Live bacteria are used in biological wastewater treatment to remove contaminants from sewage, ensuring that water quality and aquatic life are not harmed. Toilets, by-products of manufacturing processes, showers, animal slaughterhouses, and sinks, among other sources, pollute water in homes, industries, and farms. Sewage and run-off must go through several steps before being safely released into the environment in order to restore clarity, neutralize odor, and remove contaminants. The second step in this process is usually biological wastewater treatment, which focuses on reducing the amount of oxygen-demanding materials in the water.
Wastewater is piped into a treatment system, which can be on-site (such as a septic tank or biofilter) or at a water treatment plant. The location and process required to render wastewater safe are determined by local treatment regulations. The primary stage of dealing with sewage typically involves collecting the wastewater in a tank and allowing the heavy solids to settle to the bottom while the fatty solids float to the top. These solids are then skimmed off and left behind as the water moves on to the secondary stage, biological wastewater treatment, or to the outside environment.
Most of the remaining contaminants are soluble waste, or waste that dissolves in water, after the majority of the solid waste has been removed from the wastewater. It can’t be easily removed with a filter because it’s dissolved. A biological wastewater treatment system adds simple bacteria to the sewage and allows the bacteria to feed on the soluble organic waste. The bacteria remove the dissolved waste from the water, leaving behind a solid by-product that can be filtered out. Bacteria also aid in the congealment of less soluble waste that isn’t eaten, converting it to floc that can be filtered out. Floc is made up of solid clumps suspended in liquid rather than dissolved.
Biological wastewater treatment focuses on wastes that have an oxygen demand, or wastes that deplete dissolved oxygen (DO) levels in water. Low DO levels can harm aquatic ecosystems by suffocating plants and animals that need a certain amount of oxygen to survive. Eutrophication occurs when nutrients like nitrogen and phosphorous are released into an aquatic environment, causing a similar problem. Eutrophication occurs when excess nutrients are released, causing certain plants and algae to overgrow, consuming oxygen and suffocating other animals and plants. Because organic wastes such as phosphorus, nitrogen, and most oxygen-demanding wastes are organic, biological wastewater treatment is often effective in removing them.
The types of waste that can be introduced into a biological wastewater treatment system vary, as bacterial growth adapts to favor cells that can consume the waste in question. Biological wastewater treatment is typically carried out in an outdoor tank, making it susceptible to seasonal temperature variations. This is usually not a problem because bacteria can quickly adapt to changes in temperature without the need for a heating or cooling system. Following the completion of the secondary stage, wastewater may proceed to the tertiary stage, which typically includes microfiltration or chemical disinfection.