阅读说明：本技术 一种电化学协同过氧化氢去除有机物的方法 (Method for removing organic matters by electrochemical cooperation with hydrogen peroxide ) 是由 崔玉虹 薛伟俊 刘正乾 于 2018-08-29 设计创作，主要内容包括：本发明属于水处理技术领域,更具体地,涉及一种电化学协同过氧化氢去除有机物的方法。以含有过氧化氢、过渡金属离子和有机物的溶液为反应液,在低于5.0mA/cm<Sup>2</Sup>的低电流密度下,有机物与羟自由基发生电子转移反应,生成有机物自由基,所述有机物自由基之间或所述有机物自由基与所述有机物之间发生聚合反应,形成固态聚合物,通过固液分离去除固态聚合物,从而去除所述有机物。由此解决现有技术在高电流、高过氧化氢浓度或牺牲铁阳极的方式进行污染物去除方法中存在的氧化剂及能量消耗大、产生大量铁泥的技术问题,本发明还具有操作简便高效、可回收有机资源能源、减少有毒衍生物生成和降低后续生物处理过程难度等优点。(The invention belongs to the technical field of water treatment, and particularly relates to a method for removing organic matters by using electrochemistry in cooperation with hydrogen peroxide. Using solution containing hydrogen peroxide, transition metal ions and organic matter as reaction solution, and controlling the concentration of hydrogen peroxide in the reaction solution to be less than 5.0mA/cm 2 Under low current density, the organic substance and hydroxyl radical generate electron transfer reaction to generate organic substance radicalAnd carrying out polymerization reaction between organic matter free radicals or between the organic matter free radicals and the organic matter to form solid polymers, and removing the solid polymers through solid-liquid separation so as to remove the organic matter. Therefore, the method solves the technical problems of high oxidant and energy consumption and large amount of iron mud generation in the method for removing pollutants by high current, high hydrogen peroxide concentration or sacrificial iron anode in the prior art, and also has the advantages of simple and efficient operation, capability of recycling organic resource energy, reduction in generation of toxic derivatives, reduction in difficulty of subsequent biological treatment process and the like.)

1. The method for removing organic matters by electrochemical synergy of hydrogen peroxide is characterized in that a solution containing hydrogen peroxide, transition metal ions and organic matters is used as a reaction solution, and the concentration is lower than 5.0mA/cm²Under the low current density, the organic matter and hydroxyl radical generate electron transfer reaction to generate organic matter free radicals, or the organic matter free radicals and the hydroxyl radicalThe organic substances are polymerized to form a solid organic polymer, and the solid polymer is removed by solid-liquid separation, thereby removing the organic substances.

2. The method for removing organic substances according to claim 1, wherein the concentration of hydrogen peroxide in the reaction solution is 1 to 1000 mmol/L.

3. The method for removing organic substances according to claim 1, wherein the transition metal ion is at least one of cations of iron, cobalt, manganese, zinc, copper, silver, cerium, chromium, nickel, and cadmium, and the concentration of the transition metal ion in the reaction solution is 0.05 to 100 mmol/L.

4. The method for removing organic substances according to claim 1, wherein the concentration of the organic substances in the reaction solution is 0.1 to 1000 mmol/L.

5. The method for removing organic substances according to claim 1, wherein the organic substances are one or more of phenolic organic substances, aniline organic substances, alkoxybenzene organic substances, nitrobenzene organic substances, phenolic ester organic substances, biphenyl organic substances, and heterocyclic compounds.

6. The method for removing organic substances according to claim 1, wherein the reaction solution further comprises an electrolyte, the electrolyte being at least one of a strong acid, a strong base, a weak acid, a weak base, a salt, a solid electrolyte, a metal oxide, and a metal compound.

7. The method for removing organic substances according to claim 1, wherein a cathode chamber and an anode chamber are partitioned, and the reaction solution is used as a cathode reaction solution; the anode chamber comprises an anolyte, and preferably the anode chamber further comprises at least one of an oxidant selected from the group consisting of persulfates, hydrogen peroxide, potassium permanganate, and ozone, an organic contaminant, saline and alkaline water, and seawater.

