what are the objectives of waste water treatment ? The objectives of wastewater treatment are a multi-tiered, systematic system.

These objectives can be divided into the following levels:

I. Core basic objective: Eliminate direct harm to public health and the environment, which is the most original and basic objective of wastewater treatment.

• Removing pathogens (sterilization and disinfection): The wastewater contains a large number of pathogenic microorganisms such as bacteria, viruses, parasitic eggs and so on, such as E. coli, cholera arcus bacteria, etc. The primary goal of treatment is to kill these pathogens, prevent the spread of waterborne diseases, and protect public health.

• Remove suspended solids: Suspended solids in wastewater can make the water cloudy and affect the senses. More importantly, solid particles can settle in riverbeds and lake beds, consume oxygen, destroy habitats for aquatic life, and may encapsulate harmful substances.

• Stable Organic Compounds: When organic matter in wastewater (such as feces and food residues) undergoes microbial decomposition, it consumes dissolved oxygen (DO) in the water. Direct discharge of such wastewater can lead to oxygen depletion in rivers and lakes, causing fish and aquatic organisms to die, and resulting in black, foul-smelling water (indicating anaerobic conditions). The treatment objective is to decompose these organic compounds and reduce their oxygen consumption capacity.

II. Environmental Protection and Ecological Balance Objectives: Eliminate long-term and indirect hazards. After the completion of the basic objectives, the higher level treatment aims to address deeper environmental problems.

• Nutrient Removal (Eutrophication Prevention): The primary focus is on eliminating nitrogen and phosphorus. While these nutrients support plant growth, excessive discharge into water bodies (such as lakes and bays) can trigger algal blooms. When these algae die and decompose, they consume massive amounts of oxygen again, ultimately causing ecosystem collapse and creating “dead zones”.

• Removing toxic and harmful substances: This includes heavy metals (such as mercury, lead, chromium), toxic chemicals (like cyanide, pesticides, industrial solvents), and persistent organic pollutants. Even at low concentrations, these substances accumulate in organisms and are amplified through the food chain, ultimately endangering both ecosystems and human health. They carry risks of causing cancer, birth defects, and genetic mutations.

III. Resource recovery and sustainable development goals: turning waste into treasure. This is a new direction for the development of modern wastewater treatment plants, shifting from the traditional “treatment and discharge” model to the “energy plant” and “resource recovery plant” model.

• Water recycling (reclaimed water reuse): The treated water (reclaimed water) is used for agricultural irrigation, industrial cooling, urban greening, car washing, toilet flushing and even groundwater replenishment, so as to reduce the exploitation of fresh water resources and alleviate the problem of water shortage. This is the most important way of resource recovery.

• Energy recovery: The sludge generated in the process contains a large amount of organic matter, which can be digested by anaerobic digestion technology to produce biogas (mainly composed of methane), which can be used for power generation or heat production, for the use of the plant itself or even to supply power to the grid, so as to realize energy self-sufficiency or external transmission.

• Material Recovery: Nutrient Recovery: Recover nitrogen and phosphorus from sludge or wastewater for agricultural fertilizer production. Utilization of Bio-solid (Sludge): The stabilized sludge after treatment, rich in organic matter and nutrients, can serve as soil conditioner or fertilizer for agriculture and forestry. Other Resources: Explore the recovery of other valuable substances from wastewater, such as cellulose and bioplastics.

In conclusion, the goal of wastewater treatment is a progressive pyramid structure:

• Basement (basic requirements): meet the discharge standards, eliminate pollution, ensure that the effluent meets the national and local discharge standards, protect the receiving water body and public health.

• Intermediate (advanced requirements): ecological protection, environmental friendliness, deep removal of nutrients and trace toxic substances, protection of more sensitive water ecosystems.

• Top level (future direction): resource recycling, sustainable development, treat wastewater as a treasure house of resources, recycle water, energy and useful substances, realize “turn waste into treasure”, promote the development of circular economy.

Therefore, the goal of modern wastewater treatment has gone beyond the simple “purification”, but towards the protection of the environment, health, recycling of resources a trinity of comprehensive system engineering.