How to use pure oxygen in wealth for “wastewater treatment” devices

The advantages of pure oxygen aeration over the commonly used air oxygenation are as follows: Mechanism of pure oxygen aeration and comparison with air aeration. The mechanism of the pure oxygen aeration process is essentially the same as that of the air aeration activated sludge method; in both cases, aerobic microorganisms carry out biochemical reactions on the organic substances in the wastewater to purify it. The difference is that the former introduces pure oxygen into the wastewater, while the latter introduces air into it. A major advantage of the oxygen method is that its processing efficiency is significantly higher than that of the air method. To treat wastewater to the same standard, the aeration time required by the oxygen method is generally only about 1/3 of that required by the air method. This is because the concentration of pure oxygen is 4.7 times that of oxygen in air (21%), so the partial pressure of oxygen in an oxygen-based system, which is the driving force for oxygen dissolution, is also 4.7 times higher than that in an air-based system. The saturation value C of dissolved oxygen in water increases by 4.7 times as well, and the oxygenation rate increases by 4.7 times, thereby significantly increasing the oxygen transfer rate. This leads to an increase in both the concentration and activity of aerobic microorganisms, effectively addressing the shortcomings of the conventional activated sludge process. Compared with air aeration systems, pure oxygen aeration systems have the following significant advantages: (1) The dissolved oxygen concentration can reach 6–10 mg/L, resulting in a high biomass load; this enables rapid adaptation to changing organic loads. At the same time, filamental bacteria in the sludge are suppressed, leading to the formation of dense floc particles with excellent sedimentation and thickening properties, with an SVI that is only 1/2 to 1/3 that of air-stabilized activated sludge ； (2) Under high-purity oxygen conditions, organisms are in a state of intense endogenous metabolism, namely self-oxidation, as a result of which sludge production is significantly reduced; pure oxygen aeration can reduce excess sludge by up to 25% ； (3) The oxygen transfer rate and utilization efficiency are high; the oxygen utilization rate with pure oxygen aeration reaches 90%, resulting in high treatment efficiency and low energy consumption ； (4) The retention time for treating the same wastewater is only 1/3 to 1/4 of that for air aeration, so the tank volume also decreases accordingly. The actual space required for the installation of pure oxygen aeration is much smaller than that of conventional systems ； (5) The noise level of the pure oxygen aeration system is much lower than that of the blower aeration system; there is virtually no emission of volatile organic compounds (VOCs), which reduces secondary pollution from sludge and waste gases and lessens the negative impact of wastewater treatment plants on the surrounding environment.

Study on the performance of activated sludge under pure oxygen aeration. Due to the changes in the environment within the tank, particularly changes in oxygen supply conditions and nutrient levels, activated sludge in tanks using pure oxygen aeration differs from that in conventional aeration tanks; these changes are mainly reflected in: (1) Sludge morphology: the flocs are smaller and more compact； (2) Number of sludge flocs: increases, total area increases ； (3) Sludge microbial composition: many bacterial aggregates, few filaments, and many swimming ciliates, few rotifers ； (4) Sludge metabolic capacity: The vitality of molds increases, and material and energy metabolism accelerates. It is precisely because pure oxygen is used instead of air in the oxygenation tank, and high load conditions are employed rather than normal load conditions, that changes occur in the quantity (sludge volume) and quality (sludge properties, composition, activity, etc.) of the microorganisms in the oxygenation tank. As a result, even when the sludge load and sludge concentration in the oxygenation tank are much higher than those in conventional oxidation tanks, the sludge in the oxygenation tank still maintains or even exceeds the performance of sludge from conventional oxidation tanks in terms of oxidation, adsorption, sedimentation, and concentration.

