By Nneka Nwogwugwu
A visit to a plantain farm in Port Harcourt, Rivers state, revealed many ways farmers and industrialists can judiciously utilize agric waste in order to control pollution.
Agricultural wastes as defined by Nigerian Journal of Technology, are residues from the growing and processing of raw agricultural products such as fruits, vegetables, meat, poultry, dairy products, and crops.
In the farm, I discovered that there are agric wastes used as manure to help plantain suckers grow. Here, the feces of fowls are being used as manure.
Speaking to the owner of the farm, Emmanuel Nwakwuo, explained that he usually spreads the feces on the root of the suckers once a week, adding that the feces are great source of manure to the plantain.
Also, in a conversation with a business woman who owns a storage business, she explained that when rain wets her bags of garri, instead of losing her profits, she sells the affected bags to fish farmers who use them as feeds to their fishes.
In exploring more different ways to make use of agric wastes by farmers and industrialists, a research published by Nigerian Journal of Technology stated that agric waste can be generated from cultivation activities, aquaculture and livestock production.
For cultivation activities, waste generation is coming as a result of tropical climate that is favorable for growing crops, it also supports the generation and development of insects and weeds.
According to an estimate made by the Plant Protection Department (PPD), about 1.8% of the chemicals remain in the packaging of pesticides used in killing these insects. These wastes have the potential to cause unpredictable environmental consequences such as food poisoning, unsafe food hygiene and contaminated farmland due to their potentially lasting and toxic chemicals.
The growth in aquaculture has led to an increase in the use of feeds for improved production. In a properly managed farm, approximately 30% of the feed used will become solid waste. Feeding rates are dependent on the ambient temperature. Increase in temperature results in increased feeding which gives rise to increased generated waste.
Waste from livestock activities include solid waste such as manure and organic materials in the slaughterhouse; wastewater such as urine, cage wash water, wastewater from the bathing of animals and from maintaining sanitation in slaughterhouses; air pollutants such as H2S and CH4; and odors.
Francis Obi, Boniface Ugwuishiwu and Joel Nwakaire who are authors of this research recommended a number of applications these wastes can be used. They include:
1. Fertilizer Application: The utilization of animal manures for fertilizer has a definite impact on input energy requirements at the farm level. Manure could supply 19, 38 and 61% of nitrogen, phosphorus and potassium in chemical fertilizer. Adding manure to soil increases its fertility because it increases the nutrient retention capacity (or cation exchange capacity), improves the physical condition, the water holding capacity and the soil structure stability.
2. Anaerobic Digestion Methane gas can be produced from agricultural wastes particularly manures. The gas is best suited for heating purposes as in broiler operation, water heating, grain drying, etc.
Some of the major disadvantages of the digestion system are the high capital costs and the explosive properties of the methane gas. However, the advantages far outweigh the aforementioned disadvantages. Anaerobic digestion makes the treatment and disposal of large poultry, swine and diary waste feasible, minimizing the odor problem. It stabilizes the waste and the digestion sludge is relatively odour-free and yet retains the fertilizer value of the original waste.
3. Animal feed: In most developing countries, the problem with animal feed is in the limited availability of protein sources although great efforts are being made to find alternative supplements. Crop residues have high fiber content and are low in protein, starch and fat.
4. Direct combustion: The simple act of burning agricultural waste as fuel is one of the oldest biomass conversion processes known to mankind. Complete combustion of agrowaste “consists of the rapid chemical reaction (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 in the form of radiant and thermal energy provided oxidation occurs at sufficient rate; the amount of which is a function of the enthalpy of combustion of the biomass. If agricultural waste is to be utilized efficiently through thermal conversion process, there is need to fabricate these biomass wastes into solid form. It is usually burnt for heating, cooking, charcoal production, and the generation of steam, mechanical and electric power applications.
Of all the processes that can be used to convert agricultural waste to energy or fuels, combustion is still the dominant technology accounting for more than 95% of all biomass energy utilized today.