquor of MBR to mitigate fouling by adsorbing colloidal and soluble substances [54, 55].
• In addition, such integrated processes are still in their early stage of development as they are being investigated at bench and pilot scale level.

4. Energy reduction

• 1. Current state of full-scale MBRs Energy demand and related costs issues have, together with membrane fouling issues, become an essential focus point in the full-scale MBR design and operation.
• Tolkou et al. [77] highlight the biological aeration adjustment, intermittent denitrification, application of primary clarification ahead of the MBR, flow equalization, solids adjustment between the aeration and the membrane basins, intermittent air scouring or coupling of air scouring to the flux, use of flux enhancers, and pump configuration as the energy-savings solutions.
• Tao et al. [78] demonstrated, through a six-year long pilot and demonstration scale studies, the reduction of energy consumption in a municipal full-scale MBR from 1.3 kWh/m 3 down to 0.37 kWh/m 3 .
• Recent commercial developments include the introduction of new generation membranes, membrane modules and complete MBR systems.
• The energy reduction arises from a more efficient membrane air scouring system.

5. Novel configurations

• Recent R&D advances in MBRs with respect to novel configurations have focused on membrane fouling control, energy demand reduction, enhanced nutrient removal or removal of refractory compounds [2, 12, 77].
• Ibeid et al. [147] studied electrokinetic processes leading to 3 times lower fouling rate in a pilot-scale MEBR.
• 3. Enhanced nutrient and/or refractory compound removal Formation or cultivation of aerobic granules in an MBR can mitigate membrane fouling, increase permeate flux, and reduce energy consumption.
• According to the producer, the membrane couple high packing density and a back-wash capability, with low TMP and ease of operation, while reduced capital and operating costs [236].

6. Overall Life Cycle of MBRs

• A holistic evaluation over their environmental performance is required with the view to ensure their effectiveness from both a technological and an environmental point of view [239].
• The environmental impact analysis of five treatment processes performed by Hoibye et al. [246] showed that the application of advanced technologies for the improvement of treated effluent quality is often accompanied by environmental damages incurred from achieving this improvement.
• Furthermore, the authors question the reliability of the calculations regarding the energy demands of pilot-scale MBRs, since the limited scale of the study negatively affects the energy performance [255].
• Hospido et al. [239] point out that the LCA studies should not exclusively include the environmental dimension, but they should also be coupled with technical and economic aspects (constraints and benefits) in order to holistically evaluate the sustainability of a treatment process.
• The MBR has a high energy and carbon footprint due to the requirement for membrane cleaning (air scouring, chemical cleaning, etc.), while it can achieve very high treated effluent quality with low nutrient concentration and thus a very low impact to marine and fresh water eutrophication.

7. Markets for MBRs & AnMBRs

• The MBR market has seen growth albeit at a slower rate than projected around 2010.
• Demand will also vary as geographic areas or applications have varied situations.
• Thus with Ovivo being one of the largest municipal MBR systems suppliers in the US coupled with the fact that Microdyn Nadir technology is based on flat sheet membranes similar to Kubota; Mann+Hummel could threaten Kubota’s market share over time.
• AnMBR’s have also been employed in such areas as Mars chocolate in Veghel, the Netherlands (Veolia’s Memthane using Pentair X-Flow membranes) Pulp and Paper – MBR’s can process sludge prior to desalination.
• Origin Water, also from China, has over 16 patents.

8. Conclusions

• Recent developments with regard to energy reduction, membrane fouling control and novel configurations in MBRs were reviewed.
• In addition, LCA and market prospects for MBR technology were discussed.
• Finally, development of a holistic approach for the environmental impact assessment of full-scale MBRs integrating LCA, model analysis, water quality indicators and impact categories is required.
• Based on the amount of published literature in the recent years, interest from the MBR practitioners and already close relation to the practice, significant progress is anticipated in the area of novel fouling mitigation measures, particularly in effective and/or low-energy membrane cleaning.
• It is expected that recent advances in material science will also contribute towards the development of antifouling membranes.

Figures

Table 7. Number of MBR related patents in 2006-2016 period per country of patent submission