One reason is that the use of wastewater may cause the PH to drop as a result of incomplete anaerobic digestion of organic matter. This usually occurs in clay and loamy soil. Suspended solids from wastewater irrigation can cause the pores in the soil to close, thereby leading to an insufficient oxygen supply.
Wastewater is the liquid part of sludge. The liquid comes from the treatment of the sludge through the separation of solids and the stabilization of pollutants. Stabilization is the degradation of organic matter until the point at which chemical and biological reactions stop. Treatment also requires the removal of toxic or otherwise dangerous substances which are likely to distort sustainable biological cycles, even after stabilization of the organic matter. Polishing is the final stage of treatment. It is the removal of stabilized or otherwise inactive suspended substances in order to purify the water physically.
The Basics of Biological Treatment
The stabilizing part of treatment happens through the degradation of organic substances through chemical processes, which are biologically steered (bio-chemical processes). This steering process is the result of the bacterial metabolism in which complex and high-energy molecules are transformed into simpler, low-energy molecules. Metabolism is nothing but the transformation from feed to organic matter in order to gain energy for the life of the bacteria for it to break down the organic matter.
Wastewater treatment is the degradation of organic compounds, and finally the oxidization of carbon into carbon dioxide, nitrogen to nitrate, phosphorus to phosphate and sulphur to sulphate. Hydrogen is also oxidized to water.
Wastewater for Irrigation
Treated domestic or mixed community wastewater is ideal for irrigating parks, flower gardens and vegetable gardens. To avoid contamination, wastewater has to be applied to the root system. Irrigation normally occurs in the evening or early in the morning so that people cannot be disturbed by the slightly foul smell of anaerobic effluent. Nonetheless, irrigation of public parks is often forbidden.
Groundwater comes from rainwater. It is the most important source of water for domestic use, irrigation and for other purposes. The supply of ground water is not infinite. To be sustainable, it must be recharged. Organic pollution of groundwater occurs when wastewater enters underground water streams directly. Contamination can be avoided by adding a crack-free soil layer above the groundwater, thereby reducing cases of human contamination after consumption of the polluted water.
Wastewater Is Never Safe Water
Wastewater is never hygienically safe. Proper handling of wastewater and sludge is the only successful preventive health method. The farmer who uses wastewater for irrigation must consider the risk to their own health and to the health of those who consume their crops. Farmers must therefore check whether their wastewater for irrigation is suitable to the crop or pasture ground they intend to water. Fresh, untreated domestic and agricultural wastewater contains over a million bacteria per milliliter, thousands of which contain bacterial and viral pathogens. Therefore, the World Health Organization (WHO) recommends that treated wastewater for unrestricted irrigation should contain less than 10,000 feacal coliforms per liter (1000/100ml), and less than 1 helminthes eggs per liter.
DEWATS (Decentralized Wastewater Treatment Systems Technology) is mainly used by development planners who want educate communities about the proper handling of wastewater. Like all treatment systems, the DEWATS system does not remove pathogens. Long retention times increase pathogen removal rates. However, short retention times are ideal for high rate plant growth.