Table of Contents
AGRICULTURAL WASTE GENERATION
Agricultural development is usually accompanied by wastes from the application of intensive farming methods and the abuse of chemicals used in cultivation, affecting rural environments and the global environments in general. The generation of waste is dependent on agricultural activities that carried out.
Wastes from Cultivation Activities:The cultivation and growing of crops also causes the generation and development of insects and weeds. In order to kill insects and protect the spread of epidemic diseases, a greater amount of pesticides is needed. This leads to the abuse of pesticides by farmers. But after using pesticides, most of the bottles and packages holding these pesticides are thrown into fields or ponds. These wastes are toxic chemicals that last long and have the ability to cause food poisoning and contaminate farmland. In agricultural production, fertilizers play a vital role in maintaining the productivity and quality of plants. However, many farmers apply excessive fertilizer to their crops than the amount recommended. Among the fertilizer excess, a portion is retained in the soil, a portion enters ponds/rivers and a portion evaporates which results in the pollution of soil, water and air as well.
Wastes from Livestock Production:Waste from livestock activities include manure, organic materials in the slaughterhouse, wastewater for example urine, cage wash water, wastewater from the bathing of animals and from maintaining sanitation in slaughterhouses, air pollutants (H2S and CH4) and odors. In livestock waste, the amount of water volume accounts for 75–95% of total volume and the rest includes organic matter, inorganic matter, many species of microorganisms and parasite eggs. These microorganisms and substances can spread diseases to humans and cause many negative effects on the environment.
Waste from Aquaculture:The growth in aquaculture has led to an increased use of feeds for improved production. The amount of feed used in a system is the most important factor that determines the quantity of waste generated. Metabolic wastes are one of the major wastes generated in aquaculture that could be dissolved or suspended.
WASTE UTILIZATION ROUTES:
Fertilizer Application:The utilization of animal manures as fertilizer has a great impact on energy requirements at the farm level. Manure could supply 19% of nitrogen, 38% of phosphorus and 61% of potassium in chemical fertilizer. Poultry manure contains a high level of phosphorus which puts effect on the growth and productivity of crops. Adding manure to soil increases the nutrient retention capacity, water holding capacity, improves physical condition and the soil structure stability therefore increases its fertility.
Anaerobic Digestion:Methane gas can be produced from agricultural wastes specially manures and is best suited for heating purposes. The production of methane rich gas by anaerobic digestion of agricultural waste is a two-step microbial fermentation process. Initially, acid-forming bacteria converts organic wastes to volatile acids which are then utilized by methanogenic organisms to yield methane and carbon-dioxide gas. Anaerobic digestion is used in the treatment and disposal of large poultry, swine and diary wastes and minimize the odor problem.
Adsorbents in the Elimination of Heavy Metals:The industrialization and urbanization causes the excessive release of heavy metals into the environment. Heavy metal ions such as copper, cadmium, mercury, zinc, chromium and lead ions do not degrade rather sustain in the environment for long period of time. The presence of heavy metals in the environment is considered a major threat due to their toxicity to many life forms. In recent years, adsorption process has become a low-cost alternative for the treatment of effluents containing heavy metals.
Pyrolysis:In pyrolysis systems, agricultural waste is heated up to a temperature of 400-600°C in the absence of oxygen to vaporize a portion of the material, leaving a char behind. This is a much higher technology procedure for the utilization of agricultural wastes. Pyrolysis of agricultural waste produces oil, char and low heating value gas.
Animal feed:In the developing countries, the problem with animal feed is that they lack protein, starch and fat sources but have high content of fiber. Increasing livestock production by supplementing forage and pasture with grains and proteins do not meet the future meat protein requirements. Again, using of grain and protein for animal feed compete with human food.
Direct combustion:Direct combustion is one of the oldest biomass conversion processes known to mankind where the agricultural wastes are burned as fuel. Complete combustion of agricultural waste includes rapid oxidation of biomass and oxygen, the release of energy, and the simultaneous formation of the ultimate oxidation products of organic matter – CO2 and water. The energy released is usually comes in the form of radiant and thermal energy.