CA1105159A

CA1105159A - Process for the treatment of waste water

Info

Publication number: CA1105159A
Application number: CA314,560A
Authority: CA
Inventors: Emmerich Paszthory; Arnold Albers; Erich Ringel; Hans-Gerd Elinkmann
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1977-10-29
Filing date: 1978-10-27
Publication date: 1981-07-14
Also published as: ZA786067B; DE2748638A1; EP0001792A1; IT1101057B; AU4106878A; IT7829196A0; JPS5471854A; DK479778A

Abstract

PROCESS FOR THE TREATMENT OF WASTE WATER

Abstract of the disclosure:
Industrial waste waters contain frequently organic components which slow down or hinder a biological decompo-sition. However, after treating the waste waters with nitric acid or nitrates at elevated temperature, the residual organic impurities may be readily removed by biological degradation.

Description

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- 2 - ~OE 7r//F 216 The present invention relates to a process ~or the o~idative purification of waste water in the liquid state, which contains organic compounds in dissolved or suspended form. In the industry there are frequently obtained waste waters, which contain in addition to inorganic constituents organic substances. In particular in the chemical field, for example in the manufacture of organic intermediates for dyestuffs, ~or organic mas; products such as paper or for herbicides, there are frequently obtained waste waters which must be purified. A number of special processes are known for eliminating the organic compounds present in the waste water in dissolved or suspended form, for example the extraction Or soluble substances or the separation of the waste water by distillation. In most cases, however, those waste waters which contain bio-decomposable organic substances, are treated in biological sewage treatment plants. It is known, however, that in some cases the organic impurities of the waste water are decomposed very slowly in the conventional biological sewage treatment plants by bacteria ("biologically inactive compounds") or that they hinder the decomposition of other decomposable substances ("biologically toxic compounds"). This applies, for example to phenol-containing waste waters and to waste water obtained in the manufacture of herbicides, in par-ticular of fungicides.
~ known process for the decomposition of these bio-logically non-decomposable organic substances consists in submitking the waste waters to a wet combustion. In this 29 process the waste water is heated to a temperature of from ~ -;:

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- 3 ~ HOE_77/F 216 about 250 to 350C in the presence of oxygen-containing gases. This process has the disadvantage that a compli cated apparatus is required for introducing oxygen under high pressure and that relatively great quantities of oxygen are consumed.
The present invention, consequently, seeks to provide a process which does not exhiblt the above disadvantages and which permits the purification of those waste waters which are not biologically decomposable, i.e. which con-tain toxic or biologically inactive ~ubstances, to sucha degree that a subsequent biological purification is possible.
A novel process has now been found for the wet~oxi-dative decomposition of waste water containing in dissolv ed or suspended form organic compounds.The process comprises adding nitric acid or soluble nitrates to the waste water and heating the waste water to a temperature of from 100 ; to 250C. A preferred upper temperature limit for the waste water treatment is near 230C, in particular 220C. The process is preferably carried out at a temperature above 120C, in particular above 140C, preferably above 180C.
Soluble nitrates include inorganic salts, in particular salts of the alkali metals or alkaline earth metals such as NaN03 and Ca(N3)2 The process is also efficient at temperatures above 250C, however, raising temperatures entrain an increas-~: :
ing attack of the material of which the reaction vessel is made (tantalum, chromium-nickel steel, enamel). Further-: ~ ?9 more, it becomes the more difficult to construct such a :; : . ' ' :

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_ 4 _ HOE_77/F 216 vessel the higher the pressure employed.
The present process is especially suitahle for the treatment of production waste water, stemming from the ~,a-nufacture of herbicides, in particular o~ fungicides. It is surprising that it are the biologically toxic components of the waste water that are destroyed by low quantities of nitric acid while the bio-decomposable components remain substantially persistent. In case that the waste water con-tains notable quantities of voLatile solvents (such as ben-zene, toluene or xylene), it may be advisable to remove, oroptionally to recover, the main quantity of the solvent by distilling o~`f some water (together with the solvent), and to reduce thus the necessary feed quantity of HN03 or of nitrates. In addition to organic components the waste water may contain inorganic components such as sodium sul-fate, sulfuric acid or ammonium salts. Ammonium sal'cs are partially decomposed in the process of the invention.
The degree of their decomposition depends mainly on the feed quantity of nitric acid. Approximately one mol of nitric acid is required for destroying one equivalent of ammonium ions. Those waste waters which contain at most 10 weight percent of acid, calculated as H2SO49 are pre-ferred. The pH of the waste water employed is not cri-tical. ~Acid waste waters may be used as well as neutral 2~ or alkaline waste waters. This applies also to when us-ing soluble nitrates. The process according to the inven-tion is suitable in particular for those waste waters which have a CSB value of at most 100 g 2 per liter, in parti-29 cular at least 5 g 2 per liter. Low ~uantities of nitric .

