EFFECT OF SEEDING OF WOOD-ASH ON BIOGAS PRODUCTION USING PIG WASTE AND CASSAVA PEELS

EFFECT OF SEEDING OF WOOD-ASH ON BIOGAS PRODUCTION USING PIG WASTE AND CASSAVA PEELS

ABSTRACT

The increasing growth of cassava agro-industries in Nigeria has led to the enormous 13 July 2019 generation of cassava peels waste. The feasibility of generating biogas and biofertilizer for both domestic and agricultural applications from cassava peels waste with pig waste was investigated. Fresh and stale cassava peels were used in the study. Three pretreatment chemicals such as sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)₂ and ammonium chloride (NH₄Cl) buffer solutions were used in pretreating the cassava peels and pig waste slurry. Six batch anaerobic biodigesters of 10-litre capacity each were used in this study for 40 days retention period. The cassava peels pH, temperature, and volumes of biogas and methane produced were monitored and Methane recorded daily. The fertilizer qualities (total solids, volatile solids, % phosphorus, % Biogas Biofertilizernitrogen, etc.) of the digester slurry and the digester sludge after 40 days Anaerobic digestion were determined using official methods of analysis of Association of Official Analytical Chemists (AOAC). The results showed that the amount of biogas generated is 2540 cm³/day. The stale cassava peels and pig waste slurry and the use of NH₄Cl pretreatment chemical gave the best biogas production and methane yield of 104,961cm³ and 62.3% respectively. The digester sludge from the anaerobic digestion of cassava peels and pig waste showed and demonstrated good biofertilizer qualities.

 

 

 

 

 

 

 

 

CHAPTER ONE

1.0 INTRODUCTION

The continuous increase in energy demands has been a serious problem resulting from increased population growth, urbanization, and industrialization worldwide. This problem is more pronounced in underdeveloped and developing countries where the social-economic situations are quite low. Lack of infrastructures for energy generation, transmission, and distribution, unavailability of nonrenewable energy sources such as fossil fuels, low technology for energy conversion from renewable energy sources such as biogas, and lack of funds for purchase of fossil fuels, infrastructural and technology developments in energy sectors have been implicated in the near energy crisis in most underdeveloped and developing countries (Aisien, et. al., 2010; Kwasi – Effah et. al., 2015). However, since energy can be obtained from renewable energy sources such as waste materials, the issue of poverty as it relates to the energy crisis in undeveloped and developing countries can be seriously reduced. The renewable energy source such as biogas production from anaerobic digestion of organic waste materials which can be sourced from municipal solid waste, agricultural waste, industrial waste, and household waste can provide enormous energy worldwide (Aisien et. al., 2007b; Igbum, et. al., 2019). Besides, biogas can be produced from food waste (Huiru, et al., 2019). Biogas is a cheap form of renewable energy that can meet to a large extent the energy demands of the rural populace globally. It is a colourless flammable gas produced via anaerobic digestion of organic waste materials. It is a smokeless, hygienic and more convenient fuel to use than other solids fuels (Buren, 1979). The increased emphasis on the use of renewable energy from biogas over the nonrenewable energy source of fossil fuels, will not only reduce energy demands from fossil fuels which is becoming very expensive and can lead to energy crisis but will as well address the problems of greenhouse gas emissions, global warming, environmental pollution/degradation and health hazard (COP 21, 2015; Igbum, et. al., 2019). Biogas is a renewable energy source that is produced by the biological degradation of organic matters in the absence of oxygen. The biogas from anaerobic digestion of organic matters is a gas that comprises of methane (50-72 vol.%), carbon (IV) oxide (25-45 vol.%), nitrogen (>2 vol.%), hydrogen sulphide (>1 vol.%), water (2-7 vol.%) and oxygen (>2 vol.%) (Mel, et. al., 2015). There are three main biochemical processes involved in biogas production. These are hydrolysis, acidogenesis/acetogenesis and methanogenesis (Igwe, 2014) as indicated below.

(C₆H₁₀O₅)n + nH₂O → n(C₆H₁₂O₆) – Hydrolysis  (1) n(C6H₁₂O₆) → nCH₃COOH – Acetogenesis/Acidogenesis  (2) 3nCH₃COOH → nCH₄ + CO₂ – Methanogenesis  (3)

Biogas energy has been successfully used for lighting, heating, cooking, power generation and fuel for vehicles. Besides, the sludge from anaerobic digestion of waste materials can serve as a biofertilizer for the improvement of soil fertility (Aisien et al., 2007).

Nigeria is the world’s largest producer of cassava (Manihot esculenta Crantz), producing over 46 million tons of cassava per year (IITA -1). According to FAO (2001), about 250 to 300 kg of cassava peels is produced per tonne of fresh cassava root processed. Cassava peel accounts for 8-15 wt.% of the total dry matter of the root. Cassava peels composition consists of 20-31 wt.% hemicelluloses, 16 – 42 wt.% cellulose and 6-8 wt.% lignin. Other than fiber, peels also contain 81.9 – 93.9 wt.% organic matter and 4.1- 6.5 wt.% crude protein (Kongkiattikajorn and Sornvorawea, 2011). Analysis of mineral content of cassava peel indicated the following mineral content: 48.7 wt.% C; 1 wt.% N; 1.1 wt.% K; 1.6 wt.% P; 0.16 wt.% NO3; 0.15 wt.% Na; 0.9 wt.% Ca; 125 mg/kg Zn; 15 mg/kg Cu; 180 mg/kg Mn; 16.7 mg/ kg Pb; 48.7 wt.% C/N; and 52.6 wt.% ash (Adelekan and Bamgboye, 2009).

