JPH04235788A - Treatment of waste solution containing lower sulfur compound and soluble iron salt - Google Patents

Abstract

PURPOSE:To effectively, make a waste solution containing a lower sulfur compound and a soluble iron salt as environmental pollutants, for example, a waste photographic processing solution harmless without generating a problem such as an increase in expenses or the contamination of an electrode at the time of electrolysis. CONSTITUTION:A waste solution containing a lower sulfur compound and a soluble iron salt is subjected to biological treatment at first to oxidize the lower sulfur compound and the obtained solution is subjected to electrolytic treatment to decompose a hardly decomposable compound such as a chelating agent remaining after pretreatment and, subsequently, this solution is adjusted to pH 4-7.5 to precipitate and remove the iron salt as a double salt with phosphate or other inorg. salt, acid to make the waste solution harmless.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of treating wastewater containing lower sulfur compounds and soluble iron salts to make them pollution-free. Specifically, the present invention relates to a treatment method suitable for processing waste liquid from processing iron-containing ores, waste liquid from boiler cleaning, waste liquid from photographic development, and the like.

0002

[Prior Art] Currently, a huge amount of waste liquid discharged from various manufacturing plants, etc. contains harmful substances and substances that are difficult to decompose by natural microorganisms (persistent substances). Pollution has become a major social problem.

[0003] Particularly in recent years, due to the Water Pollution Control Act and stricter pollution regulations, it has become virtually impossible to dispose of these waste liquids.
Burning or dumping into the ocean are methods. In any case, none of these methods can be said to reduce the pollution burden.

[0004] As a method of reducing the pollution load, for example, activated sludge method (for example, Japanese Patent Publication No. 55
-49559 and Japanese Patent Publication No. 51-12943, etc.), electrolytic oxidation method (Japanese Patent Publication No. 48-84462, Japanese Patent Publication No. 49-119, etc.)
No. 458, Japanese Patent Publication No. 53-43478, Japanese Patent Publication No. 49-1
19457, etc.), ion exchange method (Special Publication No. 51-377)
No. 04, Special Publication No. 53-383, Special Publication No. 53-4327
1, etc.), reverse osmosis method (JP-A-50-22463), chemical treatment method (JP-A-53-12152, JP-B-Sho 57-
No. 37396, Japanese Unexamined Patent Publication No. 61-241746, etc.), but each treatment alone has not been sufficient.

For example, in the activated sludge method, although operating costs are low, there is a problem in that persistent substances such as chelating agents such as EDTA are released as they are without being treated. On the other hand, the electrolytic oxidation method requires a large amount of electricity when a large amount of oxidizable substances are contained, resulting in high operating costs.
In addition, there have been problems in that the electrodes are contaminated by waste liquids containing substances that are easily polymerized, such as waste liquids containing lower sulfur compounds. Furthermore, when resins or membranes are used, such as in the ion exchange method or reverse osmosis method, frequent replacement is required due to adsorption of substances that easily become polymeric or dirt, which tends to increase operating costs. Chemical treatment methods that use chemicals for treatment in a stoichiometric manner require the use of expensive catalysts and large amounts of chemicals in order to achieve efficient decomposition treatment, resulting in particularly high operating costs. The problem was that it became a thing.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a new processing method that effectively solves the above problems.

That is, the first object of the present invention is to establish an effective detoxification method that does not cause environmental pollution of both the water quality and the atmosphere of waste liquid.

[0008] A second object of the present invention is to provide a means for inexpensively and efficiently treating waste liquid containing difficult-to-decompose substances such as chelating agents such as EDTA.

A third object of the present invention is to provide a means for efficiently electrolytically treating waste liquid containing lower sulfur compounds without contaminating the electrodes.

0010

[Means for Solving the Problems] As a result of various studies, the present inventors have found that the object of the present invention can be effectively achieved by using the following combination means.

That is, the present invention applies the following (
This is a method for treating waste liquid, characterized by sequentially performing the treatment steps of A) to (C). (A) Microbial treatment process for treating lower sulfur compounds (
B) Electrolytic treatment step (C) A step of precipitating and removing iron salts as phosphates and/or double salts with other inorganic salts and acids at a pH of 4 to 7.5. Next, the present invention will be explained in detail.

[0012] Some lower sulfur compounds are very difficult to oxidize simply by aeration, but they can be easily oxidized by treatment with microorganisms. However, this method does not completely treat refractory substances such as EDTA, which are chelated as soluble iron salts and remain undecomposed.

