Torefiye edilmiş orman, deniz ve tarımsal biyokütle numuneleri kullanılarak atık sudan kurşun, krom ve kadmiyum giderimi
Removal of l ead, chrome and cadmium from waste water using torified forest, marine and agricultural biomass samples
Yazar: BUĞRA BİRGİLİ
Danışman: PROF. DR. HANZADE AÇMA
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Kimya Mühendisliği Ana Bilim Dalı / Kimya Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2022
Konu: Kimya = Chemistry ; Kimya Mühendisliği = Chemical Engineering ; Çevre Mühendisliği = Environmental Engineering
Dizin: Ağır metal giderimi = Heavy metal removal ; Ağır metal iyonları = Heavy metal ions ; Ağır metaller = Heavy metals ; Biyokütle = Biomass ; Deniz yosunları = Seaweeds ; Endüstriyel atık su = Industrial waste water ; Tarımsal atıklar = Agricultural wastes ; Çay atıkları = Tea wastes

Özet:
Ağır metallerin belirli konsantrasyonlar üzerinde toksik ya da eko-toksik özellik göstermeleri, yaşamsal olarak rol üstlenenler de dahil olmak üzere, nedeniyle ağır metaller ile ilişkilendirilmiş pek çok sağlık ve çevre sorunu ortaya çıkmıştır. Atık sular veya uçuşan inorganik partiküller ile ya da asit yağmurlarının toprak bileşiminden bu metalleri çözmesi ile ağır metaller denizlere ve yer altı sularına karışmaktadır. Sanayileşme ile birlikte gübreler, çimento sektörü, cam üretimi, çöp ve atık çamurlarının yakılması, termik santral ve otomobillerde fosil yakıtların yakılması gibi pek çok yaşamsal faaliyet ile ağır metaller yüksek konsantrasyonlarda doğaya salınmaktadır. Araştırmacılar, bu gibi faaliyetlerden gelen atık sulardaki ağır metalleri giderecek ucuz, etkili, kolaylıkla bulunan ve sürdürülebilir bir çözüm arayışı içerisindedir. Ülkemizin biyokütle kaynaklarının bu alanda kullanılma potansiyeli mevcuttur; ancak, bu biyokütle kaynaklarımızın torefiye işlemi gibi termal süreçlerden geçirilerek özelliklerinin iyileştirilmesi gerekmektedir. Torefiye işlemi, biyokütleyi 300 C'ye kadar inert atmosfer altında ısıtarak hemiselüloz yapılarını daha stabil hale getirir ve uçucu maddeleri azaltıp sabit karbon oranını arttırarak daha kaliteli ve hidrofobik özellik gösteren katı yakıt elde edilmesini sağlayan bir termal ön işlemdir. Ayrıca, nemin giderilmesi ve fiber yapının bozulması ile biyokütlede biyobozunma engellenir ve öğütülme daha kolay hale gelir.
Bu çalışmada ülkemizden tarımsal biyokütle olarak çay üretim atığı, mısır atığı, üzüm çekirdeği; orman biyokütlesi olarak çam kozalağı ve orman gülü; deniz biyokütlesi olarak ise yosun numunelerinin kurşun, krom ve kadmiyum ağır metallerini atık sulardan arıtma amacıyla kullanılma potansiyeli araştırılmıştır. Bu kapsamda hem biyokütle numune hazırlama sırasında hem de ağır metal tutumu sırasında kontrol edilmesi gereken parametrelerden bir kısmı incelenmiştir. Biyokütle numunesinin hazırlanması sırasında torefiye işleminin etkisi, torefiye son sıcaklığı ve torefiye son sıcaklığında bekleme süresi; ağır metal ile adsorban malzemeyi yükleme sırasında ise sıcaklık, karıştırma hızı, ve çözelti ortamı pH değeri parametrelerinin Pb, Cr, Cd tutma kapasiteleri incelenmiş ve gruplar arasındaki farklar istatistiksel analiz ile belirlenmiştir. Ayrıca, biyokütlelerin tekrarlı kullanımı ve tutulan iyonları geri kazanım performansı da incelenmiştir. Karakterizasyon çalışmalarında XRD, SEMEDS, FTIR, Zeta potansiyeli, uçucu madde ve kül tayinleri yapılmıştır.
