REMOVAL OF HEAVY METALS FROM TANNERY EFFLUENT WATER BY USING MAGNETOSOMES AND LIMESTONE

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Heavy metals, in trace amounts, are essential for human health. However, some of them are toxic to humans. Water which is an important element for life had been polluted with heavy metals from waste streams of many industries, such as metal plating facilities, mining operations, tanneries, etc. Some metals associated with these activities are cadmium, chromium, iron, nickel, lead and mercury. Thereby making it harmful for human consumption. In this present study, heavy metal removal from wastewaters was performed with Magnetosomes isolated from MTB (Magnetotactic bacteria) and limestone .The effluent water sample was collected from Ranipett (Vellore), Chennai .The water is analyzed for the primary adsorption parameters including the pH value, adsorption time, initial metal ion concentration and the biomass concentration .Many physico-chemical methods like coagulation, flocculation, ion exchange, membrane separation, oxidation, chemical precipitation and solvent extraction had been helpful to relief the harmful situation. All these methods, were not effective for the treatment of heavy metals. Major

drawbacks of these methods are high sludge production, handling and disposal problems, high cost, technical constraints, etc.To over come this we use Magnetosomes and lime stones .They have high up biosorption capacity than other conventional methods . Limestone is inexpensive and simple to use. It has the ability to remove heavy metals.MTB are group of microorganism with the ability to orient on geomagnetic field line. MTB possess magnetic moment due to the presence of membrane bounded crystals called magnetosomes (MS) .This magnetite crystal are used for orient and migrate along the local magnetic field lines. Through this special property, Magnetosomes isolated from MTB could be used in the removal of heavy metals. Batch experiments would be conducted to investigate the efficiency of biosorption using limestone and magnetosomes. Presence of this unique magnetic and crystalline properties and the natural presence of a surrounding membrane, magnetosomes might be superior in some biosorption process. The possibilities of using magneto some in combination with lime stone as a altering media for the removal of tannery effluent water contains heavy metals (Cr3+, Ni2+).The effect of removal efficiency at different concentration are determined at neutral pH.

Keywords: Heavy metals, Biosorption, Magnetosomes, Limestone, pH

INTRODUCTION

Excessive release of heavy metals into the environment due to industrialization and urbanization has posed a great problem worldwide. Unlike organic pollutants, the majority of which are susceptible to biological degradation, heavy metal ions do not degrade into harmless end products. The presence of heavy metal ions is of major concern due to their toxicity to many life forms[1]. Heavy metal contamination exists in aqueous wastes of many industries, such as metal plating, mining operations, tanneries, chloralkali, radiator manufacturing, smelting, alloy industries and storage batteries industries.Among all these untreated effluent from tanneries ranked as high pollutant and major threat to environment[2].

Tanning is the chemical process that converts animal hides and skin into leather and related products. The transformation of hides into leather is usually done by means of tanning agents and the process generates highly turbid, colored and foul smelling wastewater[3]. The major components of the effluent include sulfide, chromium, volatile organic compounds, large quantities of solid waste, suspended solids like animal hair and trimmings.The composition of tannery wastewater includesTotal suspended solids (mg/L) 925 - 36000 Total chromium (mg/L) 3 - 350 Sulfides (mg/L) 1 - 500 Chlorides (mg/L) 1500 - 28000 Total phenolic compounds (mg/L) 0.4 - 100 Ammonium nitrogen (mg/L) 17 - 380 Kjehdahl nitrogen (mg/L) 90 - 630 Fats and oils .Chromium salts used during the tanning process generate two forms of chrome; hexavalent chromium and trivalent chromium. Hexavalent chromium is highly toxic to living organisms even at low concentration causing carcinogenic effect. Several components in the effluent contain nitrogen as part of their chemical structure, which can lead to development of anaerobic conditions harmful to the aquatic life[4].

