ABSTRACT
There is a great deal of
environmental pressure in many parts of the country to ascertain how organic
waste can best be handled in the absence of appropriate disposal methods can
cause adverse environmental and health problems. Anaerobic digestion has been
considered as waste-to-energy technology, and is widely used in the treatment
of different organic wastes. The study was carried out for biogas production
from co-digestion of cow dung, horse dung and chicken feather in producing
biogas through anaerobic co-digestion with chicken feathers. This is achieved
by constructing twelve
(12) local digesters and gas collection systems mounted at the
premises of Department of Water Resources and Environmental Engineering, Ahmadu
Bello University Zaria. The digesters were used to digest the mixture of cow
dung (CD), horse dung (HD) and chicken feathers (CF) at different percentage
ratios for a period of thirty seven (37) days retention time until the biogas
reduced significantly. Inflammability test was conducted to determine the
quality of biogas produced. Proximate analysis such as nitrates, sulphates,
carbon to nitrogen ratio and phosphates were determined before and after anaerobic digestion
to rank the substrates in order of their biogas production capacity. The total
volumes of the gas produced were 2.51E-01m3, 1.71E-01m3,1.38E-01m3,
1.33E-01m3,1.04E-01m3, 9.43E-02m3, 9.43E-02m3,
5.30E-02m3, 3.59E-02m3, 5.93E-02m3, 3.59E-02m3
and 3.04E-04m3 for 25%CD-75%HD, 100%CD, 50%CD-50%HD, 100%HD,
75%CD-25%HD, 75%CD-25%CF, 75%HD-25%CF, 50%HD-50%CF, 25%HD-75%CF, 50%CD-50%CF,
25%CD-75%CF and 100%CF respectively. These implied that the mix ratio of
25%CD-75%HD produced highest biogas production. The results of carbon to
nitrogen ratio for anaerobic digestion were determined at optimum range of 20:1
to 30:1. The nitrates, sulphates and phosphates determined shown an increase
after digestion for the cow dung, horse dung and chicken feather with
percentage values of 15.1%, 9.7% and 3.2% respectively, which could be a good
source of biofertilizer. The average temperatures of the digesters recorded in
the morning, afternoon and evening range from 26°C-43°C under mesophilic
condition, and the average ambient temperature observed during the study was
34°C, the pH values of the media in all the substrates digested were found
almost in the optimal limits of methanogenic bacteria of 6.0-7.4. The modified
Gompertz equation was used to adequately describe the cumulative biogas
production from these digesters and also to assess the kinetics of the
biodegradation process. It was observed that the rates of substrate
biodegradability were obtained. The constants were determined using the
nonlinear regression approach with the aid of the solver function of the
Microsoft Excel tool pack. Biogas production was found to be feasible from the
other wastes, but CF was regarded as failed digester as it does not produce
significant amount of biogas because of inhibiting factor such as high keratin
content. The inflammability test conducted during anaerobic digestion was found
to be efficient. Biogas productions from organic wastes are having prospects in
contributing towards solving the national energy crisis of most countries.
CHAPTER ONE
INTRODUCTION
1.1 Background
of Study
Biogas is a clean, environmentally
friendly and renewable form of energy generated when micro-organisms degrade
organic materials in an oxygen free environment. The formation of biogas can
occur either in natural environment or controlled conditions in constructed
biogas plants, so called anaerobic digestion (AD). Swamps, marshes, river beds,
rumen of herbivore animal are some of the areas where biogas is formed naturally.
The same microbial activities are achieved in both natural and controlled
conditions. The feedstock for biogas production in constructed plants is more
or less any organic fractions from household organic waste to dedicated energy
crops like maize (Lantz et al., 2007). The potential feedstock for the
production of biogas include; municipal solid waste, industrial organic waste,
garden waste, agricultural waste (manure and crop residue), energy crops,
cellulose rich biomass, algae and seaweed (water based), by-products of ethanol
and bio diesel production (Lantz et al., 2007).
Inadequate energy supply and
environmental pollutions are serious problems confronting Nigeria with high
population growth rate, access to adequate energy and healthy environmental
demands for a diversification of sources of energy supply, if Nigeria is to
achieve any meaningful growth and development, biogas generation from anaerobic
digestion of readily available wastes could contribute to solving these
problems. From the global perspective, the over- dependence on fossil fuels as
primary source of energy has resulted in climate change, many environmental
destruction and related human health problems (Budiyono et al., 2010). The
joint challenge of global pollution and depletion of fossil fuels is driving
intense research into alternative renewable energy sources, among which is the
biogas. Biogas is produced by the
anaerobic digestion (AD) of organic
waste through the synergistic metabolic activities of consortia of hydrolytic,
acidinogenic, acetogenic and methanogenic bacteria on organic materials (Yebo et
al., 2011).
