FIELD OF THE INVENTION

The present invention relates to processes for removing ammonium nitrogen from a wastewater stream, and more particularly to a mainstream deammonification process.

BACKGROUND

Typically, wastewater influent includes ammonium nitrogen, NH ₄ -N. Conventionally, to remove ammonium nitrogen, a two-step process is called for, nitrification and denitrification. In this conventional approach to removing ammonium nitrogen, the process entails a first step referred to as a nitrification step and which converts ammonium nitrogen to nitrate and a very small amount of nitrite, both commonly referred to as NO _x . Many conventional activated sludge wastewater treatment processes accomplish nitrification in an aerobic treatment zone. In the aerobic treatment zone, the wastewater containing the ammonium nitrogen is subjected to aeration and this gives rise to a microorganism culture that effectively converts the ammonium nitrogen to NO _x . Once the ammonium nitrogen has been converted to NO _x , then the ΝΟχ- containing wastewater is typically transferred to an anoxic zone for the purpose of denitrification. In the denitrification treatment zone, the NO _x -containing wastewater is held in a basin where there is no supplied air and this is conventionally referred to as an anoxic treatment zone. Here a different culture of microorganisms operate to use the NO _x as an oxidation agent and thereby reduces the NO _x to free nitrogen gas which escapes to the atmosphere.

Conventional nitrification and denitrification processes have a number of drawbacks. First, conventional nitrification and denitrification processes require substantial energy in the form of oxygen generation that is required during the nitrification phase. Further, conventional denitrification require a substantial supply of external carbon source.

In recent years it has been discovered that ammonium in certain waste stream can be removed by utilizing different bacteria from those normally associated with conventional nitrification-denitrification. In this case, a typical process combines aerobic nitritation and an anaerobic ammonium oxidation (ANAMMOX). In the nitritation step, aerobic oxidizing bacteria (AOB) oxidize a substantial portion of the ammonium in the waste stream to nitrite (N0 ₂ ^" )- Then in the second step, the ANAMMOX bacteria or biomass converts the remaining ammonium and the nitrite to nitrogen gas (N ₂ ) and in some cases a small amount of nitrate (N0 ₃ ^" ). The total process, i.e. nitritation and the ANAMMOX process, is referred to as deammonification. One particular application of this process is a sidestream process where the waste stream includes a relatively high concentration of ammonium, a relatively low concentration of carbon and a relatively high temperature. SU MMARY OF EXEMPLARY EMBODIMENTS

Disclosed herein is a mainstream deammonification process for removing ammonium nitrogen from a wastewater stream that suppresses nitrite oxidizing bacteria (NOB) growth in the nitritation stage of the deammonification process. This is accomplished by creating or maintaining a phosphorus deficiency to NOB in the deammonification process. It is

hypothesized that NOB will not flourish and grow in an environment with some degree of phosphorus deficiency, and that, in the absence of substantial or significant NOB, the nitritation phase will generate sufficient nitrite to support a robust ANAMMOX process.

In one embodiment, the phosphorus concentration in a deammonification reactor is controlled through chemical precipitation. By employing online measurement of the phosphorus concentration in the deammonification reactor and controlling chemical dosing, the phosphorus concentration in the reactor is continuously and accurately controlled. While various phosphorus concentration limits may be employed, it is hypothesized that, in one embodiment for suspended growth systems, it is desirable to limit the phosphorus concentration in the deammonification reactor to a range of 0.5 to 0.01 mg-P/L. For biofilm systems, it may be possible to suppress NOB growth by limiting the phosphorus concentration in the reactor to between 0.01 and 0.5 mg/L.

Other objects and advantages of the present invention will become apparent and obvious from a study of the following description and the accompanying drawings which are merely illustrative of such invention.

DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic illustration of a single stage mainstream deammonification process where pre-treatment is carried out by a chemical enhanced primary treatment unit.

Figure 2 is a schematic illustration of a mainstream dual stage deammonification process where pre-treatment is carried out by a chemical enhanced primary treatment unit.

Figure 3 is a schematic illustration of a single stage mainstream deammonification process where pre-treatment is carried out by a primary clarifier and a high rate biological treatment unit.

Figure 4 is a schematic illustration of a mainstream deammonification process that is similar to the process shown in Figure 3 except that the deammonification process is a dual stage deammonification process.

Figure 5 is a schematic illustration of a mainstream single stage deammonification process where an industrial wastewater stream being treated contains little or no phosphorus and the process provides for phosphorus addition and control.