Treatment processes for heavy metal removal from wastewater include precipitation, membrane filtration, ion exchange, adsorption, and co-precipitation/adsorption. Studies on the treatment of effluent bearing heavy metals have revealed adsorption to be a highly effective technique for the removal of heavy metals from waste stream and activated carbon has been widely used as an adsorbent[5]. Despite its extensive use in water and wastewater treatment industries, activated carbon remains an expensive material. Biological treatment of wastewater is more favorable and cost effective as compared to other physiochemical methods. Various microorganisms are capable of reducing the content of pollutants significantly by utilizing them as energy and nutrient source in the presence or absence of oxygen. Compared with the conventional methods, the biosorption process was more economical, efficient and environmentally friendly. However, the serious problem of the biosorption technology was difficult to separate the microorganisms which has loading metal ions from the aqueous solution[6].

Magnetotactic bacteria (MTB), first discovered by Blakemorein 1975, could be a feasible alternative to resolve the problem. MTB possess a magnetic moment due to the presence of membrane bounded crystals called magnetosomes within their intracellular. The magnetosomes mineral phase consists of single crystals of either the ferrimagnetic iron oxide, magnetite (Fe3O4), or the iron sulfide, greigite (Fe3S4). The size of magnetosome crystals, regardless of whether they consist of magnetite or greigite, depends on the species of MTB and generally ranges from 35–120 nm. This is the size range where magnetite crystals are expected to be limited to a single magnetic domain. Magnetic properties of MTB have been a subject of growing interest in recent years[7].

In this paper, we explores the possibilities of using magneto some in combination with lime stone as a altering method for the removal of tannery effluent water contains heavy metals (Cr3+, Ni2+).The effect of removal efficiency at different concentration are dertermined at neutral pH.

Material and methods:

Sample Collection

Heavy metal containing effluent water sample were collected from Ranipet, Vellore (12 56’ northern latitude and 79 20’ eastern longitude) . Effluent water were collected and transferred to a sterile plastic bottle. Samples were transported to the laboratory aseptically and kept at room temperature.

Bacterial strain:

Bacterial magnetosomes were synthesized by biomineralization process of magnetotactic bacteria. Magnetospirillum gryphiswaldense (MSR1) strain was purchased from DSMZ, Germany.The bacteria are gram-negative α-proteobacterium that is more oxygen-tolerant bacteria and produced magnetite - Fe3O4 particles[8].

Culture medium (MSGM):

Vitamin solution 10.00 ml

Trace elements 5.00 ml

Fe(III) quinate solution 2.00 ml

Resazurin 0.50 mg

KH2PO4 0.68 g

NaNO3 0.12 g

Na-thioglycolate 0.05 g

L(+)-Tartaric acid 0.37 g

Succinic acid 0.37 g

Na-acetate 0.05 g

Distilled water 1000.00 ml

Dissolve ingredients (except thioglycolate) in the order given, adjust pH to 6.75 with

NaOH and boil medium for 1 min

Ferric Quinate Solution, 0.01 M :

FeCl3 x 6 H2O 0.45 g

Quinic acid 0.19 g

Distilled water 100.00 ml

Add the medium with N2 gas for 10 min and dispense under the same gas atmosphere in anoxic vials. Seal vials with screw caps and gas tight rubber closures. Autoclave at 121ºC for 15 min. Before inoculation add thioglycolate from a 3% (w/v) solution, freshly prepared under N2 and filter-sterilized. Then add sterile air (with hypodermic syringe through the rubber closure) to 1% O2 concentration in the gas phase[8].

Magnetosome extration

For the isolation of the magnetosome particles from bacterial body we have used the modified method described by Karen Gruenberg et. MTB were separated from the culture medium by centrifugation at 8000 rpm for 20 minutes at 4 °c. The centrifuged pellet is being resuspended in the 10ml distilled water . Add 10ml Tris Hcl buffer and crashed (600 W/cm , 2.5 mins, 30 pluses) by Ultrasonic crasher surrounded with ice for one hou at 30 wats .The magnetosomes were suspended in a 1 % SDS solution. Then placed the agitated solution in water bath at 90°c for 5hrs. The black magnetosomes sediment at the bottom of the tube and the residual contaminating cellular material was retained in upper part. Then we used magnetic iron close the bottom of beaker to attract the magnetosomes[8].

