Yemek Atığından Anaerobik Membran Biyoreaktör İle Biyohidrojen Üretimi
Yemek Atığından Anaerobik Membran Biyoreaktör İle Biyohidrojen Üretimi
Dosyalar
Tarih
2014-02-28
Yazarlar
Bostancı, Okan
Süreli Yayın başlığı
Süreli Yayın ISSN
Cilt Başlığı
Yayınevi
Fen Bilimleri Enstitüsü
Institute of Science and Technology
Institute of Science and Technology
Özet
Yüzyıllar boyunca fosil yakıtlar endüstriyel gelişmede önemli rol oynadılar. Fakat sera gazı salınımı azaltımı ile ilgili gelişmeler ve gelişen çevre bilinci insanları bu yakıtları daha az kullanmaya yöneltti. Bu yakıtların kullanımı sonucunda ortaya çıkması muhtemel çevre sorunlarını ortadan kaldırmak için hidrojenin yakıt olarak kullanılması umut veren bir alternatif olacaktır. Hidrojen, bilinen birim ağırlık başına en yüksek enerji veren yakıttır (142kJ/g) ve evsel/endüstriyel kullanım için taşınması mümkündür. Hidrojen, dünyamız için güvenli, yenilenebilir ve sera etkisine katkısı olmayan bir enerji kaynağı olarak kabul edilmektedir. Hidrojen yanması sonucunda karbondioksit oluşturmayan yani 0 karbon ayak izi olan tek yakıttır ve içten yanmalı motorlarda veya yakıt hücrelerinde kullanılabilir. Son zamanlarda, fermantasyon yolu ile biyohidrojen üretimi, düşük enerji ihtiyacı ve çevre dostu oluşu nedeniyle yenilebilir enerji sektöründe çok ilgi çekmiştir. Fermantatif ve fotosentetik bakteriler ve algler gibi pek çok mikroorganizma türlerinin H2 ürettiği bilinmektedir. Bunların yanısıra fermantatif anaerobik bakteriler H2 üretiminde atıkları hammadde olarak kullanabilirler. Sürekli fermantatif hidrojen üretimi genellikle tam karışımlı reaktör (TKR) ile yapılır. Çünkü TKR’nin kullanımı kolay ve biyokütlenin hammadde ile teması tam karışım sayesinde en yüksek düzeydedir fakat TKR’nin en önemli kısıtı sistemden hidrojen üreten mikroorganizmaların çıkış akımı içerisinde çıkmasıdır. Bununla mücadele etmeninde tek yolu bir yandan hidrojen üreten hücreleri sistem içinde tutarken öteki yandan sisteme yüksek organik yükleme yapabilmektir. Son zamanlarda membran biyoreaktörler (MBR) biyokütleyi dışarı geçirmeyerek etkin olarak sistem içinde tutma özellikleri ile öne çıktılar. Membran ile ayırma diğer biyokütleyi reaktörde tutan sistemlerle karşılaştırıldığında reaktördeki hidrojen üreten biyokütleyi tutma konusunda daha başarılıdır bu yüzdende gerçek ölçekte uygulaması mümkündür. MBR organik atıklardan hidrojen üretimi için önemli bir alternatiftir. Türkiye’de toplanan evsel katı atığın büyük bir bölümü yemek atığıdır. Yemek atığı, içeriğindeki yüksek miktardaki uçucu katı madde ve nem nedeniyle toplama, taşıma ve depolamadaki çürüme, koku ve sızıntı suyunun ana kaynağıdır. Atık azaltımı yaparken yemek atığının yüksek enerji içeriğinden faydalanarak enerji üretmek ideal bir çözüm olarak düşünülmektedir. Bu çalışmanın amacı, yemek atıklarından biyohidrojen üretiminin araştırılmasıdır. Bu kapsamda anaerobik membran biyoreaktör sistemi kullanılarak hidrojen üretimi için optimum koşullar incelenmiştir. Sistem, öncelikle sabit pH’da (pH=7) 4 farklı HBS’de (Değişken, 10 gün, 5 gün ve 2,5 gün) işletilmiş, daha sonra HBS sabit tutularak (5 gün), 4 farklı pH (8, 6, 5,5, değişken) koşulu denenmiştir. Çalışmada kullanılan anaerobik membran biyoreaktör sistemi iki ana birleşenden oluşmaktadır. Bunlar fermantasyon reaktörü ve batık membran ünitesidir. Fermantasyon reaktörünün hacmi 5L olup, 55o C de işletilmiştir. Membran modül 3,5 L’dir ve içerisindeki membranlar batık haldedir. Fermantasyon reaktörü ile membran modülü arasında pompayla sürekli bir devir daim yapılmıştır. Biyohidrojen üretiminde kullanılan yemek atıkları, İTÜ Ayazağa yerleşkesinde yer alan merkez yemekhaneden temin edilmiştir. Beslenen yemek atığı asidik olup, ortalama katı maddesi % 4,6, UKM/TKM oranı %91 civarında oldukça kuvvetli organik karakterdedir. Anaerobik membran biyoreaktör ile sabit pH’da (pH=7) 4 farklı HBS ’de (Değişken, 10 gün, 5 gün ve 2,5 gün) yapılan çalışmalarda en yüksek hidrojen üretimi HBS= 5 günde 110,9 mL H2/g UKM olarak elde edilmiştir. Sonraki aşamlarda, ilk aşamada optimum olarak belirlenen HBS= 5 gün sabit tutularak, farklı pH aralıkları test edilmiştir. pH 8’de 8,4 mL H2/g UKM, asidik pH’larda ise (pH 4,5-6) 0,9-2 mL H2/g UKM seviyelerinde bir hidrojen üretimi gözlenmiştir. Buna göre en yüksek biyolojik hidrojen üretimi HBS’nin 5 ve pH’nın 7 olduğu 3. dönemde 110,9 H2/UKMeklenen olarak belirlenmiştir.
