Mikrobiyel yakıt hücresinde Shewanella putrefaciens tarafından organik atıklardan elektrik üretimi

Abstract

A microbial fuel cell (MFC) is a bioreactor that converts chemical energy in the chemical bonds in organic compounds to electrical energy through catalytic reactions of microorganisms under anaerobic conditions. Typical two chambered MFC systems are consist of conductive anode (such as carbon cloth or carbon paper) and cathode material (with platinum), proton exchange membrane (PEM), anolyte and catholyte, external conductive wire, and digital multimeter system and computer. In a MFC, power can be generated from the oxidation of organic matter by bacteria at the anode, with reduction of oxygen at the cathode. Anodic and cathodic chambers partitioned by a PEM. A bacterium in the anode compartment transfers electrons obtained from an electron donor (e.g. glucose, acetate) to the anode electrode. This occurs either through direct contact (nanowires) or mobile electron shuttles. During electron production protons are also produced in excess. These protons migrate through the PEM into the cathode chamber. Electrons can be also transferred to the anode by electron chemical mediator. But the toxicity and instability of synthetic mediators limit their applications in MFCs. Shewanella putrefaciens is bioelectrochemically active and can form a biofilm on the anode surface and transfer electrons directly (without mediator) by conductance through the membrane. When they are used, the anode acts as the final electron acceptor in the dissimilatory respiratory chain of the microbes in the biofilm. S. putrefacience was grown on LB broth. For aerobic growth, cultures were shaken continuously on a cooling rotary shaker-incubator at 160 rpm at 25°C. For anaerobic growth, approximately 1.25 liter of anaerobically prepare (in the athmosphere controlled chamber) LB broth in glass bottle was inoculated with 12.5 mL of an aerobically grown overnight culture and incubated without agitation. After 96 h of growth, the cells will be harvested under anaerobic conditions by a continuous centrifugation system at 4800 rpm at 4°C. The cell paste will be washed three times in 50mM sodium phosphate buffer containing 0.1 M NaCl . The washed cells was re-suspended in the buffer and transferred to 100 mL capacity anode compartment of the MFC on anaerobic conditions. The two chambered microbial fuel cells (TCMFC) were constructed using two glass bottles. Each bottle's volumes were 100 mL. Each cell compartment had three ports at the top, for electrode wire, addition and sampling of solutions, and gassing. Two compartments were separated by a PEM. The anode compartment was loaded with freshly prepared bacterial suspension (suspended in 50 mM Na-phosphate buffer (pH 7.0) containing 0.1 M NaCl, vitamin, mineral solution and substrate (acetate, ethanol and propionic acid). The cathode compartment was loaded with 50 mM Na-phosphate buffer (pH 7.0) containing 0.1 M NaCl. Nitrogen and air were continuously purged through anode and cathode compartments to maintain anoxic and aerobic conditions, respectively (flow rate of nitrogen gas was approximately 15 mL per min). The microbial fuel cell was immersed in a water bath to maintain temperature (25°C). Cooler was used to supply for summer conditions and heater was used to supply for winter conditions. The air conditioner was also used to supply constant temperature. Voltage (V, volt) or current (I, amper) was measured using a multimeter with a data acquisition system. Power density (mW/m2) was calculated according to P=Current*Voltage /projected area of the anode (P= IV/A.) When the anode compartment of the microbial fuel cells were loaded with freshly prepared S. putrefaciens, potential development was measured under open circuit conditions. Before the fuel (carbon source) was added, open circuit voltage (OCV) approximately 100-200 mV were observed from the microbial fuel cell containing suspensions of S. Putrefaciens. The addition of substrate as the fuel to the cell containing S. Putrefaciens resulted in a rapid rise in OCV up to 780-840 mV. Maximum OCV observed 832 mV, 777 mV and 810 mV for 10 mM glucose centrifuged from anaerobic growth of 1250 mL, 2500 mL and 800 mL from pure culture, respectively. The addition of ethanol was OCV up to 670 mV and addition of propionic acid was OCV up to 803 mV. A membrane MFC inoculated with S.putrefaciens and the circuit was completed with a fixed load of 5000 W were used to determine the power generation as function of load. 10 mM glucose produced 4 µA current. Power density was 0.8 mW/m2. Keywords: Microbial fuel cell, electricity production, Shewanella putrefaciens, voltage, power density. Mikrobiyal yakıt hücreleri (MYH) oksijensiz ortamda elektrojen mikroorganizmaları biyokatalizör olarak kullanarak organik maddelerden elde edilen kimyasal enerjiyi doğrudan elektrik enerjisine çeviren sistemlerdir.Tipik bir MYH’si anot, katot, proton geçirgen membran ve voltaj yada akım değerlerini ölçen veri toplama cihazından oluşur.Elektrojen bakteri oksijensiz ortamda anot üzerinde biyofilm tabakası oluşturarak organik maddeleri, karbondioksit, elektron ve protona çevirir. Bu çalışmada, iki hazneli MYH ve saf kültür Shewanella putrefaciens kullanılmıştır. Bu saf kültür bakterisinin seçilmesindeki amaç, dış membran enzimlerini doğal olarak kullanma yeteneğinde olduğundan elektronlarını iletken bir anota verme kabiliyetine sahip olmasıdır. Böylece bakteri tarafından üretilen elektronları anot elektroduna iletecek dışarıdan kimyasal bir medyatör kullanma gerekliliği ortadan kalkmıştır. Bu çalışmada, MYH’de farklı organik maddelerden ve farklı miktarlarda çoğaltılan saf kültür S. putrefaciens kullanılarak açık devre voltajları ölçülmüştür. 10 mM glikoz kullanılarak 1250 mL besi maddesi içinde çoğaltılan saf kültürün santrifüjünden elde edilen devre voltajı 832 mV iken, 2500 mL saf kültür için 777 mV, 800 mL saf kültür için ise 810 mV olarak ölçülmüştür.10 mM etanol kullanılarak 1250 mL saf kültürden 670 mV, 10 mM propiyonik asit kullanılarak 1250 mL saf kültür için ise açık devre voltajı 803mV bulunmuştur. Besi maddesi olarak 10 mM glikoz kullanıldığında 5000 Ω dış direnç ile çalıştırıldığında amper değeri 4 µA ölçülmüştür. Güç yoğunluğu olarak 0.8 mA/m2bulunmuştur.  Anahtar Kelimeler: Mikrobiyal yakıt hücresi,elektrik üretimi, Shewanella putrefaciens, voltaj, güç yoğunluğu