Lime stone:

Lime stone was obtained from Vellore ,Tamil Nadu it showed the presence of CaCO3 and trace amount of silica.The weight percent of element is 55.91 % O, 6.10% C, 37.67% Ca and si 0.32.

Biosorption process

The initial solution of chromium and nickel was prepared by dissolving a weighed quantity of chromium nitrate and nickel nitrate in deionized distilled water. The solutions were diluted to different concentration levels using deionized water. The concentrations of metal ions were measured by inductively Atomic Absorption Spectrophotometry[9].

Measurement of metal ions

At the end of the mixing period, 10 ml of the samples were taken and filtered with Millipore filters of 0.22 μm pore size, and the filtrate was collected for (Cr3+,Ni2+) analysis. The concentration of (Cr3+, Ni2+) in solution was determined using Atomic Absorption Spectrophotometry[9].

Batch experiment:

Batch experiment were designed to investigate the efficiency of Cr3+ and Ni2+removal with different concentration of magnetosome and lime stone. The intial concentration of Cr3+ and Ni2+ respectively at the concentration of magnetosome and lime stone. The different concentration magnetosome and lime stone was prepared in PBS solution of pH 6.5. The experiment was conducted in three batch. The first batch containing 40ml metal ion containing water sample and different concentration (50-400mg/µl) of magnetosome. The second batch containing 40ml metal ion containing water sample and different concentration of lime stone(50-400mg/µl).The third batch is prepared with 40 ml of sample and combination magnetosome with lime stone in the concentration of (50-400mg/µl).The solution were placed on a mechanical shaker at room temperature for 24 hr .The flask was then removed and filtered for clear supernatant. The removal efficiency of magnetosome and lime stone on this metal ion in the water sample was observed by Atomic Absorption Spectrophotometry[10]. The adsorption experiments were performed and the average values are determined.The removal efficiency (%) and equilibrium adsorbed concentration, q (mg/g) of metal "" ions were calculated as follows[9].

C0- Intial concentration of metal ions

Ct- Residual concentration of metal ion

V- Total volume of solution

M- Absorbent mass

Result and Discussion:

Batch experiment:

Removal efficiency of magnetosome and limestone: Cr3+

""

In the present studies it is reported as , The sorption capacity of the adsorbent increases with increase in intial concentration of the magnetosome and lime stone solution, after which the equilibrium was obtained at 200 mg/µl for magnetosome ,250 mg/µl for lime stone and maximum adsorption concentration was occurred at 300 mg/µl for magnetosome with lime stone. so the maximum removal efficiency in case of cr3+ was shown by magnetosome with lime stone that was around 52%.After that the process become in a state of equilibrium where there is no further absorption process take place.

Removal efficiency of limestone and magnetosomes: Ni2+

""

In the present studies it is reported that , the sorption capacity of the adsorbent increases with increase in intial concentration of the magnetosome and lime stone solution, after which the equilibrium was obtained at 150 mg/µl for magnetosome ,200 mg/µl for lime stone and maximum adsorption concentration was occurred at 250 mg/µl for magnetosome with lime stone. so the maximum removal efficiency in case of Ni2+ was shown by magnetosome with lime stone that was around 42%.After that the process become in a state of equilibrium where there is no further absorption process take place.

CONCLUSION:

MTB possess magnetic moment due to the membrane bounded crystal called magnetosome. Presence of this unique magnetic and crystalline properties and the natural presence of a surrounding membrane, magnetosomes are used for the biosorption process. Limestone is inexpensive and simple to use. It has the ability to remove heavy metals because of the presence of caco3 and silica particles. Using magnetosome in combination with limestone as a altering method for the removal of heavy metals(Cr3+, Ni2+) from tannery effluent water .In this study, the addition of magnetosome with limestone enhance the removal efficiency of Cr3+ and Ni2+ from the waste water than addition of limestone and magnetosome separately into to the sample.

Thus we can reveal that the combination of limestone with magnetosome has most biosorbent capacity to absorbe Cr3+ (52%) and Ni2+ (42%) from the sample at neutral pH .

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