Method and system to emulate reactive flowing fluid in a pipe using a recirculating loop reactor

Abstract

An apparatus and / or system herein includes at least one module, a liquid feed line including a pump to feed liquid into the module, at least one dosing inlet to feed a chemical, biochemical, or biological agent into the module, and an effluent collector to collect liquid exiting the module. Each module includes at least one line through which the liquid is able to flow, the line comprising a line inlet and a line outlet, the line inlet receiving the liquid, a recirculation line associated with the at least one line, the recirculation line capable of feeding at least some of the liquid back through the line prior to leaving the line via the line outlet, and a recirculation pump for each recirculation line. The apparatus accurately emulates a piping system conveying a reactive fluid, and thus predicts the effect of operational and design changes in, for example, a full-scale wastewater collection system.

Description

METHOD AND SYSTEM TO EMULATE REACTIVE FLOWING FLUID IN A PIPE USING A RECIRCULATING LOOP REACTORBACKGROUND

[0001] Conveyance of water in pipes capable of supporting microbiological growth is common among cities and industries throughout the world. Left unaddressed, the cultivated biofilm can degrade water quality and corrode piping infrastructure. As a result, considerable resources are spent on additives (chemical, biochemical, and biological) to attenuate the adverse impacts. Entities impacted include e.g., municipal water / wastewater agencies, food and beverage facilities, biomass processing plants, and oil production / pipeline companies. The collection and treatment of municipal wastewater is a particular area where new tools are needed to accelerate development and deployment of advanced eco-friendly technologies. For this reason, the examples of use provided herein are oriented toward municipal wastewater collection systems.

[0002] Biofilm management, hydrogen sulfide production and accumulation, odor formation and corrosion in a wastewater sewage system, i.e., a sewer, are major problems that concern most all municipalities, and are typically more or less addressed through operational changes, engineering solutions, and using chemicals dosed into the sewer. Given the dynamic nature of wastewater flows and composition, the development of advanced chemical dosing control strategies is required to optimize the chemical cost and enhance odor control. Further, the most cost-effective treatment solutions continuously undergo developments and optimization, to ensure that they are effective and efficient. Similar issues are faced in other applications, for example disinfection in open channel systems, disinfection in pipe networks, and so on. In all cases, it is important to ensure that pilot studies are conducted under conditions that are highly representative of the hydraulics, and the physico-chemical and biochemical conditions of the full-scale system being studied.

[0003] During chemical treatment of water, wastewater and sewage, the development and optimization of advanced dosing regimens and trials for full-scale systems (such as an actual sewers or actual disinfection systems) is a very expensive task if conducted without a detailed understanding of the specific characteristics of the underlying hydraulics, physico-chemical and biological processes. In an effort to reduce the cost of full-scale trials while maximizing the information content and the scalability of results collected with laboratory and pilot studies, a scaling down technique is needed for odor and corrosion management in sewers(and dose optimization in disinfection systems). Once developed, such a technique will enable improvements to be tested and refined on a laboratory or pilot apparatus. The speed and efficiency afforded at this smaller scale allows for accelerated evaluation of operational or design options, particularly those related to new and innovative dosing strategies and new environmentally-friendly chemical and biological products.

[0004] Municipal water and wastewater infrastructure is comprised of drinking water plants (and associated distribution systems) and wastewater plants (and associated collection systems). The wastewater collection system component is comprised of branched pipes of increasing size closer to the treatment plants. A similar structure is present in drinking water distribution systems. The conveyance of organic- and nutrient-rich raw wastewater necessarily propagates the establishment and growth of microbial biofilms attached to the inner pipe surface. The nature of the wastewater (e.g., aerobic or anaerobic) defines the nature of the biofilm and thus its growth properties and metabolites. These microbial inputs / outputs in turn influence the vapor composition within the sewer system as well as the water quality that enters the treatment plant. Developing an understanding of these sewer biofilm processes is thus important in devising and controlling mitigation measures that, for example, minimize odor production, encourage soluble carbon production, reduce greenhouse gas emissions, and remove nutrients.

[0005] Given the difficulties / impracticalities of conducting sewer biofilm studies in the field (in terms of, e.g., labor, access, and costs), efforts have been made to devise scaled down models of sewer pipes that can be operated in laboratories under controlled conditions and close supervision. Early attempts at such scaled down models involved a series of reactors in which a biofloc suspension was permitted to grow in a retained compartment in each reactor. See Zan et al., “Ground food waste discharge to sewer enhances methane gas emission: A lab-scale investigation,” Water Res., vol. 174, p. 115616 (2020). This approach mimicked certain of the biochemical transformations, and so enabled refinement of the existing sewer process models. See Gutierrez et al., “SCORe-CT: A new method for testing effectiveness of sulfide-control chemicals used in sewer systems,” Water Set. TechnoL, vol. 64, no. 12, pp. 2381-2388 (2011). However, this early version grew suspended biofloc - not biofilm - and so failed to accurately mimic sewer microbial processes.

