Patent Description:
Various methods for the treatment of wastewater involve biological treatment of the wastewater in aerobic and/or anaerobic treatment units to reduce the total organic content and/or biochemical oxygen demand of the wastewater. The treatment methods may include physical and/or chemical treatment of wastewater in coagulation and/or flocculation units using coagulants and/or polymers to remove organic and/or inorganic contaminants from the wastewater. Various methods of wastewater treatment may also involve the removal of flocculated solids formed by a coagulation/flocculation process from treated wastewater. These forms of biological, physical and/or chemical treatment typically result in the formation of sludge. Sludge may comprise dead bacteria and byproducts of the biological treatment. In some methods, the sludge is removed from the wastewater after undergoing biological, physical, and/or chemical treatment by settling in a settling unit or clarifier. <CIT> describes a method of treating wastewater to remove BOD and ammonium from the wastewater incorporating dual influent lines firstly into an activated sludge system and secondly into a bio contact tank.

Aspects and embodiments are directed to systems and methods for treating wastewater. In accordance with the invention there is provided a system for treating wastewater as claimed in the claims.

In accordance with the invention the digester of the treatment subsystem has an inlet for receiving ballasted WAS and is configured to provide the ballasted and digested WAS to the outlet of the treatment subsystem.

The WAS provided by the solids-liquid separation system is the ballasted WAS received by the inlet of the digester.

In accordance with some embodiments the treatment subsystem further comprises a holding tank positioned upstream from the digester and having an outlet for providing the ballasted WAS to the inlet of the digester. In accordance with some embodiments the holding tank is configured to thicken the ballasted WAS. In accordance with some embodiments the holding tank is in fluid communication with the inlet of the treatment subsystem, and the ballast feed system is configured to feed ballast to the holding tank of the treatment subsystem. In accordance with some embodiments the holding tank is configured to incorporate ballast into the WAS to generate the ballasted WAS.

In accordance with some embodiments the treatment subsystem further comprises a ballast impregnation system in fluid communication with the inlet of the treatment subsystem and positioned upstream from the holding tank, and the ballast feed system is configured to feed ballast to the ballast impregnation system (not claimed).

In accordance with some embodiments the ballast impregnation system is configured to incorporate ballast into the WAS to generate the ballasted WAS and provide the ballasted WAS to an inlet of the holding tank (not claimed).

In accordance with some embodiments the treatment subsystem is configured to receive at least one of a coagulant, a flocculant, and an adsorbent.

In accordance with some embodiments the ballast comprises at least one of a magnetic material and sand. In accordance with some embodiments the magnetic material is magnetite.

In accordance with another aspect of the present disclosure, there is provided a method of treating wastewater as claimed in claims <NUM> to <NUM>.

In accordance with some embodiments the method further comprises passing the ballasted and digested WAS through a ballast recovery system to produce recovered ballast and unballasted digested WAS. In accordance with some embodiments (not claimed)
ballasting one of the WAS and the wastewater with a ballast comprises introducing recovered ballast to the WAS after settling and prior to digesting. In accordance with some embodiments ballasting the WAS comprises introducing the recovered ballast to a ballast impregnation system and impregnating the WAS with the recovered ballast. In accordance with some embodiments the method further comprises thickening the ballasted WAS prior to digestion.

In accordance with another aspect of the present disclosure, there is provided a method of treating wastewater. The method comprises receiving wastewater from a source of wastewater in a biological treatment unit, biologically treating the wastewater in the biological treatment unit to produce a biologically treated wastewater, settling the biologically treated wastewater to generate waste activated sludge (WAS), and ballasting the WAS with a ballast to generate ballasted WAS.

In accordance with some embodiments the method further comprises passing the ballasted WAS to a ballast recovery system to produce recovered ballast. In accordance with some embodiments ballasting the WAS comprises impregnating the WAS with the recovered ballast. In accordance with some embodiments the method further comprises thickening the ballasted WAS prior to passing the ballasted WAS to the ballast recovery system.

One or more further aspects of the present disclosure (not claimed) are directed to a
method of facilitating treatment of wastewater in a wastewater treatment system. The method of facilitating can comprise receiving wastewater from a source of wastewater in a biological treatment unit, biologically treating the wastewater in the biological treatment unit to produce a biologically treated wastewater, settling the biologically treated wastewater to generate waste activated sludge (WAS), providing a ballast feed system configured to deliver ballast to one of the wastewater and the WAS, ballasting the one of the WAS and the wastewater with the delivered ballast to generate ballasted WAS; and digesting at least a portion of the ballasted WAS to produced ballasted and digested WAS.

One or more further aspects of the present disclosure (not claimed) are directed to a
method of facilitating treatment of wastewater in a wastewater treatment system. The method of facilitating can comprise receiving wastewater from a source of wastewater in a biological treatment unit, biologically treating the wastewater in the biological treatment unit to produce a biologically treated wastewater, settling the biologically treated wastewater to generate waste activated sludge (WAS), providing a ballast feed system configured to deliver ballast to the WAS, and ballasting the WAS with the delivered ballast to generate ballasted WAS.

Still other aspects, embodiments, and advantages of these example aspects and embodiments, are discussed in detail below. Moreover, it is to be understood that both the foregoing information and the following detailed description are merely illustrative examples of various aspects and embodiments, and are intended to provide an overview or framework for understanding the nature and character of the claimed aspects and embodiments. Embodiments disclosed herein may be combined with other embodiments, and references to "an embodiment," "an example," "some embodiments," "some examples," "an alternate embodiment," "various embodiments," "one embodiment," "at least one embodiment," "this and other embodiments," "certain embodiments," or the like are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described may be included in at least one embodiment. The appearances of such terms herein are not necessarily all referring to the same embodiment.

For purposes of clarity, not every component may be labelled in every figure. In the figures:.

Municipal or industrial wastewater treatment systems include biological treatment units that produce waste activated sludge (WAS). WAS is typically removed from the treatment process and may undergo further processing. Processes that improve the settling properties of WAS can beneficially impact wastewater treatment plants by reducing the size of solids-liquid separation systems, such as centrifuges or clarifiers, and providing increased efficiency to the system, such as by increasing the flow rate through the separation systems, and reducing transport and/or disposal costs.

The aspects disclosed herein are not limited in their application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. These aspects are capable of assuming other embodiments and of being practiced or of being carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. In particular, acts, components, elements, and features discussed in connection with any one or more embodiments are not intended to be excluded from a similar role in any other embodiments.

Any references to examples, embodiments, components, elements or acts of the systems and methods herein referred to in the singular may also embrace embodiments including a plurality, and any references in plural to any embodiment, component, element or act herein may also embrace embodiments including only a singularity. References in the singular or plural form are not intended to limit the presently disclosed systems or methods, their components, acts, or elements. The use herein of "including," "comprising," "having," "containing," "involving," and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to "or" may be construed as inclusive so that any terms described using "or" may indicate any of a single, more than one, and all of the described terms. In addition, in the event of inconsistent usages of terms between this document and documents incorporated herein by reference, the term usage in the incorporated reference is supplementary to that of this document; for irreconcilable inconsistencies, the term usage in this document controls.