The increase in population growth coupled with the low cost of living in Nigeria has led to a drastic increase in cassava utilization in garri, starch, fufu, lafu, and flour production. This has contributed to a tremendous increase in cassava peels waste generation. The other wastes from cassava processing in Nigeria include; cassava wastewater, sievates and offal (wastes from “foo-foo” production). International livestock research institute (ILRI), 2015 reported that approximately 98% of Nigeria’s cassava peels annually are wasted due to constraints associated with drying and was concerned about its safe use, particularly the presence of hydrocyanide and mycotoxins-related food poisoning. The indiscriminate disposal of cassava peels in landfills/waste dump sites has led to serious environmental pollution. This waste degrades to produce noxious leachate that contaminates both surface and underground water sources and other products that cause air pollution. The effects of these pollution problems associated with the degradation of cassava peels in dumpsites include foul odor and sometimes poisonous and polluted air, which when inhaled by man or animals may result in infection and diseases that may take a long time to manifest. In the same vein, vegetation and soil around the cassava peels’ dumpsites are rendered unproductive and devastated due to biological and chemical reactions taking place during the degradation of cassava peels. Cassava peels have been used as a feedstuff for various livestock. Besides, cassava peels have found applications in the production of reducing sugar, bioethanol, biogas and biofertilizer (Aisien et al., 2010; Anaeto, et al., 2013; Kongkiattikajorn and Sornvorawea, 2011 and Olanbiwoninu and Odunfa, 2012).

Many types of research have been carried out with cassava peels waste alone and cassava peels with other waste materials especially animal wastes for biogas production.

Adelekan and Bamgboye (2009) and Ofoefule and Uzodimma (2009) reported that biogas production and methane yield improved significantly when cassava peels were combined with different animal wastes. They also stated that the ratio of cassava peels to animals waste that is, carbon to nitrogen ratio was very important to ensure increased production of biogas and methane yield. Besides, Ezekoye and Ezekoye (2009), Ilaboya et al. (2010), Ilori, et al., (2007) and Adeyanju, (2008) reported that the blending of cassava peels with other plants waste. They found out that there is the need to apply some small quantity of animal wastes as inoculum in other to achieve an appreciable increase in biogas production and methane yield. Bayitse et. al., 2014 reported that cassava peels co – digested with manure produce biogas and biofertilizer by optimizing carbon to nitrogen ratio. Nkodi et. al., 2018 and Olaniyan, et. al., 2017 stated that the combination of cassava peels with animal waste yield a larger volume of biogas compare with cassava peels alone. Besides, Sawyeer et. al., 2017; Onuorah, et. al., 2016 and Ben and Michael, 2018 reported that the appropriate carbon to nitrogen ratio must be maintained. They stated that cassava peel to the animal waste ratio of 30: 20 is required for maximum biogas yield. Olawale et. al., 2017 reported that the addition of pig waste (animal manure) lowered the C : N ratio of the cassava peels to value between 20: 1 and 30: 1, which make co–substrate ideal for anaerobic digestion. Many other researchers have appreciated the unique nature of cassava peels substrate in terms of high concentration of cyanide. They reported that for sufficient biogas production from cassava peels there must be an appropriate pretreatment method in place (Deepanraj et. al., 2014; Nkodi, et. al., 2016; Mel, et. al., 2015; Ben and Michael, 2018; Igbum, et. al., 2019; Onuorah, et. al., 2016, Shah, et. al., 2015; Gopinattan, et al., 2015). They employed various chemical pretreatment methods such as the use of alkalis (NaOH, KOH, NaHCO₃, Ca(OH)₂) of different concentration in the maintenance of the slurry/ substrate pH for optimum biogas production. However, the application of a buffer solution was not considered, which we believed would resist more change in slurry pH when compare with alkalis solutions. Another gap identified from previous studies on cassava peels conversion to biogas was that investigation on stale cassava peels bio-digestion was neglected. It is the stale cassava peels that are abundant in most cassava peels dumpsites that usually constitute its associated environmental pollution and health hazard. Therefore, this study is designed to address these gaps. The application of an acid buffer solution will be investigated together with the alkaline solution as pretreatment chemicals. Besides, fresh and stale cassava peels will be studied. A comparison will be made and the conclusion drawn.

Therefore, the focus of this study is to investigate the production of biogas from cassava peels, as a potential alternative source of energy using pig waste as an inoculum. Besides, to determine whether the digested sludge from the anaerobic digestion can be used as a source of biofertilizer. As a result of the identified gaps in previous research works on cassava peels for biogas production, the objective of the research was to investigate the effect of the nature of cassava peels, (fresh and stale) and the applications of different pretreatment chemicals (alkaline and acid buffer solutions) on biogas production and methane yield.

