Reduction of ferrous iron from azole-treated wastewater.

Abstract

The present disclosure provides a method for removing iron from a wastewater stream, including chemical mechanical polishing wastewater from which azole compounds have previously been removed by the Fenton reaction. The method includes adding an iron-containing chemical to the wastewater stream to form an iron-loaded wastewater stream, adjusting the pH of the iron-loaded wastewater stream to a pH that precipitates iron compounds from the iron-loaded wastewater stream, and performing a solid / liquid separation on the pH-adjusted, iron-loaded wastewater stream to separate the pH-adjusted, iron-loaded wastewater stream into a low-iron treated water stream and an iron-rich waste stream containing the iron compounds.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Patent Application No. 63 / 432,341, entitled "Reduction of Ferrous Iron from Azole-Treated Wastewater," filed December 13, 2022, the entire disclosure of which is incorporated herein by reference in its entirety for all purposes.

[0002] (Technical field) Aspects and embodiments disclosed herein relate to systems and methods for removing iron from azole-treated chemical mechanical polishing (CMP) wastewater. The methods disclosed herein provide for the removal of iron from the wastewater, at least in part, by removing concentrated azole compounds produced during semiconductor facility operation. Summary of the Invention

[0003] According to one aspect, a method for removing iron from a wastewater stream comprising chemical mechanical polishing wastewater from which azole compounds have previously been removed by the Fenton reaction is provided. The method includes adding an iron-containing chemical to a wastewater stream to form an iron-loaded wastewater stream; adjusting the pH of the iron-loaded wastewater stream to a pH that precipitates iron compounds from the iron-loaded wastewater stream; and performing solid / liquid separation on the pH-adjusted, iron-loaded wastewater stream to separate the pH-adjusted, iron-loaded wastewater stream into an iron treatment stream having an iron concentration that is lower than the iron concentration of the pH-adjusted, iron-loaded wastewater stream and a waste product containing iron compounds.

[0004] In some embodiments, adding an iron-containing chemical to the wastewater stream comprises adding one of iron sulfate or iron chloride to the wastewater stream.

[0005] In some embodiments, adjusting the pH of the iron-loaded wastewater stream comprises adding one of sodium hydroxide or lime to the iron-loaded wastewater stream.

[0006] In some embodiments, performing a solid / liquid separation on the pH-adjusted, iron-loaded wastewater stream comprises performing a filtration operation on the pH-adjusted, iron-loaded wastewater stream.

[0007] In some embodiments, performing a filtration operation on the pH-adjusted, iron-loaded wastewater stream comprises filtering the pH-adjusted, iron-loaded wastewater stream with a membrane filter.

[0008] In some embodiments, performing a filtration operation on the pH-adjusted, iron-loaded wastewater stream comprises filtering the pH-adjusted, iron-loaded wastewater stream with one of a microfilter or an ultrafilter.

[0009] In some embodiments, performing solid / liquid separation on the pH-adjusted, iron-loaded wastewater stream comprises treating the pH-adjusted, iron-loaded wastewater stream in a gravity separation system.

[0010] In some embodiments, the method further comprises enhancing solid / liquid separation of the pH-adjusted, iron-loaded wastewater stream by adding a flocculant to the pH-adjusted, iron-loaded wastewater stream either upstream of or within the gravity separation system.

[0011] In some embodiments, the method further comprises enhancing solid / liquid separation of the pH-adjusted, iron-loaded wastewater stream by adding a ballast agent to the pH-adjusted, iron-loaded wastewater stream either upstream of or within the gravity separation system.

[0012] In some embodiments, adding a ballasting agent to the pH-adjusted, iron-loaded wastewater stream upstream of or within the gravity separation system comprises adding magnetite to the pH-adjusted, iron-loaded wastewater stream.

[0013] In some embodiments, the method further comprises recovering magnetite from the solids separated from the pH-adjusted, iron-loaded wastewater stream.

[0014] In some embodiments, performing solid / liquid separation on the pH-adjusted, iron-loaded wastewater stream comprises removing silica from the pH-adjusted, iron-loaded wastewater stream.

[0015] In some embodiments, the method results in a low-iron treated water stream having an iron concentration of less than 2 mg / l.