[0013] The environmental standards for iron ions, which are harmful to the environment, are strictly regulated to a discharge concentration of 10 ppm or less (both in rivers and sewers), and iron ions must be removed strictly. To remove the iron ions solubilized by the chelating agent as mentioned above, a large excess of calcium ions is generally used, and the coordination metal of the chelating agent is replaced with calcium.
The conventional method is to precipitate it as alkaline and insoluble iron hydroxide. However, since the waste liquid targeted by the present invention contains a large amount of lower sulfur compounds, sulfurous acid and sulfuric acid produced by oxidation with air cause a large amount of precipitate as calcium salts. This precipitate contains iron ions, which are environmentally harmful, and requires special disposal methods.

[0014] We have sincerely considered this issue. It has been found that by combining the following treatment steps, it is possible to efficiently detoxify wastewater containing lower sulfur compounds and iron salts solubilized by a chelating agent.

[0015] The lower sulfur compounds as used in the present invention refer to inorganic sulfur compounds that are reduced from sulfuric acid, which is a stable oxidized sulfuric acid, and specifically include sulfurous acid, hyposulfite, thiosulfuric acid, thionic acid, thionous acid, etc. and its salts (sodium, potassium, calcium, ammonium, etc.), hydrogen sulfide and its salts, and inorganic sulfur compounds such as sulfur alone.

The iron salt solubilized with a chelating agent as used in the present invention refers to an iron salt that has been solubilized by adding a so-called chelating agent to prevent it from being insolubilized and precipitated in water (for example, EDTA (ethylene diamine)). -tetraacetic acid) iron salt, PD
TA (1,3-propanediamine-tetraacetic acid) iron salt, NT
A (nitrilo-triacetic acid) iron salt, DTPA (bisethylenediamine-pentaacetic acid) iron salt, 2-hydroxy-1,3-propanediamine-tetraacetic acid iron salt, EDDA (ethylenediamine-diacetic acid) iron salt, 1-hydroxy (e.g., ethylidene bis(phosphonic acid) iron salt, phenanthroline iron salt, etc.).

That is, (A) lower sulfur compounds can be converted into stable substances such as sulfuric acid by the above-mentioned biological treatment for degrading compounds that can be easily decomposed by living organisms (easily degradable compounds). Convert to . (B) Hard-to-decompose compounds such as chelating agents remaining after the treatment in (A) are electrolytically treated to completely decompose them, or to partially decompose them to easily decomposable compounds. (C) Next, the product treated with the above (B) has a pH of 4 to 7.
5, and the iron salt is precipitated and removed by forming a double salt with a phosphate and/or other inorganic salt/acid.

[0018] In many cases, the above process can bring the waste liquid to a level that allows it to be discharged into sewers or rivers, but especially when using highly concentrated waste liquid, further biological treatment and/or activated carbon adsorption treatment may be combined with the waste liquid. You can lower the level. In particular, since many easily decomposable compounds remain in the electrolytic treatment of step (B), it is preferable to combine the step (C) with biological treatment (D) using the commonly used activated sludge method. Furthermore, for more advanced treatment, activated carbon adsorption, ozone treatment, etc. can be combined.

The microbial treatment method in step (A) includes the aeration lagoon method, stabilization pond method, trickling filter method, contact filter method, contact aeration method, rotary contact method, activated sludge method, biofilm method, etc. (For details, see "Wastewater treatment process, design theory and experimental methods" W
．． W. Eckenfelder, D. L. Written by Ford, translated by Saburo Matsui, published by Gihodo Publishing, and published in ``Biological Water Treatment Technology and Devices'', edited by Japan Society of Chemical Engineers, Baifukan. ) can be used in any aerobic manner, such as aeration or contact with air or oxygen. In particular, microorganisms such as sulfur-oxidizing bacteria (e.g., Thiobacillus spp., Thiothrix
genus Beggiatoa, etc.), the treatment efficiency is significantly increased, which is preferable. In addition, as this microbial treatment method, the trickling filter method, the contact filter method, the contact aeration method, and the activated sludge method are preferred, and the activated sludge method is particularly preferred (in this case, even if the normal dispersed floc type is used, it will not stick to the carrier). ).

