Tannery industries generate wastewater containing high concentrations of sulfur. Most of wastes are liquid (effluent). The river section and tanning are the source of most tannery waste. Dehairing is a process of separation of hair and epidermis. Lime and sulfides are used for this process. Thus, sulfur in wastewater dehairing occurs as sulfide. Today, catalysis is at the centre of major societal concerns about energy, environment and sustainable development. The discovery of new catalytic processes and the improvement of existing ones are also critically important for improving the quality of life while simultaneously reducing the adverse impact of human activities on the environment. With a substitution approach of a catalyst MnSO 4 by multiple wastes from tannery and the metallurgical sector, this study investigated the recycle of waste from dehairing process and waste from metallurgical industry. The results indicated 32% of oxidized sulfur for the first waste derived from process of depilation and 30% for the second waste from metallurgical process industry. A preliminary cost analysis demonstrated that the proposed solution is much cheaper than the discharging of waste and wastewater in a WWTP; however, the sustainability of the proposed solution provided a second alternative, to alleviate the operational costs of installations wastewater from tanneries, without significantly impacting the environment.
Tannery is an industry with strong potential of pollution. The incidences upon the environment which it is advisable to take into account understand not only the charges and the concentration of the traditional pollutants, but also the use of certain chemicals. Water is mixed with organic matter (proteins, peptides, and amino, acid ac- ids fatty, sulfur and trivalent chromium). They are highly polluted [
Without water purification (dysfunction of the installations) and in the absence of an effective technology of recovery, the unit loses annually on one hand:
・ 140 kilogram/day of chromium with their prices with 1.22 ?kg, are equivalent to 51879.77 ?year;
・ 162.4 kilogram/day of sulfides with their prices with 0.3 ?kg, are equivalent to 16577.76 ?year.
This heavy heritage of industry consuming water and import chemicals, the managers are forced to exert a responsibility. Management that implies, for example, to know well the chemicals implemented in the process (including the very prepared products). To take the safety measures for the protection of people, the environment and finally optimizes the operation of the waste water treatment installations in order to answer the multiple requirements and environmental stakes, social and economic [
On the other hand in Algeria, the steel industry activity’s generates an important production of industrial waste (slag) which raises a problem of storage and pollution. Following the example of industrial nations this product, presents a plentiful raw material or low cost. Who must be exploited on a large scale in operations “sometimes without interest for the administrators” for example the operations of waste water treatment [
The purpose of this research is to choose among the existing waste that can be reused. Within the framework of the application of the best available techniques, the goal is double: reusing waste and substitution with other products used in processes.
Several campaigns of data collecting were led to the exit of the stages of production, and at the level of the pond of collection where moved towards all the waste water generated by the company. Two modes data collecting are adopted:
Immediate grips and average samples constituted by the mixture of several collect distributed throughout the day at the rate of a collecting per hour.
Sulfur and other chemical parameters were analyzed according to the normalized (standardized) methods AFNOR [
To study the effectiveness of purification station of the unit by the new substituent, we carried out a partner of taking away of basic effluents (rejection between 6 A.M and 10 A.M of the morning) and acid (rejection between 10 A.M and 14 P.M), starting from the gutters of collection.
However, the objective of our partner was obtaining representative data collecting with an aim of being able to study on pilot the effectiveness of the station, and for this reason we based ourselves on the principal operations of purification, namely the desulfurization and precipitation of chromium.
The elimination of sulfur contained in water of river, is carried out by oxidation with contribution of air according to reaction, refer to “(1)”
Thus the sulfur will be transformed into thiosulfate. The Pourbaix curves clearly show the distribution of the species of sulfur according to the pH and the potential (see
To desulphurize the effluents of pre-hardening and hardening, a volume of effluent is collected at the end of the operations chain containing considerable quantities of sulfur. The rejections will be oxidized one taking account certain necessary parameters for the optimization of desulfurization results: (contribution of oxygen (O2), mechanical agitation, time):
・ Firstly: A contribution of air, during 3 hours using a compressor (a volume of anti-foamer is added to the reaction to avoid the foam formation which could obstruct the good diffusion of the air and thus the transfer of oxygen in water.
・ Secondly: Then by agitation during 3 hours, using a surface aerator (propeller electro-agitator);
・ Thirdly: Then a volume of manganese sulphate adds some MnSO4 (catalyst to be substituted there after by the ferrous waste of the iron and steel industry) used to obtain a complete and more rapid.
Initial volume of effluent = 464 mg/l.