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5 - ~IOE 77/F 216 acid are sufficient to render the waste waters bio-decom-posable. The quantities of the additives ~epend on the quantity and on the nature of the impurities and are in the range of from 1 to 18, in particular of from 1.5 to 8, preferably of from 2 to 5 weight percent, of nitric acid (anhydrous). An equivalent quantity of nitrates may be used alternatively instead of HN03.
- When adding considerable quantities of oxidants, the process of the invention may lead to a nearly complete de-composition of all organic products and of ammonium ions.
To achieve such a decomposition, correspondingly greater stoichiometrical quantities of nitric acid or of` nitrates, - proportionally to the measured CSB-value, are required.
The process is suitably carried out in a way that with low quantities of nitric acid or nitrates mainly the biolo-gically toxic compounds are destroyed. The waste water re-covered after this treatment may be subjected subsequently to a biological purification by activated sludge. In some cases the waste water obtained during the oxidation is so ~ 20 pure that it may be reused as process water.
; The process according to the invention may be perform-ed continuously, for example in a tube reactor or disconti-nuously, for example~in batchwise operation.
The following examples illustrate the invention:
E X A M P L E 1:
In the manufacture of the fungicide 2-carbomethoxyamino-benzimidazole there is obtained a production waste water ` : : :
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~ 6 ~IOE 77/F 216 The waste water is clark brown and contains dark co-lored flocculi. The content of 2-carbomethoxyamino~benz~
imidazole is approximately 10 ppm. The p~ is ~.2, the CSB-value 50,000 mg 02/l (the CSB value indicates the amount of chemically bound oxygen, expressed as mg 02/l, whlch is required for oxidizing the organic compounds completely to give C02 and H20. The CSB value is determined accord-ing to a standardized method using K2Cr207 in dilute sul-furic acid in the presence of Ag~ ions.) In a pressurized vessel having a volume of 3 m3 which is tantalum-coated there are placed 2 m3 of the waste water of the above type with 60 kg of nitric acid of 65 %
strength and the batch is heated to 195C. The tempera-ture of the contents of the vessel rises to about 212C
(pressure: 20 bars) during this operation. On attaining this temperature peak, the batch is cooled immediately.
The resulting waste water is light yellow to red brown colored and practically inodorous. The CSB-value is 33,000 mg 02/l, the BSB5-value 19,000 mg 02/l, the pH 7.8. When used in a dilution of 1:200, the waste water thus treated is not toxic to fishes.
E X A_M P L E ?:
30 kg/h of nitric acid of 65 % strength and 500 l/h of the waste water, decribed in Example 1 are fed to a flow tube coated with tantalum and having an inner diame-ter of 50 mm, simultaneously and uniformously, and the contents are heated with direct steam. The volume of the flow tube is 40 liters. The pressure of the system is ad-29 justed to 32 bars by means of a pressure-maintaining valve, : . . ~ :
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which corresponds to a temperature of frorn 212 to 215C
The continuously withdrawn waste water is light yel-low colored, has a CSB-value of 14,000 mg O2/l, a BSB5-value of 8,800 mg O2/l and a pH of about 1Ø
The waste water treated in said manner is no longer toxic biologically and may, consequently, be subjected to a biological sewage treatment plant.
E X A M P L E 3:
Example 1 is repeated, expect that only 25 kg of` ni-tric acid are used and that the batch is heated to a tem-perature of only 180 to 185C.
After cooling of the contents of the vessel, there is obtained a waste water which has a CSB-value of 40,000 mg O2/l, a BSB5-value of 20,000 mg O2/l and a pH of 7Ø
The waste water is no longer toxic to fishes.
E X A M P L E 4:
During the manu~acture of 1-phenyl-semicarbazide from phenylhydrazine, urea and water there is obtained a waste water which is toxic and not decomposable biologically be-cause of its phenylhydrazine content of about 0.05 %.
The CBS-value is 37,000 mg O2/l, the content of am-- monium chlorïde 15 %, the pH is 6.2.
. 2,000 liters of this waste water are treated as des-; cribed in Example 1 with 80 kg of nitric acid, at 210C.
25 The resultlng waste water has a CSB-value of 149500 mg 2~
1, a BSB5-value of 9,000 mg O2/l and a pH of 5Ø The phe-nylhydrazine content is below 1;ppm, the ammonium chloride content is about 11 %.
29 The waste water thus treated may be easily purified .

