CS196814B1 - Method of pre-treatment of waste water in textile industry,containing compounds of hexavalent chromium - Google Patents

Description

BACKGROUND OF THE INVENTION The present invention relates to a process for pretreating waste water in the 6+ textile industry containing Cr chromium compounds.

Waste waters in the textile industry, mainly wool, are not capable of direct biological treatment in urban wastewater treatment plants unless they are largely undiluted by urban sewage. The greatest problems arise from the discharge of compounds of the tremendous Cr ⁶⁺ , which is toxic to biological treatment. Chromium Cr compounds enter wastewater from wool dyes where alizarin chromium dyes are used. So far, the contaminated groundwater has been disposed of in plant chemical treatment plants by adding clarifiers, most often FeSO4 and CaO. The low purification effect of chemical treatment plants and the high salinity of the treated wastewater do not meet today's requirements for the purity of discharged water into streams, where it significantly increases their pollution, especially in low water flows. For these reasons, the public authorities require the purification of these chemically treated waters at biological stage.

The above drawbacks are overcome by the method of pretreatment of the wastewater in the textile industry containing the chromium compounds of the invention, which consists in treating the wastewater containing the chromium compounds Cr 8 ⁺ with an eightfold amount of sodium sulfide, technical, by mixing and mix. The proposed method of wastewater treatment consists in the fact that ae in the waste water effluent from the paint plant eliminates the presence of Cr by means of Na ₂ S, so that from the original concentrations of chromium compounds in the effluent discharges 0.2 mg / l Cr ⁺ . , 4 mg / 1 Cr ⁶⁺ adjusts their incidence to 0, - mg / 1 Cr ⁶⁺ and maximum

0.48 mg / l of Cr ^ ^{+ +} .

The proposed method of wastewater treatment will allow the elimination of chemical clarification and elimination of Cr® ⁺ chromium compounds in these waters. It will enable their direct cleaning even in small and medium-scale biological treatment plants, where there is little undilution by urban sewage. A further advantage of this wastewater treatment method is that it does not require high investment costs for the construction of a wastewater treatment plant and provides savings in operating costs for their pretreatment for biological treatment, where labor saving is currently the most interesting.

Example 1

The reduction of a substantial portion of the chromium Cr ⁶⁺ compounds in the chromation baths can be carried out directly in the boiling tank of the dyeing apparatus. The bromination bath is pumped from the dyed material back to the weighing tank, where for each mass. the amount of K ₂ Cr ₂ O y used to chromate the alizarin dye is added eight times by weight. The amount of technical Na ₂ S is discharged. Biological treatment is discharged through a buffer tank with a capacity of 1,200 m < 2 > The effluents thus treated contain 0.1 mg / l of Cr ^ ⁺ and a maximum of 0.48 mg / l of Cr ^ ⁺ .

Example 2

In the case of the dyeing apparatus, where the chromating bath cannot be pumped back to the boiling tank, it is dosed into an eight-fold mass. amount of technical Na ₂ S as mass. the amount of K ₂ Cr ₂ O 4 used to chromate the alizarin chromium dye while draining the chromation baths. The discharge for biological treatment takes place via a buffer tank of * 5 _v

1,200 m, where these treated waters are diluted with the other effluents of the plant and part of the Cr ³⁺ ee present is bound to the sludge present. The effluent discharges of the plant then contain 0.1 mg / l Cr & lt ^{; +} & gt ^; and a maximum of 0.48 mg / l Cr ^< ^{+ >} .

Example 3

3+

All plant effluents containing up to 3 mg / l Cr ^J and 0,2 mg / l Cr ^{J +} at the time of chromation bath discharges are alternately infused into two mixing tanks where they are treated with other alkaline plant water or by addition of chemicals to pH 4 to 6 and determine the content of K ₂ Cr ₂ O ₂ . For the disposal of each identified mass. amount of K ₂ Cr ₂ O 2 se

- 3 196814 adds eightfold mass. amount of technical NSgS and after thorough mixing are released for biological purification. The effluents thus treated contain 0.1 mg / l of Cr ^ ⁺ and a maximum of 0.48 mg / l of Cr ^ ⁺ .

Claims (1)

Object of the invention Method for pretreatment of waste waters in the textile industry containing Cr ²⁺ compounds, characterized in that waste waters containing Cr ²⁺ compounds in which the pH has been adjusted to between 4 and 6 by alkaline waste water are treated by mixing and mixing the technical sulfide sodium salt by an eightfold weight amount, such as the detected amount of potassium dichromate in the chromating bath.