Wastewater is water that has come into contact with any of a variety of contaminants and is not fit for human consumption. Most often, wastewater has its source in domestic settings, commercial operations, industry and agriculture. Groundwater becomes contaminated from many sources. “Point” sources include municipal landfills, leaking gasoline storage tanks, leaking septic tanks, accidental spills and industrial waste disposal sites. “Non-point” sources include runoff and seepage from agricultural lands containing pesticides and fertilizers.
Blackwater refers to wastewater that contains human waste, usually from lavatories. This also becomes sewage, when it empties into a municipal sewage system. Greywater is that water that contains contaminants from washing; laundry, bath, shower, dishes. Stormwater is the runoff after a rainstorm, and most often runs into a municipal sewage system. Otherwise, it flows into creeks, rivers and oceans.
Domestic- source wastewater contains food, cooking oils, drinks, pesticides, paint, cleaning fluids, rainfall from roofs, which contain oils, fuels and litter. Wastewater from roads also is contaminated from fuels, salt, rubber residue, animal excrement and litter. Industrial sources of wastewater contain contaminants including oils, chemical residues, pharmaceuticals, pesticides, silt, cooling compounds, metal plating, and a variety of other by-products of manufacturing processes.
Water that has been used for cooling in a manufacturing process becomes wastewater after if has warmed. Other industrial processes require de-ionized water. When this water has been used in that process, it becomes wastewater.
One drop of oil can make twenty-five liters of water unfit for drinking and one gram of a common household herbicide can make ten million liters of water unfit for drinking. Only one gram of PCB can contaminate one billion liters of water, making it unfit for aquatic life. One gram of lead in 20,000 liters of water renders it unfit for drinking.
Oil and gas drilling is a worrisome source of wastewater, as more attempts are proceeding to find local sources of these fuels. The contaminants resulting from these operations contain cadmium and benzene, both carcinogenic elements. They are released into the massive amounts of water injected under pressure to force gas out of the ground. A more dangerous contaminant resulting from drilling is the grit, called Totally Dissolved Solids (TDS) that are dredged from deep underground. TDS contains minerals and salts in such concentrations that the wastewater resulting from contamination by TDS is five times as salty as seawater. It alters the taste of groundwater, but more dangerously clogs rivers and streams and affects the health of those waters. With increased drilling, the bio-systems are becoming overwhelmed in their capacity to neutralize these contaminants.
Wastewater is primarily treated at municipal water treatment plants in North America. These plants separate solid and liquid waste. The liquids are typically sent off to further filtering and treatment by bacteria and chlorine, while the solid wastes are often treated with micro-organisms that are able to break down the sludge and absorb and neutralize contaminants. Septic systems use gravel, sand or reed beds to hold and filter the liquids, while the solids are contained and physically removed when the tank is full.