Nature of Municipal Wastewater

An understanding of the nature of wastewater is fundamental for the design of appropriate wastewater treatment plants and the selection of effective treatment technologies. The Wastewater originates predominantly from water usage by residences and commercial and industrial establishments, together along with groundwater, surface water and stormwater. Consequently, wastewater flow fluctuates with variations in water usage, that is affected through a multitude of factors involving climate, community size, living standards, dependability and quality of water supply, water conservation needs or practices, and the extent of meter services, further to the degree of industrialization, cost of supply and water pressure. Huge variations in wastewater flow rates may, therefore, be expected to occur within a community.

Wastewater quality may be defined by its chemical, physical and biological characteristics. Physical parameters include color, odour, temperature, and turbidity. Insoluble contents such as solids, oil and grease, also fall into this category. Solids may be further subdivided into suspended and dissolved solids as well as organic (volatile) and inorganic (fixed) fractions.

Chemical parameters associated with the organic content of wastewater include biochemical oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC) and total oxygen demand (TOD). Inorganic chemical parameters include salinity, hardness, pH, acidity and alkalinity, as known as concentrations of ionized metals like as iron and manganese, and anionic entities like as chlorides, sulphides, sulphates, nitrates and phosphates. Bacteriological parameters involve coliforms, fecal coliforms, specific pathogens, and viruses. Both constituents and concentrations vary along with time and local conditions.

The effects of the discharge of untreated wastewater within the environment are manifold and depend on the categories and concentrations of pollutants. Significant contaminants in terms of their potential effects on receiving waters and treatment concerns are shortly explained below.

Suspended solids (SS) could lead to development of sludge deposits and anaerobic conditions while untreated wastewater is discharged within the aquatic environment.

Biodegradable organics are principally made up of proteins, carbohydrates and fats. They are generally measured in terms of BOD and COD. If discharged within inland rivers, streams or lakes, that biological stabilization could deplete natural oxygen resources and cause septic conditions which are detrimental to aquatic species.

Pathogenic organisms found within wastewater could cause infectious diseases.

Priority pollutants, involving organic and inorganic compounds, might be highly toxic, carcinogenic, mutagenic or teratogenic.

Refractory organics that tend to resist conventional wastewater treatment involves surfactants, phenols and agricultural pesticides.

Heavy metals usually added through commercial and industrial activities must be erased for reuse of the wastewater.

Dissolved inorganic constituents just like as calcium, sodium and sulphate are frequent initially added to domestic water supplies, and might have to be removed for waste-water reuse.