Wastewater treatment facilities often include primary, secondary, and tertiary processes to treat wastewater to remove contaminants, such as suspended solids, biodegradable organics, phosphorus, nitrogen, microbiological contaminants, and the like, to provide a clean effluent.

The first or primary treatment process typically involves mechanically separating large solids and other suspended matter in the wastewater from the less dense solids and liquid in the wastewater. Primary treatment processes are typically done in sedimentation tanks using gravity and provide a primary effluent.

Secondary treatment typically includes biological treatment of the primary effluent. The biological treatment units or vessels used for secondary treatment typically include bacteria that break down components of the wastewater, such as organic components. The biological treatment processes in the biological treatment units or vessels may reduce the total organic content and/or biochemical oxygen demand of the wastewater. Biological treatment processes often result in the formation of floc, which refers to aggregations of suspended particles or solids, and includes biological, physical, and/or chemical floc.

Activated sludge is one type of secondary process that utilizes an aeration tank(s) that contains microorganisms that ingest contaminants in the primary effluent to form biological flocs. Oxygen is typically fed into the aeration tank(s) to promote grown of these biological flocs. The microorganisms of the activated sludge consume and digest suspended and colloidal organic solids by breaking down complex organic molecules into simple waste products that may, in turn, be broken down by other microorganisms. The microorganisms in the aeration tank grow and multiply as allowed by the quantities of air and consumable solids available. The combination of primary effluent, or in some cases raw sewage, and biological flocs is commonly known as "mixed liquor.

Mixed liquor from the aeration tank is directed to a solids-liquid separation system such as a secondary clarifier or secondary sedimentation tank. During the separation process, biological flocs in the mixed liquor are separated from the mixed liquor as settled sludge and the secondary effluent, or "clean" effluent, may be discharged back to the environment or undergo further treatment using tertiary treatment processes. The settled sludge in the secondary clarifier may be recycled back to the aeration tank(s) by a return activated sludge subsystem. The remaining excess sludge is typically wasted from the system to control the population of microorganisms in the mixed liquor, otherwise referred to as mixed liquor suspended solids (MLSS).

The settling vessels or clarifiers of the solids-liquid separation system are used to remove suspended solids, including biological, physical, and/or chemical floc (referred to herein as "floc") and/or sludge from the wastewater subsequent to biological, physical, and/or chemical treatment. Floc may have a density close to that of water (<NUM>/cm<NUM>). Gravitational settling of floc and/or other suspended solids having a density close to that of the medium, for example, water, in which they are entrained will typically occur slowly, if at all. Settling and removal of floc in a settling vessel or clarifier may require a long retention time and therefore the secondary clarifier may be a bottleneck in the wastewater treatment process.

One process which may be used to improve the settling of floc in the solids-liquid separation system such as the secondary clarifier is to impregnate the floc with a weighting agent or ballast that will bond to the floc and form a "ballasted floc. " Impregnating the floc with a ballast will thus cause the floc to settle much more rapidly than it would otherwise settle. Ballasted systems may comprise a ballast reactor tank configured to provide a ballasted effluent and a source of ballast material fluidly connected to the ballast reactor tank. One or more additives may also be introduced to the ballast reactor tank to aid in increasing the specific gravity of the floc. Non-limiting examples of such additives include coagulants, such as ferric sulfates, flocculants, such as anionic polymers, and adsorbents, such as powdered activated carbon (PAC). The addition of ballast, and optionally one or more additives, improves the removal of dissolved, colloidal, particulate, and microbiological solids. The precipitation and enhanced settleability of ballasted solids provides for a more efficient solids-liquid separation system. For example, the clarification step is faster, which allows for smaller separation systems as compared to conventional clarification systems that comprise biological and clarification steps.

A system for treating wastewater in accordance with at least one embodiment is illustrated schematically in <FIG>, indicated generally at <NUM>. The system includes at least one biological reactor <NUM>, a solids-liquid separation system <NUM>, a treatment subsystem <NUM>, and a ballast feed system <NUM>. The wastewater treatment system <NUM> may also include a controller <NUM> for controlling one or more components of the system <NUM>. The wastewater treatment system <NUM> may be configured to treat wastewater from one or more sources of wastewater <NUM>. For instance, the wastewater <NUM> (also referred to herein as "feed wastewater") may be municipal wastewater or industrial wastewater, such as output wastewater from electric power plants, agricultural and food operations, chemical plants, or manufacturing plants.

The biological reactor(s) <NUM> may have an inlet and an outlet. The inlet of the biological reactor <NUM> may be in fluid communication with the source of wastewater <NUM>. The biological reactor <NUM> is configured to treat the wastewater <NUM>, including primary effluent from a primary separation process. For instance, the biological reactor <NUM> may be configured as an aeration tank as described above to biologically treat the wastewater and output a biologically treated wastewater <NUM> through the outlet of the biological reactor. The biological reactor <NUM> may include a source of air or oxygen <NUM> that is introduced to a population of microorganisms for purposes of promoting growth of biological flocs in mixed liquor. The mixed liquor includes a combination of wastewater and biological flocs and resides in the biological reactor <NUM> until a predetermined concentration of mixed liquor suspended solids (MLSS) is achieved. For example, in some instances the concentration of MLSS is about <NUM>/L, although this value may depend on the different factors, such as the application and the size of the facility.

The biological reactor <NUM> may include a source of air <NUM> to introduce oxygen to the microorganisms residing in the reactor. A mixer 176a may also be used in the biological reactor <NUM> for maintaining floc material in suspension. A flocculant <NUM> and/or a coagulant <NUM> may be added to biologically treated wastewater <NUM> exiting the biological reactor <NUM>. For instance, an injection port positioned downstream from the biological reactor <NUM> may be used for injecting a flocculant <NUM> and/or coagulant <NUM> into the biologically treated wastewater <NUM>.

Flocculation may be described as a process of contact and adhesion whereby particles and colloids in liquid such as a water or wastewater form larger-sized clusters of material. The flocculant <NUM> may comprise a material or a chemical that promotes flocculation by causing colloids and particles or other suspended particles in liquids to aggregate, forming a floc. The effect causes particles to cluster together into a floc. The flocculant <NUM> therefore enhances the formation of WAS <NUM> in the solids-liquid separation system <NUM>. Certain polymers may be used as flocculants. For example, polyacrylamides are one non-limiting example of a suitable flocculant that may be used according to one or more embodiments. Anionic polymers may be created by copolymerizing acrylamide with acrylic acid, and cationic polymers may be prepared by copolymerizing acrylamide with a cationic monomer. Modified polyacrylamides are also an example of a polymer that may be used as a flocculant. In one example, the flocculant <NUM> may be an anionic polyacrylamide such as Drewfloc® <NUM> (Ashland Chemical, Boonton, New Jersey).