8. The method for removing organic substances according to claim 7, wherein the electrode material of the cathode is selected from the group consisting of a metal material, a carbon material, and a conductive ceramic material; wherein the metal material is one or more of copper, iron, aluminum, gold, silver, platinum, titanium, nickel, zinc, rhenium, barium, osmium, manganese, lead, cobalt, tin, tungsten, palladium, iridium, rhodium, molybdenum, cerium, vanadium, chromium, niobium, tantalum, zirconium, bismuth and ruthenium; the carbon material is selected from the group consisting of graphite, graphene oxide, boron-doped diamond, carbon sponge, carbon nanotubes, carbon fibers, activated carbon, and glassy carbon.

9. The method for removing organic substances according to claim 7, wherein the electrode material of the anode is selected from the group consisting of a metal material, a metal hydroxide material, a metal oxide material, a carbon material, and a conductive ceramic material.

10. The method for removing organic substances according to claim 1, wherein the reaction is carried out for 0.1 to 24 hours under stirring.

Technical Field

The invention belongs to the technical field of water treatment, and particularly relates to a method for removing organic matters by using electrochemistry in cooperation with hydrogen peroxide.

Background

The vigorous development of modern industrial production has led to an increase in the amount of industrial waste water year after year, and such waste water often contains a large amount of artificially synthesized refractory organic pollutants. On one hand, pollutants cannot be completely degraded or transferred by adopting a simple physical and chemical treatment method, and on the other hand, the requirements of treating the pollutants which are difficult to degrade and have toxic and harmful effects cannot be met by adopting a biological treatment technology. Advanced oxidation techniques for hydrogen peroxide, such as: UV/H₂O₂、O₃/H₂O₂Fenton and Fenton-like technologies, etc., by generating OH (E) having a strong oxidizing property⁰1.8-2.7V), can decompose refractory organic pollutants into biodegradable small molecular organic matters and even mineralize, so the method is considered to be an effective pretreatment means for the high-concentration refractory organic wastewater.

The traditional Fenton technique is to use H₂O₂And ferrous iron to produce OH, thereby degrading organic pollutants.

H₂O₂+Fe²⁺→·OH+OH-+Fe³⁺

However, Fe²⁺Will be gradually consumed along with the generation of OH and converted into Fe³⁺Therefore, constant Fe input is required²⁺To ensure the production rate of OH. In one aspect, Fe²⁺Is uneconomical in practice, on the other hand, Fe²⁺Not only can generate a large amount of iron mud to cause secondary pollution, but also excessive Fe²⁺It reacts with OH, resulting in waste of the oxidizing agent.

Fe²⁺+·OH→Fe³⁺+OH^-

Combining electrochemistry with Fenton's technique, Fe can be formed by oxidation-reduction of electrodes²⁺And Fe³⁺The circulation of (2) effectively reduces the total iron dosage, and the principle is as follows:

(1)Fe⁰at the anode, electrons are lost and oxidized into Fe²⁺，Fe²⁺And H₂O₂After reaction, becomes Fe³⁺，Fe³⁺Reduced to Fe at the cathode²⁺Is continued with H₂O₂The reaction takes place.

(2)Fe³⁺Electrons obtained at the cathode are reduced to Fe²⁺，Fe²⁺And H₂O₂After reaction, becomes Fe³⁺，Fe³⁺Reduced to Fe at the cathode²⁺Is continued with H₂O₂The reaction takes place.

By controlling the reaction conditions, a stable Fe content can be maintained in the reaction system²⁺Concentration, maintaining OH production rate, and preventing excessive Fe²⁺Quenching effect on OH, increasing H₂O₂The utilization ratio of (2).

However, the above systems still have some disadvantages: (1) the reaction process needs to provide high current density for a long time until most target pollutants are oxidized and decomposed into small molecular organic matters and even completely mineralized, so that the energy consumption of the system is high; (2) oxidant (H) due to longer target contaminant degradation path₂O₂) The consumption of the method is large; (3) other derivative organic matters with higher toxicity can be generated in the oxidative degradation process of the target pollutants, so that the subsequent biodegradation is not facilitated.

