SIMULTANEOUS PHASE OPERATED ANAEROBIC SEQUENTIAL BATCH REACTOR

Abstract

Process for treating an aqueous fluid whereby a biogas is produced in an installation comprising a bioreactor and a separate container, the process comprising (i) a bioreactor feeding stage; (ii) a batch reaction stage, wherein biogas is formed and formed biogas is temporarily stored in the separate container, and at least one further stage (iii) comprising a settling stage and/or an aqueous fluid effluent discharge stage, wherein the biogas stored in the separate container is used to reduce fluctuations in a biogas exit flow from the installation. An installation for carrying out the process and the use thereof.

Claims

1. Process for treating an aqueous fluid, whereby a biogas is produced in an installation comprising a bioreactor (1), preferably a bioreactor operating under anaerobic conditions, and a separate container (2), wherein the process comprises (i) a bioreactor feeding stage, thereafter (ii) a batch reaction stage, wherein biogas is formed and formed biogas is temporarily stored in the separate container (2), and thereafter at least one further stage (iii) comprising a settling stage and/or an aqueous fluid effluent discharge stage, wherein the biogas stored in the separate container (2) is used to reduce fluctuations in a biogas exit flow (15) from the installation, which further stage (iii) comprises settling of aqueous suspension and/or a discharge of fluid effluent.

2. Process according to claim 1, wherein during at least a part of the (ii) batch reaction stage the separate container (2) is used as a settler wherein solid particles are allowed to settle from an aqueous suspension present in the container.

3. Process according to claim 2, wherein during the batch reaction stage (ii) biogas is formed in the bioreactor (1) and simultaneously any aqueous suspension originating from the bioreactor (1) that has previously been introduced into a first section (2a) of separate container (2) is allowed to settle in said container (2).

4. Process according to claim 3, wherein in (i) the bioreactor feeding stage the aqueous fluid comprising the biodegradable organic substance is fed into the bioreactor (1) via said inlet (14) for aqueous fluid, preferably whilst agitating, and which inlet (14) is situated in an upper part of the bioreactor, gas present in the bioreactor is displaced by the aqueous fluid fed into the bioreactor (1) and said gas forms at least part of the biogas exit flow (15) during the feeding stage any aqueous suspension originating from the bioreactor (1) that has previously been introduced into a first section (2a) of separate container (2) is allowed to settle in the first section (2a), thereby forming an upper fluid phase that has a reduced solid particle content compared to said suspension (which upper fluid phase is preferably free at least substantially free of a solid phase) and a lower sludge phase that has an increased solid particle content compared to said suspension; (ii) the batch-reactor stage comprises (iia) a first batch-reactor phase and (iib) a second batch-reactor phase in which phases biodegradable organic substance is converted by the micro-organisms in the bioreactor (1) whilst agitating the suspension in the bioreactor (1) wherein in (iia) the first batch-reactor phase any suspension originating from the bioreactor (1) that has previously been introduced into the first section (2a) of separate container (2) is continued to be allowed to settle in the first section (2a) wherein in (iib) the second batch-reactor phase at least part of the settled sludge that has formed in a bottom sub-section of first section (2a) is returned to the bioreactor via a conduit between an outlet (6) of the first section (2a) and inlet (8) in a bottom section of the bioreactor (1) and wherein surplus sludge is discharged from the installation, directly from bioreactor part of the biogas formed in bioreactor (1) is stored in second section (2b) of the container (2) wherein in (iii) a fluid effluent discharge stage, following or preceding the second batch-reactor phase, the aqueous fluid phase is withdrawn from the first section (2a) via outlet (6) and discharge (7) after essentially all sludge has been removed from the first section (2a) gas is removed from the suspension in the bioreactor (1), whilst agitating the suspension, and wherein after the second batch-reactor phase and fluid effluent discharge stage in (iv) a bioreactor discharge stage, at least a part of the degassed suspension is withdrawn from the bioreactor (1) from a bottom section of the bioreactor (1) via an outlet (16) and fed into first section (2a) of the container (2) via inlet (3) connected to outlet (16) via a conduit.

5. Process according to any of the preceding claims, wherein stage (iii) comprises settling solids of an aqueous suspension, in particular sludge, taken from the bioreactor (1) in the separate container (2), thereby forming a phase comprising the settled solids and returning said phase to the bioreactor via a conduit between an outlet (6) of the separate container (2) and an inlet (8) in a bottom section of the bioreactor (1) and wherein surplus suspension, in particular sludge, is discharged from the installation, directly from the bioreactor.

