CHAPTER FIVE
SOLID WASTE AND AGRICULTURAL DEVELOPMENT IN SCHOOL INTRODUCTION
(B) Minerals: The mineral potion of solid waste is largely made up of soluble salt. These solids are of interest because of their effect on the ground water, and their related possibility of degrading thinking and irrigation waters. The public health services have set preferable limits around 500 mg/kg on the total soluble content of farm lands. But in the most rest standards published by environment protection Agency (USA), only specific inorganic constituents are noted.
The risk assessment performed to develop the EPA regulation found that these heavy metals can pose potential risks to human health and the environment in surface disposal solid wastes. These are organic chromium and nickel (US EPA 1992) (a) 1. Therefore pollutant limits were set for these metals in sewage sludge placed on surface disposal sit.
Saline and alkaline soils are the result of concentrating salts in the root zone of soils. The continuous application of wastes containing soluble solids could result in the build up of salts and other dissolved solids within the soil profile in areas where the ever “potranspiration” rate is significant. This build up of salt in the soil solution can deter crop growth. Salt build up is controllable by including a leaching factor during the solid waste land application as will be seen in the later part of this presentation. It must be stressed that the salt concentration in general acceptable for crop irrigation.
NUTRIENTS
Nutrients found in solid waste that have caused concern c1udes nitrogen and phosphorous. These are essential nutrients for crop production. However, when the amount available exceed the demand, leaching of these nutrients to ground and surface waters may occur. A major concept here will be on the design of systems based on the pollutant which causes the strictest limitation. Nitrogen is clearly the most common limiting waste constituent for land application in both solid waste constituent for land application in both solid waste and most organic sludges for a given waste.
This means that the greatest land areas will most often be required based on the nitrogen present in that waste.
(A) Nitrogen: Nitrogen in solid wastes, especially semi solid and sludges in particular may be present as anmionium (NH), organic nitrogen (N-org or as amines R-NH2) and nitrate nitrogen (NO3). These three forms are determined when evaluating a waste for land application. Ammonium and organic nitrogen are usually the principal forms found in raw sewages nitrogen in ammonium form (NH) will usually absorb the negative charged soil, but nitrate is soluble and will move with the soil water, Movement of these nutrients and water to the vegetative crop. Where excesses of nitrogen are applied, the potential of causing nitrogen accumulations in the ground water exists.
Emeka Jilly Ejiowhor
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