Which biological treatment process is known for its high efficiency in removing both organic matter and phosphorus?

The Enhanced Biological Phosphorus Removal (EBPR) process is known for its high efficiency in removing both organic matter and phosphorus from wastewater. Wastewater treatment aims to clean water polluted by human and industrial activities, making it safe to return to the environment. Organic matter refers to carbon-containing compounds in wastewater, often from things like food waste and sewage. Phosphorus is a nutrient that, if present in high concentrations in waterways, can cause excessive algae growth (eutrophication), harming aquatic life. Traditional biological wastewater treatment, often using activated sludge, primarily focuses on removing organic matter through the action of microorganisms. These microorganisms consume the organic matter as food, breaking it down. However, phosphorus removal in conventional activated sludge is limited, relying on naturally occurring biological phosphorus uptake. EBPR significantly improves phosphorus removal by manipulating the conditions within the treatment system to encourage the growth of specific microorganisms called Phosphorus Accumulating Organisms (PAOs). PAOs are bacteria that have a unique ability: they can store excess phosphorus within their cells under alternating anaerobic and aerobic conditions.

EBPR operates in a sequence of distinct zones. First, the *anaerobic zone* is where PAOs are starved of readily available organic matter (like sugars). During this phase, PAOs release the phosphorus they previously stored, converting it into polyphosphate (a complex form of phosphorus stored within the cell) and using acetate (a simple organic acid) as an energy source. This release lowers the phosphorus concentration in the wastewater. Next, the *aerobic zone* provides oxygen. Here, PAOs consume readily available organic matter, using the energy gained to take up phosphorus from the wastewater and store it as polyphosphate within their cells. This uptake significantly reduces the phosphorus concentration. The sludge containing the PAOs, now rich in phosphorus, is then removed from the system. This removal prevents the phosphorus from being released back into the environment and allows for potential phosphorus recovery (e.g., creating fertilizer). The alternating anaerobic and aerobic conditions are crucial for the PAOs to function effectively. Without the anaerobic phase to release phosphorus, the aerobic phase would not be as efficient at uptake. The process also effectively removes organic matter, as the PAOs, like other microorganisms in biological treatment, consume it as a food source. EBPR is more complex than conventional activated sludge, requiring careful control of operating parameters like pH, dissolved oxygen, and the ratio of readily biodegradable to slowly biodegradable organic matter. However, its superior phosphorus removal capabilities make it a preferred choice for wastewater treatment plants facing stringent phosphorus discharge limits.