Process and apparatus for reduction in microbial growth in solutions of sugars extracted from waste materials

Abstract

A process for reducing microbial growth in solutions of sugars extracted from waste materials, the process comprising monitoring indicators of microbial growth in the solution in situ and administering an antimicrobial; a sugar substrate obtained by concentrating a solution of sugar treated using the process; an apparatus for extracting sugars from waste materials, the apparatus comprising a reaction vessel (10), one or more sensors (15,20) for monitoring indicators of microbial growth in the reaction vessel, a software for analysing signals from the sensor and a source of antimicrobial.

Claims

1. A process for reducing microbial growth in a solution of sugars extracted from waste materials, the process comprising: a. monitoring one or more indicators of microbial growth in the solution in situ; and b. administering one or more antimicrobials in response to microbial growth being detected based on the one or more indicators of microbial growth, wherein the one or more indicators of microbial growth comprise dissolved oxygen.

2. A process according to claim 1, wherein the one or more indicators of microbial growth further comprises pH.

3. A process according to claim 1, wherein the one or more indicators of microbial growth is a concentration of dissolved oxygen in a range of 0-1 mg/L.

4. A process according to claim 1, wherein the microbial growth is growth selected from bacterial growth, fungal growth, viral growth, protistal growth, archaeal growth and combinations thereof.

5. A process according to claim 4, wherein the microbial growth is growth selected from bacterial growth, fungal growth, viral growth, and combinations thereof.

6. A process according to claim 1, wherein the one or more antimicrobials are selected from antibiotics, disinfectants, antiseptics or combinations thereof.

7. A process according to claim 6, wherein the one or more antimicrobials are selected from disinfectants, antiseptics or combinations thereof.

8. A process according to claim 1, wherein the one or more antimicrobials are selected from ozone, sodium azide, chlorine dioxide, benzisothiazolinone (BIT) or combinations thereof.

9. A process according to claim 8, wherein the one or more antimicrobials are administered at levels in a range of 0.005-0.015 wt % for sodium azide; 2.5?10.sup.?4-0.05 wt % for BIT; 0.01-0.35 wt % for chlorine dioxide or 0.002-0.05 wt % for virginiamycin.

10. A process according to claim 1, wherein the one or more antimicrobials are administered when a gradient of a decrease of oxygen in the solution of sugars is in the range ?0.025 to ?0.030 mg/L.

11. An apparatus for extracting sugars from waste materials, the apparatus comprising: a. a reaction vessel; b. one or more sensors for monitoring one or more indicators of microbial growth in the reaction vessel, wherein the one or more indicators of microbial growth comprises dissolved oxygen; c. software for analysing signals from the one or more sensors and controlling administering of an antimicrobial in response to signals from the one or more sensors; and d. a source of the antimicrobial.

12. An apparatus according to claim 11, wherein the one or more sensors are in contact with a solution of sugar extracted from waste materials.

13. An apparatus according to claim 11, wherein the one or more sensors comprise one or more sensors selected from a pH sensor and/or an oxygen sensor.

14. An apparatus according to claim 11, wherein the one or more sensors comprise an oxygen sensor.

15. An apparatus according to claim 11, wherein the one or more sensors comprise an electrochemical sensor.

16. An apparatus according to claim 11, wherein the software comprises closed-loop feedback control software.

17. An apparatus according to claim 11, further comprising an actuator for administering the antimicrobial to the reaction vessel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order that the invention may be more readily understood, it will be described further with reference to the figures and to the specific examples hereinafter.

(2) FIG. 1 is a schematic representation of an apparatus of the invention;

(3) FIG. 2 is a graph illustrating the dissolved oxygen response of a solution of sugars over time with no microbial control. The area in the rectangle shows the onset of microbial growth;

(4) FIG. 3 is a graph illustrating the dissolved oxygen (lower line) and pH (upper line) responses of a solution of sugars over time with the addition of sodium azide at T=0;

(5) FIG. 4 is a graph illustrating the dissolved oxygen (lower line) and pH (upper line) responses of a solution of sugars over time with the addition of sodium azide at T=5 hrs 45 mins;

