The Use of NaOH Solutions for Fouling Control in a Membrane Bioreactor: A Feasibility Study

Abstract

Nowadays, the microbial production of 1,3-propanediol (1,3-PD) is recognized as preferable to the chemical synthesis. However, finding a technological approach allowing the production of 1,3-PD in the membrane bioreactor (MBR) is a great challenge. In the present study, a ceramic ultrafiltration (UF) membrane (8 kDa) for treatment of 1,3-PD broths was used. It has been demonstrated that the membrane used provides the stable permeate flux that is necessary to ensure the stability of the fermentation process in MBR technology. It was noticed that the broth pH has a significant impact on both the final 1,3-PD concentration and permeate flux. Moreover, the feasibility of using NaOH for fouling control in the MBR was evaluated. It has been shown that 1% NaOH solution is effective in restoring the initial membrane performance. To the best of our knowledge, this study is the first to shed light onto the possibility of reducing the amount of the alkaline solutions generated during the MBR operation. Indeed, it has been found that 1% NaOH solution can be successfully used several times for both membrane cleaning and to stabilize the broth pH. Finally, based on the results obtained, the technological conceptions of the MBR technology were designed.

Keywords: ceramic membrane; fermentation; fouling; membrane bioreactor design; membrane cleaning; sodium hydroxide; ultrafiltration.

Figure 1

Schematic diagram of a bioreactor coupled with an external installation with the UF membrane module. 1—bioreactor, 2—pH sensor, 3—NaOH dosing unit, 4—NaOH tank, 5—feed tank, 6-pump, 7—membrane module, 8—heater, V1–V4—valves, P—manometer.

Figure 2

The changes of glycerol and 1,3-propanediol concentrations and number of viable cells of bacteria in the broth during the fermentation process, under conditions of uncontrolled pH. Initial glycerol concentration: (a) 20 g/L; (b) 10 g/L.

Figure 3

The changes of carboxylic acids concentrations and broth pH during the glycerol fermentation process, under conditions of uncontrolled pH. Initial glycerol concentration: (a) 20 g/L; (b) 10 g/L.

Figure 4

The changes of glycerol and 1,3-propanediol concentrations and number of viable cells bacteria in the broth during the fermentation process with pH regulation (broth pH = 7). Initial glycerol concentration: 20 g/L.

Figure 5

The changes of carboxylic acids concentrations and broth pH during the glycerol fermentation process with pH regulation (broth pH = 7). Initial glycerol concentration: 20 g/L.

Figure 6

Changes in the permeate flux during the UF process of a fermentation broth (pH = 7). The blue line represents cleaning of the membrane module with 1% NaOH solution (15 min).

Figure 7

Changes in the relative flux of UF membrane. Relative flux: 1—steady-state, after 180 min of the broth filtration process, 2—after membrane rinsing with water, 3—after membrane cleaning with 1% NaOH solution (5 min), 4—after membrane cleaning with 1% NaOH solution (10 min).

Figure 8

Changes in the permeate flux during the UF process of a fermentation broth (pH = 8.5).

Figure 9

Changes in the performance of the UF membrane during the cyclically repeated operation: filtration-rinsing with 1% NaOH solution. J₀—initial (maximum) permeate flux, J_s—steady-state permeate flux, J_w—permeate flux after membrane rinsing with water.

Figure 10

The technological conception of UF installation with a membrane-cleaning system with NaOH solution. 1—feed tank, 2—pH sensor, 3—NaOH dosing unit, 4—NaOH tank, 5—pump, 6—membrane module, 7—retentate tank, V1–V6—valves, P—manometer.

Figure 11

The technological conception of membrane bioreactor with cleaning system with NaOH solution. 1—bioreactor, 2—pH sensor, 3—NaOH dosing unit, 4—NaOH tank, 5—pump, 6—membrane module, 7—pH sensor, V1–V5—valves, P—manometer.