Wastewater Treatment Using Lagoons and Nitrification without Subsequent Clarification or Polishing

Abstract

The disclosed lagoon biological treatment system helps existing wastewater treatment facilities meet stricter discharge permits mandated by the EPA utilizing a facility's existing wastewater treatment infrastructure. Influent is pumped into and processed in an aerated or non-aerated lagoon system, thus initially treating the wastewater to reduce BODS (Biochemical Oxygen Demand) and TSS (Total Suspended Solids) to approximately 20-30 mg/L. Then the wastewater is transferred to and processed in a nitrification reactor, where sufficient nitrifying bacteria is present to reduce nitrogen levels to regulation-acceptable levels without needing to regulate temperature of the water in the nitrification reactor. Wastewater may also be further processed in a denitrifying reactor if necessary to meet local requirement. Post-nitrification polishing of the wastewater is foregone.

Claims

1. A method for treating wastewater in a treatment system, comprising: introducing influent wastewater into a lagoon and allowing the wastewater to remain within the lagoon for a period of time to reduce biochemical oxygen demand (BOD5) and total suspended solids (TSS) levels within the wastewater; after the wastewater has sat for said period of time, transferring partially processed wastewater having reduced levels of BOD5 and TSS from the lagoon to a moving-bed nitrification reactor containing high-surface-area media providing about 2,000 square meters or more of surface area per cubic meter of media; aerating the wastewater within the moving-bed nitrification reactor by means of fine-bubble aeration; allowing ammonia levels within the wastewater held within the moving-bed nitrification reactor to be reduced through aerobic, bacterial-based nitrification using nitrifying bacteria that have colonized the high-surface-area media; and discharging product fluid from the moving-bed nitrification reactor, the product fluid comprising wastewater that has been processed to reduce BOD5, TSS, and ammonia levels to at or below predetermined maximum levels.

2. The method of claim 1, wherein processed wastewater is discharged from the treatment system without clarifying or polishing the product fluid that has been discharged from the moving-bed nitrification reactor to remove solids.

3. The method of claim 1, wherein the temperature of the wastewater within the nitrification reactor is not regulated and is 1° C. or less.

4. The method of claim 1, further comprising treating the wastewater in the lagoon to facilitate reduction of BOD5 and/or TSS.

5. The method of claim 4, wherein the wastewater in the lagoon is aerated.

6. The method of claim 4, wherein the wastewater in the lagoon is mixed.

7. The method of claim 4, wherein the wastewater in the lagoon is covered to retard algae growth.

8. The method of claim 1, further comprising transferring the product fluid from the moving-bed nitrification reactor to a denitrification reactor and allowing nitrate to be removed from the product fluid in the denitrification reactor via anaerobic, bacterial-based denitrification.

9. The method of claim 8, further comprising dosing carbon to the denitrification reactor to support the anaerobic bacteria therein.

10. The method of claim 9, wherein carbon is dosed from a synthetic source.

11. The method of claim 9, wherein carbon is dosed by mixing a portion of influent wastewater with wastewater contained within the denitrification reactor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is a schematic diagram illustrating a wastewater processing facility arranged to implement the inventive method;

[0019] FIG. 2 is a schematic diagram illustrating a nitrification reactor utilized in the wastewater processing facility shown in FIG. 1; and

[0020] FIG. 3 is a schematic diagram (plan view) illustrating a fine bubble-producing aerator that may be used in the nitrification reactor shown in FIG. 2.

EXEMPLARY EMBODIMENTS

[0021] The present invention provides a method and system for new or existing wastewater lagoon systems, either aerated or non-aerated, to cost effectively meet more stringent effluent discharge requirements, including improving treatment of Ammonia, Nitrite+Nitrate, Total Nitrogen, BOD, and TSS. With the disclosed method, a new or existing lagoon system will be able to accept raw wastewater from either a municipal or industrial source and through both aerobic and anoxic processes, achieve approximate effluent of 20-25 mg/L BOD/TSS, less than mg/L Ammonia, and 5-10 mg/L Nitrate or Total Nitrogen without the need to build a fully mechanical treatment system, such as an activated sludge plant.

