JP4522302B2 - Detoxification method of organic arsenic - Google Patents

Description

  The present invention relates to a method for detoxifying organic arsenic, and includes organic arsenic contained in wastewater such as industrial wastewater, sewage, clean water, landfill leachate, groundwater, river water, pond water, lake water, and illegal dumping groundwater and leachate. This is related to technology for detoxification.

  First, organic arsenic in the environment will be described. An example of organic arsenic present in the environment is monophenylarsonic acid. As shown in the chemical formula 1, it is considered that the reddening agent (diphenylcyanoarsine and diphenylchloroarsine) decomposes stepwise in the environment to monophenylarsonic acid via diphenylcyanoarsinic acid. Acid becomes inorganic arsenic by biodegradation.

また、土壌中では生物分解・反応の一つとして、有機化合物がメチル化する反応が知られており、化２式に示すように、フェニルメチルアルシン酸についてもモノフェニルアルソン酸がメチル化した可能性がある。

In addition, the reaction of methylation of organic compounds is known as one of the biodegradation / reactions in soil. As shown in Chemical Formula 2, monophenylarsonic acid can be methylated with respect to phenylmethylarsinic acid. There is sex.

次に、既に提案されている有機金属化合物の除去方法を図３において説明する。図３において、除去設備は、産業廃水、下水、上水、埋立浸出水、地下水、河川水、池水、湖沼水、不法投棄現場の地下水や浸出水等の被処理水に含まれる有機金属化合物を除去するものであり、酸化処理工程を行う反応槽１と、無機金属除去工程を行う活性アルミナ吸着処理塔からなる無機金属除去装置２と、処理水貯槽３とからなる。

Next, an already proposed method for removing an organometallic compound will be described with reference to FIG. In Fig. 3, the removal equipment is an organic metal compound contained in treated water such as industrial wastewater, sewage, clean water, landfill leachate, groundwater, river water, pond water, lake water, illegal dumping groundwater and leachate. It consists of a reaction tank 1 that performs an oxidation treatment step, an inorganic metal removal device 2 that includes an activated alumina adsorption treatment tower that performs an inorganic metal removal step, and a treated water storage tank 3.

The reaction tank 1 is provided with an ultraviolet irradiation device 4 (lamp or the like) for irradiating ultraviolet rays, an ozone supply device 5 for injecting ozone, and a pH adjusting device 6 for injecting a pH adjusting agent.
In the reaction tank 1, the water to be treated containing the organic metal compound is irradiated with ultraviolet rays by the ultraviolet irradiation device 4, and ozone is blown from the ozone supply device 5. And As prior art documents, there are Patent Documents 1 and 2.
JP-A-9-75957 JP 2000-176468 A

By the way, in the above-described treatment, it is difficult to remove inorganic arsenic present in the form of arsenic oxides of AsO and As ₂ O _{3 in} the water to be treated, and the removal level of inorganic arsenic is stably adjusted to T-As0. There was a problem that the treatment to make it 01 mg / L or less could not be performed. Moreover, there was a problem that organic arsenic could not be processed to a removal level of an undetected value of 0.001 mg / L (arsenic conversion value) or less. Furthermore, since dissolved oxygen and dissolved ozone in the water to be treated deteriorate the chelate and activated alumina, there is a problem that the running cost required for operating the apparatus is increased.

  This invention solves the above-mentioned subject, and it aims at providing the detoxification method of organic arsenic which can suppress degradation of a chelate and activated alumina, and can promote decomposition and removal of organic arsenic and removal of inorganic arsenic. .

In order to solve the above problems, the method of detoxifying the organic arsenic present invention, photochemical decomposition step the water to be treated, the dissolved ozone decomposing step is intended for processing in the adsorption step, the water to be treated in a photochemical decomposition step pH5 The ozone supplied by the photochemical decomposition process in the dissolved ozone decomposition process by irradiating ultraviolet rays in the presence of ozone while maintaining at -9, oxidizing and dechlorinating the organic arsenic in the water to be treated by the generated hydroxyl radicals It dissolves and removes dissolved ozone in the treated water, and adsorbs and removes inorganic arsenic in the ozone removed treated water supplied from the dissolved ozone decomposing process in the adsorption process.

