WO2024129837A1

WO2024129837A1 - Reduction of ferrous iron from azole-treated wastewater

Info

Publication number: WO2024129837A1
Application number: PCT/US2023/083800
Authority: WO
Inventors: Alan Knapp; James P. KRIZNER
Original assignee: Evoqua Water Technologies Llc
Priority date: 2022-12-13
Filing date: 2023-12-13
Publication date: 2024-06-20

Abstract

A method of removing iron from a wastewater stream including chemical mechanical polishing wastewater from which an azole compound has been previously removed by a Fenton's reaction. The method comprises adding an iron-containing chemical to the wastewater stream to form an iron-dosed wastewater stream, adjusting a pH of the iron-dosed wastewater stream to a pH at which an iron compound precipitates from the iron-dosed wastewater stream, and performing solid/liquid separation on the pH-adjusted iron-dosed wastewater stream to separate the pH-adjusted iron-dosed wastewater stream into a low iron treated water stream and a high iron waste product including the iron compound.

Description

REDUCTION OF FERROUS IRON FROM AZOLE-TREATED WASTEWATER

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application Serial No. 63/432,341, filed on December 13, 2022 and titled “‘Reduction of Ferrous Iron from Azole- Treated Wastewater/’ the entire disclosure of which is hereby incorporated herein by reference in its entirety for all purposes.

FIELD OF TECHNOLOGY

Aspects and embodiments disclosed herein relate to systems and methods for the reduction of iron from azole-treated chemical-mechanical polishing (CMP) wastewater. The methods disclosed herein provide for the reduction of iron from wastewater caused at least in part by the removal of concentrated azole compounds generated during semiconductor facility operations.

SUMMARY

In accordance w ith one aspect, there is provided a method of removing iron from a wastewater stream including chemical mechanical polishing wastewater from which an azole compound has been previously removed by a Fenton’s reaction. The method comprises adding an iron-containing chemical to the w astew ater stream to form an iron-dosed wastewater stream, adjusting a pH of the iron-dosed wastewater stream to a pH at which an iron compound precipitates from the iron-dosed wastewater stream, and performing solid/liquid separation on the pH-adjusted iron-dosed wastewater stream to separate the pH- adjusted iron-dosed wastewater stream into an iron-treated water stream with an iron concentration less than an iron concentration of the pH-adjusted iron-dosed wastewater stream and a waste product including the iron compound.

In some embodiments, adding the iron-containing chemical to the wastewater stream includes adding one of ferric sulfate or ferric chloride to the wastewater stream.

In some embodiments, adjusting the pH of the iron-dosed w astew ater stream includes adding one of sodium hydroxide or lime to the iron-dosed w astew ater stream.

In some embodiments, performing solid/liquid separation on the pH-adjusted iron- dosed wastewater stream includes performing a filtration operation on the pH-adjusted iron- dosed wastewater stream. In some embodiments, performing the filtration operation on the pH-adjusted iron- dosed wastewater stream includes filtering the pH-adjusted iron-dosed wastewater stream with a membrane filter.

In some embodiments, performing the filtration operation on the pH-adjusted iron- dosed wastewater stream includes filtering the pH-adjusted iron-dosed wastewater stream with one of a microfilter or an ultrafilter.

In some embodiments, performing solid/liquid separation on the pH-adjusted iron- dosed wastewater stream includes treating the pH-adjusted iron-dosed wastewater stream in a gravity -based separation system.

In some embodiments, the method further comprises facilitating solid/liquid separation of the pH-adjusted iron-dosed wastewater stream by adding a flocculant to the pH- adjusted iron-dosed wastewater stream one of upstream of or within the gravity -based separation system.

In some embodiments, The method further comprises facilitating solid/liquid separation of the pH-adjusted iron-dosed wastewater stream by adding a ballasting agent to the pH-adjusted iron-dosed wastewater stream one of upstream of or within the gravity-based separation system.

In some embodiments, adding the ballasting agent to the pH-adjusted iron-dosed wastewater stream one of upstream of or within the gravity-based separation system includes adding magnetite to the pH-adjusted iron-dosed wastewater stream.

In some embodiments, The method further comprises recovering magnetite from solids separated from the pH-adjusted iron-dosed wastewater stream.

In some embodiments, performing solid/liquid separation on the pH-adjusted iron- dosed wastewater stream includes removing silica from the pH-adjusted iron-dosed w astewater stream.

In some embodiments, the method results in the low- iron treated water stream having an iron concentration of less than 2 mg/1.

