Aktif ve kimyasal çamurların pirolizi

Abstract

Atıksuların sorumsuzca uzaklaştırılması sonucu ortaya çıkan çevre kirliliği sorunu ve bunun insan sağlığını tehdit eden boyutları, günümüzde su ve normal yaşa mı etkileyen en güncel konulardan birisidir. Atıksuların çeşitli sistemlerle arıtılması sonucun da oluşan organik veya inorganik kökenli çamurların gelişigüzel atılması ya da kullanılması, çevre kirliliğini daha farklı bir şekilde etkilemekte ve bazı özel durumlarda da, insan sağlığı için direkt tehlikeler oluştura bilmektedir. Biyolojik ve kimyasal çamurların bertaraf edilmemesi çevre kirliliğinin sudan karaya transferi olayıdır. Ortaya çıkan bu çamurların en uygun sistemlerde arıtılıp, sorunsuz olarak, yine en uygun yöntemlerle uzaklaştırılmaları gerekir. Çamur arıtımından beklenen arıtma sistemlerinden çıkan çamuru yoğunlaştırmak, gerektiği durumlarda stabilize etmek ve suyunu giderdikten sonra katı madde konsantrasyonunu arttırarak hacmini azaltmak ve çamurun imhası sırasında. taşıma maliyetini en aza indirmektir. Çamurun imhası ise, çamuru tekrar kullanılır hale getirmek ve çevreye zarar vermeyecek şekilde bertaraf edilmesini sağlamaktır. Bu çalışmada atıksu arıtımından elde edilen aktif ve kimyasal çamurların normal atmosfer şartı altında piroliz deneyleri gerçekleştirilmiştir. Piroliz deneyleri Heinze retordunda k C/dakika ısıtma hızı ile 550 C ve 9DGDC sıcaklıklara kadar gerçekleştirilmiş ve elde edilen sıvı ürünler kolon kromatograf isi kullanılarak frak- sine edilmiştir. Sıvı ürünün adsorbsiyon kolonundaki f raksinasyonundan sonra ele geçen aromatik ürüne gaz kromatografi analizi uygulanmıştır.