Figure 6 is a schematic illustration of a mainstream deammonification process similar to that shown in Figure 5 except that the deammonification process in this case includes a dual stage deammonification process. DESCRIPTION OF EXEMPLARY EMBODIMENTS

Developing a reliable and efficient mainstream deammonification process is challenging. Nitritation appears to be the key to a successful mainstream deammonification process.

Overcoming the adverse effects of nitrite oxidizing bacteria (NOB) is one concern. This is because nitritation produces nitrite that forms the substrate for the ANAMMOX bacteria. Thus, in a mainstream deammonification process, it is advantageous in the nitritation process to sustain the growth of AOB and limit or suppress the growth of NOB. When the growth of NOB is limited or suppressed, this eliminates or reduces the ANAMMOX bacteria's competition for nitrite. Further, by limiting the growth of NOB, this may reduce the formation of nitrate which consumes oxygen and may require carbon for denitrification. Moreover, the problem presented by the presence of significant NOB is even more challenging in conditions of low temperature and low ammonium nitrogen concentration because these conditions tend to favor the growth of NOB.

The mainstream deammonification process typically includes a pre-treatment unit followed by a deammonification process which includes nitritation and an ANAMMOX process carried out in a single stage or a dual stage. Various forms of pre-treatment can be employed. For example, the pre-treatment unit may include what is generally referred to as a chemical enhanced primary treatment (CEPT) unit 12 or a high rate biological treatment process 14. In any event, the processes of the present invention entails mixing a phosphorus precipitating chemical, such as FeCI ₃ , with the wastewater and causing phosphorus to precipitate. The precipitated phosphorus is removed from the process through a conventional sludge removal process. By continuously monitoring the phosphorus concentration in the deammonification reactor and adjusting the dosing of the phosphorus precipitating chemical, the phosphorus concentration in the reactor can be controlled and limited. By limiting the phosphorus concentration in the reactor , it is hypothesized that this suppresses and limits the growth of NOB in the deammonification reactor and overcomes the adverse effects of NOB in a deammonification process. As used herein, the term "phosphorus" means microbially available phosphorus (MAP).

With respect to Figure 1 , there is shown therein a mainstream single stage

deammonification process. In this case, raw sewage or wastewater is directed into a chemical enhanced primary treatment (CEPT) unit 12. Chemically enhanced primary treatment is a process by which chemicals, typically metal salts and/or polymers in the form of organic polyelectrolytes, are added to a primary sedimentation basin. The chemicals cause the suspended solids in the influent to clump together through a coagulation and flocculation process. The suspended solids aggregate or form floes which settle faster, thereby enhancing treatment efficiency. Chemicals utilized in the CEPT unit 12 can vary but would typically include chemicals such as ferric chloride or aluminum sulfate. In the process of Figure 1 , the CEPT unit 12 is utilized to remove phosphorus from the raw sewage or wastewater. By mixing a phosphorus precipitating chemical, such as an aluminum or iron salt, with the wastewater upstream of the CEPT unit 12 and/or after the CEPT unit, precipitated phosphorus species can be removed from the wastewater stream. Effluent from the CEPT unit 12 is then directed to the one-stage mainstream deammonification reactor 16 which, through nitritation and the ANAMMOX process, removes ammonium nitrogen from the raw sewage.

The process shown in Figure 1 is designed to suppress NOB and limit the phosphorus concentration in the deammonification reactor 16. To suppress the NOB growth, the process aims to substantially reduce and control the phosphorus concentration in the deammonification system. It is hypothesized that if there is a significant phosphorus deficiency in the

deammonification reactor 16, this will effectively suppress the growth of NOB and facilitate the growth and proliferation of AOB so as to produce a stable nitritation process in the

deammonification process. As noted above, it is hypothesized that, in one embodiment, an appropriate target phosphorus concentration range to achieve this goal is in the range of 0.01 to 0.5 mg/L in the reactor. Expressed differently, the process is designed to control the phosphorus concentration in the deammonification process such that the phosphorus concentration therein does not generally exceed 0.5 mg/L. In one embodiment of the present invention, the process includes maintaining the phosphorus concentration in the

