Characters of Inulin Conversion Induced by Inulinase in Ultrafiltration Membrane Bioreactor

Abstract

The objective of this study was to convert inulin to high output fructose with the commercial inulinase in the continuous ultrafiltration membrane bioreactor (UFMB). The effects of operational conditions were explored for the volumetric productivity. The model equations of kinetics and membrane fouling were also founded. The stable fructose production with the volumetric productivity was attained at the optimum condition of inulin concentration (100 g/L), E/S ratio (40 U/g) and residence time (20 min). The kinetics results showed that the experimental data obtained were fit to the model equations. Preliminary experimental results were attained the fundamental membrane fouling mechanism. These results demonstrated its feasibility and availability for efficient fructose production, which were beneficial to provide theoretical basis for further researches.

Graphic Abstract

The operational conditions were explored for the volumetric productivity. Model equations and parameters of kinetics were founded and obtained. The membrane fouling mechanism of UFMB system was founded.

Appendix

$$P_{v} \left( t \right) = \frac{{\sum\nolimits_{0}^{t} {m_{p} \left( {permeate,\,t} \right)} }}{{0.43L}} \times \frac{{{{60\min } \mathord{\left/ {\vphantom {{60\min } h}} \right. \kern-\nulldelimiterspace} h}}}{t}\,\sum\nolimits_{0}^{t} {m_{p} \left( {permeate,\,t} \right)}$$

(1)

was defined as the total mass of fructose (g) gained in all permeates gathered up to time t; t was equal to the collection time (min); 0.43 L was determined as the total volume of the reaction mixture.

$$FS_{l0} - FS_{l} = V_{R} \left( { - v} \right)$$

(2)

S_lo substrate concentration (g/L) in the inlet feed, S_l substrate concentration (g/L) in the outlet stream, (-v) rate of substrate depletion, F flow rate (mL/min) of the feed and the filtrate, V_R bioreactor volume (mL).

$$v = \frac{{V_{\max } S_{t} }}{{K_{m} + S_{t} }}\,{\text{and}}\,\left( { - v} \right) = \frac{{k_{2} E}}{{1 + \frac{{S_{l} }}{{K_{is} }}}} \cdot \frac{{S_{l} - \frac{{P^{2} }}{{K_{eq} }}}}{{S_{l} + K_{m} }}$$

(3)

$k2$ kinetic constant (V_max = k₂S_l0E), K_is inhibition constant for substrate, P production concentration, K_eq equilibrium constant, K_m Michaelis constant.

$$X = \frac{{S_{l0} - S_{l} }}{{S_{l0} }} = \frac{P}{{S_{l0} }} \Rightarrow S_{l} = S_{l0} \left( {1 - X} \right),\,P = XS_{l0}$$

(4)

$$\left( { - v} \right) = \frac{{k_{2} }}{{1 + \frac{{S_{l0} \left( {1 - X} \right)}}{{K_{is} }}}} \cdot \frac{{S_{l0} \left( {1 - X} \right) - \frac{{\left( {S_{l0} X} \right)^{2} }}{{K_{eq} }}}}{{S_{l0} \left( {1 - X} \right) + K_{m} }}$$

(5)

$$J = L_{p} \Delta P$$

(6)

L_p and ΔP are defined as the parameters of the linear coefficient and transmembrane pressure, respectively.

$$J = \frac{\Delta P}{{\mu R}}$$

(7)

J (L/h/m²) is permeate flux, ΔP (bar) is transmembrane pressure, $\mu \left( {{\text{P}}_{{\text{a}}} \cdot {\text{s}}} \right)$ is liquor viscosity and R (1/m) is hydraulic resistance.

$$R = \frac{1}{{\mu L_{p} }}$$

(8)

$$R_{t} = R_{m} + R_{r} + R_{i}$$

(9)

R_m is membrane resistance that reckoned on regarding the pure water permeability of unused UF membrane; R_r is reversible fouling resistance, R_i is irreversible fouling resistance that calculated regarding the pure water permeability after rinsing steps. The overall fouling resistance (R_f) is given by the sum of R_r and R_i.

$$P_{f} = \frac{\Delta M}{{\rho A\Delta t}}\left( {{L \mathord{\left/ {\vphantom {L {{{m^{2} } \mathord{\left/ {\vphantom {{m^{2} } h}} \right. \kern-\nulldelimiterspace} h}}}} \right. \kern-\nulldelimiterspace} {{{m^{2} } \mathord{\left/ {\vphantom {{m^{2} } h}} \right. \kern-\nulldelimiterspace} h}}}} \right)$$

(10)

ΔM is the permeate gathered during the period of time (Δt), $\rho$ is the solution density and A is the filtration area of UF membrane.