تحويل المخلفات العضوية الى طاقة كهربائية باستخدام الاحياء المجهرية اللامرضية

Abstract

Abstract Constructing and testing of a microbial fuel cell (MFC) had been accomplished in this research. Two MFC chambers connected with salt bridge had been operated and studied using synthetic waste water and real waste water as anode chamber solution. Operating temperature and pH value were investigated by changing temperature from (25 to 30 °C) and reducing pH from (6.7 to 6.5). The results revealed that increasing operation temperature had a significant effect on reducing operation time while decreasing pH improved the measured voltage and current besides reducing operation time to just five days. The cell was tested in the presence of real waste water under the best temperature and pH, and the results proved the capability of the manufacture cell in treating such contaminate material in relatively short operation time. The COD levels for the adopted experiments revealed reduction above 60% proving the ability of the living microorganisms in digesting the used substrate producing electrical power.

الخلاصة انشئت واختبرت في هذا البحث خلية وقود مايكروبية. شغلت واختبرت الخلية ذات الوعائين المربوطين بجسر ملحي بوجود مياه مخلفات مصنعة و مياه مخلفات حقيقية كمحلول لوعاء المصعد (Anode ) . درست تاثيرات درجة حرارة التشغيل و الدالة الحامضية لمحلول المصعد عن طريق رفع درجة الحرارة من( 25 الى 30) °م وخفض الدالة الحامضية من (6.7 – 6.5). اظهرت النتائج ان رفع درجة الحرارة كان له تأثير ملحوظ في تقليل زمن التشغيل بينما خفض الدالة الحامضية كان سببا في رفع قيم التيار وفرق الجهد للخلية فضلا عن تقليل زمن التشغيل الى خمسة أيام فقط . اختبرت الخلية تحت درجة الحرارة والدالة الحامضية الأفضل بوجود مياه مخلفات حقيقية وأظهرت النتائج قدرة الخلية المصنعة على معالجة هذه المادة الملوثة خلال وقت تشغيل قصير نسبيا. بينت قياسات مستويات الاوكسجين المتطلبة كيمياويا انخفاضا بعد انتهاء التشغيل للتجارب المعتمدة وصل الى اكثرمن 60 % مما عززقدرة الأحياء المجهرية الميكروبية في هضم المادة الغذائية وتحويلها الى طاقة كهربائية.

Introduction In recent years, the trends for new alternative renewable energies were gradually increased. [3]Major efforts were devoted to develop alternative electricity generation method. Among renewable alternatives, microbial fuel cell (MFC) achieved great interests by many researchers due to its possibility of directly harvesting electricity from organic wastes and renewable biomass. [4]. MFCs are attractive for wastewater treatment as they could allow harvesting energy from wastewater producing electricity and generate clean water. The anaerobic microbes required for MFCs are commonly found in wastewater. [5]. so influent wastewater could act as both a substrate and source of microorganisms. 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. It has been known for many years that it is possible to electricity directly by using bacteria to break down organic substrate.

Experimental Work: MFC Components MFC consists of an anode compartment separated from a cathode compartment by a membrane that is permeable to ions but not to microorganisms and organic matter or by a salt bridge that contain salts to provide suitable medium for ions transition, which represent the internal circuit. The external circuit is a wire connecting the anode and the cathode passing through appropriate electrical resistance. In the anode compartment, microorganisms oxidize the organic matter in wastewater and transfer the electrons to the cathode. The hydrogen ions produced by the oxidation half reaction pass through the membrane or salt bridge to the cathode compartment where they reduce oxygen and form water (the reduction half reaction). As a result of these two half reactions, a potential difference develops between the anode and the cathode and current flows in the external circuit. Fig (1) illustrates the typical MFC construction.

Figure 1. Typical MFC with membrane separatio

Operation Conditions The cell was tested at four conditions , three were related to operation conditions and the fourth was related to the nature of waste water . In the first experiment, the synthesized waste water was conducted while PH and temperature fixed at (6.7) and (25° C) respectively .Secondly , the same condition were kept and the temperature was raised to (30 o C) to investigate the influence of temperature . The third experiment was conducted at (30 °C) and Ph of (6.5) to show the effect of solution acidity. The fourth experiment was conducted with the presence of real waste water taken directly from sewage system . The water was filtered and yeast added without further treatment. The operation conditions were (30°C) of temperature and PH of (6.5).

Results and Discussion For each experiment, COD values were measured before starting up and after the shutting down of the cell. The recorded values with operation times were presented in Table (1)

Experiment Operation time (day) Initial COD Final COD 1 21 24585 7850 2 12 24585 8020 3 5 24585 9200 4 5 73000 27200 Table 1. COD values before and after cell operation. The results in terms of produced voltage and current revealed that increasing the temperature affected positively in terms of reduction in operation time. In another hand, the anode chamber pH had been studied by changing from (6.7 to 6.5). Good results were recorded and operation time was reduced to five working days. Testing the cell in the presence of real waste water revealed the ability of the used yeast in dealing with such contaminated material. The results showed that (0.443 mV and 8.3µA) were generated at the end of the fifth day. Testing COD levels before and after operations, revealed significant reduction for all experiments. This gave a significant prove that the cell can be used for real waste water treatment and can be further scale up to be used in more economical aspect .

References 1- Paprika M. (2004) Global Biomass Fuel Resources. Biomass and Bioenergy, 27, 613-620. 2- Lovely D. (2006) Microbial Fuel Cells: Novel Microbial Physiologies and Engineering Approaches. Current opinion in biotechnology, 17, 327-332. 3- Liu H., Logan B. (2004) Production of Electricity during Wastewater Treatment Using a Single Chamber Microbial Fuel Cell. Environmental Science and Technology, 7, 2281-2295.