Regarding the microbial treatment in step (A), as described above, alkali (sodium hydroxide, sodium hydroxide,
potassium hydroxide, calcium hydroxide, sodium carbonate)
It is preferable to adjust the pH so as not to lower it too much by adding the like, and the preferred pH range is 5.5 to 8.5, particularly preferably 5.8 to 7.5. Also, process (A)
In microbial treatment, the COD:N:P ratio is 100:5:1, or N.
It is preferable to keep P higher than that. In particular, it is preferable to add phosphorus in an amount sufficient to remove the iron salt later, and it is preferable to add phosphorus in an amount equal to or more than the iron salt contained. If the concentration of inorganic salts in the liquid to be treated is too high,
It is preferable to reduce the concentration of inorganic salts to 5% or less by dilution, and more preferably to 3% or less because this stabilizes the biota. The COD of the liquid to be treated is 3000p
It is preferable that it is pm or more. In addition, if the liquid to be treated lacks phosphorus, 0.1 of the COD value is added as phosphorus.
Phosphate (e.g. KH2 PO4
・K2 HPO4 , NaH2 PO4 ・2H2 O
, Na2 HPO4) is preferably added.

[0021] The microbial treatment in step (A) may be a continuous activated sludge method or a batch activated sludge method, and the treatment time, aeration method, etc. are determined by the optimum conditions depending on the treatment liquid used. It will be held in accordance with the Details are described in ``Activated Sludge Method Maintenance and Management Technology,'' edited by Toshiro Sakurai and Ryuichi Sudo (Science and Technology Development Center).

[0022] In the electrolytic treatment of step (B), any noble electrode that does not wear out even if the anodic oxidation is performed continuously can be used without any particular restrictions. When the waste liquid contains highly reducing organic compounds such as developing agents and alcohols, a sufficiently noble electrode that is resistant to oxidation is preferred. Specifically, the surface of the titanium base material is covered with lead dioxide, platinum, platinum iridium, iridium dioxide, etc. (for example,
(trade name: Exerode, manufactured by Nippon Carlit Co., Ltd.) is preferred. These anodes can apply high voltage and can efficiently electrolytically oxidize alcohols, aldehydes, carboxylic acids, etc. 2-10V per electrode pair, preferably 2-8V
voltage. On the other hand, as the cathode, any material may be used as long as it has corrosion resistance and conductivity so as not to cause corrosion while electrolysis is stopped, but a stainless steel plate (or rod) is most suitable. Of course, various carbon electrodes and various metal electrodes can also be used. Anode/cathode pairs can be made by placing the respective electrode plates facing each other at appropriate intervals, or by sandwich-type pairs in which an anode is sandwiched between cathode plates from both sides, or a cathode is sandwiched between anodes from both sides. structure is taken. Here, the shape of the electrode may be any shape such as linear, plate-like, net-like, cloth-like, or spherical, but it is preferable that the electrode has a larger surface area. The amount of energization expressed as the product of flowing current and time is preferably 0.1 to 1000 times the equivalent to the COD value, and more preferably 0.5 to 100 times. Here, the equivalent to the COD value is expressed as the product of the COD value divided by the atomic weight of oxygen and the Faraday constant. The electrolytic cell may be either a continuous type or a batch type, as long as the filtered separation liquid remains there for a sufficient period of time required for the reaction. In addition, stirring in the electrolytic cell can be done by rotating electrodes, using gas generated by electrolysis, blowing gas, moving the liquid with a rotating plate or rod, moving the liquid using a pump or gravity, etc. Any material that moves on the electrode surface may be used.

[0023] In order to insolubilize the iron salt in step (C), the fact that iron and phosphoric acid form a sparingly soluble salt is utilized. That is, iron phosphate has a particularly low solubility product in the pH range of 4 to 7.5, and in order to clear pollution regulations, iron can be precipitated and removed within this range. In addition, when containing substances such as aluminum that form poorly soluble salts like phosphoric acid, the same iron removal efficiency can be obtained at the above pH, and iron salts and phosphoric acid can be simultaneously precipitated by adjusting the addition of aluminum salt etc. It can also be removed, making it a preferable treatment for regulations in closed water systems. A pH of 5 to 7 is particularly preferred from the viewpoint of solubility. According to the method of the present invention, the iron salt is obtained as a powdery precipitate with good filterability, and it is also possible to suppress the amount of coagulation and sedimentation agent used during filtration. If the amount of phosphoric acid added in step (A) is insufficient, phosphoric acid is further added in this step.

The treatment method of the present invention efficiently treats high-concentration waste liquid containing lower sulfur compounds, difficult-to-decompose compounds, substances that turn into tar during electrolytic decomposition, iron salts that have strict regulations regarding pollution, and detoxifies them. It is something to do.

