1.1 INTRODUCTION
The genus Manihotincorporates will over 200 species of which Manihotesculent or crantz is the most important, from the nutritional and economic point of view commonly known as cassava, manioc, tapioca and yucca cassava(Manihotesculenta Crantz) is a root tuber crop that is widely cultivated in the tropical regions of the world (Obohand Akindahunsi, 2003). It is mainly a food crop whose tubers are harvested between 7-13months based on the cultivars planted the tubers are quite rich in carbohydrate (85.9%) with very small amount of protein (1.3%) in addition to cyanogericglucoside (Nwabueze and Odunsi, 2007). This high carbohydrate content makes cassava a major food items especially for the low income earners in most tropical countries especially Africa and Asia (Desse and Taye 2006)
Cassava is believed to have originated from south America to other Northern America, cassava was introduced in the 16th
century around Congo river basins (Cock,1985). In sub Sahara Africa, cassava is a major stable food that is consumed in processed forms in many areas. In WestAfrica and Nigeria in a particular the crop is mostly consumed as garri, a dry granulated meal made from fermentedcassava (IITA,1990). Currently, Nigeria is the highest producer of cassava in the world with growth and processing of more cassava for domestic and international needs.However if the contribution that cassava can make to the live hood of poor people is to be increased, there is need to consider also its post harvest handing, processing, and marketing. Both cassava roots and leaves can be used as food , but economically the roofs are usually more important, although in some part of African countries, the leaves may be more important or more important than the roofs. Cassava is one of the most important food crops in Africa. It derives its importance from the fact that its starch, thickened tuberous roots are valuable source of cheap calories especially in developing countries;carlories,caloric deficiency and malnutrition are wide spread. Over two thirds of the total production of cassava is consumed in various forms by humans, its usage as a source of ethanol for fuel, energy in animal feed and starch for industry increasing. The crops are amenable to agronomic as well as genetic improvement, has a high yield potential under good contrition’s and performs better than other crops under sub-optional conditions. It is grown widely in several countries in sub-Sahara Africa and Madagascar the importance of cassava in food security and nutritional issues has led IITA (international institute of Tropical Agriculture ) and the united nations children’s education fund (UNICEF) to establish their joint household food security and nutrition programs with the goals of extending the benefits of IITA research to Africa countries through UNICEF’s country programs of social mobilization development (Nweke, 1992). Africa as one of the largest produce worldwide produces over 50 million tones of cassava annually (FAO, 1992). Total world cassava use is expected to increase from 172.7 million tons to 275 million tons in the period of 1993-2020 using the international food policy. Research institutes (IFPRI’s) base line data. As higher prediction of demand and production growth puts the 2020 production at 291million tons (Scott et al; 2000).
Traditional garri production is associated with discharged of large amount of water, hydrocyanic acid and organic matter in the form of peels and sieves from the pulp as waste products. Around cassava mill, the liquid waste is indiscriminately discharged and allowed to accumulate, producing offensive odour and unsightly scenarivs (FAO, 2004; Okafor, 2008; shiadgonareetal; 2009). The high cyanide content from the effluent equally posses significant threat to humans and the environment, which calls for regulations in the discharge of the waste generated (Akaniet al; 2006; Adewoyeet al; 2005). Kolwanet al, 2006) defined soil as the top layer of the earth’s lithosphere , formed from weathered rock that has been transformed by living organisms soil formation is the result of the combination action of weathering and Coloiyationof geological material by microbes ( Wiley et al;2008). Soil also has many layers, with the topsoil being the most productive. The biological components of the topsoil consist mainly of soil organisms especially microorganisms which are key players in the cycling of nitrogen, sulphur and phosphorus and the decomposition of organic residues these affects nutrient and carbon cycling on global scale (burning and Jimenez, 2003). The topsoil receive the greatest impact from pollutants. The effluents when incorporated into the soil exert effects on the soil itself. When discharged, it is acted upon by nutrients and soil microorganisms, releasing gases into the soil which other breakdown products are trapped in the soil(Pelczaret al; 1993).
1.2 Aim and objectives