CS243521B1 - Method of waste waters recycling originating from tannery raw materials' liming - Google Patents

Description

The present invention relates to a process for recycling waste water from leaching of a tanning raw material, carried out in two separate peeling and liming operations, after which the skins are washed separately and waste water from both the leaching operations and both subsequent washes is separately collected into containers.

The development of the leather industry must also take account of environmental protection, not only by reducing the quantity but also by contaminating waste water. The problem can be solved either by treating waste water with a lower content of pollutants.

Leaching is the strongest source of tannic wastewater pollution. Significant amounts of degraded proteins in these waters cause high oxygen consumption and, together with lime, produce a large amount of primary sludge.

In addition, the most widely used and practically cheapest sodium sulfide, quickly and reliably dissolving hair, is a steep one for aquatic fauna. Therefore, great attention is paid to leaching, and the most suitable method for reducing the amount and degree of contamination of waste is to return the used bath back to the process cycle.

Several such processes are known which differ not only in the demands on the equipment but also in their efficiency. For example, MS. 210 593 protects waste liquor waste recycling in combination with mechanical treatment by sedimentation, filtration and ultrafiltration, but in this process there is always a relatively high residual wastewater pollution, mainly due to daily sewage sediment or unusable excess wash water after leaching.

Moreover, recycled liquors of this type are very rapidly thickened by increasing the content of salts and degraded proteins, so that the peeling and swelling ability of the liquor is reduced and the usable number of cycles is reduced.

A disadvantage of more complicated recycling systems, such as recycling associated with mechanical purification and supplemented by chemical acidification, precipitates dissolved proteins and discharges sodium sulfide in the form of hydrogen sulfide according to US. АО 133 077 are high investment costs for necessary equipment, chemical costs and demands on work organization.

The described deficiencies are eliminated by the method of recycling waste water from leaching of tanning raw material, following the method of leaching in two separately separate baths after peeling and liming, always followed by separate washing and collection of waste water according to MS. 237 460.

The essence of the recycling process according to the invention is that, in the amount of 60 to 135 parts by weight, based on 100 parts by weight of the waste, the waste water from peeling and liming is returned to the subsequent cycles of the same operation, together with 5 to 80 parts by weight of the waste water. after dehumidification and after lime scrubbing, 50 to 125 parts by weight and 15 to 90 parts by weight respectively are fed into the subsequent cycles of the tanning raw material operation, i.e. after the shoulder, being added to the dewatering waste water. In relation to the weight of the skins, 1 to 1.8% by weight of sodium girder, 0.01 to 1.0% by weight of calcium hydroxide, 0.01 to 1.0% by weight of sodium hydroxide, or 0.1 to 2.0% by weight of carbonate %, while 1.0 to 2.5 percent by weight calcium hydroxide and 0.01 to 1.0 percent by weight sodium hydroxide are added to the liming effluent recycled to subsequent liming cycles.

According to what. 237460, the leaching is decomposed into separate peeling and liming itself. When peeling occurs the required loosening and swelling of the clearing.

Between the two operations, washing is included so that the sulphide from the peeling is introduced into the limestone bath in the lowest possible amount.

³ 243521

In the method according to the invention, the peeling and lime baths are separately captured and reused for the same purpose. The scrubbing washing water is partly used to replenish the volume of the scrubbing bath and the remainder is used as a soaking bath which is made up to the required volume with either pure water or scrubbing water after liming.

The sodium sulfide present in the soaked soaking bath raises the pH to 8-10, which positively affects the intensification of the shoulder. Sodium sulfide is decomposed from the bath during treatment, both by reaction with hairy keratin and by oxidation with air oxygen.

The waste water bath is then virtually free of sulphide or contains only traces. The gradually decreasing efficiency of the peeling or lime solution is restored by mechanically cleaning and replenishing the active chemicals, i.e., sodium sulfide into the peeling bath, and the calcium hydroxide into the lime bath.

However, even in this way the efficiency of these baths changes with the gradual increase of the individual cycles, and therefore, in the process according to the invention, chemicals are added to keep the effects of both solutions within the desired range.

