Views: 315 Author: Site Editor Publish Time: 2024-09-13 Origin: Site
In wastewater treatment, total nitrogen and phosphorus are two key indicators, respectively, reflecting the nitrogen and phosphorus content in the water body. Excessive discharge of these elements will lead to eutrophication of water bodies and cause water pollution problems.
Table of contents（Click to go to where you want to see）
1. Wastewater treatment index Total nitrogen (TN)
1.1 Main sources of total nitrogen (TN) in wastewater
1.2 Methods for Removing Total Nitrogen (TN) from Wastewater
1.3 What is the indicator of total nitrogen (TN) in wastewater treatment?
2. Wastewater treatment Total Phosphorus (TP)
2.1 How Total Phosphorus (TP) in Wastewater is Generated
2.2 How to remove total phosphorus (TP) during wastewater treatment?
Domestic sewage is one of the main sources of total nitrogen in urban sewage. This mainly comes from people's daily life, such as washing, excretion, eating, etc. Among them, the nitrogen-containing substances in human excrement, under the action of bacteria, undergo processes such as ammoniation and nitrification, and finally form ammonia nitrogen, nitrate nitrogen and other forms in sewage1. In addition, food residues, detergents, etc. also contain a certain amount of nitrogen.
Nitrogen-containing wastewater is produced in many industrial production processes, such as chemical, pharmaceutical, food processing and other industries. The nitrogen in these wastewaters mainly comes from raw materials, intermediates and final products, as well as wastewater discharge during the production process. For example, the total nitrogen in printing and dyeing wastewater mainly comes from urea and nitrogen-containing organic dyes.
In agricultural production, fertilizers, pesticides, livestock and poultry breeding, etc. will produce nitrogen-containing wastewater. In particular, the use of fertilizers, the nitrogen in which is easily flushed into the water body by rainwater, causing nitrogen pollution in the water body.
In addition to the above three main sources, total nitrogen in urban sewage may also come from other sources, such as atmospheric deposition, rainwater erosion, etc. Although these sources contribute relatively little to total nitrogen, they may also become important sources of nitrogen pollution in certain specific cases.
Many industrial wastewaters contain a large amount of nitrate nitrogen. For example, the chemical and defense industries use nitrate materials as raw materials or oxidants, and livestock feed factories use nitrates or nitrites as antioxidants, which can produce wastewater containing nitrate nitrogen.
Organic nitrogen compounds are decomposed and converted into ammonia nitrogen under the action of ammonifying bacteria. This process is called ammoniation reaction. For example, amino acids are decomposed into ammonia nitrogen and carbon dioxide under the action of ammonifying bacteria.
Nitrifying bacteria convert ammonia nitrogen into nitrite and nitrate. This process involves two steps: first, ammonia nitrogen is oxidized to nitrite, and then nitrite is further oxidized to nitrate.
Under anaerobic conditions, denitrifying bacteria reduce nitrates to nitrogen gas, thereby removing total nitrogen. This method is suitable for treating wastewater with high nitrogen concentrations.
In summary, total nitrogen in wastewater mainly comes from domestic sewage, industrial wastewater, agricultural drainage and other pathways, including organic nitrogen conversion, nitrification and denitrification. These sources and conversion processes together lead to the production of total nitrogen in wastewater.
In wastewater treatment, total nitrogen (TN) is an important water quality indicator, and its removal methods mainly include biological, chemical, and physical methods. The following are detailed removal methods and their applications:
The biological method mainly converts total nitrogen into harmless substances through the action of microorganisms.
Biological denitrification
Anaerobic/anoxic/aerobic (A2/O) process: This wastewater treatment process can simultaneously remove nitrogen and phosphorus, including three stages: anaerobic, anoxic, and aerobic. In the anaerobic stage, anaerobic microorganisms are used to treat organic matter in wastewater to produce biogas; in the anoxic stage, denitrifying bacteria are used to convert nitrate nitrogen into nitrogen gas; in the aerobic stage, nitrifying bacteria are used to convert ammonia nitrogen into nitrate nitrogen.
Denitrifying polyphosphate strains: Denitrifying polyphosphate strains selected from the activated sludge in the outer ditch of the oxidation ditch of the sewage treatment plant can remove nitrate nitrogen and total phosphorus in the wastewater.
The chemical method mainly removes these pollutants by adding chemical agents to react with total nitrogen to generate precipitates or gases.
Ammonia nitrogen remover: suitable for removing ammonia nitrogen from total nitrogen. Depending on the water quality, the treatment effect is different.
Ion exchange: remove total nitrogen by exchanging ion exchange resin with nitrogen ions in wastewater.
Membrane permeation: using membrane permeation technology, remove total nitrogen from wastewater through the selective permeation of semipermeable membrane1.
Adsorption method: The treatment effect is better to sing activated carbon and other adsorbents to adsorb nitrogen in wastewater.
The physical method mainly removes total nitrogen through physical means, such as filtration and precipitation.
Activated carbon adsorption: Using the enormous specific surface area of activated carbon to absorb the residual phosphorus in the wastewater fully makes the treatment effect better.
In wastewater treatment, the methods for effectively removing total nitrogen mainly include biological, chemical, and physical processes. Each method has its scope of application and advantages and disadvantages. In practical applications, multiple techniques are usually combined to achieve the best treatment effect.