[0025] The content of the present invention was achieved only by carefully examining and considering how the contents change and what remains unchanged with each treatment method, and then combining the most suitable treatments. It is not just a combination of conventional techniques.

[0026] That is, in the subsequent electrolytic treatment, substances that cause tar and generation of harmful gases are removed by microbial treatment, and then the chelating agent that has solubilized iron that cannot be processed by microorganisms is electrolyzed. By oxidative decomposition during treatment, iron can be removed efficiently.

[0027] Preferably, photographic processing waste liquid is used in the processing of the present invention. The photographic waste liquid used in the processing method of the present invention is a processing waste liquid generated when a silver halide photosensitive material is developed. Here, the photosensitive materials include color photosensitive materials as well as black and white photosensitive materials. For example, in addition to color paper, color reversal paper, color negative film for photography, color reversal film, negative or positive film for movies, direct positive color photosensitive materials,
Examples include ray film, photosensitive materials for printing, microfilm, and black and white film for photography.

The photographic processing waste liquid will be explained below. The photographic processing waste liquid is mainly composed of photographic processing liquid components. In addition, photographic processing waste liquid also contains reaction products such as oxidized products of developing agents, sulfates, and halides produced during photographic processing, as well as components such as trace amounts of gelatin and surfactants dissolved from photosensitive materials. ing.

Photographic processing solutions include color developing solution, bleaching solution, fixing solution, bleach-fixing solution, rinsing solution, washing water and image stabilizing solution in color processing, black and white developing solution, fixing solution and washing water in black and white processing, Consists of reducing fluid used in plate-making work, cleaning fluid for development processing tanks, etc.

Many color paper developers contain alkylene glycols and benzyl alcohols along with color developing agents, sulfites, hydroxylamine salts, carbonates, water softeners, and the like. On the other hand, color negative developer,
Developer solutions for color positives and some developer solutions for color paper do not contain these alcohols.

Color developers usually contain aromatic primary amine color developing agents. It is mainly a p-phenylenediamine derivative, a typical example being N,N-diethyl-
p-phenylenediamine, 2-amino-5-diethylaminotoluene, 2-methyl-4-[N-ethyl-N-(
β-hydroxyethyl)amino]aniline, N-ethyl-N-(β-methanesulfonamidoethyl)-3-methyl-4-aminoaniline. In addition, these p-phenylenediamine derivatives are sulfates, hydrochlorides, sulfites,
It is a salt such as p-toluenesulfonate. The content of the aromatic primary amine developing agent ranges from about 0.5 g to about 10 g per liter of color developer.

Color developing solutions contain various hydroxylamines as preservatives. Both substituted and unsubstituted hydroxylamines can be used. Examples of substituted hydroxylamines include those in which the nitrogen atom of hydroxylamines is substituted with a lower alkyl group, particularly hydroxylamines substituted with two alkyl groups (for example, carbon atoms 1 to 3). The content of hydroxylamines is 0 to 5 g per liter of color developer.

In addition, 1-phenyl-3 is contained in the black and white developer.
-pyrazolidone, 1-phenyl-4-hydroxymethyl-4-methyl-3-pyrazolidone, N-methyl-p-aminophenol and its sulfate, hydroquinone and its sulfonate, and the like.

[0034] Color and black and white developers (hereinafter both may be collectively referred to simply as developer) contain preservatives such as
It usually contains sulfites such as sodium sulfite, potassium sulfite, sodium bisulfite, potassium bisulfite, sodium metasulfite, potassium metasulfite, and carbonyl sulfite adducts, and the content of these is 0g to 5g/
It is a liter. Other preservatives used in color and black-and-white developers are combinations of N,N-dialkyl-substituted hydroxylamines and alkanolamines such as triethanolamine. Color and black and white developers have a pH of 9~
It is 12. Various buffers are used to maintain the above pH. Buffers include carbonate, phosphate, borate, tetraborate, hydroxybenzoate, glycine salt, N,N-dimethylglycine salt, leucine salt, norleucine salt, guanine salt, 3,4- Dihydroxyphenylalanine salt, alanine salt, aminobutyrate, 2-amino-
2-methyl-1,3-propanediol salt, valine salt,
Proline salts, trishydrocyaminomethane salts, lysine salts, etc. can be used. In particular, carbonates, phosphates, tetraborates, and hydroxybenzoates have low solubility and pH of 9.
These buffers are often used because they have excellent buffering ability in the high pH range of 0 or higher, have no adverse effects on photographic performance (fogging, etc.) when added to developing solutions, and are inexpensive. . The amount of the buffer added to the developer is usually 0.1 mol/liter to 1 mol/liter.

[0035] In addition, the developer solution contains various chelating agents which are added as calcium and magnesium precipitation inhibitors or to improve the stability of the developer solution. Typical examples are nitrilotriacetic acid, diethylenetriaminepentaacetic acid, nitrilo-N,N,N-trimethylenephosphonic acid, ethylenediamine-N,N,N',N'-tetramethylenephosphonic acid, 1,3-diamino-2 -propanoltetraacetic acid, transcyclohexanediaminetetraacetic acid, 1
, 3-diaminopropanetetraacetic acid, 2-phosphonobutane-
These include 1,2,4-tricarboxylic acid and 1-hydroxyethylidene-1,1 diphosphonic acid. Two or more of these chelating agents may be used in combination, if necessary.

The developer contains various development accelerators. As the development accelerator, thioether compounds, p-phenylenediamine compounds, quaternary ammonium salts, p-
These include aminophenols, amine compounds, polyalkylene oxides, 1-phenyl-3-pyrazolidones, hydrazines, mesoion type compounds, thione type compounds, imidazoles, and the like.

[0037]Although the developer often contains bromide ions for the purpose of preventing fogging, it is also possible to use a developer that does not contain bromide ions for photosensitive materials containing silver chloride as the main ingredient. be. In addition, N is used as an inorganic antifoggant.
It may contain a compound that provides chlorine ions, such as aCl or KCl. Additionally, various organic antifoggants may be contained as required. As an organic antifoggant,
For example, it may contain adenines, benzimidazoles, benztriazoles, and tetrazoles. The content of these antifoggants is 0.010 g to 2 g per liter of developer. These antifoggants include those that are eluted from the photosensitive material during processing and accumulate in the developer.

[0038] If necessary, various surfactants such as alkylphosphonic acids, arylphosphonic acids, fatty acid carboxylic acids, aromatic carboxylic acids, etc. may be contained.

In black-and-white photographic processing, a fixing process is performed after the developing process. Furthermore, in color photographic processing, bleaching is usually carried out between development and fixing, and sometimes bleaching is carried out simultaneously with fixing in one-bath bleach-fixing (Brix). The bleaching solution contains iron (III) or Co (III) EDTA, diethylenetriaminepentaacetic acid, nitrilotriacetic acid, 1,3
Contains -diamino-propane tetraacetate, phosphonocarboxylate, persulfates, quinones, etc. In addition, it may contain appropriate rehalogenating agents such as alkali bromide and ammonium bromide, borates, carbonates, and nitrates. The fixing solution and bleach-fixing solution contain thiosulfate (sodium salt, ammonium salt), acetate,
It may also contain borate, ammonium or potassium alum sulfite.

In the processing of silver halide photographic light-sensitive materials, after the fixing treatment or the one-bath bleach-fixing treatment,
It is common to perform washing with water and/or stabilization treatment.

The pH of the washing water in the processing of photosensitive materials is
4-9, preferably 5-8. Furthermore, instead of washing with water, the photosensitive material can be directly processed with a stabilizing solution. In such stabilization treatment, Japanese Patent Application Laid-Open Nos. 57-8,543, 58-14,834, and 60-2
All known methods described in US Pat. No. 20,345 can be used.

[0042]Furthermore, following the water washing process, a further stabilization process may be carried out, and an example thereof is a stabilizing bath containing formalin and a surfactant, which is used as a final bath for color photosensitive materials for photography. be able to. Various chelating agents and antifungal agents can also be added to this stabilizing bath.

[0043] The waste liquid containing silver is subjected to silver recovery treatment and then subjected to microbial treatment. Methods for recovering silver include a method in which silver is precipitated using electrolysis, a method in which steel wool is introduced and silver in the solution is precipitated on the steel wool by utilizing the difference in ionization tendency between iron and silver; A method of adding a sodium sulfide solution to precipitate silver as silver sulfide can be used.