Calcium hydroxide in an amount of from 0.01 8 to 1.0% and sodium hydroxide in an amount of from 0.01% to 1.0% or sodium carbonate in an amount of from 0.1 to 2.0 are specifically added for the peeling bath. %, all based on the weight of the skins.

For the calcium bath, sodium hydroxide is added in an amount of from 0.01% to 1.0%. Wastewater recycling after leaching thus decomposed to peeling and liming can be used to produce the desired quality of the soil, since loosening and swelling takes place already in the peeled state, while the increasing content of dissolved degraded products of proteins, salts and other impurities is divided into two baths. achieve a high number of usable recycling cycles.

Excess washing water after liming falling into the sewer is very poor in sodium sulfide and its concentration does not exceed 0.1 - 0.2 g / l, with a total volume of max.

In the process according to the invention, pure water is used in the process only for washing, while for efficient operations, ie, watering, peeling and liming, water is recycled.

The process of the invention is illustrated in more detail by an exemplary embodiment which includes, for clarity, an initial, so-called zero-cycle, in which fresh baths are used, most suitably AO 237460 'and other cycles using baths recycled by the process of the invention.

Example

The amount of water used depends essentially on the type of vessel used, the temperature according to custom. All percentages are by weight based on skin weight.

Soak for prime cycle water ^and from 22 to 24 ° C, sodium carbonate, sodium polyglycol movement time bath is drained into the sewer

140 _%

0.2%

0,5 «

150-180 min for additional washes wash cycle

110-125% after peeling washing bath after liming sodium polyglycol ether sulphate movement time bath is drained into the sewer

30-15 '%

0.2%

150-180 min Zero cycle water 22-24 ° C sodium sulphide technical movement time 180 minutes bath overflow through sieves and pumped into tank

140%

2.4 for the next cycle, the peeling bath falls off

washing waste bath after peeling sodium sulfide technical calcium hydroxide sodium hydroxide movement time 180 minutes, the bath is sieved through a sieve and pumped into a reservoir.

120-135%

20-5%

1,4-1,6

0,3-0,2

0,1-0,2

Washing after unhairing and a ^d 22 to 24 ° C for 30 minutes travel time, bath off and pumped into the reservoir.

140% for přefilVápnění ^d prime cycle at 22-24 ° C and calcium hydroxide movement time till morning calm morning. movement 30 minutes. pumped into the tank

140 ΐ

1,8-3,0 180-240 min bath for further cycles lime waste bath renegade washing bath after lime calcium hydroxide sodium hydroxide time to morning rest, move 30 minutes in the morning, the bath is pumped into a reservoir

120-135%

20-5%

1,3-1,5

0,1-0,2

180-240%

% min

Washing after liming water 22-24 ° C movement time 30 minutes The bath is partially pumped into the reservoir, partially drained into the sewer.

100%

Washing of the ground takes place as usual until the ground is not slippery to the touch

Claims (2)

1. A method for recycling waste water derived from leaching of a tanning raw material, in which the skins likely to be separately collected by liming, are returned to a large number of downstream washings after dewatering in two separate dewatering and liming operations, flax and waste water from both operations. The waste water from peeling and from 6o to 135 tonnage parts, based on 100 hours of leather parts, cycles of the same operation, together with 5 to 80 waste parts of washing or after washing The amount of lime, and the remainder of the effluent from the scrubbing and lime scrubbing processes are added to the subsequent cycles of the tanning raw material, i.e. to the seam, at a quantity of 50 to 125 tonnage portions and 15 to 90 mass portions respectively. 2. A method according to claim 1, characterized in that from 1 to 1.8% by weight of sodium sulfide is added to the dewatering waste water recycled to the subsequent dewatering cycles, from 0.01 to 1.0% by weight of sodium sulfide. % by weight calcium hydroxide, 0.01 to 1.0 hour sodium hydroxide or 0.1 to 2.0% sodium carbonate, while 1.0 to 2 is added to the liming effluent recycled to subsequent liming cycles, 5% by weight of calcium hydroxide and 0.01 to 1.0% by weight of sodium hydroxide.