For centuries, fossil fuels were considered to be the growth engine for industrial development. However, there have been growing concerns of greenhouse gas emissions and other pressing environmental issues over the use of fossil fuels. Hydrogen fuel is a promising alternative to conventional fossil fuels because it has the potential to eradicate all the environmental problems that the fossil fuels would create. Hydrogen (H2) is the most promising in the succession of fuel evolution, with several technical, socio-economic and environmental benefits to its credit. It has the highest energy content per unit weight of any known fuel (142 kJ/g) and can be transported for domestic/industrial consumption through conventional means. H2 is now universally accepted as an environmentally safe, renewable energy resource and an ideal alternative to fossil fuels that doesn’t contribute to the greenhouse effect. The only carbon-free fuel, H2 upon oxidation produces water alone. H2 can be used either as the fuel for direct combustion in an internal combustion engine or as the fuel for a fuel cell. Recently, biohydrogen production via fermentation, in light of its low energy intensiveness and marked friendliness to the environment, has received much attention as a renewable energy carrier. Many kinds of microorganisms such as fermentative and photosynthetic bacteria as well as algae, are known to produce H2. Among them, fermentative anaerobic bacteria can produce H2 gas utilizing waste as the raw material. Continuous fermentative H2 production is usually conducted via a continuous flow stirred tank reactor (CSTR) because it is easy to operate and can provide a good substrate biomass contact by vigorous mixing. However, one of the major limitations of CSTR is the poor cell retention resulting in poor H2-producing efficiency due to cell washout. To cope with this problem, there is a need to develop a H2 production system able to retain sufficient active H2 producing cells in the reactor against high organic loading and hydraulic pressure. Membrane bioreactors (MBRs) have recently emerged as an effective means for performance improvement in wastewater treatment due to their capability of increasing biomass retention. Compared with other cell retention approaches, such as cell immobilization, utilizing membrane separation to retain biomass would not cause mass transfer limitation and is thus of great interest in practical application. Therefore, MBR is a promising alternative of bioprocess for H2 production from organic substrates. Municipal solid waste consists of considerable amount of food waste in Turkey. Food waste is the main source of decay, odor and leachate in collection and transportation due to its high volatile solids and moisture content. However, as food waste has a high energy content, energy generation while reducing the waste seems ideal. Hydrogen recovery from food waste also has a potential to enhance the economic feasibility of waste treatment. The aim of this study was to research biohydrogen production from food waste. Optimum conditions were researched using anaerobic membrane bioreactor. Firstly pH was set at 7 with 4 different hydraulic retention time (HRT) (variable,10, 5, 2,5 days) were tested, then HRT set at 5 days with different pH (8, 6, 5,5, variable) were tested. There were two main component of the anaerobic membran bioreactor system which was used in study. Components called fermentation reactor and submerged membran module. Volume of fermentation module was 5 L and membrane module was 3,5L and its operating temperature was 55o C and same with two modules. Membranes are submerged in the membrane module. There was a nonstop circulation between fermentation module and submerged membrane module. Food waste used for biohydrogen production was taken form ITU Ayazaga Dining Hall. Food waste used as substrate was acidic, had 4,6% total solids, 91% Volatile Solids/Total Solids ratio and quite strong organic character. Studies with anaerobic membrane bioreactor at pH=7 with different HRT (variable,10, 5, 2,5 days), the highest hydrogen production was measured 110mL H2/g VSSadded in a day at HRT=5 days. Optimum HRT was chosen as 5 days and different pH (8, 6, 5,5, variable) was tested in the next step. The highest hydrogen production was measured 8,4 mL H2/g VSadded in a day at pH=8 and 0,9-2 mL H2/g VSadded in a day at acidic pH (4,5-6). According to all measures, the highest biohydrogen production was measured 110mL H2/g VSSadded at pH 7 and HRT=5.