[0022] One embodiment of such a system is illustrated in FIG. 1. As illustrated therein, with the present method, first wastewater is introduced into the wastewater lagoon facility where the initial objective is to reduce BOD and TSS to lower levels to promote ammonia removal through nitrification. This happens initially in the lagoon portion 1. Research in the field of activated sludge wastewater treatment has demonstrated that the BOD should be sufficiently reduced to eliminate bacterial competition; generally, achieving a BOD level of 20-25 mg/L (as well as similar level of TSS) is ideal. Most currently existing lagoon systems, if operated according to this method, have the facilities already in place to achieve BOD/TSS removal down to 20-25 mg/L at design flow and loadings. In certain circumstances, additional equipment such as mixers and/or aerators can be added to the lagoon to improve the treatment of BOD, reduce/eliminate spring/fall turnover, and mitigate algae growth. Therefore, the disclosed process can utilize this pre-existing capability to avoid the need to upgrade this component if such an upgrade is not otherwise necessary (e.g., for equipment-related reasons).

[0023] There are two benefits to this approach. First, in this initial stage, the lagoon does not absolutely or necessarily have to be aerated; regardless of whether there is partial-mix, complete-mix, or no aeration at all, the disclosed method can achieve the stricter discharge standards. The only requirement is that the new or existing infrastructure be capable of reducing the majority of the BOD/TSS to levels approximately of 20-25 mg/L each, when operated appropriately. As a result, in instances of an existing non-aerated lagoon or a partial mix aerated lagoon, both equipment and energy costs are saved by not needing to install new aeration equipment. Second, because the disclosed method can incorporate this existing infrastructure, as opposed to the activated sludge alternative that replaces it, costs are saved on both equipment and infrastructure. Moreover, operation and maintenance costs remain the same for that portion of the system, giving a measure of predictability for future budgeting. (As alluded to above, it may be necessary or desirable, to achieve adequate treatment prior to the reactor, to install equipment to reduce BOD5, seasonal turnover, and/or algae growth within the lagoon.)

[0024] After the wastewater has been initially processed in the lagoon portion 1, it is transferred to the part of the system where ammonia can be removed via nitrification in a nitrification reactor 3, which provides an environment for nitrifying bacteria of various art-known species to nitrify and remove ammonia. Optionally, the wastewater may be treated in a further settling or clarifying lagoon 2 before it is transferred to the nitrification reactor 3, as illustrated in FIG. 1. While some (or even all) of the necessary nitrification can be achieved in the lagoon portion 1 during the summer months, in winter, most of the ammonia removal occurs in this part of the process, i.e., in the nitrification reactor 3.

[0025] As illustrated in FIG. 1, the nitrification reactor 3 can include two wastewater tanks operated in series with submerged aeration devices 5 and attached-growth media 4. As noted above, the reactor 3 utilizes media 4 such as “moving bed” media that provides a tremendous amount of surface area (e.g., on the order of 2500 square meters or more of surface area per cubic meter of media) on which the nitrifying bacteria can grow; therefore, a larger bacterial colony can build on it, thus allowing for nitrification to be achieved even at relatively cold water temperatures, e.g., water temperatures as low as 0.1-0.2° C. (For lagoons located in colder climates, typical surface discharge water from the primary treatment section can be less than 1° C. during the winter, so this low temperature nitrification capability is extremely beneficial.) Suitably, the nitrification reactors 3 are on the order of 10% to 50% filled with the media 4, to ensure adequate nitrification capability.

[0026] Furthermore, as indicated above, the nitrification reactor 3 is most preferably aerated using aerators 5 that are configured to produce fine bubbles (as defined according to industry standards), i.e., bubbles having diameters on the order of 0.5 mm to 3 mm as produced by the aerators (i.e., before rising within the water column and expanding). In this regard, and as illustrated in FIGS. 2 and 3, the aerators 5 may suitably be constructed as dual-action aerators in accordance with the disclosure of U.S. Pub. 2020/0114319 (co-pending application Ser. No. 16/598,842), the contents of which are incorporated by reference. (FIG. 2 is not to scale, and many more aerators 5—which are not as large relative to the nitrification reactor 3 as the figure suggests—than is shown would be provided.) Such aerators have a central tube 7 designed to release medium or coarse bubbles, which facilitate mixing and movement of the moving bed media 4 within the nitrification reactor 3, and a number of arms 8 extending radially outwardly from a central hub, which arms produce a fizzing “cascade” of fine bubbles. The aerators 5 are provided with air from the surface via an air-supply line 9.

