Why can biological enzyme degradation of organic matter in wastewater prevent eutrophication of water bodies?

Water eutrophication refers to the process in which large amounts of elements such as nitrogen, phosphorus, and potassium are released into surface waters with slow flow rates and long renewal cycles. This leads to excessive growth and reproduction of aquatic organisms like algae, causing the rate of organic matter production to far exceed its rate of consumption. As a result, organic matter accumulates in the water, disrupting the aquatic ecological balance. Definition: Water eutrophication refers to the phenomenon where, as a result of human activities, large amounts of nutrients such as nitrogen and phosphorus, which are essential for organisms, enter slow-flowing water bodies such as lakes, rivers, and bays. This leads to rapid proliferation of algae and other plankton, a decrease in dissolved oxygen levels in the water, deterioration of water quality, and mass deaths of fish and other aquatic organisms. Under natural conditions, lakes can also transition from eutrophic to oligotrophic states, although this natural process is very slow. Eutrophication of water bodies caused by the artificial discharge of nutrient-rich industrial wastewater and domestic sewage can occur in a short period of time. When water bodies become eutrophic, phytoplankton multiply in large numbers, resulting in algal blooms (a natural ecological phenomenon characterized by the excessive growth of algae in freshwater bodies). Due to the different colors of the dominant phytoplankton, the water surface often appears blue, red, brown, milky white, and so on. This phenomenon is called red tide in the oceans. Mechanism: In surface freshwater systems, phosphates are usually the limiting factor for plant growth, whereas in seawater systems, ammonia and nitrate are those that limit plant growth and overall productivity. The substances that cause eutrophication are often nutrients that are present in limited amounts in these water systems. For example, in normal freshwater systems, phosphorus is usually limited; therefore, an increase in phosphate levels leads to excessive growth of plants. In seawater systems, phosphorus is not scarce, but nitrogen is limited, so the addition of nitrogen-containing pollutants eliminates this constraint, resulting in excessive plant growth. Domestic wastewater, as well as wastewater from industries such as fertilizer and food production, as well as agricultural drainage, all contain large amounts of nitrogen, phosphorus, and other inorganic salts. After natural water bodies absorb these wastewater streams, the nutrients in the water increase, which promotes the vigorous growth of autotrophic organisms; in particular, the numbers of blue-green and red algae increase rapidly, while other types of algae gradually decline. Algae in water bodies are primarily diatoms and green algae; an increase in blue algae is a sign of eutrophication, and as eutrophication progresses, blue algae eventually become the dominant type. Algae reproduce rapidly and have a short growth cycle. After algae and other plankton die, they are decomposed by aerobic microorganisms, which continuously consume the dissolved oxygen in the water; or they are decomposed by anaerobic microorganisms, which produce gases such as hydrogen sulfide, thereby deteriorating water quality in two ways and leading to the mass death of fish and other aquatic organisms. As algae and other planktonic organisms decompose, they release large amounts of nutrients such as nitrogen and phosphorus into the water, which are then available for use by new generations of algae and other organisms. Therefore, in eutrophied water bodies, even if the source of external nutrients is cut off, it is very difficult for the water to purify itself and return to a normal state.

While degrading the organic matter in wastewater, ammonia nitrogen, total phosphorus, and other substances are removed as well.