[0016] In some embodiments, the method results in a low-iron treated water stream having an iron concentration of less than 0.5 mg / l.

[0017] In some embodiments, the method further comprises performing dewatering of the waste material.

[0018] In some embodiments, performing dewatering comprises removing water from the waste in a filter press.

[0019] According to another aspect, a method for treating chemical mechanical polisher (CMP) wastewater is provided, the method including removing azole compounds from the CMP wastewater via a Fenton reaction to form a second wastewater stream, adding an iron-containing chemical to the second wastewater stream to form an iron-loaded wastewater stream, adjusting the pH of the iron-loaded wastewater stream to precipitate iron compounds from the iron-loaded wastewater stream, and separating the pH-adjusted iron-loaded wastewater stream into a treated water stream and a waste product containing the iron compounds.

[0020] According to another aspect, a system for removing iron from chemical mechanical polishing wastewater from which azole compounds have previously been removed by the Fenton reaction is provided, comprising: a source of iron-containing chemical configured to dose an iron-containing chemical to a wastewater stream to produce an iron-loaded wastewater stream; a source of pH-adjusting chemical configured to dose a pH-adjusting chemical to the iron-loaded wastewater stream in an amount sufficient to precipitate iron compounds from the iron-loaded wastewater stream; and a solid / liquid separation subsystem configured to separate the pH-adjusted iron-loaded wastewater stream into a treatment water stream and a waste product containing iron compounds.

[0021] According to another aspect, a method for enhancing iron removal from chemical mechanical polishing wastewater from which azole compounds have previously been removed by the Fenton reaction is provided. The method includes connecting a source of iron-containing chemical to one of the vessels or conduits through which the wastewater passes, the source of iron-containing chemical configured to dose the iron-containing chemical to the wastewater stream to produce an iron-loaded wastewater stream, connecting a source of pH-adjusting chemical to one of the vessels or conduits through which the iron-loaded wastewater stream passes, the source of pH-adjusting chemical configured to dose the pH-adjusting chemical to the iron-loaded wastewater stream in an amount sufficient to precipitate iron compounds from the iron-loaded wastewater stream, and providing a solid / liquid separation subsystem configured to receive the pH-adjusted iron-loaded wastewater stream and separate the pH-adjusted iron-loaded wastewater stream into a treated water stream and a waste product containing iron compounds.

[0022] In some embodiments, the method further includes providing a controller in communication with one of the source of iron-containing chemicals or the source of pH-adjusting chemicals and configured to control the amount of chemical added by the source of iron-containing chemicals or the source of pH-adjusting chemicals based on one or more measured parameters of the wastewater stream, the iron-added wastewater stream, or the pH-adjusted iron-added wastewater stream.

[0023] The accompanying drawings are not drawn to scale. In the drawings, each identical or nearly identical component shown is represented by a similar number. Also, for clarity of the drawings, not all components may be labeled. In the drawings: [Brief explanation of the drawings]

[0024] [Figure 1] 1 is an example of a system disclosed herein. DETAILED DESCRIPTION OF THE INVENTION

[0025] The CMP planarization process involves polishing with oxidizers, abrasives, complexing agents, and additional additives to remove and / or etch semiconductor wafers during the manufacturing process. Polishing is performed using a polishing pad to remove excess copper from the semiconductor wafer. Silicon, copper, and various trace metals are removed from the silicon structure via a polishing slurry. The polishing slurry is introduced to the silicon wafer on the planarization table in conjunction with the polishing pad. Oxidizers and etching solutions are introduced to control material removal. Ultrapure water (UPW) rinses are typically used to remove debris from silicon wafers. UPW, such as reverse osmosis (RO) water, demineralized water, and polishing water, can also be used to rinse silicon wafers in semiconductor manufacturing equipment tools.

[0026] In some cases, wastewater from semiconductor fabrication plants or other industrial sources may contain high levels of azoles, such as from about 20 mg / L to about 200 mg / L or more of total azoles, which are used as corrosion inhibitors during wafer planarization and polishing processes. Wastewater from these processes may also contain heavy metals, additional organic compounds such as alcohols, and / or surfactants such as ammonium salts, and inorganic abrasives such as colloidal silica, all of which must be removed before the wastewater is discharged. These additional contaminants may be present at levels of about 0.01% to about 1% by weight. The wastewater may also have high background total organic carbon (TOC) concentrations, with total azoles comprising a portion of the TOC. For example, oxidizers such as hydrogen peroxide (H2O2), commonly used to aid in the dissolution of copper from microchips, may be present in CMP wastewater at concentrations exceeding 1,000 mg / L or 0.1 wt%. The increasing integration density of modern semiconductor devices is increasing the number of micro-polishing steps performed per wafer or microchip, generating an increasing amount of CMP wastewater that requires treatment.

