Characterization of Wastewaters Obtained from Hatay Tanneries

The leather tanning industry is one of the most significant pollutants in terms of both conventional and toxic parameters. On the other hand, leather industry has an important economic role both in Turkey and in the World. In this study, wastewater samples were taken from 15 different tanneries in the Hatay Region. Wastewaters obtained from liming process and chromium tanning process was analyzed. Sulfide, chromium (III), chromium (VI), oil and grease, total suspended solids (TSS), organic matters, biochemical oxygen demand (BOD), chemical oxygen demand (COD), pH and alkalinity were determined according to Turkish Standard Methods.The determined averages values belong to wastewaters obtained from liming process were as following: pH 11.71; COD 16821 mg L; BOD 4357 mg L; TSS 39023 mg L; oil and grease 364 mg L; S concentration 802 mg L; alkalinity 2115 mg L. The determined averages values belong to wastewaters obtained from chromium tanning process were also as following: pH 4.23; COD 6740 mg L; BOD 377 mg L; Cr concentrations 372 mg L; Cr concentrations 127 mg L; TSS 14553 mg L; oil and grease 343 mg L.The results of all analyzes were higher than wastewater discharge standards. As a result, it’s necessary to use more effective treatments in order to reduce the negative impacts of leather tanning industry that affect environment, natural water resources and at last human health and welfare.


Introduction
In the leather tannery industry, animal hides are transformed into leather in a succession of many complex stages, consuming high quantities of water and using large amount of chemicals.Tannery wastewaters are mainly characterized by several key parameters such as sulfide, chromium, nitrogen, oil and grease, suspended solids, COD and BOD.The beamhouse and tanning processes are the most contaminating: the former mainly because of its high organic load and sulfide content, the latter principally because of inorganic salts of chloride, ammonia, chromium and sulfate (Cooman et al., 2003).For this reason, wastewaters obtained from liming and chromium tanning processes were used in this study.
Hatay is located in the eastern Mediterranean region of Turkey.The province lies the banks of the Orontes (Asi) River, approximately 22 km inland from the Mediterranean.There are about 15 small sized leather tannery enterprises in Hatay Region.These tanneries are located inside of the town and their waste waters are released to the Orontes River without any purification process.The daily quantity of the liming effluent and of the chromium tanning effluent is about 50 m 3 , of which 55-65 % is from the liming process and 35-45 % from the tanning process.The polluted waters from the liming process are discharged in to the river separately from the polluted waters of the chromium tanning process.This situation is caused an important risk in natural physical environment.
The technological process can be separated in two parts: liming process and tanning process.In liming process: The skins are first washed to remove dirt and blood.Then they are soaked in special vats of cold water for the removal of salt and for softening.The next step is the removal of muscle and fatty tissue adhering to the corium layer by means of revolving knives.Liming is done to swell the skins for the better penetration of the tanning agents and for the hair removal.The unhairing of the hides is accomplished mechanically by means of rolling knives.The skins are washed and then subjected to a process known as bating.After bating, the hides are ready for tanning.The bated hides are first soaked in a solution of sulfuric acid and salt (5-15 kg / 1000 kg raw hide), for 10-16 hours.This operation is called pickling.After pickling, the hides are kept in contact with the tanning solution containing salts of Cr +3 (such as Cr2(SO4)3).After tanning, the produced leather is lubricated to make it soft.A series of operations known as finishing processes are carried out to produce different types of leather (Tünay et al., 1995).Manufacturing steps were shown in Figure 1.Wastewater discharge regulations are help to reduce the pollution of waters and maintain the quality of life of the community.Water discharges standards belong to various countries were described in Table 1.In the literature, there are a number of studies for the characterization of tannery wastewaters (Szpyrkowicz et al., 1991;Şengül & Gürel, 1993;Tünay et al., 1994;Namasivayam & Senthilkumar, 1994;Ateş et al., 1997;Bajza & Vrcek, 2001;Cooman et al., 2003;Floqi et al., 2007;Mandi et al., 2009;Jahan et al., 2014;Islam et al., 2014).Furthermore, there are also some reviews releated to tanning processes methods and environmental problems (Thanikaivelan et al., 2005;Covington, 1997).But, there is not any study in this matter for the Hatay region of Turkey.The main aim of this study was defined the wastewater characteristics of a group of leather tanning industries located in the Hatay Region.

Materials and Methods
Samples of wastewater were obtained from 15 different commercial tanneries in Hatay Region.Tanneries are in two sections: One is the limehouse which has a separate wastewater channel; the other is the tanyard where pickling, tanning, retanning, fatliquoring and other finishing processes are carried out.This section has also a separate channel.In this study, samples of waste solutions derived from liming and tanning of sheep leather were used.Twelve hour composite samples were taken and stored in 2.5 L polyethylene containers.In the analyses, pH, alkalinity, TSS (total suspended solids), organic matters, BOD (biochemical oxygen demand), COD (chemical oxygen demand), oil and grease and sulfide concentrations were determined according to Turkish Standard Methods.Cr +3 and Cr +6 and total chromium were determineted by UV-vis spectrometric method, Cr +3 is converted to Cr +6 using permanganate and 30% H2O2.The Cr +3 is oxidized to Cr2O7 -2 (dichromate) with KMnO4 and determined coloimetrically using 1,5-diphenylcarbazide to form a purple-violet colored complex.The absorbance of the colored complex was measured in a double beam spectrophotometer, at a wavelength of 540 nm, and chromium concentration of tested samples was determined by a calibration curve prepared using standard solutions of concentrations of Cr +6 .All analysis was made in triplicate.All chemicals used were of analytical grade.

