Patent Application
20190337829
This disclosure relates generally to biomass reactors and, more specifically, to covers for anaerobic sequencing batch reactors.
Anaerobic Sequencing Batch Reactors (“ASBR”), or alternatively ASBR digesters, are able to achieve high levels of treatment of low-solids, high strength wastewaters by retaining an active biomass in the reactor while operating at Hydraulic Retention Times (HRT, i.e., the average amount of time liquids remain in reactor) on the order of 4 to 6 days.
ASBR digesters are a low-cost option for treating any low-solids, high energy wastewater. For example, this sort of digester can be used for mixtures of biodiesel production wastewaters, food processing wastes, hydrolyzed domestic and municipal wastes, brewery wastewaters, flushed human waste and animal manures, etc.
In a conventional ASBR reactor, solids are retained by sequencing the gas tight reactor through an operational cycle consisting of four phases (
An ASBR is a high rate digestion system that retains microflora in the reactor by sequentially feeding influent, mixing the reactor, settling solids, and decanting effluent from the top of the reactor. ASBR reactors are highly efficient (e.g., up to 0.55 m3 CH4 kg−1 VS methane yields, 80 to 95% influent to decant organic matter reduction efficiencies), and are ideal for treating liquid waste streams containing low concentrations of suspended solids such as effluent from hydrolysis reactors. For example, working with liquid swine manure, researchers in North America have found that, by judiciously removing sludge at regular intervals, Solids Retention Time (SRT, i.e., the average time solids are held in the reactor) may be held much longer than 30 days, while operating at a HRT as short as 4 to 5 days.
The simple method of separating liquid from settled solids provides superior quality effluent. Since decanting is decoupled from feeding, the problem of intermittent loads of high solids influent washing out microflora experienced with Upflow Sludge Blanket (USB) reactors is eliminated. ASBR digesters have a much smaller footprint and have more efficient nutrient removal schedules than Covered Lagoon digesters.
If the quantity of suspended solids leaving the reactor during the decant phase is low, the SRT can be separated from (and ideally made much longer than) HRT. A high SRT means slow-growing methane producing microorganisms are retained in the reactor long enough to reproduce, even if the reactor has an extremely short HRT. Reactor size is directly related to HRT. In other words, a reactor with high SRT is able to reduce organic matter better than one with a low SRT; low HRT reactors are smaller than high HRT reactors, making them less expensive to build and operate.
As popular and versatile as these reactors are, they are subject to certain problems. The potential niche for ASBR digesters is currently being filled by more complex and expensive Attached-Growth and Upflow Anaerobic Sludge Blanket (UASB) reactors. These sorts of digesters are also problematic to operate. They can be completely disabled if a slug of high solids wastewater passes through the reactor. The potential to replace attached-growth and UASB with ASBR is enormous, but very few ASBR digesters have been built to date.
Even with these apparent advantages over other digestion technologies, very few anaerobic sequencing batch reactors are operating outside of laboratory situations. Among others, two problems have contributed to this situation.
First, there have been construction problems in designing reactors that accommodate the fluctuating pressure within the reactor. The falling and rising liquid level during the decant and fill phases acts like a piston inside the ASBR and tends to separate tops from reactor vessels. Digesters with rigid roofs can fail due to cracking in the sidewall, and detachment of the rigid roof from the sidewall. Attempts to remedy this problem with a simple, flexible membrane roof have generally failed due to leaking membrane and detachment of the membrane from the sidewall.
Additionally, poor decant quality is often experienced due to difficulties settling retained solids when large masses of solids are carried in the reactor, thereby tending to limit the length of SRT and reducing Organic Matter Loading Rates (OLR). The settling rate of the expanded sludge bed during the settle phase is directly related to concentration of retained solids in the bed. Retained solids concentration needs to be sufficiently high to maintain SRT. Decanting in current ASBR designs rely on removing liquid at a fixed point in the reactor vessel. If the solids cannot settle beyond this fixed point, suspended solids will be carried out of the digester. The limitations associated with completely separating SRT from HRT have been well documented in the literature, as has the ability to attain organic matter reduction levels in practice that are achievable in a laboratory studies.
