Damlatmalı filtrelerde metal zehirliğinin etkisinin incelenmesi

Abstract

ÖZET Atık suları arıtma metotları mekanik arıtma, biyolojik arıt ma, kimyasal arıtma olarak ayrılabilir. Bunlardan biyolojik arıt ma metodu kendi arasında doğal biyolojik arıtma ve suni biyolojik arıtma olarak iki kısma ayrılabilir. Damlatmalı filtreler suni biyolojik arıtma sistemlerinin bir çeşitidir. Günümüzde işler haldeki pek çok biyolojik arıtma sisteminde damlatmalı filtreler kullanılmakla birlikte, kirleticilerin bun lara ??_ tesirleri üzerinde eldeki data miktarı azdır. Aerobik biyolojik arıtma üzerinde bu konudaki çalışmalar aktif çamur te sisleri üzerinde yoğunlaşmıştır. Bu çalışmada laboratuvar ölçekli polivinil klorür yataklı bir damlatmalı filtre üzerinde CUSO4, HgCl^ ve KSCN bileşikleri nin etkisi incelendi. Bu çalışmanın birinci bölümünde atık suların özellikleri, mikrobiyolojik karakteristikler, mikroorganizmaların çeşitleri, biyolojik oksidasyon ve biyolojik oksidasyonu etkileyen faktör ler verildi. İkinci bölümde, atık su arıtma yöntemleri ve aerobik biyolo jik arıtma sistemleri kısaca sıralanarak, damlatmalı filtrelerin; yapısı, sistemleri, içindeki biyolojik oksidasyonun nasıl gerçek leştiği ve sınıflandırılması açıklandı. Üçüncü bölümde, sistemde etkisi incelenen bakır, civa ve si yanür bileşiklerinin tabiatta bulunuş şekilleri ve bunlarla ilgi li literatür araştırmaları verildi. Dördüncü bölümde çalışmada kullanılan materyal ve metod an latıldı. Son bölümde bulgular, tartışma ve sonuçlar verildi. Bu sistemde kullanılan yapay atık su et özütü ve glikoz ka rışımı olarak hazırlandı. Deney süresince homojen bir atık su temin ederek, sistem veriminin organik madde konsantrasyonu deği şiminden etkilenmesi önlendi. Çalışma kontrol altında tutulan pH, sıcaklık, ve akış mikta rı koşulları altında yapıldı. BOt ölçümleri respirometre ile alındı. Kimyasal maddeler sisteme devamlı olarak gönderildi. Ar tan madde konsantrasyonu artan etkiye sebep oldu. Bu çalışma so nucu sistemin veriminin BÖt hesabı ile %60 civarında olduğu gö rüldü. Sisteme verilen kimyasal maddelerin belirli bir konsantras yonunun üstünde uygulanmaları halinde sistemin verimi tamamen durdu. Damlatmalı filtrelerin endüstriyel atık suların, ve bunları içeren evsel atık suların arıtılmasında diğe:t sistemlere alter natif olabileceği gösterildi.

