In this study, a series of lab scale digesters were operated in batch mode to study the biogas production from the medical cotton mixed wastes. Basically, the apparatus used to carry out the processes of the anaerobic co-digestion comprised of 500-mL Pyrex borosilicate heatproof code glass bottles act as the digesters. The components of each digester were maintained at 1:10 which is equivalent to 40 g solid waste material: 400 mL (inoculum slurry or distilled water). Each digester was tightly plugged with rubber stopper contains 2 holes each of 4 mm diameter through which a piece of glass tube was submersed into the digester and the other end of the glass tube was connected with rubber tube for the produced biogas transfer to the gas measuring section. The rubber stoppers were tightly wrapped with parafilm to prevent any release of the produced gas. In order to achieve anaerobic conditions in the digesters, they were flushed with nitrogen for 10 min to provide anaerobic environment conditions. Digesters were immersed in a thermostatic water bath to maintain the required temperature conditions. Manual shaking of digesters was performed daily to insure that substrate molecules and bacteria come into close. Sodium bicarbonate (NaHCO) was used for pH adjustment and phenolphthalein was used to color the water in the displacement bottle. Table 1 describes the experimental conditions for each digester taking into consideration that each digester was preparedin triplicate resulted in preparing a total of 12 digesters.
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