The onset of flammability also took place at different lag periods (which is from the time of charging the digester to the onset of gas flammability). The paper waste alone system (PW) became flammable within 24hr of charging the digester, even though gas production reduced drastically and flammability also discontinued only to resume after 14 days. The cumulative biogas yield of the paper waste was lower than that of the blended system (Table 2). Waste containing cellulose, hemicellulose, pectin, lignin and plant wax are very difficult to biodegrade and their hydrolysis can be the rate determining step in the anaerobic digestion process [16]. The initial combustion of the gas may have been as a result of the initial microbes in the charged digester. When hydrolysis and acidogenesis commenced, there may have been a higher release of free fatty acids making the environment hostile to the microbes that convert wastes to biogas which are known to be very sensitive to pH and survive optimally at pH range of 6.5 to 8.0 [26]. This may have brought about the sudden drop in biogas production. However when the flammable biogas production resumed, it was observed that the gas production was quite high and continued long after the blend had nearly stopped production. The physicochemical properties of the waste showed that it had less favourable properties that affect biogas production like the volatile solids (which is the biodegradable portion of the waste), nutrients (crude fat and protein), Energy content and carbon to nitrogen (C/N) ratio (Table 1). Adequate physicochemical properties are known to affect biogas production. The volatile solids (VS) should be high enough to effect reasonable biogas production. The C/N ratio has been given to be optimum in the range of 20-30:1 [27]. This is because the microbes that convert waste to biogas take up carbon 30 times faster than nitrogen [28]. The C/N ratio of the paper waste was much higher than the optimum range required for effective biogas production and may have also affected the yield. The paper waste and cow dung (PW: CD) became flammable on the 6th day and the flammability was sustained throughout the retention period. Blending the paper waste with cow dung brought about the sustained onset of gas flammability with higher cumulative biogas yield during the chosen retention period. This is also because blending the waste with cow dung favourably enhanced the physicochemical properties of the wastes (Table 1) as well as the microbial load of the blend especially at point of charging and peak of production (Table 3).
The onset of flammability also took place at different lag periods (which is from the time of charging the digester to the onset of gas flammability). The paper waste alone system (PW) became flammable within 24hr of charging the digester, even though gas production reduced drastically and flammability also discontinued only to resume after 14 days. The cumulative biogas yield of the paper waste was lower than that of the blended system (Table 2). Waste containing cellulose, hemicellulose, pectin, lignin and plant wax are very difficult to biodegrade and their hydrolysis can be the rate determining step in the anaerobic digestion process [16]. The initial combustion of the gas may have been as a result of the initial microbes in the charged digester. When hydrolysis and acidogenesis commenced, there may have been a higher release of free fatty acids making the environment hostile to the microbes that convert wastes to biogas which are known to be very sensitive to pH and survive optimally at pH range of 6.5 to 8.0 [26]. This may have brought about the sudden drop in biogas production. However when the flammable biogas production resumed, it was observed that the gas production was quite high and continued long after the blend had nearly stopped production. The physicochemical properties of the waste showed that it had less favourable properties that affect biogas production like the volatile solids (which is the biodegradable portion of the waste), nutrients (crude fat and protein), Energy content and carbon to nitrogen (C/N) ratio (Table 1). Adequate physicochemical properties are known to affect biogas production. The volatile solids (VS) should be high enough to effect reasonable biogas production. The C/N ratio has been given to be optimum in the range of 20-30:1 [27]. This is because the microbes that convert waste to biogas take up carbon 30 times faster than nitrogen [28]. The C/N ratio of the paper waste was much higher than the optimum range required for effective biogas production and may have also affected the yield. The paper waste and cow dung (PW: CD) became flammable on the 6th day and the flammability was sustained throughout the retention period. Blending the paper waste with cow dung brought about the sustained onset of gas flammability with higher cumulative biogas yield during the chosen retention period. This is also because blending the waste with cow dung favourably enhanced the physicochemical properties of the wastes (Table 1) as well as the microbial load of the blend especially at point of charging and peak of production (Table 3).
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