Atık sularda sülfat parçalanması
Başlık çevirisi mevcut değil.
- Tez No: 55770
- Danışmanlar: PROF.DR. NURAN DEVECİ
- Tez Türü: Yüksek Lisans
- Konular: Kimya Mühendisliği, Chemical Engineering
- Anahtar Kelimeler: Anaerobik arıtma, Atık su, Sülfat, Anaerobic treatment, Waste water, Sulfate
- Yıl: 1996
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: Belirtilmemiş.
Özet
ÖZET Artan dünya nüfusu ve bununla birlikte artan endüstri üretim kapasiteleri beraberinde büyük boyutlar da olan çevre kirliliğini de ortaya çıkarmaktadır. Günümüzün önemli sorunlarından olan çevre kirliliğinin mümkün mertebede azaltılması için yapılan pekçok çalışma mevcuttur. Biz bu doğrultuda, endüstriyel atık- suların sülfat içeriklerini esas alarak hazırladığımız karışımlarda sülfatın anaerobik olarak parçalanmasını gerçekleştirmeyi amaçladık. Bunun için laboratuvarda çeşitli konsantrasyonlarda sülfat içeren l\la"SQ, çözeltileri hazırlanmış ve sülfatın anaerobik olarak parçalanması sağlanmıştır. Ayrıca bu çalışmaya etkiyen parametrelerden, anaerobik çamur miktarı, sıcaklık ve çözeltinin sülfat içeriğinin parçalanmaya olan etkisi incelenmiştir.
Özet (Çeviri)
ANAERDBIC BIODEGRADATION OF SULFATE RICH WASTEWATERS SUMMARY Anaerobic biological waste treatment systems are now recognized to offer many advantages for industrial waste water treatment over conventional waste treatment proces ses. Anaerobic treatment processes have been applied to several industrial waste treatment situations. Some of these wastes, such as waste from the paper and pulp, fermentation, edible oil, petrochemical, and mining industry, contain significant quantities of sulfate and/ or sulfide. Anaerobic biotechnology is economically and ecologi cally a significant step forward in industrial and muni cipal wastewater treatment. One of the most important and basic raw materials is sulfur which can exist in a variety of oxidation states within organic and inorganic compounds, at industries of chemical processes. The oxidation states of sulfur in various compounds were given in Table 1. Table 1. Dxidation States of Sulfur In Various Compounds Form Example Dxidation State S° Elemental Sulfur D S~ Inorganic Sulfides -2 S2[“ SD, 5^,0- Thiosulfates + 2 * Sulfates +6 Microorganisms catalyse the oxidation and reduction of different forms of sulfur establishing a sulfur cycle. A simple representation of the sulfur cycle was shown in Figure 1. VllInorganic Loop 1 K\ O IS”Igiemental v^_/ sulfur Phoiosynthellc sulfide oxidation Organic Loop Hydrogen sulfide Thio<s (e.g.. cysteine) Figure 1. A Simple Representation of The Sulfur Cycle Sulfur is an essential component of living systems because it is contained in several amino acids in the form of sulfhydryl (-SH) groups. Inorganic sulfur-con taining compounds serve as sources of sulfur for plants and other macraorganisms, and some are also important because of the toxicity to biological systems. Organic sulfur-containing compounds can be desul- furized by a variety of microorganisms. Under aerobic conditions the final inorganic sulfur-containing compound produced from decomposition of organic sulfur compounds normally is sulfate. Under anaerobic conditions the final sulfur-containing product normally is hydrogen sulfide. A variety of mercaptans are also formed during tha anaerobic decomposition of organic sulfur-containing compounds. The release of volatile sulfur-containing compounds during the anaerobic decomposition of organic matter produces strong odors, e.g., the characteristic smell of rotting eggs. Hydrogen sulfide is a highly reactive compound and is subject to biological as well as nonbiological oxidation. In the presence of oxygen, hydrogen sulfide can be nonbiologically transformed to elemental sulfur and thiosulfate. Biologically, hydrogen Vlllsulfide can be oxidized to sulfur and sulfate under aerobic as well as anaerobic conditions. Some microorganims are able to utilize sulfate as the terminal electron acceptor in anaerobic respiration. Bacteria which utilize sulfate as an electron acceptor carry out dissimilatory sulfate reduction. These bacteria are known as sulfate reducers and are obligate anaerobes. Sulf