[0027] Although azoles are not currently subject to maximum contaminant levels (MCLs) by U.S. regulatory agencies, they are considered to pose adverse environmental impacts when discharged into open waterways. Recent evidence suggests bioaccumulation of azoles in fish and toxicity due to naturally occurring algal blooms, necessitating their removal from treated waters before discharge.

[0028] As described in U.S. Patent No. 8,801,937, the disclosure of which is incorporated herein by reference in its entirety for all purposes, azole compounds are widely used in the semiconductor industry as corrosion inhibitors for copper during silicon wafer processing. Examples of such azole compounds include, but are not limited to, imidazole, pyrazole, oxazole, isoxazole, thiazole, isothiazole, selenazole, 1,2,3-triazole, 1,2,4-triazole, 1,2,5-oxadiazole, 1,3,4-oxadiazole, 1,2,3-thiadiazole, 1,2,4-thiadiazole, 1,3,4-thiadiazole, tetrazole, 1,2,3,4-thiatriazole, any derivatives thereof, amine salts thereof, and metal salts thereof. Examples of the azole derivative include compounds having a condensed ring of an azole ring and a benzene ring, such as indazole, benzimidazole, benzotriazole, and benzothiazole, and further include alkylbenzotriazoles (e.g., benzotriazole, o-tolyltriazole, m-tolyltriazole, p-tolyltriazole, 5-ethylbenzotriazole, 5-n-propylbenzotriazole, 5-isobutylbenzotriazole, 4-methylbenzotriazole, etc.), alkoxybenzotriazoles (e.g., 5-methoxybenzotriazole, etc.), alkylaminobenzotriazoles, alkylaminosulfonylbenzotriazoles, mercaptobenzotriazole, hydroxybenzotriazole, and nitrobenzotriazoles (e.g., 4-nitrobenzotriazole, etc.). Included are halobenzotriazoles (e.g., 5-chlorobenzotriazole), hydroxyalkylbenzotriazoles, hydrobenzotriazoles, aminobenzotriazoles, (substituted aminomethyl)-tolyltriazoles, carboxybenzotriazoles, N-alkylbenzotriazoles, bisbenzotriazoles, naphthotriazoles, mercaptobenzothiazoles, aminobenzothiazoles, and their derivatives, amine salts, and metal salts.

[0029] Because azoles are chemically stable, they are difficult to remove from solution and are not easily biodegradable. Conventional wastewater treatment of azole-containing corrosion inhibitors involves decomposing azole compounds using highly oxidizing agents such as ozone (O3), ultraviolet light (UV), or hydrogen peroxide, or an advanced oxidation process in which wastewater is treated with a mixture of these oxidizing agents. Due to the high chemical stability of azole compounds, conventional azole removal processes have several drawbacks. For example, all of the above methods require large amounts of chemicals for the decomposition reaction, increasing treatment costs.

[0030] U.S. Patent Application Publication No. 2022 / 0298045, the disclosure of which is incorporated herein by reference in its entirety for all purposes, details several methods for treating CMP wastewater from azoles. However, while the disclosed methods effectively treat the wastewater from azoles, measures to reduce azole concentrations may also introduce ferrous iron into the wastewater, for example, in the form of ferrous sulfate. Because increased ferrous iron concentrations in wastewater are undesirable, methods for reducing iron concentrations are also needed. Below are various methods for reducing iron concentrations in wastewater after azole treatment according to embodiments of the present disclosure.