deammonification system or process between 0.5 mg/L and 0.01 mg/L. Therefore, in the case of the embodiment in Figure 1 , there is provided an online phosphorus measurement sensor 18 disposed in the deammonification reactor 16. Although it is preferable for the phosphorus measurement sensor 18 to sense the phosphorus concentration in the deammonification reactor 16, in a one-stage process or in the nitration reactor 16A in a dual-stage deammonification process, it should be pointed out that in some cases it may be permissible to sense the phosphorus concentration upstream of the deammonification reactor 16 or upstream of the nitration reactor 16A. In the case of Figure 1 , the phosphorus concentration measurement is conducted in the deammonification system. Various chemicals can be added to the raw sewage or directly to the deammonification reactor 16 to precipitate phosphorus. As noted above, aluminum and iron salts, such as aluminum sulfate and ferric chloride, can be added to the wastewater stream or directly to the deammonification reactor to precipitate phosphorus. The phosphorus precipitating chemical is dosed by one or more chemical dosing pumps (controlled, for example, by a programmed logic controller) based on the measured phosphorus concentration in the deammonification reactor 16 and the target phosphorus concentration. By employing a programmed controller, the chemical dosing pumps maintain the phosphorus concentration in the deammonification reactor 16 in an appropriate range, depending upon whether suspended biomass or fixed film biomass is being employed in the deammonification system. Turning to the Figure 2 process, it is similar in many respects to the process described in Figure 1 . The main difference is that the deammonification process shown in Figure 2 is a two- stage process. That is, the first stage comprises a mainstream nitritation reactor 16A and the second stage comprises a mainstream ANAMMOX reactor 16B. Here, the phosphorus concentration should be controlled to a target level just upstream of the nitritation reactor 16A or in the nitritation reactor itself. Thus, the process proceeds as discussed with respect to Figure 1 in that the phosphorus concentration is measured and compared to the target phosphorus concentration. Based on this, a phosphorus precipitating chemical is added at one or more points in the process to precipitate phosphorus and control the phosphorus concentration at the target concentration.

Note that the nitration reactor 16A may produce nitration sludge and that the ANAMMOX reactor 16B may produce ANAMMOX sludge. Thus, the reactors 16A and 16B may incorporate a solids-liquid separation process into the reactors or downstream solids-liquid separation processes may be provided with respect to the reactors 16A and 16B.

There may be cases where it is prudent or advisable to add a phosphorus source to the wastewater stream in order to support the ANAMMOX bacteria. Note in Figure 2 where a phosphorus source, P0 ₄ -P, is added to the wastewater stream between the mainstream nitritation reactor 16A and the mainstream ANAMMOX reactor 16B or directly into the

ANAMMOX reactor itself.

In Figure 3, the mainstream deammonification process is similar to that described in

Figure 1 except for pre-treatment. In this case, the CEPT unit 12 has been replaced by a primary clarifier 13 and a high rate biological treatment unit 14 for carbon removal. Here again, the phosphorus precipitating chemical can be added at one or more points as indicated in Figure 3. The phosphorus precipitating chemical mixes with the raw sewage and causes various forms of phosphorus to precipitate in the primary clarifier 13 and/or the high rate biological treatment unit 14. The precipitated phosphorus is removed from the process via the primary sludge and the C-stage sludge. Again, the process is essentially the same in that prior to entering the deammonification process 16 of Figure 3, an online phosphorus sensor 18 or measurement device determines the phosphorus concentration in the deammonification process. That phosphorus concentration measurement is utilized to determine if there should be chemical addition and if so, how much. Like the preceding processes, the aim of the process of Figure 3 is to suppress NOB in the deammonification reactor, particularly during the nitritation process, so that nitritation is stable and produces appreciable nitrite for consumption in the ANAMMOX process.

In the process shown in Figure 4, one sees that it is essentially the same as the process shown in Figure 3 except the deammonification system in Figure 4 is a two-stage system as opposed to the single stage system shown in Figure 3. That is, the deammonification system includes a nitration reactor 16A and an ANAMMOX reactor 16B. However, the basic process remains the same.

Figures 5 and 6 show two mainstream deammonification processes that may be used when treating industrial wastewater. In many cases, industrial wastewaters contain little or no phosphorus. Phosphorus must be added to the biological process for efficient treatment. As used herein, when it is stated that the wastewaters contain little or no phosphorus, it is meant that phosphorus concentration is below approximately 0.2 mg/L. The processes of Figures 5 and 6 entail adding sufficient phosphorus to the wastewater to sustain AOB and ANAMMOX bacteria, but at the same time limit the phosphorus concentration in a single stage

