Fosfojipsiyum'dan mikrobiyel proses ile hidrojen sülfür (H²S) eldesi

Abstract

Bilindiği gibi çevre kirlenmesi ve bunun için ön lemlerin alınması, günümüzün en önemli problemini oluş turmaktadır. Çevre kirleticilerin başında endüstriyel atıklar gelmektedir. Endüstrideki üretim kapasitelerine bağlı olarak ortaya çıkan miktarları da çok büyük miktar lara ulaşmaktadır. Atık miktarı büyük boyuta ulaşanlar dan biri de Gübre sanayiidir. Bilindiği gibi Gübre Sanayiinde fosfat kayasından fosforik asit eldesinde atık olarak jips ortaya çıkmak tadır ve atık jips bir potansiyel oluşturmaktadır. Son zamanlarda atık değerlendirilmesinde büyük önem kazanmaya başlayan yöntemlerden birisi de, bakteriyel özütlemedir. Sülfat indirgeyici bakteri ile, jipsten iki aşamada gerçekleşen indirgeme reaksiyonu ile kükürt elde etmek mümkündür. Bu çalışmada, Gübre Sanayii atığı olan jips'in, bak teriyel özütleme işlemi ile değerlendirilmesi amaçlanmış tır. Deneysel çalışmalarda kullanılacak jips'in önce yapı analizi yapılmıştır. Çalışmada kullanılacak olan D. desulf uricans, Deutch Sammlung Von Mikroorganismen und Zellkulturen GmbH(DSM) ' den temin edilerek, saptanmış olan besiyerinde üretilmiştir. Üretilen saf kültürler kulla nılarak jips'in bakteriyel özütlemesindeki ilk aşama ger çekleştirilerek hidrojen sülfür üretilmiştir.

