This crucial process protects water bodies and the environment
Phosphorus removal is a vital aspect of wastewater treatment that protects water bodies from nutrient pollution. By removing phosphorus, wastewater treatment plants help prevent algal blooms and eutrophication, ensuring healthier aquatic ecosystems, safer drinking water, and better recreational water quality. Below we explore some of the methods used to remove phosphorus from wastewater.
What happens if phosphorus isn’t removed from wastewater?
Phosphorus is a key plant nutrient that, in excess, can result in nutrient enrichment that leads to severe degradation in aquatic ecosystems. Phosphorus is a limiting nutrient for algal growth in many freshwater systems. When excessive amounts of phosphorus enter water bodies, it stimulates algal growth and dense algal blooms, known as eutrophication, which can pose a risk to environmental and public health.
These blooms can produce harmful toxins, deplete oxygen levels, and prevent sunlight from penetrating the water, harming water quality and aquatic life. Once the algae have consumed all the nutrients, they die and decompose, consuming dissolved oxygen in the water. This drop in oxygen levels can lead to mass die-offs of fish and other aquatic organisms that can’t tolerate the hypoxic conditions. This leads to a loss of biodiversity in freshwater systems.
Algal blooms can affect drinking water sources, leading to taste and odor problems, and algal toxins pose health risks to humans and animals. In 2021, the U.S. Centers for Disease Control and Prevention reported 117 human cases of illness and at least 2,715 animal cases of illness.
Eutrophic conditions can also affect recreational waters, making them unsafe for swimming and fishing, sometimes with socio-economic implications. Algal blooms cost the U.S. an estimated $10-100 million each year.
When excessive amounts of phosphorus enter water bodies, it promotes algal growth, leading to dense algal blooms, a phenomenon known as eutrophication, which can threaten both environmental and public health.
How is phosphorus removed from wastewater?
There are several processes that wastewater treatment plants can employ to remove phosphorus before discharging wastewater effluent into the environment. Some of the more common methods include chemical precipitation, biological removal, and advanced wastewater treatment technologies such as membrane filtration.
Chemical Precipitation: This method involves adding chemicals such as aluminum sulfate, ferric chloride, or lime to the wastewater. These chemicals react with dissolved phosphorus to form insoluble compounds that can be settled out and removed as sludge, or the resulting precipitate can be removed by filtration. Chemical precipitation can achieve high phosphorus removal efficiencies, often exceeding 90% depending on the chemical used, dosage, pH, and initial phosphorus concentration.
The advantage of chemical precipitation is that it is relatively simple to implement and very effective at achieving significant phosphorus reduction. The drawbacks of this method are that it can increase operational costs because of the chemicals, and it generates chemical sludge that must be disposed of.
Enhanced Biological Phosphorus Removal (EBPR): This treatment technology uses phosphate-accumulating organisms (PAO) that are cultivated in anaerobic conditions and released into aerobic conditions of an aeration tank. In an anaerobic environment, PAOs take up volatile fatty acids and release phosphorus into the water. In an aerobic environment, PAOs take up phosphorus from the wastewater and store it as polyphosphate. Once all the phosphorus has been consumed, the biomass containing PAOs is separated from the treated water, removing the stored phosphorus. EBPR processes can achieve phosphorus removal efficiencies in the 80-95% range.
The advantage of using EBPR over chemical precipitation for phosphorus removal is that it does not require chemicals and can be integrated into existing biological treatment processes, including conventional activated sludge and biological nutrient removal systems that target both nitrogen and phosphorus. It also produces significantly less sludge and does not produce a precipitate that may need to be removed by filtration. The drawback of using EBPR is that it requires careful control of environmental conditions and may be less effective in colder climates or inconsistent influent conditions.
Membrane Filtration: This advanced treatment technology uses semipermeable membranes to physically separate phosphorus and other contaminants from the water. There are four types of membrane filtration technologies commonly used in wastewater treatment processes: microfiltration, ultrafiltration, nanofiltration, and reverse osmosis.
Microfiltration and ultrafiltration membranes can remove suspended solids and some larger dissolved organic molecules. While they are not very effective at removing phosphorus directly, they are often used in conjunction with chemical precipitation, where phosphorus is converted into a particulate form that can then be removed by microfiltration or ultrafiltration membranes to enhance phosphorus removal efficiency.
Nanofiltration and reverse osmosis membranes have much smaller pore sizes compared to microfiltration and ultrafiltration, and they remove dissolved salts, organic molecules, and even monovalent ions (in the case of reverse osmosis). As nanofiltration and reverse osmosis membranes can achieve high removal efficiencies for dissolved phosphorus, often exceeding 90%, their high rejection rates allow them to be used in stand-alone systems to directly remove dissolved phosphorus from wastewater in the form of phosphate ions.
Membrane filtration is an effective method for the removal of dissolved phosphorus from wastewater. While it offers high efficiency and consistent effluent quality, the technology requires careful management of fouling, substantial energy input, and considerable investment. However, by integrating membrane filtration with other treatment processes, wastewater treatment plants can enhance phosphorus removal capabilities and help prevent eutrophication in receiving water bodies.
Each of these removal methods, whether chemical, biological, or advanced membrane filtration technologies, plays a crucial role in maintaining the balance of nutrients and preventing the detrimental impacts of excessive phosphorus in the environment. Contact Seven Seas Water Group to learn more about the innovative solutions we offer and which would be best for your application.
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