For example, an electro-Fenton technique provided in patent publication No. CN101798130A, which generates H by applying a high current (0.6A) and a stainless steel mesh as the anode and cathode and introducing oxygen₂O₂Meanwhile, the stainless steel mesh electrode of the anode can release Fe²⁺So that Fenton reaction occurs to carry out oxidative decomposition on the organic pollutants in the aqueous solution. For example, patent publication No. CN107337301A discloses a method for treating waste water by electro-FentonThe method adopts a higher current density (5-30 mA/cm)²) Fe is generated by using an iron electrode as a sacrificial anode²⁺By addition of H₂O₂The method has the advantages that the Fenton reaction is carried out to treat the wastewater, operation steps such as aeration and the like are required to be added in the treatment process, and a large amount of iron mud is generated after the reaction. In the two patent technologies, a cathode and an anode are required to coexist in one chamber, and a larger current is introduced, and the service life of the electrode is shorter by adopting a sacrificial anode mode. In the above two patent technologies, organic pollutants are mainly removed by oxidation and degradation into small molecular substances or mineralization, the degradation path of target pollutants is long, and the oxidant (H) is₂O₂) The consumption and energy consumption are large, and on the other hand, the organic matter can also generate a derivative with higher toxicity in the oxidation process, thereby bringing difficulty to the subsequent biological treatment.

Disclosure of Invention

Aiming at the defects or improvement requirements of the prior art, the invention provides a method for removing organic matters by electrochemical synergy of hydrogen peroxide, which aims to ensure that most of organic pollutants react with OH under lower current density to lose electrons to generate organic matter free radicals by controlling reaction parameters, then, free radical polymerization reaction is carried out between organic matter monomers to form a polymerization chain, when the polymerization chain reaches a certain length, the polymer is separated out from a liquid phase to form a solid polymer, and most of the organic pollutants can be removed from water by solid-liquid separation after the reaction is finished, thereby solving the technical problems of large consumption of oxidant and energy and generation of a large amount of iron mud in the method for removing pollutants by high current, high hydrogen peroxide concentration or sacrificial iron anode in the prior art.

In order to achieve the above object, according to one aspect of the present invention, there is provided a method for removing organic matters by electrochemical synergy with hydrogen peroxide, wherein a solution containing hydrogen peroxide, transition metal ions and organic matters is used as a reaction solution, and the concentration of the reaction solution is less than 5.0mA/cm²Under the low current density, organic matter and hydroxyl radical produce electron transfer reaction to produce organic matter free radical, and the organic matter free radical or the organic matter free radical and the organic matter produce polymerizationReacting to form solid organic polymer, and removing the solid polymer through solid-liquid separation to remove the organic matters.

Preferably, the concentration of the hydrogen peroxide in the reaction liquid is 1-1000 mmol/L.

Preferably, the transition metal ion is at least one of cations in any valence state of iron, cobalt, manganese, zinc, copper, silver, cerium, chromium, nickel and cadmium, and the concentration of the transition metal ion in the reaction solution is 0.05-100 mmol/L.

Preferably, the concentration of the organic matter in the reaction liquid is 0.1-1000 mmol/L.

Preferably, in order to improve the conductivity, an electrolyte may be included in the reaction solution, the electrolyte being at least one of a strong acid, a strong base, a weak acid, a weak base, a salt, a solid electrolyte, a metal oxide, and a metal compound.

Preferably, the cathode chamber and the anode chamber are separated, and the reaction solution is used as a cathode reaction solution. The reaction can be carried out in a reaction chamber with a coexisting cathode and anode, or in a cathode chamber separated from the cathode chamber and the anode chamber. When the reaction is carried out in a cathode chamber separated from an anode chamber, the anode chamber may contain other substances in addition to the electrolyte; preferably, the other substances include at least one of an oxidizing agent selected from the group consisting of persulfates, hydrogen peroxide, potassium permanganate, and ozone, an organic pollutant, saline and alkaline water, and seawater.

Preferably, the electrode material of the cathode is selected from the group consisting of a metal material, a carbon material, and a conductive ceramic material; wherein the metal material comprises one or more of copper, iron, aluminum, gold, silver, platinum, titanium, nickel, zinc, rhenium, barium, osmium, manganese, lead, cobalt, tin, tungsten, palladium, iridium, rhodium, molybdenum, cerium, vanadium, chromium, niobium, tantalum, zirconium, bismuth and ruthenium; the carbon material is selected from the group consisting of graphite, graphene oxide, boron-doped diamond, carbon sponge, carbon nanotubes, carbon fibers, activated carbon, and glassy carbon.

