الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The anaerobic digester has a great possibility and can be a robust technique for efficient conversion of agricultural, municipal and household wastes into green energy. High solids concentration in the digester offers an option to remarkably decrease the size of the reactor. The economics of anaerobic digestion of wastes could also be enhanced if the reactor volume could be reduced significantly, The experiments of this study was undertaken at the aiming to assess the efficiency of four similar laboratory biogas digesters which were fed with fresh cattle dung at two different concentrations of total solids of 10 and15% and two hydraulic retention time of 20 and 25 days. Fresh cattle dung was collected from the dairy animal farm of the Faculty of Agriculture, Alexandria University, Alexandria Province. The cattle dung was taken directly and analyzed to determine some chemical characteristics such as total solids, organic carbon, volatile solids, and total nitrogen concentration. Both rates of hydraulic retention time were evaluated at 120 rpm stirrer speed. The stirring duration was 15 min. of stirring every 4 hrs. The digesters were put in a water bath to maintain the mesophilic digestion temperature at a certain temperature (40 ± 2 ºC). The evaluation also, includes the estimation of energy production, energy consumption, and the net energy gained and the obtained results can be summarized as follows: • Biogas production through the batch phase at 10 % TS Interestingly the biogas was produced from the first day following the digesters feeding and which may have been a result of the active inoculums applied with fresh cattle dung during the digesters feeding. The rate of biogas production increased with the time reaching the greatest value of 5.29 L /day at 26 days of HRT. • Biogas production rate at continuous feeding conditions: 1. Ultrasonic pretreatments increased the biogas production rate for all treatments compared with the control. This increasing on the biogas production rate may be attributed to higher temperature and pressure which disrupt and break down the fibers (in the case of manure and lignocelluloses materials) and microorganisms’ cell walls (in the case of activated sludge and microalgae). 2. The total solids concentration of 15% with 20 days’ HRT produced the greatest biogas rate when using ultrasonic waves as compared with the other ones. The average increasing ratios at 15% TS were 115.4, 152.8 and 133.7 % at 20, 30 and 40 kHz, respectively, compared with the control, and these values were 69.043, 102.272, and 93.721 % with the same ultrasonic waves of 20 30 and 40 kHz, respectively, at 10 % TS concentration with 20 days’ HRT. 3. The obtained results demonstrated that the biogas productivity with volatile solid destroyed was as the total solid concentrations increased from 10 to 15 %. decreased biogas production rates The decreasing ratios were from; 35.2 to 27.5, from 39.3 to 30.1 and from 26.2 to 21.1% with using ultrasonic waves of 20, 30, and 40 kHz, respectively. 4. The results further showed that the methane content in biogas was not significantly affected by different frequencies. 5. The maximum energy production of 21.6 kWh was recorded with ultrasonic treatment of 30 kHz, 20 days HRT and 15% TS followed by ultrasonic treatment of 40 kHz, 20-day HRT and 15% TS (19.9 kWh) and ultrasonic treatment of 30 kHz, 25-day hydraulic retention time and 15% total solids (19.610 kWh). The control treatment produced minimum energy production of 5.9 kWh at 25-day HRT and 10% TS. 6. The energy consumption was about 3.6 kWh for the maximum energy production and 2.7 kWh for the minimum energy production. 7. The highest value of net energy gain was 17.9 kWh which recorded with ultrasonic treatment of 30 kHz, 20-day HRT and 15% TS followed by ultrasonic treatment of 40 kHz, 20-day HRT and 15% TS (16.2 kWh) and ultrasonic treatment of 30 kHz, 25-day HRT and 15% TS (15.9 kWh). On the other hand, the minimum energy net gain was 3.156 kWh which occurred with control digester 25-day hydraulic retention time and 10% total solids.