WO2011116027A2

WO2011116027A2 - Method and apparatus for the treatment of waste effluent

Info

Publication number: WO2011116027A2
Application number: PCT/US2011/028568
Authority: WO
Inventors: T. Guy Roberts; Peregrine Scofield
Original assignee: Avatar Energy
Priority date: 2010-03-16
Filing date: 2011-03-15
Publication date: 2011-09-22
Also published as: WO2011116027A3

Abstract

This invention relates to an apparatus and method for the treatment of effluent from agricultural anaerobic digesters or other processes. In the preferred embodiment, effluent from a tank is pumped to distribution channels, allowing effluent to overflow and trickle on to filtration media. A portion of the liquid can continue past the channels and return to the tank. The filtration media creates enhanced gas exchange and an environment that promotes the growth of microbes with the desired biological activities. A recirculation leg allows a portion of the pumped liquid to promote the circular flow of liquids in the tank, which accumulates suspended solids at the center of the bottom of the tank.

Description

Method and Apparatus for the Treatment of Waste Effluent INVENTORS

T. GUY ROBERTS, RICHMOND VT USA; PEREGRINE S. SCOFIELD, SOUTH BURLINGTON VT USA

CROSS-REFERENCE TO RELATED APPLICATION

The application claims benefit of priority to US provisional patent application serial number 61/340,366, filed March 16, 2010.

BACKGROUND: FIELD OF THE INVENTION

This invention relates to the treatment of effluent from agricultural anaerobic digesters or other processes that produce high concentrations of ammonia or other chemically reduced compounds. Such wastes can be difficult to adequately dispose of or utilize as soil amendments. One, example would be the use of digester effluent as a fertilizer for direct application onto growing crops. The effluent from anaerobic digesters on dairy farms contains between 10 and 40 lbs of ammonia per 1000 gallons of effluent, providing substantial nutrient value, but crops could be damaged if this level of ammonia were applied directly onto plants. If the ammonia could be converted to nitrate, then plants would not suffer due to direct application and farmers could avoid storing digester effluent until after the crops have been harvested by spreading the effluent regularly on farm fields. There are currently few treatment options for digester effluent that retain fertilizer value.

In addition, this invention provides a means of reducing the levels of phosphorus in the digester effluent. Phosphorus plays an important role in the pollution of surface waters by nutrients and farmers are experiencing increasing regulatory pressure to reduce the amount that is spread on croplands. However, if the spreading of manure is curtailed, then farmers become more dependent on synthetic fertilizer to provide the needed nitrogen. This invention allows the phosphorus to be partitioned into a separate form from nitrogen. BACKGROUND: BRIEF SUMMARY OF THE INVENTION

BACKGROUND: DESCRIPTION OF RELATED ART

Trickling filters have been used for municipal sewage treatment for decades. Numerous variations on the concept have been utilized for various applications, but none are designed to be low-cost and modular, nor do existing designs include mechanisms to optimize the flow of effluent and removal of excess solids, nor do current design address related filtration channelization problems. Currently, the technology is not affordable for small to medium sized farm operations, where organic wastes can lead to significant degradation of surface and groundwater quality as well as producing noxious odors.

Commonly used trickling filters typically fall into three categories:

The first are those with submerged biofilm support media for removing dissolved components from liquids. These typically supply oxygen for aerobic processes either by bubbling air upwards through the bed or by providing oxygen through semi-permeable membranes that also support the biofilm.

The second are those that use non-submerged filter media beds, but use a sprayer/distributor to spread the liquids evenly across the media bed. This category includes the traditional gravel bed filters commonly used by sewage treatment plants, but also would include more recently used media, such as looped string and layered corrugated sheets for high flow media.

The third includes those designed to remove gas components from a gas stream. These typically locate a suspended or packed bed media within a container through which the gas stream flows. Water flows over the media to support the growth of the biofilm. These have been used to remove pollutants from natural gas streams or factory air.

The present invention uses non- submerged, suspended media, but does not employ sprayers or nozzles of any kind, which can become plugged by particulates in the waste stream being treated. An issue that arises with most non-submerged media trickling filters is that surface tension causes the liquids flowing across the media to collect in streams that leave much of the media unused. It is problematic to maintain an even flow of liquid across a significant amount of the filter media. Sprayers or tubular distributors that allow drips or streams to flow through orifices in the distributors still do not achieve uniform flow of the waste stream down all surfaces of the media.

