Reduction of ferrous iron from wastewater treated with azoles

Abstract

A method of removing iron from a wastewater stream that includes chemical mechanical polishing wastewater from which an azole compound has been previously removed by a Fenton reaction. The method includes adding an iron-containing chemical to the wastewater stream to form an iron-dosed wastewater stream, adjusting the pH of the iron-dosed wastewater stream to a pH at which iron compounds precipitate 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 comprising iron compounds.

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority of U.S. Provisional Patent Application 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 by reference in its entirety for all purposes. Technical field

[0003] Aspects and embodiments disclosed herein relate to systems and methods for reducing iron from azole - treated chemical - mechanical polishing (CMP) wastewater. The methods disclosed herein provide for reducing iron from wastewater that is at least partially caused by the removal of concentrated azole compounds generated during the operation of semiconductor facilities.

[0004] Overview

[0005] According to one aspect, a method for removing iron from a wastewater stream is provided, the wastewater stream including chemical - mechanical polishing wastewater from which azole compounds have been previously removed by a Fenton reaction. The method includes adding an iron - containing chemical to the wastewater stream to form an iron - dosed wastewater stream; adjusting the pH of the iron - dosed wastewater stream to a pH at which iron compounds precipitate from the iron - dosed wastewater stream; and performing a 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 and a waste including iron compounds, the iron concentration of the iron - treated water stream being less than the iron concentration of the pH - adjusted iron - dosed wastewater stream.

[0006] In some embodiments, adding an iron - containing chemical to the wastewater stream includes adding one of ferric sulfate or ferric chloride to the wastewater stream.

[0007] In some embodiments, adjusting the pH of the iron - dosed wastewater stream includes adding one of sodium hydroxide or lime to the iron - dosed wastewater stream.

[0008] In some embodiments, performing a solid / liquid separation on the pH - adjusted iron - dosed wastewater stream includes performing a filtration operation on the pH - adjusted iron - dosed wastewater stream.

[0009] In some embodiments, performing a filtration operation on the pH - adjusted iron - dosed wastewater stream includes filtering the pH - adjusted iron - dosed wastewater stream with a membrane filter.

[0010] In some embodiments, filtering the pH-adjusted iron-dosed wastewater stream includes filtering the pH-adjusted iron-dosed wastewater stream with either a microfilter or an ultrafilter.

[0011] In some embodiments, solid / liquid separation of the pH-adjusted iron-dosed wastewater stream includes treating the pH-adjusted iron-dosed wastewater stream in a gravity-based separation system.

[0012] In some embodiments, the method further includes promoting solid / liquid separation of the pH-adjusted iron-dosed wastewater stream by adding a flocculant to the pH-adjusted iron-dosed wastewater stream either upstream of the gravity-based separation system or within the gravity-based separation system.

[0013] In some embodiments, the method further includes promoting solid / liquid separation of the pH-adjusted iron-dosed wastewater stream by adding a ballasting agent to the pH-adjusted iron-dosed wastewater stream either upstream of the gravity-based separation system or within the gravity-based separation system.

[0014] In some embodiments, adding a ballasting agent to the pH-adjusted iron-dosed wastewater stream either upstream of the gravity-based separation system or within the gravity-based separation system includes adding magnetite to the pH-adjusted iron-dosed wastewater stream.

[0015] In some embodiments, the method further includes recovering magnetite from the solids separated from the pH-adjusted iron-dosed wastewater stream.

[0016] In some embodiments, solid / liquid separation of the pH-adjusted iron-dosed wastewater stream includes removing silica from the pH-adjusted iron-dosed wastewater stream.

[0017] In some embodiments, the method produces a low-iron treated water stream having an iron concentration of less than 2 mg / l.

[0018] In some embodiments, the method produces a low-iron treated water stream having an iron concentration of less than 0.5 mg / l.

[0019] In some embodiments, the method further includes dewatering the waste.

[0020] In some embodiments, performing dewatering includes removing water from the waste in a filter press.