[0006] What is still desired is a scaled down sewer apparatus that mimics the velocities and approximates as closely as possible the hydraulics, the physico-chemical and biochemicalrate characteristics of a full-scale sewer system. Among those, the surface-to-volume ratios of an actual sewer system, where the biofilm affixes both to the pipe walls and to the settled deposits, is an example. Other examples are the shear forces at the pipe wall and the residence time of the bulk flow, since these dictate the thickness of the biofilm and the kinetic of transformation of liquid, solids and gaseous species into products. As well, the apparatus should be programmable and able to decouple the residence time distribution of the sewage from the hydraulic regimes inside the pipe, such that the instantaneous flow could also mimic the diurnal patterns typical of municipal sewers where deposition-resuspension occurs and biofilm thickness is impacted by shear forces exerted by the flowing wastewater while also being able to mimic the different effects of pressure and gravity flows within the system. Similar needs apply to disinfection scale-down apparatus, where it is essential to approximate the disinfection process (in this case, microbial inactivation rather than growth) that occurs under known contact tank hydraulics and, ideally, under nearly identical mixing and settling conditions.SUMMARY

[0007] An object of this application is to provide a method and treatment apparatus or system that accurately mimics full-scale treatment performance within a system using a recirculating loop reactor system. The system ensures that the main dimensionless numbers describing the physics, the biological and the chemical reactions occurring in a full-scale system are kept as close as possible to the scaled down system employed for product development, research and optimization studies. The method also ensures that the residence time of the bulk flow is decoupled by the hydraulic regime of the pipe or channel system, such that these two aspects can be controlled individually and independently. The scaled down system thus enables the investigation of multiple process and multiple process variables while conducting research and product development studies, which eliminates the need for costly field trials at the early stages of development.

[0008] The system can find application in several areas of water and wastewater treatment, including, for example, odor and corrosion control in sewers, water and wastewater effluent disinfection, alkalinity supplementation studies, pipe reactor studies, biofilm studies, greenhouse gas formation studies, and so on. The system can have even broader applications, though, including in, for example, industrial process water circuits, petroleum transfer piping, and food and beverage piping systems.

[0009] An immediate advantage of the proposed methodology is that it allows the decoupling of fluid velocity within the system and sewage residence time in the system (while controlling the shape of the residence time distribution by virtue of addition of an arbitrary number of fully-mixed reactors in series, ranging from completely stirred residence time distribution to plug flow residence time distribution). Notably, the same methodology could also be applied to other wastewater treatment applications such as disinfection, primary settling, biological treatment processes, sludge treatment processes, anaerobic digestion, drinking water networks, and centrifugation. Moreover, it is also possible to use the same methodology to study emerging issues in pipe networks in sewers, drinking water systems and municipal and industrial water reuse systems. Such emerging issues could include sewer epidemiology studies, sewer sociology studies, greenhouse gas studies, antibiotic resistance studies, gene studies, pathogen studies, chemical decay studies, nanoparticle treatment studies and bioaugmentation studies.

[0010] The system and apparatus herein can be used as a predictive tool and as an optimization tool that considers the complex factors affecting biofilm formation and growth in flowing pipes. The use of a recirculation loop that is incorporated into a section of pipe that comprises a single pipe conduit train, for example a conduit train of 3-5 sections of pipe, provides for this result.

[0011] The foregoing is a summary and thus may contain simplifications, generalizations, and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting.

[0012] For a better understanding of the embodiments, together with other and further features and advantages thereof, reference is made to the following description, taken in conjunction with the accompanying drawings. The scope of the invention will be pointed out in the appended claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Fig. 1 A is a front view and Fig. IB is a rear view of a sample module of the system.

[0014] Fig. 2 is a schematic of a sample line within the module, including a recirculation line.

[0015] Fig. 3 illustrates a simple loop configuration for a four line / recirculation line module.

[0016] Fig. 4 illustrates an example of a complex line / recirculation line loop with split lines and split recirculation lines.

[0017] Fig. 5 is a view of a three rack apparatus, each with ten vertically stacked modules therein.

[0018] Fig. 6A illustrates an overview of a full-scale system with multiple sections in series, Fig. 6B illustrates an overview of a single section of the system without recirculation flow, and Fig. 6C illustrates an overview of a single section with recirculation flow.

[0019] Fig. 7A illustrates an overview of a full scale system with multiple sections in series, Fig. 7B illustrates an overview of a model system with recirculation after every 5th section, and Fig. 7C illustrates an overview of a model system with recirculation after every section.

[0020] Figs. 8A-16B are charts showing chemical concentrations within a full scale system (Figs. 8A, 9A, 10A, 11 A, 12A, 13A, 14A, 15A and 16A) as compared to a scaled down model of the application with recirculation as shown in Fig. 7C (Figs. 8B, 9B, 10B, 11B, 12B, 13B, 14B, 15B and 16B).DETAILED DESCRIPTION OF EMBODIMENTS

[0021] It will be readily understood that the components of the embodiments, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations in addition to the described example embodiments. Thus, the following more detailed description of the example embodiments, as represented in the figures, is not intended to limit the scope of the embodiments, as claimed, but is merely representative of example embodiments.

[0022] Reference throughout this specification to “one embodiment” or “an embodiment” (or the like) means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” or the like in various places throughout this specification are not necessarily all referring to the same embodiment.

[0023] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments. One skilled in the relevant art will recognize, however, that the various embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, et cetera. In other instances, well-known structures, materials, or operations are not shown or described in detail. The following description is intended only by way of example, and simply illustrates certain example embodiments.

[0024] Described herein is an apparatus functioning as a scaled down emulator of a full- scale piping system, in which the apparatus comprises at least one module, a liquid feed line including a pump to feed liquid into the module, at least one chemical dosing inlet to feed a chemical into the module, and an effluent collector to collect liquid exiting the module. Each module is comprised of at least one line through which the liquid is able to flow, the line comprising a line inlet and a line outlet, the line inlet receiving the liquid, a recirculation line associated with the at least one line, the recirculation line capable of feeding at least some of the liquid back through the line prior to leaving the line via the line outlet, and a recirculation pump for each recirculation line.

