A Novel Anaerobic Gravity-Driven Dynamic Membrane Bioreactor (AnGDMBR): Performance and Fouling Characterization

Abstract

Despite numerous studies undertaken to define the development and significance of the dynamic membrane (DM) formed on some coarse materials, the optimization of reactor configuration and the control of the membrane fouling of anaerobic dynamic membrane bioreactor (AnDMBR) need to be further investigated. The aim of this study was to design a novel anaerobic gravity-driven dynamic membrane bioreactor (AnGDMBR) for the effective and low-cost treatment of municipal wastewater. An 800 mesh nylon net was determined as the optimal support material based on its less irreversible fouling and higher effluent quality by the dead-end filtration experiments. During the continuous operation period of 44 days, the reactor performance, DM filtration behavior and microbial characteristics were studied and compared with the results of recent studies. AnGDMBR had a higher removal rate of chemical oxygen demand (COD) of 85.45 ± 7.06%. Photometric analysis integrating with three-dimensional excitation-emission matrix fluorescence spectra showed that the DM effectively intercepted organics (46.34 ± 16.50%, 75.24 ± 17.35%, and 66.39 ± 17.66% for COD, polysaccharides, and proteins). The addition of suspended carriers effectively removed the DM layer by mechanical scouring, and the growth rate of transmembrane pressure (TMP) and the decreasing rate of flux were reduced from 18.7 to 4.7 Pa/h and 0.07 to 0.01 L/(m²·h²), respectively. However, a dense and thin morphological structure of the DM layer was still observed in the end of reactor operation and plenty of filamentous microorganisms (i.e., SJA-15 and Anaerolineaceae) and the acidogens (i.e., Aeromonadaceae) predominated in the DM layer, which was also embedded in the membrane pore and led to severe irreversible fouling. In summary, the novel AnGDMBR has a superior performance (higher organic removal and lower fouling rates), which provides useful information on the configuration and operation of AnDMBRs for municipal wastewater treatment.

Keywords: cake layer; irreversible fouling; membrane bioreactor; non-woven fabric; nylon net.

Figure 1

(a) Setup of AnGDMBR and (b) cross section of membrane modules.

Figure 2

Dead-end filtration curve (a) and fouling resistance distribution (b) of the different supporting materials. R_c, R_b, R_f, and R_m refer to the fouling resistances of cake layers, pore-blocking, organic-bound fouling, and new support filters which were measured through the following cleaning procedures (i.e., cake removal with sponges, backwashing with 50 mL of DI water at 30 kPa, and 0.3% NaClO cleaning for 12 h).

Figure 3

Fouling behavior of (a) 50 g non-woven fabric, (b) 800 mesh nylon net in multiple filtration-physical cleaning cycle tests. Fouled membrane images were showed after each filtration and physical cleaning.

Figure 4

COD (a), PS (b), and PN (c) concentrations in the influent, supernatant, and effluent and the related removal and retention rates of these organics in the AnGDMBR.

Figure 5

EEM fluorescence spectra of DOM in the influent (a), supernatant (b), effluent (c), and cake layer (d). Peaks A, B, C and D mean the aromatic protein-like, tryptophan protein-like, humic acid-like and fulvic acid-like compounds, respectively.

Figure 6

The AnGDMBR in the long-term operation: (a) variations in the transmembrane pressure (TMP); (b) changes in the flux, and (c) effect of filtration cycles on membrane fouling (i.e., reversible, irreversible, and total fouling).

Figure 7

Scanning electron microscope (SEM) images for the biofilms on the support materials of a new nylon net (a–c) and used membrane after fouling (d–f), after physical cleaning (g–i), and after chemical cleaning (j–l).

Figure 8

(a) Shannon and Simpson indexes of bulk sludge and cake layer samples. (b) Principal coordinate analysis (PCoA) plot analysis of community differences between bulk sludge and cake layer samples. (c) Relative abundances of the phylum (top 12) and family (top 30) in bulk sludge and cake layer samples.