As such, what is needed is an improved ASBR which does not suffer the limitations of the prior art.
Before proceeding to a description of the present invention, however, it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be construed as limiting the invention to the examples (or embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of this invention within the ambit of the appended claims.
An embodiment of a self-contained floating cover and operating system for Anaerobic Sequencing Batch Reactor (ASBR) digesters that combines the functions of an ASBR in one package, while substantially improving on current ASBR designs. As such, there is provided herein a roof for a reactor vessel that utilizes a weighted floating cover. The cover is designed to be free to move up and down within the vessel as the fluid level changes during the operational cycle. In some embodiment, the cover itself is not directly connected to the reactor vessel or its sidewall, but instead is held in place and supported from above by truss-like support members that are free to move vertically by means of casters contained in a “C” channel to permit movement of the cover in concert with the changing fluid level in the vessel. In an embodiment, the support members are anchored proximate to, but outside of, the top of the reactor vessel.
In various embodiments, a plurality of pass-through conduits penetrate the surface of the cover and extend downward into the ASBR tank. In some embodiments the conduits are affixed to the cover and are adapted to move up and down along with it. The conduits might serve functions such as providing for the release of gas from the cover, mixing the reactor with a jet, intake of clarified liquid above the expanded sludge bed for jet mixing, feeding, decanting, sampling, and sludge or scum removal. Such functionality is well known to those of ordinary skill in the art.
Advantages of various embodiments are numerous. For example, a constant pressure can be maintained in the reactor vessel using a weighted floating cover of the sort taught herein. Various embodiments are self-contained operational units. In operation, the functions of an embodiment of the instant digester operation are accomplished with the cover and a pump-valve-control building located above or to the side of the digester. The floating cover is supported externally, allowing a simple buried or free-standing tank, designed to withstand a constant bursting pressure, to serve as the reactor vessel.
The foregoing has outlined in broad terms some of the more important features of the invention disclosed herein so that the detailed description that follows may be more clearly understood, and so that the contribution of the instant inventors to the art may be better appreciated. The instant invention is not to be limited in its application to the details of the construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. Rather, the invention is capable of other embodiments and of being practiced and carried out in various other ways not specifically enumerated herein. Finally, it should be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting, unless the specification specifically so limits the invention.
These and further aspects of the invention are described in detail in the following examples and accompanying drawings.
While this invention is susceptible of embodiment in many different forms, there is shown in the drawings, and will herein be described hereinafter in detail, some specific embodiments of the instant invention. It should be understood, however, that the present disclosure is to be considered an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments or algorithms so described.
A schematic drawing of an embodiment of the cover 140 for use with ASBR Digesters is given in
As can generally be seen in
Turning now to a discussion of the embodiment
As is further indicated in
Continuing with the present embodiment, lateral support arms 215 and 220, which are affixed or otherwise in mechanical communication at one end with the cover 140, preferably at connector 235, t are free to move vertically guided by the rolling casters 210 which are situated within vertical “C” channels 280. This configuration allows the instant cover 140 to respond to and accommodate the up and down motion that is occasioned by the changing fluid level in the reactor tank 190 during its operational cycle.
Note that in the embodiment of
Additionally,
In practice, the liquid level in the tank 190 is controlled by the decant and feeding pumps which are activated by a timer and moderated through feedback signals received from the vertical position of the cover 140, which is free to move up and down as the fluid level changes. Such arrangements are common and need not be explained here, as they are well within the knowledge of one of ordinary skill in the art.
In the embodiment of
In
In addition, note that the number of pass-through conduits might be reduced by using some of them for more than one purpose. For example, feeding and mixing could be combined to use a single jet. The same conduit could be used as an intake for both mixing intake and decanting. Also, the sampling tube(s) (125/130) could also be used for sludge removal. In another variation, each of the key functions might be performed by more than one conduit. For example, two or more conduits might be used for mixing intake or decanting to increase the flow while minimizing disturbance of the cloud of solids below. Such arrangement are well known to those of ordinary skill in the art.