In the preferred embodiment a sheet of textured or perforated material, woven fabric, or an arrangement of fibers or strings, or netting is attached directly to a distributor channel. Here a trough-like distribution channel is employed. In the preferred embodiment, the channel is comprised of a tube that has had the upper section machined away, leaving the ends of the tube intact to allow the channel to be attached to a manifold using standard pipe fittings. The filtration media devices are attached to the outer surface of the channel in such a way that liquid pumped into the channel can overflow from the channel onto the attached media devices. By adjusting the flow into the channel, a thin film of wastewater overflows from the full length of both sides of the channel, allowing the liquid to flow evenly across the entire width of the media devices attached on either side of the channel, providing a large

continuously wetted surface area. Oxygen required to support aerobic biological processes is more rapidly transferred across the thin film of liquid that forms on the suspended filter media devices, compared to the conditions found in other types of non-submerged media where oxygen must be supplied by external processes, or gas exchange is impaired by rapid flow of wastewater in streams, rather than the slower, sheet-flow of waste water created by the present invention.

The present invention also combines the use of a trickling filter with a swirl separator to combine the conversion of ammonia to nitrate with the settlement of phosphorus-rich particulates. By suspending the distribution channels and their attached media devices above the liquid level of a reservoir which has a swirling circulation, both these important treatment steps can be done simultaneously. In the preferred embodiment, the distribution channels and media are positioned directly above the reservoir, but could also be placed adjacent to, or at some distance from the reservoir with flow from the filter media being directed into the reservoir.

BRIEF DESCRIPTION OF THE FIGURES

FIG 1 is a side view of the trickling filter unit that depicts the lower tank as being transparent to allow all components to be viewed.

FIG 2 shows a side view of the trickling filter unit that depicts the lower tank as being opaque.

FIG 3 shows an overhead view of a preferred embodiment of the trickling filter unit. The distributor manifold assembly is in the foreground, showing the components of the assembly and the pathways of liquid flow.

DETAILED DESCRIPTION OF THE INVENTION

The feedstock for the trickling filters includes waste streams from agriculture, food processing, manufacturing or municipal, institutional or domestic wastes with a solids concentration that is, or can be, adjusted to between 0 to 6% solids. Said feedstock can be treated to significantly reduce solids content and to substantially transform reduced compounds, such as ammonia, into oxidized forms through biological activity of immobilized microbial communities. In many cases, in particular where there is direct exposure to the natural environment, the microbial communities are self-forming. However, inoculation of organisms may accelerate the development of said microbial communities. Examples of microbes that are useful include, but are not limited to, organisms of the genus Nitrosomonas and Nitwbacter, which promote the conversion of ammonium to nitrate. The conditions will vary according to the source of material being processed (examples would be, but are not limited to bovine, swine, and poultry waste products). The present invention could also be placed in a chamber having an atmosphere with different composition to effect different chemical transformations.

The trickling filter system is comprised of one or more storage tanks for receiving the feedstock. These trickling tanks can be from 1 to 100 feet high

(preferably 5 to 15 ft) and 1 to 100 feet in diameter (preferably 3 to 10 ft). In the event that more than one trickling tank is used, the tanks can be placed in either a parallel or serial configuration. While the preferred embodiment uses storage tanks, other types of feedstock storage such as ponds or lagoons may also be used, and the term reservoir describes any such storage element. A pump is positioned to push these liquids upwards into a set of open-topped channels positioned above the trickling filter tank. The liquid overflows from these channels onto media devices that can act as a support for the growth of microbial biofilms. The number of media devices can range from 1 to 1,000 per tank and the size of these devices can be proportioned appropriately depending on the size of the recirculation reservoir and properties of the effluent (examples would be, but are not limited to nitrogen content, phosphate content, effluent flow rate, solids content, and retention time in the digester).

The overflowing liquid maintains wetted surfaces on the suspended media providing a large surface area for enhanced gas exchange and an environment that promotes the growth of microbes with the desired biological activities. The availability of oxygen, for example, in the liquid promotes the growth of aerobic microorganisms that transform ammonia/ammonium into nitrate via the process of nitrification. Other aerobic activities will be supported that will diminish odors emitted by the liquid and will reduce the content of suspended particles. Liquid flowing from the suspended media is returned to the recirculation tank, where a pump is positioned to receive and recirculate these liquids back to the distributor assembly. The trickling tanks can be conical, tubular, rectangular, or square in shape and can be manufactured out of metal or a derivative thereof, plastic or a derivative thereof, fiberglass or a derivative thereof, or composite polymer or a derivative thereof. The trickling tanks may or may not require insulation depending on the ambient temperature in which they operate.