ate-reducing bacteria include Desulfovibrio, Desulfo- tomaculum and Desulf omonas. The reduction of sulfate results in production of hydrogen sulfide according to the following equation: 4H2 + SG^~ - H2S + 2H20 + 2 OH“ Sulfate reduction can occur over a wide range of pH, pressure, temperature and salinity conditions. Sulfate reduction is inhibited by the presence of oxygen, nitrate or ferric ions. The production of even small amounts of hydrogen sulfide by sulfate reducers can have a marked effect on populations within the habitat. Hydrogen sulfide is extremely toxic to aerobic organisms, since it reacts with the heavy metal groups of the cytochrome systems. In sulfate reduction, sulfate reducing bacteria(SRB ) cause serious problems in sanitary sewer systems and industrial water systems because of production of highly toxic and corrorsive hydrogen sulfide gas. The treatment of hydrogen sulfide is accomplished by two general process types radsorption and absorption. Adsorption systems remove hydrogen sulfide from foul air by means of adsorbing on holding the hydrogen sulfide on to the porous structure of on adsorbing material such as activated carbon. Absorption is a mass-transfer process where the H”S in the foul air is transferred into a scrubbing solution. Dnce the hydrogen sulfide is absorbed it can be oxidized to a nonadorrous compound or disposed of in solution. The dissolved sulfides can be altered by oxidation to nonodarous elemental sulfur or sulfate. These compounds are more stable than the dissolved sulfides and can be disposed of without the treat of H“S escaping. The oxidation of sulfides can be accomplished using various strong IXoxidizing agents including, but not limited to, chlorine, hypochlorite » ar|d hydrogen peroxide. The end products of the sulfide oxidation-elemental sulfur or sulfate-are determined by the pH and redox potential (Eh) of the scrubbing solution. The addition of oxidizing agents increases the redox potential of the scrubbing solution. In an anaerobic system uihere sulfate loading is significant, methanogenic bacteria must coexist with sul- f ate-reducing bacteria (5RB), and process kinetics and thermodynamics become more complicated. The reduction of sulfate to sulfide reduces the quantity of organics available for conversion to methane. The presence of sulfide can cause precipitation of iron, cobalt, nickel and other metals which are essential nutrients. Toxicity due to increased levels of sulfide and un-ionized hydrogen sulfide leads to diminished process performance. A currently available model of sulfate reduction in anaerobic systems assumes that two-thirds of available CDD is converted to acetate, and the remaining one-third is converted to hydrogen. All the acetate is assumed to be involved in methanogenesis, while all the hydrogen is assumed to be used in sulfate reduction. If the level of sulfide becomes high, the methanogenesis portion of the pathway is stressed and leads to lowered methane production. There are several groups, of bacteria involved in the system, and depending on the thermodynamics of the situation, sulfate reduction may not be limited to the case where hydrogen is the electron donor, but may involve other groups of sulfate reducers which oxidize more complex substrates such as propionate and lactate. There are several groups of organisms involved in the anaerobic breakdown of organics. The first is the group of fermenters involved in the breakdown of lactate and glucose to propionate, acetate and hydrogen. A second group is the acetogens, which are involved in the breakdown of propionate to acetate and hydrogen. A third group is the sulfate reducers, which are involved in the utilization of lactate, propionate, acetate and hydrogen with production of sulfide. This group may include two sets of SRB: the complete oxidizers including such genera as Desulf obacter, Desulf ococcus, Desulfosarcina, Desul- fonema and Desulf obacterium which convert the organic matter into carbon dioxide and water in the course of sulfate reduction; and the incomplete oxidizers such as Desulf otomaculum and Desulf avibrio which produce inter mediates such as acetate and propionate during sulfate reduction. A fourth group of bacteria involved in the methanogens which are responsible for the conversion of acetate and hydrogen to methane.Anaerobic breakdown reactions of a mixture of acetate, propionate, butyrate and sulfate are listed below. CH3CH2Cno”+ 3h20 - CH3CDD“+HC03”+ H++2H2 CH3CH2C00“ + 0.74S0^ CH3CQ0~+HC0~+a. 75HS~+0. 