[0021] According to another aspect, a method for treating chemical mechanical polishing (CMP) wastewater is provided. The method includes 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-dosed wastewater stream; adjusting the pH of the iron-dosed wastewater stream to precipitate iron compounds from the iron-dosed wastewater stream; and separating the pH-adjusted iron-dosed wastewater stream into a treated water stream and a waste including iron compounds.

[0022] According to another aspect, a system for removing iron from chemical mechanical polishing wastewater is provided, wherein azole compounds have been previously removed from the chemical mechanical polishing wastewater via a Fenton reaction. The system includes: a source of an iron-containing chemical, configured to dose the iron-containing chemical into a wastewater stream and produce an iron-dosed wastewater stream; a source of a pH-adjusting chemical, configured to dose a sufficient amount of the pH-adjusting chemical into the iron-dosed wastewater stream to precipitate iron compounds from the iron-dosed wastewater stream; and a solid / liquid separation system, configured to separate the pH-adjusted iron-dosed wastewater stream into a treated water stream and a waste including iron compounds.

[0023] According to another aspect, a method for facilitating the removal of iron from chemical mechanical polishing wastewater is provided, wherein azole compounds have been previously removed from the chemical mechanical polishing wastewater via a Fenton reaction. The method includes: connecting a source of an iron-containing chemical to one of a container or a conduit through which the wastewater passes, the source of the iron-containing chemical being configured to dose the iron-containing chemical into the wastewater stream and produce an iron-dosed wastewater stream; connecting a source of a pH-adjusting chemical to one of a container or a conduit through which the iron-dosed wastewater stream passes, the source of the pH-adjusting chemical being configured to dose a sufficient amount of the pH-adjusting chemical into the iron-dosed wastewater stream to precipitate iron compounds from the iron-dosed wastewater stream; and providing a solid / liquid separation system, the solid / liquid separation system being 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 including iron compounds.

[0024] In some embodiments, the method further includes providing a controller that communicates with one of the source of the iron-containing chemical or the source of the pH-adjusting chemical and is configured to control the amount of chemical dosed by one of the source of the iron-containing chemical or the source of the pH-adjusting chemical based on 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 Drawings

[0026] The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown is denoted by the same reference numeral. For clarity, not every component may be labeled. In the drawings:

[0027] Figure 1 The figure shows an example of a system as disclosed herein.

[0028] Detailed description

[0029] The CMP planarization process involves polishing, which includes an oxidizing agent, an abrasive, a complexing agent, and additional additives to remove and / or etch a semiconductor wafer during a 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 and the polishing pad are introduced together onto the silicon wafer on a planarization table. An oxidizing agent and an etching solution are introduced to control the removal of materials. Ultra-pure water (UPW) rinsing is typically used to remove debris from the semiconductor wafer. UPW from reverse osmosis (RO), demineralized water, and polishing water can also be used in semiconductor manufacturing equipment tools to rinse the silicon wafer.

[0030] In some cases, wastewater from a semiconductor manufacturing plant or other industrial sources can contain high levels of azoles, such as from about 20 mg / l up to about 200 mg / l of total azoles or more, which are used as preservatives during the wafer planarization and polishing processes. The wastewater from these processes can also contain heavy metals, additional organic compounds, such as alcohols, and / or surfactants, such as ammonium salts, as well as inorganic abrasives, such as colloidal silica, all of which should be removed before the discharge of the wastewater. These additional contaminants can be present at levels from about 0.01 wt% up to about 1 wt%. The wastewater can also have a high background total organic carbon (TOC) concentration, where the total azoles form part of the TOC. For example, an oxidizing agent such as hydrogen peroxide (H 2 O 2 ) is typically used to help dissolve copper from the microchip and can be present in the CMP wastewater at a concentration of more than 1,000 mg / L or 0.1 wt%. The increasing integration of modern semiconductor devices has increased the number of fine polishing steps performed per wafer or microchip, thus increasing the volume of CMP wastewater generated that needs to be treated.