The test and the proportioning of sulfur by ferricyanides of potassium show us that the elimination of sulfur by oxidation to the air in the presence of catalyst MnSO4 gives excellent results. Elimination of 99.43% of sulfur (refer to Graphics 1-3). These results will be taken as means of comparison with the results of the substitute (ferrous waste resulting from the activity of iron and steel industry). The results obtained, show us that the treatment of desulphurization envisaged is very effective. However the reaction time and the operating conditions must be well controlled (parameters). The study on pilot of the influence of these parameters with use of MnSO4 like catalyst, gives us the results (see
Indeed the results obtained, show us clearly and allow us to say that the best desulfurization is carried out by oxidation with contribution of air, and that simple agitation without contribution of air will not be enough to in any case with the desulfurization of the effluent ensures. But the frequent use of MnSO4 costs very expensive to the company (product of importation) and that always presents a charge leather for the industry.
Graphic 1. Percentage of oxidized sulfur (with 2 ml MnSO4).
Graphic 2. Comparison of the desulfurization results with (2 ml of MnSO4). (a) With variation parameters (Contribution of air and agitation); (b) Without variation parameters (without contribution of air agitation).
1) Objectives:
In order to decrease the importation of the products and thus to reduce the very high cost in currency for the leather company on the one hand, to find other exits for waste of another company of other share. We carried out tests of substitution of one of the products used in the station of waste water treatment (catalyst sulphate MnSO4 manganese) by another product (ferrous waste resulting from the iron and steel industry) available in Algeria and from which the chemical characteristics are not very different from that of catalyst used. The product used for substitution is FeSO4.
While being based on the fact that this product, when is oxide is become oxidants very strong and can thus take part in the oxidation of sulfur and replace catalyst envisaged MnSO4.
2) Experimental results of substitution:
Graphic 3. Comparison of the results of percentage desulphurized sulfur.
Time (hours) | Percentage oxidized sulfur (with parameters variation) |
---|---|
First hour | 51.73% |
Second hour | 79.32% |
Third hour | 86.21% |
Fourth hour | 93.91% |
Fifth hour | 98.28% |
Sixth hour | 99.43% |
Time (hours) | Percentage oxidized sulfur (with parameters variation) | Percentage oxidized sulfur (without parameters variation) |
---|---|---|
First hour | 51.73% | 0.0% |
Second hour | 79.32% | 0.0% |
Third hour | 86.21% | 0.0% |
Fourth hour | 93.91% | 3.68% |
Fifth hour | 98.28% | 4.90% |
Sixth hour | 99.43% | 7.36% |
For the oxidation of sulfur with use of the FeSO4 catalyst (
・ Test: 10 ml;
・ Sulfur concentration: 2816 mg/l.
From the tests on pilot, it arises that the MnSO4 catalyst used for the oxidation of sulfur definitely more effective and in conformity than the ferrous sulphate FeSO4 compared here to ferrous waste of the iron and steel sector.
Time (hours) | Sulfur concentration | Percentage oxidized sulfur |
---|---|---|
First hour | 2608 | 0% |
Second hour | 2608 | 0% |
Third hour | 2608 | 0% |
Fourth hour | 2512 | 3.68% |
Fifth hour | 2480 | 4.90% |
Sixth hour | 2416 | 7.36% |
Time (hours) | Sulfur concentration | Percentage oxidized sulfur |
---|---|---|
First hour | 2752 | 2.27% |
Second hour | 2528 | 10.23% |
Third hour | 2240 | 20.45% |
Fourth hour | 2128 | 24.43% |
Fifth hour | 1984 | 29.54% |
Sixth hour | 1860 | 33.24% |
That could be the consequence proportion of iron which precipitates neighbors pH from 4.6 to 6 and thus does not take part has the oxidation of sulfur, whereas that of sulfur takes part has close pH has 8. The Pourbaix curves also inform us about this aspect of appearance of new species according to the pH [
Stricter legal limits on sulfur levels require measures to reduce their value in the wastewater final tannery. Removal of wastewater containing high sulfur concentrations contributes significantly to the overall effluent. However, the final sulfate concentration in the tannery wastewater is still too high to meet future standards. Separate results remain low, 32% for waste from the tannery, and 30% for the waste from the steel industry. But the sum of the results of the two waste give better results desulfurization, or 60% of oxidized sulfur. The companies have great possibilities of minimizing the economic losses, and to preserve the natural environment. The review of EU waste legislation offers the chance to revolutionize the way we think about and deal with waste. Turning waste into a valuable resource should be among the cornerstones of a resource-efficient in world. However, this will require combining ambitious targets with intelligent policy tools and rigorous application. Tannery industry shows a clear example of what can be gained if we succeed. Substitution by waste also underscores the enormous potential of waste to make a positive contribution to the environment and society as a whole.
The authors would like to thank Kamel Eddine BOUHIDEL and Hamel Benmoussa for their support and contribution to the work.