Currently popular sewage water treatment technologies include: AB process, SBR process, oxidation ditch process, conventional aeration process, membrane separation and so on, each with its own characteristics.
This process divides the aeration tank into two levels according to high and low loads. Level A has a high load, a short aeration time, a large amount of sludge produced, a sludge load of more than 2.5kgBOD/(kgMLSS•d), and a volumetric load of more than 6kgBOD/(m3•d). Level B has a low load and a longer sludge age. Level A and B can also be built in stages, and an intermediate settling tank is set between the two levels. The F/M (the ratio of pollutants to microbes) of the two levels of tanks are different, forming different microbial communities. Although AB process has the advantage of energy saving, it is not suitable for low concentration water quality.
This sewage water treatment process completes the processes of inflow, aeration, precipitation and outflow in a single tank. It is generally composed of 3-4 tanks that operate in a cyclical and periodic manner, also known as sequencing batch activated sludge process. The characteristic of this integrated process is its simplicity. As there is only one reaction tank and no need for secondary sedimentation tanks, return sludge or related equipment, and often no need for a regulating tank, and in most cases, the primary sedimentation tank can be omitted, thus saving land and investment. The process is resilient to shock loads, and its operation is flexible enough to arrange different aeration, anoxic and anaerobic states to achieve the purpose of phosphorus and nitrogen removal.
The conventional aeration process has good actual treatment effect and can handle large amounts of sewage. For sludge digestion tanks built in a centralized manner, the produced biogas can be used as an energy source. The shortcoming of the traditional aeration process is that it can only be used as a conventional secondary treatment and does not have denitrification and phosphorus removal functions. In recent years, in engineering practices, denitrification can be achieved by reducing the volumetric load of conventional aeration tanks. Phosphorus can be removed by setting an anoxic zone before the conventional aeration tank, or by chemical means. There are various forms of conventional aeration methods for BOD removal, such as oxidation ditch, which is called a variant process of the conventional aeration process, which can also be collectively referred to as a conventional aeration process.
It was developed and formed in the early 1950s. Due to its simple structure and easy management, it was quickly promoted and continuously innovated. At present, the oxidation ditch has developed into many forms, including:
Pasveer, also known as single ditch type, uses brush aerator on the surface, with a water depth generally ranging from 2.5-3.5m.
Orbal, also known as concentric circle type, mostly consists of elliptical three-loop channels, such as outer loop is 0, middle loop is 1, and inner loop is 2, which is conducive to denitrification and phosphorus removal. A disc aerator is used with a water depth generally around 4.0-4.5m.
Carrousel, also known as circulating flow type, uses inverted umbrella-shaped impeller aerator, with a water depth generally around 3.0m, but sludge is easily deposited.
Triple-ditch oxidation ditch process is composed of three tanks, with the middle tank serving as the aeration tank, and the other two tanks serving as the sedimentation tank and the aeration tank. Its characteristic is to use brush aerator, shallow water depth, large land area, no anoxic tank, and no phosphorus removal function.
Replacing sedimentation with membrane separation for sludge/water separation brings the following changes to the activated sludge process:
No more sludge bulking problems. When adjusting the activated sludge system, there is no need to consider the sedimentation performance of the sludge, making process control much simpler;
The sludge concentration in the aeration tank will be greatly improved, and the MLSS can be higher than 20g/L, which enables the system to operate under ultra-long sludge age and ultra-low load conditions, fully meeting the needs of removing various pollutants;
Under the same processing requirements, the volume of the aeration tank can be greatly reduced, saving the land area of the plant;
Due to the high sludge concentration, a higher aerator rate is required, and therefore pure oxygen aeration will be widely used with the separation of the membrane.