Physiological Approach of Municipal Solid Waste to Biogas leading to Low Cost Energy Generation

摘要

Physical principles ,energy correlation ,production, destruction and interaction of the substances is influenced by four metabolic stages can be distinguished in the overall anaerobic digestion of the bio-waste (i)Hydrolysis : complex insoluble organic material is solubilized by enzymes excreted by hydrolytic microorganisms (ii)Acidogenesis: soluble organic components including the products of hydrolysis are converted into organic acids ,alcohol ,hydrogen and carbon dioxide (iii)Acetogenesis ; the products of Acetogenesis are converted into acetic acid ,hydrogen, and Carbon-di-Oxide and (iv)Methanogenesis: Methane is produced from acetic acid ,hydrogen and carbon di oxide as well as directly from other substrate of formic acid and methanol are the most important. In a well balanced anaerobic digestion process, all products of a previous metabolic stage are converted into next one without significant build up of intermediary products. The overall result is a nearly complete conversion of the an-aerobically biodegradable organic material into end products like methane, carbon di oxide, hydrogen sulphide and ammonia .On the other hand waste is used reduced to slurry which has high nutrient content that make an ideal fertilizer. The biochemical reaction in the digester is temperature dependent. During winter when temperature goes down below 10U C, the production of gas is completely reduced. Biogas produced may be used in a number of ways. The amount of biogas required for different applications are in (i)consumption for cooking meal per person /day 0.30m3 (ii)one gas mantle lamp requires 0.10 -0.15m~3/hr (iii)requirement of biogas per BHP/hr = 0.45 - 0.50 m~3 (iv) requirement of biogas for generation of one KWH = 0.60 - 0.70m~3rnThe energy changes due to chemical reactions analyzed quantitatively in terms of thermodynamics, which are combined into the equation hG-hH-Th S. Under conditions in which biological reactions occur i.e. constant temperature and pressure .Chemical reactions proceed in such a direction that at equilibrium the entropy S of the system plus surroundings is at a maximum and the free energy G of the system alone is at a minimum . Every chemical reaction has a characteristic standard free energy change hGU1 at standard temperature and pressure with all reactants and product at 1M concentration and pH = 7.0. It can be calculated from the equilibrium constant for the reaction by the equation h G U1 = -2.303 RT log K 'eq .Standard free energy changes can also be calculated from equilibrium data of a consecutive series of reactions or from the difference in the standard free energy of formation of reactants and products. rnFor conversion of biogas into electrical energy, the biogas is passed through a dual -fuel engine coupled with alternator. The dual-fuel engine while running consumes only about 15 - 20 % of the diesel normally required. The balance 80 % of the fuel need is satisfied by the biogas .The diesel is used for starting the engine and as soon as the engine starts, the valve of biogas is opened and biogas starts passing in the engine for combustion through suitably adapted inlet system and minimizes the cost of consumption..