For centuries, fossil fuels were considered to be the growth engine for industrial development. However, there have been growing concerns of greenhouse gas emissions and other pressing environmental issues over the use of fossil fuels. Hydrogen fuel is a promising alternative to conventional fossil fuels because it has the potential to eradicate all the environmental problems that the fossil fuels would create. Hydrogen (H2) is the most promising in the succession of fuel evolution, with several technical, socio-economic and environmental benefits to its credit. It has the highest energy content per unit weight of any known fuel (142 kJ/g) and can be transported for domestic/industrial consumption through conventional means. H2 is now universally accepted as an environmentally safe, renewable energy resource and an ideal alternative to fossil fuels that doesn’t contribute to the greenhouse effect. The only carbon-free fuel, H2 upon oxidation produces water alone. H2 can be used either as the fuel for direct combustion in an internal combustion engine or as the fuel for a fuel cell. Recently, biohydrogen production via fermentation, in light of its low energy intensiveness and marked friendliness to the environment, has received much attention as a renewable energy carrier. Many kinds of microorganisms such as fermentative and photosynthetic bacteria as well as algae, are known to produce H2. Among them, fermentative anaerobic bacteria can produce H2 gas utilizing waste as the raw material. Continuous fermentative H2 production is usually conducted via a continuous flow stirred tank reactor (CSTR) because it is easy to operate and can provide a good substrate biomass contact by vigorous mixing. However, one of the major limitations of CSTR is the poor cell retention resulting in poor H2-producing efficiency due to cell washout. To cope with this problem, there is a need to develop a H2 production system able to retain sufficient active H2 producing cells in the reactor against high organic loading and hydraulic pressure. Membrane bioreactors (MBRs) have recently emerged as an effective means for performance improvement in wastewater treatment due to their capability of increasing biomass retention. Compared with other cell retention approaches, such as cell immobilization, utilizing membrane separation to retain biomass would not cause mass transfer limitation and is thus of great interest in practical application. Therefore, MBR is a promising alternative of bioprocess for H2 production from organic substrates. Municipal solid waste consists of considerable amount of food waste in Turkey. Food waste is the main source of decay, odor and leachate in collection and transportation due to its high volatile solids and moisture content. However, as food waste has a high energy content, energy generation while reducing the waste seems ideal. Hydrogen recovery from food waste also has a potential to enhance the economic feasibility of waste treatment. The aim of this study was to research biohydrogen production from food waste. Optimum conditions were researched using anaerobic membrane bioreactor. Firstly pH was set at 7 with 4 different hydraulic retention time (HRT) (variable,10, 5, 2,5 days) were tested, then HRT set at 5 days with different pH (8, 6, 5,5, variable) were tested. There were two main component of the anaerobic membran bioreactor system which was used in study. Components called fermentation reactor and submerged membran module. Volume of fermentation module was 5 L and membrane module was 3,5L and its operating temperature was 55o C and same with two modules. Membranes are submerged in the membrane module. There was a nonstop circulation between fermentation module and submerged membrane module. Food waste used for biohydrogen production was taken form ITU Ayazaga Dining Hall. Food waste used as substrate was acidic, had 4,6% total solids, 91% Volatile Solids/Total Solids ratio and quite strong organic character. Studies with anaerobic membrane bioreactor at pH=7 with different HRT (variable,10, 5, 2,5 days), the highest hydrogen production was measured 110mL H2/g VSSadded in a day at HRT=5 days. Optimum HRT was chosen as 5 days and different pH (8, 6, 5,5, variable) was tested in the next step. The highest hydrogen production was measured 8,4 mL H2/g VSadded in a day at pH=8 and 0,9-2 mL H2/g VSadded in a day at acidic pH (4,5-6). According to all measures, the highest biohydrogen production was measured 110mL H2/g VSSadded at pH 7 and HRT=5.
Açıklama
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2014
Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2014
Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2014
Anahtar kelimeler
yemek atığı,
çevre,
enerji,
hidrojen,
sürdürülebilir,
food waste,
environment,
energy,
hydrogen,
sustainable