[0031] U.S. regulatory agencies currently do not regulate the maximum contaminant level (MCL) for azoles, but it is believed that azoles have a negative impact on the environment when discharged into open waterways. Recent evidence has indicated the bioaccumulation of azoles in fish and the toxic incidence of naturally occurring algal blooms, which requires their removal from the process water before discharge.

[0032] As described in US 8,801,937, the disclosure of US 8,801,937 is incorporated herein by reference in its entirety for all purposes. Azole compounds are widely used as copper preservatives during silicon wafer processing in the semiconductor industry. 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, their amine salts, and their metal salts. 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 also include their derivatives, such as alkylbenzotriazoles (e.g., benzotriazole, o-tolyltriazole, m-tolyltriazole, p-tolyltriazole, 5-ethylbenzotriazole, 5-n-propylbenzotriazole, 5-isobutylbenzotriazole, and 4-methylbenzotriazole), alkoxybenzotriazoles (e.g., 5-methoxybenzotriazole), alkylaminobenzotriazoles, alkylaminosulfonylbenzotriazoles, mercaptobenzotriazoles, hydroxybenzotriazoles, nitrobenzotriazoles (e.g., 4-nitrobenzotriazole), halogenatedbenzotriazoles (e.g., 5-chlorobenzotriazole), hydroxyalkylbenzotriazoles, hydrobenzotriazoles, aminobenzotriazoles, (substituted aminomethyl)-tolyltriazole, carboxybenzotriazole, N-alkylbenzotriazoles, bisbenzotriazole, naphthotriazole, mercaptobenzothiazoles, aminobenzothiazole, their amine salts, and their metal salts.

[0033] Azoles have high chemical stability and are thus difficult to remove from solution and are additionally not readily biodegradable. In conventional wastewater treatment for azole-containing preservatives, oxidants with high oxidation ability such as ozone (O 3 ), ultraviolet (UV) light, hydrogen peroxide, or advanced oxidation processes are used to decompose azole compounds, where these oxidants are combined to treat the collected wastewater. Due to the high chemical stability of azole compounds, conventional processes for azole removal have several drawbacks. For example, for any of the conventional methods described above, a large amount of chemicals are required for the decomposition reaction, thus increasing the cost of treatment.

[0034] US2022 / 0298045 (the disclosure of which is incorporated herein by reference in its entirety for all purposes) details various methods for treating azoles in CMP wastewater. However, while the disclosed methods effectively treat azoles in the wastewater, measures to reduce the azole concentration can also introduce ferrous iron in the form of, for example, ferrous sulfate into the wastewater. Elevated levels of ferrous iron in the wastewater are also undesirable, and thus methods for reducing the iron concentration are also desired. The following are various methods for reducing the iron concentration in the wastewater after azole treatment according to aspects of the present disclosure.

[0035] As mentioned above, iron is added as a treatment chemical in the azole treatment process. In some embodiments, the treatment limit for iron is expected to be in the low single digits (mg / l) range (e.g., <2 mg / l). According to the present disclosure, various methods for reducing the iron concentration to an acceptable level are disclosed. One method utilizes a ballasted flocculation system (e.g., from Evoqua Water Technologies LLC, Pittsburgh, PA ). Another method according to the present disclosure utilizes a microfiltration membrane or an ultrafiltration membrane. The effluent limit can be achieved by either method. In some embodiments, the microfilter / ultrafilter can achieve, for example, <0.5 mg / l of iron. Assuming a TSS of 5 mg / l in the floc, the ballasted flocculation system can achieve, for example, 3 mg / l of iron. 5 mg / l TSS in the treated wastewater contains approximately 2.5 mg / l of insoluble iron plus approximately 0.5 mg / l of soluble iron, for a total of approximately 3 mg / l of iron.