(6) FIG. 5 is a graph illustrating the dissolved oxygen (lower line) and pH (upper line) responses of a solution of sugars over time with the addition of lactrol at T=7 hrs;

(7) FIG. 6 is a graph illustrating the dissolved oxygen (lower line) and pH (upper line) responses of a solution of sugars over time with the addition of chlorine dioxide (0.35 wt % Fermasure?) at T=8 hrs 45 mins; and

(8) FIG. 7 is a graph illustrating the dissolved oxygen (lower line) and pH (upper line) responses of a solution of sugars over time with the addition of chlorine dioxide (0.05 wt % Fermasure?) at T=5 hrs 45 mins, T=50 hrs 30 mins and T=73 hrs 30 mins. Data missing for time period 36-50 hours, but expected to follow the trend of the Figure as a whole.

DETAILED DESCRIPTION

(9) The apparatus 5 of the invention is shown in FIG. 1. The apparatus comprises reaction vessel 10, a pH sensor 15, oxygen sensor 20 and a source of antimicrobial (not shown). In this example, stirring of the solution of sugars 25 is provided for using an agitator, the agitator comprising an agitator motor 30 and agitator blades 40. The pH 15 and oxygen 20 sensors send signals to a control unit 35, which analyses those signals and controls the administration of antimicrobial. Once enzymic digestion of the organic substrate is complete, the solution of sugars 25 can be released from the reaction vessel 10 through outlet 45.

EXAMPLES

Process ProcedureSingle Solids Addition (1 Litre Reaction Vessel)

(10) The process described is based upon the Fiberight industrial scale process, modified for a 1 litre reaction vessel. The amount of organic substrate used in the process is dependent on the required total solids (TS) content of the process. Typically, TS will be between 5-25%. TS is calculated using the required reaction mass and the solids content of the organic substrate, which is typically between 10-70%. (For a reaction mass of 1 kg, with a required TS of 8% (w/w), using organic substrate with a solids content of 32% (w/w), the amount of organic substrate needed for the process is 250 g). The organic substrate is sterilised in an autoclave at 125? C. for 1 hour immediately prior to use.

(11) The reaction vessel is sterilised prior to use by filling with sodium hydroxide and stirring for 1 hour. The ethanol is then drained and the heating jacket set to 50? C. prior to addition of the reaction components (water, organic substrate, and enzyme).

(12) The organic substrate is added to a preheated reaction vessel (50? C.) in one portion followed by sterilised water (the mass of water required=total reaction mass?mass of organic substrate) and stirred at between 200-600 RPM, depending on TS (higher TS requires a higher RPM to ensure thorough mixing). The pH, and dissolved oxygen (DO) sensors are each inserted into the reaction mixture (solution of sugars) at the top of the reaction vessel and positioned so that the tips are within a mixing zone created by the presence of an agitator, typically 20-30 mm above the agitator blades. The sensors are turned on and measurements initiated. If the pH of the reaction is below 5 then ammonium hydroxide is added in small portions until the pH is between 5 and 6. The required amount of enzyme, typically between 0.5-3% (w/w) of the TS, is then added to the reaction vessel. The point at which the enzyme is added is the start of the process (T=0 hours). Throughout the process pH is maintained between 5-6 (with the addition of an alkali agent as required). DO readings are taken throughout the process and are typically between 3-8 mg/L if no contamination is present. Between T=0-3 hours DO readings are not constant and can vary significantly, due to changes in the viscosity of the process as the enzyme breaks down the organic substrate. Typically this stops after T=3 hours and maintains linear readings. If contamination occurs the DO reading can drop to 0 mg/L, which typically happens between T=5-8 hours. The end of the process is typically between T=90-110 hours, when no further increase in sugar concentration is observed. For TS between 5-20%, final sugar concentrations will typically be between 30-100 g/L.

(13) At the end of the process the reaction vessel is drained and the reaction mixture is filtered under vacuum to separate the residual post-hydrolysis solids (PHS) from the sugar solution. The sugar solution is then concentrated by vacuum distillation to the required concentration for use.