In the preferred embodiment, the trickling filter distributor assembly is self- cleaning with an outlet manifold and distributor outlet pipe provided. Some liquid is allowed to pass through the distributor assembly without overflowing onto the suspended media. This 'pass-through' liquid sweeps sediments back into the recirculation tank where the sediments can settle to the bottom of the tank and can be removed periodically from the tank through the recirculation tank drain valve.

While the preferred embodiment describes includes an outlet pipe system with an associated manifold, the invention can also be configured without such an outlet system. In this case, all of the effluent overflows from the distributor channels on to the suspended media. Similarly, another alternate embodiment uses a single distribution tube and corresponding suspended media, eliminating the need for the manifold and multiple distribution tube system. Such a single tube system can be used with or without a outlet pipe.

In the preferred embodiment shown in Figs 1 through 3, a recirculation leg is provided that promotes the circular flow of liquids in the tank. It is known to those skilled in the art that circular flow around the perimeter of a cylindrical tank leads to the accumulation of suspended solids at the center of the bottom of the tank. If the lower portion of the tank is conical, fluted, or otherwise slopes downward towards the center of the tank bottom, or if the overall shape of the tank is conical, fluted, or otherwise slopes downward towards the tank's center, the sediments will collect over a centrally located drain valve and can be removed from the tank by briefly opening the drain valve. Depending on the waste stream being treated, these suspended sediments may have value as a fertilizer or soil amendment.

Referring to the drawings for a better understanding of the invention, Fig 1 shows a view of a preferred embodiment of the trickling filter module. The basic function of the trickling filter is achieved when liquids needing treatment are pumped or flow passively into the trickling filter's recirculation tank 24. Once in the recirculation tank, the liquids are pumped with a recirculation pump 26 to the distributor assembly 4 that is located above the recirculation tank. The recirculation pump is plumbed into a distributor inlet 12 pipe that is equipped with flow adjustment valves 16a, 16b. These valves are used to balance the flow of liquids to either the distributor assembly or the recirculation leg 18. Liquids flowing through the recirculation leg promote the radial flow of liquids within the recirculation tank, which reduces foaming on the liquid surface 34. Liquids that enter the distributor assembly flow into the inlet end of distributor tubes 8 through the inlet distributor manifold 6a. Some of the liquid then exits the distributor assembly through the outlet end of distributor tubes 8 and into outlet distributor manifold 6b, but much of the liquid will overflow from the distributor channels 10 through the distributor channel cutaways 10 onto the filtration media 22 and flow back into the recirculation tank. This flow pattern creates a thin layer of flowing liquid on the filtration media that is exposed to the surrounding atmosphere for rapid gas exchange. In an alternate embodiment, there is no outlet distributor 6b or outlet pipe 14, with all of the liquid flowing overflowing from channels 10. The microenvironment that is created by the flow of a thin film of liquid over the filtration media promotes the attached growth of micro-organisms on the filtration media that perform useful transformations of chemical compounds in the liquid, such as nitrification, reduction of biological oxygen demand (BOD), and oxidation of reduced sulfur compounds when the trickling filter is operated in an aerobic environment.

The recirculation pump must be rated to pump at a high enough rate to cause overflow of the distributor channels as well as permit flow out of the distributor outlet manifold 6b into the distributor outlet 14 pipe. The flow of a percentage of the liquids through the distributor assembly and into the distributor outlet prevents the build-up of solids that might otherwise settle out in the distributor channels. The distributor outlet adjustment valve 20 can be set to reduce the rate of liquid flow to prevent foaming at the liquid surface in the recirculation tank.

The trickling filter module shown in Fig. 1 can be arranged in series to provide greater treatment capacity. The recirculation tank is fitted with a supply opening 30a and a drain opening 30b in order to allow trickling filter units to be connected. The height of the inlet and outlet determine the liquid surface level within each trickling filter unit. In order to insure that liquids flow moves progressively from one trickling filter unit to the next in series, it will be important to either set the units at

progressively lower elevations or place the supply opening and outlet at progressively lower positions on the recirculation tanks. It is also an option to use a pump to transfer liquid from one tank to the next.

A further function of the trickling filter unit is to promote the settling of suspended solids that may be carried in the liquid being treated. By exposing the liquid to an aerobic environment, oxidative metabolism destroys suspended organic particles in the liquid, reducing the viscosity and promoting the settling of

undigestible suspended solids. The recirculation and changing direction of flow also promotes the settling of suspended solids in the recirculation tank. For this reason the recirculation tank has a sloped bottom that allows settled materials to be removed through the recirculation tank drain valve 28. In many cases, this settled material, or sludge, has intrinsic value as a fertilizer or soil amendment and can be used to offset costs or be sold.

