The jet aeration activated sludge system mainly includes an integrated reactor, two-phase nozzles, sedimentation tank, and supporting pipelines and pumps. The integrated reactor is a circular container, with its outer cylinder closed at both ends and connected to various pipelines; The two ends of the inner cylinder are open, and the two-phase nozzles are installed in the center of the upper part of the reactor. The circulating water pump lifts the high-pressure water flow through the nozzle and injects it into the reactor, while also sucking in a large amount of air due to negative pressure. The combined action of water flow and air flow creates a high-speed turbulent shear zone below the nozzle, dispersing the inhaled gas into small bubbles. After the mixed sewage rich in dissolved oxygen reaches the bottom of the reactor through the guide tube, it flows back upwards to form a circulation, and then undergoes shear and downward jet flow, thus running in a cyclic manner. So, the sewage is repeatedly oxygenated, and bubbles and microbial communities are continuously sheared and refined, forming dense and fine flocs.
The jet aeration activated sludge process integrates current high-speed jet aeration, phase enhanced transfer, turbulent shear and other technologies, and has the characteristics of deep well aeration and fluidized sludge bed. Therefore, its high conversion rate of air oxygen, large reactor capacity load, and short hydraulic retention time are widely accepted as efficient aerobic biological treatment methods in Western countries. Compared with the traditional continuous activated sludge process, this system also has the following five characteristics:
The system occupies less land and has lower infrastructure costs.
The jet aeration activated sludge system generally occupies very little land, for three main reasons: firstly, the system design is compact and the structure is reasonable, reducing land occupation; Secondly, the reactor has a high aspect ratio and is partially buried underground, effectively utilizing vertical space and reducing the footprint on the plane; Thirdly, the required hydraulic retention time is very short, and the volumetric load and sludge load are both high, reducing the volume of the reactor. According to the comparison of existing engineering settlement results, using jet aeration activated sludge process to treat the same amount of sewage reduces the infrastructure cost by more than 40% compared to activated sludge process.
High utilization rate of air oxygen conversion, high volumetric load and sludge load
The aeration method of jet aeration activated sludge process adopts jet diffusion type, and through vertical circulation mixing, the dissolved oxygen reaches the maximum value. High speed jet forms turbulent hydraulic shear, making the bubbles highly refined and evenly dispersed, which determines the high conversion and utilization efficiency of air oxygen in this method. Adequate dissolved oxygen is the condition for ensuring high load operation of aerobic biological treatment systems, which is also the advantage of jet aeration activated sludge process. In general, the sludge concentration of the jet aeration activated sludge system is around 6-10g/L, and can exceed 15g/L. The large biomass in the reactor determines that its load value is inevitably high. The operational results of existing projects have shown that the maximum volumetric load of jet aerated activated sludge can reach 70kg BOD5/(m3 · d), and its sludge load value can exceed 6kg BOD5/(kgSS · d).
Good solid-liquid separation effect with less residual sludge
The microbial community particles in the mixed wastewater of jet aeration activated sludge process are small, and their settling performance is good, which is one of its significant characteristics. The residence time of sludge in the settling tank is generally only about 40 minutes. The residual sludge generated by this process for every 1kg of BOD degradation is reduced by an average of about 40% compared to other aerobic methods, greatly reducing the sludge treatment capacity. There are two main reasons for the low amount of remaining sludge: firstly, strong aeration accelerates microbial metabolism, which may increase endogenous consumption and result in relatively low remaining sludge; Secondly, due to the high-speed circulating liquid flow shearing the mixed sewage in the reactor, the microbial clusters are continuously segmented and refined, and the pores inside the clusters are reduced, resulting in a relative increase in density and a decrease in overall volume.
Strong ability to withstand impact loads
Jet aeration activated sludge operates in a fully mixed mode, where the raw water is first combined with the reflux sewage before entering the reactor and immediately being rapidly circulated and mixed. When high concentration COD or toxic wastewater impacts the system, they are actually diluted before entering the reactor, and quickly and uniformly mixed after entering the reactor, greatly reducing the concentration of the impact liquid flow and effectively improving the anti impact load capacity of the jet aeration activated sludge system. In addition, strong aeration can accelerate the metabolism of microorganisms, which may also reduce some of the impact caused by shock.
The system operation is simple and flexible, and the processing effect is guaranteed
The circulating water volume, supplementary aeration volume, and sludge reflux rate of the jet aeration activated sludge system can be adjusted as needed to facilitate the selection of the optimal combination effect. Therefore, the use of jet aeration activated sludge process can easily ensure a high COD removal rate.