İstatistiksel analiz sonuçlarına göre torefiye sıcaklığında 30 dakika bekleme süresi vermek, ağır metal tutma kapasitesine olumlu katkı sağlamaktayken, yüksek torefiye sıcaklıklarının anlamlı bir katkısının olmadığı bulunmuştur. Karıştırma hızının anlamlı bir katkısı görülmemiştir.Yükleme ortamı pH değerlerinden ise istatistiksel olarak önemli derecede farklı olanları, zeta potansiyelleri de göz önünde bulundurularak pH 3-5 aralığında çalışmanın optimum sonuç vereceği şeklinde yorumlanmıştır. Yükleme sıcaklığı olarak 50 ℃'de çalışmanın bu çalışma içerisinde istatistiksel olarak anlamı bir katkısının bulunmadığı ancak literatürdeki mevcut bulgularla uyumlu sonuç verdiği görülmüştür. XRD Analizi ile ağır metallerin adsorblandığı ve FTIR verilerine göre ise moleküler yapıda önemli bir değişiklik olmadığı ispatlanmıştır. Torefiye çay atığı biyokütlesinin performansını yitirmeden üç kere kullanılabilir olduğu ve tutulan ağır metallerin istenirse geri kazanılabildiği de gösterilmiştir.

Abstract:
The physical definition of heavy metals is that any metal or semi-metal (metalloid) with an atomic number greater than 20 and a density greater than 5 g/cm3; as well as, their biological definition is that all the metals with toxicity or eco-toxicity regardless of their density. Although some heavy metals are defined as vital (essential) due to their presence in the composition of enzyme cofactors, vitamins and hormones or in the structure of organisms in biological processes; there are also some heavy metals which are not vital (non-essential) and demonstrate a toxic effect even at their very low concentrations in the biostructures. These metals can be mixed into rivers, lakes and underground waters by their dissolution in the discharged wastewater or via acid rains passing throught the soil. The heavy metals demonstrate serious effects on plant, animal and human health directly by the erosion of soil which contaminated with heavy metals or indirectly by mixing with the aquatic ecosystem through particles contaminated with heavy metals. According to the definitions of heavy metals, the heavy metal expression includes around 60-70 metals, mainly cadmium (Cd), chromium (Cr) and lead (Pb). According to the 2019 data in Turkey, the average Pb pollution in the air is more than 5.8 ng/m3 in the Marmara and Aegean regions. The lead accumulation in the water bodies also reports that besides the Marmara and Aegean regions, Şanlıurfa and its surroundings, where industrialization is high, have an annual Pb pollution accumulation of more than 0.86 kg/km2. Similarly, the average Cd pollution in the air is more than 0.29 ng/m3 in the Marmara and Aegean regions, similar to the Pb pollution. The amount of Cd accumulation in water bodies was reported as a high pollution rate in the Marmara and Aegean regions as well as in the South East Anatolia region. In terms of the Cr, it was stated that 6700 tons of Cr precipitates on the sea and ocean floors in the world annually. Today fertilizers, cement production plants, glass production plants, garbage and waste sludge incineration plants, waste water treatment plants, thermal power plants, oil plants, iron-steel plants and transportation sector are the leading industrial facilities where heavy metals are most widely spread to the environment. These industrial facilities are obliged to reduce their discharged heavy metal amounts below the values determined by the regulations during their waste disposal. Although the pollutants in the wastewater from factories and facilities are cleaned by physical, chemical or advanced treatment methods, these techniques are quite expensive in terms of both capital and operating costs. For this purpose, researchers are in search of finding cheap, effective, easily available and sustainable solutions with the use of natural resources. Our country's natural biomass resources have the potential to be used in such environmental issues. However, these biomass resources need to undergo thermal processes such as torrefaction. Torrefaction is a pre-thermal process applied to produce quality fuel by heating the biomass to a relatively low temperature (200-300 ℃) in an inert atmosphere, making the hemicellulose structure more stable. As a result of torefication, the biomass possess an increased C ratio in the structure of the biomass while reducing the amount of O2 and moisture, gains hydrophobic properties, its moisture and ome of the volatile substances are removed from the body. Another positive effect is that with the removal of moisture, the fibrous structures gradually degrade and due to the low moisture content, the biodegradation of the torified biomass is prevented and the grinding process can be done more easily. According to the data of the United Nations Food and Agriculture Organization (FAO) and ÇAYKUR, Turkey is the fifth largest producer country of tea in the world with an annual tea