[0031] As described above, iron is added as a treatment chemical in the azole treatment process. In some embodiments, iron treatment limits are expected to be in the low single-digit (mg / L) range (e.g., less than 2 mg / L). Various methods are disclosed herein for reducing iron concentrations to acceptable levels. One method utilizes a ballasted flocculation system (e.g., CoMag®, manufactured by Evoqua Water Technologies LLC, Pittsburgh, PA). Another method according to the present disclosure utilizes microfiltration or ultrafiltration membranes. Either method may achieve discharge limits. In some embodiments, microfilters / ultrafilters may achieve iron concentrations of less than 0.5 mg / L, for example. A ballasted flocculation system may achieve, for example, 3 mg / L of iron, assuming a total sulfur dioxide release (TSS) of 5 mg / L from the flocculate. A 5 mg / L TSS contains approximately 2.5 mg / L of insoluble iron and approximately 0.5 mg / L of soluble iron, resulting in a total iron concentration in the treated wastewater of approximately 3 mg / L.

[0032] To remove dissolved iron from wastewater, the wastewater can first be treated to precipitate the dissolved iron as a solid compound or flocculate, and then removed using a solid / liquid separation system such as filtration or gravity separation (e.g., CoMag® gravity separator, manufactured by Evoqua Water Technologies LLC, Pittsburgh, Pennsylvania). Dissolved iron can be precipitated from the wastewater by increasing the pH of the wastewater, for example, by adding NaOH, lime, or other suitable chemicals, until the pH is increased to a level at which the iron precipitates, for example, as iron hydroxide. It has been observed that iron in chemical mechanical polishing wastewater from which azole compounds have been previously removed by a process involving the addition of ferrous iron to the wastewater (e.g., the Fenton reaction) tends not to precipitate as readily as expected, even when the pH is adjusted. Without being bound by theory, this may be due to the presence of chelating substances in the pretreated chemical mechanical polishing wastewater. Counterintuitively, it has been discovered that adding additional ferrous iron, for example, in the form of ferrous sulfate or ferrous chloride, to CMP wastewater from which azole compounds have been previously removed as described above enhances the extent of iron precipitation in the pretreated wastewater. After the additional ferrous iron addition, sufficient iron precipitates from the CMP wastewater so that, after precipitation of the iron compounds, the resulting wastewater has a lower iron content than if the additional iron dosage had not been performed.

[0033] An example of a CMP wastewater treatment system and method is shown schematically in FIG. 1. The CMP wastewater enters a first vessel / treatment operation 110, where azoles can be removed from the CMP wastewater, as described, for example, in U.S. Patent Application Publication No. 2022 / 0298045. The first vessel / treatment operation 110 that can be used to remove azoles from the CMP wastewater can be a dissolved iron treatment process, such as a wastewater treatment system utilizing the Fenton reaction. The Fenton reagent used to remove azoles is a mixture of about 500 mg / L to about 3,000 mg / L of an oxidizing agent, such as hydrogen peroxide or persulfate, and about 50 mg / L to about 300 mg / L of a soluble iron compound, such as ferrous sulfate (Fe). 2+)) to form the Fenton reaction. The Fenton reaction can also decompose at least a portion of the hydrogen peroxide present in the CPM wastewater before adding larger amounts of hydrogen peroxide or persulfate. The Fenton reaction proceeds according to the following chemical equations (1)-(3): Fe 2+ +H2O2→Fe 3+ +HO.+OH - Formula (1) Fe 3+ +H2O2→Fe 2+ +HOO.+H + Formula (2) Fe 2+ +S2O8 2- →Fe 3+ +SO4. - +SO4 2- Formula (3)

[0034] Persulfate, and Fe 2+ Oxide of Fe 3+ The hydroxyl radicals, hydroperoxyl radicals, and persulfate radicals formed by the reduction of OH can react with and decompose the azoles in the CMP wastewater, primarily to nitrogen oxides (NO2 / NO3), carbon dioxide, and water. Without wishing to be bound by any particular theory, it is believed that the decomposition of nitrogen-containing organic molecules such as azoles occurs via the reaction shown in Equation 4. C x N y H z +OH.→CO2+NO3+H2O Formula (4)

[0035] In some embodiments, when dissolved iron compounds are used to treat wastewater containing azoles, the method can include introducing the dissolved iron compounds and an oxidizing agent to the wastewater at an acidic pH to generate free radicals for decomposing the azoles. The pH can be adjusted or maintained at about 3, e.g., in the range of 2 to 5, by adding an acid, such as sulfuric acid. The oxidizing agent introduced to the wastewater can include peroxides, such as hydrogen peroxide, or persulfates, such as ammonium persulfate, potassium persulfate, or sodium persulfate; the present invention is not limited by the type of oxidizing agent added as part of the dissolved iron treatment system. As described herein, peroxides react with dissolved iron compounds to generate hydroxyl radicals and hydroperoxyl radicals, and persulfates generate persulfate radicals.

