عنوان مقاله [English]
Introduction Anaerobic digestion has progressed rapidly since the late 1960s. With the progress of the anaerobic fermentation process in the world, anaerobic reactors have been developed to digest different types of organic wastes in each country. So various types of reactors have been built, and that they have been in different shapes, dimensions, and operating conditions. One of these reactors is the static granular bed reactor (SGBR). SGBR with its granular bed digests a substrate in less hydraulic retention time (HRT). SGBR is a downstream reactor that consists of active anaerobic granules. The biomass contacts the granular surfaces and does not require the use of mixers, gas, solid, and a separator. The reactor startup is very short since there is no need for some operations, such as extra time to grow microorganisms in the granule. One of the most important residues in the alcohol production plant from molasses is vinesse which has become a major problem in this industry. The conversion of vinasse to biogas and using it to supply the energy of the industry is one of the basic ways to solve this problem. Several studies have been conducted in this field by using various reactors, but there is no research about SGBR. In this study, an SGBR producing biogas from vinasse has been designed and constructed. Also, the performance of the reactor was investigated at three HRTs (2, 3, and 4 days) and the thermophile temperature of 55 °C.
Materials and Methods The best diameter to height ratio (reactor volume) in the SGBR is 1:7. Accordingly, the shape of the reactor is a pipe. Based on the volume of the reactor and the maximum pressure inside it, a 4-inch polyethylene tube with a height of 1 meter was selected to carry out the testes. According to the thermophile temperature (55 °C) and the accuracy of the element (0.9 °C), the maximum temperature of the reactor is 329 K. Therefore, the minimum power for obtaining this temperature is 405.316 watts. The water displacement method was used to measure the amount of biogas. An iron sponge was used for removing hydrogen sulfide gas from biogas. Sodium hydroxide solution was used to remove carbon dioxide from biogas.
Results and Discussion The reactors were loaded daily with organic matter (86002, 28667, and 21500 mgCOD/L.d) for different HRTs (2, 3, and 4 days). For three HRTs, the amount of methane production was high during the first day which is due to the thermal shock caused by the microorganisms in the granule. Methane production in HRT of 2 days had fewer variations than HRT of 3 and 4 days, and after 13 days, it reached a nearly constant value of 4600 ml/day. For HRT of 3 days, the daily rate of methane production reached a constant value of 4800 ml/day after 12 days and for HRT of 4 days, it reached 4,900 ml/day after 10 days. For HRTs of 2 and 3 days, the rate of methane production per unit of volatile solids had less variation and remained constant approximately after 7 days. The average methane production per unit of volatile solids at HRT of 4 is days higher than the other HRTs. The average methane production for HRTs of 2, 3, and 4 was 379, 380, and 433 CH4 (L)/VS (kg), respectively. The maximum value of methane production was 582 m3/kgCOD, which was obtained at HRT of 2 days. In this study, 31 liters of methane were produced per one liter of vinasse at HRT of 4 days, which was more than other studies.
Conclusion In this study, the required heat power and pressure inside the SGBR laboratory have been calculated. The minimum required heat is 261 watts. Also, this reactor should be able to bear at least 4.34 bar for biogas production. The average amount of methane production per unit of volatile solids was 379, 380, and 433 CH4 (L)/VS (kg) at HRTs of 2, 3, and 4 days, respectively. The maximum amount of produced methane was 582 m3/kgCOD, which was achieved at HRT of 2 days, and the maximum percentage of COD reduction was 39%, which was achieved at HRT of 4 days. In general, the results indicated that SGBR produced higher biogas from vinasse than other reactors, but it is not suitable for reducing pollutions.