Coagulation may be described as a process of consolidating particles, such as colloidal solids. A coagulant may include cations or other positively charged molecules, such as cations of aluminum, iron, calcium, and magnesium. The cations are capable of interacting with negatively charged particles and molecules such that barriers to aggregation are reduced. For instance, the coagulant <NUM> may remove phosphorus from the biologically treated wastewater <NUM>. Non-limiting examples of a coagulant <NUM> include bentonite clay, polyaluminum chloride, polyaluminium hydroxychloride, aluminum chloride, aluminum chlorohydrate, aluminum sulfate, ferric chloride, ferric sulfate, and ferrous sulfate monohydrate.

The wastewater treatment system <NUM> also includes a solids-liquid separation system <NUM> positioned downstream from the biological reactor <NUM>. The solids-liquid separation system <NUM> may have an inlet and an outlet. The inlet of the solids-separation system <NUM> is in fluid communication with the outlet of the biological reactor <NUM>. After sufficient treatment in the biological reactor <NUM>, biological treated wastewater <NUM> enters the solids-liquid separation system <NUM>, which is configured to separate the biologically treated wastewater <NUM> into a solids-lean effluent <NUM> and a solids-rich waste activated sludge (WAS) <NUM>. The separation process may include one or more biological, physical, and/or chemical treatment units or vessels, and separation may be accomplished using any one of a variety of methods. The separation mechanism shown in the solids-liquid separation system <NUM> of <FIG> is gravity such that WAS <NUM> collects at the bottom of the solids-liquid separation system <NUM> and solids-lean effluent <NUM> is extracted near or from the top. The solids-separation system <NUM> may further include a scraper <NUM> driven by a motor <NUM>. The scraper <NUM> may facilitate directing WAS into the outlet of the solids-separation system <NUM>. Other devices may also be used to enhance separation in the solids-liquid separation system <NUM> and are within the scope of this disclosure.

A portion of the WAS exiting the solids-separation system <NUM> may be recycled back to the biological reactor <NUM> as return activated sludge (RAS) <NUM>. Fur purposes of simplicity, each of the systems shown in <FIG>, <FIG>, <FIG>, <FIG>, and <FIG> indicate this recycled sludge as RAS <NUM>.

Although the system <NUM> of <FIG> uses gravity as a separation mechanism in solids-liquid separation system <NUM>, other separation mechanisms and systems may also be used. For instance, centrifuges or chemical separation techniques may also be used or applied to aid in separating WAS from the biological treated wastewater <NUM>. Dissolved air flotation (DAF) clarifiers may also be used as a solids-liquid separation system.

The wastewater treatment system <NUM> of <FIG> shows an embodiment where the biological treatment of the wastewater occurs in a separate vessel (i.e., biological reactor <NUM>) than the settling/separation process (i.e., solids-liquid separation system <NUM>). According to another embodiment the biological and settling processes are combined in a single reaction vessel, such as a sequencing batch reactor (SBR).

The wastewater treatment system <NUM> also includes ballast feed system <NUM>. The ballast feed system <NUM> is configured to deliver ballast to one of the biological reactor <NUM> (according to the invention) and the treatment subsystem <NUM> (not claimed and discussed below). Ballasted systems include the addition of a ballast <NUM>, and optionally, a coagulant and/or flocculant (discussed further below) to improve the removal of dissolved, colloidal, particulate, and microbiological solids.

The ballast feed system <NUM> may obtain ballast <NUM> from one or more sources. For instance, recovered ballast <NUM> from ballast recovery system <NUM> (discussed below) may be delivered to the ballast feed system <NUM>. In addition, fresh or raw ballast <NUM> may be delivered and used by the ballast feed system <NUM>. The source of ballast may comprise a powdered ballast, and may be added in dry powdered form (i.e., not be in a liquid). In some embodiments, the ballast <NUM> may be added by an operator or by machinery, such as by a dry feeder.

The ballast <NUM> may be provided in the form of small particles or as a powder. The particle sizes of the powder may be in a range of, for example, from about <NUM> micron to about <NUM> microns in diameter. In some embodiments, the particle size of the powder may be in a range of from about <NUM> micron to about <NUM> microns in diameter. According to one embodiment, the particle size of the powder may be in a range of from about <NUM> micron to about <NUM> microns in diameter, with <NUM>% of the particles having a diameter that is less than <NUM> microns. According to another embodiment, the particle size of the powder may be in a range of from about <NUM> micron to about <NUM> microns in diameter, with <NUM>% of the particles having a diameter that is less than <NUM> microns. According to certain embodiments, the particle size of the ballast <NUM> may be less than about <NUM> microns. In some embodiments, the particle size of the ballast may be less than about <NUM> microns. In one embodiment, the particle size of the ballast <NUM> may be less than about <NUM> microns. In some embodiments, the particle size of the ballast may be between about <NUM> microns to about <NUM> microns, between about <NUM> microns to about <NUM> microns, between about <NUM> microns to about <NUM> microns, between about <NUM> microns to about <NUM> microns, or between about <NUM> micron to about <NUM> microns. Different sizes of ballast may be utilized in different embodiments depending, for example, on the nature and quantity of floc and/or other suspended solids to be removed in a settling process. The benefit of ballast <NUM> is to increase the efficiency of separating liquids from solids which increases the efficiency of the clarification performed in the solids-liquid separation system <NUM> and/or a thickening process performed in the holding tank <NUM> of the treatment subsystem <NUM>.

According to one embodiment, the ballast <NUM> (otherwise referred to herein as a "weighting agent") may comprise a magnetic ballast. The magnetic ballast may comprise an inert material. The magnetic ballast may comprise a ferromagnetic material. The magnetic ballast may comprise iron-containing material. In certain embodiments, the magnetic ballast may comprise an iron oxide material. For example, the magnetic ballast may comprise magnetite. Magnetite has a much higher density, approximately <NUM>/cm<NUM>, than typical floc formed in biological, physical, and/or chemical wastewater treatment methods. Magnetite is a fully oxidized iron ore (Fe<NUM>O<NUM>). Magnetite is inert, does not rust, and does not react or otherwise interfere with chemical or biological floc. Magnetite also does not stick to metal, meaning that while it is attracted to magnets, it does not attach to metal surfaces, such as steel pipes. The magnetic ballast may have a particle size that allows it to bind with biological and chemical flocs to provide enhanced settling or clarification, and allows it to be attracted to a magnet so that it may be separated from the flocs.

According to other embodiments, the ballast <NUM> may comprise sand. Sand ballasted systems may implement larger ballast sizes to effectively recover the ballast. For instance, sand particles may range in size from <NUM> microns to about <NUM> microns. Sand ballast is non-magnetic. Sand ballasted systems and methods may implement the use of cleaning agents to separate the biological solids from the sand particle ballast. The use of a cleaning agent may be related to the large surface area of the sand ballast where bacteria attach to the sand material. Mechanical energy alone (i.e., shearing forces from a vortex flow pattern) may be insufficient for removing biological solids from the surface of the sand particle and chemical methods may be utilized to react with and dissolve chemical bonds present on the surface of the sand particle that bind the sand to the biological solids.