[0036] During the decomposition of azoles using a dissolved iron treatment system, a by-product containing excess dissolved iron is formed. To remove the dissolved iron, the azole-removed CMP wastewater is fed to mixing vessel 120, where the pH of the wastewater is adjusted to a pH at which iron hydroxide precipitation occurs, such as about 6-10 or about 8, by adding, for example, NaOH or lime. As described above, the precipitation of iron hydroxide from the azole-removed CMP wastewater is facilitated by adding an iron-containing compound, such as iron sulfate or iron chloride, to the CMP wastewater to form an iron-loaded wastewater stream. The iron-containing compound and / or pH adjuster can be added directly to mixing vessel 120 and / or to the conduit through which the CMP wastewater flows from first vessel / treatment operation 110 to mixing vessel 120. Iron dosing can occur before, after, or simultaneously with the pH adjustment. While mixing vessel 120 is illustrated as a separate unit operation, the mixing vessel can be part of conduit 115, a static mixer disposed within conduit 115, or other mixing systems known in the art. In response to iron dosing and pH adjustment, iron compounds, such as iron hydroxide, begin to precipitate from solution.

[0037] The pH-adjusted, iron-loaded wastewater is then subjected to solid / liquid separation to separate the pH-adjusted, iron-loaded wastewater stream into a low-iron treated water stream, e.g., having an iron content of less than 2 mg / L or less than 0.5 mg / L, and a high-iron waste stream containing iron compounds (e.g., iron hydroxide). In some embodiments, other solids, such as slurry residues (e.g., silica), may also be separated from the pH-adjusted, iron-loaded wastewater stream in the solid / liquid separation. To perform solid / liquid separation on the pH-adjusted, iron-loaded wastewater stream, the stream is directed to solid / liquid separation unit operation 130. In some embodiments, solid / liquid separation unit operation 130 is or includes a filtration operation. The filtration operation may utilize one or more membrane filtration units, such as microfiltration or ultrafiltration units sold by Evoqua Water Technologies LLC. In other embodiments, a gravity separation system may be used to perform the solid / liquid separation operation in addition to or instead of filtration. To facilitate solid / liquid separation in a gravity separation system, one or more flocculants or ballast agents known in the art may be added to the pH-adjusted, iron-added wastewater stream either upstream of or within the vessel performing the solid / liquid separation. In some embodiments, the ballast may be or include magnetite, and the solid / liquid separator may include a CoMag® gravity separator manufactured by Evoqua Water Technologies LLC.

[0038] The solid / liquid separator can separate the pH-adjusted, iron-loaded wastewater stream into a low-iron treated water stream that can be discharged to the system or wafer factory, recycled, or sent for further processing, and a high-iron waste stream containing iron compounds. The high-iron waste stream can be sent to downstream operations 135, such as a filter press, for additional solid / liquid separation or dewatering. The recovered water can be recycled to the system or wafer factory, discharged to the environment, or sent for further processing. The downstream operations 135 can additionally or alternatively incorporate a ballast recovery system, such as a magnetite recovery system. The ballast recovery system can include a shear crusher, a hydrocyclone, and / or a rotating drum equipped with a fixed array of rare earth magnets. One example of a magnetic drum that may be utilized in embodiments of the ballast recovery system of the present disclosure is disclosed in commonly owned PCT Application Publication No. WO2014 / 088620, entitled "MAGNETIC DRUM INLET SLIDE AND SCRAPER BLADE," which is incorporated herein by reference in its entirety for all purposes.

