As Owerri get urbanized and population expands, the urgency of adopting better ways of managing the escalating volume of wastes being generated becomes expedient. I am keen to know if the Imo State government has ever thought about the future of the state, say by the year 2050.Whatever it may be I have decided to discuss sanitary landfill as a best available waste option.
The forerunner of the modern sanitary landfill was the open dump. Here rubbish was dumped and often burned. Dumps are eyesores which also become breeding grounds for flies, cockroaches, mosquitoes, rats, snakes and mice etc; and cause odor problems, water pollution from runoff, and air pollution from burning.
Most municipal solid waste in Nigeria is disposed of in dump sites instead of landfill sites. However, the construction of landfill sites has become more difficult both due to technical reasons relating to hydro-geological suitability of sites, and because of vastly increased public opposition, as seen by the ‘’NIMBY’’ (Not In My Back Yard) syndrome.
An increase in land filling costs reflects both construction difficulties and new landfill construction requirements intended to limit the potential for groundwater contamination. Despite these problems, it is generally recognized that solid waste management is always going to require the availability of landfills, because there are some materials that can be disposed of in no other reasonable way.
Sanitary landfills typically could be described as a place where the controlled deposition of waste takes place in an environmentally responsible manner, and as such has a significant improvement over open dumps. However, new problems needed to be dealt with including leaching of contaminants into ground water causing problems, and methane gas generation. Leachate is liquid seepage from landfills. The main sources of leachate are; water and other liquids already present in the waste; liquid by-products of microbial action during the anaerobic degradation of waste; and rain.
As the water passes through the landfill, it picks up soluble portions of the decomposing waste. When the leachate leaves the landfill, it may contaminate either groundwater or surface water, thus acting as a vehicle for carrying potentially toxic materials from the landfill to water sources used for human activities.
Municipal landfills are now constructed with the potential for groundwater pollution in mind. This includes provision for liners at the bottom of the landfill to help prevent leachate seepage, capture and treatment of the leachate before it leaves the site, as well as consideration of the geological location of the landfill and its proximity to ground and surface waters.
There are also regulations for the types of wastes which are allowed to enter municipal solid waste landfills. Special facilities are required for the safe disposal of hazardous waste, and various regulations governing the manufacture and transport as well as disposal of hazardous materials are designed in part to prevent their illegal disposal in municipal landfills.
Household hazardous waste is also gaining increasing attention. A number of US communities have initiated programs for disposal of certain household items which have been deemed to be a problem in municipal landfills. Waste oil is a frequent target, but many other household items such as paints, solvents, batteries, and insecticides are included in some programs.
Waste is placed on the ground or liner, spread in layers, and driven over with special bulldozer called a landfill compactor. A thin cover of soil is used at the end of each day to stop rats and flies reaching it and prevent the rubbish blowing about.
When the landfill site is full, it is covered with a thick layer of soil and allowed to settle. Eventually the land can be used for farming, forestry or recreation. Landfill sites, however, are rarely sufficiently stable for building on. Once a landfill has reached capacity, it must be properly closed and maintained for a number of years. Indigenous trees, shrubs, ground covers and wild grass could be planted to blend naturally with the surrounding vegetation to re-establish natural vegetation.
After the landfill is closed, decomposition of the waste continues with some physical and chemical changes. The final depth of the landfill may be as much as 30 percent less than the original. It is estimated that 90% of the settling will occur in the first five years. Bacterial activity also occurs in the landfill. This begins with aerobic decomposition of the waste, with carbon dioxide, water and nitrates as the primary products. When the oxygen supply is depleted, the bacterial activity changes and a new process led by anaerobic micro-organisms produce volatile fatty acids and carbon dioxide. Later, methane-producing bacterial reduce the volatile acids to methane and carbon dioxide, known as landfill gas. The rate of decomposition depends on a variety of factors including moisture, temperature, pH, and permeability of the soil cover. The entire process may take decades to complete.
Landfill gas comprises mainly of methane and carbon dioxide. Not only is methane a cause for concern because of its significant contribution to the greenhouse effect but also because of its explosive nature. Methane nevertheless can also provide a valuable source of alternative energy if the landfill is set up to collect it.
There could be cases of lateral migration of landfill gas from the landfill site to neighboring subsurface areas e.g. the DSW in Durban South Africa discovered the lateral migration of landfill gas from the Bisasar Road Landfill site into the weighbridge and office complex. A gas curtain was installed whereby a series of wells were sunk into the refuse from which gas is actively pumped from the area and flared.
Flaring landfill gas converts the methane component to carbon dioxide and water vapor. As an alternative source of energy it can be used to generate electricity, fire incinerators and boilers and kilns to make bricks.
It should be noted that methane generation is not limited to landfills; swamps produce large quantities of methane where it is known as ‘’swamp gas’’, and it is also produced in volume by volcanoes, cows, rice paddies and termites. In addition to methane and carbon dioxide, minor amounts of 80 other gases including nitrogen, oxygen, hydrogen, hydrogen sulfide, and carbon monoxide have been identified in landfill gas. Examples of well maintained sanitary landfills are found at Marian Hills land fill, Durban South Africa, and the Canterbury land fill, Canterbury, England.
Certainly as a state that prides itself as “Clean and Green” it is high time Imo State, Nigeria develops a sanitary landfill in Owerri.