SUMMARY In an effort to describe inhibitory effects, treatment processes and interfering substances are grouped into broad categories. Three basic catagories of treatment processes are delineated, including aerobic processes, anaerobic processes and nitrification. The aerobic processes are further subdivi ded into activated sludge and trickling filter operations, while anaerobic processes consist essentially of sludge digestion. In the percolating filters microorganisms are encouraged to form colonies in artificial beds of clinker or other rough, hard material over which the settled sewage is sprinkled by mechanical distributors. These beds are usually called trick-. ling filters, but are sometimes referred to as biological filters or bacteria beds. They do not filter in the sense of straining out impurities: rather they allow the settled sewage and fresh air to penetrate among the colonies of bacteria which form a film over each piece of the material. Other forms of staall life also colonise the filter beds, notably worms, springtails and various flies whose grub graze on the bacterial film and perform an important function: they convert the film into humus, which is washed out of the filter with the treated sewage effluent, and prevent the film from growing so thick as to choke the bad. Cold winter weather causes these `scouring` organisms to retreat deeper into the filter and this may result in some surface choking of the filter. When warmer weather returns they attack the surface layers again and liberate an abnormally large quantity of humus. The efficiency of a trickling filter depends upon the even distribution of the settled sewage over the whole surface of the filter, and on the provision of a good circulation of air through the bed which must reach the surface of each piece of the filter material to keep the right kind of bacteria and other organisms alive and active. Although many currently operating biological treatment plants utilize the trickling filter processes, relatively little data available on pollutant interferences. Consequently, the information on aerobic biological treatment presented is predominantly concerned with the activated sludge process. Since both activated sludge and trickling filtration are aerobic processes, the lack of information on trickling filtration ten ded to be compensated for by coutiously parallels with acti vated sludge data. The general categories established for interfering substan ces are inorganics and organics, with acidity, alkalinity, pH, ammonia, transition metals, metals, sulfate and sulfide comprising the major components of the inorganic category. Organic substances include alcohols» amines, chlorinated hydrocarbons, pesticides and herbicides, phenol, surfactants and miscellaneous organic chemicals. Whether a substance is VJinhibitory depends on a number of factors, including its con centration and the presence of other chemicals which have synergistic or antagonistic effects. Some substances, such as mercury, present in wastewater at a very low concentration can disturb one or more functions of a biological treatment system. Other substances such as chloride ion, are inhibitory only at relatively high concentrations. Copper is a transition metal which forms salts and other compounds. The majority of copper compounds are insoluble and therefore do not pose a problem to sewage systems in that form. However, copper nitrate, sulfate, chloride salts and a number of copper complexes are soluble and these may pose problems when discharged to sewage treatment plants. Copper compounds are discharged from a number of operations such as metal cleaning and electroplating operations. Engraving, jewelry, electrical manufacturing, chemical industrial pro cesses, and algicide and insecticide uses all add copper to industrial wastewaters. Copper is an essential nutritional food element for man and lower organisms, and is no doubt essential to the proper operation of biological waste treatment systems at some unde termined trace level. At extremely high concentration levels (about 1000 mg/1 and above) essentially all forms of living species are destroyed and essentially sterile water results. For the operation of sewage treatment plants the interme diate concentration levels, at which copper-bearing waste water may be processed through the system without causing significant plant upset are considered. Above this safe cop per concentrations various inhibitory effects may result. It is expected that the various biological treatment systems may respond differently to the same level of copper in waste water. Researches with activated sludge systems have shown that 100 mg/1 copper seriously suppressed the efficiency of these treatment systems. The cyanide ion KSCN is a pollutant parameter of signifi-r cant interest in environment. Its poisonous character is uni versally known, and accounts for the interest in this pollu tant. The poisonous nature of.cyanide is actually associated more with hydrogen cyanide which is more prevalent below pH 7, than with the free cyanide ion. Therefore cynide toxicity is directly tied to the pH of wastewater. Another interesting aspect of its poisonous character is that toxicity is princip ally applicable to higher life forms. Microorganisms present in sewage treatment plants can adopt to the presence of cyanide, and metabolize and destroy it even at fairly high concent ration levels. An important property of the cyanide, ion is that it is a powerful complexing agent and can bind with transition and other heavy metal ions to form metal cyanide complexes. These complexes exibit neither the properties of the metal ion nor the cyanide ion, and thus are actually different chemical substances. Cyanide is not a normal constituent of domestic sewage, and its presence in wastewaters is almost exclusively a result of manufacturing processes and commercial operations. viiPrinciple sources of cynide in wastewater are electroplating, coke, petroleum gas, steel, plastics and chemical industries. The electroplating industry is particularly noteworthy beca use it combines cynide wastes with transition and heavy me tal ion wastes. Researches carried out on activated sludge plants have shown that 500 mg/1 cynide could seriously suppress the plant operation. Mercuric forms series of salts, the monovalent mercurous salts and the divalent mercury salts. Most mercury salts are considered to be insoluble or sparingly soluble. However, because of the severe toxicity of mercury to man, fish, wild life, and lower microorganisms even the slight solubility poses a substantial threat. Mercury is found in typical domestic wastewaters at extremely low levels. Commercial cont ributions occur principally from the Ghlor-alkali industry. Other sources include chemical, drug, herbicide, fungicide, and paper products from these industries. Researches on activated sludge plants have shown that 200 mg/1 mercury seriously suppressed the plant efficiency. Synergism can be generally characterized as an increase in the inhibitory effect of one substance by the presence of another. Synergism as well as its opposite antagonism is fo und to be most prevalent when considering combinations of transition metals or heavy metals. The inhibitory effects of these metallic constituents are also enhanced by acidity. The synergistic effects of metals with acidity is under standable in terns of the chemistry of these metals. The transition and heavy metals tend to be insoluble'by hydroly sis in the pH range of sewage influent. They therefore tend to precipitate or absorb on solids, and interact with poly- electrolytes or various chemical species containing anionic functional groups. Acidity suppresses hydrolysis, and the hydrogen ion competes with the metal ion for adsorption sites on solids or anionic functional groups in solution. Another type of synergism is encountered with cynide or other complexing substances which are easily biodegradable. In these cases, it is possible for the microorganisms to ingest excessive levels of complexed metal ion and then to destroy by assimilation the complexing substance which is shielding the microorganism from metal ion. The result is the release of an excessive level of the metal within the organism, upsetting its biological life processes. Antagonism is the opposite of synergism in that it is characterized as a decrease in the inhibitory effect of one substance by the presence of another. The most notable antagonistic effects occur with the combination of metallic and anionic pollutants. When a biomass becomes accustomed to the presence of a normally inhibitory concentration of a substance, it can be characterized as acclimated to that pollutant. Sludge digesti on and nitrification do not have the same flexibility of adaptation to changing environmental conditions as do other biological processes. Both nitrification and sludge digestion are biological processes that rely on particular strains of.. a Vlllbacteria. Because of this reason, when adverse conditions are encountered in this processes there is no possibility of. anot her organism taking over for the affected strain of bacteria. Consequently, neither nitrification nor sludge digestion are readily acclimated to a new pollutant and may be easily upset when new conditions are encountered. In this research inhibitory effects of CUS04, HgCl2, KSCN compounds on a laboratory scale trickling filter plant was investigated. The main aim of this research is to bring out some information on the toxicity effects of these chemicals which appears to be lacking in the literature. Trickling fil ter system consisted of a trickling filter column and a sett ling tank. Polyvinylchloride media was used as a trickling filter. Research was carried out under controlled conditions (pH, temperature, f lowrate). Data obtained from this research was compared with the data previously found from activated sludge systems. This showed that trickling filtres are to be considered as a waste water treatment system alternative to the other systems for the treatment of industrial wastewaters. BOD and COD measure ments were used for the investigation of the system behaviour under controlled conditions. IX