[0036] To remove dissolved iron from the wastewater, the wastewater can first be treated to precipitate the dissolved iron as a solid compound or floc, and then it can be separated by a solid / liquid separation system such as filtration or gravity separation (e.g., from Evoqua Water Technologies LLC, Pittsburgh, PA A gravity separation device removes solid compounds or flocs. Dissolved iron can be precipitated from wastewater by increasing the pH of the wastewater by adding, for example, NaOH, lime, or other suitable chemicals until the pH of the wastewater is at a level at which iron precipitates as, for example, iron hydroxide. It has been observed that iron in chemical mechanical polishing wastewater from which azole compounds have previously been removed by a process including adding ferrous (e.g., Fenton reaction) to the wastewater tends not to precipitate as readily as expected with the adjustment of pH. Without wishing to be bound by a particular theory, this may be due to the presence of chelating materials in the previously treated chemical mechanical polishing wastewater. It has been observed, counterintuitively, that adding additional ferrous in the form of, for example, iron sulfate or iron chloride to the CMP wastewater enhances the degree of iron precipitation in the previously treated wastewater from which azole compounds have previously been removed as described above. Sufficient iron precipitates from the CMP wastewater after adding the additional ferrous such that, after the iron compound precipitates, the resulting wastewater has a lower iron content than when no additional iron dosing is performed.

[0037] An example of a system and method for treating CMP wastewater is schematically shown in Figure 1 . The CMP wastewater enters a first vessel / treatment operation 110 where azoles can be removed from the CMP wastewater, for example, as described in US2022 / 0298045. The first vessel / treatment operation 110 for removing azoles from the CMP wastewater can be a dissolved iron treatment process, such as a wastewater treatment system utilizing Fenton chemistry. The Fenton reagent for removing azoles can be formed by adding an oxidizing agent such as hydrogen peroxide or persulfate at about 500 mg / l to about 3,000 mg / l to a soluble iron compound at about 50 mg / l to about 300 mg / l (e.g., ferrous sulfate (Fe 2+ )). Prior to adding a larger amount of hydrogen peroxide or persulfate, the Fenton reaction can also decompose at least a portion of any hydrogen peroxide present in the CPM wastewater. The Fenton reaction can occur according to chemical equations (1) - (3):

[0038] Fe 2+ +H 2 O 2 →Fe 3+ +HO.+OH - (1)

[0039] Fe 3+ +H 2 O 2 →Fe 2+ +HOO.+H + (2)

[0040] Fe 2+ +S 2O 8 2- →Fe 3+ +SO 4 . + +SO 4 2- (3).

[0041] Persulfates and hydroxyl radicals, peroxohydroxyl radicals, and persulfate radicals formed by the oxidation of Fe 2+ or the reduction of Fe 3+ can react with azoles in CMP wastewater and decompose the azoles mainly into nitrogen oxides (NO 2 / NO 3 ), carbon dioxide, and water. Without wishing to be bound by any particular theory, the decomposition of nitrogen-containing organic molecules such as azoles can occur through the reactions shown in Equation 4:

[0042] C x N y H z +OH.→CO 2 +NO 3 +H 2 O (4).

[0043] In some embodiments, when a dissolved iron compound is used to treat wastewater containing azoles, the method can include introducing the dissolved iron compound and an oxidant into the wastewater at an acidic pH to generate free radicals to decompose the azoles. By adding an acid such as sulfuric acid, the pH can be adjusted or maintained at a pH of about 3, such as a pH between 2 and 5. The oxidant introduced into the wastewater can include peroxides such as hydrogen peroxide, or persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate, and the present invention is not limited by the type of oxidant added as part of the dissolved iron treatment system. As described herein, peroxides generate hydroxyl radicals and peroxohydroxyl radicals when reacting with dissolved iron compounds and persulfates generate persulfate radicals.