production of 225000 tons in 2014 and around 5 % powdered tea production waste is released from those production sites. The tea wastes affects the working order because it covers a large area in the usage area of the factories, and since it is not evaluated in food economy, it is thrown into the nature as waste in wild storage and so demonstrates an environmental problem. Another important biomass is corn, which is one of the most planted crops in the world and their cobs, stalks and leaves which cannot be consumed as food are burned as agricultural waste. With this feature, corn stalks are an easily available and ecologically acceptable biomass source. As the basic raw material of the grape, fruit juice and wine industry, 58 million tons of grapes are produced in 7 million hectares of land in the world, and from this processes, solid waste (pulp), which is rich in bioactive components, and lignocellulosic compounds with active functional groups comes out. 38-52% of this pulp is grape seed and these seeds have been stated as a potential adsorbent candidate where heavy metals such as Cr (VI) can be adsorbed. Pine trees are a type of tree that can grow in most regions of the world and in different climatic conditions, they stay green all year long, they can grow up to 50 m in height, they can live longer than 100 years, and 4000 tons of pinecone waste is produced in our country annually. Pine cone is a solid forest waste that can be found in large quantities in the world, which poses a problem for disposal because it has no economic value. Rhododendrons (rhododendrons) draw attention with their purple flowers among moist forest species and are found in forest areas on the coasts of the Eastern Black Sea region in our country. In the world, there are more than 800 species of rhododendrons in the northern hemisphere and can remain green throughout the year. Another type of potential biomass source is dead algae masses which accumulate in the beaches and coastal areas through the tides and waves in the seas, or for touristic reasons, the algae are cleaned from the coasts and disposed of as waste. However, due to the alginate-rich brown macroalgae it contains, it has a very high potential to bind to metal ions. Therefore, we have studied tea wastes, corn stalk wastes and grape seed wastes as agricultural biomass source; pinecone and rhododendron as forest biomass; and seaweeds as marine biomass as a potential biosorbent to treat lead, chromium and cadmium heavy metals from simulated wastewater. In this context, some parameters which need to be controlled during both biomass sample preparation and heavy metal removal were examined. During the preparation of the biomass sample, the torrefaction temperature and the waiting time at the torrefaction temperature were investigated. During the loading of heavy metal to the adsorbent material, the loading temperature, stirring speed, and pH parameters were examined and their group differences were analysed by statistical analyses. In addition, the repetitive use of biomass and the recovery performance of captured ions were also investigated. In characterization studies, XRD, SEM-EDS, FTIR, Zeta potential, volatile matter and ash determinations were made. The major findings of this study was that when the Pb, Cr and Cd holding capacities of the the waste sample were examined, regarding the change of the zeta potential with pH, the results indicated that the high capacity for Cd was seen when the sample entered the stable region around pH 7 and the surface charge was found to be negative. The findings can be attributed to the low capacitance for both Pb and Cd around pH 2 to the fact that the zeta value was close to zero and the electrostatic interactions have decreased. Moreover, Rhododendron sample had increased Pb and Cd capacity with increasing pH because between pH 2 and pH 7, the zeta potential passed from positive to negative and increased in absolute value. In addition, the algae sample showed a similar fluctuation between pH3-pH5 for Pb holding capacity, again in the same pH range for zeta potential. Although the loading temperature did not make a statistically significant difference, it was observed that the heavy metal retention performance increased with the increase in temperature, as explored in the combined effect studies. All in all, experimenting around pH 5 with the aforementioned samples (e.g., Pb, Cr) was in line with with the existing studies in the related literature and also in line with the surface charge characteristics of the biomass samples. In the current study, the fact that heavy metals had successfully adsorbed was proved by XRD Analysis. According to the FTIR data, we did not observe a significant change in the molecular structure. The tea waste biomass sample could be used three times without losing its performance and that the loaded heavy metals can be recovered if desired.