Unlike sand-based ballast that requires growth of biological floc around relatively large-sized sand particles, magnetite ballast is smaller in size (e.g., less than <NUM> microns), allowing for the magnetite particles to impregnate existing biological floc.

In accordance with one embodiment, the use of a magnetic ballast may provide advantages over the use of other types of ballast material, such as sand. For instance, as described further below, a magnetic drum provided in the ballast recovery system <NUM> may be used to separate the biological solids from the magnetic ballast in an efficient manner.

Although magnetite may be utilized as ballast material in some aspects of the present disclosure, these aspects are not limited to the use of magnetite as the ballast <NUM>. Other materials, including sand as discussed above may additionally or alternatively be used as a ballast material. Further materials which may additionally or alternatively be used as ballast materials include any materials which may be attracted to a magnetic field, for example, particles or powders comprising nickel, chromium, iron, and/or various forms of iron oxide. According to one embodiment, the ballast comprises at least one of a magnetic material and sand.

Returning to <FIG>, the ballast feed system <NUM> may include one or more tanks or vessels where the recovered ballast <NUM> is combined with the raw ballast <NUM>. The ballast feed system <NUM> may be equipped with a mixer (not shown) that mixes the ballast material prior to delivering the ballast to the one of the biological reactor <NUM> (according to the invention) and the treatment subsystem <NUM> (not claimed).

In alternative embodiments, the ballast feed system <NUM> may comprise separate conduits that deliver ballast material to the biological reactor <NUM>, an impregnation tank (not claimed and discussed further below) or a holding tank (not claimed and also discussed below). For example, one conduit of the ballast feed system <NUM> may transport fresh ballast <NUM>, and a second conduit of the ballast feed system <NUM> may transport recovered ballast <NUM>. Therefore, the fresh ballast <NUM> and the recovered ballast <NUM> may not be mixed together or otherwise combined prior to being introduced to these other system components. Thus, according to some embodiments, the wastewater treatment system <NUM> does not include a separate vessel used to mix and deliver ballast such as the ballast feed system <NUM>. For instance, raw ballast <NUM> and recovered ballast <NUM> may be delivered to a ballast impregnation system and mixed with WAS <NUM> to form ballasted WAS (not claimed), or ballast may be mixed with mixed liquor from the biological reactor <NUM>, which settles to form ballasted WAS.

According to the invention, the ballast feed system <NUM> delivers ballast to the biological reactor <NUM>, which is shown in further detail in the wastewater treatment system 100a of <FIG>. As described above, the ballast <NUM> mixes and bonds with floc in the mixed liquor of the biological reactor <NUM>, which aids in settling the WAS in the solids-liquid separation system <NUM>. In this type of configuration, the WAS <NUM> exiting the solids-liquid separation system <NUM> of <FIG> is ballasted WAS <NUM>, as shown in <FIG>.

According to some embodiments, the ballasted WAS <NUM> has a concentration of ballast in a range of between zero and about <NUM>/L, or up to about <NUM>% by volume.

At least a portion of the ballasted WAS <NUM> exiting the solids-liquid separation system <NUM> may undergo further treatment in the treatment subsystem <NUM>. The treatment subsystem <NUM> is positioned downstream from the solids-liquid separation system <NUM>. The treatment subsystem <NUM> may perform one or more functions, including improving the settling properties of the ballasted WAS <NUM> and includes one or more subsystems, including a digester <NUM>, and optionally, a holding tank <NUM>, each of which is described in further detail below.

Ballasted WAS not sent to the treatment subsystem <NUM> may be recirculated back and re-introduced to the biological reactor <NUM> as RAS <NUM>, as shown in <FIG>.

According to some embodiments (not claimed), ballasted WAS <NUM> may be introduced to the holding tank <NUM> of the treatment subsystem <NUM> prior to being introduced to the digester <NUM>. The ballasted WAS <NUM> may undergo thickening in the holding tank <NUM> to further concentrate solids of the ballasted WAS <NUM>, and therefore the holding tank <NUM> may be configured to thicken the ballasted WAS <NUM> by increasing the solids content of the ballasted WAS <NUM>. The term "thickening" may refer to any process that increases the concentration of solids present in the holding tank <NUM> by the separation of a portion of the liquid phase of these solids. Thickening therefore results in the removal of water from solids comprising the ballasted WAS <NUM> present in the holding tank <NUM>. According to one embodiment, the holding tank <NUM> thickens the ballasted WAS to less than <NUM>% (by volume) biological solids. In some embodiments, the holding tank <NUM> thickens the ballasted WAS to less than <NUM>% biological solids. These values reflect the exclusion of ballast, and according to one example, the ballasted WAS may be thickened to less than <NUM>% total solids when ballast is taken into consideration.

Thickening may be performed using any one or more techniques, including gravity settling, flotation, and centrifugation. In addition, the holding tank <NUM> may include a mixer and/or be aerated. According to some embodiments, gravity thickening is used as a thickening process whereby the force of gravity is used as the main agent in the settling and thickening process. During the thickening process, a sludge "blanket" will form over a high density underflow of sludge. The high density sludge material of the ballasted WAS <NUM> may be further treated in the digester <NUM> of the treatment subsystem <NUM>. According to one example, the solids content of the ballasted WAS <NUM> entering the holding tank <NUM> is less than <NUM>%, and after thickening, enters the digester <NUM> with a solids content of greater than <NUM>%.

One or more of a flocculant <NUM>, coagulant <NUM>, and/or adsorbent <NUM> may be added to the ballasted WAS <NUM> to enhance thickening. One or more of these materials may be added to the holding tank <NUM>, or may be added to the ballasted WAS <NUM> prior to entering the holding tank <NUM>, either in a separate tank or in-line. For instance, coagulant <NUM> may be added to precipitate phosphorous, thereby reducing the phosphorous from supernatant removed from the process. Flocculant <NUM> may be used to further increase settling to enhance thickening. An adsorbent <NUM>, discussed further below, may optionally be used.

Adsorption may be described as a physical and chemical process of accumulating a substance at the interface between liquid and solids phases. According to some embodiments, the adsorbent <NUM> may be a powdered activated carbon (PAC). PAC is an effective adsorbent because it is a highly porous material and provides a large surface area to which contaminants may adsorb. PAC may have a diameter of less than <NUM> and an apparent density ranging between <NUM> and about <NUM> lbs/ft<NUM> (between about <NUM>/m<NUM> and about <NUM>/m<NUM>). PAC may have a minimum iodine number of <NUM> as specified by AWWA (American Water Works Association) standards.

The holding tank <NUM> is positioned upstream from the digester <NUM> such that the holding tank <NUM> is configured to deliver ballasted WAS <NUM> through an outlet of the holding tank <NUM> to an inlet of the digester <NUM>. The digester <NUM> is configured to digest at least a portion of the ballasted WAS <NUM> to produce ballasted and digested WAS <NUM>. As used herein, the term "digestion" refers to any process that includes microbial breakdown of the solids in the digester <NUM>.