[0025] Also described is a method of setting up an apparatus to emulate reactive flowing fluid in a pipe, wherein the apparatus comprises at least one module, a liquid feed line including a pump to feed liquid into the module, at least one chemical dosing inlet to feed a chemical into the module, and an effluent collector to collect liquid exiting the module. Each module comprises at least one line through which the liquid is able to flow, the line comprising a line inlet and a line outlet, the line inlet receiving the liquid, a recirculation line associated with the at least one line, the recirculation line capable of feeding at least some of the liquid back through the line prior to leaving the line via the line outlet, and a recirculation pump for each recirculation line. The method comprises obtaining information relating to the flow of liquid in a pipe including shear forces at walls within the pipe and residence time of bulk flow in the pipe, and based on the obtained information, setting the number of lines to be open for use in each module.

[0026] Reactive flows are generated when the transport of one or more fluids (single phase or multiphase) is accompanied by physical, chemical, and biochemical reactions within the same fluid phases or across different fluid phases (gas, liquid, solid).

[0027] The apparatus will be further described with reference to the Figures, which are not intended to be to scale.

[0028] Figs. 1 A and IB depict the front and back views of a sample module 10. In the illustrated module, the module includes 15 total lines divided into three groups of 5 lines each. As described further below, a module is not limited to this number of lines and groups, but may include any number of lines and groups as needed. In this regard, the apparatus is readily adaptable to be increased or decreased in size / capacity to mimic a particular full-scale wastewater treatment system, and may include as few as one group with one total line, or asmany lines and groups as needed, and may include multiple modules connected in series, if necessary.

[0029] As shown in Fig. 2, a group 20 of the module includes at least one line 22. Liquid, such as raw wastewater, preferably taken directly from a wastewater system that the apparatus is intended to model, is feed into the module by way of a pump 30 that feeds the liquid into the module via liquid feed line 31. Each group within a module preferably includes an associated pump 30 and liquid feed line 31, although this is not required. The flow rate should be selected based on the volume of the module and the volume of the entire apparatus (obtained connecting multiple modules in series or parallel) in order to control the hydraulic residence time of the liquid in the range of 0.1-10 hours per module, and preferably in the range 0.5-5 hours. For example, an apparatus consisting of ten modules of 1 L volume each, connected in series to simulate a sewer force main of 10-hour residence time, should be fed with a wastewater flowrate of 1 L per hour such that the residence time of each module is 1 hour and the overall residence time of the pilot apparatus is 10 hours.

[0030] The apparatus also includes a chemical feed pump 40 for feeding a desired chemical, if any, into the system at a chemical dosing inlet 46 via a feed valve 45. The type and dosing amount of the chemical can thus be controlled, and the effectiveness of the dosing regimen evaluated using the apparatus.

[0031] Line 22 may be of any appropriate dimension (diameter) without restriction. Pipe diameters of 0.1 to 10 inches or more may be mentioned as examples. The pipes may be fully enclosed or open, for example open on a top side of the pipe so as to be a channel.

[0032] At least one line of the module includes a recirculation line 25 associated therewith, wherein the recirculation line may have a same diameter as the line 22, or may have a smaller or larger diameter. The recirculation line, when valve 65 is open, recirculates at least some of the liquid and chemical within the line back through the line prior to leaving the line via the line outlet 27. Each recirculation line desirably includes a recirculation pump 60 for moving the liquid and chemical through the recirculation line and back into the line. The recirculation line may be closed, for example by closing valve 65, in which case the liquid and chemical moves only through the line and not the recirculation line.

[0033] A group of lines within the module, if present, includes one or more lines, and a group with multiple lines may include both lines with recirculation lines and lines without recirculation lines, as necessary to mimic a full-scale system. A line without a recirculationline can either be designed without a recirculation line, or more easily can be achieved by closing a recirculation valve for that particular line / recirculation line.

[0034] Further, although multiple lines and / or groups may be present in the module, unnecessary lines and / or groups for a given arrangement may be closed off and not used by closing the valve 65.

[0035] In this regard, most wastewater systems can be effectively and accurately mimicked using the apparatus by adjusting the number of groups and / or lines / recirculation lines in use within the apparatus such as shown in Figs. 1 A and IB, to reflect more complex sewer systems where multiple zones within the same sewer exist. For example, a complex sewer system with a major gravity main of five hours residence time, followed by a minor pressurized main of one hour residence time, could be scaled down using five pipes in the top portion of the apparatus (where gravity flow in partially filled pipes can be established, also in presence of oxygen or any other gas phase) and one pipe in the bottom portion of the apparatus (where pressurized flow conditions exists).

[0036] The line and recirculation line together may have any configuration. A simple configuration may have a single loop formed by the line and recirculation line, for example as shown in the simple configuration of a group of four lines in Fig. 3. Alternatively, as shown in Fig. 2, the line and recirculation line may have a multiple stacked back and forth loop configuration. Further, as shown in Fig. 4, the line and recirculation line may each or both have split sub-lines therein, Fig. 4 showing one example configuration in which line 22 is comprised of two sub-lines connected in a loop and the recirculation line 25 includes four sub-lines connected together. In this regard, the line and recirculation line can each have a desired number of connected sub-lines. These different configurations are important in order to match, as closely as possible, the relative proportion of gravity-driven sewer (where aerobic conditions may occur due the presence of atmospheric oxygen) versus pressurized sewer (where the sewer is mostly anaerobic). Moreover, multiple horizontal passes may be needed when the pilot apparatus has to match very long pipe systems where significantly settling would occur.

