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Advanced technology like reverse osmosis in tannery effluent treatment to enhance the reusing potential of treated effluent at various stages of tanning process.

Introduction

The transformation of the raw hides into Chrome leather requires various mechanical treatments and also a series of chemical treatments. Chemical processing is generally carried out using different chemicals; e.g., acids, alkalis, salts of sodium and chromium, dyes, etc. [1] Another process of East Indian (EI) tanning continues to be by and large the same as that of the earlier times. The curing of skins and hides with common salt, swelling by lime of stones, un haring with sulphides, de liming with ammonium salts, bating with enzymes followed by EI tanning remain to this date. The processes in the EI tanning demand large quantity of water. Water is needed to rinse the material and dissolve the leather chemicals and about 25 to 30 [M.sup.3] water is required to process one tonne of skins and hides. The generated liquid waste is let out to Effluent treatment Plant. The waste water from leather industries is characterized by high oxygen demand, total dissolved salts and Hazardous Inorganic chemical waste etc., which are present in all forms from large solids through colloids to dissolved salts. The flow and composition of the effluent also varies considerably during the day and from the various stages of the tanning process [2].

Effluent Treatment Plant

The effluent treatment plant consists of screening, pre-settlement, Equalization, Flash mixture and sedimentation. This follows biological treatment with two stage aerobic steps. The aerobic biological treatment is being operated as an Activated Biological System with surface Aerators, The bio treated water is pumped to pressure sand filter, activated carbon filter followed by Reverse osmosis process. The clear outlet water from the RO flows to recycle water sump. The Activated Sludge Process and RO plant are designed to provide for up to 60% water recycling. The RO concentrate is further treated in Solar Evaporation pans to remove salt content in water. The schematic of the treatment of the effluent is shown in Fig. 1.

[FIGURE 1 OMITTED]

Primary, Secondary and Tertiary Treatment Process

The treatment process consists of Primary, Secondary and Tertiary. The primary treatment process includes Pre treatment chamber, Equalization tank, Flash mixture and settling using coagulants like aluminium sulphate and poly electrolyte. The secondary treatment process consists of two stage aerobic system with clarifier. A two stage biological process is employed in the Aeration tank for the degradation of the pollutant load based on the activated sludge process. The activated sludge generally consists of bacteria, microorganisms like protozoa, rotifers, etc. The process involves stabilization of organic matter by the action of various micro organisms in the presence of dissolved oxygen. The required Mixed liquor suspended solids are maintained by the recirculation of sludge settle in the clarifier. The tertiary treatment process consists of Pressure sand filter, Activated carbon filter, Micron filter and Reverse Osmosis membrane. The main theme of this paper was to study the reusing potential of treated effluent before and after processing of Reverse Osmosis Plant. In recent years, a number of researchers have carried out studies on Recycling of Tannery effluent. Shankar et al. (1997) have studied the extend of Recycling of Tannery effluent through Photo-oxidation method and reported that the parameters like Chemical Oxygen Demand and Bio chemical Oxygen Demand in the treated effluent were drastically reduced [3].

Water recycling plant with Reverse Osmosis

Reverse Osmosis treatment is considered as Best available technology, to remove salts from tannery effluents. The high quality RO water can be re-used as process water in the tannery. However the operation of Reverse Osmosis requires an efficient pre-treatment and a feed water quality with no suspended solids and a minimum of [BOD.sub.5] [4]. Activated sludge process and filter treatment is the preferable pre-treatment for Reverse Osmosis plants due to the complete elimination of [BOD.sub.5] and suspended solids. Even small concentrations of [BOD.sub.5] after conventional treatment can cause bio-fouling of RO membranes and residual suspended solids physically block the spaces of a spiral RO module. The combination of a Reverse Osmosis plant applied as a polishing step after Activated sludge process with filter treatment allows recycling of desalinated water back into the tannery process [5]. The RO pre-treatment comprises of a multilayer bed filter with sand and activated carbon. Following this pre-treatment, Micron filter membrane filtration using Hollow Fibre membranes provide for final polishing before RO treatment. The Micron filters membrane plant with 100 [m.sup.3]/hr capacity. The RO plant is designed with 6 membrane modules in series. The material of the installed membranes is a cross-linked fully aromatic polyamide composite. The RO plants are designed to be operated at a permeate recovery of 60 % and produces up to 54 [m.sup.3] permeate and 36 m concentrate per hour. The RO concentrate is then further treated in a separate solar evaporation pans.