Process ProcedureMultiple Solids Addition (10 Litre Reaction Vessel)

(14) The process described is based upon the Fiberight industrial scale process, modified for a 10 litre reaction vessel. The single solids addition procedure outlined above becomes difficult to use for TS>10% because the reaction vessel contents do not mix sufficiently. To address this, a multiple solids addition strategy is used. In this example, the multiple solids addition strategy is conducted in a reaction vessel volume of >10 litres. The required mass of organic substrate is separated into 6-8 portions. The first two portions are added to the reaction vessel according the procedure outlined above (T=0 hours). The remaining 4-6 portions are added to the reaction vessel one at a time at T=9, 18, 27, 36 hours if four portions and additionally at T=45, 54 hours if five or six portions. After the final portion of organic substrate has been added the procedure outlined above is followed to completion.

Microbial Contamination Control Procedure

(15) Several sterilisation agents have been tested to determine their effectiveness in controlling microbial growth in solutions of sugar. The sterilisation agents were either introduced at T=0 or at the point that microbial growth is observed, which can be measured by the DO sensor. Typically, contamination can be said to occur when the DO reading starts to drop exponentially, eventually reaching 0 mg/L if no sterilisation agent is added. In these tests, software was used to monitor the DO readings and trigger the addition of an antimicrobial. Typically this happens when the gradient of the decrease is in the range ?0.025 and ?0.030. Once a sterilisation agent has been added the DO readings will start to increase within 5-10 minutes.

(16) The results are illustrated in FIGS. 2-7. In these figures, FIG. 2 is a control example, where microbial growth is allowed to proceed without intervention. As can be seen, the oxygen content of the solution of sugars drops markedly in the period 4-4.5 hours, indicating the onset of microbial growth.

(17) FIGS. 3 and 4 show the addition of sodium azide, in FIG. 3 at T=0, and in FIG. 4, in response to a drop in the levels of dissolved oxygen in the sugar solution, at T=5 hrs 45 mins. As can be seen, the addition of sodium azide at T=0 results in stable pH and oxygen levels throughout the test, indicating an absence of microbial growth. However, this can also be achieved, through the monitoring of pH and/or oxygen levels and, as shown in FIG. 4, the addition of sodium azide only when needed. In this case, at around 5 hr 45 minutes when both the level of dissolved oxygen and the pH drop. This provides a solution of sugars which is apparently free from microbial growth for the remainder of the test, and shows that the addition of sodium azide is capable of preventing microbial growth for the duration of the test, whether added initially or later in the process.

(18) FIG. 5 shows a test where the antibiotic lactrol was added to the solution of sugars at T=7 hrs, directly in response to an observed drop in dissolved oxygen and pH. The result was the stabilisation of these parameters for the duration of the test.

(19) FIGS. 6 and 7 show systems where chlorine dioxide (Fermasure?) was used to stabilise dissolved oxygen and pH levels, thereby preventing further microbial growth. In these figures, pH drop is less marked as chlorine dioxide was added in response to the drop in dissolved oxygen. As the drop in dissolved oxygen occurs before the pH drop, pH drop (evidence of lactic acid production) was prevented. In FIG. 6, 0.35 wt % chlorine dioxide was added at T=8 hrs 45 mins in a single aliquot, in FIG. 7 a lower concentration of chlorine dioxide, 0.05 wt %, was added at T=5 hrs 45 mins, T=50 hrs 30 mins and T=73 hrs 30 mins in response to recurrent microbial growth instances, as indicated by a reduction in pH and dissolved oxygen. A comparison of the tests of FIGS. 6 and 7 shows that a reduction in total antimicrobial used can be achieved using the process of the invention. This is because repeated dosing of the solution of sugars can be achieved with lower concentrations of antimicrobial, hence, even though several additions are required, less of the active is needed to control microbial levels. This provides cost savings and reduces the environmental impact of the process claimed.

(20) It has therefore been shown that a wide range of antimicrobials can be used to control the microbial growth in the solutions of sugars. Further, it is clear that both pH and oxygen levels can be used as an indicator of microbial growth, as both pH and oxygen levels return to previous levels after addition of the antimicrobial.

(21) It should be appreciated that the processes and apparatus of the invention are capable of being implemented in a variety of ways, only a few of which have been illustrated and described above.