[0037] A given apparatus may have multiple linked modules therein. Modules may be bypassed similar to lines, and thus here again the overall desired fluid flow for the apparatus to function as a scaled down emulator of a full-scale piping system can be achieved throughselection of the necessary number of modules to include. Modules can be added, removed and / or bypassed in the apparatus as necessary to achieve the desired fluid flow.

[0038] Fig. 5 shows an example system in which an apparatus includes ten modules 10 stacked vertically in a rack 15, the overall system including three such apparatuses. Each module contains a recirculation loop with sampling ports. In this type of stacked system, fluid flowing through a rack may flow from the top down by gravity flow, the system comprising stacked loops in series. In this regard, the lines may be comprised of open pipes, for example channels. Flow between vertically stacked channels, including flow between modules within the rack, may be achieved by vertical piping between the channels and modules, which piping may be located centrally and / or at a low point of a channel. The embodiment of Fig. 5 may be used to, for example, evaluate the performance of performic acid (PF A) as a wastewater disinfectant compared to other liquid chemical disinfectants such as peracetic acid (PAA) and chlorine (as sodium hypochlorite).

[0039] Even with recirculation, a portion of the liquid and chemical within the line will exit the line at line outlet 27. The liquid and chemical exiting the line either proceeds to a next line in series, or to the effluent collector 80 exiting the module.

[0040] In a preferred embodiment, the effluent line outlet is located at a top point of the pipe / recirculation pipe configuration, and a height of the effluent collector is above the apparatus.

[0041] When a group of lines within the module is comprised of multiple lines, the group is desirably comprised of one pump 30 for feeding liquid into the group of lines, at least one chemical dosing inlet 46 for introducing chemical into the group of lines, and one outlet line that feeds liquid and any remaining chemical exiting the group of lines to the effluent collector. The first line in the group includes the inlet to accept feed liquid from liquid feed line 31. The lines are connected in series, with the first line feeding effluent therefrom to the second line, and so on. The last line in the group includes the outlet feeding the effluent to the effluent collector and / or to the next group of lines in the module. If there is a further group of lines in use in the module, some effluent is fed to the effluent collector and the remainder is fed to the inlet of the next group of lines. The last line in the last group of lines feeds the total effluent to the effluent collector.

[0042] For flow between adjacent lines within a group, the connection point may desirably be alternated between the front of the apparatus / module and the rear of the apparatus / module.For example, the connection point (pipe outlet to next pipe inlet) for the first to the second pipes may be at a point located at the front of the apparatus, while the connection point (pipe outlet to next pipe inlet) for the second to the third pipes may be at a point located at the rear of the apparatus. Most preferably, the connection has as close to a straight shape, parallel with the base of the apparatus, as possible in order to avoid produced gas from the system from accumulating within the connection. Gas accumulation within the system may affect pH and performance since the gas may contain oxygen.

[0043] As explained further in Example 1 herein, Buckingham Pi theorem relates to dimensionless groups, and the second pi-group therefrom establishes the Reynolds number of the wastewater flowing through the sewer pipe. This can inform on the number of pipes, groups and modules need to effectively and accurately mimic a full-scale system. ForV*D example, to keep the second pi-group (n2= — ) identical between the pilot apparatus and full-scale, the recirculating flow in the system should be increased proportionally to the reduction in pipe diameter applied to the pilot system (relative to full-scale). That is, a pipe diameter reduced in half (relative to full-scale) imposes an increase in velocity of two times (relative to the full-scale) such that the second pi-groups (i.e., Reynolds number) remains the same. It should be noted, however, that the selection of the pi-groups to be matched between full-scale and the pilot apparatus depends on the questions being investigated. A mixing study may indeed require that the second pi-group is closely matched, as Reynolds number is known to dictate the turbulence regime established in the pipe. On the contrary, a biofilm study may suggest that the pi-group to be matched is rather the one describing the shear effects at the pipe wall, since it is known that the biofilm characteristics strongly depend on that variable. Generalizing the approach, the pi-groups should be used as algebraic equations during the design of the pilot apparatus: first, to determine which pi-groups are important to be matched based on the physics of interest, then to estimate those pi-groups values for the full-scale, and finally solve the system of equations containing the design variables (pipe diameter, pipe length, pipe configuration, recirculation velocity, etc.) for the scaled down apparatus.

[0044] The chemical dosing inlet may be associated with any one or more lines within a group. In the case of a five-line group as shown in Figs. 1 A and IB, each line may include a chemical dosing port, which enables assessment of chemical efficacy in various locationssuch as upstream and downstream. In other embodiments, the chemical dosing port is only utilized for the first, second and / or third lines of the group.

[0045] The module also preferably includes an air bleeding valve 90 with an outlet 70, desirably associated with each line within the module as shown in Figs. 1 A and IB. This allows for avoidance of air intrusion and for release of produced gas within the line(s). Air intrusion can affect the system performance because the system needs to be under anaerobic condition as a wastewater collection system. Also, to maintain the correct pressure within the system, releasing the produced gas is desired, and the air bleeding valve permits appropriate control.