The digestion process functions to enhance the separation of ballast material from the WAS in the ballast recovery system <NUM>, which is positioned downstream from the treatment subsystem <NUM>. The digester <NUM> functions to biologically degrade solids of the ballasted WAS <NUM>. The digestion process enhances settling properties in the digester <NUM> to allow further thickening. Digestion of the ballasted WAS <NUM> offers several advantages to recovery processes of the wastewater treatment system. Ballast that is not recovered as recovered ballast <NUM> may be supplemented with raw ballast <NUM>. Increasing the percentage of recovered ballast <NUM> from the WAS reduces operation costs of the wastewater treatment system <NUM>. According to various aspects, WAS entering the ballast recovery system <NUM> as ballasted and digested WAS <NUM> allows for enhanced recovery of ballast material than a system that does not subject WAS to ballasting and digestion. According to another aspect, ballasting and digesting WAS allows for the system to have enhanced recovery of biosolids than a system that does not include WAS ballasting and digestion.

The digester <NUM> may be configured to implement one or more digestion processes, including anaerobic digestion, aerobic digestion, and facultative digestion. Anaerobic digestion processes typically decompose or otherwise break down organic compounds present in the solids decompose in the absence of oxygen by facultative and anaerobic microorganisms which convert a substantial portion of the stored carbon into methane. In contrast, during aerobic digestion aerobic and facultative microorganisms use oxygen to produce mainly carbon dioxide and water. Therefore, the digester <NUM> may be in in fluid communication with a source of air or oxygen <NUM> for purposes of providing oxygen to aerobic digestion processes.

WAS, including ballasted WAS <NUM> entering the digester <NUM> may have a total dry solids (TS) concentration in a range of about <NUM>-<NUM>% and a volatile solids (VS) concentration in a range of about <NUM>-<NUM>%. According to one example, when ballast is taken into account, the WAS <NUM> entering the digester <NUM> may have a TS concentration in a range of about <NUM>-<NUM>%, and a VS concentration in a range of about <NUM>-<NUM>%. Once the digestion process is complete, the ballasted and digested WAS <NUM> exiting the digester may have similar TS and VS concentration values.

According to another embodiment, ballasted WAS <NUM> exiting the solids-separation system <NUM> of wastewater treatment system 100a may be directly introduced to the digester <NUM> of the treatment subsystem <NUM>. Therefore, a separate holding tank <NUM> may not be used. The ballasted WAS <NUM> undergoes a digestion process as described above before being transferred to the ballast recovery system <NUM> as ballasted and digested WAS <NUM>.

According to another embodiment, the ballast feed system <NUM> delivers ballast to the treatment subsystem <NUM>, which is shown in further detail in the wastewater treatment system 100b of <FIG>. This type of configuration may be performed in systems where ballast is not introduced in any upstream biological or separation processes. WAS <NUM> exiting the solids-liquid separation system <NUM> may therefore not contain any ballast when it enters the treatment subsystem <NUM>. Implementing ballasting systems in upstream or existing biological and separation systems may be expensive or otherwise difficult to perform. The configuration shown in the system 100b of <FIG> allows for municipalities to add ballast to WAS and enhance the thickening of WAS by implementing a ballasting process downstream from a planned or existing biological and separation treatment process.

As discussed above, the treatment subsystem <NUM> is positioned downstream from the solids-separation system <NUM>, and is configured to receive WAS <NUM> from the solids-liquid separation system <NUM>, as discussed above in reference to <FIG>. In addition, the treatment system <NUM> may be configured to receive at least a portion of WAS <NUM>, which is unballasted, from the solids-liquid separation system <NUM>. The portion of WAS <NUM> not sent to the treatment subsystem <NUM> may be recirculated back and re-introduced to the biological reactor <NUM> as RAS <NUM>, as shown in <FIG>.

The treatment subsystem <NUM> may perform one or more functions, including improving the settling properties of WAS <NUM> and includes one or more subsystems, including the digester <NUM> as discussed above, a holding tank <NUM>, and optionally, a ballast impregnation system <NUM>. Each of the ballast impregnation system <NUM>, the holding tank <NUM>, and the digester <NUM> may comprise one or more vessels or tanks, and may be positioned separately from one another to form their respective function, or in some instances, may be combined to perform multiple functions. For instance, according to one embodiment (not claimed), , ballast <NUM> may be introduced to the holding tank <NUM> and mixed with the WAS <NUM> exiting the solids-separation system <NUM> to form ballasted WAS <NUM>. The holding tank <NUM> may therefore be configured to perform the function of the impregnation system <NUM>.

As shown in <FIG>, according to some embodiments, the treatment subsystem <NUM> may include a ballast impregnation system <NUM> (otherwise referred to herein as simply an "impregnation system") where ballast <NUM> is introduced to and mixed with WAS <NUM> to form ballasted WAS <NUM> (not claimed). The impregnation system <NUM> may be in fluid communication with the inlet of the treatment subsystem <NUM> such that at least a portion of the WAS <NUM> exiting the solids-liquid separation system <NUM> enters the impregnation system <NUM>. The impregnation system <NUM> is positioned upstream from the digester <NUM> of the treatment subsystem <NUM> and the holding tank <NUM>. The impregnation system <NUM> may be configured to incorporate ballast <NUM> into the WAS <NUM> to generate ballasted WAS <NUM>. The impregnation system <NUM> may include a mixer 176b that mixes the ballast with the WAS.

According to some embodiments (not claimed), recovered ballast <NUM> and/or raw ballast <NUM> may be introduced directly to the impregnation system <NUM>, and the impregnation system <NUM> is configured to mix the recovered ballast <NUM>, raw ballast <NUM>, and WAS <NUM> together to generate ballasted WAS <NUM>. A separate ballast feed system <NUM> may therefore not be utilized.

Ballasted WAS <NUM> that exits the impregnation system <NUM> is provided to an inlet of the holding tank <NUM>. The ballasted WAS <NUM> may then undergo a thickening process, as described above, before it is transferred to the digester <NUM>, where it is digested to generate ballasted and digested WAS <NUM> that is delivered to the ballast recovery system <NUM>.

According to an alternative embodiment (not claimed), ballast <NUM> is introduced to the holding tank <NUM> of the treatment subsystem <NUM> and the holding tank <NUM> functions to incorporate ballast <NUM> into the WAS <NUM> to generate ballasted WAS <NUM>. In this configuration, the treatment subsystem <NUM> may not include a separate impregnation system <NUM>. The holding tank <NUM> may be in fluid communication with the inlet of the treatment subsystem <NUM> for purposes of receiving WAS <NUM> from the solids-liquid separation system <NUM>, and the ballast feed system <NUM> may be configured to feed or otherwise deliver ballast <NUM> to the holding tank <NUM>. In some instances, and as mentioned above, recovered ballast <NUM> and/or raw ballast <NUM> may be delivered directly to the holding tank <NUM> (not claimed) and the treatment system may not comprise a separate mixing vessel that functions as the ballast feed system <NUM>. The holding tank <NUM> may include a mixer (not shown) used to mix the WAS <NUM> with the ballast material.