[0027] As further indicated above, it may be advisable or even necessary to service such fine bubble-producing aerators 5 more frequently than is the case with respect to medium or coarse bubble-producing aerators, to avoid clogging or fouling of the bubble-producing arms 8. Therefore, to facilitate such servicing of the aerators 5, tethers 10 may be connected to the aerators 5 at one end and connected to an easily accessible location—e.g., a sidewall of the nitrification reaction 3, at a location above the surface of the water being processed within the reactor 3—at the opposite end. Thus, the tethers 10 can be used to pull the aerators 5 up from bottom of the nitrification reactor 3 relatively easily.

[0028] Further still, to facilitate maintenance of the aerators 5, it may be advantageous to provide the nitrification reactor 3 with guide rails 11 extending up from the bottom of the nitrification reactor 3 to above the surface of the wastewater within the nitrification reactor 3. As illustrated, the aerators 5 are ideally configured to fit down over the guide rails 11, so that they can be lowered back down into the nitrification reactor 3 after cleaning with the proper placement and orientation of the aerators 5 maintained.

[0029] Although the primary mechanism used to achieve mandated discharge levels according to this disclosure is to provide massive amounts of surface area for nitrifying bacteria to colonize in the nitrification reactor (so that sheer volume of bacteria offsets biological slowdown in cold temperatures), the reactors 3 may also be designed to—at least marginally—maintain the water temperature, to ensure the water does not become colder while in the nitrification reactor 3. This can be achieved by utilizing any number of measures that are considered current best practices to prevent cooling and heat loss from the water. For example, the various wastewater tanks can be buried in the ground, thereby utilizing the ground as insulation. Moreover, insulated covers 6, to prevent heat loss due to evaporation and contact with the ambient air, can be provided to cover the various tanks. The specific methods of maintaining water temperature may, of course, depend on the particular needs and conditions of each specific installation.

[0030] As noted above, each tank within the nitrification reactor 3 is aerated, and the included moving-bed media may be comprised by small biofilm carriers which yields a very high surface area that provide a habitat for nitrifying bacteria to attach to and grow, thereby exponentially increasing the net rate of biological activity. Air (i.e., oxygen) is supplied to the nitrification reactor 3 by a motor-operated blower (not shown) or equivalent device and is diffused into the wastewater via the aerators 5. The diffused aeration provides oxygen necessary for the nitrifying bacteria to thrive, and it mixes the water to ensure that there are no stagnant areas in the tank. Through the combination of oxygen from the air diffusers, appropriate water temperature as a result of regulation, and attached growth media that promote enhanced bacterial activity and retention time, the nitrification reactor is able to rapidly nitrify ammonia regardless of ambient temperatures.

[0031] (One of the benefits of such a nitrification system 3 is very low maintenance and relatively long product life. This is primarily due to the fact that the attached growth media pieces are self-cleaning; as they tumble in the water column, they are constantly hitting against each other, thereby knocking off excess biomass. As a result, maintenance costs are minimized, as no substantial replacement is necessary for approximately 15-20 years.)

[0032] After nitrification in the nitrification reactor 3, the water can be directly discharged as effluent. Because the reactor influent water comes from the back end of the lagoon system (including a polishing lagoon 2 if desired, as noted above), where it would normally be discharged, the levels of BOD/TSS are typically lower, below 30 mg/L, or typically low enough to discharge out of the plant. The reactor 30 either does not, itself, add any solids or only adds very minimal solids because the nitrifying bacteria grow a very thin biofilm that does not produce TSS when it dies naturally. This makes the system easier to install, as it can simply be located where the effluent pipe is coming from the lagoon, with minimal piping requirements needed.

[0033] Because the lagoon portion 1 can experience turnover in spring/fall, which can temporarily increase the suspended solids in the influent, the TSS of effluent coming out of the lagoon 1 can occasionally exceed 40 mg/L, which could ordinarily be problematic to fixed media systems. In contrast, the moving-bed media utilized within the disclosed reactor 3 will not clog—or it will clog much less frequently, at the very least—as it is constantly in suspension and being thoroughly mixed to ensure that any solids that come in will pass out the discharge. To guard against exceeding permit during times when 40 mg/L TSS effluent may occur due to algae or seasonal turnover, equipment can be added to the lagoon 1, to ensure that the lagoon is continually destratified, so that turnover has less of an effect.

[0034] The foregoing disclosure is only intended to be exemplary of the methods and products of the present invention. Departures from and modifications to the disclosed embodiments may occur to those having skill in the art.

[0035] The scope of the invention is set forth in the following claims.