[0046] One or more lines within the module may also include a sampling port 51 for taking and removing a liquid sample from a given line within the module, a flowmeter 53 for monitoring and maintaining proper liquid flow rates within the lines, and a pressure sensor 52 for monitoring pressure within the lines. Further, the overall system, including the pumps, meters, etc., can be connected to a control system including a processor that receives data from meters, and can control the pumps, valves, etc., to adjust the liquid flows and chemical dosing within the system. In this regard, a tubular flowmeter that has a transparent flow indicator so that it is easy to know if the flowmeter works can be used. Alternatively, a clamp-on ultrasonic flow sensor can be used, installed along the exterior of the pipe at any location. The flow reading is not interfered with or underestimated because the sensor uses ultrasonic waves to measure the flow. Pressure sensors can be installed on each line to monitor the pressure change due to flow rate change.

[0047] If desired to operate the system in an automatic mode, this may be achieved by, for example, establishing an events schedule table for the feed pump, recirculation pump and dosing pump, and setting the time for operation for all pumps, speed of recirculation pump and dosing pump flow rate. Recirculation pump speed can be set based on the pump running rate and pipe pressure, depending on the needs. Sensors could also be integrated in the system and utilized to operate the system in automated mode. Such automation could also include optimization algorithms to drive the process towards the most cost-effective operating points. Such algorithms could also include artificial intelligence components and systems.

[0048] The apparatus may be employed as a tool to be used to refine wastewater collection system practices so that treatment capabilities and capacities of the sewer infrastructure complement those of the treatment plant. Examples of such uses include assessing the impactof piping or flow changes, new industrial discharges, or chemical / biological additives. In such instances, the apparatus can be designed in a mobile format where it can be deployed in the sewer system and run continuously using a small slipstream of actual wastewater.The apparatus can also be used in a laboratory setting to develop new treatments or additives that positively impact the biofilm - be that in favoring certain metabolic activities or in removing / hindering / killing the biofilm altogether.

[0049] The apparatus can also be used to study biofilm transformations in non-sewer applications, e.g., industrial process water circuits where conveyance piping supports the growth of biofilms. Of particular relevance is the study of Clean-In-Place techniques deployed in the food and beverage industry. In that case, chemicals such as acids or bases, or oxidants (ozone, hydrogen peroxide, chlorine, permanganate, etc.) could be used. Acids or bases are typically used to clean inorganic pipe fouling by changing the solubility of the inorganic matter deposited at the pipe walls. Similarly, oxidants can be used against organic matter grown at the pipe wall.

[0050] The apparatus and method of using will be further illustrated by way of the following non-limiting Examples.

[0051] Example 1

[0052] This Example illustrates and confirms the function of the apparatus to mimic full- scale wastewater treatment systems.

[0053] Buckingham Pi theorem is the obvious way to drive a dimensionless group from equations 1-3. dCV ■ — = Q ■ Cin— Q. C + r ■ V (1) at r = kvC + kbfAbfC + ksAsC + ksedVsedC (2)Knowing the number of physical variables (9), and the number of physical dimensions (2), 7 dimensionless groups can be constructed from the original variables as shown in the following Error! Reference source not found..Table 1 : dimensionless groups

[0054] The first dimensionless pi-group establishes the relationship between thelength and the diameter of any scaled-down system that could mimic the reference system, while the second pi-group establishes the Reynolds number of the wastewater flowing through the sewer pipe. These two groups cannot be maintained for any scaled-down system unless (1) a velocity change occurs in the scaled-down system, and (2) the hydraulic retention time (HRT) of the scaled-down system is different than that of the actual system. Changing the velocity and / or the HRT will affect the effluent characteristics.

[0055] Buckingham Pi theorem limitations include: (a) scouring velocity is an important factor for the sedimentation accumulation level - changing the wastewater velocity inside the scaled-down model from that of the reference system will change the species production rate from the sedimentation; (b) HRT is a system characteristic, and changing the HRT of the scaled-down system will affect the effluent; and (c) the product! on / depleti on terms are a fluid property, and they cannot be scaled down.

[0056] An objective of the present application is to present a feasible way to scale down actual sewer systems to accelerate innovations and to decrease the costly dosing trials. Fig. 6A represents a full scale reference sewer system to be scaled down to a pilot scale system in Fig. 6B. However, the Buckingham pi theorem requires keeping the Reynolds number inside the pipe of both systems constant, while the HRT must be constant for both systems. The lab-scale system in Fig. 4B fails to satisfy both conditions. To keep the same HRT inside a lab-scale system with shorter length, the flow rate must be decreased. But decreasing the flow rate will change the pipe velocity, which will affect the sedimentation accumulation depending on the scouring velocity value. To maintain both the pipe velocity and the HRT, it has been discovered by the present inventors to add recirculation as shown in Fig. 6C, wherein the feed wastewater and the outlet are constant and equal to Qowhich is calculated to satisfy the HRT condition. The volumetric flow rate inside the lab-scale pipe is Qtot=Qo+Qr where Qris the recirculated flow rate, which is calculated to satisfy the constant pipe velocity condition.

[0057] Example 2

[0058] This Example illustrates a case study based on the Example 1 discussion above.

[0059] Within sewer networks, sulfide tends to be formed mainly in completely filled rising main sections, more prone to septicity than partially filled gravity sections where re-aeration from a gas phase can occur. Therefore, a rising main sewer system will be adopted in this study.