Preferably, the electrode material of the anode is selected from the group consisting of metal materials, metal hydroxide materials, metal oxide materials, carbon materials and conductive ceramic materials.

Preferably, the solid-liquid separation is filtration, static sedimentation or centrifugation.

Preferably, the reaction is carried out for 0.1-24 h under the condition of stirring.

In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:

(1) the low current density is adopted, and the concentration of each component is controlled at the same time, so that the reaction rate is controlled within a certain range, organic pollutants are mainly removed through polymerization, complete oxidative decomposition of the organic pollutants is not needed, the current efficiency is high, the reaction time is short, and the energy consumption is saved.

(2) The oxidant consumption is less, the utilization rate is high, and the resources are saved.

(3) Can effectively remove target organic pollutants in the wastewater, greatly reduce COD and TOC of the wastewater, reduce the possibility of generating toxic derivatives and reduce the difficulty of the subsequent biological treatment process.

(4) The reaction can be carried out in a reaction chamber with the cathode and the anode coexisting, or can be carried out in a cathode chamber with the cathode and the anode separated, and other reactions can be synchronously operated in the anode chamber after separation, so that the energy consumption is saved.

(5) Organic carbon resources and energy can be recovered by separating the organic solid polymer produced after the reaction.

Drawings

FIG. 1 is a schematic view of the structure of a reactor in example 1;

FIG. 2 is a graph of time versus phenol removal in example 1;

FIG. 3 is a graph showing the comparison of the COD removal rate of the phenol aqueous solution and the COD removal rate of example 1 by different systems in example 2;

FIG. 4 is a graph comparing the COD removal rates of the aqueous solutions of aniline of different systems in example 7 with those of examples 6 and 11;

FIG. 5 is a schematic view of the structure of a reactor in example 11.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

The invention provides a method for removing organic pollutants in wastewater by electrochemical synergy of hydrogen peroxide, which comprises the following steps: hydrogen peroxide, transition metal ions and waste water containing organic pollutants are added into a reaction chamber as reaction liquid, and the cathode current density is controlled to be less than 5.0mA/cm²The current density is low, then stirring reaction is carried out for 0.1-24 h, the target pollutants are subjected to electron transfer reaction to generate organic matter free radicals, and then organic polymers with large molecular weight are generated to be separated out from the solution and uniformly dispersed in the solution, so that the electrodes cannot be passivated; after the reaction is finished, carrying out solid-liquid separation on the reaction liquid, wherein the liquid obtained by separation treatment is the treated wastewater after the organic pollutants are removed. The reaction can be carried out in a reaction chamber with a cathode and an anode coexisting, or can be carried out in a cathode chamber with a cathode chamber and an anode chamber separated, and other reactions can be synchronously operated in the separated anode chamber, so that the energy consumption is saved.

In a further preferred embodiment of the present invention, the concentration of hydrogen peroxide in the reaction solution is 1 to 1000 mmol/L.

In a further preferred embodiment of the present invention, the transition metal ion includes at least one of cations in any valence state of iron, cobalt, manganese, zinc, copper, silver, cerium, chromium, nickel, and cadmium, and the concentration of the transition metal ion in the reaction solution is 0.05 to 100 mmol/L.

As a further preferred aspect of the present invention, in order to improve the conductivity, the reaction solution may contain an electrolyte including at least one of a strong acid, a strong base, a weak acid, a weak base, a salt, a solid electrolyte, a metal oxide, and a metal compound.

In a further preferred embodiment of the present invention, the reaction may be carried out in a reaction chamber in which a cathode and an anode coexist, or in a cathode chamber in which a cathode chamber and an anode chamber are separated. When the reaction is carried out in a cathode chamber separated from an anode chamber, the cathode chamber and the anode chamber may be separated using a salt bridge or a proton membrane, and the anode chamber includes an anode electrolyte including at least one of a strong acid, a strong base, a weak acid, a weak base, a salt, a solid electrolyte, a metal oxide, and a metal compound.

