الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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Abstract
The rapid increase of population in Egypt makes the intensive cultivation the only option to meet the increasing demand for food, fibre and feed. Intensive cultivation necessitates organic manuring to sustain soil fertility of old land and to build up soil fertility of newly reclaimed soils. human and agricultural refuses are now wasted by improper management. Biodegradation of these city and farm wastes, from human, animal or plant sources, under anaerobic conditions, is four-appealing : it has roles in energy generation, counteracts deterioration of the environment, resolves prob¬lems in waste management,and produces a good quality manure.
The biogas generation provides an excellent option to recycle organic residues, provides rural population with cle¬an and efficient fuel, saves raw materials for feeding ani¬mals and improves health of man, animal and plant.
The present study aims at evaluating the production of biogas and its composition, in laboratory experiments using two-litre batch digester with working volume of 1.5 L, th¬rough anaerobic fermentation of human(sewage sludge), animal (cow dung) and plant (Zea mays stalks) wastes. Methanogenesis took place by either mesophilic (37°C) or thermophilic(55°C) bacteria. Different factors that may affect the process were Studied,e.g. pH, addition of different volatile fatty acids, and mixtures of different wastes (fermenting material). This study needed determination of total solids (TS), volatile solids (VS), total nitrogen (TN), C/N ratio, total volatile fatty acids (VFA’s), individual volatile fatty acids, and pH value. In all cases, total biogas and its components (CH4, c02) were measured.
The findings of the present study can be summarized in the following:
1-The mean biogas volume/day at 37 C was very low for plant waste while it was higher in case of animal and human wastes.
2- At 55 C, the mean biogas values/day, cumulative biogas production and the change rates in total VFA’s were higher than their corresponding values at 37 C.
3- The pH values, at both fermentation temperatures, ranged between 6.42 to 7.45 for human waste, 7.35 to 7.90 for animal waste and 7.33 - 8.25 for plant waste.
4- The cumulative biogas production (ml/L) in relation to time and different waste types at both temperatures showed a linear relation at almost all treatments.
5- The human waste showed the highest values of cumulative biogas production followed by animal waste,then plant waste.
6- The percentages of CH4 at 55 C and 37 C were as follows: human waste 77.8 and 71.0 %, animal waste 69.0 and 66.0 %, plant waste 53.5 and 52.0%.In all cases the reverse was true for the percentage of C02 component in the produced biogas.
7- The initial TS were 120 g/digester in all cases (i.e. 8% Ts). The initial VS added were 108.7, 86.5 and 86.1 g/diges¬ter while the initial TN were 0.98, 1.95 and 2.42 g/digester for plant, animal and human wastes respectively.
8-At both temperatures,the greatest loss percentages of TS land VS was recorded in human waste followed by plant waste and then animal waste. The highest loss percentage in TN was recorded in human waste followed by animal waste, then plant baste.
9-The plant waste showed the least rates of both biogas and methane production at both temperatures as L/Kg VS added or as L/Kg VS consumed. These rates in both animal and human wastes at both temperatures were more than double the rates possessed by plant waste. The biogas and methane production rates/VS consumed were 4-5 times higher than those rates/VS added. In all cases, the estimated biogas and methane production rates at 55 C were higher than at 37 c.
10- The rates of biogas and methane production of animal and human wastes were nearly similar when calculated on the bas¬is of VS added, while these rates were much more higher in case of animal waste as compared to human waste when calcul¬ated on the basis of VS consumed.
11- At both temperatures, the pH 7 was the most suitable for biogas and methane production for the three waste types where the amounts of the produced biogas were the highest as compared to the other pH values (5 - 9) or even the control (pH 7.5).
12- The effect of addition, separately, of different conce¬ntrations (250, 500 and 1000 mg/L) of acetic, propionic and butyric acids on anaerobic digestion of the three waste types by either mesophilic or thermophilic methane bacteria re¬vealed .
13-Detection of the individual VFA’s due to the addition of 1000 mg/L of acetic, propionic or butyric acids and after 12 hours of anaerobic fermentation at either 37 C or 55 C .
14- Mixtures of the waste types in their different ratios were used as fermentation material at 37 C.
15- The biogas and CH4 production were inversely proportio¬nal with the C/N ratio of the fermenting material ( whether pure or in mixture ).