Various mechanisms useful in the operations of an ASBR digester (e.g., pumps, valves, etc.) that are routinely situated external to the cover system 100 are not pictured in
The method of forming a gas tight seal underneath the cover 140 while allowing for complete vertical adjustment relative to the cover and locking of the conduit positions is one aspect of an embodiment that is not disclosed by prior art ASBR covers. The method of feeding, controlling reactor liquid level, and preventing spillage when the instant cover is utilized is also unique to this invention.
That is, the height of sludge blanket expansion during the react phase can be regulated by adjusting position of the jet mixing nozzle, nozzle size, and flow rate through the nozzle. Entrainment and crushing of suspended solids in the mixing pump during the react phase is avoided in this embodiment by raising the mixing withdrawal point above the top of the expanded sludge blanket (
With respect to one particular embodiment, two experiments were performed to compare reactor performance under full and partial mixing schemes when used with an embodiment of the instant invention. All reactors were fed a mixture of liquid swine manure and glycerol. Full mixing is the traditional method of operating an anaerobic sequencing reactor (ASBR). Partial mixing is one aspect of this invention.
The full mix reactor(s) were vigorously mixed using a single point liquid jet mixer so that the entire reactor had homogenous solids concentration. Liquid was removed from the mid-point of the reactor and reentered the reactor through a nozzle pointed towards the bottom of the reactor. Suspended solids entrained in the liquid passed through a centrifugal pump and the nozzle before returning to the reactor.
The partial mix reactor(s) were also mixed using a single point liquid jet mixer; however, mixing intensity was reduced so that a cloud of suspend solids only partially filled the reactor. Liquid used for mixing was removed from above the suspended solids cloud and reentered the reactor through an identical nozzle pointed towards the bottom of the reactor. Suspended solids were not entrained in the liquid stream used to mix the reactor.
In the first experiment, two 36 L reactors were simultaneously operated using the same operating conditions. One reactor had full mixing, the other partial mixing. Results are given in Table 1 below.
In the second experiment, five 36 L reactors were operated using identical operating conditions under the full mixing scheme, and were switched to the partial mixing scheme under similarly identical operating conditions. The test results are given in Table 2. Full mix results were measured during the 6 weeks immediately prior to the switch to partial mixing. Partial mix results were measured during a 6-week period, four months (8 Hydraulic Retention Times, HRT) after the switch to partial mixing.
Both experiments show that a greater mass of Volatile Suspended Solids (VSS), and thus active biomass, was retained in the reactors under partial mixing. Solids Retention Time (SRT, the mass of VSS retained in the reactor divided by VSS leaving the reactor each day) increased by a factor of 4 to 10 under the partial mix scheme. This result tends to demonstrate that various embodiments will increase retention of biota in the reactor.
Reactor stability, measured as pH at the end of the react phase, is statistically similar under both mixing schemes. Volatile Fatty Acid Concentration (VFA) increased with partial mixing. This is due to the greater mass of biologically active solids retained in the reactor. The ratio of VFA to Bicarbonate Alkalinity (VFA:HCO3 Alk); did not reach critical values (0.6 VFA:HCO3 Alk measured in mmol), however.
Reactor performance measured in biogas production, biogas yield per mass of organic matter (OM, measured as Volatile Solids (VS) and Chemical Oxygen Demand (COD)) added, and organic matter removal increased under partial mixing compared to full mixing. These two results support the claim that various embodiments would increase digester performance without affecting stability.
Perhaps one of the greatest and most beneficial effects of changing from full to partial mixing is the increase in effluent quality.
1Neglecting Solids Removed for Sampling
2Measured at End of React Phase
1Neglecting Solids Removed for Sampling
2Measured at End of React Phase
Various embodiments of the instant self-contained floating cover and operating system for ASBR Digesters addresses at least the following issues with prior art problems with ASBR Digesters.
Construction Problems Due to Fluctuating Pressure within the Reactor:
Since the floating cover rises and falls with liquid level, pressure under the bowl does not change. Biogas pressure can be set to meet the needs of downstream devices (H2S filter, engine-generator, fuel cell, etc.) using a pressure regulating devise such as a water trap or spring-loaded pressure relief valve.
