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Analysis of Air Flotation Technology in Sewage Treatment


Sewage has always been an important factor affecting environmental pollution. Scientific methods should be found as soon as possible to solve the sewage discharge and disposal problems for the society sustainable development. So far the most important method is air floatation, this article mainly introduces the principle of air floatation treatment of sewage in the process of industrial development, and describes the classification, influencing factors and research status of air floatation technology.


Analysis of Air Flotation Technology in Sewage Treatment


1.Introduction

In today’s society, the material life is increasingly abundant, the environmental pollution has become the focus of global attention. Sewage has caused great harm to humans, animals, plants and even the entire ecosystem. Therefore the sewage treatment and recycling have become an important part of environmental protection.

Currently, the wastewater treatment process include air flotation treatment, microbial treatment and sedimentation. The air flotation treatment is a solid-liquid separation or liquid-liquid separation technology, as an effective separation technology, it will surely be promoted.


2.Air Flotation Technology Overview

Air flotation technology has been developed in China for decades. The basic principle is to introduce certain air into the sewage to produce a large amount of small air bubbles in water, then the impurity particles will adhere to the air bubbles and float together with the air bubbles, then separate the impurities from the water. The water treated by the air flotation technology is generally added appropriate flocculants to form a floc which is filled with water and network structure. The flocculation has a slow sedimentation velocity, so that the proportion of the floc which adheres to a certain amount of bubbles will be smaller than the proportion of the water, this will makes the floc floating speed faster than the initial floc falling speed, and the air flotation separation time will be greatly shortened.


2.1 Air flotation technology features

Although the process of air floatation is complicated and not easy to operate, but the advantages make it widely popularized. Due to the high surface loading of air flotation tanks, the solid-liquid separation time is short, and the reaction to coagulation has low requirements and floor space which could save much land resources. The water and scum in the air flotation tank contain oxygen, so that the sludge is not easily corroded and convenient for later treatment or reuse. Especially for some difficult-to-precipitate low-turbidity algae water, after the air flotation process, the dross has low moisture content and small volume, which is beneficial to the subsequent treatment of sludge. Air flotation requires less chemical dosing than precipitation.


2.2 Air flotation technology influence factors

There are many influencing factors in the air flotation technology, including floc impurity particles, air bubbles, added air volume, gas velocity, flotation agent and temperature etc. Here we mainly introduce four factors: temperature, added air volume, gas velocity and flotation agent.


2.2.1 Temperature

The temperature can significantly change the state of the entire system, such as the solubility and stability of the entire system. The affect of temperature on the entire system depends mainly on the type of the entire airfoil system. If there is different airfloat systems, the temperature will have different effects on different systems.

Cause that the entire adsorption reaction will release a large amount of heat, the adsorption reaction will be slowed by the increase of temperature, which is the advantage of physical adsorption. If the dissociation situation varies with the increase of temperature, which is the advantage of chemical adsorption. In the process of solvent frothing, as the absorption is an exothermic process, the separation efficiency will generally decrease as the temperature increases. When the temperature decreases, the absorbed amount of flotation compound on the bubbles increases, and the separation efficiency increases. In the process of precipitation and air flotation, the increase of temperature will be beneficial to the growth of the particles, but at the same time, it also increases the solubility of the precipitate, reduces the stability of the foam, and it’s not conducive to the entire process of the air flotation process.


2.2.2 Added air volume

The so called dissolved air flotation technology is that the high pressure dissolves the air in the water, then releases the air dissolved in the water to provide a large number of bubbles for the following step. We should make the amount of gas introduced into the air more than the solubility of air in water, so that it can make the air in the water saturated environment. If the capacity of the gas is too small, it is very bad for air flotation because it cannot provide a large number of small air bubbles. However, if there is a lot of undissolved air in the device, when the pressure is released, these undissolved air will produce large bubbles to affect the air flotation effect. Others believe that the number of air bubbles required by air flotation technology is related to the turbidity of sewage. When the turbidity is high, more air bubbles are required and appropriate amount of air intake should be increased.


2.2.3 Gas velocity

Another important factor affecting the flotation process is the gas flow rate. When the ions and solvent float, the plate needs to have a small pore size. When the airflow rate is low, the separation effect will vary according to the change of airflow. However, in the case of high gas flow rates, there is no proportional relationship between gas-liquid separation and gas velocity. This is because the size of the bubble depends on the size of the gas velocity, and the larger the gas velocity is, the larger the bubble will be. At the same time, large bubbles can float faster, reducing the time for bubbles in the water. Therefore, it can be concluded that under the premise of ensuring the bubble size, it is advantageous to increase the air flow rate for air flotation.

 

2.2.4 Flotation agent

The addition of pharmaceutical agents has a great influence on the effect of air flotation on sewage treatment and it will sometimes plays a decisive role. The use of some auxiliary agents in the process of sewage treatment can well improve the efficiency of air flotation technology. Generally, non-hydrophilic contaminant particles tend to stick together with air bubbles, and hydrophilic contaminant particles do not easily float. In order to allow the hydrophilic impurities in the sewage to float out more easily, some different flotation agents are generally put into the sewage treatment process. The flotation agent can significantly enhance some of the surface characteristics of the impurity particles, making it easier for the impurity particles to adhere to the bubbles and float to the surface. Flotation agents are generally polar, or non-polar surfactants that have adsorbed, wetted. In order to improve the deoiling efficiency of air flotation, it is advisable to add some coagulants, demulsifiers and the like before the air flotation in order to allow air bubbles to adhere to the floc particles.

No category May 23,2018 HNAC Comments are closed

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