In some embodiments, the method results in the low iron treated water stream having an iron concentration of less than 0.5 mg/1.

In some embodiments, The method further comprises performing dewatering on the waste product.

In some embodiments, performing the dewatering includes removing water from the waste product in a filter press. In accordance with another aspect, there is provided method of treating chemical mechanical polisher (CMP) wastewater. The method comprises removing an azole compound from the CMP wastewater via a Fenton’s reaction to form a second wastewater stream, adding an iron-containing chemical to the second w astew ater stream to form an iron- dosed wastewater stream, adjusting a pH of the iron-dosed wastewater stream to precipitate an iron compound from the iron-dosed waste ater stream, and separating the pH-adjusted iron-dosed wastewater stream into a treated water stream and a waste product including the iron compound.

In accordance with another aspect, there is provided a system for removing iron from chemical mechanical polishing wastew ater from which an azole compound has been previously removed by a Fenton’s reaction. The system comprises a source of an iron- containing chemical configured to dose the wastewater stream with the iron-containing chemical and produce an iron-dosed w astew ater stream, a source of pH adjustment chemical configured to dose the iron-dosed w astewater stream with a sufficient amount of the pH adjustment chemical to cause an iron compound to precipitate from the iron-dosed wastewater stream, and a solid/liquid separation sub-system configured to separate the pH- adjusted iron-dosed wastewater stream into a treated water stream and a waste product including the iron compound.

In accordance with another aspect, there is provided a method of facilitating removal of iron from chemical mechanical polishing wastewater from which an azole compound has been previously removed by a Fenton’s reaction. The method comprises connecting a source of an iron-containing chemical to one of a vessel or conduit through which the w astew ater passes, the source of the iron-containing chemical configured to dose the wastewater stream with the iron- containing chemical and produce an iron-dosed wastewater stream, connecting a source of pH adjustment chemical to one of a vessel or conduit through w hich the iron- dosed wastewater stream passes, the source of pH adjustment chemical configured to dose the iron-dosed wastewater stream with a sufficient amount of the pH adjustment chemical to cause an iron compound to precipitate from the iron-dosed wastewater stream, and providing a solid/liquid separation sub-system configured to receive the pH-adjusted iron-dosed wastewater stream and separate the pH-adjusted iron-dosed wastewater stream into a treated water stream and a w aste product including the iron compound.

In some embodiments, The method further comprises providing a controller in communication with one of the source of iron-containing chemical or the source of pH adjustment chemical and configured to control an amount of chemical dosed by the one of the source of iron-containing chemical or the source of pH adjustment chemical based upon one or more measured parameters of one or more of the wastewater stream, the iron-dosed wastewater stream, or the pH-adjusted iron-dosed wastewater stream.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawing is not intended to be drawn to scale. In the drawing, each identical or nearly identical component that is illustrated is represented by a like numeral. For purposes of clarity, not even' component may be labeled. In the drawings:

FIG. 1 illustrates an example of a system as disclosed herein.

DETAILED DESCRIPTION

The CMP planarization process involves a polishing comprising an oxidant, and abrasive, complexing agents, and additional additives to remove and/or etch semiconducting wafers during the manufacturing process. The polishing is performed with a polishing pad to remove excess copper from the semiconductor wafers. Silicon, copper, and various trace metals are removed from the silicon structure via the polishing slurry. The polishing slurry is introduced to the silicon wafer on a planarization table in conj unction with polishing pads. Oxidizing agents and etching solutions are introduced to control the removal of material. Ultrapure water (UPW) rinses are generally employed to remove debris from the silicon wafer. UPW from reverse osmosis (RO), demineralized, and polished water may also be used in the semiconductor fabrication facility tools to rinse the silicon wafer.

In some instances, the wastewater from semiconductor fabrication plants or other industrial sources may include high levels of azoles, for example, from about 20 mg/1 up to about 200 mg/1 total azoles or greater, that are used as anticorrosive agents during the wafer planarization and polishing process. The wastewater from these processes may also include heavy metals, additional organic compounds, for example, alcohols, and/or surfactants such as ammonium salts, and inorganic abrasives, such as colloidal silica, all of which should be removed prior to discharge of the wastewater. These additional contaminants may be present at levels from about 0.01 wt% up to about 1 wt%. The wastewater may further have a high background total organic carbon (TOC) concentration, with the total azoles comprising a portion of the TOC. For example, oxidizers such as hydrogen peroxide (H2O2) are generally used to assist in dissolving copper from microchips and may be present in CMP wastewater at concentrations exceeding 1,000 mg/L or 0. 1 wt%. The increase in the degree of integration of modem semiconductor devices has increased the number of fine polishing steps that are carried out per wafer or microchip, thus increasing the volume of CMP wastewater produced requiring treatment.