Poor Decant Quality Due to Difficulties Settling Retained Solids:
With various embodiments, position of decant withdrawal is fixed relative to the cover—rather than to the reactor (e.g., see
It is to be understood that the terms “including”, “comprising”, “consisting” and grammatical variants thereof do not preclude the addition of one or more components, features, steps, or integers or groups thereof and that the terms are to be construed as specifying components, features, steps or integers.
If the specification or claims refer to “an additional” element, that does not preclude there being more than one of the additional element.
It is to be understood that where the claims or specification refer to “a” or “an” element, such reference is not be construed that there is only one of that element.
It is to be understood that where the specification states that a component, feature, structure, or characteristic “may”, “might”, “can” or “could” be included, that particular component, feature, structure, or characteristic is not required to be included.
Where applicable, although state diagrams, flow diagrams or both may be used to describe embodiments, the invention is not limited to those diagrams or to the corresponding descriptions. For example, flow need not move through each illustrated box or state, or in exactly the same order as illustrated and described.
Methods of the present invention may be implemented by performing or completing manually, automatically, or a combination thereof, selected steps or tasks.
The term “method” may refer to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of the art to which the invention belongs.
For purposes of the instant disclosure, the term “at least” followed by a number is used herein to denote the start of a range beginning with that number (which may be a ranger having an upper limit or no upper limit, depending on the variable being defined). For example, “at least 1” means 1 or more than 1. The term “at most” followed by a number is used herein to denote the end of a range ending with that number (which may be a range having 1 or 0 as its lower limit, or a range having no lower limit, depending upon the variable being defined). For example, “at most 4” means 4 or less than 4, and “at most 40%” means 40% or less than 40%. Terms of approximation (e.g., “about”, “substantially”, “approximately”, etc.) should be interpreted according to their ordinary and customary meanings as used in the associated art unless indicated otherwise. Absent a specific definition and absent ordinary and customary usage in the associated art, such terms should be interpreted to be ±10% of the base value.
When, in this document, a range is given as “(a first number) to (a second number)” or “(a first number)-(a second number)”, this means a range whose lower limit is the first number and whose upper limit is the second number. For example, 25 to 100 should be interpreted to mean a range whose lower limit is 25 and whose upper limit is 100. Additionally, it should be noted that where a range is given, every possible subrange or interval within that range is also specifically intended unless the context indicates to the contrary. For example, if the specification indicates a range of 25 to 100 such range is also intended to include subranges such as 26-100, 27-100, etc., 25-99, 25-98, etc., as well as any other possible combination of lower and upper values within the stated range, e.g., 33-47, 60-97, 41-45, 28-96, etc. Note that integer range values have been used in this paragraph for purposes of illustration only and decimal and fractional values (e.g., 46.7-91.3) should also be understood to be intended as possible subrange endpoints unless specifically excluded.
It should be noted that where reference is made herein to a method comprising two or more defined steps, the defined steps can be carried out in any order or simultaneously (except where context excludes that possibility), and the method can also include one or more other steps which are carried out before any of the defined steps, between two of the defined steps, or after all of the defined steps (except where context excludes that possibility).
Further, it should be noted that terms of approximation (e.g., “about”, “substantially”, “approximately”, etc.) are to be interpreted according to their ordinary and customary meanings as used in the associated art unless indicated otherwise herein. Absent a specific definition within this disclosure, and absent ordinary and customary usage in the associated art, such terms should be interpreted to be plus or minus 10% of the base value.
Still further, additional aspects of the instant invention may be found in one or more appendices attached hereto and/or filed herewith, the disclosures of which are incorporated herein by reference as if fully set out at this point.
Thus, the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned above as well as those inherent therein. While the inventive device has been described and illustrated herein by reference to certain preferred embodiments in relation to the drawings attached thereto, various changes and further modifications, apart from those shown or suggested herein, may be made therein by those of ordinary skill in the art, without departing from the spirit of the inventive concept the scope of which is to be determined by the following claims.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/666,975 filed on May 4, 2018, and incorporates said provisional application by reference into this document as if fully set out at this point.
| Number | Date | Country | |
|---|---|---|---|
| 62666975 | May 2018 | US |
