Recycling of Agricultural Wastes: Treatment and Uses
Z. Ioannou, V. Kavvadias and C. Karasavvidis
Hellenic Agricultural Organization - DEMETER, Soil Science Institute of Athens, Sof.,
Lycovrissi, Attiki, Greece
Agricultural wastes (AW) can be defined as the residues from the growing and first processing of raw agricultural products such as fruits, vegetables, meat, poultry, dairy products and crops. AW can be in the form of solid, liquid or slurries depending on the nature of agricultural activities. Agricultural industry residues and wastes constitute a significant proportion of worldwide agricultural productivity. Although the quantity of wastes produced by the agricultural sector is significantly low compared to wastes generated by other industries, the pollution potential of agricultural wastes is high on a long-term basis. The opportunity and feasibility for recycling these wastes comes from two directions: the care for environment reflected by new sets of rules and regulation and the potential to add value to these wastes by adding positive elements. Moreover, they can be used as precursors in many other sectors such as membranes, biosorbents or activated carbons for the removal of dyes, organic molecules, heavy metals and fertilizers. Different types of agricultural wastes, i.e., deoiled soya, coconut shell, neem leaves, hyacinth roots, rice husk, rice straw, rice bran, lemon leaf, tea waste, potato plants wastes, tomato wastes, sesame hull, garlic peel, peanut hull, carrot stem, carrot leave, barley straw, banana stalk, olive stones, almond shells, peach stones, apricot stones, cherry stones, grape seeds, Trapa natans husk, bamboo, doum-palm seed coat, walnut shells, rose seed, pine sawdust and coir pith are ideal raw materials for different industrial applications due to their low cost, non-toxic content and their abundance. The final products derived from agricultural wastes have shown equal or even better properties compared to conventional products concerning separation, adsorption and fertility. Previous studies and projects dedicated to the development of AW treatment technologies focused mainly on the reduction of the wastes organic load and on the reduction or the recovery of valuable substances and succeeded to develop suitable technologies and methods. However, if land distribution is planned the organic load and the toxic substances of treated wastes should not be the only issues of concern. Specific care
should be taken also for inorganic constituents and especially for K, Cl", NO3", SO42", P, Mg, Fe, Zn and others, since the very high concentrations disposed on soil change its quality properties drastically, while electrical conductivity and the concentrations of inorganic soil constituents such as K, P, Fe, Cu remain high even after many years from the last disposal. These practices must take into account important specific local conditions, such as waste characteristic, soil type, background levels of nutrients and pollutants for soil, water and plants, the climate, the relevant crops and the local agricultural practices. Emphasis will be given on specific knowledge and technologies developed so far in Mediterranean countries, their impacts, and constraints and knowledge gaps. Furthermore, policy issues for AW use in Europe and especially in the Mediterranean countries at various levels will be considered. Therefore the aim of this study is to examine the properties and uses of new products derived from agricultural wastes and to research and advance agricultural practices with the use of treated agricultural wastes by recycling nutrients and water from treated agricultural wastes.
Keywords: agricultural wastes, nutrients, inorganic elements, new products