Energy is an integral component of any socio-economic development and a central factor for eliminating poverty in any society (Aderemi et al., 2009). In Nigeria located on the west coast of Africa, lack of access to wide range of modern energy services has remained a major barrier to improving key indicators of human development (Onafeso, 2006). Presently over 60% of the country population depends almost entirely on fire wood for cooking, heating and agroprocessing activities. Petroleum products such as kigasoline and kerosene are marked by acute shortages and mounting price, with the product sold over 300% above the official pump price (Anonymous, 2008). Additionally, electricity which is the foundation of modern economies is non-available and if available is of poor quality or better still unreliable as less than 4,000 MW of the 7,876 MW installed electricity capacity is been generated (Sambo et al., 2010).

The introduction of mechanization and automation of food processing operations to drive conveyors, pumps, compressors and equipments like steam boilers, dryers, refrigeration equipments, ventilation and ovens has made the use of electricity critical in food industries. The non-availability of electricity supply or poor quality and unreliable nature of electricity supply by Power Holding Company of Nigeria (PHCN) has resulted in the increasing use of stand-by generators of various shapes and sizes (Adegoke and Akintude, 2000), which depends entirely on petroleum products as fuel.  In spite of the obvious advantage offered by these stand-by generators as a dependable solution to erratic power supply; the re-current perennial petroleum products scarcity and it rising cost contribute to high cost of production and loss of competitive advantage of processed foods when placed side-by-side with the imported ones (Aderemi et al., 2009).  Additionally, petroleum products are finite in nature and their combustion bye products are major contributors to environmental degradation, climate change and global warmng (Das et al., 2000). Awareness of the limitations of the convectional fuel has enhanced the growing interest in the search for alternate cleaner and sustainable source of energy (Goodger, 1980).  Biogas which has a relatively significant comparative advantage due to the country huge biomass potential estimated to be about 8 x 10² MJ offers a promising sustainable solution (Nwoke and Okonkwo, 2006), however the wastes are usually dumped indiscriminately in landfills and unauthorized areas contributing further to environmental degradation and global warming (Adeola, 1996; Igbinomwanhia and Olanikpekun, 2009). In-order to reduce the current over dependence on fossil fuel, enhance energy availability and safeguard the natural eco-system in the face of Nigeria huge biomass potential (Garba and Sambo, 1992), biogas technology represents a viable alternative due to its simple technology and rural possible adaptability. (Diaho et al., 2005). Biogas is a fuel gas consisting of a mixture of methane (CH₄), carbon dioxide (CO₂) and traces of other gases, produced through microbial processes under anaerobic conditions from bio-degradable materials (Dennis and Burke, 2001). It’s a renewable high quality fuel that burns without leaving soot’s or particulate matter (Merchaim, 1992). Although biogas technology is yet to be adequately exploited in Nigeria and other Africa countries, the technology is a common place in countries like India, China, Pakistan, U.S.A and most European nations (Nwoke and Okonkwo, 2006). Utilization of biogas as fuel in internal combustion engines have witnessed a substantial breakthrough and improvement over the years (Mitzlaff and Mkumbwa, 1980; Mitzlaff, 1988; Huang and Crookes, 1998; Midkiff et al, 2001; Eshan and Naznin, 2005) Although biogas engines are presently not available in Nigeria markets; the crippling fuel prices and high cost of food processing coupled with the growing problem of food wastes management has remain an intractable national problem. Modifying these existing engines via rural adaptable technology to use biogas produced from these food wastes is an essential springboard for a shift to an eco-system friendly technology and sustainable rural development.

1.2 Problem Statement

Energy is a key instrument in accelerating economic growth, alleviating poverty and creating employment opportunities. Epileptic power failure has resulted in an over-dependence on generators driven by fossil fuel. Apart from this, fossil fuel is non-renewable and fast depleting and contributes to ecological degradation. Due to the endemic power shortage in the country and the current fragile enforcement laws governing waste management and use of generators in Nigeria, it is highly appropriate to researched on the use of biogas produced from food and other biodegradable wastes as alternative fuel source for internal combustion engines.

Gasoline generators represented almost 80% of the population source of independent energy supply. Given that over 70% of the country estimated 150 million people are involved in agricultural activities, and producing diverse varieties of plants and animal wastes. Transforming these wastes into biogas energy for use in existing gasoline generator represents a long-term sustainable approach to energy self-sufficiency and economic development.

1.3 Objectives

1.3.1 General Objective

The broad objective of this research was to adapt gasoline generator for biogas utilization for lower cost energy alternatives from available food and agro-allied wastes.

1.3.2 Specific Objectives

The specific objectives of this research were to:

• Modify a generator for biogas utilization
• Evaluate the electricity voltage output and load bearing characteristics of the modified generator
• Determine the exhaust gas emission and temperature in comparison to petrol based generator

 

EFFECT OF SEEDING OF WOOD-ASH ON BIOGAS PRODUCTION USING PIG WASTE AND CASSAVA PEELS

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