[0039] Aspects and embodiments disclosed herein also relate to a method for promoting iron removal from chemical mechanical polishing wastewater in which azole compounds have been removed by the Fenton reaction. The method may include connecting a source of iron-containing chemicals ("Iron Dosing / pH Adjustment" in FIG. 1 ) to one of the vessels 120 or conduits 115 through which the wastewater passes. The source of iron-containing chemicals is configured to dose the iron-containing chemicals to the wastewater stream to generate an iron-loaded wastewater stream. The method may further include connecting a source of pH-adjusting chemicals ("Iron Dosing / pH Adjustment" in FIG. 1 ) to one of the vessels 120 or conduits 115 through which the iron-loaded wastewater stream passes. The pH-adjusting chemical source is configured to add a sufficient amount of pH-adjusting chemical to the iron-loaded wastewater stream to precipitate iron compounds from the iron-loaded wastewater stream. The method may further include providing a solid / liquid separation subsystem 130 configured to receive the pH-adjusted, iron-loaded wastewater stream and separate the pH-adjusted, iron-loaded wastewater stream into a low-iron treated water stream and a high-iron waste stream containing iron compounds.

[0040] The method may further include providing a controller in communication with one of the sources of iron-containing chemicals or pH-adjusting chemicals and configured to control the amount of chemical added by one of the sources of iron-containing chemicals or pH-adjusting chemicals based on one or more measured parameters of the wastewater stream, the iron-loaded wastewater stream, or the pH-adjusted iron-loaded wastewater stream. The controller is shown in FIG. 1 at 140. Sensors S may be located in any of the unit operations 110, 120, 130, 135 and may provide the controller 140 with information on one or more of pH, temperature, pressure, one or more chemical concentrations, or other useful characteristics of the unit operations of the system. Communication lines between the controller 140 and the iron-dosing / pH-adjusting sources are not shown for clarity. The controller 140 may be implemented as a general-purpose computer programmed to perform the functions disclosed herein or as a dedicated system such as an ASIC or FPGA.

[0041] The phrases and terms used herein are for purposes of description and not limitation. As used herein, the term "plurality" refers to two or more items or components. The terms "comprise," "include," "carry," "have," "contain," and "comprehensive" are open-ended terms, meaning "including, but not limited to," in the specification or claims. Thus, the use of these terms is intended to encompass the subsequently listed items, their equivalents, and additional items. Only the transitional phrases "consisting of" and "consisting essentially of" are closed or semi-closed transitional phrases, respectively, with respect to the claims. The use of ordinal numbers such as "first," "second," and "third" to modify claim elements in the claims does not, in and of itself, imply that a claim element has priority, precedence, or order over other claim elements, or the chronological order in which method actions are performed. They are merely used as labels to distinguish a claim element having a particular name from another element having the same name (except for the use of ordinal numbers) and are used to distinguish claim elements. [Prior art documents] [Patent documents]

[0042] [Patent Document 1] U.S. Patent No. 8,801,937 [Patent Document 2] US Patent Application Publication No. 2022 / 0298045

Claims

1. adding an iron-containing chemical to the wastewater stream to form an iron-loaded wastewater stream; adjusting the pH of the iron-loaded wastewater stream to a pH that precipitates iron compounds from the iron-loaded wastewater stream; performing a solid / liquid separation on the pH-adjusted, iron-loaded wastewater stream to separate the pH-adjusted, iron-loaded wastewater stream into an iron treatment stream having an iron concentration lower than the iron concentration of the pH-adjusted, iron-loaded wastewater stream and a waste product containing the iron compounds; 1. A method for removing iron from a wastewater stream comprising chemical mechanical polishing wastewater from which azole compounds have previously been removed by a Fenton reaction, comprising:

2. 10. The method of claim 1, wherein the step of adding the iron-containing chemical to the wastewater stream comprises adding one of iron sulfate or iron chloride to the wastewater stream.

3. 10. The method of claim 1, wherein adjusting the pH of the iron-loaded wastewater stream comprises adding one of sodium hydroxide or lime to the iron-loaded wastewater stream.

4. 10. The method of claim 1, wherein performing solid / liquid separation on the pH-adjusted, iron-loaded wastewater stream comprises performing a filtration operation on the pH-adjusted, iron-loaded wastewater stream.

5. 5. The method of claim 4, wherein the step of performing a filtration operation on the pH-adjusted, iron-loaded wastewater stream comprises filtering the pH-adjusted, iron-loaded wastewater stream with a membrane filter.