Azoles are not currently regulated for maximum contaminant levels (MCL) by regulatory authorities in the United States but are believed to have a negative impact on the environment upon discharge into open waterways. Recent evidence has indicated bioaccumulation of azoles in fish and incidences of toxicity of naturally occurring algae blooms, necessitating their removal from process water before discharge.

As described in US 8,801,937, the disclosure of which is herein incorporated by reference in its entirety for all purposes, azole compounds are widely used in the semiconductor industry as anticorrosive agents 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 azole derivatives include compounds having a fused ring of an azole ring and a benzene ring or the like, such as indazole, benzimidazole, benzotriazole, and benzothiazole, and further include derivatives thereof, such as alkylbenzotriazoles (e.g., benzotriazole, o-tolyltriazole, m-tolyl tri azole, -tolvltnazole. 5-ethylbenzotriazole. 5-n- propylbenzotriazole, 5 -isobutylbenzotri azole, and 4-methylbenzotriazole), alkoxy benzotriazoles (e.g., 5-methoxybenzotriazole), alkylaminobenzotriazoles, alkylaminosulfonylbenzotriazoles, mercaptobenzotriazoles, hydroxybenzotriazoles, nitrobenzotriazoles (e.g.. 4-nitrobenzotriazole), halobenzotriazoles (e g., 5- chlorobenzotriazole), hydroxyalkylbenzotriazoles, hydrobenzotriazoles, aminobenzotriazoles, (substituted aminomethyl)-tolyltriazole, carboxybenzotriazole, N-alkylbenzotriazoles, bisbenzotriazole, naphthotriazole, mercaptobenzothiazoles, aminobenzothiazole, amine salts thereof, and metal salts thereof.

Azoles have high chemical stability and are thus difficult to remove from solution and, furthermore, are not easily biodegraded. In conventional wastewater treatments for azole-containing anticorrosive agents, the azole compounds are decomposed using an oxidizing agent having a high oxidizing power, such as ozone (O₃), ultraviolet (UV) light, hydrogen peroxide, or an advanced oxidation process where these oxidants are combined to treat collected wastewater. The conventional processes for azole removal have several drawbacks due to the high chemical stability of the azole compounds. For example, for any of the conventional methods described above, large amounts of chemicals are required for the decomposition reactions, thus increasing the costs of treatment.

US 2022/0298045, the disclosure of which is herein incorporated by reference in its entirety for all purposes, details a number of methods for treating CMP wastewater for azoles. However, while the disclosed methods effectively treat the wastewater for azoles, the measures to reduce azole concentration may also introduce ferrous iron in the form of, e.g., ferrous sulfate, into the wastewater. Elevated levels of ferrous iron in wastewater are also undesirable, so methods to reduce iron concentrations are also desired. Below are various methods for reducing iron concentrations in post-azole treated wastewater in accordance with aspects of the present disclosure.

As noted above, iron is added as a treatment chemical in the azole treatment process. In some embodiments, the treatment limit for the iron is expected to be in the low single digit (mg/1) range (e.g., < 2 mg/1). In accordance with the present disclosure, various methods of reducing iron concentrations to acceptable levels are disclosed. One method utilizes a ballasted flocculation system (e.g.. CoMag® from Evoqua Water Technologies LLC, Pittsburgh, PA). Another method in accordance with the present disclosure utilizes microfiltration or ultrafiltration membranes. The effluent limit can be achieved by either method. In some embodiments, the microfilter/ultrafilter may achieve, e.g., < 0.5 mg/1 iron. The ballasted flocculation system may achieve, e.g., 3 mg/1 iron, assuming 5 mg/1 TSS out of the floc. 5 mg/1 TSS contains about 2.5 mg/1 of insoluble iron plus about 0.5 mg/1 of soluble iron totaling about 3 mg/1 of iron in the treated wastewater.

