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The basic method of wastewater treatment
The principle of wastewater treatment involves separating or breaking down the various pollutants present in the water into harmless substances, allowing the water to be purified and returned to the environment safely. To effectively apply wastewater treatment methods, it's essential to understand the nature, form, and physical-chemical properties of the pollutants. Generally, pollutants can be categorized into three main types: suspended solids, colloidal particles, and dissolved substances. However, classification is often based on particle size rather than strict definitions. Suspended solids typically range from 1 to 100 micrometers, colloids from 1 nanometer to 1 micrometer, and dissolved substances are smaller than 1 nanometer.
The size of the pollutants significantly influences the treatment approach. Larger particles like suspended solids are easier to remove through processes such as sedimentation, filtration, and flotation. In contrast, colloidal and dissolved substances require more advanced techniques, such as coagulation, chemical precipitation, adsorption, or membrane filtration, to increase their size or make them removable.
Wastewater treatment fundamentally aims to separate, remove, recycle, or convert pollutants into non-hazardous forms, ensuring that the treated water meets environmental and health standards. Modern treatment technologies are generally classified into three categories: physical, chemical, and biological treatments.
Physical treatment methods rely on physical forces to remove contaminants. Common techniques include screening, sedimentation, flotation, filtration, and reverse osmosis. These methods are effective for removing larger particles and some organic matter.
Chemical treatment involves using chemical reactions to remove or neutralize pollutants. Techniques include neutralization, coagulation, oxidation-reduction, adsorption, ion exchange, and electrodialysis. These methods are particularly useful for treating dissolved and colloidal pollutants.
Biological treatment utilizes microorganisms to break down organic pollutants. This method is divided into aerobic and anaerobic processes. Aerobic treatment, which uses oxygen-dependent bacteria, is widely used for municipal and industrial wastewater. Anaerobic treatment, which occurs without oxygen, is commonly applied to high-strength organic waste and sludge. Both methods are crucial in reducing organic load and improving water quality.
In addition to these, natural biological treatment methods such as stabilization ponds and land treatment are also used. Stabilization ponds use natural biological processes to purify wastewater, while land treatment involves distributing wastewater over land where soil and plants help filter and treat it.
The complexity of urban and industrial wastewater often requires a combination of treatment methods to meet discharge standards. Modern wastewater treatment systems are usually divided into primary, secondary, and advanced stages. Primary treatment focuses on removing floating and suspended materials through sedimentation. Secondary treatment uses biological processes to remove finer particles, colloids, and dissolved organic matter, including nitrogen and phosphorus. Advanced treatment further removes remaining contaminants using techniques like coagulation, adsorption, ion exchange, and membrane filtration.
When selecting a treatment method, it's important to consider the type of wastewater and the desired outcome. For organic wastewater, initial tests like BOD and COD measurements guide the choice between biological, chemical, or advanced treatments. For inorganic wastewater, settling tests and chemical adjustments may be necessary before considering further treatment steps.
If conventional methods fail, advanced techniques such as adsorption or ion exchange may be required. In extreme cases, changing the production process itself might be necessary to reduce the difficulty of treating the wastewater.
Overall, wastewater treatment is a complex but essential process that ensures the protection of water resources and public health. By understanding the nature of pollutants and applying the most suitable treatment methods, we can achieve effective and sustainable water purification.