Portable Bio Digester

1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
One of the main environmental problems of today‘s society is the continuously increasing production of organic wastes.In many countries, sustainable waste management as well as waste prevention and reduction have become major political priorities, representing an important share of the common efforts to reduce pollution and green house gas emissions and to mitigate global climate changes. Uncontrolled waste dumping is no longer acceptable today and evencontrolled landfill disposal and incineration of organic wastes are not considered optimal practices, as environmental standards here of are increasingly stricter and energy recovery and recycling of nutrients and organic matter is aimed.

In 2015, the United Nations Development Programme (UNDP) identified 17 Sustainable Development Goals (SDGs) to be reached by 2030. Goal number seven of the UNDP SDGs states the need for affordable, clean, and sustainable energy access for all. One in seven people worldwide does not have access to electricity; most of these people are in rural areas, in addition to three billion people using unhealthy fuels for cooking (United Nations Development Programme, 2018). Biogas digesters can be used in those rural areas to meet the energy demands and satisfy the UNDP goals with an emphasis on clean and sustainable energy under responsible consumption and production.

Waste management is one of the major challenges that face society, especially in developing countries. In several countries, waste management and reduction climbed to the top of their priorities’ list because of their negative environmental effects, representing a very important share of the common responsibilities and efforts in the endeavor to reduce the pollution and greenhouse gas emissions that cause global climate change. The old way of disposing wastes is unacceptable today; because of its undesirable effects, even using landfills for controlled waste disposal is not considered an optimal practice, as environmental standards call for the utilization of waste management through the recovery process, recycling nutrients, and using organic matter to produce biogas.

Production of biogas through anaerobic digestion (AD) of animal manure and slurries as well as of a wide range of digestible organic wastes, converts these substrates into renewable energy and offers a natural fertiliser for agriculture.At the same time, it removes the organic fraction from the overall waste streams, increasing this way the efficiency of energy conversion by incineration of the remaining wastes and the biochemical stability of land fill sites.

Biogas is a by-product of the anaerobic decomposition process of organic matter. It is a combustible gas consisting primarily of methane, carbon dioxide, and small amounts of other gases that are produced when the waste is fermented in the absence of the oxygen. The solid material that remains in the digester after the fermentation, which is rich in macro and micronutrients, can be used as an organic fertilizer.

Biogas digesters use the anaerobic fermentation of organic matter in the absence of oxygen to produce biogas (Walekhwa et al., 2009). The AD is applied globally as a wastewater treatment method for methane production with livestock manures (Global Methane Initiative, 2014). Several factors can affect the anaerobic digestion process; different feedstock will degrade at different rates and produce different amounts of methane. Different wastes with wastewaters can be mixed together and treated in the co-digestion schemes; the mixing process of different substrates improves the methane production and reduces the life cycle costs.

A biogas digester is an airtight enclosed container that aims to enhance the anaerobic digestion process of biodegradable waste such as animal manure and domestic wastes (Spuhler, 2014). Biogas digesters can be classified into three categories: (i) passive systems, where recovered biogas is added to an existing waste treatment facility and there is little control of the anaerobic digestion process; (ii) low rate systems, where the wastes flows through the digester and only leaves when the designed hydraulic retention time (HRT) ends; and (iii) high rate systems, where the methane-forming bacteria is trapped in the digester to enhance the biogas production efficiency.

Biogas installations, processing agricultural substrates, are some of the most important applications of AD today. The purpose of this work is to build a portable bio digester.

1.2 PROBLEM STATEMENT
Essential energy needs are not always met in poor and rural areas of developing counties; therefore, natural energy sources are necessary to mitigate this problem. Rural areas inhabitants utilize methane as a replacement for cooking gas to reduce their gas bill. Methane gas can be produced from a biogas digester; however, operating a large digester in a densely populated village in Ghana can be challenging due to inefficient village waste management systems, and the cost of buying a cooking gas is high. On the other hand, using a small-scale portable biogas digester to generate biogas could overcome these problems. In this work, a portable biogas digester from natural sources available in Ghanaian villages such as human and animal waste were designed and evaluated.

1.3 AIM AND OBJECTIVES OF THE STUDY
The main aim of this study is to fabricate a portable bio digester which is an airtight enclosed container that aims to enhance the anaerobic digestion process of biodegradable waste such as animal manure and domestic wastes.

The objectives of this project are:

To fabricate a portable biodigester to be used in all weather conditions.
Consideration of economic and ergonomic factors with maximum efficiency in production of methane gas through domestic waste.
To reduce environmental waste and high cost of buying commercial cooking gas.

1.4 SCOPE OF THE STUDY
The scope of this work covers building a digester that is able to digest a mixture of human, animal and food waste, this digester met the portable size requirement in rural communities of any country.

1.5 SIGNIFICANCE OF THE STUDY
Firstly, investment in a portable digester can solve the waste management of rural populations and reduce a family’s gas bill. Secondly, it has been noticed that a farm animal manure digester has the highest biogas productivity, and it covers four times the gas demand of one five-member family; however, with a volume of 2.1 m3, it is oversized for portable applications. Thirdly, organic fertilizers can be made from the slurry generated after the biogas production process.