[0060] Fig. 7A shows a schematic diagram of an actual sewer system with a total length LRef= 10000 m, and a diameter of DRef = 0.5 m. The system receives a wastewater flow of QoRef = 200 m3 / hr, giving a flow velocity of VNOm=0.2829 m / s, while the scouring velocity is assumed to be VSco= 0.3048 m / s, leading to sedimentation accumulation. The accumulation of sediment decreases the cross-sectional area to 0.1823 m2, at which the sedimentation build-up is stopped. The system was divided into 3000 CSTR (continuous stirred-tank reactors). The inlet concentration of a chemical species (C) is assumed to be 100 gm / m3, while the depletion rates of C are: kvv = -0.1264 (-Y kbf= -0.03134 2.69(^-) \hjin3h

[0061] With the previously mentioned conditions, the outlet concentration of the species C at the effluent was found to be 1 gm / m3.

[0062] In Fig. 7C, a scaled-down model length was LSD = 2.5 m, and a diameter of DSD = 0.5 m, the species C inlet concentration, and the depletion rate terms remained the same as in the reference model. The flow rate of the wastewater entering the model was QOSD = 0.05 m3 / hr to maintain the same HRT as the reference model. To maintain the tube velocity constant as that of the reference model, a recirculation flow of QRec= 195.95 m3 / hr was recirculated between the outlet of each CSTR to the inlet of the same CSTR as shown in Fig. 7C.

[0063] The time needed for the fresh feed (Qosd) to pass a single CSTR equal the total HRTHRT divided by the number of CSTRs (rg„D), and the time needed for the total flow (QOSD+ I _C S I RQRec) to pass the same CSTR is calculated as:During the period required for the fresh feed (QOSD) to pass one CSTR one time, the total flowz_ > . . > ___zHRT QoSD+ QRec. . . . . ,, . . . .(QOSD+ QRCC) passes the same CSTR ( - = - ) times, hence this factor should beHRTRQC QOSD multiplied by the reaction rate at the wall biofilm, sedimentation surface, and sedimentation volume. The general expression of the change rate of a species (C, g / m3) is defined as:

[0064] In Fig. 7B, the same procedure was adopted but instead of circulating from each CSTR, the circulation occurred between each 5thCSTR to the 1stCSTR in series. TheHRT previous factor ( - ) was also implemented in the general expression of the change rateHRTReC

[0065] To predict the concentration of the effluent of the reference and scaled-down sewer systems, a numerical model was developed for the reactive tracer test using MATLAB. The following Table 2 provides the specifications and concentration predictions of both the reference model and the scaled-down models.Table 2: Specifications and results of both the full scale and the scaled-down models.Note that in the table, common data that is identical for the four simulated scenarios is listed at the beginning of the table.

[0066] Species C concentration vs. time at the NthCSTR for both the reference model and the scaled-down model C are shown in Figs. 8 A (reference model) and 8B (model of Fig. 7C). Species C concentration vs. distance along the pipe for both the reference model and the scaled-down model C are shown Figs. 9A (reference model) and 9B (model of Fig. 7C).

[0067] As seen in Table 1 and Figs. 8 A, 8B, 9 A and 9B, the system with recirculation accurately reflects the actual conditions within the full scale sewer system, including with respect to sedimentation and chemical species concentrations, thus permitting the apparatus of the present application to be used for evaluation of treatments to be applied to the full scale system.

[0068] Example 3

[0069] In Example 2, the change rates of the species kv, kbf, ksand ksedwere considered depletion terms only (-ve), and the inlet and initial concentrations were 100 gm / m3. In this Example, the depletion kv, kbf, ksand ksedare assumed to be production rates (+ve), while the inlet and initial concentrations are assumed to be 1 gm / m3. The following Table 3 provides the specifications and concentration predictions of both the reference model and the scaled-down models with a production change rates.Table 3 - Additional scenarios modeled in the simulations.Note that in the table, common data that is identical for the different scenarios is listed at the beginning of the table.

[0070] Species C concentration vs. time at the NthCSTR for both the reference model and the scaled-down model are shown in Figs. 10A (reference model) and 10B (model of Fig. 7C). Species C concentration vs. distance along the pipe for both the reference model and the scaled-down model are shown Figs. 11 A (reference model) and 1 IB (model of Fig. 7C).

[0071] As seen in Table 2 and Figs. 10A, 10B, 11 A and 1 IB, the system with recirculation accurately reflects the actual conditions within the full scale sewer system, including with respect to sedimentation and chemical species concentrations, thus permitting the apparatusof the present application to be used for evaluation of treatments to be applied to the full scale system.

[0072] Example 4

[0073] High inlet and initial concentration rates (100 gm / m3)

[0074] In this Example, the two change rates of the species kv, and ksare considered depletion terms only (-ve), while the other two change rates kbf and ksedare considered a production rate (+ve). The inlet and initial concentrations will be assumed to be 100 gm / m3. The following Table 4 provides the specifications and concentration predictions of both the reference model and the scaled-down models with a production change rates.Table 4 - Additional scenarios modeled in the simulations.Note that in the table, common data that is identical for the different scenarios is listed at the beginning of the table.

[0075] Species C concentration vs. time at the NthCSTR for both the reference model and the scaled-down model are shown in Figs. 12A (reference model) and 12B (model of Fig. 7C).

