Liquid waste refers to any discarded material in a liquid state. It includes substances from residential, commercial, industrial, and agricultural activities that require careful management due to their potential impact on human health and the environment. Unlike solid waste, liquid waste spreads easily, making its proper containment and treatment important to prevent pollution. Its composition varies depending on its origin.
General Designations
Wastewater is a broad term for water used in domestic, industrial, commercial, and agricultural activities that has been affected in quality. Its composition is dynamic, typically consisting of about 99.9% water and 0.1% dissolved or suspended waste materials, including organic matter, microorganisms, and inorganic compounds.
A more specific term, “sewage,” refers to wastewater produced by communities, primarily from residential and commercial facilities. It is transported through sewer systems and contains human excreta, used water from bathrooms, and food preparation wastes. Though often used interchangeably with municipal wastewater, sewage is a subset of the broader wastewater category.
“Effluent” describes liquid discharged from a process or system, often treated. In the context of liquid waste, effluent refers to treated water released from wastewater treatment plants into natural environments. Discharge must meet regulatory standards to minimize environmental harm.
Categorizing Liquid Waste
“Domestic wastewater,” also known as sanitary sewage, originates from daily household activities such as bathing, dishwashing, laundry, and toilet flushing. It contains organic matter, nutrients, cleaning agents, and microorganisms.
“Industrial wastewater” is generated from manufacturing and commercial processes. Its composition varies significantly by industry, and it can contain diverse contaminants like heavy metals, chemicals, and organic pollutants requiring specialized treatment.
Precipitation flowing over land and impervious surfaces, like rooftops and paved areas, is termed “stormwater runoff.” This water picks up pollutants such as trash, chemicals, and sediment before entering waterways. Similarly, “agricultural runoff” is water from farms, from rain or irrigation, that flows over fields and collects fertilizers, pesticides, and animal waste.
Leachate is a liquid formed when water percolates through waste materials, dissolving contaminants. It is commonly observed in landfills, where rainwater seeps through decomposing garbage, creating a highly contaminated liquid that can pose risks to groundwater and surface water if not properly managed.
Within domestic wastewater are two classifications: “greywater” and “blackwater.” Greywater comes from non-toilet sources like sinks, showers, bathtubs, and washing machines, and contains fewer pathogens than blackwater. In contrast, “blackwater” is wastewater specifically from toilets, containing fecal matter, urine, and toilet paper, making it the most contaminated domestic wastewater due to high levels of pathogens and organic material.