Currently, AD is used to treat more
than 10% of organic wastes for the generation of energy in several European
countries (Baere, 2000). Nigeria can do likewise. The industrial viability of
this process requires a suitable combination of physical and chemical process
parameters and a low- cost substrate, hence the need for process optimization.
Attempts have been made to improve biogas production using mixed co-substrates
(Dalhat et al., 2015). Anaerobic co-digestion of a simulated organic fraction
of municipal solid wastes and fats of animal and vegetable origin has been
reported (Fernandez et al., 2005). A substrate of kitchen waste with cow manure
has been used to achieve a yield increase of 44% (Rongpin et al., 2009).
Kaparaju and Rintala (2005) have examined the co-digestion of pig manure,
potato tuber and its industrial by-products. The co-digestion of fruit and vegetable
wastes, cattle slurry and chicken manure or sewage sludge for biogas production
has also been studied (Ritz et al., 2007; Gomez et al., 2006). The best
combination of various substrates for optimal yield remains a big problem
despite the enormous number of potential substrates. It is worthy of note that
the technical and economical feasibility of an industrial anaerobic digestion
plant depends on how much methane is yielded and the purity and on the
composition and process variables (temperature, retention time and pH).
These performances are often not
available in literature; thus this could entail an increase of the risk of
investments due to excessive uncertainties in the design phase. Although the
anaerobic digestion of animal manures has been extensively researched and
demonstrated, however, based on investment returns from energy production, the
economics of diary digesters are not favorable due to the relatively low
biodegradability
and biogas yield of diary manure as
compared to many other types of organic wastes such as food waste. One of the
approaches for improving the economics of diary digesters is to increase their
biogas production rate by co-digesting the manure with more degradable waste such
as food wastes as long as such wastes are available in the vicinity (Hamed and
Ruihong, 2010). Co-digestion of different materials may enhance the anaerobic
digestion process due to better carbon and nitrogen balance (Mshandete et al.,
2004; Parawira et al., 2004). According to Mata-Alvarez et al., (2000).
Co-digestion i.e digestion of more than one substrate in the same digester can
establish positive synergism and the added nutrients can support microbial
growth.
The process of fermentation in
bio-digesters results in transformation of organically bound carbon into
gaseous carbon dioxide and methane. The anaerobic environment and extended
retention time also inhibit the growth of most pathogenic organisms and prevent
the survival of intestinal parasites. It is therefore to be expected that both
the chemical and biological parameters of livestock excreta will be improved
upon by passage through bio-digesters.
The prospect of this technology is
bright in developing countries like Nigeria. This is because Nigeria is an
energy resource rich country in terms of both fossil fuels (such as crude oil,
natural gas, coal), and renewable energy resources like solar, wind and biomass
(Mshandete and Parawira, 2009). The technology can be utilized to provide
energy for households, rural communities, farms and industries.
Anaerobic digestion (AD) is a
highly promising technology for converting biomass waste into vast quantities
of biogas (methane and carbon dioxide), which may directly be used as an energy
source or converted to hydrogen.
Since
biogas is a mixture of methane (also known as marsh gas or natural gas, CH4)
and carbon dioxide, it is a renewable fuel produced from waste treatment.
Anaerobic digestion is basically a simple process carried out in a number of
steps that can use almost any organic material as a substrate. It occurs in
digestive systems, marshes, rubbish dumps, septic tanks and the Arctic Tundra
(Ola, 2008). The process does not require large expenditures of energy, as it
is biologically driven by a mixed culture of bacteria in the absence of oxygen.
Biogas is considered to be carbon neutral because all of the carbon released
during combustion has been recently taken from the atmosphere through photosynthesis,
unlike fossil fuels that have stored carbon for millions of years (Ryank et al,
2008). Thus biogas is a sustainable alternative to natural gas. Since anaerobic
digestion only releases carbon to the gas phase, the other nutrients (nitrogen,
phosphorus, and micronutrients) remain in the effluent, which makes it a high
quality organic fertilizer and soil amendment wastes (Igboro, 2011). Fig 1.1
shows the biogas cycle.
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