As a further preference of the present invention, when the reaction is carried out in a cathode chamber separated from an anode chamber, the electrolyte of the anode chamber may contain other substances in addition to the anolyte; preferably, the other substances include at least one of an oxidizing agent, an organic pollutant, saline-alkali water, and seawater, and the oxidizing agent includes at least one of persulfate, hydrogen peroxide, potassium permanganate, and ozone.

As a further preferred aspect of the present invention, the reaction occurring in the reaction solution is:

H₂O₂+M^(n-1)+＝·OH+OH^-+Mⁿ⁺

Mⁿ⁺+e^-＝M^(n-1)+

OH + organic contaminants ═ OH^-+ solid precipitate + soluble oxidation product

Wherein M isⁿ⁺Representing a transition metal ion of high valency, M^(n-1)+Represents a transition metal ion in a lower valence state.

In a further preferred embodiment of the present invention, the organic contaminant is one or more of a phenol-based organic substance, an aniline-based organic substance, an alkoxybenzene-based organic substance, a nitrobenzene-based organic substance, a phenol ester-based organic substance, a biphenyl-based organic substance, or a heterocyclic compound, and specifically includes a monohydric phenol, a halogenated monohydric phenol, a hydrocarbyl-substituted monohydric phenol, an amino-substituted monohydric phenol, a nitro-substituted monohydric phenol, a polyhydric phenol, a halogenated polyhydric phenol, a hydrocarbyl-substituted polyhydric phenol, an amino-substituted polyhydric phenol, a nitro-substituted diphenol, a halogenated diphenol, a hydrocarbyl-substituted diphenol, an amino-substituted diphenol, a nitro-substituted alkoxybenzene, a halogenated alkoxybenzene, a hydrocarbyl-substituted alkoxybenzene, an amino-substituted alkoxybenzene, a nitro-substituted alkoxybenzene, an alkoxybiphenyl, or a heterocyclic compound, Halogen-substituted products of alkoxy biphenyl, alkyl substituted products of alkoxy biphenyl, amino substituted products of alkoxy biphenyl, nitro substituted products of alkoxy biphenyl, nitrobenzene, aniline, halogen-substituted products of aniline, alkyl substituted products of aniline, nitro substituted products of benzidine, halogen-substituted products of benzidine, alkyl substituted products of benzidine, nitro substituted products of benzidine, naphthol, halogen-substituted products of naphthol, alkyl substituted products of naphthol, amino substituted products of naphthol, nitro substituted products of naphthol, anthraphenol, halogen-substituted products of anthraphenol, alkyl substituted products of anthraphenol, amino substituted products of anthraphenol, nitro substituted products of anthraphenol, phenol carboxylate, phenol dicarboxylate, pyrrole, alkyl substituted products of pyrrole, halogen-substituted products of pyrrole, nitro substituted products of pyrrole, alkoxy substituted products of pyrrole, amino pyrrole, thiophene, halogen-substituted products of thiophene, alkyl substituted products of thiophene, nitro substituted products of thiophene, phenol ester of biphenyl, aniline, nitro substituted products of naphthol, at least one of a nitro substituent of thiophene, an alkoxy substituent of thiophene, bithiophene and aminothiophene.

The concentration of the organic pollutants in the reaction liquid is preferably 0.1-1000 mmol/L.

The current density is lower than 5.0mA/cm²Preferably less than 2.0mA/cm²(ii) a The concentration of the hydrogen peroxide is 1-1000 mmol/L, preferably 1-600 mmol/L; the concentration of the transition metal ions is 0.05-100.00 mmol/L, preferably 0.2-50.00 mmol/L; the concentration of the organic matters is 0.1-1000 mmol/L, more than 50% of the removed organic pollutants are precipitated in the form of solid organic polymers and are finally separated and removed.

As a further preference of the method, the cathode electrode material comprises at least one of a metal material, a carbon material, a conductive ceramic material or a mixed material; wherein the metal material comprises at least one or an alloy of copper, iron, aluminum, gold, silver, platinum, titanium, nickel, zinc, rhenium, barium, osmium, manganese, lead, cobalt, tin, tungsten, palladium, iridium, rhodium, molybdenum, cerium, vanadium, chromium, niobium, tantalum, zirconium, bismuth and ruthenium; the carbon material comprises at least one of graphite, graphene oxide, boron-doped diamond, carbon sponge, carbon nano tubes, carbon fibers, activated carbon and glassy carbon or a mixed material.