[0044] During the decomposition of azoles using a dissolved iron treatment system, by-products including excessive dissolved iron will be formed. To remove the dissolved iron, CMP wastewater from which the azole compounds have been removed can be directed to a mixing vessel 120 where the pH of the wastewater is adjusted, e.g., by adding NaOH or lime, to a pH at which precipitation of iron hydroxide occurs, e.g., between about 6 and 10 or a pH of about 8. As mentioned above, precipitation of iron hydroxide from the CMP wastewater can be facilitated by adding an iron-containing compound such as iron sulfate or iron chloride to the CMP wastewater from which the azole compounds have been removed to form an iron-dosed wastewater stream. The iron-containing compound and / or the pH regulator can be added directly to the mixing vessel 120 and / or added to a conduit through which the CMP wastewater flows from a first vessel / processing operation 110 into the mixing vessel 120. Iron dosing can occur before, after, or simultaneously with pH adjustment. Although the mixing vessel 120 is illustrated as a separate unit operation, the mixing vessel can alternatively be a part of the conduit 115, a static mixer disposed within the conduit 115, or other mixing systems known in the art. In response to iron dosing and pH adjustment, an iron compound, e.g., iron hydroxide, will begin to precipitate out of solution.

[0045] Then, the pH-adjusted iron-dosed wastewater is subjected to solid-liquid separation to separate the pH-adjusted iron-dosed wastewater stream into a low-iron treated water stream and a high-iron waste including an iron compound (e.g., iron hydroxide), the low-iron treated water stream having an iron content of, e.g., less than 2 mg / l or less than 0.5 mg / l. In some embodiments, other solids such as slurry residues (e.g., silica) can also be separated from the pH-adjusted iron-dosed wastewater stream in the solid / liquid separation operation. To perform solid / liquid separation on the pH-adjusted iron-dosed wastewater stream, the stream is directed to a solid / liquid separation unit operation 130. In some embodiments, the solid / liquid separation unit operation 130 is a filtration operation or includes a filtration operation. The filtration operation can utilize one or more membrane filtration units, e.g., microfiltration units or ultrafiltration units, such as membrane filtration units available from Evoqua Water Technologies LLC. In other embodiments, in addition to or as an alternative to filtration, a gravity-based separation system can be utilized to perform the solid / liquid separation operation. To facilitate solid / liquid separation in the gravity-based separation system, one or more flocculants or ballast agents known in the art can be added to the pH-adjusted iron-dosed wastewater stream upstream of or within the vessel used for performing the solid / liquid separation. In some embodiments, the ballast can be magnetite or can include magnetite, and the solid / liquid separation equipment can include a gravity separation equipment from Evoqua Water Technologies LLC.

[0046] A solid / liquid separation device can separate a pH-adjusted iron-dosed wastewater stream into a low-iron treated water stream and a high-iron waste including iron compounds. The low-iron treated water stream can be discharged, recycled to the system or the fab, or sent for further treatment. The high-iron waste can be sent to a downstream operation 135, such as a filter press for additional solid / liquid separation or dewatering. The recovered water can be recycled back to the system or the fab, discharged to the environment, or sent for further treatment. The downstream operation 135 can additionally or alternatively include a ballast recovery system, such as a magnetite recovery system. The ballast recovery system can include a shear mill, a hydrocyclone, and / or a rotating drum including a fixed array of rare earth magnets. An example of a magnetic drum that can be used in an embodiment of the ballast recovery system disclosed in the present invention is disclosed in co-owned PCT Application Publication No. WO2014 / 088620 titled "MAGNETIC DRUM INLET SLIDE AND SCRAPER BLADE", which is incorporated herein by reference in its entirety for all purposes.

[0047] Aspects and embodiments disclosed herein also relate to methods for facilitating the removal of iron from chemical mechanical polishing wastewater from which azole compounds have previously been removed by a Fenton reaction. The method can include connecting a source of an iron-containing chemical ( Figure 1 "iron dosing / pH adjustment" in ) to one of a container 120 or a conduit 115 through which the wastewater passes. The source of the iron-containing chemical is configured to dose the iron-containing chemical into the wastewater stream and produce an iron-dosed wastewater stream; the method can also include connecting a source of a pH-adjusting chemical ( Figure 1 "iron dosing / pH adjustment" in ) to one of a container 120 or a conduit 115 through which the iron-dosed wastewater stream passes. The source of the pH-adjusting chemical is configured to dose a sufficient amount of the pH-adjusting chemical into the iron-dosed wastewater stream to precipitate iron compounds from the iron-dosed wastewater stream. The method can also include providing a solid / liquid separation subsystem 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 including iron compounds.