The index of total nitrogen (TN) in wastewater treatment refers to the sum of all nitrogen compounds in wastewater, mainly including the following forms:
Organic nitrogen:
nitrogen present in organic matter such as proteins and amino acids.
Ammonia nitrogen (NH₃-N):
nitrogen in the form of ammonia or ammonium ions in wastewater.
Nitrite nitrogen (NO₂-N):
nitrogen in the form of nitrite in wastewater.
Nitrate nitrogen (NO₃-N):
nitrogen in the form of nitrate in wastewater.
The index of total nitrogen usually includes the following aspects:
Total nitrogen concentration is usually expressed in millimoles per liter (mmol/L) or milligrams per liter (mg/L).
In wastewater treatment, the total nitrogen removal rate is an essential indicator for measuring the treatment effect. The removal rate refers to the ratio of the total nitrogen concentration in the water after treatment to the total nitrogen concentration before treatment.
Different countries and regions have different standards for the total nitrogen content in wastewater discharge. For example, China's Integrated Wastewater Discharge Standard (GB 8978-1996) stipulates different levels of discharge standards.
To ensure the effectiveness of wastewater treatment, the total nitrogen concentration needs to be monitored regularly. Online monitoring equipment can monitor the total nitrogen concentration in wastewater in real-time to help control and adjust the treatment process.
Domestic sewage is one of the primary sources of total phosphorus. Using phosphorus-containing detergents is the primary source of phosphorus in domestic wastewater. The phosphates in these detergents flow into water bodies with sewage, causing a significant increase in phosphorus content in water bodies.
Human waste is also an essential source of phosphorus in domestic sewage.
Phosphorus in industrial wastewater mainly comes from chemical, papermaking, rubber, dye, textile printing and dyeing, pesticide, coking, petrochemical, fermentation, pharmaceutical and medical, and food industries. Wastewater discharged from these industries often contains organophosphorus compounds.
The sources of phosphorus in industrial wastewater also include phosphate wastewater generated during the production of phosphorus chemicals and metal surface treatment.
Agricultural drainage is another important source of total phosphorus. Excessive use of phosphate fertilizers is the primary source of phosphorus in agricultural drainage water.
Agricultural waste, such as livestock manure, is also an essential source of phosphorus.
Rainfall and snowfall also bring some phosphorus, albeit in lower amounts.
Surface runoff and groundwater can also carry phosphorus into water bodies.
Phosphorus contained in sediments within water bodies can also be released into water bodies under certain conditions, especially when water bodies become eutrophic.
To sum up, total phosphorus in wastewater mainly comes from releasing domestic sewage, industrial wastewater, agricultural drainage, and sediment sediments inside water bodies. These sources together lead to the accumulation of total phosphorus in water bodies, which may lead to problems such as eutrophication of water bodies.
In the process of wastewater treatment, the methods for removing total phosphorus (TP) mainly include chemical precipitation, biological treatment, adsorption, membrane separation, plant absorption and pretreatment. The following is a detailed introduction to these methods:
Chemical precipitation method is to add chemical agents (such as aluminum salts, iron salts, calcium salts, etc.) to the wastewater to react with phosphates in the water to form insoluble phosphate precipitates, and then remove them from the water by precipitation or filtration. This method is fast, but the cost is high.
The biological treatment method mainly uses the action of microorganisms to absorb phosphorus into cells through cell synthesis, and then release phosphorus under anaerobic conditions, and achieve phosphorus removal by discharging phosphorus-rich residual sludge. This method is low-cost, but the cycle is long.
The adsorption method uses materials with high phosphorus adsorption capacity (such as zeolite, activated carbon, bone charcoal, etc.) to adsorb phosphates in water. This method has the advantages of large capacity, low energy consumption, low pollution, fast removal and recyclability.
Membrane separation method includes technologies such as reverse osmosis (RO) and nanofiltration (NF), which can effectively remove phosphates from water. This method is suitable for the treatment of high-concentration phosphorus, but the equipment investment and operating costs are high.
In wetland or artificial wetland systems, aquatic plants can absorb phosphorus in water, and then remove phosphorus by harvesting plants. This method is suitable for the treatment of low-concentration phosphorus and has ecological benefits.
Through pretreatment steps such as pre-oxidation and pre-acidification, the existence form of phosphorus is changed to make it easier to remove in subsequent treatment processes. This method can improve the efficiency of subsequent treatment processes.
Electrodialysis method is a membrane separation technology that uses the voltage between the positive and negative membranes to remove solids from the aqueous solution, produce two types of phosphorus-containing wastewater, and then precipitate the high-phosphorus wastewater with metal salts.
Ion exchange method uses ion exchange resin to exchange with phosphate in water to remove phosphorus. This method is suitable for the treatment of high-concentration phosphorus, but the resin needs to be regenerated regularly.
In practical applications, it is usually necessary to combine multiple methods to achieve the goal of phosphorus removal in order to meet environmental protection standards and water protection requirements. For example, chemical precipitation and biological treatment can be used in combination to improve treatment efficiency and reduce costs.
In summary, the removal of total phosphorus (TP) in wastewater can be achieved through a variety of methods, and the specific method to be selected depends on factors such as the specific properties of the water, the concentration of phosphorus, the required effluent quality, and cost-effectiveness.
