Sewage Treatment: Origins, Composition, and Collection
Sewage Treatment: Origins and Composition
Residual water, posing a danger due to its high content of substances and microorganisms, requires disposal. This includes:
Types of Wastewater
Domestic Sewage
Originating from human waste, kitchen, and bathroom activities, this type contains organic matter, microorganisms, soap remnants, detergents, lye, and fats.
White Water
This can be atmospheric (rain, snow, or ice melt) or from irrigation and street cleaning.
Industrial Wastewater
Derived from factories and industrial establishments, this type contains oils, detergents, antibiotics, fatty acids, minerals, chemicals, and plant or animal products. Its composition varies significantly depending on the industry.
Agricultural Wastewater
Originating from farming activities, this type is often combined with urban wastewater for agricultural irrigation, sometimes without prior treatment.
Composition of Sewage
Sewage contains a wide variety of products, including organic oils like polycyclic aromatic hydrocarbons (some carcinogenic). Phenols cause odor and flavor issues when reacting with chlorine during water chlorination. Organometallic compounds, even in small concentrations, can affect the food chain, accumulating in organisms. Heavy metals like lead, cadmium, tin, and mercury are of particular concern. Surfactants create foams that trap organisms, inhibiting oxidation and treatment processes. Inorganic compounds include ammonia, fluorides, sulfides, sulfites, nitrites, and heavy metals. Acid mine drainage is a significant pollutant from industrial waste. Agricultural effluents contain nitrates, phosphates, ammonium, sulfides, and potentially toxic silo drainage. Fertilizers, herbicides, fungicides, and insecticides are the most toxic components. Trihalomethanes, including the potentially carcinogenic chloroform, are formed during water treatment.
Wastewater Collection
Cesspools, which contaminated drinking water wells, have been replaced by channeled waste systems. However, sewer lines must follow a slope, often discharging into streams at lower levels. Developed cities use sewerage systems to transport wastewater to treatment plants. These systems are categorized into:
Types of Collection Systems
Separated Systems
These use two separate pipelines: one for domestic and industrial wastewater, and another for surface runoff, often discharged directly into waterways.
Combined Systems
These systems combine both types of wastewater in a single pipe.
Wastewater Treatment
Purification
Water purification is the process of removing substances carried by water through natural dragging or discharge of liquid waste. These substances can be:
Biodegradable
These organic substances are degraded by microorganisms as nutrients. Soluble nitrates are easily accessible, while insoluble ones require bacterial exoenzymes.
Non-Biodegradable (Persistent)
Factors Influencing Self-Purification
Decomposition of organic matter by microflora for respiration and assimilation.
Use of dissolved oxygen by aerobic microorganisms to oxidize organic matter, sometimes supplemented by atmospheric oxygen.
Action of facultative anaerobes on settled organic matter in low-oxygen environments.
Dilution of wastewater with less concentrated substances.
Death of pathogens due to adverse environmental conditions.
Sunlight’s effect on aquatic flora.