As a further preference of the method, the anode electrode material comprises at least one of a metal material, a metal hydroxide material, a metal oxide material, a carbon material, an electrically conductive ceramic material, or a mixed material; wherein the metal material comprises at least one or an alloy of copper, iron, aluminum, gold, silver, platinum, titanium, nickel, zinc, rhenium, barium, osmium, manganese, lead, cobalt, tin, tungsten, palladium, iridium, rhodium, molybdenum, cerium, vanadium, chromium, niobium, tantalum, zirconium, bismuth and ruthenium; the metal hydroxide material comprises at least one of copper hydroxide, iron hydroxide, aluminum hydroxide, gold hydroxide, silver hydroxide, platinum hydroxide, titanium hydroxide, nickel hydroxide, zinc hydroxide, rhenium hydroxide, barium hydroxide, osmium hydroxide, manganese hydroxide, lead hydroxide, cobalt hydroxide, tin hydroxide, tungsten hydroxide, palladium hydroxide, iridium hydroxide, rhodium hydroxide, molybdenum hydroxide, cerium hydroxide, vanadium hydroxide, chromium hydroxide, niobium hydroxide, tantalum hydroxide, zirconium hydroxide, bismuth hydroxide, ruthenium oxide or a mixed material; the metal oxide material comprises at least one of copper oxide, iron oxide, aluminum oxide, metal oxide, silver oxide, platinum oxide, titanium oxide, nickel oxide, zinc oxide, rhenium oxide, barium oxide, osmium oxide, manganese oxide, lead oxide, cobalt oxide, tin oxide, tungsten oxide, palladium oxide, iridium oxide, rhodium oxide, molybdenum oxide, cerium oxide, vanadium oxide, chromium oxide, niobium oxide, tantalum oxide, zirconium oxide, bismuth oxide and ruthenium oxide or a mixed material; the carbon material comprises at least one of graphite, graphene oxide, boron-doped diamond, carbon sponge, carbon nano tubes, carbon fibers, activated carbon and glassy carbon or a mixed material.

The electrode shape of the cathode electrode and the anode electrode includes any one of a sheet, a rod, a cylinder, a ring, a wire, a granule, a sponge, a mesh, and a porous structure.

As a further preferred mode of the invention, the solid-liquid separation is performed by filtration, static sedimentation or centrifugation.

The invention adopts a method of combining electrochemistry with hydrogen peroxide, leads organic pollutants in the wastewater to have polymerization reaction under the electrolysis condition of low current density to form solid precipitate substances by controlling the electrode current density which is a key parameter in the reaction process, and then effectively removes the organic pollutants in the wastewater through solid-liquid separation operation.

Compared with the existing electro-Fenton technology for removing organic pollutants in wastewater, the reaction process of the invention adopts lower current density, the organic pollutants are separated and removed from the water mainly through generating solid organic polymeric substances through polymerization, the organic pollutants are not required to be decomposed into small molecular substances and mineralized, the reaction time is short, and the oxidant (H) is used₂O₂) The utilization rate is high, and the energy consumption and the oxidant consumption are effectively reduced; organic solid polymers generated after the separation reaction can be recycled and used as organic carbon resources; in addition, the reaction process of the invention can be carried out in a reaction chamber with a cathode and an anode coexisting, or can be carried out in a cathode chamber with a cathode chamber and an anode chamber separated, and the separated anode chamber can synchronously run other reactions without mutual interference, thereby further saving energy consumption.

Compared with the prior art that the organic pollutants are polymerized directly through anodic oxidation, the organic pollutants react with OH in the solution to generate organic free radicals and then undergo polymerization in the solution, but not on the surface of the electrode, so that the polymerization products can be continuously generated and uniformly distributed in the reaction solution, and cannot be attached to the surface of the electrode to passivate the electrode and cause the electrode to lose efficacy. After the reaction is finished, the reaction liquid is subjected to solid-liquid separation, so that the target organic pollutants, COD and TOC in the wastewater can be effectively removed, and meanwhile, the solid organic polymer can be recovered. Meanwhile, the invention also has the advantages of simple operation, high efficiency, energy saving, reduction of the generation of toxic derivatives, reduction of the difficulty of the subsequent biological treatment process and the like.

The following are examples: