Role of Mesh Pore Size in Dynamic Membrane Bioreactors

Pompilio Vergine,Alfieri Pollice,Carlo Salerno,Giovanni Berardi,Barbara Casale

doi:10.3390/ijerph18041472

Abstract

Two identical bench-scale Self-Forming Dynamic Membrane BioReactors (SFD MBR) were set-up and operated for the treatment of real urban wastewater. The two bioreactors were equipped with meshes of different mesh pore size. Meshes having pore size values of 20 and 50 µm were tested under solid retention time (SRT) of 15 d, whereas meshes with 50 and 100 µm pore sizes were compared under SRT of 50 d. The results of long-term experiments showed very good overall performances by all systems at the steady state. High flux (in the range 61–71 L m−2 h−1) and very good effluent quality were obtained, with average suspended solids and chemical oxygen demanding values below 10 mg L−1 and 35 mg L−1, respectively. The mesh pore size did not have a major influence on the average cleaning frequency. However, the pore size affected the effluent quality in correspondence of two particular conditions: (i) immediately after mesh cleaning; and (ii) during operation under high suction pressures (mesh clogging not promptly removed through cleaning). Moreover, the mesh cleaning frequency was observed to be dependent on the SRT. In tests with 50 d SRT, the cleaning requirements were very low (one every five days), and this limited the influence of the mesh pore size on the effluent quality. In conclusion, in SFD MBR, the role of the mesh pore size on the effluent quality may be more or less relevant depending on the operating conditions that directly influence the Dynamic Membrane formation.

Highlights

Effluent turbidity values above 10 nephelometric turbidity unit (NTU) were occasionally observed during run R100_50. This is the only noticeable difference between the performance of runs R50_50 and R100_50, and, considering the identical operating conditions of the two tests, it was reasonably due to the different mesh pore sizes (50 vs. 100 μm)
R50_50 and R100_50, and, considering the identical operating conditions of the two tests, it was reasonably due to the different mesh pore sizes (50 vs. 100 μ m)
During a long-term study conducted with two pairs of bench-scale Self-Forming Dynamic Membrane BioReactors (SFD Membrane BioReactor (MBR)), four runs were performed in order to evaluate the role of the mesh pore size under different solid retention time (SRT) (15 and 50 d)

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The Membrane BioReactor (MBR) is a wastewater treatment technology resulting from the integration of membrane filtration into the activated sludge process, and it is one of the most important innovations developed in this field [1]. The main benefit of the MBR is the production of high-quality effluents without any further treatment. 30 years of application of ultrafiltration-based MBR have shown that membrane fouling may rapidly reduce the system’s productivity, i.e., the flow rate produced per unit of pressure applied, and increase its management costs [2]. This, together with the relatively high costs and fragility of polymeric membranes, limits the application of the MBR in large-scale urban wastewater treatment plants (WWTPs)

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