6. Process according to any of the preceding claims, wherein the bioreactor (1) contains an aqueous suspension, which suspension comprises an aqueous liquid phase and a solid phase, the suspension containing anaerobic micro-organisms, wherein the separate container (2) is for holding treated aqueous fluid (2a) from the bioreactor (1) and for holding biogas from (2b) the bioreactor (1), the process comprising (i) a bioreactor feeding stage, wherein the aqueous fluid comprising the biodegradable organic substance is fed into the bioreactor (1), and thereafter (ii) a batch reaction stage, wherein biodegradable organic substance is converted by anaerobic micro-organisms in the bioreactor (1), thereby forming biogas, during which batch reaction phase a biogas exit flow out of the installation is maintained, wherein at least during a part of the batch reaction phase at least a part of the formed biogas is temporarily stored in the separate container (2), followed by (iii) at least one further stage, which at least one further stage comprises a settling stage and/or an aqueous fluid effluent discharge stage and wherein the biogas stored in the separate container (2) is used to reduce fluctuations in the biogas exit flow (15) during the batch reaction stage or thereafter.

7. A process according to any of the preceding claims, wherein the bioreactor contains a flocculent biomass.

8. A process according to any of the preceding claims, wherein the biogas is stored in an upper part of the separate container (2) and the separate container (2) has a flexible upper cover (17), which upper cover (17) comprises an inflatable double membrane, having a first and a second membrane wherein a upon inflation a space is created between said first and second membrane.

9. A process according to claim 8, wherein the space between the first and the second membrane is inflated or deflated so as to maintain a pressure of the biogas (2b) inside the separate container (2) within a defined range.

10. A process according to claim 8 or 9, wherein the space between the first and the second membrane is increased in order to cause biogas (2b) stored in the container (2) to the biogas exit (15) when the biogas exit flow is below a lower threshold value and/or wherein the space between the first and the second membrane is decreased to allow storage of more biogas when the biogas production rate is above an upper threshold value.

11. A process according to any of the preceding claims, wherein the biogas flow out of the bioreactor (1) or the biogas production rate of the bioreactor (1) is monitored at least during (ii) batch reaction stage and used to determine when to proceed to the next stage.

12. A process according to claim 1 or any of the claims 5-11 dependent on claim 1, which process is preferably operated under anaerobic conditions, wherein bioreactor (1) comprises an internal separator system (11) present in the bioreactor (1) which internal separator system (11) is positioned above an inlet (14) for aqueous fluid comprising the biodegradable substance and below an outlet (16) for treated aqueous fluid, out of the bioreactor, which separator system (11) is used to separate aqueous fluid of the suspension from the solid phase and the biogas and which separated aqueous fluid is collected in an upper part of the bioreactor (1), i.e. above the separator system (11), wherein in (i) the bioreactor feeding stage the aqueous fluid comprising the biodegradable organic substance is fed into the bioreactor (1) via said inlet (14) for aqueous fluid (without substantial agitation other than any agitation caused by the feeding), the separated aqueous fluid is withdrawn from the bioreactor through outlet (16) and at least part thereof is fed into a first section (2a) of the separate container (2) if needed, biogas present in a second section (2b) of the separate container (2b) is used to provide at least part of the biogas exit flow (15) during the feeding stage; in (ii) the batch reaction stage the aqueous suspension in the bioreactor (1) is agitated if desired, aqueous suspension, is withdrawn from the bioreactor through outlet (16) positioned above the internal separator system (11) and recycled to the bioreactor via recycle (12b) of which the inlet is positioned below internal separator system (11) aqueous fluid stored in the first section (2a) is withdrawn from the installation via the outlet (6) for aqueous fluid and wherein (ii) the batch reaction stage is followed by (iii) a settling stage, during which stage conversion of biodegradable organic substance by the micro-organisms may continue, the settling stage comprising settling of solids in the bioreactor whereby an aqueous fluid phase forms above the internal separator system aqueous fluid stored in the first section (2a) is withdrawn from the installation via the outlet (6) for aqueous fluid if present, surplus of suspension is discarded from the bioreactor via an outlet (9), in a lower part of the bioreactor when needed, biogas from the second section (2b) is used to provide at least part of the biogas exit flow (15) during the settling stage.