Although the present invention has been described with respect to one or more embodiments, it will be understood that other embodiments of the present invention may be made without departing from the spirit and scope of the present invention. Hence, the present invention is deemed limited only by the appended claims and the reasonable interpretation thereof.

Claims

What Is Claimed:

1. An apparatus for treating waste effluent comprising:

a recirculation reservoir containing at least one supply opening and at least one drain opening;

a recirculation pump;

an inlet pipe, with the lower end of the inlet pipe connected to the pump; at least one distributor tube whose inlet is connected to the upper end of the inlet pipe;

a filtration media device below the distributor tube and above the reservoir; wherein the effluent in the reservoir is circulated by the pump and spills out of the distributor tube on to the filtration media device, and compounds within the effluent are transformed from chemically reduced forms to chemically oxidized forms.

2. The apparatus of claim 1, further comprising an outlet pipe and an outlet flow adjustment valve connected to the outlet end of the distributor tube, with the outlet pipe directed back to the reservoir, wherein a portion of the effluent spills out of the distributor tube on to the filtration media device and the remaining effluent travels into the outlet pipe.

3. The apparatus of claim 1 wherein the effluent is received from an anaerobic digester.

4. The apparatus of claim 1 wherein the reservoir is cylindrical with an open top, a closed conical bottom section, and a drain valve located at the bottom of the conical section.

5. The apparatus of claim 2 further comprising a plurality of distributor tubes and filtration media devices, with the inlet portion of the distributor tubes connected by an inlet manifold and the outlet portion of the distributor tubes connected by an outlet manifold.

6. The apparatus of claim 1, wherein the pump additionally creates circular flow within the reservoir.

7. The apparatus of claim 6, wherein the circular flow is created by further including at least one flow adjustment valve to direct a portion of the effluent in the inlet pipe to a recirculation leg.

8. The apparatus of claim 1, further comprising a plurality of apparatuses connected together, where the connection type is series or parallel.

9. A method for treating waste effluent comprising the steps of:

providing a recirculation reservoir containing at least one supply opening and at least one drain opening;

providing a recirculation pump;

providing an inlet pipe, with the lower end of the inlet pipe connected to the pump;

connecting the inlet end of at least one distributor tube to the upper end of the inlet pipe;

positioning a filtration media device below the distributor tube and above the reservoir;

circulating the effluent in the reservoir with the pump so that the effluent spills from the distributor tube on to the filtration media device, thereby

transforming compounds within the effluent from chemically reduced forms to chemically oxidized forms.

10. The method of claim 9 further comprising the step of attaching an outlet pipe and an outlet flow adjustment valve to the outlet end of the distributor tube, with the outlet pipe directed back to the reservoir, wherein a portion of the effluent spills out of the distributor tube on to the filtration media device and the remaining effluent travels into the outlet pipe.

11. The method of claim 9 wherein the effluent is received from an anaerobic digester.

12. The method of claim 9 wherein the reservoir is configured as a cylinder with an open top, a closed conical bottom section, and a drain valve located at the bottom of the conical section.

13. The method of claim 10 further comprising providing a plurality of distributor tubes and filtration media devices, with the inlet portion of the distributor tubes connected by an inlet manifold and the outlet portion of the distributor tubes connected by an outlet manifold.

14. The method of claim 9, further comprising the step of using the pump to create circular flow within the reservoir.

15. The method of claim 14, further comprising creating circular flow by using at least one flow adjustment valve to direct a portion of the effluent in the inlet pipe to a recirculation leg.

16. The method of claim 9, further comprising connecting a plurality of apparatuses together, where the connection type is series or parallel.

17. A device for delivering effluent to a filtration media device comprising:

an inlet pipe for transferring effluent from an effluent supply;

at least one distributor tube for receiving the effluent from the inlet pipe; a filtration media device below the distributor tube;

wherein a portion of the effluent spills out of the distributor tube on to the filtration media device, and compounds within the effluent are transformed from chemically reduced forms to chemically oxidized forms.

18. The apparatus of claim 17 wherein the effluent is received from an anaerobic digester.

19. The apparatus of claim 17 further comprising a plurality of distributor tubes and filtration media devices, with the inlet portion of the distributor tubes connected by an inlet manifold.

20. The apparatus of claim 19 further comprising an outlet pipe connected to the outlet end of the distributor tube, wherein a portion of the effluent spills out of the distributor tube on to the filtration media device and the remaining effluent travels into the outlet pipe.