Influencing factors of principle, configuration and efficiency of biological aerated filter 1

The application of biofilm process in wastewater treatment has a long history. As early as 1914, before the invention of activated sludge process, biofilm process had been applied to wastewater treatment. Since the technology has been applied rapidly, it has attracted the attention of researchers all over the world. Through continuous research, the process has developed from low-load biofilter, high-load biofilter, tower biofilter (the first generation biofilm process) to biological contact oxidation, submerged biofilter, biological fluidized bed (the second generation biofilm process) and other processes. Until the late 1980s and early 1990s, the third generation of biofilm technology - Biological Aerated Filter (BAF).

The process was initially applied to the three stage treatment of sewage, and then developed into direct two stage treatment. At present, it is widely used in Europe, America, Japan and other developed countries. At present, more than 3500 sewage treatment plants in the world use this technology. In China, this technology is gradually used in sewage treatment.

Classification of biological aerated filter

Biological aerated filters can be classified into:

DC-BAF, which aims at organic matter removal, is used in industrial wastewater with good biodegradability and domestic wastewater without special requirements for ammonia nitrogen. It mainly removes organic carbide from wastewater and suspended solids in intercepted wastewater, i.e. removing BOD, COD and SS.

N-BAF with the goal of nitrification removal: Suitable for situations where nitrification is only required (emission standards only require ammonia nitrogen but not total nitrogen). The whole filter is in aerobic condition and the main microorganism is autotrophic nitrifying bacteria.

DN-BAF for nitrogen removal: suitable for occasions where water is required for total nitrogen. The filter has no aeration pipeline and is in anaerobic state. Under anaerobic conditions, NO3 - N and NO2 - N are reduced to N2 by nitrifying bacteria.

NP-BAF for nitrogen and phosphorus removal is achieved by adding chemical phosphorus removal agents to remove phosphorus from the filter. Under the action of filter media induced flocculation, sediment intercepted in the filter bed, through periodic backwashing, phosphorus will be excluded from the system, to achieve the purpose of phosphorus removal. The excess sludge increased by 15%-50%.

Principles of biological aerated filter technology

The principle of biofilter water purification is the oxidation and decomposition of microorganisms in the biofilm growing on the filter media, the adsorption and interception of filter media and biofilm, the graded predation of food chain along the direction of water flow, and the denitrification of micro-environment and anaerobic section in the biofilm.

When the sewage flows through the filter media, the biofilm with high activity is attached on the surface of the filter material and aerated inside the filter. When the biofilm is mature, the organic pollutants in the sewage are absorbed and degraded by the microorganisms in the biofilm, and then purified. The surface layer of biofilm grows aerobic and facultative microorganisms. Organic pollutants are degraded by aerobic metabolism of microorganisms. The end products are H2O, CO2, NO3 - and so on. Oxygen has been exhausted on the surface of the biofilm, and the microorganisms in the inner layer of the biofilm are in anaerobic state. The end products are organic acids, ethanol, aldehydes, H2S, N2 and so on. The filter media itself can intercept and absorb suspended substances in sewage. In addition, a large number of microorganisms grow on the filter media after culture. The viscous substances produced by the metabolism of microorganisms, such as polysaccharides and esters, act as adsorption bridging, and bind with suspended particles and colloidal particles to form small flocs, passing through. It is removed by contact flocculation.

Due to the continuous propagation of microorganisms, the biofilm gradually thickens. After exceeding a certain thickness, the absorbed organic matter has been metabolized before it is transferred to the microorganisms in the biofilm inner layer. At this point, the inner microorganisms can not get enough nutrition and enter the endogenous metabolism, losing its adherence to the filter media performance, peeling off with water out of the filter, filter media surface re-grow a new biofilm.