Method of desalination and wastewater treatment in a microbial desalination cell reactor

Abstract

Method of desalination and wastewater treatment in a microbial desalination cell reactor is provided, the microbial desalination cell reactor has three compartments, an anodic compartment, a cathodic compartment and a saline compartment, the method is carried out by (a) adding electrically conductive particles or electrically conductive material in the anodic compartment and cathodic compartment, (b) adding bacteria species of the genus Geobacter in the anodic compartment and several solutions in the compartments (c) replacing the solutions in the cathodic compartment and in the saline compartment and (d) oxidizing organic matter present in wastewater by bacteria from the genus Geobacter in the anodic compartment and desalinating the solution in the saline compartment and (e)after 20 to 30 operation cycles, replacing the solution in the saline compartment by a solution of hypochlorite salt.

Claims

1. A method of desalination and wastewater treatment in a microbial desalination cell reactor, wherein the microbial desalination cell reactor comprises three compartments, an anodic compartment, a cathodic compartment and a saline compartment, wherein an anionic exchange membrane is placed between the anodic compartment and the saline compartment and a cationic exchange membrane is placed between the cathodic compartment and the saline compartment, the method comprising: (a) adding electrically conductive particles or electrically conductive material in the anodic compartment and cathodic compartment, (b) adding bacteria species of the genus Geobacter in the anodic compartment, adding an aqueous solution comprising an electrolyte, as catholyte, in the cathodic compartment, adding a saline solution in the saline compartment and desalinating said saline solution by applying an external power supply, (c) when constant electric current is achieved, replacing the solution in the cathodic compartment by a first hypochlorite solution comprising soluble hypochlorite salts and replacing the external power supply by an external circuit or connecting anode and cathode to produce short circuit conditions, (d) oxidizing organic matter present in wastewater by bacteria from. the genus Geobacter in the anodic compartment, and desalinating said saline solution in the saline compartment and (e) after 20 to 30 operation cycles, replacing the solution in the cathodic compartment by a solution of a second hypochlorite solution comprising soluble hypochlorite salts.

2. The method according to claim 1, wherein said electrically conductive particles or electrically conductive material is selected from the group consisting of graphite particles, activated carbon, vitreous carbon and carbon felt.

3. The method according to claim 1, wherein said aqueous solution comprising an electrolyte, as catholyte, is an aqueous solution of a sulphate salt.

4. The method according to claim 1, wherein said saline solution is a solution comprising soluble bicarbonate salts.

5. The method according to claim 1, wherein said external circuit is selected from the group consisting of resistor, DC-DC converter and electric accumulator.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1. Scheme of Microbial Desalination Cell operating with hypochlorite as electron acceptor in the cathodic compartment.

(2) FIG. 2. MDC system flow chart diagram.

(3) FIG. 3. MDC elements and configuration. MDC elements: 6: end plates. 7: end gaskets, 8: end compartment (inlets-outlets), 9: inner gaskets, 10: electrode collector, 11: ion exchange membrane, 12: compartment+turbulence promoter (desalination chamber).

(4) FIG. 4. MDC desalination experiments examples. Time-evolution of current density (upper row) and saline tank conductivity (lower row). Operation conditions: anolyte conductivity 4.1 mS/cm, catholyte conductivity 6.3 mS/cm. Anolyte tank: 10 L, catholyte tank: 10 L, and saline tank: 2 L. Flow rate: 100 mL/min. Operation under short circuit conditions with two different initial conductivities 4 and 8 mS/cm (A and D). Operation with two different compartment lengths under short circuit conditions and 8 mS/cm initial conductivity (B and E). Operation with a saline compartment of 6 mm long and initial conductivity 8 mS/cm under short circuit conditions and external resistor of 2 Ohm (C and F).

DESCRIPTION OF EMBODIMENTS

Example 1

Simultaneous Oxidation of Organic Matter, Saline Water Desalination and Electric Power Generation in a Microbial Desalination Cell.