According to some embodiments, the ballasted WAS <NUM> generated by the treatment subsystem <NUM> has a concentration of ballast in a range of between zero and about <NUM>/L, or up to about <NUM>% by volume.

According to some embodiments, once the ballasted WAS <NUM> has been generated in the holding tank <NUM>, it may undergo a thickening process, as described above, before it is transferred to the digester <NUM>, where it is digested according to any of the digestion processes as previously described. The ballasted and digested WAS <NUM> is then delivered from the digester <NUM> to the ballast recovery system <NUM>.

One or more of a flocculant <NUM>, coagulant <NUM>, and/or adsorbent <NUM> may be added to WAS <NUM> entering the treatment subsystem <NUM>. One or more of these materials may be added directly to the impregnation system <NUM> and/or the holding tank <NUM>, in line prior to entry of the WAS material into the impregnation system <NUM> and/or the holding tank <NUM>, and/or may be introduced via separated tanks. For instance, according to one embodiment, the WAS <NUM> may be introduced to a coagulant tank, into which a coagulant <NUM> is added. The coagulated effluent may then be introduced to the impregnation system <NUM>, into which the ballast <NUM> is added, and the ballasted effluent may then flow to a flocculant tank, into which a flocculant <NUM> is added. The flocculant effluent may then flow to the holding tank <NUM>. According to another embodiment, a flocculant tank and flocculant <NUM> may not be included. In other embodiments, a coagulant tank and coagulant <NUM> may not be included.

The holding tank <NUM> of systems 100a and 100b shown in <FIG> and <FIG> is positioned upstream from the digester <NUM> such that the holding tank <NUM> is configured to deliver ballasted WAS <NUM> through an outlet of the holding tank <NUM> to an inlet of the digester <NUM>. In some embodiments, the holding tank <NUM> thickens the ballasted WAS <NUM>. The ballasted WAS <NUM> may be delivered to the holding tank <NUM> from the impregnation system <NUM>, or delivered from the solids-liquid separation system <NUM>, or generated within the holding tank itself <NUM> (e.g., by mixing ballast with unballasted WAS such as WAS <NUM>). The ballasted WAS <NUM> may then be introduced to the digester <NUM>.

An alternative embodiment to system 100b of <FIG> is shown as system 100c in <FIG> (not claimed).

This system is similar to system 100b in that WAS <NUM> exiting the solids-liquid separation system <NUM> does not contain ballast when it enters the treatment subsystem <NUM>. In addition, ballast <NUM> may be introduced to the holding tank <NUM> and mixed with the WAS <NUM> exiting the solids-separation system <NUM> to form ballasted WAS <NUM>, and therefore the holding tank <NUM> may be configured to perform the function of the impregnation system <NUM>. In the alternative, as discussed above, the impregnation system <NUM> may be configured to incorporate ballast <NUM> into the WAS <NUM> to generate ballasted WAS <NUM>. The ballasted WAS <NUM> may then be introduced to the holding tank <NUM> to undergo a thickening process, as described above. However, in the configuration of system 100c of <FIG>, the digestion process is optional. Therefore, at least a portion of the ballasted WAS <NUM> may be sent to the ballast recovery system <NUM> without undergoing a digestion process in the digester <NUM>.

Returning to <FIG>, the wastewater treatment system <NUM> may further include a ballast recovery system <NUM>. The ballast recovery system <NUM> may be configured to receive the ballasted and digested WAS <NUM> from an outlet of the treatment subsystem <NUM>. For instance, ballasted and digested WAS <NUM> exiting the digester <NUM> may be introduced to the ballast recovery system <NUM>. The ballast recovery system <NUM> is configured to separate unballasted digested WAS from ballast in the ballasted and digested WAS <NUM>, and to provide recovered ballast <NUM> that is delivered to one of the biological reactor <NUM> and the treatment subsystem <NUM>.

According to an alternative embodiment as shown in <FIG> (not claimed), the ballast recovery system <NUM> is configured to receive ballasted WAS <NUM> from an outlet of the treatment subsystem <NUM>. For instance, ballasted WAS <NUM> exiting the holding tank <NUM> may be introduced to the ballast recovery system <NUM>. The ballast recovery system <NUM> in this instance is configured to separate unballasted WAS from ballast in the ballasted WAS <NUM>, and to provide recovered ballast <NUM> that is delivered to the treatment subsystem <NUM> (such as the holding tank <NUM> or the impregnation system <NUM>).

Recovery of ballast may occur using one or more techniques or devices, including specific gravity or magnetic separation methods that may include but are not limited to magnetic recovery drums, hydrocyclones, magnetic assisted hydrocyclones, classifying selectors, and flux selector columns. Using ballasted and digested WAS (or ballasted WAS) as the input stream to the ballast recovery system <NUM> may allow for several advantages over a substantially similar system that does not include the treatment subsystem <NUM>. For instance, an amount of ballast material recovered by the ballast recovery system <NUM> may be higher than a substantially similar system that does not include the treatment subsystem <NUM> and does not use ballasted and/or digested WAS in the recovery system <NUM>. An additional benefit of ballasting and/or digesting WAS is that more biosolids may be recovered, which means less sludge is wasted than a substantially similar system that does not implement the ballasting and digestion of WAS.

The ballast recovery system <NUM> may also be configured to provide unballasted WAS (<FIG>) or unballasted and digested WAS (<FIG>, <FIG>, <FIG>), both referred to in the figures as <NUM> and also referred to herein as "recovered WAS" to at least one of the biological reactor <NUM> and the treatment subsystem <NUM>, including at least one of the impregnation system <NUM>, holding tank <NUM>, and digester <NUM>. For instance, at least a portion of the recovered WAS <NUM> may be directed to the impregnation system <NUM> for purposes of impregnating floc material in the unballasted digested WAS with ballast. At least a portion of the recovered WAS <NUM> may be introduced to the holding tank <NUM> in instances where the holding tank <NUM> is configured to impregnate the floc material with ballast <NUM>. In addition, at least a portion of the recovered WAS <NUM> may be introduced to the digester <NUM> for purposes of controlling the population of microorganisms in the digester <NUM>. Recirculation of settled solids to at least one of the biological reactor <NUM> and the treatment subsystem further enhances performance and reliability, and allows for additional flexibility for treating and recovering process control during process upsets or start-up processes.

According to some embodiments, at least a portion of the recovered WAS <NUM> may be introduced to the impregnation system <NUM> of either the treatment subsystem <NUM>, or the impregnation system <NUM> discussed below in reference to the biological reactor <NUM> of the system <NUM> shown in <FIG>. The recovered WAS <NUM> contains floc material that can be weighted to form weighted biological floc that aids in separation processes.