  With the above-described configuration, inorganicization of organic arsenic is promoted by oxidation and dechlorination in the photochemical decomposition step. Dissolved ozone in the ozone-treated water that has undergone the photochemical decomposition process can be eliminated by decomposing and removing in the dissolved ozone decomposition process, preventing the deterioration of chelates and activated alumina due to ozone and hydroxy radicals in the adsorption process, The adsorption process for adsorbing and removing inorganic arsenic can be performed stably.

The organic arsenic detoxification method of the present invention treats treated water in a photochemical decomposition step, decomposition / reduction step, and adsorption step, and maintains the treated water at a pH of 5 to 9 in the photochemical decomposition step. Irradiate ultraviolet rays in the presence, and oxidize, dechlorinate, decompose and remove organic arsenic in the treated water by the generated hydroxy radicals, and decompose and remove dissolved ozone in the ozone treated water supplied from the photochemical decomposition process in the decomposition and reduction process At the same time, the arsenic oxide is reduced, and the arsenic in the ozone removal treated water supplied from the decomposition / reduction process is adsorbed and removed in the adsorption process.

  With the above-described configuration, inorganicization of organic arsenic is promoted by oxidation and dechlorination in the photochemical decomposition step. Decomposition and removal of dissolved ozone in the ozone-treated water in the decomposition and reduction process eliminates the adverse effects of ozone, and reduces and ionizes arsenic oxide, thereby reducing chelate and activated alumina due to ozone and hydroxy radicals in the adsorption process. In addition, the adsorption process of adsorbing and removing arsenic can be performed stably while preventing the removal rate of inorganic arsenic to T-As 0.01 mg / L or less.

  As described above, according to the present invention, the process of oxidizing and dechlorinating organic arsenic and the process of adsorbing mineralized arsenic are performed non-serially, and dissolved ozone and hydroxy radicals are removed between the two processes. Thus, it is possible to prevent deterioration of the chelate and activated alumina in the adsorption process. In addition, the organic arsenic can be completely mineralized by oxidation and dechlorination in the photochemical decomposition step. Further, arsenic oxide can be removed by reduction.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiment shown in FIG. 1 has a configuration suitable for groundwater having a concentration of organic arsenic of T-As 50 mg / L or less as water to be treated.

In FIG. 1, a photochemical decomposition tower 2 having a sealed structure into which water to be treated 21 flows has an ultraviolet lamp 23 serving as an ultraviolet irradiation device disposed therein, and an air diffuser 24 disposed at the bottom. An ozone generator 25 is connected to the diffuser 24, and the ozone generator 25 supplies an ozone-containing gas having an ozone concentration of 5 to 50 g / Nm ³ to the diffuser 24. The photochemical decomposition tower 22 communicates with a pH adjusting tank 27 through a circulation system 26, and the pH adjusting tank 27 has a chemical supply system 28 for supplying NaOH as a pH adjusting agent and a stirring device 29. .

  The dissolved ozone decomposition tower 30 into which the ozone treated water that has passed through the photochemical decomposition tower 22 flows is communicated with the pH adjusting tank 27 through the ozone treated water supply system 32 having the pump 31 and filled with activated carbon as a catalyst. The ozone-treated water is passed through the catalyst packed bed 33 in a downward flow.

  The adsorption tower 34 into which the ozone removal treated water that has passed through the dissolved ozone decomposition tower 30 flows is communicated with the lower part of the dissolved ozone decomposition tower 30 through the ozone removal treated water supply system 35 and contains activated alumina (adsorbent) as an adsorbent inside. Or an adsorbent packed bed 36 filled with chelate), and ozone removal treated water is passed through the adsorbent packed bed 36 in a downward flow. The adsorption tower 34 communicates with the treated water storage tank 38 via the treated water supply system 37, and a discharge system 39 is connected to the treated water storage tank 38.

Hereinafter, the operation of the above-described configuration will be described. The treated water 21 containing organic arsenic is sequentially treated in a photochemical decomposition tower 22, a dissolved ozone decomposition tower 30, and an adsorption tower 34.
In the photochemical decomposition tower 22, ozone-containing gas having a predetermined ozone concentration of 5 to 50 g / Nm ³ is supplied from the ozone generator 25 to the diffuser 24, and the ozone-containing gas is diffused from the diffuser 24 to treat ozone. Pour into water 21.