To remove dissolved iron from wastewater one may first treat the wastewater to cause the dissolved iron to precipitate out as solid compounds or flocs which can then be removed by sohd/liquid separation systems such as filtration or gravity separation (e.g., CoMag® gravity separation apparatus from Evoqua Water Technologies LLC, Pittsburgh, PA). The dissolved iron may be precipitated from the wastewater by increasing the pH of the wastewater by the addition of, for example, NaOH, lime, or other suitable chemicals until the pH of the wastewater is at a level at which the iron precipitates as, for example, iron hydroxide. It has been observed that iron in chemical mechanical polishing wastewater from which an azole compound has been previously removed by processes including addition of ferrous iron (e.g., Fenton’s reaction) to the wastewater tends not to precipitate as readily as expected with adjustments in pH. Without wishing to be bound to a particular theory’, this may be due to the presence of chelating material in the previously treated chemical mechanical polishing wastewater. It has been discovered that, counterintuitively, the addition of additional ferrous iron in the form of. for example, ferric sulfate or ferric chloride to CMP wastewater from which azole compound(s) have been previously removed as described above enhances the degree to which iron in the previously treated wastewater precipitates. Sufficient iron precipitates from the CMP wastewater after the additional ferrous iron addition such that after precipitation of the iron compounds, the resultant wastewater has a lower iron content than if the additional iron dosage was not performed.

One example of a system and method for the treatment of CMP wastewater is illustrated schematically in FIG. 1. CMP wastewater enters a first vessel/treatment operation 110 in which azoles may be removed from the CMP wastewater, for example, as described in US 2022/0298045. The first vessel/treatment operation 110 used to remove azoles from the CMP wastewater may be a dissolved iron treatment process, such as wastewater treatment system utilizing Fenton chemistry. The Fenton's reagent used for the removal of azoles may be formed by adding about 500 mg/1 to about 3,000 mg/1 of an oxidant, such as hydrogen peroxide or a persulfate salt, to about 50 mg/1 to about 300 mg/1 of a soluble iron compound (e.g.. ferrous (Fe²⁺) sulfate). The Fenton's reactions may also decompose at least a portion of any hydrogen peroxide present in the CPM wastewater prior to the addition of a larger quantity⁷ of hydrogen peroxide or a persulfate. The Fenton's reaction may occur in accordance with chemical equations (l)-(3):

Fe²⁺ + H₂O₂ - Fe³⁺ + HO. + OH (1)

Fe³⁺ + H2O2 Fe²⁺ + HOO. + H⁺ (2)

Fe²⁺ + S₂O_s ² Fe³⁺ + SO4.’ + SO4² (3)

The persulfate salt and the hydroxyl, hydroperoxy!, and persulfate radicals formed by the oxidation of Fe²⁺ or the reduction of Fe³⁺ may react with and decompose the azoles in the CMP wastewater into primarily nitrogen oxides (NO2/NO3), carbon dioxide and water. Without wishing to be bound by any particular theory, the decomposition of a nitrogenous organic molecule, such as an azole, may occur by the reaction illustrated in equation 4:

C_xN_yH_z + OH. CO₂ + NO3 + H₂O (4) In some embodiments, when a dissolved iron compound is used for treating the wastewater comprising azoles, the method may include introducing the dissolved iron compound and an oxidizer to the wastewater at an acidic pH to produce free radicals to decompose the azoles. The pH may be adjusted or maintained at a pH of about 3, such as between 2 and 5, by the addition of an acid, such as sulfuric acid. The oxidizer introduced into the wastewater may include a peroxide, such as hydrogen peroxide, or a persulfate salt such as ammonium persulfate, potassium persulfate, and sodium persulfate, and the invention is not limited by the type of oxidant added as part of the dissolved iron treatment system. As described herein, peroxides produce hydroxyl and hydroperoxyl radicals and persulfates produce persulfate radicals when reacting with the dissolved iron compounds.

During the decomposition of azoles using a dissolved iron treatment system, a byproduct will be formed which comprises an excess of dissolved iron. To remove the dissolved iron, the CMP wastew ater from which the azole compound has been removed may be directed into a mixing vessel 120 in which the pH of the wastewater is adjusted, for example, by the addition of NaOH or lime to a pH at which the precipitation of iron hydroxide occurs, for example, a pH between about 6 and 10 or about 8. As noted above, precipitation of iron hydroxide from the CMP wastew ater from which the azole compound has been removed may be facilitated by the addition of an iron-containing compound such as ferric sulfate or ferric chloride to the CMP waste water to form an iron-dosed wastewater stream. The iron-containing compound and/or pH adjustment agent may be added directly into the mixing vessel 120 and/or into a conduit through which the CMP wastewater flows from the first vessel/treatment operation 110 into the mixing vessel 120. The iron dosing may occur before, after, or concurrent with the pH adjustment. Although mixing vessel 120 is illustrated as a separate unit operation, the mixing vessel may instead be a portion of the conduit 1 15, a static mixer disposed within the conduit 115, or other mixing system known in the art. Responsive to the iron dosing and pH adjustment an iron compound, for example, iron hydroxide will begin to precipitate out of solution.