[0048] The method can also include providing a controller that communicates with one of the source of the iron-containing chemical or the source of the pH-adjusting chemical and is configured to control the amount of chemical dosed by one of the source of the iron-containing chemical or the source of the pH-adjusting chemical based on 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 in Figure 1It is indicated by 140. The sensor S can be disposed in any one of the unit operations 110, 120, 130, 135 and can provide an indication of any one or more of pH, temperature, pressure, one or more chemical concentrations, or any other useful property within any unit operation of the system. For clarity, the communication line between the controller 140 and the iron dosing source / pH adjustment source is not shown. The controller 140 can be implemented as a general-purpose computer programmed to perform the functions disclosed herein or a special-purpose system such as an ASIC or FPGA.

[0049] The language and terminology used herein are for descriptive purposes and should not be regarded as restrictive. As used herein, the term "plurality" means two or more items or components. The terms "comprising", "including", "carrying", "having", "containing", and "involving", whether in the written description, claims, or the like, are open-ended terms, i.e., meaning "including but not limited to". Thus, the use of such terms is intended to cover the items listed thereafter and their equivalents, as well as additional items. With respect to claims, only the transitional phrases "consisting of" and "consisting essentially of" are closed transitional phrases or semi-closed transitional phrases, respectively. The use of ordinal terms such as "first", "second", "third", and the like, which modify claim elements in claims, does not by itself imply any precedence, priority, or order of one claim element over another or the temporal order in which the acts of a method are performed, but is merely used as a label to distinguish one claim element having a certain name from another element having the same name (but using an ordinal term) to distinguish claim elements.

Claims

1. A method for removing iron from a wastewater stream, the wastewater stream including chemical mechanical polishing wastewater from which azole compounds have been previously removed by a Fenton reaction, the method comprises: adding an iron-containing chemical to the wastewater stream to form an iron-dosed wastewater stream; adjusting the pH of the iron-dosed wastewater stream to a pH at which iron compounds precipitate 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 and a waste including the iron compounds, the iron concentration of the iron-treated water stream being less than the iron concentration of the pH-adjusted iron-dosed wastewater stream.

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

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

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

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

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

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

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

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

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

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

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

13. The method according to claim 1, which produces a low-iron treated water stream having an iron concentration of less than 2 mg / l.

14. The method according to claim 1, which produces a low-iron treated water stream having an iron concentration of less than 0.5 mg / l.

15. The method according to claim 1, further comprising dewatering the waste.

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

17. A method for treating chemical mechanical polishing machine (CMP) wastewater, the method comprising: 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-dosed wastewater stream; adjusting the pH of the iron-dosed wastewater stream to precipitate iron compounds from the iron-dosed wastewater stream; and separating the pH-adjusted iron-dosed wastewater stream into a treated water stream and a waste comprising the iron compounds.

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

19. A method for facilitating the removal of iron from chemical mechanical polishing wastewater, from which azole compounds have previously been removed by a Fenton reaction, the method comprising: connecting a source of an iron-containing chemical to one of a container or conduit through which the wastewater passes, the source of the iron-containing chemical being configured to dose the iron-containing chemical to a wastewater stream and produce an iron-dosed wastewater stream; connecting a source of a pH-adjusting chemical to one of a container or conduit through which the iron-dosed wastewater stream passes, the source of the pH-adjusting chemical being configured to dose a sufficient amount of the pH-adjusting chemical to the iron-dosed wastewater stream to precipitate iron compounds from the iron-dosed wastewater stream; and providing a solid / liquid separation subsystem, which is 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 comprising the iron compounds.

20. The method according to claim 19 further provides a controller that communicates with one of the source of the iron-containing chemical or the source of the pH-adjusting chemical and is configured to control the amount of the chemical dosed by one of the source of the iron-containing chemical or the source of the pH-adjusting chemical based on 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.

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