Electrochemical processes for acid whey treatment and reuse

Abstract

Electrochemical devices capable of converting acidic aqueous byproducts of strained yogurt production into value-added materials, as well as methods of making and using these devices, are described herein. Assembly of an electrolytic cell or series of cells that contain an anode that oxidizes organic substances in the aqueous byproduct stream and a cathode that either reduces organic species or water is described. Electrolysis serves to break down the organic matter present in the liquid, such as lactic acid and lactose, as well as aid in the separation of whey protein matter. Gaseous products of this electrolysis process can be either sold or used in waste-to-energy schemes, thereby introducing an environmentally-friendly method for the electrolytic treatment of acid whey.

Claims

1. A method for treating the acidic whey byproduct of strained yogurt production using electrolysis, wherein the method comprises: flowing the liquid byproduct into an electrolytic cell, wherein organic matter in the byproduct is oxidized at an anode applying a voltage between an anode and cathode to provide a driving force for he electrolytic oxidation reactions at the anode discharge of treated wastewater that possesses a lower concentration of organic material than the input acid whey byproduct

2. The method of claim 1, wherein the treated wastewater discharge has a pH higher than the acid whey byproduct

3. The method of claim 2, wherein the treated wastewater is of a pH between 5 and 8.

4. The method of claim 1, wherein a membrane is present between the anode and cathode.

5. The method of claim 4, wherein the membrane is a polymer electrolyte membrane.

6. The method of claim 5, wherein the membrane is part of a membrane electrode assembly (MEA).

7. The method of claim 6, wherein the MEA is housed in a polymer electrolyte membrane electrolyzer.

8. The method of claim 1, wherein a catalyst is adhered to the surface of the anode in order to facilitate oxidation and/or prevent fouling.

9. The method of claim 8, wherein the catalyst is a carbon-based material.

10. The method of claim 8, wherein the catalyst contains a transition metal element.

11. The method of claim 10, wherein the catalyst is an iridium-containing material.

12. The method of claim 1, wherein a filtration, flocculation, screening, centrifugation, and/or settling system is used on the acidic whey byproduct prior to flowing into the electrolytic cell, in order to prevent electrode or membrane fouling.

13. The method of claim 1, wherein gaseous products are evolved at the anode and/or cathode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 shows a schematic of one embodiment of the system. Acid whey is fed from a holding silo (1) using a pump (2) into an ultrafiltration system (3), which filters out whey proteins. The wet whey proteins are further concentrated using a screw press (4). The remaining filtered acid whey is fed via a flow plate (5) to an anode chamber (6) that contacts the anode (7) on the surface of a membrane (8) that are part of a membrane electrode assembly. At the anode, the dissolved organics in the filtered acid whey stream are oxidized into carbon dioxide, protons (that are transported across the membrane), and electrons (that are transported to the cathode via the external circuit). Reduction of protons transported across the membrane occurs at the cathode (9) on the opposite side of the membrane electrode assembly, and hydrogen gas is generated in the cathode chamber (10). A feedback loop with a variable-speed peristaltic pump (11) allows for multiple passes of the filtered acid whey through the electrolysis system for further treatment of the stream, and a DC power source (12) is connected between the anode and cathode to supply electrical energy.

[0014] FIG. 2 shows cyclic voltammograms (CVs) of an antimony-doped tin oxide (ATO) anode immersed in a solution of acid whey both with and without an appropriate catalyst, demonstrating catalytic oxidation of the acid whey organic matter into carbon dioxide and concomitant evolution of hydrogen gas at a platinum cathode, at moderate potentials which enables high efficiency.

