Soils are an effective medium of treatment for septic system effluent because they contain complex biological communities. A tablespoon of soil may contain over a million of microscopic organisms including protozoa, molds, fungi, bacteria and other creatures. The microorganisms and bacteria in the soil purify the water before it reaches the underground water. The septic effluent must pass through the soil gradually enough to provide adequate contact with microorganisms. One of the major components in wastewater effluent is nitrogen which exists in different forms. These forms include nitrates (NO3), ammonia (NH3), and nitrites (NO2). Nitrates are essential plant nutrients, but in surplus amounts, they can quicken eutrophication that can lead to an increase aquatic plant growth. The contamination and fate of nitrates in the soil treatment is dependent upon the form of nitrogen that is getting to the soil and the biological conversions that follows. Nitrates forms through nitrification, which is an aerobic reaction process that depends on the availability of oxygen in the soil. If nitrates and nitrites levels are not reduced, they may end up in rivers and streams. This will cause excess growth of algae and deplete oxygen in those rivers and streams, resulting to the death of aquatic life like fish and other organisms. Nitrates also react directly with hemoglobin in human blood and other warm blooded animals to produce “methemoglobin” which lowers the ability of red blood cells to carry oxygen. The condition with humans is especially serious in babies under four months old. The concentrations of Nitrates in septic effluent are approximately 60 mg/L. These are excess levels for human health and hence it is important to monitor Nitrates levels in septic systems. Research indicates that approximately 10-50% of septic effluent Nitrates may be removed by passing the wastewaters through water-unsaturated soil before the affluent reaches the ground water.
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