  In the presence of ozone, ultraviolet rays are irradiated from the ultraviolet lamp 23 to generate hydroxy radicals, and the organic arsenic contained in the treated water 21 is oxidized and dechlorinated by the hydroxy radicals, and the treated water 21 is photochemically decomposed. It circulates between the tower 22 and the pH adjustment tank 27, and it processes, maintaining at pH 5-9 (optimum pH 7-8). In this photochemical decomposition tower 22, decomposition and removal of organic arsenic can be promoted by oxidation and dechlorination, and the organic arsenic can be substantially completely mineralized.

  In the dissolved ozone decomposition tower 30, the ozone treated water supplied from the photochemical decomposition tower 22 through the ozone treated water supply system 32 is passed through the catalyst packed bed 33, and the dissolved ozone is decomposed and removed by the catalytic action of activated carbon into oxygen. The activated carbon in the catalyst packed bed 33 serves not as an adsorption action but as a catalyst, so it does not break through and can be used for a long time.

  In the adsorption tower 34, the ozone removal treated water supplied from the dissolved ozone decomposition tower 30 through the ozone removal treated water supply system 35 is passed through the adsorbent packed bed 36, and inorganic arsenic in the ozone removal treated water is removed by the adsorption action of activated alumina. Remove by adsorption.

  In addition, in the adsorption tower 34, the inflowing ozone removal treated water is obtained by decomposing and removing dissolved ozone in the dissolved ozone decomposition tower 30, so that it is not adversely affected by ozone and prevents deterioration of activated alumina by ozone and hydroxy radicals. In addition, the adsorption step of adsorbing and removing inorganic arsenic can be performed stably.

  As a result, T-As in the treated water is below the detection limit (T-As ≦ 0.001 mg / L). The treated water is supplied to the treated water storage tank 38 through the treated water supply system 37 and discharged from the discharge system 39 to the river or the like.

  FIG. 2 shows another embodiment of the present invention, which is a configuration suitable for wastewater having an organic arsenic content concentration of T-As 50 mg / L or more as water to be treated. Constituent elements that perform the same operations as those of the previous embodiment are denoted by the same reference numerals and description thereof is omitted.

In FIG. 2, a decomposition / reduction facility 50 into which ozone-treated water flows through the photochemical decomposition tower 22 has a dissolved ozone decomposition tower 30 and a reduction treatment tank 51 communicated with each other through a circulation system 52. The reduction treatment tank 51 has a reducing agent supply system 53 for supplying a reducing agent such as Na ₂ SO ₃ and a stirring device 54. It is also possible to provide an inert gas supply system (indicated by a broken line in the figure) 55 for supplying an inert gas such as nitrogen gas to the dissolved ozonolysis tower 30 instead of using a reducing agent. In this case, the reduction treatment tank 51 is unnecessary, and only the circulation system 52 is used.

The reduction treatment tank 51 communicates with the agglomeration tank 56, and the agglomeration tank 56 has a flocculant supply system 57 for supplying FeCl ₃ as a flocculant and a membrane separation device 58, and the membrane separation device 58 is a membrane for supplying a membrane permeate. It communicates with the adsorption tower 34 via the treated water supply system 59. Although not shown, a treated water storage tank is provided at the rear stage of the adsorption tower 34 as in the previous embodiment.

Hereinafter, the operation of the above-described configuration will be described. The treated water 21 containing organic arsenic is sequentially processed in the photochemical decomposition tower 22, the decomposition / reduction facility 50, and the adsorption tower 34.
In the photochemical decomposition tower 22, ozone-containing gas having a predetermined ozone concentration of 5 to 50 g / Nm ³ is supplied from the ozone generator 25 to the diffuser 24, and the ozone-containing gas is diffused from the diffuser 24 to treat ozone. Pour into water 21.

  In the presence of ozone, ultraviolet rays are irradiated from the ultraviolet lamp 23 to generate hydroxy radicals, and the organic arsenic contained in the treated water 21 is oxidized and dechlorinated by the hydroxy radicals, and the treated water 21 is photochemically decomposed. It circulates between the tower 22 and the pH adjustment tank 27, and it processes, maintaining at pH 5-9 (optimum pH 7-8). In the photochemical decomposition tower 22, the decomposition and removal of organic arsenic can be promoted by oxidation and dechlorination, so that the organic arsenic can be completely mineralized.

In the decomposition / reduction facility 51, the ozone treatment water supplied from the photochemical decomposition tower 22 through the ozone treatment water supply system 32 in the dissolved ozone decomposition tower 30 is passed through the catalyst packed bed 33, and the dissolved ozone is decomposed and removed by the catalytic action of activated carbon. To do. Furthermore, the ozone-treated water circulates between the reduction treatment tank 51 through the circulation system 52, and arsenic oxide AsO, As ₂ O ₃ by the reducing action of the reducing agent supplied from the reducing agent supply system 53 in the reduction treatment tank 51. ^Are ionized to As ⁺ , As ^{2+, and the} like.

The ozone-treated water from which dissolved ozone is removed by the decomposition / reduction facility 50 and arsenic oxide is reduced is subjected to the agglomeration membrane separation treatment in the agglomeration tank 56 and then supplied to the adsorption tower 34 as a membrane permeate.
In the adsorption tower 34, the membrane permeate supplied from the reduction treatment tank 51 through the membrane treated water supply system 59 is passed through the adsorbent packed bed 36, and the ionized arsenic in the membrane permeate is adsorbed and removed by the adsorption action of activated alumina. To do. In this adsorption tower 34, the inflowing membrane permeate is obtained by decomposing and removing dissolved ozone in the dissolved ozone decomposition tower 30, so that it is not adversely affected by ozone and can prevent deterioration of activated alumina due to ozone and hydroxy radicals. In addition, the adsorption process for adsorbing and removing arsenic can be performed stably.

  As a result, by reducing and adsorbing arsenic oxide, inorganic arsenic in the treated water is T-As 0.01 mg / L or less, and organic arsenic is below the detection limit (T-As ≦ 0.001 mg / L). . Similar effects can be obtained even when an inert gas such as nitrogen gas is used instead of the reducing agent.

The schematic diagram which shows the apparatus structure in embodiment of this invention The schematic diagram which shows the apparatus structure in other embodiment of this invention. Schematic diagram showing a conventional device configuration

Explanation of symbols

21 Water to be treated 22 Photochemical decomposition tower 23 Ultraviolet lamp 24 Air diffuser 25 Ozone generator 26 Circulation system 27 pH adjustment tank 28 Drug supply system 29 Stirrer 30 Dissolved ozone decomposition tower 31 Pump 32 Ozone treated water supply system 33 Catalyst packed bed 34 Adsorption tower 35 Ozone-removed treated water supply system 36 Adsorbent packed bed 37 Treated water supply system 38 Treated water storage tank 39 Discharge system 50 Decomposition / reduction equipment 51 Reduction treatment tank 52 Circulation system 53 Reductant supply system 54 Stirrer 55 Not Active gas supply system 56 Coagulation tank 57 Coagulant supply system 58 Membrane separation device 59 Membrane treated water supply system

Claims (2)

Hydroxy to be generated by treating the water to be treated in the photochemical decomposition step, dissolved ozonolysis step, and adsorption step, maintaining the water to be treated at pH 5-9 in the photochemical decomposition step and irradiating with ultraviolet rays in the presence of ozone. Organic arsenic in treated water is oxidized, dechlorinated and decomposed and removed by radicals, dissolved ozone in ozone-treated water supplied from the photochemical decomposition process in the dissolved ozone decomposition process is decomposed and supplied from the dissolved ozone decomposition process in the adsorption process An organic arsenic detoxification method comprising adsorbing and removing inorganic arsenic in ozone-depleted treated water. Hydroxy is produced by treating the water to be treated in the photochemical decomposition step, decomposition / reduction step, and adsorption step, and maintaining the water to be treated at pH 5-9 in the photochemical decomposition step and irradiating with ultraviolet rays in the presence of ozone. Organic radicals are oxidized, dechlorinated and decomposed and removed by radicals, and dissolved ozone in the ozone-treated water supplied from the photochemical decomposition process is decomposed and removed in the decomposition and reduction process, and arsenic oxide is reduced and adsorbed. An organic arsenic detoxification method characterized by adsorbing and removing arsenic in ozone-removed treated water supplied from a decomposition / reduction process in the process.

Images