DETAILED DESCRIPTION OF THE INVENTION

[0015] Acid whey is typically produced on the scale of thousands of gallons per day. This requires a system that is able to operate using large volumes. The acid whey first is pumped or otherwise flows into a filtration system wherein protein-based solids are removed from the stream using a process or processes that include, but are not limited to, ultrafiltration, filtration, flocculation, electroflocculation, screening, centrifugation, and/or settling system, in order to prevent electrode or membrane fouling by the whey solids. The resulting stream possesses a lower percentage of solids, and is fed into the electrochemical device which is comprised of an anode and cathode, in some embodiments separated by a membrane. A schematic depicting an example of this process is shown in FIG. 1.

[0016] The electrochemical device, specifically an electrolysis system that is an object of this invention, contains an anode and cathode. Upon application of an electric potential from a DC electrical source including, but not limited to, a rectifier, battery, or solar panels, electrochemical reactions take place on the surface of the anode and cathode. In some embodiments, these electrochemical reactions result in the generation of carbon dioxide gas from the oxidation of organic matter at the surface of the anode, while hydrogen gas is generated by the reduction of water at the cathode. Furthermore, in some embodiments gas bubbles generated may serve to float any remaining whey solids to the surface of the anode and/or cathode chamber, where they can then be collected. Additionally, in other embodiments these electrochemical reactions oxidize organic contaminants, water, and other substrates in the water to form a mixture of inert gases that include, but are not limited to, oxygen, carbon dioxide, and nitrogen.

[0017] Since the majority of the acid whey stream is water, in some embodiments of the present invention the highest percent by weight output will also be water. In some cases, the electrochemical device serves to neutralize the water by removing acid equivalents using a pH gradient across a cation exchange membrane, bipolar membrane, or other technology known to those skilled in the art. In some others, the water output stream may also have a lower concentration of organic contaminants due to oxidation during the electrolysis process.

[0018] In some embodiments, a catalyst is present on the surface of the anode to facilitate oxidation of organic matter. FIG. 2 shows the effect of a precious metal catalyst on an antimony-doped tin oxide anode using cyclic voltammograms to electrochemically probe the system. Catalytic currents shown in the cyclic voltammograms are proportional to rates of reaction for the oxidation of hydrocarbons, such as lactic acid, to carbon dioxide, and can be significantly increased with the presence of a catalyst. Sampling of the gas output streams demonstrate that the faradaic efficiency of this reaction is at least 0.5%, 1%, 5%, 10%, 20%, 40%, 60%, 80%, 90%, 95%, 98%, 99%, 99.5%, 99.9%, or higher with the presence of a suitable catalyst. Faradaic efficiency, in the manner it is used herein, refers to the coulombic efficiency of the system. This is a ratio of the theoretical maximum amount of carbon dioxide produced as calculated from the measured current flow, assuming four electrons are withdrawn from each lactic acid molecule per molecule of carbon dioxide produced, with the amount of carbon dioxide measured that is evolved from the anode. Catalyst includes, but is not limited to, iridium oxides, molecular heterogeneous iridium species, iridium-based species, platinum metal or platinum-based species, cobalt metal or cobalt-based species, manganese metal or manganese-based species such as manganese oxide, iron or iron-based species, or any combination of the aforementioned materials in alloys, mixed metal oxides, molecular species, or the like. In most cases, these catalysts selected for this process are capable of oxidizing the organic material in acid whey, including lactic acid and lactose, into carbon dioxide.

[0019] In some embodiments, hydrogen generated at the surface of the cathode due to water reduction can be fed into a hydrogen fuel cell system to recapture some of the energy required to oxidize the organic material in the acid whey stream. This reaction has the potential to be thermodynamically downhill, since the hydrogen gas is generated by oxidation of hydrocarbons (an electrochemical reaction possessing a reversible potential lower than 1.23 V), then combined in a fuel cell to produce water (an electrochemical reaction possessing a reversible potential of 1.23 V). Furthermore, in some embodiments, carbon dioxide that is generated electrochemically at the surface of the anode can be purified, compressed, solidified, and/or liquefied and sold as a product.

[0020] Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of skill in the art to which the disclosed invention belongs. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims.