Wastewaters are liquids and solids which are water borne and are discharged to sewers, representing waste water derived from community life as well as industrial sources. Waste water composition includes suspended and dissolved organic solids. These are biologically decomposable or ‘putrescible’.
Innumerable numbers of living organism are contained in domestic waste water. These are bacteria or other such micro-organisms whose life activities result in process of decomposition. In cases where decomposition is anaerobic- in absence of oxygen- offensive conditions like hideousness and bad odour results. But when decomposition is aerobic involving dissolved oxygen, offensive conditions can be avoided and water treatment proceeds.
The complete philosophy of waste water sanitation consists of removing, controlling and treating wastewater in a location which is remote or isolated from centre of activity. Down the years, management practices of waste water treatment have evolved into technologically complicated body of knowledge based on environmental science, applied engineering and past practices.
There are two general objectives of water treatment Australia:
- Minimizing or reducing of public health hazards of waste water. These are basic treatment methods used to prevent pathogens from reaching back the consumer.
- Minimizing, reducing and eliminating the harmful impact of waste water on the quality of the receiving water body
There is much distinction between waste water treatment and waste water disposal. The complete waste water must be disposed away. Before disposal, some waste water is subject to different types of treatment before disposal but some may not be treated.
Waste Water Treatment
It is a process in which solids in waste water are removed partially or changed partially by decomposing complex, highly putrescible organic solids to minerals or organic solids which are relatively stable. The quantum of change depends on the process of treatment. After completion of treatment process, it is vital to dispose away solids and liquids which have been removed.
Waste Water Disposal
There are 3 methods using which final disposal of waste water can be accomplished. The common problem areas in final disposal are pathogenic microbes, heavy metals and organic compounds which are biologically resistant like insecticides or pesticides which enter water supply. In recent times, there has been concern about use of land in both sub surface and surface disposal after treatment of waste water.
This is disposal through irrigation. This consists of spreading waste water over the ground surface, usually via irrigation ditches. There is a certain amount of evaporation, but major amounts of water soaks into the ground and supplies moisture with small amounts of fertilizing compounds for plants.
This method of waste water disposal is suited to small populations where land area is available and nuisances will not be created. It is much suitable to semi-arid or arid areas, where moisture has critical value.
Sub Surface Disposal
In this, waste water is introduced to the ground underneath its surface via tile fields or pits. It is popularly used for disposal of settled waste water from domestic as well as institutional users where there is only a limited amount of waste water.
The critical factor in treatment and disposal is the quantum of organic matter that is readily decomposable. Another factor is dissolved oxygen in the receiving water body.