The following content is excerpted from the Internet and is for educational purposes only: 1. Aeration process and pure oxygen aeration. Aeration refers to the process in which water comes into contact with gas, thereby increasing the dissolved oxygen level or removing dissolved gases and volatile substances from the water. It is a process of forcing oxygen from the air into the liquid, with the aim of obtaining sufficient dissolved oxygen. In the activated sludge process for wastewater treatment, the dissolved oxygen in the mixed liquor must be replenished through aeration. 　　 Aeration can be achieved by the following methods: (1) Spraying the liquid into the air, such as in a biological filter ； 　　 (2) Allow air bubbles to diffuse through the liquid, such as by forced aeration ； 　　 (3) Continuously updating the liquid level to promote the transfer of air from the interface to the liquid phase, such as through mechanical aeration. Air aeration is a technique widely used in water treatment processes. However, since the oxygen content in air is only 21% and oxygen is a gas that is poorly soluble in water, using air aeration results in larger equipment sizes, greater land requirements, and higher investment costs. Thus, the pure oxygen aeration method, which uses pure oxygen instead of air, was developed. 　 Pure oxygen aeration activated sludge process is an efficient wastewater treatment method that was developed in the 1860s by Western countries on the basis of the traditional activated sludge process. In the United States and Europe, pure oxygen technology has been successfully applied to municipal and industrial wastewater treatment, with over 500 projects undertaken for the construction of new plants and the renovation of existing ones. These projects have achieved good results in improving the quality of wastewater discharged, increasing treatment capacity, enhancing flexibility, reducing energy consumption, and minimizing the amount of excess sludge. 　 Over 80% of the existing urban sewage treatment plants in our country use the conventional aeration activated sludge process, which presents problems such as high construction costs, large land requirements, susceptibility to shock loads, high energy consumption, and high production of excess sludge. In addition, some sewage treatment plants in China are currently operating beyond their capacity. Moreover, China’s newly issued \"Emission Standards for Pollutants from Urban Sewage Treatment Plants\" (GB18918-2002) came into effect on July 1, 2003, setting relatively strict standards for the emission of nitrogen and phosphorus by urban sewage treatment plants; as a result, existing plants face the need for further upgrades to meet these higher standards. Therefore, the pure oxygen aeration method, which uses pure oxygen instead of air, is attracting increasing attention. II. Introduction to the pure oxygen aeration process: The NUOX technology developed by United Carbon Corporation is the earliest and, at present, the most mature technology for wastewater treatment using pure oxygen aeration. This system features closed aeration tanks, allowing for optimal utilization of oxygen within those tanks. In the 1980s, our country introduced 6 UNOX systems, all of which were used for the treatment of petrochemical wastewater. Other pure oxygen aeration systems include the VITOX system from the British company ROC, the BIOX system developed by Messer (which is a microbubble pure oxygen aeration process), the Oxy-Dep system developed by Air Products and Chemicals, as well as PRAXAIR’s I-SOTM pure oxygen aeration technology. The application of pure oxygen aeration in China started with the petrochemical industry, and it has a wide range of applications in the treatment of refractory wastewater from other industries such as chemicals, light industry, metallurgy, pharmaceuticals, and especially the paper and dye industries. Currently, it is also used for reoxygenation of river waters and iron removal from groundwater, with good results achieved in both cases. Based on practical experience, pure oxygen aeration is more suitable for industrial wastewater with high concentrations and poor biodegradability. Oxygen is a gas that is poorly soluble in water. Experiments have shown that at a total pressure of 101.3–1013 KPa, its solubility follows Henry’s law. At normal temperature and pressure, the solubility of oxygen in water from the air is approximately 10 mg/L. Air aeration can increase the saturation level of dissolved oxygen in water to 80%-90%, meaning that the maximum concentration of dissolved oxygen in water can reach 8-9 mg/L. This is insufficient for some water treatment processes that require a high oxygen level. The oxygen percentage in pure oxygen is almost 5 times that in air; therefore, at normal temperature and pressure, pure oxygen can increase the solubility of oxygen in water to as high as 50 mg/L. When using pure oxygen for aeration, the concentration of dissolved oxygen in water can reach 40–45 mg/L. This is a significant improvement compared to air aeration, and the pure oxygen aeration method also allows for easy control of the dissolved oxygen concentration in water by adjusting the oxygen flow rate and pressure, thereby meeting the requirements of various water treatment applications. Oxygen mass transfer process: When temperature, water quality, and the intensity of gas-liquid mixing remain constant, the mass transfer rate of oxygen in water increases as its solubility rises, that is, as the oxygen partial pressure increases. Clearly, compared to air aeration, pure oxygen aeration can significantly increase the oxygen mass transfer rate. Replacing air with pure oxygen results in a higher mass transfer rate, thereby allowing the size of the aeration equipment to be reduced or increasing the oxygen supply capacity of the equipment. This is the theoretical basis for reducing equipment investment and floor space. III. Mechanism of pure oxygen aeration and comparison with air aeration The mechanism of the pure oxygen aeration process is essentially the same as that of the air aeration activated sludge process; in both cases, aerobic microorganisms carry out biochemical reactions on the organic substances in wastewater to purify it. The difference is that the former introduces pure oxygen into the wastewater, while the latter introduces air into it. A major advantage of the oxygen method is that its processing efficiency is significantly higher than that of the air method. To treat wastewater to the same standard, the aeration time required by the oxygen method is generally only about 1/3 of that required by the air method. This is because the concentration of pure oxygen is 4.7 times that of oxygen in air (21%), so the partial pressure of oxygen in an oxygen-based system, which is the driving force for oxygen dissolution, is also 4.7 times higher than that in an air-based system. The saturation value CS of dissolved oxygen in water increases by 4.7 times as well, and the oxygenation rate increases by 4.7 times, thereby significantly increasing the oxygen