IMPROVING ENERGY UTILIZATION IN MEMBRANE

BIOREACTOR SYSTEMS

INDIVIDUAL RESEARCH PROJECT ER2

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THE CHALLENGE

The membrane bioreactor (MBRs) is a low-footprint and robust technology that constitutes the state-of-the-art in wastewater treatment and reclamation. Through the com-bination of a suspended growth bioreactor and a mem-brane process for solids separation, MBR processes deliver a high-quality effluent that is amenable for reuse. Howev-er, a more widespread implementation of MBRs has been hampered to date by their relatively high energy consump-tion per volume of treated water. The main source of en-ergy consumption in MBRs is the aeration system, which is used to provide the biological process with oxygen and to control membrane fouling through scouring (Figure 1). The identification of a strategy or technological modification that effectively improves energy utilization in MBRs would reduce significantly the cost of wastewater reuse and thus promote better utilization of fundamental resources such as water and energy. Acciona Agua has identified this po-tential to cut back on operational costs while enhancing

Fellow in charge: Marina ArnaldosSupervisor: Teresa de la TorreAcciona Agua

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the sustainability of wastewater treatment and thus has embarked on a project aimed at identifying different approaches to improve energy usage in MBR systems.

Figure I: Energetic Costs in MBR Systems.

BENEFITS

The project benefits include:

• Lowering the operational costs of MBR systems, potentially resulting in an increased implementation of the technology.

• The development of an energy and water-sustainable technology that promotes wastewater reuse.

Figure 3: Widespread implementation of MBR technology could enhance wastewater reuse.

THE PROJECT

The overall aim of the project is to identify different approaches to improve energy utilization in MBR systems. This general aim has been structured in three different sub-objectives:

• Optimization of existing aeration devices. Of particular interest is the evaluation of novel spherical-cap aeration systems (Figure 2). These aeration devices could promote higher membrane scouring with lower energy consumption as compared to conventional devices.

• Development and feasibility study of an emerging MBR technology, the forward-osmosis (FO) MBR process. This technology does not require aeration for membrane fouling prevention and thus could represent significant energy savings.

• Identification of novel advanced control strategies to optimize the overall operation of MBR systems. The use of an effective advanced control strategy for membrane scouring could enhance energy savings in MBR systems.

Figure 2: Scouring Behavior of Conventional Aeration (Left) and Spherical-Cap Aeration (Right).

METHODOLOGY AND RESULTS

The project work programme has been broken down into a number of key tasks to be undertaken, culminating in a final report:

• Evaluation of the energy consumption of an MBR system using a spherical-cap aeration device. This was carried out using a pilot-scale MBR facility operated by Acciona Agua.

• Optimization of the operational parameters of such system using mathematical modelling approaches to minimize costs. The conclusion of this study was validated at the MBR pilot plant.

• Identification of promising control strategies to optimize aeration in MBR systems. This was carried out by performing advanced mathematical modelling of the MBR system; both membrane separation and biological processes was taken into account, as well as the hydrodynamics of the process. The results was validated by implementing the selected control in the MBR pilot plant.

• Optimization study of the performance of a FO-MBR system through mathematical modelling ap-proaches. Validation of the conclusions obtained in a FO-MBR pilot plant designed and constructed for the study.

• Testing the feasibility of scaling-up the FO-MBR technology by operating the pilot plant long term and with real wastewater as feed.

These tasks approach energy optimization in MBRs from different angles, and thus ensure the identifi-cation of different energy-saving strategies. This project started in October 2012 and it was completed in October 2014.

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The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme FP7/2007-2013, under REA agreement 289193. This publication reflects only the authors’ views and the European Union is not liable for any use that may be made of the information contained therein.

Coordinator: Joaquim Comas, LEQUIA - Universitat de Girona, joaquim.comas@udg.edu

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Böhm et al., 2012 and cortesy of GE.