Results
Eight main critical parameters to wastewaters obtained from liming and chromium tanning processes were shown in Table 2 and 3 respectively.The beam house wastewater was characterized by an alkaline pH (11.71) and the tanning effluent a very acid pH (4.23).The COD values of the liming wastewaters and the tanning wastewaters were found to be 16821 mg L -1 and 6740 mg L -1 , respectively.The BOD values of the liming wastewaters and the tanning wastewaters were found to be 4357 mg L -1 and 377 mg L -1 , respectively.The effluents were all characterized by high amounts of TSS (12662 -39023 mg L -1 ).The high concentrations of S -2 (802 mg L -1 ) and high alkalinity value (2115 mg L -1 ) were detected in the beam house effluent, whereas the tanning wastewater contained an important amount of total chromium (499 mg L -1 ).Oil and grease values were found 343 and 364 mg L -1 for the liming and tanning wastewaters respectively.

Table 3. Characteristics of the different tanning wastewaters
Literature data taken from national and international sources were given in Table 4.As can be seen Table 4, pH, COD, BOD and TSS amounts were within the interval given in the literature.Cr +6 concentration and alkalinity values were higher than that of literature values.On the other hand, Cr +3 and total chromium concentrations were lower than the literature values.However, the results of all the analysis were higher than wastewater discharge standards.
Many conventional processes are being carried out to treat wastewater from tannery industry such as biological process, oxidation process and chemical process.Among these, physical and chemical methods are quite expensive in terms of energy and reagents consumption.Whereas the mixing method of liming and chrome tanning wastewaters is an extremely convenient method of reducing pollution.Data belong to wastewaters obtained by the mixing of waste solutions derived from liming and chrome tanning were represented in Table 5.As can be seen in Table 5, pH value was reduced to 7.34 in the ratio 1:9 (v/v).TSS, BOD and COD values were reduced from 78428 to 18430 mg L -1 and from 6450 to 1300 mg L -1 and from 6227 to 3500 mg L -1 in the ratio 1:9 (v/v) respectively.The lowest concentration of Cr +3 was found in the ratio 9:1(v/v) (98 mg L -1 ).The smallest value for S -2 concentration was observed in the ratio 1:9 (v/v) (200 mg L -1 ).Saydam, 1998; 2 Tünay et al., 1994; 3 Şengül and Gürel, 1993; 4 Ateş et al., 1997; 5 Bajza and Vrcek,  2001; 6 Floqi et al., 2007;   7 Cooman et al., 2003; 8 Jahan et al., 2014; 9 Namasiyavam & Senthilkumar, 1994; 10 Szpyrkowıcz et al., 1991;  11 Mandi et al., 2009; 12 Islam et al., 2014   Table 5.Data belong to Wastewaters Obtained from the Mixing of Waste Solutions

Discussion
It is revealed with this study that all wastewater analysis results are much higher than national and international wastewater discharge standards.For this reason, wastewater of leather industry must not be discharged to any point before treated.
As a results of literature review, it is seen that physical, chemical, biological, advanced methods and combination of these all methods are utilized in order to improve the quality of leather industry wastewaters.Ateş et al. (1997) reported that they obtained yields of TSS of 73 %, COD of 51 % and Cr removal by 64 % by pre-precipitation method in leather wastewater.In their study, Kabdaşlı and Tünay (1992) performed chemical precipitation process to leather wastewater and removed 73.9 % of COD while Cr is completely removed.Şengül et al. (1993) also performed chemical precipitation method utilizing MnSO4 catalyst and achieved 72 % S -2 removal.Leta et al. (2004) obtained 98 % COD removal efficiency in their study of effluent wastewater treatment by activated sludge process.Abalı et al. (2014) obtained 50 % COD, 55 % TSS, 33 % BOD and 80 % Cr +6 adsorption yields of leather wastewater using clinoptilolite and active clinoptilolite respectively.All of these improvements are carried out at very high costs.
However, significant improvements in pH, COD, BOD, TSS and Cr +3 , S -2 values can be achieved as we applied at a much lower cost by mixing the wastewater resulting from liming and chrome tanning process at different ratios (v/v).This procedure (mixing 1:9 ratio v/v) has resulted in a reduction of 52.8 % in TSS, 70.2 % in BOD, 79.2 % in COD, 64.24 % in Cr +3 and 75.1 % in S -2 concentrations.
These procedures can be used in order to obtain more acceptable ecological parameters.Thus, the negative impacts of leather tanning industry that affect environment, natural water resources, at last, human health and welfare can be reduced.
As a result, this study will be an example to the studies which related to reduction of pollution of leather tanning industry in different countries.

Table 4 .
Pollution Characteristics a Tannery wastewater; b Beamhouse wastewater; c General wastewater * This study; 1