[0076] Example 5

[0077] Low inlet and initial concentration rates (1 gm / m3)

[0078] In this Example, the two change rates of the species kv, and ksare considered production terms (+ve), while the other two change rates kbf and ksedare considered a depletion rate (-ve). The inlet and initial concentrations will be assumed to be 1 gm / m3. The following Table 5 provides the specifications and concentration predictions of both the reference model and the scaled-down models with a production change rates.Table 5Note that in the table, common data that is identical for the different scenarios is listed at the beginning of the table.

[0079] Species C concentration vs. time at the NthCSTR for both the reference model and the scaled-down model are shown in Figs. 13 A (reference model) and 13B (model of Fig. 7C).

[0080] Example 6

[0081] Unequal reaction rates

[0082] In this Example, the contribution of each reaction to the total reaction rate r will be different, however each reaction can decrease an inlet concentration of 100 gm / m3to 75% ifit was the only reaction considered. The values of kv, kbf, ksand ksedare 0.03156 (1 / hr.), 0.00752 (1 / hr.m2), 0.02868(l / hr.m2), and 0.6725 (1 / hr.m3), respectively. Assuming an inlet and initial concentration of concentration of 100 gm / m3, the species C concentration vs. time at the NthCSTR for both the reference model and the scaled-down model are shown in Figs. 14A (reference model) and 14B (scaled down model of Fig. 7C).

[0083] Example 7

[0084] Equal reaction rates

[0085] In this Example, the values of the four reaction terms have the same values but with two are depletion and two are production rates as kv, kbf, ksand ksedare -0.025 (1 / hr.), +0.025 (1 / hr.m2), -0.025(l / hr.m2), and +0.025 (1 / hr.m3). Assuming an inlet and initial concentration of concentration of 100 gm / m3. The species C concentration vs. time at the NthCSTR for both the reference model and the scaled-down model are shown in Figs. 15 A (reference model) and 15B (scaled down model of Fig. 7C).

[0086] Example 8

[0087] In this Example, the values of the four reaction terms have the same values but with two are depletion and two are production rates as kv, kbf, ksand ksedare +0.1 (1 / hr.), +0.1 (1 / hr.m2), -0.1 (1 / hr.m2), and -0.1 (1 / hr.m3). Assuming an inlet and initial concentration of concentration of 1 gm / m3. Species C concentration vs. time at the NthCSTR for both the reference model and the scaled-down model C are shown in Figs. 16A (reference model) and 16B (scaled down model of Fig. 7C).

[0088] The foregoing Examples demonstrate that the system with recirculation is adaptable to different systems and conditions, and can accurately reflect the actual conditions within a given full scale sewer system, including with respect to sedimentation and chemical species concentrations, thus permitting the apparatus of the present application to be used for evaluation of treatments.

[0089] The apparatus and system described herein has numerous practical advantages over prior approaches to attempt to scale down and mimic performance of a full scale wastewater treatment system. For example, the scaled down method with recirculation closely mimics an actual size sewer system. The apparatus is easily adaptable to different wastewater treatment systems, and further is readily portable to be deployed in an actual system if necessary. The apparatus maintains the same HRT constant for both the full scale and the scaled down systems. The apparatus also maintains pipe velocity for the scaled down system to be thesame as of the full scale reference model, which thus does not affect the sedimentation accumulation. The apparatus thus allows ready development of appropriate chemical treatments and dosing regimens to maintain the full scale system.

[0090] Examples 9-11 below discuss the experimental observations during biofilm development and H2S (hydrogen sulfide) production at various operating conditions. The biotransformation in the simulated sewer was found to be comparable to a typical forced main in a sewer collection system.

[0091] The system evaluated in Examples 9-11 consists of three simulated sewers (groups) operating in parallel. Each sewer (group) consists of five loops in series with a total volume of 5.5L. The system can be operated at a temperature between 23°C-25°C. The HRT of the system was varied from 9 h to 18 h. The in-pipe flow velocities were maintained at 0.25 and 0.5 m / s using recirculation pumps. Influent-effluent characteristics were routinely monitored to track biofilm development and sulfate reducing bacteria (SRB) activity in the sewer.Spatial sulfide profile was obtained to evaluate the SRB activity distribution along the sewer length. Inline kinetic studies were also conducted to evaluate the sulfide generation rate in the bioactive region of the sewer. Kinetic tests were conducted by adding synthetic sulfate solution into the system via a chemical dosing port and temporal sulfide generation in the system.

[0092] Example 9

[0093] Operating conditions: HRT = 18 hr, temperature = 23°C-25°C, and flow velocity = 0.25 m / s, and the influent is raw waste water.Table 6 - Influent-effluent characteristics (day 1 - day 99)Table 7 - Sulfur profile along sewer pipeTable 8 - Sulfide production rate along sewer pipe

[0094] From the results, the following observations are made. On an average from day 1 to day 99 of the operation, more than 90% influent SO42’S was converted to sulfides (see Table 5). S-balance for group 1, group 2 and group 3 were closed within 15% (1-14.1 / 16.6), 20% (1-13.3 / 16.6), and 22% (1-13 / 16.6) margin of error, respectively (see Table 5). COD balance (on sCOD basis) for group 1, group 2, and group 3 were closed within 22% (l-(74- 51) / (2*14.6)), 25 % (l-(74-52) / (2*14.7)), and 30% (l-(74-55) / (2*15)) margin of error compared to the theoretical chemical oxygen demand (see Table 6). Nitrogen and phosphorus concentrations were found to be mostly conserved throughout the sewer (see Table 6). Table 7 indicates that more than 90% of the influent sulfates are converted to sulfide within the first two loops of the system. As shown in Table 8, SRB activity was found to be highest in loop 1 and the sulfide reducing bacterial activity gradually diminished along pipe length. The sulfide production rate in loop 1 is nearly the double of sulfide production rate in loop 2.