6. 6. The method of claim 5, wherein the step of performing a filtration operation on the pH-adjusted, iron-loaded wastewater stream comprises filtering the pH-adjusted, iron-loaded wastewater stream with one of a microfilter or an ultrafilter.

7. 10. The method of claim 1, wherein performing solid / liquid separation on the pH-adjusted, iron-loaded wastewater stream comprises treating the pH-adjusted, iron-loaded wastewater stream in a gravity separation system.

8. 8. The method of claim 7, further comprising the step of enhancing solid / liquid separation of the pH-adjusted, iron-loaded wastewater stream by adding a flocculant to the pH-adjusted, iron-loaded wastewater stream one upstream of or within the gravity separation system.

9. 8. The method of claim 7, further comprising the step of facilitating solid / liquid separation of the pH-adjusted, iron-loaded wastewater stream by adding a ballast agent to the pH-adjusted, iron-loaded wastewater stream one upstream of or within the gravity separation system.

10. 10. The method of claim 9, wherein the step of adding a ballast agent to the pH-adjusted, iron-loaded wastewater stream one upstream of or within the gravity separation system comprises adding magnetite to the pH-adjusted, iron-loaded wastewater stream.

11. 11. The method of claim 10, further comprising recovering magnetite from solids separated from the pH-adjusted, iron-loaded wastewater stream.

12. 10. The method of claim 1, wherein performing solid / liquid separation on the pH-adjusted, iron-loaded wastewater stream comprises removing silica from the pH-adjusted, iron-loaded wastewater stream.

13. 10. The method of claim 1, wherein a low-iron treated water stream is obtained having an iron concentration of less than 2 mg / l.

14. 10. The method of claim 1, wherein a low-iron treated water stream is obtained having an iron concentration of less than 0.5 mg / l.

15. The method of claim 1 further comprising the step of performing dewatering on the waste material.

16. 16. The method of claim 15, wherein the step of performing dewatering comprises removing water from the waste in a filter press.

17. 1. A method for treating chemical mechanical polisher (CMP) wastewater, comprising: removing azole compounds from said CMP wastewater via a Fenton reaction to form a second wastewater stream; adding an iron-containing chemical to the second wastewater stream to form an iron-loaded wastewater stream; adjusting the pH of the iron-loaded wastewater stream to precipitate iron compounds from the iron-loaded wastewater stream; separating said pH-adjusted, iron-loaded wastewater stream into a treated water stream and a waste stream containing said iron compounds.

18. a source of iron-containing chemicals configured to dose the wastewater stream with an iron-containing chemical to produce an iron-loaded wastewater stream; a source of pH-adjusting chemical configured to administer a sufficient amount of a pH-adjusting chemical to the iron-loaded wastewater stream to precipitate iron compounds from the iron-loaded wastewater stream; a solid / liquid separation subsystem configured to separate the pH-adjusted, iron-spiked wastewater stream into a treated water stream and a waste product containing said iron compounds; 1. A system for removing iron from chemical mechanical polishing wastewater from which azole compounds have previously been removed by a Fenton reaction, comprising:

19. connecting a source of an iron-containing chemical to one of the vessels or conduits through which the wastewater passes, the source of iron-containing chemical configured to dose the iron-containing chemical into the wastewater stream to produce an iron-loaded wastewater stream; connecting a source of pH-adjusting chemical to one of the vessels or conduits through which the iron-loaded wastewater stream passes, the source of pH-adjusting chemical configured to dose the iron-loaded wastewater stream with a sufficient amount of pH-adjusting chemical to precipitate iron compounds from the iron-loaded wastewater stream; providing a solid / liquid separation subsystem configured to receive the pH-adjusted, iron-loaded wastewater stream and separate the pH-adjusted, iron-loaded wastewater stream into a treated water stream and a waste product containing the iron compounds; A method for enhancing iron removal from chemical mechanical polishing wastewater in which azole compounds have been previously removed by the Fenton reaction.

20. 20. The method of claim 19, further comprising a controller in communication with one of the iron-containing chemical source or the pH-adjusting chemical source and configured to control the amount of chemical added by one of the iron-containing chemical source or the pH-adjusting chemical source based on one or more measured parameters of the wastewater stream, the iron-loaded wastewater stream, or the pH-adjusted iron-loaded wastewater stream.

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