25H + CH”CH0CDa~ + 1.75507 3HC0~+1. 75HS~+Q. 5H++0.250H~ 3 2 k 3 CH3CH2CH2C00“ +2H2Q.» 2CH3C00”+ H+ + 2H2 CH3CH2CH2Ca0“+0.D5S0^ 2CH3CD0”+a.5HS“+0. 5H+ CH3CH2CH2C00”+2.5SCI^= ^ 4HC03+2. 5HS“+0. 75H++Q.25DH~ CH,C00~ + 507 ?» 2HCG,”+ HS“ 3 k 3 CH3C00~ + H2Q ^'CH4 + HCa3 kH2 + E0k= + H+ HS”+ 4H2D kW2 + HC03“ + H+ »? CH^+ 3H2D The objective of this study was to treat the waste waters which contain significant quantities of sulfate according to the following reaction; (sa^r h2s SD Sulfate can be reduce by sulfate reducing bacteria and can obtained elemental sulfur from these process. The aim in this study is to turn sulfate into hydrogen sulfide at the first step and into elemental sulfur at the second step and also to examine the factors isuch as tempera ture, amount of sulfate in solution and amount of 55, which affect the operation. To do this, sulfate solutions con taining sulfate (1DG0-1DDQQ mg S0İ”/l) were prepared. In the lab, an anaerobic jar of 1 2 cm of diameter and 25 cm of height and 2 litres of volume has been used. The test to assure there is no leaking has been done because of working in anaerobic conditions. The jar lid used in the experiment has two opening tubes so they are used for feeding or taking samples and XIfor measuring the volume of the gas formed. The studies, where temperature is controlled, has been done in four erlenmayers at 37 C in shaker baths by testing to assure there is no leaking. In order to examine the anaerobic degradation process of sulfate, sulfate solutions at various concentrations have been prepared. In anaerobic jars, they are fed with saccharose to provide the necessary activites of anaero bic sludge and to maintain the CDD. This process has been observed in a certain period. During the experimental studies, we took samples at start-up and shut-down and did the following analyses. Chemical Oxygen Demand (COD), Total Solids (TS), Suspended Solids (SS), Total Dissolved Solids(TDS) and. Volatile Suspended SalidsCVSS) analyses were performed according to the procedures described in the standard Methods for the Examination of Water and Wastewater. Total sulfide content of the solution was measured by the Iodimetric method. Sulfate content was determined by the Turbidimetric method. Total sulfur content in solid was determined by the Eschka method. The concentration of the H"S, C02 and CH, in gas phase was measured by gas chromotography. According to the results of the test where the sulfate concentrations were changed, when the value of SS was 24500 mg/1, in the solutions which contained 5900 mg/1 and 10 760 mg/1 sulfate, the sulfate reduction amount was maximum 3 600-mg/l. In the solutions which contained 945. mg/1 and 2945 mg/1 sulfate, the reduction amount of sulfate was less than the others. The change in the value of the total sulfur in the solid phase was parallel to degradation amount of sulfate. The value of reduction the percantage of COD increased up to 5900 mg/1 sulfate concentration and then this value also decreased. In the studies where the value of SS was changed, the sulfate reduction amount linearly increased rapidly, until the value of SS was 20620 mg/1 and then degrada tion of sulfate became slower. According to the Table 5.3, for the value of SS at 20620 mg/1, the transfor mation, acconding the reaction given below ; XII(sıv occures without the accumulation of S~. The increase in the ss value also increased the removal value of the percantage of COD. Finally, experiment where the temperature was control led at 37 C, showed that when themperature increased, the removal value of percantage sulfate, the change in the value of the total sulfur in the solid phase and the reduction value of percantage COD increased. xin
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