13. Process according to any of the preceding claims, wherein said stages are repeated a plurality of cycles, and wherein at least after the first cycle an at least substantially constant biogas exit flow is maintained during said stages.

14. Process according to any of the preceding claims, wherein the aqueous fluid to be treated has a total organic substance content in the range of 0.3-100 g COD/l and/or a total suspended solids content in the range of 1-30 g/l.

15. Process according to any of the preceding claims, wherein from the first section (2a) of the separate container (2) an aqueous effluent is withdrawn that is at least substantially free of solid particles visible to the naked eye.

16. Process according to any of the preceding claims, wherein downstream of the installation, effluent (7) from the first section (2a) of the container (2) is subjected to a purification step.

17. A process according to claim 16, wherein the (i) bioreactor feeding stage, the (ii) batch reaction stage and the (iii) settling stage and/or the fluid effluent discharge stage are carried out simultaneously for at least a substantial part.

18. Installation for microbiologically treating an aqueous fluid comprising biodegradable organic substance, wherein the installation comprises a bioreactor (1), the bioreactor comprising an agitator for agitating the aqueous fluid in the bioreactor (1) and a separate container (2), the separate container (2) comprising a first section (2a) for holding treated aqueous fluid from the bioreactor (1) which first section comprises an inlet for the treated aqueous fluid that is connected to an outlet for treated aqueous fluid from the bioreactor (1) via a closable conduit (3) and an outlet for removing contents of the first section via a closable conduit (6) and a second section (2b) for holding biogas, comprising an inlet for biogas that is connected to an outlet for biogas from the bioreactor (1) via a conduit (4) the installation further comprises an inlet (14) for fluid aqueous waste stream into the installation, an outlet (15) for biogas from the installation and a discharge (7) for aqueous effluent and an outlet (9) for sludge from the installation.

19. Installation according to claim 18, wherein the second section (2b) occupies an upper part of the separate container (2) and has an expandable upper cover (17), preferably a double membrane.

20. Installation according to claim 18 or 19, wherein the installation comprises a biogas controlling system adapted to regulate an exit flow (15) of biogas from the installation, when the installation is used to microbiologically treat an aqueous fluid comprising biodegradable organic substance.

21. Installation according to any of the claims 18-20, wherein the first section (2a) contains a liquid-solid separator, having tilted internals adapted to enhance the settleability of solid particles in an aqueous fluid (such as a suspension or sludge).

22. Installation according to claim 21, wherein the liquid-solid separator is a tilted plate settler.

23. Use of an installation according to any of the claims 18-20 in the microbiological treatment of an aqueous fluid comprising a biodegradable organic substance whereby biogas is formed from said biodegradable substance, preferably in a process according to any of the claims 1-17.

Description

EXAMPLE 1

[0110] Dairy wastewater with a high suspended solids (2-5 g TSS/L) content and a high FOG (>600 mg/L) content was treated in a Simultaneous Phase Operated Anaerobic Sequential Batch Reactor according to the invention (see e.g. FIG. 3) in a process similar to FIG. 5, wherein the stages III and IV are carried out in a reversed order. The reactor was operated for 235 days in total. First, influent was fed into the reactor and the external container was degassed, during which phase a reaction, i.e. the conversion of pollutants from the wastewater into biogas, already took place in both reactor and external container. Next, the sludge was allowed to settle into the external container and was subsequently decanted and effluent was withdrawn from the external container afterwards. Meanwhile, the reaction was continued in the reactor. Finally, sludge was removed from the external container and fed into the bioreactor and then returned from the bioreactor into the external container.

[0111] High volumetric loading rate (VLR) of 8-10 g COD/L.Math.day for over 100 days was achieved (FIG. 7). The total COD (TCOD) removal and soluble COD (SCOD) removal were monitored over time (FIGS. 8&9). High TCOD removal of between 90-95% and excellent >98% SCOD removal during the operation time was achieved. In addition, the effluent had TSS concentrations consistently below 0.2-0.5 g/L; considered satisfactory for this type of flocculent anaerobic sludge systems with settling based separation (FIG. 10). Furthermore, sludge settleability was between 50-70% of the external container volume during the settling phase (FIG. 11). During operation time, no biomass loss as a result of accumulation of FOG in the form of floating sludge layers during settling and or fat balls in the reactor was observed.