With the growing demerits of fossil fuels - its finitude and its negative impact on the environment and public health - renewable energy is becoming a favoured emerging alternative. For over a millennium anaerobic digestion (AD) has been employed in treating organic waste (biomass). The two main products of anaerobic digestion, biogas and biofertilizer, are very important resources. Since organic wastes are always available and unavoidable too, anaerobic digestion provides an efficient means of converting organic waste to profitable resources. This paper elucidates the potential benefits of organic waste generated in Nigeria as a renewable source of biofuel and biofertilizer. The selected organic wastes studied in this work are livestock wastes (cattle excreta, sheep and goat excreta, pig excreta, poultry excreta; and abattoir waste), human excreta, crop residue, and municipal solid waste (MSW). Using mathematical computation based on standard measurements, Nigeria generates about 542.5 million tons of the above selected organic waste per annum. This in turn has the potential of yielding about 25.53 billion m³ of biogas (about 169 541.66 MWh) and 88.19 million tons of biofertilizer per annum. Both have a combined estimated value of about N 4.54 trillion ($ 29.29 billion). This potential biogas yield will be able to completely displace the use of kerosene and coal for domestic cooking, and reduce the consumption of wood fuel by 66%. An effective biogas programme in Nigeria will also remarkably reduce environmental and public health concerns, deforestation, and greenhouse gas (GHG) emissions.

With the growing demerits of fossil fuels - its finitude and its negative impact on the environment and public health - renewable energy is becoming a favored emerging alternative.  For over a millennium, anaerobic digestion (AD) has been employed in treating organic waste (biomass).  The two main products of anaerobic digestion, biogas and biofertilizer, are very important resources.  Since organic wastes are always available and unavoidable, too, anaerobic digestion provides an efficient means of converting organic waste to profitable resources.  This paper elucidates the potential benefits of organic waste generated in Nigeria as a renewable source of biofuel and biofertilizer.  The selected organic wastes studied in this work are livestock wastes (cattle manure, sheep and goat manure, pig manure, poultry manure; and abattoir waste), human manure, crop residue, and municipal solid waste (MSW).  Using mathematical computation based on the standard measurements, Nigeria generates about 542.5 million tons of the above selected organic waste per annum.  This, in turn, has the potential of yielding about 25.53 billion m³ of biogas (about 169, 541.66 MWh) and 88.19 million tons of biofertilizer per annum.  Both have a combined estimated value of about N 4.54 trillion ($ 29.29 billion).  This potential biogas yield will be able to completely replace the use of kerosene and coal for domestic cooking, and reduce the consumption of wood fuel by 66%.  An effective biogas program in Nigeria will also remarkably reduce environmental and public health concerns, deforestation, and greenhouse gas (GHG) emissions.

DOI: http://dx.doi.org/10.5755/j01.erem.63.1.2912

Axonopus fissifolius commonly called "carpet grass" was subjected to anaerobic digestion for 30 days. Anaerobic digestion was carried out in a batch-fed process at the ambient temperature of 27-29 0 C. Biomethane measurements were obtained by measuring the volume displacement of a saturated filtered calcium hydroxide solution in a transparent calibrated vessel. 42.7g of fresh carpet grass clippings yielded 1.955 L of biomethane. Biomethane potential (BMP) of carpet grass for a 30 day anaerobic digestion was 0.05 m 3 CH 4 kg-1 TS. The rates of biomethane potentials for the first, second, third, fourth and fifth six-day intervals were 1.5mL g-1 TS (2.81%), 6.4mL g-1 TS (14.58%), 16.1mL g-1 TS (30.18%), 17.74mL g-1 TS (33.25%), and 10.23mL g-1 TS (19.81%) respectively. The total solids, volatile solids and pH of feedstock and digestate were 85.80% and 85.56%, 90.91% and 87.58%, 6.6 (27 o C) and 6.9 (27 o C) respectively. The relatively high biomethane potential of carpet grass at the ambient temperature presented in this paper depicts anaerobic digestion as a viable means of profitably treating grass waste for both sanitation and generating biomethane especially in the tropics where the ambient temperatures are usually favourable for optimum biomethanation for most part of the year, thus making the process affordable and less cumbersome.

This study investigated the effects of initiating anaerobic digestion (AD) of dry layer-hen poultry dung at the sub-atmospheric pressure of -30 cmHg on biodegradation, biogasification, and biomethanation. The setup was performed as a batch process at an average ambient temperature of 29±2 0 C and a retention time of 15 days. Comparisons were made with two other experiments which were both begun at ambient atmospheric pressure; one was inoculated with digestate from a previous layer-hen dung AD, while the other was not inoculated. The bioreactors initiated at sub-atmospheric pressure, ambient atmospheric pressure without inoculum, and ambient atmospheric pressure with inoculum showed the following for biogas and biomethane yields respectively: 16. 6 cfu mL -1 for volatile solids and total viable count respectively. There was a slight difference in the volatile solids of the digestates of the three bioreactors after AD. The pH recorded for the feedstock slurry before AD was 7.9 at 30 o C, while after AD, the digestates from all the three bioreactors showed the same pH of 5.9 at 29 0 C. Statistical analysis using ANOVA showed no significant difference in biogas yields of the feedstock for the three bioreactors (A, B, C). ANOVA showed no significant difference for biomethane yields in the bioreactors initiated at sub-atmospheric pressure and for those initiated at ambient atmospheric pressure with inoculums. However, it showed significant difference in the bioreactor initiated at sub-atmospheric pressure and that initiated at ambient atmospheric pressure without inoculums, and significant difference in the two sets of bioreactors initiated at ambient atmospheric pressure (with and without inoculum). Initiating AD at reduced atmospheric pressure (-30 cmHg) and the addition of inoculum at ambient atmospheric pressure both increased biomethanation, by 20.31% and 15.80% respectively. The AD initiated at sub-atmospheric pressure yielded the least amount of carbon dioxide (a greenhouse gas), and improved biodegradation and biomethanation. The results also suggest that biomethane production is dependent on specific methanogenic growth. Analyzing the populations of methanogens isolated from the different bioreactors in relation to their biomethane yields suggests that Methanosarcina barkeri may have been largely responsible for the differences in biomethane yields. Efeitos do início da digestão anaeróbica da camada de esterco de aves à pressão sub-atmosférica RESUMOOs efeitos do início da digestão anaeróbica (DA) da camada de estrume seco de galinha à pressão sub-atmosférica de -30 cmHg na biodegradação, biogaseificação, e biometanização foram investigados. Foi realizado um processo em lote a uma temperatura ambiente média de 29 ± 2 0 C e um tempo de retenção de 15 dias. As comparações foram feitas com duas outras experiências; ambas foram iniciadas à pressão atmosférica ambiente, enquanto que uma foi previamente inoculada com digestores de uma camada de estrume de galinha AD, a outra sem inoculação. Os biorreatore...