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.

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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

The impacts of Hg 2+ , Cd 2+ and Zn 2+ on the activities of periplasmic nitrate reductase (NAP) and dehydrogenase (DHA) enzymes of three organisms isolated from soil and sediment-water interface were analysed in liquid culture studies. NAP and DHA activities were estimated from nitrite and triphenyl formazan produced respectively after 4h incubation at 28 ± 2 o C. Hg 2+ completely inhibited NAP activity in Escherichia and Pseudomonas spp. at all the concentrations (0.2 -1mM) while progressive inhibitions of NAP activity were observed in Escherichia and Pseudomonas spp. with increasing concentrations of Zn 2+ and Cd 2+ . Both metals were stimulatory to NAP of Acinetobacter sp. at 0.2 -1mM. Apart from stimulation of DHA activity by Zn 2+ (0.2 -1mM) in Escherichia sp., Cd 2+ (0.4 -1.0mM) in Acinetobacter sp. and (1.0mM) in Pseudomonas sp., all the metals progressively inhibited DHA activities in the three organisms. In Escherichia sp., the activities of the two enzymes were negatively correlated on exposure to Zn 2+ (r = -0.91) and positively correlated (r = >0.90) on exposure to Cd 2+ and Hg 2+ . Based on IC 50 values of the metals for the DHA and NAP enzymes, the most resistant of the three organisms were Escherichia sp. and Acinetobacter sp. respectively. Quantitatively, NAP with its lower IC 50 values than DHA was a more sensitive toxicity measure for Hg 2+ in all the organisms. The sensitivity of microbial metabolic enzymes to the toxic effects of metals varies with the type of enzyme, metal and the microorganism involved. Keywords: Periplasmic nitrate reductase; Dehydrogenase; Escherichia sp.; Pseudomonas sp.; Acinetobacter sp.; IC 50 ; Hg 2+ ; Cd 2+ and Zn 2+ . Palavras-chave: Reductase do nitrato periplásmico; dehidrogenase; Escherichia sp; Pseudomonas sp; de Acinetobactéria sp; IC 50 ; Hg 2+ ; Cd 2 + e Zn 2+ .

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