Every community produces both liquid and solid wastes. The liquid portion- wastewater-is essentially the water supply of the community after it has been fouled by a variety of uses. If untreated wastewater is allowed to accumulate, the decomposition of the organic materials it contains can lead to the production of large quantities of ma lodorous gases. In addition, untreated wastewater usually contains numerous pathogenic or disease-causing microorganisms that dwell in the human intestinal tract or that may be present in certain industrial wastes. It also contains nutrients, which can stimulate the growth of aquatic plants, and it may contain toxic com pounds. For these reasons, wastewater should be treated. Methods of treatment in which the application of physical forces predominate are known as unit operations. Met hods of treatment in which the removal of contaminants is brought about by chemical or biological reactions are known as unit processes. At the present time, unit operations and processes are grouped together to provi de what is known as primary, secondary and tertiary (or advanced) treatment. In primary treatment, physi cal operations are used to remove the floating and settleable solids found in wastewater. In secondary treatment, biological and chemical processes are used tD remove most of the organic matter. In tertiary treatment, additional combinations of unit operations and processes are used to remove other constituents, such as nitrogen and phosphorus, which are not removed by secondary treatment. The objectives of the biological treatment of wastewater are to coagulate and remave the nonsettle- able colloidal solids and to stabilize the organic mat ter. Vll ThE major biological processes used for wastewa ter treatment are identified in four major groups: aerobic processes, anoxic processes, anaerobic proces ses and a combination of the aerobic/anoxic or anaero bic processes. Basic to design of a biological -treatment process or to the selection of the type of process to be used,is an understanding of the form, structure, and biochemical activities of the important microorganisms. The impor - tant microorganisms are classified with the characteris tics in biological-treatment processes. These are, 1)- bacteria, 2)- fungi, 3)- algae, ^)-protozoa, 5)-ro- tifers, 6)- crustaceans, and 7)-viruses. At this point bacteria can be considered as tiny automatic chemical reactors. Bacteria oxidize wastes to provide themselves with sufficient energy to enable them synthesize the complex molecules such as proteins and polysaccharides which are needed to build new cells. Waste oxidation is des cribed as "aerobic" when molecular oxygen is used as the terminal oxidizing agent. The "equation": bacteria Wastes + Oxygen *? Oxidized waste + IMew bacteria The one of the most important aerobic treatment processes is the activated sludge process. The developlent of environmentally sound methods of wastewater treatment and sludge disposal has been a continual challenge. The treatment of wastewaters not only produces purified effluent, but also a signi ficant quantity of sludge. Activated sludge processes or chemical sludge processes generate wastewater slud ge. The operations carried out on wastewater sludge are conveniently divided into treatment operations, such as thickening, stabilization, and dewatering; and dis posal operations, which include ocean disposal, incine ration, co-combustion, wet air oxidation, pyrolysis, composting, landfills and land spreading. Vlll In the land applications, the site should be loca ted where groundwater contamination is not passible, and any leachate should be collected and treated. It is clear that the environmental effects of ocean sludge disposal are not easily controlled after the sludge is disposed of in the ocean. There is inade quate information on the dispersal of sludge solids; rates of decomposition; the nature of benthic fauna in areas receiving sludge and in nonsludged areas; uptake of toxics and transport of pathogens; and production of aquatic life in the offshore sludge and nonsludged regions. When properly carried out, incineration is a satis factory means of disposing of the great majority of hazardous sludges. A major problem with incineration is poor operation, this can be corrected by good operat ing procedures and modern control devices. Pyrolysis is the destructive distillation and de- isition of organic so! 370 to 87DDC in the i which support combustion. composition of organic solids at temperatures ranging from 370 to 87D C in the absence of air or other gases The characteristics of the three major component fractions resulting from the pyrolysis are: 1)- A gas stream containing primarily hydrogen, methane, carbon monoxide, carbon dioxide, and various other gases, depending on the organic characteristics of the material being pyrolyzed. 2)- A fraction that consists of a tar and/or oil stream that is liquid at room temperatures and has been found to contain chemicals such as acetic acid, acetone, and methanol. 3)- A char consisting of almost pure carbon plus any inert material that may have entered the process. IX In this study activated and chemical sludges uhich are obtained from the wastewater treatment plants of two different factories were pyrolyzed. The experimen tal studies were carried out in a Heinze type retort. It was operated with 20 gr. samples. In all the ex perimental runs the retort was started at room tempe rature. The system was held 3D minutes at the maximum temperature and a 4DC/min heating rate was used for all experiment. The all experiments were carried out at normal atmosphere. In the later stages of study the produced sludge oil was characterized using chromato- grahic methods. For this purpose the oils are fracti onated into aliphatics, aramatics and polars by eluding them with n-heksan, benzene and methanol using column chromatography. After the fractionation, the aromatic fractions was subjected to capillary GC analysis with FID on a 25 m X D. 22mm i. d. silica capillary column coated with biphenly group (SB Biphenly 30) for the presence of PAH. 1 u.1 sample solution was injected on-column into Hewlett PacKard 5890 GC operating under a temperature program Dg 50DC (10 min) to 275 C (5min) at a ramp rate of 5 C/min. The carrier gas was helium. Compounds detec ted by FID were identified using the Lee linear reten tion indices for PAH products. For this purpose benzene, naphthalene, phenanthrene, chrysene and picene were used as internal standarts corresponding to the 100,200, 300,400,50D linear retention indices. The chromatograms of the aromatic fractions are shown in the Appendix A. The compounds identified for each chromatogram are given in Appendix B. Additionaly, the compounds identified in activated and chemical sludge tars aromatic fractions are shown in Appendix C with their carcinogenecities by column number which are given in Appendix B. Proximate and ultimate analysis of activated and chemical sludges which are used in the experimental studies are given in the following table: Weight % Chemical Sludge Activated Sludge Moisture Aah Volatile Matter Fixed Carbon C H 67AQ Sit. 20 41.96 82. 64 33.58 5.72 91.40 78.01 8.05 82.25 35.03 5.96 Some of the important experimental results obtained for this studies are summariezed in the fallowing table: Weight % Activated Sludge Chemical Sludge 0-0.125 0.63-1 0-0.125 0.63-1(mm) As the overall conclusion of this study it in found that as the particle size distribution was increa sed the tar yield was also increased. Comparing the activated sludge and chemical sludge self-generated pyrolysis products shows that both has the same amount of n-heksane solubles. However, the distribution of lower fractions has differences. Aliphatics and polars are distinctly different. As the particle size distribution in chemical sludge are increased the proportion of aliphatic and aromatic fraction are also increased, while the proportion of polar fraction decreased. The effect of product distributions was also ob served from the capillary column chromatographic analy sis of aromatic fractions. As the particle size distri bution in activated sludge are increased the proportion of aliphatic and aromatic fraction are decreased while the proportion of polar fraction increased. XI The majority Df the compounds identified were PAH. Hut same nitrogen and sulphur heterapolycyclics were also identified. The greatest number of components observed were one ring compounds fallowed by two rings compounds.