deammonification process or limit the phosphorus concentration in the nitration process in a dual-stage deammonification process. As noted above, in one embodiment, the phosphorus concentration is limited such that it does not exceed 0.5 mg/L. Figure 5 shows a one-stage deammonification process. Here, phosphorus can be added at one or more points in the process as shown in Figure 5. This can provide for adequate control of the phosphorus concentration in the deammonification process and by controlling the phosphorus concentration in the deammonification process to relatively low levels, this suppresses the NOB in the deammonification reactor. In the case of the Figure 5 process, phosphorus is added, but at the same time by measuring the phosphorus concentration in the deammonification reactor 16, the process is controlled by only adding so much phosphorus that the phosphorus concentration does not exceed 0.5 mg/L in a preferred embodiment. Figure 6 is similar to Figure 5 except the Figure 6 process is a dual-stage deammonification process. Here, phosphorus addition can occur before pre-treatment, between pre-treatment and the nitritation stage, and/or between the nitritation reactor and the ANAMMOX reactor. In the case of the Figure 6 process, there is phosphorus addition but again the amount of phosphorus added is controlled such that the phosphorus concentration in the nitration reactor 16A is maintained at 0.5 mg/L or less. The amount of phosphorus added downstream of the nitration reactor 16A is not so critical. The concern for the NOB is with respect to the nitration process that takes place in the nitration reactor 16A.

Depending on the impact of phosphorus deficiency on ANAMMOX bacteria, the present process entails two applications. If the low phosphorus concentration does not impact the growth of ANAMMOX bacteria, this process (P-deficiency) can be applied to a one-stage deammonification process. In this case, the online phosphorus measurement in the deammonification system or reactor will be used to control the addition of one or more phosphorus precipitating chemicals. The dosing point can be one point, such as the CEPT unit 12 or the high rate biological treatment unit 14 or the deammonification system or reactor, or at other multiple points in the process. The impact of the phosphorus deficiency on ANAMMOX bacteria may not be totally known at this time. If the low phosphorus level does affect the growth of ANAMMOX bacteria, then this deammonification process with P deficiency can be applied to suppress NOB in the nitritation stage of a two-stage deammonification process. After the nitritation stage, the phosphorus concentration in the effluent will be low. If necessary, a small amount of phosphorus can be added back to the ANAMMOX stage to alleviate the phosphorus limitation.

Thus, these process embodiments show that NOB growth can be suppressed in a deammonification process by controlling the phosphorus concentration to a target concentration or a target concentration range. By limiting the phosphorus concentration in the nitritation phase of the deammonification process, AOB is able to thrive and provide the necessary nitrite required by the ANAMMOX criteria. This approach to suppressing NOB growth may, in many cases, be sufficient to yield an effective and efficient mainstream deammonification process. However, this particular approach to suppressing NOB growth can be combined with other mainstream deammonification processes for enhanced efficiency and effectiveness.

Many operating parameters, either individual or a combination of multiple parameters, may limit NOB growth in both one-stage and two-stage deammonification processes. These operating parameters include high temperature, controlled SRT, free ammonia (FA) , pH, high salt concentration, and low dissolved oxygen (DO). Also, alternating anoxic and aerobic conditions with high DO, free nitrous acid (FNA) inhibition, adequate C/N ratio, real-time control and bio-augmentation may be helpful in limiting NOB growth. Even with applications of the above mentioned control parameters, repression of NOB in the mainstream ANAMMOX process may remain unstable due to low ammonia and low temperature of the sewage.

For example, the process of limiting the phosphorus concentration in the one-stage deammonification process can be combined with an integrated fixed film and activated sludge (IFAS) configuration that employs intermittent aeration with dissolved oxygen control and solids retention time (SRT) control for NOB repression. The cycle lengths of the intermittent aeration can be controlled by a timer and a relatively high dissolved oxygen can be maintained during the air-on period. In the IFAS configuration, the SRT of the suspended growth is controlled by sludge wasting from the system. Together, these two processes appropriately coupled may provide an effective mainstream deammonification process.

Another example is that this P limiting process in the nitritation stage can be combined with a bioaugmentation approach utilized in a two stage mainstream deammonification process. For a plant employing both side-stream and mainstream deammonification processes using moving bed biofilm reactor systems, the bioaugmentation approach is to exchange the biofilm carriers between the two streams. With the bioaugmentation and low DO control in the nitritation stage MBBR, the two-stage mainstream deammonification may achieve some degree of NOB repression. With additional P limiting condition in the first stage MBBR reactor, the NOB repression will be more stable and consistent.

The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the scope and the essential characteristics of the invention. The present embodiments are therefore to be construed in all aspects as illustrative and not restrictive and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.