One of the most important and basic raw material is sulfur at industries of chemical processes. During the period 1960-65 sulfur consumption in the United States rose kQ percent to 7.96 million long tons. Since 1963, while demand has exceeded production, withdrawals from producer stocks have met the deficit. An assured steady supply of sulfur is essential for the national interest. Its applications are so diverse that the quantity used is an accurate measure of a nation's strength but also its cantinued growth in an expanding economy. Such materials as anhydrite, gypsum, sea water and hydrous calcium- sulfate, a by product of the fertilizer industry, are potential sources of almost unlimited quantities of sulfur. Anhydrite and gypsum are being used in limited quantities in the United Kingdom and ot her European countries to make sulfuric acid and cement clinker. This is practical only when limestone and other necessary raw materials for conventional cement manufac ture are not available locally. Cheap energy is also essential; the cost of energy has prohibited wider use of this recovery method. If these sulfur sources could be converted biologically to hydrogen sulfide and then converted chemically or biologically to elemental sulfur, these materials might become available on a more competi tive basis. VI Dn the other hand, the problem of sulfate disposal exists with many major industrial effluents including excess sulfuric acid, gypsum, coal desulf urization by products, acid-mine waters and general metallurgical effluents. This study includesthe microbial conversion of the gypsum sulfate to hydrogen sulfide. Gypsum, a chemically synthesized waste, which is produced by the addition of lime to soluble sulfates produced from a variety of industrial processes such as the use of sul furic acid in the production of phosphate fertilizers. Formation of gypsum from waste sulfate solutions and microbial conversion of gypsum sulfate to hydrogen sul fide has been suggested for many years as a practical alternative. Gypsum is the most common of the naturally occurring sulfate minerals. It is found in very extensive, bedded sedimentary deposits all over the world and is associated with limestones, shales and sandstones, marls and clays. Crude commercial yypsum is generally highgrade material, the major portion Df which can be utilized with no bene- f iciation. The mineral term "gypsum" (CaSD,.2H20) is used as a commercial and generic term for all calcxum sulfate ma terials. Anhydrite is calcium sulfate, CaSD,, with no water of crystallization. Gypsum is dehydrate calcium sulfate, CaSO,.2H_D. Belenite is well-formed, transpa rent crystals of gypsum, CaSD,.2H2D. Calcined gypsum is hemihydrated calcium sulfate, CaSD,. 1/2H"D. Anhydrite and gypsum usually occur together, but calcined gypsum is a manufactured product. All these minerals and mate rials, including the articles molded from the plaster, are called gypsum. Gypsum is a naturally occuring mineral with a com position of 79% calcium sulfate and 21% water. The finely crystallized variety is called selenite. The massive variety is called alabaster and can be easily carved. The fibrous, silky variety is called satin spar, Gypsite is a mixture of clay and gypsum crystals. Anhydrite is a naturally occurring mineral, CaSD,, with no water of crystallization. When gypsum is cal cined at higher temperatures, it is converted to anhyd rite. Vll Commercially calcined gypsum, CaSO,. 1/2H"D, is a manufactured hemihydrate product produced by partial calcination of gypsum. It is produced by heating gypsum at gradually increasing temperatures from 394 K to 450 K for about 2 hours. ; When mater is added to the calcined material, plaster of Paris is formed, which quickly sets and hardens to gypsum again. Byproduct gypsum is a chemical product of manufac turing processes such as phosphoric acid, hydrofluoric acid, citric acid and titanium dioxide from ilmenite. The sludge produced from scrubbers in the desulfuriza- tion of stack gas in thermal power plants is also bypro duct gypsum. The gypsum industry is worldwide, with consumption occurring principally at industrial centers and urban concentrations in developed countries. The United States is the leading producer, with 19 % Df production. Other leading producing countries were Canada (11 %), Iron (10 %), France (9 50 and the USSR (8 50. A variety. of microorganisms are capable of metabo lizing sulfate to sulfide. In nature, these processes are generally slow and yield products toxic to the en- viroment D.desulf uricans is useful for sulfate conversion to sulfide. Therefore experiments were carried out with this microorganism. D.desulf uricans was provided from Deutch Sammlung Von Mikroorganismen und Zellkulturen GmbH (DSM). D.desulf uricans was grown in three different media. Two of them have same contents approximately, except pH value. One of these medias1 pH was adjustd to 7.4 and the other was adjusted to 7.8. These two media were based on DSM. Third media was the modified media of starkey. The contents of these three media were shown below. The contents of DSM media Solution A: Compound g/liter *2HPD4 NH^Cl IMa"S0. 2 4 Vlll Compound g/liter CaCl2.2H2D MgSG4.7H2D DL. Sodium Lactate(%60) Yeast Extract Resazurine Distilled water D.1 2.G 2. D 1.0 1.D(mg) 980 ( ml) Solution B: Compound FeSD^.7H2G Distilled water g/liter D.5 1D (ml) Solution C: Compound Südyum thioglycolat Ascorbic acid Distilled water g/liter D.1 D.1 1D(ml) Solution A was boiled for a few minutes, then cod- ledto room temperature and added solutions Bandc, pH was adjusted to 7.8 with NaOH, and finally was autoclaved 15 min at 121 C. Solution I Compound g/liter H2HPD4 0.5 I\IH, CI 1.0 IMa^O^ 1.0 CaCl2.2H20 0.1 MgS0if.7H2D 2.0 DL. Sodium Lactate(%60) 3.5 Yeast Extract 1.0 Distilled water 980(ml) IX Solution II Compound g/liter FeSO..7H"0 D.5 k 2 Distilled water 1D.D (ml) Solution III Compound g/liter Sodium thyoglicalate 0.1 Ascorbic acid D.1 Distilled water 10. D (ml) The pH of Solution I and III were adjusted to 7.4 with IMaOH, solution II's pH was left acidic. They were sterilized separately by autoclaving 15 min at 394 K and mixed when cold. The pH was adjusted to 7.0 with IMaOH and sterilized by autoclaving at the same conditions above. The bacteria which was used this study is slightly curved rods of variable length, usually occurring singly or sometimes in short chains. This bacteria, namely D. desulf uricans is gram-negative, actively motile by a po lar flagellum, and measure 0,5 to 1.0 micron in width and 1 to 5 microns long. It is strict anaerobe which reduce sulfates tD hydrogen sulfide utilizing. In most instan ces, an organic compound as a hydrogen donor and a source of carbon for cell structure. A typical reaction that this organism brings about may be found in the equation below: 2CH3CHDHCDDNa + CaSD4.2H2D, Bactena> H2S+2CH3CDDI\!a+ CaCD3+3H2D +CD2 The basic design of reactor was employed in this studies is shown in the next pages. It was charged with salt solution, hydrous calcium sulfate, sodium lactate and after sterilization by autoclaving 15 min at 39*t K. was inoculated with sulf ate-reducing bacteria obtained from DSM. Nitrogen gas was used as the sweeping gas for hydrogen sulfide and was fed in to the bottom of the reactor at various rates. Thes reactor was operated at approximately 3G3-3DB H. Stirring was accomplished with a magnetic stirring bar and was just fast enough to keep the hydrous calcium sulfate suspended. Hydrogen sulfide was obtained swept into the washing bottle by nitrogen gas and was absorbed from ammoniacal cadmium clorür which was used as absorbent. Then the amount of hydrogen sulfide was estimated with the iodimet- ric titration of solution of washing bottle. Dur results are shown at the end of this study.