Membrane bioreactor better than activated sludge

Membrane bioreactor better than activated sludge

More wastewater treatment plants (WWTPs) are transitioning from conventional activated sludge to the membrane bioreactor process. This is due to the membrane bioreactor’s small footprint and high effluent quality To better achieve environmental goals.

However, retrofitting WWTPs from conventional activated sludge to membrane bioreactor (MBR) has been controversial. That is due to the high energy consumption and membrane fouling in membrane bioreactor applications. It is essential to solve this issue by comparing the techno-economy of conventional activated sludge with that of membrane bioreactors.

On the one hand, energy consumption accounts for the largest proportion of operating costs and is a key factor restricting the sustainable development of wastewater treatment processes. A membrane bioreactor normally has higher energy consumption than conventional activated sludge. On the other hand, are often associated with high returns. A membrane bioreactor obtains higher environmental benefits from higher effluent quality than conventional activated sludge.

Therefore, a justified techno-economic assessment of membrane bioreactors vs. conventional activated sludge requires comprehensively considering and environmental benefits. However, the previously reported techno-economic evaluation of WWTPs mostly lacked a systematic comparison between the conventional activated sludge and membrane bioreactor processes, especially a strict paired comparison between them in the same WWTP.

Who did the membrane bioreactor (MBR) research?

A research group from the University of Chinese Academy of Sciences studied the techno-economic characteristics of 20 full-scale WWTPs that had been retrofitted from conventional activated sludge to membrane bioreactor via the  and data envelopment analysis. The results were published in Frontiers of Environmental Science & Engineering.

They found that after the retrofitting from conventional activated sludge to membrane bioreactor, the effluent quality improved significantly, accompanied by an increase in energy consumption from 0.40 to 0.57 kWh/m3. At the same time, the change in operating cost was not so significant. The average marginal environmental benefit increased remarkably after the retrofitting, leading to an increase in the average net profit, which indicates the techno-economic feasibility of the retrofitting.

After the retrofitting, the relative cost efficiency increased from 0.70 to 0.73, while the relative energy efficiency did not change significantly. The techno-economy is closely related to the effluent standard adopted. An MBR is more profitable than conventional activated sludge, given stricter effluent standards.

The researchers argue that MBRs perform better than conventional activated sludge in cases of strict effluent standards and pollutant-sensitive destinations. There is still much room for further reducing the of an MBR.

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