Experimental

The present study was undertaken in Tanning Industry is situated at Sempattu 6 Km south of Tiruchirappalli junction. The Tannery produces semi finished vegetable tanned leathers. Before installing Reverse Osmosis Plant, the ground water is the main source for various leather processing operations. About 150 [M.sup.3] per day waste water has been generated from different processing units of the Industry. The Tannery has installed an Effluent treatment plant with Reverse Osmosis at the cost of 7 crores to treat the tannery waste water. The plant is designed to treat the effluent at the rate of 150 [M.sup.3] per day. The effluent treatment plant has primary, secondary and tertiary treatment systems with Reverse Osmosis Unit.

Sampling

To evaluate the reusing potential of treated effluent at the Tanning process, samples was collected from the outlet of Activated carbon filter and outlet of Reverse Osmosis Plant during the month of Feb. 2009. Samples were refrigerated in laboratory at 4[degrees]C. Background information regarding the location of the samples was recorded. The samples were analyzed for the water quality parameters such as pH, Total suspended solids, Total dissolved solids, Chlorides, Chemical Oxygen Demand and Biochemical Oxygen Demand.

Chemicals Used

All the chemicals, required for the determination of COD and [BOD.sub.5], Chlorides are procured from Loba Chemie India. All chemicals are of analytical grade and are used without further treatment.

Analysis

The pH of the water was measured using a digital pH meter (Elico Model No. LI 120). The dissolved oxygen was recorded at the site of collection following Winkler's method [6] and the results were expressed in mg/L. Chemical oxygen demand (COD) is the measure of oxygen consumed during the oxidation of the oxidizable organic matter by a strong oxidizing agent. Potassium dichromate in the presence of sulphuric acid is used as an oxidizing agent in determination of COD. The sample is refluxed with [K.sub.2][Cr.sub.2][O.sub.7] and [H.sub.2]S[O.sub.4] in presence of mercuric sulphate to neutralize the effect of chlorides, and silver sulphate (catalyst). The excess of potassium dichromate is titrated against ferrous ammonium sulphate using ferroin as an indicator. The amount of [K.sub.2][Cr.sub.2][O.sub.7] used is proportional to the oxidizable organic matter present in the sample. The biological oxygen demand ([BOD.sub.5]) test measures the amount of oxygen used by the microorganisms as they utilize the substrate (food) in wastewater. The dissolved oxygen (DO) is measured at the beginning of the test and recorded, during the five days, microorganisms in the sample break down complex organic matter in the sample using oxygen in the process. After five-day dark incubation period, the DO is again determined; the [BOD.sub.5] is then calculated on the basis of the reduction of DO and the size of the sample. This test is an estimation of the availability of food in the sample (organisms that take up oxygen) expressed in terms of oxygen use samples are incubated for standard period of five days, because a fraction of the total [BOD.sub.5] will be exerted during this period. [BOD.sub.5] was determined according to the standard procedure. Estimation of remaining parameters was also carried out following the methods described by APHA (1992)[6].

Results and Discussion

The present study was undertaken to assess the reusing potential of Treated Effluent at various stages of Tanning process including the Reverse Osmosis (RO) plant and its influence on the efficiency of treated water was also investigated. The mean quantity of water used for the production of 1 kg of semi finished leather at different stages are soaking 5.0 L, Liming 4.0 L, Fleshing 2.0 L, De liming and Bating 6.0 L, Pickling 1.o L, Pre tanning and Tanning 4.0 L, and washing 3.0 L are tabulated in Table 1. It is clear from the Table 1 that percentage of water utilized with regard to above stages were 20%, 16%, 8%, 24%, 4% ,16%, and 12% respectively. The outlet of Activated carbon filter taken out and its parameters, e.g., pH, TSS, TDS,Chlorides, COD, and [BOD.sub.5] are measured. These parameters are tabulated in Table 2. It is clear from Table 2 that pH 6.63; Total suspended solids 25 mg/L; Total Dissolved Salts 2650 mg/L; Chlorides 1490 mg/L;COD 110 mg/L; [BOD.sub.5] 34 mg/L. The effluent quality at the out let of Activated carbon filter is nearly comparable with the Tamil Nadu Pollution Control Board discharge consents for tannery effluents. Table 3 shows the water quality parameters of Product water of Reverse Osmosis during Feb. 2009. The pH 6.31; Total Suspended Solids NIL; Total Dissolved Solids 560 mg/L; Chlorides 100 mg/L; Chemical Oxygen Demand 10 mg/L ; and Biochemical Oxygen Demand 3 mg/L. It is clear from the Table 3 that a maximum efficiency was recorded after processing the Reverse Osmosis Plant. Due to Reverse Osmosis techniques the Total Dissolved Solids, Chlorides, COD and [BOD.sub.5] values reached a minimal level. Before the Reverse Osmosis plant, the outlet of Activated carbon filter water can be reused at Soaking process, Machine cleaning and Place washing. After drastic reduction of dissolved salt content due to RO process, now the treated water is reusing at all stages of semi finished tanning processes. By which the vital role of Reverse Osmosis is amply demonstrated.

