There are several methods used to treat wastewater containing phosphate, including biological and chemical processes. Chemical methods use a chemical coagulant to break down phosphate, which is the main component of SS. These methods are also known as Enhanced treatment systems. However, there are several differences between biological and chemical processes. Here is a brief look at some of the differences.
Chemical methods
Chemical methods for treating wastewater from phosphate industry operations use chemical processes to remove phosphates. The process works by precipitating dissolved phosphates with the help of a trivalent metal ion. The ions are then released into the water and combined with dissolved phosphates to form a gel-like precipitate. This gel-like precipitate is removed from the water phase using filtration or clarification methods. This technique is rarely used as a stand-alone treatment method but is usually used as a downstream step to clarification.
The DM water treatment process uses deionisation to remove dissolved minerals from the water. The natural water contains a high level of dissolved salts, anions (sulphate), and cations (iron, calcium, sodium, copper, and bromide). These dissolved salts are detrimental to metal oxidation, scaling, and corrosion. DM plants are highly effective in removing these dissolved salts, leaving the water ultra-pure.
Phosphorus is a common water pollutant arising from a variety of processes. It is released into the water during fertilizer production, mineral processing, textile and leather processing, pigment formulation, and wastewater treatment. Phosphorus has caused significant eutrophication problems, resulting in changes in water discharge legislation worldwide. Currently, phosphorus concentration in wastewater is regulated to a maximum of two mg/l in sensitive waterways.
Chemical methods for treating wastewater from phosphate industry processes can efficiently remove phosphorus from effluents. These treatments can reduce P concentrations to as low as 0.5 mg/l. Moreover, they can improve settling efficiency and allow for cleaner clarifiers. Chemical methods are also cost-effective. Chemical methods require less maintenance and lower total costs than biological phosphorus removal. They can also provide a return on investment sooner than biological methods.
Biological methods
The process of treating wastewater from the phosphate industry involves removing inorganic phosphates from it using chemical precipitation. This process uses multivalent metal ions, such as calcium and aluminum, to precipitate phosphorus and other chemicals from the wastewater. Lime is a commonly used coagulant in this process. The lime increases the pH of the water, which is beneficial for phosphate removal. In addition, lime increases the concentration of calcium ions, which reacts with phosphates to precipitate hydroxyapatite.
The removal of phosphorus from wastewater requires a combination of chemical and biological methods. Chemical methods remove phosphorus through a gaseous phase, while biological methods involve the introduction of bacteria into the wastewater. The bacteria collect phosphorus in the water, forming a biodegradable sludge. The method selection depends on the region's water quality, the size of the wastewater treatment plant, and economic considerations.
Enhanced treatment systems
Enhanced treatment systems for wastewater phosphate industry operations use biological processes to remove phosphate from wastewater and recover it in a form more suitable for reuse. Biological processes are becoming more valuable as they can protect human health and the environment. Some biotechnologies also generate value-added chemicals and energy. Enhanced biological phosphorus removal systems are among the latest wastewater treatment configurations. They remove phosphate from wastewater by incorporating it into biological solids or chemical precipitates.
Phosphorus removal is the primary purpose of postprecipitation, a traditional treatment method for secondary effluent. This process removes P up to 0.5 mg/l by incorporating metallic reagents. However, it is important to note that postprecipitation can result in diluting the effluent.
Some enhanced treatment systems are equipped with a coagulant to further reduce phosphorus levels in wastewater. However, these systems are costly for municipalities and treatment plants. Other plants opt to optimize their existing equipment instead. This method saves energy and treatment chemicals and may be less expensive.
Biological phosphorus removal
Traditional chemical treatment systems are ineffective for reducing phosphorus in wastewater. Instead, facilities often respond by adding more chemicals, resulting in higher costs and more sludge and handling problems. Biological phosphorus removal is an alternative solution. Biological processes are not limited to phosphate industries.
Biological phosphorus removal is achieved by using bacteria that grow in an aerobic environment. These bacteria are able to accumulate and process large amounts of polyphosphate. The phosphate in wastewater is a nutrient for the bacteria and a source of energy. All bacteria contain phosphorus in their cellular components, including deoxyribonucleic acid (DNA) and membrane phospholipids. Bacteria also use this nutrient for energy and cellular maintenance.
The final phosphorus concentration in wastewater is lower than 0.5 mg/l. The dosage of lime is dependent on the pH level and the alkalinity of the wastewater. Using diagrams, phosphorus removal can be calculated by determining the amount of lime needed to raise pH levels.
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