Recovered WAS not recirculated to at least one of the biological reactor <NUM> and treatment subsystem <NUM> may exit the system <NUM> as wasted unballasted WAS <NUM> (and when passed through the digester <NUM> of the treatment subsystem <NUM> may also be digested) and sent for further processing and/or to waste. This may be done to control the population of microorganisms in the biological reactor <NUM> and/or treatment subsystem <NUM>. Recirculation of the recovered WAS <NUM> also reduces the amount of wasted unballasted WAS <NUM> that is sent to waste.

In accordance with one embodiment, the use of magnetic ballast may provide advantages over the use of other types of ballast material, such as sand. For instance, a magnetic drum may be included in the ballast recovery system <NUM> that functions to separate the biological solids (i.e., recovered WAS <NUM>) from the magnetic ballast in an efficient manner. According to some embodiments, cleaning solutions are unnecessary in separating ballast from WAS material.

The ballast recovery system <NUM> may include any known apparatus or device(s) for separating ballast from sludge. According to one example, the ballast recovery system <NUM> includes a shear mill as illustrated generally at <NUM> in <FIG> and <FIG>. The shear mill <NUM> shears the ballasted digested WAS to separate the ballast from the sludge. The shear mill <NUM> may includes a rotor <NUM> and stator <NUM>. In operation, the ballasted digested sludge <NUM> enters the shear mill <NUM> and flows in the direction of arrows <NUM> and enters the rotor <NUM> and then the stator <NUM>. The shear mill <NUM> may be designed such that there is a close tolerance between the rotor <NUM> and the stator <NUM>, as shown at <NUM> in <FIG>. The rotor <NUM> is in some embodiments driven at high rotational speeds, for example, greater than about <NUM>,<NUM> rpm to form a mixture of ballast and substantially ballast free obliterated flocs of sludge in area <NUM> (<FIG>) of the shear mill <NUM>. The mixture of ballast and obliterated flocs exits the shear mill <NUM> through conduit <NUM>, as shown by arrows <NUM>. The conduit <NUM>, in some embodiments, leads to a separate subsystem of the ballast recovery system <NUM> that divides the ballast and substantially ballast-free obliterated flocs of sludge into separate streams which are output as recovered ballast <NUM> and recovered WAS <NUM> respectively.

In some embodiments the rotor <NUM> and/or stator <NUM> include slots which function as a centrifugal pump to draw the sludge from above and below rotor <NUM> and stator <NUM>, as shown by paths <NUM> in <FIG>. The rotor and stator then hurl the materials off the slot tips at a very high speed to break the ballasted sludge into the mixture of ballast and obliterated flocs of sludge. For example, the rotor <NUM> may include slots <NUM>, and the stator <NUM> may include slots <NUM>. The slots <NUM> in the rotor <NUM> and/or the slots <NUM> in the stator <NUM> may be designed to increase shear energy to efficiently separate the ballast from the ballast containing sludge. The shear developed by the rotor <NUM> and stator <NUM> may depend on the width of slots <NUM> and <NUM>, the tolerance between the rotor <NUM> and stator <NUM>, and the rotor tip speed. The result is that the shear mill <NUM> provides a shearing effect that effectively and efficiently separates the ballast from the ballasted sludge to facilitate recovery of the ballast.

According to another example, the ballast recovery system <NUM> may use ultrasound as a separation mechanism. For example, the ballast recovery system <NUM> may include one or more ultrasonic transducers. The ultrasonic transducers generate fluctuations of pressure and cavitation in the ballasted and digested WAS <NUM> (or ballasted WAS <NUM>, as in system 100c of <FIG>), which results in microturbulences that produce a shearing effect to create a mixture of ballast and obliterated flocs of sludge to effectively separate the ballast from the recovered WAS <NUM>. The resulting mixture of ballast and obliterated flocs comprising the recovered WAS <NUM> may exit the ultrasonic separator and pass through a separate subsystem of the ballast recovery system <NUM> which divides the recovered ballast and substantially ballast free obliterated flocs of sludge into separate streams which are output as recovered ballast <NUM> and recovered WAS <NUM>, respectively.

According to another example, the ballast recovery system <NUM> may use centrifugal force as a separation mechanism. For instance, in some embodiments the mixture of ballast and obliterated flocs exiting the shear mill <NUM> of <FIG> and <FIG> or the ultrasonic separator described above may be divided into separate streams in a centrifugal separator. The centrifugal separator generates centrifugal force that causes the denser ballast to be separated from the flocs of sludge in the mixture and exit the ballast recovery system as recovered ballast <NUM>. The less dense flocs of sludge exit the ballast recovery system as recovered WAS <NUM>.

According to some embodiments, the ballast recovery system <NUM> may use centrifugal force alone without a shear mill or ultrasonic separation device. According to other embodiments, the ballast recovery system <NUM> may include a shear mill, an ultrasonic separator, and/or a centrifugal separator. Other types of separation devices may be included in the ballast recovery system <NUM>. For instance, the ballast recovery system <NUM> may include a tubular bowl, a chamber bowl, an imperforate basket, a disk stack separator, or other forms of separation systems known by those skilled in the art.

In some embodiments, ballast recovery system <NUM> includes a magnetic drum separator. For example, the mixture of ballast and obliterated flocs of sludge exiting the shear mill <NUM> of <FIG>, or exiting an ultrasonic separator as described above may be divided into separate streams in a magnetic drum separator. One example of a magnetic drum separator is indicated generally at 500A in <FIG>. The magnetic drum separator 500A includes a drum <NUM> in which is disposed a magnet <NUM>. The drum rotates in the direction of arrow <NUM>, clockwise in this example. A mixture of ballast <NUM>, represented by the colored circles in <FIG>, and obliterated flocs of sludge (recovered WAS <NUM>), represented by the empty circles in <FIG>, are introduced to the surface of the rotating drum <NUM> through a conduit or feed ramp <NUM>. The ballast, when comprised of a magnetic material, for example, magnetite, adheres more strongly to the drum <NUM> than the obliterated flocs of sludge due to the presence of the magnet <NUM>. The obliterated flocs of sludge will fall off of the drum, in some examples aided by centripetal force generated by the rotating drum, before the ballast. A division vane <NUM> may separate the recovered ballast <NUM> and obliterated flocs of sludge (recovered WAS <NUM>) into two separate output streams <NUM> (as recovered ballast <NUM>), and <NUM> (as recovered WAS <NUM>), respectively.

In another embodiment of the magnetic separator, indicated generally at 500B in <FIG>, the mixture of ballast and obliterated flocs of sludge is introduced by a conduit or feed ramp <NUM> to a position proximate and to the side of the rotating drum <NUM>. The ballast, when comprised of a magnetic material such as magnetite, adheres to the rotating drum <NUM> due to the presence of the magnet <NUM> and may be removed from the rotating drum on the opposite side from the conduit or feed ramp <NUM> by, for example, a scraper or division vane <NUM>. The obliterated flocs of sludge do not adhere to the rotating drum <NUM> and instead drop from the end of the conduit or feed ramp <NUM>. The result is the production of separate streams <NUM> (as recovered ballast <NUM>) and <NUM> (as recovered WAS <NUM>).