[0095] Example 10

[0096] Operating conditions: HRT = 9 hr, temperature = 23°C-25°C, and flow velocity = 0.25 m / s, and the influent is raw wastewater.Table 9 - Influent-effluent characteristics (day 103 - day 117)Table 10 - Sulfur profile along sewer pipe

[0097] From the results, the following observations are made. The influent SO42S was completely converted to sulfides. On an average, sulfur balance was closed within 5% margin of error. On an average, COD balance (on sCOD basis) was closed within 9% margin of error compared to the theoretical chemical oxygen demand. Similar to Example 9, nitrogen and phosphorus concentrations were conserved in the sewer. Table 10 shows that influent sulfate was completely converted to sulfide within the first two loops.

[0098] Example 11

[0099] Operating conditions: HRT = 9 hr, temperature = 23°C-25°C, and flow velocity = 0.5 m / s, and the influent is raw wastewater (SO42’S concentration was spiked by 16 mg / L to facilitate biofilm development in the downstream pipe).Table 11 - Group 1 - wastewater constituent profile along sewer pipe (day 137 - day 153)**all concentrations in mg / L** as CaCO3***ffCOD-Filtered and flocculated CODTable 12 - Group 2 - wastewater constituent profile along sewer pipe (day 137 - day 153)Table 13 - Group 3 - wastewater constituent profile along sewer pipe (day 137 - day 153)

[0100] From the results, the following observations are made. Increased sulfate concentration in the influent facilitated SRB activity up to loop 3. On an average, sulfur mass balance was closed within 10% margin of error. On an average, alkalinity produced / sulfate-S reduced was found to be 3.3, which is close the theoretical value of 3.2 (see Hao et al., A review of biological sulfate conversions in wastewater treatment, Water Research, 65, 1-21 (2014)). On an average, COD consumed to sulfate reduced was observed to be 2.7 ((339- 251) / 32.5)), which is higher than the theoretical value of 2.0 (again see Hao et al.). From loop 1 to loop 5, approximately 24% VSS reduction was observed. On an average, effluent ammonia-N was increased by about 16%. sCOD and VFA concentration remained mostly unchanged throughout the sewer whereas COD and ffCOD was reduced by 25% and 41% , respectively.

[0101] Examples 9-11 also demonstrate the following. SRB was successfully grown on the biofilm of the sewer pipe using raw wastewater as influent. S, COD, and alkalinity balance are closed within acceptable margin. Both the in-pipe sulfur profile and sulfide generation kinetics confirmed that under the given condition SRB activity is mostly developed in the first 2-3 loops in the system. Given a very high specific surface area of the current system (-240 m2 / m3), SRB activity was primarily developed in the upstream portion of the sewer. Reducing the HRT from 18h to 9h did not have a significant effect on the sulfide generation profile in the sewer. In Example 11, VSS reduction and the higher COD-consumed-to- sulfate-reduced ratio suggests some hydrolysis / sedimentation of the suspended biomass. Overall, the operational performance of the three group system is effectively representative of a full scale sewer system.

Claims

WHAT IS CLAIMED IS:

1. An apparatus comprising at least one module, a liquid feed line including a liquid feed pump to feed liquid into the module, at least one dosing inlet to feed an agent into the module, and an effluent collector to collect liquid exiting the apparatus, wherein each module comprises at least one line through which the liquid is able to flow, the line comprising a line inlet and a line outlet, the line inlet receiving the liquid, a recirculation line associated with the at least one line, the recirculation line capable of feeding at least a portion of the liquid back through the at least one line prior to leaving the at least one line via the line outlet, and a recirculation pump for each recirculation line.

2. The apparatus according to claim 1, wherein the at least one module comprises at least two lines connected in series, connected such that liquid exiting a first of the at least two lines flows to a second of the at least two lines.

3. The apparatus according to claim 2, wherein the at least two lines are fed liquid by a same liquid feed pump.

4. The apparatus according to claim 1, wherein the at least one line includes at least two sub-lines forming a loop.

5. The apparatus according to claim 1, wherein the recirculation line includes at least two sub-lines connected together.

6. The apparatus according to claim 1, wherein the apparatus includes two or more modules connected in series.

7. The apparatus according to claim 6, wherein the apparatus is capable of being adjusted by removing at least one module from the apparatus or bypassing at least one module by closing of the at least one module from flow of the liquid.

8. The apparatus according to claim 1, wherein the recirculation line may be closed off to liquid flow by a valve in the recirculation line.

9. The apparatus according to claim 1, wherein the at least one line includes an air bleeding valve.

10. The apparatus according to claim 1, wherein the number of lines to be open for use in each module is determined by obtaining information relating to a full-scale pipe system including shear forces at walls within the system and residence time of bulk flow in the system, and based on the obtained information, setting the number of lines to be open for use in each module.

11. The apparatus according to claim 10, wherein the apparatus includes more than one module, and the setting the number of lines to be open for use in each module includes setting up the apparatus by removing at least one module from the apparatus or by bypassing at least one module by closing of the at least one module from flow of the liquid.

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