[0044]

[Example] Description of the waste liquid used in the example Silver recovery system waste liquid (fixer for color photographic processing "CN-16", "CN-16Q
” bleaching solution, fixing solution, “CP-20” bleach-fixing solution, “
CP-23'' bleach-fix solution, and black and white photographic processing fixing solution ``Fuji F'' and ``GRFI'' waste solution and water at a ratio of 4:1, respectively.
:3:2:7:3:2 mixture and then subjected to silver recovery treatment) and developer system waste liquid (color photographic processing "CN-1")
6", "CN-16Q", "CP-20", "CP-2
3” each developer and black and white photographic processing developer “RD3”
, the waste liquid and water of “GRD1” were mixed in a ratio of 4:1:3:2:
(mixed at a ratio of 7:3:2) and were mixed at a volume ratio of 1:1.

[0045] Here, all characters in parentheses are trade names of processing liquids manufactured by Fuji Photo Film Co., Ltd. This mixed solution contained the following lower sulfur compounds. sulfite ion
8600ppm thiosulfate ion
34,300ppm and iron ion is iron EDT
It contained 3200 ppm of A. This solution has a high concentration of inorganic salts of 12%, so it was diluted 10 times with tap water to make it suitable for biological treatment (COD in untreated state).
(According to the manganese method, hereinafter the same) was 4700 ppm).

Example 1 Step (A) For the microbial treatment, activated sludge was used which had been acclimatized for one month using a continuous method using a 10-fold dilution of silver recovery system waste liquid with a residence time of 2 days. 150 ppm of potassium hydrogen phosphate was added to the diluted waste liquid (COD 4700 ppm, Fe 47 ppm), and the treatment was continued for a residence time of 2 days. Use a pH controller (Tokyo Rika FC-10 model) to keep the pH of the aeration tank at 6.6 or higher.
A 10% aqueous sodium hydroxide solution was added using a . Table 1 shows the data of the treated water when it reached a steady state one month after the start of addition.

[0047]

[Table 1]

Step (B) The filtrate (200 ml) obtained by filtering and removing suspended matter from the treated water from step (A) was heated using a lead dioxide electrode (LD400 type, manufactured by Nippon Carlit Co., Ltd.) as the anode and a stainless steel (SUS3) as the cathode.
16) Oxidation treatment was carried out in an electrolytic bath in which plates were attached on both sides of the anode. While stirring the liquid in the electrolytic cell, a current of 2.5 A was applied with an interelectrode voltage of 3.8 V. Table 1 shows data on the treated water after the times shown in Table 1.

Step (C) The treated water obtained from step (B) was adjusted to the pH shown in Table 1. After stirring for 15 minutes, a flocculant (DIC-A500 manufactured by Dainippon Ink Co., Ltd.) was added, stirring for 30 minutes, and filtering the treated water using filter paper. Table 1 shows the data of the treated water.

Example 2 Treated water treated up to step (C) (
Standard No. 2) was treated using activated sludge from the Ashigara factory of Fuji Photo Film Co., Ltd. in a continuous method with a residence time of 1 day. After two weeks, the COD of the treated water was 96 ppm and the BOD5 was 5 ppm.
Hereinafter, very good treated water with iron content of 1 ppm or less was obtained (step (D)).

Example 3 Treated water treated up to step (C) (
Standard No. When the treated water treated through steps 2) and (D) was passed through a column packed with granular activated carbon TYPESGL (manufactured by Toyo Calgon Co., Ltd.), the COD of the treated water obtained was 48 ppm and 15 ppm, respectively, indicating good treated water. was gotten.

[0052]

[Effects of the Invention] According to the present invention, waste liquids containing lower sulfur compounds and soluble iron salts as pollutants, such as photographic processing waste liquids, can be efficiently collected without increasing operating costs or causing problems such as electrode contamination during electrolysis. Can be rendered harmless.

Claims (4)

[Claims] 1. A method for treating a waste liquid, which comprises sequentially performing the following treatment steps (A) to (C) on a waste liquid containing a lower sulfur compound and an iron salt solubilized with a chelating agent. (A) Microbial treatment step for treating lower sulfur compounds;
(B) Electrolytic treatment step, (C) Ferrous ions are converted into phosphate and/or at pH 4-7.5.
Or the process of precipitating and removing it as a double salt with other inorganic salts and acids. 2. The method for treating waste liquid according to claim 1, wherein the microbial treatment in step (A) is activated sludge treatment. [Claim 3] Claim (1) characterized in that microbial treatment is further combined as a step (D) after the treatment of all the steps.
) How to treat the waste liquid described. 4. The method for treating waste liquid according to claim 1, wherein the waste liquid to be treated is a photographic development processing waste liquid.