The wastewater treatment system <NUM> may include one or more additional devices that are not explicitly shown in <FIG>. For instance, according to some embodiments, mixing within the treatment subsystem <NUM>, including one or more of the impregnation system <NUM>, holding tank <NUM>, and digester <NUM> may be performed and achieved using one or more methods, including mechanical mixers, diffused air, and jet mixers/aerators. Anoxic and anaerobic treatments in the digester <NUM> may be mixed with either submerged or floating mechanical mixers, and aerobic treatments in the digester <NUM> may be mixed with either fine or coarse bubble aeration, jet aeration, or any combination thereof. For instance, in some instances fine or coarse aeration may be used with mixing. One or more pumps or valves may also be used in the wastewater treatment system <NUM> for moving and routing fluids between components of the system. For instance, a pump may be used to pump sludge between one or more components of the treatment subsystem <NUM>, and a pump may be used to recirculate RAS <NUM> to the biological reactor <NUM>. One or more sensors may also be used in the wastewater treatment system. For instance, sensors may be used to measure one or more physical properties (e.g., TOC) of sludge entering and exiting components of the system, such as the holding tank <NUM>, digester <NUM>, the solids-liquid separation system <NUM>, and/or the biological reactor <NUM>. The controller <NUM> may be in communication with these sensors and use the measured data to control one or more components of the system, such as the rate of entry or exit of fluids entering or exiting a vessel, residence time, etc..

According to at least one embodiment (not claimed), an impregnation system <NUM> may be used for introducing ballast to the biological reactor <NUM>. An example of such a configuration is shown generally at <NUM> in <FIG>. The impregnation system <NUM> functions in a similar manner as the impregnation system discussed above in reference to <FIG>. Recovered ballast <NUM> from the ballast recovery system <NUM> and/or raw ballast <NUM> from a source of raw ballast are introduced to the impregnation system <NUM>. The impregnation system <NUM> mixes mixed liquor <NUM> from the biological reactor <NUM> with the recovered ballast <NUM> and the raw ballast <NUM> (if used), to impregnate the ballast material into flocs, including biological flocs, suspended in the mixed liquor <NUM> to form weighted biological flocs <NUM>, which are then introduced to the biological reactor <NUM>. The impregnation system <NUM> may also include a mixer 176b which provides mixing energy sufficient to impregnate the ballast into the suspended flocs of the mixed liquor <NUM>. One or more additives may also be added to the impregnation system, such as a coagulant, flocculant, and/or adsorbent as previously described.

Returning to <FIG>, controller <NUM> can be configured to receive any one or more input signals and generate one or more drive, output, and control signals to any one or more components of the wastewater treatment systems discussed herein. The controller <NUM> may, for example, receive an indication of a flow rate, a TOC level, or both, of the feed wastewater <NUM>, the WAS (<NUM> or <NUM>) exiting the solids-liquid separation system <NUM> or the treatment subsystem <NUM>, the RAS <NUM>, the ballasted and digested WAS <NUM> exiting the treatment subsystem <NUM>, and/or from another position within the system. The controller <NUM> may generate and transmit a drive signal or otherwise control any of the components of the system, such as the biological reactor <NUM>, the solids-liquid separation system <NUM>, the ballast recovery system <NUM>, the ballast feed system <NUM> (and including the fresh ballast <NUM> and the recovered ballast <NUM>), and/or any of the components of the treatment subsystem <NUM> in response to the input signals. For instance, the controller <NUM> may generate and transmit a drive signal to the ballast feed system <NUM>, including the fresh ballast <NUM> and the recovered ballast <NUM> to, if necessary, adjust the rate of addition of fresh ballast <NUM> and/or recovered ballast <NUM> to the impregnation system <NUM> or the holding tank <NUM> or the biological reactor <NUM>. The drive signal may be based on one or more input signals and a target or predetermined value or set-point. The target value may be application specific and may vary from installation to installation.

At least one further embodiment (not claimed) is directed to one or more methods of facilitating treatment of wastewater in a wastewater treatment system. The method of facilitating may function to enhance the recovery of ballast in a ballasted process and/or to enhance the settling properties of a waste solids. The method may facilitate improved operations of one or more parts or components or subsystems of a pre-existing treatment system. The method may comprise using one or more of the components of the treatment subsystem disclosed herein together with a pre-existing wastewater treatment system. The method may facilitate improvement in operations of a stand-alone treatment system. The disclosure contemplates the modification of existing facilities to retrofit one or more systems or components to implement the techniques of the invention. For example, an existing wastewater treatment system may be modified in accordance with one or more embodiments exemplarily discussed herein utilizing at least some of the preexisting components.

The method of facilitating may comprise receiving wastewater from a source of wastewater in a biological treatment unit, biologically treating the wastewater in the biological treatment unit to produce a biologically treated wastewater, settling the biologically treated wastewater to generate waste activated sludge (WAS), providing a ballast feed system configured to deliver ballast to one of the wastewater and the WAS, ballasting the one of the WAS and the wastewater with the delivered ballast to generate ballasted WAS, and digesting at least a portion of the ballasted WAS to produce ballasted and digested WAS. According to aspects of this example, a ballasted process may implement a treatment subsystem as discussed herein comprising a digester <NUM> and optionally, a holding tank <NUM>.

According to another aspect, the method of facilitating can comprise receiving wastewater from a source of wastewater in a biological treatment unit, biologically treating the wastewater in the biological treatment unit to produce a biologically treated wastewater, settling the biologically treated wastewater to generate waste activated sludge (WAS), providing a ballast feed system configured to deliver ballast to the WAS, and ballasting the WAS with the delivered ballast to generate ballasted WAS. According to aspects of this example, an unballasted process may implement a treatment subsystem as discussed herein comprising a holding tank <NUM>, and optionally an impregnation system <NUM> and/or a digester <NUM>. This configuration allows for existing secondary separation processes that do not use ballast to implement ballast downstream from the secondary clarifier and enhance sludge settling properties.

Claim 1:
A system (<NUM>) for treating wastewater, comprising:
a biological reactor (<NUM>) having an inlet in fluid communication with a source of wastewater (<NUM>) and an outlet, the biological reactor (<NUM>) configured to treat wastewater from the source of wastewater (<NUM>) and output a biologically treated wastewater from the outlet;
a solids-liquid separation system (<NUM>) having an inlet in fluid communication with the outlet of the biological reactor (<NUM>) and configured to separate the biologically treated wastewater into a solids-lean effluent and a solids-rich waste activated sludge (WAS);
a treatment subsystem (<NUM>) comprising a digester (<NUM>), an inlet in fluid communication with a WAS outlet of the solids-liquid separation system (<NUM>), and an outlet for providing ballasted and digested WAS; and
characterised by a ballast feed system (<NUM>) configured to deliver ballast to the biological reactor (<NUM>); and further comprising a ballast recovery system (<NUM>) configured to receive the ballasted and digested WAS (<NUM>) from the outlet of the treatment subsystem (<NUM>).