The pH-adjusted iron-dosed wastewater is then subjected to solid/liquid separation to separate the pH-adjusted iron-dosed wastewater stream into a low iron treated water stream having an iron content of, for example, less than 2 mg/1 or less than 0.5 mg/1, and a high iron waste product including the iron compound (e.g., iron hydroxide). In some embodiments other solids such as slurry residue (e.g., silica) may also be separated from the pH-adjusted iron-dosed wastewater stream in the solid/liquid separation operation. To perform the solid/liquid separation on the pH-adjusted iron-dosed wastewater stream the stream is directed into a solid/liquid separation unit operation 130. In some embodiments, the solid/liquid separation unit operation 130 is or includes a filtration operation. The filtration operation may utilize one or more membrane filtration units, for example, microfiltration or ultrafiltration units such as those available from Evoqua Water Technologies LLC. In other embodiments in addition to or as an alternative to filtration a gravity-based separation system may be utilized to perform the solid/liquid separation operation. To facilitate the solid/liquid separation in the gravity -based separation system one or more flocculants or ballasting agents as known in the art may be added to the pH-adjusted iron-dosed wastewater stream either upstream of or within a vessel used to perform the solid/liquid separation. In some embodiments, the ballast may be or may include magnetite and the solid/liquid separation apparatus may include a CoMag® gravity separation apparatus from Evoqua Water Technologies LLC.

The solids/liquid separation apparatus may separate the pH-adjusted iron-dosed wastewater stream into low iron treated water stream that may be discharged, recycled to the system or wafer factory, or sent for further treatment, and a high iron waste product including the iron compound. The high iron waste product may be sent to a downstream operation 135, for example, a filter press for additional solid/liquid separation or dewatering. Recovered water may be recycled back into the system or wafer factory, discharged to the environment, or sent for further processing. The downstream operation 135 may additionally or alternately include a ballast recovery system, for example, a magnetite recovery system. The ballast recovery system may include a shear mill, a hydrocyclone and/or a rotating drum comprising a fixed array of rare-earth magnets. An example of a magnetic drum that may be utilized in embodiments of the presently disclosed ballast recovery system is disclosed in co-owned PCT application Publication No. WO 2014/088620. titled “MAGNETIC DRUM INLET SLIDE AND SCRAPER BLADE’⁷ which is incorporated herein by reference in its entirety for all purposes.

Aspects and embodiments disclosed herein are also directed to a method of facilitating removal of iron from chemical mechanical polishing wastewater from which an azole compound has been previously removed by a Fenton’s reaction. The method may include connecting a source of an iron-containing chemical (“Iron dosing/pH adjustment” in FIG. 1) to one of a vessel 120 or conduit 115 through which the wastewater passes. The source of the iron-containing chemical is configured to dose the wastewater stream with the iron-containing chemical and produce an iron-dosed wastewater stream. The method may further include connecting a source of pH adjustment chemical (“Iron dosing/pH adjustment” in FIG. 1) to one of a vessel 120 or conduit 115 through which the iron-dosed wastewater stream passes. The source of pH adjustment chemical configured to dose the iron-dosed wastewater stream with a sufficient amount of the pH adjustment chemical to cause an iron compound to precipitate from the iron-dosed wastewater stream. The method may further include providing a solid/liquid separation sub-system 130 configured to receive the pH- adjusted iron-dosed wastewater stream and separate the pH-adjusted iron-dosed wastewater stream into a low iron treated water stream and a high iron waste product including the iron compound.

The method may further include providing a controller in communication with one of the source of iron-containing chemical or the source of pH adjustment chemical and configured to control an amount of chemical dosed by the one of the source of iron- containing chemical or the source of pH adjustment chemical based upon one or more measured parameters of one or more of the wastewater stream, the iron-dosed wastewater stream, or the pH-adjusted iron-dosed wastewater stream. The controller is indicated at 140 in FIG. 1. Sensors S may be disposed in any of the unit operations 110, 120, 130, 135 and may provide the controller 140 with indications of any one or more of pH, temperature, pressure, one or more chemical concentrations, or any other useful property within any of the unit operations of the system. Communication lines between the controller 140 and iron dosing/pH adjustment source(s) are not shown for sake of clarity. The controller 140 may be implemented as a general-purpose computer programmed to perform the functions disclosed herein or a specialized system such as an ASIC or FPGA.

The phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. As used herein, the term “plurality ” refers to tw o or more items or components. The terms “comprising,” “including,” “carrying,” “having,” “containing,” and “involving,” whether in the written description or the claims and the like, are open-ended terms, i.e., to mean “including but not limited to.” Thus, the use of such terms is meant to encompass the items listed thereafter, and equivalents thereof, as well as 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. Use of ordinal terms such as “first,” “second,” “third,” and the like in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

Claims

What is claimed is: CLAIMS

1. A method of removing iron from a wastewater stream including chemical mechanical polishing wastewater from which an azole compound has been previously removed by a Fenton’s reaction, the method comprising: adding an iron-containing chemical to the wastewater stream to form an iron-dosed w astew ater stream; adjusting a pH of the iron-dosed w astew ater stream to a pH at w hich an iron compound precipitates from the iron-dosed wastewater stream; and performing solid/liquid separation on the pH-adjusted iron-dosed wastewater stream to separate the pH-adjusted iron-dosed wastewater stream into an iron-treated water stream with an iron concentration less than an iron concentration of the pH-adjusted iron-dosed wastewater stream and a waste product including the iron compound.

2. The method of claim 1, wherein adding the iron-containing chemical to the wastew ater stream includes adding one of ferric sulfate or ferric chloride to the w astew ater stream.

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

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

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

6. The method of claim 5, w herein performing the filtration operation on the pH- adjusted iron-dosed wastewater stream includes filtering the pH-adjusted iron-dosed wastewater stream with one of a microfilter or an ultrafilter.

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

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

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

10. The method of claim 9, wherein adding the ballasting agent to the pH-adjusted iron- dosed wastewater stream one of upstream of or within the gravity-based separation system includes adding magnetite to the pH-adjusted iron-dosed wastewater stream.

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

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

13. The method of claim 1, resulting in the low iron treated water stream having an iron concentration of less than 2 mg/1.

14. The method of claim 1, resulting in the low iron treated water stream having an iron concentration of less than 0.5 mg/1.

15. The method of claim 1, further comprising performing dewatering on the waste product.

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

17. A method of treating chemical mechanical polisher (CMP) wastewater, the method comprising: removing an azole compound from the CMP wastewater via a Fenton’s reaction to form a second wastewater stream; adding an iron-containing chemical to the second wastewater stream to form an iron- dosed w astewater stream; adjusting a pH of the iron-dosed wastewater stream to precipitate an iron compound from the iron-dosed wastewater stream; and separating the pH-adjusted iron-dosed wastewater stream into a treated water stream and a waste product including the iron compound.

18. A system for removing iron from chemical mechanical polishing wastewater from which an azole compound has been previously removed by a Fenton’s reaction, the system comprising: a source of an iron-containing chemical configured to dose the w astew ater stream with the iron- containing chemical and produce an iron-dosed wastewater stream; a source of pH adjustment chemical configured to dose the iron-dosed wastewater stream with a sufficient amount of the pH adjustment chemical to cause an iron compound to precipitate from the iron-dosed w astew ater stream; and a solid/liquid separation sub-system configured to separate the pH-adjusted iron- dosed wastewater stream into a treated water stream and a waste product including the iron compound.

19. A method of facilitating removal of iron from chemical mechanical polishing wastewater from which an azole compound has been previously removed by a Fenton's reaction, the method comprising: connecting a source of an iron-containing chemical to one of a vessel or conduit through which the wastewater passes, the source of the iron-containing chemical configured to dose the wastewater stream with the iron-containing chemical and produce an iron-dosed wastewater stream: connecting a source of pH adjustment chemical to one of a vessel or conduit through which the iron-dosed wastewater stream passes, the source of pH adjustment chemical configured to dose the iron-dosed wastewater stream with a sufficient amount of the pH adjustment chemical to cause an iron compound to precipitate from the iron-dosed wastewater stream; and providing a solid/liquid separation sub-system configured to receive the pH-adjusted iron-dosed wastewater stream and separate the pH-adjusted iron-dosed wastewater stream into a treated water stream and a waste product including the iron compound.

20. The method of claim 19, further providing a controller in communication with one of the source of iron-containing chemical or the source of pH adjustment chemical and configured to control an amount of chemical dosed by the one of the source of iron- containing chemical or the source of pH adjustment chemical based upon one or more measured parameters of one or more of the wastewater stream, the iron-dosed wastewater stream, or the pH-adjusted iron-dosed wastewater stream.