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8 HOE 77/~ ? l 6 in a biologically sewage treatment plant. It may alter~
natively be reused in the manufacture of 1-phenyl-.semicar-bazide.
E X A_M P L E 5:
During the treatment of cellulose in an alkaline me-dium with ethylene oxide there are obtained waste waters which contain in addition to high molecular components about 0.3 % of glycols in dissolved form. Their CSB-va-lue is 33,100 mg 02/l, the pH is 8.7, the total carbon content 9,000 mg 02/l. When diluted in a ratio of 1:100, the waste water may be decomposed biologically. From the found oxygen consumption a BSB5 content of 27,500 mg 2/
l may be deduced.
2 liters of this waste water and 20 g/l of nitric acid of 65 % concentration are placed in a tantalum bornb, heated for 50 minutes to 250C and kept thereafter at this temperature for 1 hour. The final pressure is about 40 bars. The bomb is cooled with cold air to 86C within 3 hours and emptied thereafter. The treated waste water has a BSB-value of 22,800 mg 02/l, a BSB5-value of 14,800 mg 02/l and a pH of 2.9. It is bio-decomposable even when not diluted. The total carbon content is 5,530 mg C/l.
E X A M P L E 6:
Example 5 is repeated except that 2 liters of waste water are treated with 40 g/l of nitric acid. The con-tents of the bomb are heated to 215C for 30 minutes and kept at this temperature for 1 hour under a pressure of 24 bars. The contents are cooled within 3 hours and the bomb 29 is emptied. The waste water has a CSB-value of 18,150 mg ,., . ` ' ': ' : ' , ' ,::: ` - -. : : ' :
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~ 9 ~ _O 77 _ 216 02/l, a BSB5-value of llJ,lO0 mg O2/l and a pH of 2.6~
The waste water thus oxidi.~.ed can be directly purified in a biological sewage treatment plant.
E X A M P L E 7:
When treating 2 liters of the waste water according to Example 5 with only lO g/l of nitric acid according to the procedure of Example 6, there is obtained a waste wa-tera which has a CSB-value of 26~400 mg O2/l and a BSB5-value of 24,750 mg O2/l. This waste water, too, may be directly conducted to a bilogical sewage purification plant.
.E X A M P L E 8:
Example 5 is repeated except that instead of nitric acid there is used sodium nitrate at a rate of 8.8 g/l.
After addition of sodium nitrate, the pH of the solution is about 8.7, after the oxydation at 215C about 4.1. The The CSB-value is 26,250 mg 2/l '.

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Claims

What is claimed is:

1. A process for the oxidative purification of waste wa-ter containing toxic and/or biologically inactive or-ganic substances in dissolved or suspended form, at elevated temperature, which comprises adding nitric acid or soluble nitrates to the waste water and heat-ing the latter to a temperature of from 100 to 250°C.

2. The process as claimed in claim l, which comprises heating to a temperature of from 180 to 220°C.

3. The process as claimed in claim l, which comprises cooling the treated waste water after oxidation and subjecting it to the activated sludge process whereby the residual organic impurities are biologically de-graded.

4. The process as claimed in claim 1, which comprises ad-justing the quantity of nitric acid or nitrate in such a manner that the chemically decomposable compounds are only partially decomposed.

5. The process as claimed in claim l, which comprises treating a production waste water obtained in the manufacture of organic intermediates or final products.

6. The process as claimed in claim 5, which comprises using waste water stemming from the manufacture of pesticides.

7. The process as claimed in claim 6, which comprises using waste water stemming from the manufacture of fungicides.

8. The process as claimed in claim 6, in which the waste water employed contains 2-carbomethoxybenzimidazole.