Conclusion

The application of activated sludge process with multi media filter treatment is a promising treatment concept for low cost tannery effluent treatment. This unique combination has shown high reductions of COD and [BOD.sub.5]. But the combination of activated sludge process with multi media filter treatment along with a Reverse Osmosis has shown to achieve 60% recovery of high quality desalinated water at lowest costs and average reduction of 91% COD and 91% [BOD.sub.5] and a stable membrane performance was achieved.. The outlet of Activated carbon filter water can be reused at Soaking process, Machine cleaning and Place washing alone. But after the drastic reduction of dissolved salt content due to RO process, now the treated water is reusing at all stages of tanning processes. By which the vital role of Reverse Osmosis is amply demonstrated. This recycling scheme actually achieves cost savings due to reduction of fresh water consumption and discharge costs. The development of solar evaporation pans achieves a solution to the RO concentrate issue that is both legal and cost effective.

References

[1] Dutta, S.S. (1999) An Introduction to the Principles of Leather Manufacture; Indian Leather Technologists' Association: Calcutta.

[2] Integrated Pollution Prevention and Control (IPPC), Reference document on Best Available Techniques for the Tanning of Hides and Skins, February 2003.

[3] Shankar, M., Sekaran, G., Sadulla, S., Shanmugasundaram, K.A and Mariappan, M., 1997. Recycling of Tannery Effluent through Photo Oxidation method, IJEP 18 (3) : 206-210.

[4] Scholz W.G., "Membrane Technologies for Recovery of water from tannery effluents", Proceedings for the 42nd LERIG conference, Chennai India, p. 3745, 28-30th January, 2008.

[5] R. Suthanthararajan, et.al. "Membrane application for recovery and reuse of water from treated tannery wastewater", Desalination, 164, 2004 p. 151-156.

[6] APHA, Standard methods for the examination of water and wastewater; American water works association, water environment federation., 8th ed. American Public Health Association, Washington, 1992, 126.

(1) K. Gokulakrishnan and (2) K. Balamurugan

(1) Head, Department of Chemistry

(2) Prist University, East Campus, Thanjavur-Pin-613403. Tamilnadu, India.

(1) E-mail: nandu_gokul@yahoo.com

(2) E-mail: kbalmurugan@hotmail.com
Table 1: Mean quantity of water used at different stages of
Tanning for the production of 1 kg of semi finished leather.

S.NO. Stages of Tanning Water Utilized Water
 L/kg) Utilized (%)

1 Soaking 5.0 20
2 Liming 4.0 16
3 Fleshing 2.0 8
4 De liming and Bating 6.0 24
5 Pickling 1.0 4
6 Pre tanning & Tanning 4.0 16
7 Washing 3.0 12
Total 25 100

Table 2: Water quality parameters at the out let
of Activated Carbon Filter.

Serial Parameters Out let of Activated TNPCB
No. Carbon Filter Standard

1 pH 6.63 6-9.0
2 Total Suspended Solids 25 100
3 Total Dissolved solids 2650 2100
4 Chlorides 1490 1000
5 Chemical Oxygen Demand 110 250
6 Biochemical Oxygen Demand 34 30

All the values are in mg/L except pH.

Table 3: Water quality parameters at the out let
of Reverse Osmosis plant.

Serial Parameters RO Percentage of RO
No. out efficiency compare to
 let Activated Carbon Outlet.

1 pH 6.31 4.8%
2 Total Suspended Solids NIL 100%
3 Total Dissolved solids 560 79%
4 Chlorides 100 93%
5 Chemical Oxygen Demand 10 91%
6 Biochemical Oxygen Demand 3 91%

All the values are in mg/L except pH.
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Author:Gokulakrishnan, K.; Balamurugan, K.
Publication:International Journal of Applied Environmental Sciences
Date:May 1, 2010
Words:2287
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