transfer rate. This leads to an increase in both the concentration and activity of aerobic microorganisms, effectively addressing the shortcomings of the conventional activated sludge process. A comparison of the various parameters for pure oxygen aeration and air aeration is shown in Table 1. Compared with air aeration systems, pure oxygen aeration systems have the following significant advantages: (1) The dissolved oxygen concentration can reach 6–10 mg/L, resulting in a high biomass load; this enables rapid adaptation to changing organic loads. At the same time, filamentous bacteria in the sludge are suppressed, leading to the formation of dense floc particles with excellent sedimentation and thickening properties, with an SVI that is only 1/2 to 1/3 that of air-activated sludge; (2) Under high-purity oxygen conditions, microorganisms are in a state of intense endogenous metabolism, i.e., self-oxidation, which significantly reduces sludge production – pure oxygen aeration can reduce excess sludge by up to 25%; (3) The oxygen transfer rate and utilization efficiency are high; the oxygen utilization rate with pure oxygen aeration reaches 90%, resulting in high treatment efficiency and low energy consumption; (4) The retention time required to treat the same amount of wastewater is only 1/3 to 1/4 of that in air aeration systems, so the volume of the treatment tank also decreases accordingly. The actual space required for the installation of pure oxygen aeration systems is much smaller than that of conventional systems; (5) the noise level of pure oxygen aeration systems is significantly lower than that of blower-based aeration systems, and there is virtually no emission of volatile organic compounds (VOCs), which reduces secondary pollution from sludge and waste gases and lessens the negative impact of wastewater treatment plants on the surrounding environment. IV. Common Types of Oxygen Aeration Tanks and Selection of Oxygen Supply Methods Common types of oxygen aeration tanks There are three common types of oxygen aeration tanks: (1) The covered surface aeration impeller type oxygen aeration tank is the most commonly used type. It is generally divided into 3 to 4 sections, with one aeration machine in each section. (2) The combined aeration oxygenation tank is an oxygenation tank equipped with a covered and sealed underwater impeller; it requires less space and is suitable for areas with limited land availability, but its construction cost is relatively high. (3) Open-type ultra-fine bubble oxygen aeration tanks can be easily modified from existing air aeration tanks, and their construction cost is low; meanwhile, to improve the utilization rate of oxygen, ultra-fine bubble diffusers must be used. Selection of oxygen supply method: There are mainly four options for selecting the oxygen supply method: (1) Transporting liquid oxygen purchased externally by vehicle. This method is the least economical and is limited to small treatment facilities. (2) Purchased oxygen is transported via pipelines. Suitable for large treatment facilities that are located near oxygen production plants, where the price of oxygen is lower than the cost of producing it internally. (3) On-site oxygen production. Deep-cold separation for oxygen production is a state-of-the-art oxygen generation technology, particularly suitable for large sewage treatment plants; currently, petrochemical companies such as Jinshan and Daqing use this method. Molecular sieve oxygen production is used more often in small sewage treatment plants. (4) Utilizing the oxygen released from nearby air separation plants: There are many nitrogen production air separation plants in China, and near those plants that release oxygen, this oxygen can be utilized comprehensively for wastewater treatment; at the current stage in China, this represents the best option. Study on the performance of activated sludge under pure oxygen aeration. Due to the changes in the environment within the tank, such as alterations in oxygen supply conditions and nutrient levels, activated sludge in tanks using pure oxygen aeration differs from that in conventional aeration tanks; there is a qualitative change, which is mainly reflected in: (1) Sludge morphology: the flocs are smaller and more compact ； (2) Number of sludge flocs: Increased, total area increased ； (3) Sludge microbial composition: Many bacterial aggregates, few filaments, and many swimming ciliates, few rotifers ； (4) Sludge metabolic capacity: The vitality of molds increases, and material and energy metabolism accelerates. It is precisely because pure oxygen is used instead of air in the oxygenation tank, and high loads are employed rather than normal loads, that changes occur in the quantity (sludge volume) and quality (sludge properties, composition, activity, etc.) of the microorganisms in the oxygenation tank. As a result, even when the sludge load and sludge concentration in the oxygenation tank are much higher than those in conventional oxidation tanks, the sludge in the oxygenation tank still maintains or even exceeds the performance of sludge from conventional oxidation tanks in terms of oxidation and decomposition, adsorption, sedimentation, and concentration. V. Selection of pure oxygen aeration methods: The following methods are commonly used for pure oxygen aeration: (1) The NUOX pure oxygen aeration activated sludge process developed by United Carbon Corporation, which utilizes a covered, sealed aeration tank along with impeller-type surface aerators; the tank is divided into 3–4 sections, with one surface aerator installed in each section. The 5 petrochemical companies of Sinopec in our country have adopted this technology. This technology uses surface aeration, which results in high energy consumption for aeration, and the cost of covering the aeration tank is also high. (2) The improved activated sludge treatment process developed by the American company Filter/Kruger (referred to as the OASES process) also uses covered, airtight aeration tanks. The interior of these tanks is divided into several compartments, with openings between them at the top of the tank, allowing the gas and liquid to flow sequentially from one compartment to another. Oxygen is supplied to the first compartment’s liquid surface from the top using a centrifugal compressor; it then enters the submersible impeller through its hollow shaft and is released into the wastewater being treated via nozzles on the impeller. Both the wastewater and oxygen enter through the first compartment, while the effluent and exhaust gas exit from the last compartment. The oxygen utilization rate can reach 90%. (3) The Biox-N process developed by the German company Messer is known as the open-type microbubble pure oxygen aeration activated sludge process. This process uses an open-type aeration tank, and the microbubbles used for pure oxygen aeration are generated by oxygen delivery pads made of special rubber materials with excellent elasticity and durability; the walls of these hoses are equipped with uniformly distributed tiny pores, through which oxygen can pass