(5) Stage 1: The MDC reactor is a three chamber electrochemical reactor with a collector area of 100 cm.sup.2 and a compartment length of 12 mm (E-Cell). The anodic chamber is filled with carbon felt RVC 4000 (Mersen Ltd) and a graphite plate was used as electric current collector. Conducting paste was used to glue the carbon felt to the collector. A graphite plate was used as cathode, and a turbulence promoter was located inside the cathodic chamber.

(6) Electrodialysis conventional membranes, AMX (anionic) and CMX (cationic) (Astom Corporation) were used as ion exchange membranes. Two reference electrodes (Ag/AgCl 3.5 M) were placed in the geometric centre of both anodic and cathodic compartments in order to measure anodic and cathodic potentials.

(7) G. sulfurreducens is cultured in batch using a fresh water medium (FWM) containing: 10 mM Acetate/40 mM Fumarate, flushed with oxygen-free N.sub.2/CO.sub.2 (80/20, v/v) at 30 C. Inoculation of 1/10 of a stationary phase culture (0.4 Optical Density units) into the MDC anodic compartment containing FWM with 20 mM acetate (anode electrode as sole electron acceptor) is carried out. A sodium bicarbonate (NaHCO.sub.3) 30 mM (pH 8.7, electrical conductivity (EC) 5.1 mS cm.sup.1) solution is used as saline stream. As cathodic stream, an aqueous solution of sodium sulphate (Na.sub.2SO.sub.4) 25 mM is used. An external power supply is employed to apply a cell potential of 1-3 V between anode (positive terminal) and cathode (negative terminal). Saline stream (NaHCO.sub.3) is circulated through the desalination compartment. The anode was maintained at +0.3-0.5 V (batch mode) during the biofilm growing period, until reaching steady-state (constant electric current).

(8) Stage 2: Once the bioanode is fully developed in the anodic compartment (constant current at stage 1), bicarbonate stream is replaced by saline stream (i.e. aqueous solution to be desalinated, for example, NaCl 5-10 g L.sup.1). Catholyte is replaced by sodium hypochlorite (for example, NaClO 3% solution, pH 11.1, EC 14.57 mS cm.sup.1).

(9) Then, power supply/potentiostat is removed from the system; an external load is connected to anodic and cathodic electric collectors. When needed, the external load could be substituted by an electric wire (External resistance0 ) to obtain maximum desalination rate. The electric current decreases when desalination is completed. Then, a next batch of saline water is fed in the desalination compartment to initiate the desalination process. When the electric current is not enough to drive the migration of ions, wastewater and/or sodium hypochlorite is again introduced in the system to recover the system performance.

(10) Stage 3: Clean-In-Place procedure is operated every 20-30 cycles, in order to remove biofouling formed on the membranes surface. Once the hypochlorite is circulated through the middle compartment, the system is then operated as stage 2. This cleaning strategy enhances the stability and performance during the long-term operation of the MDC system.

Example 2

Experiments of Simultaneous Oxidation of Organic Matter, Saline Water Desalination and Electric Power Generation in a Microbial Desalination Cell

(11) Six experiments according to the process of the invention were carried out in the operation conditions disclosed in Table 1. The results are also shown in FIG. 4.

(12) TABLE-US-00001 TABLE 1 Results: final conductivity 0.5 mS/cm, anolyte 20 mM Acetate + fresh water medium (FWM), catholyte NaClO (3%). Initial/ Desalination Volume Saline Final time (h)/ Anolyte/Catholyte/ compartment Conductivity External Energy Water Experiment Saline Tanks length (mS/cm resistor produced production id (L) (mm) 25 C.) (Ohm) (Wh/m.sup.2) (m.sup.3/day m.sup.2) 1 10/10/2 12 8-0.5 0 0 18.2-0.27 2 10/10/2 6 4-0.5 0 0 11.0-0.43 3 10/10/2 6 8-0.5 0 0 17.6-0.27 4 10/10/2 6 4-0.5 2 52.7 15.0-0.32 5 10/10/2 6 8-0.5 2 137.8 24.5-0.18 6 10/10/1 6 20-0.5 2 213.8 28.3-0.08

(13) The time-evolution of current density (A, B and C) and saline tanks conductivity (D, E and F) is shown in FIG. 4.

(14) The Project leading to this application has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 685793.