Views: 214 Author: nanombr Publish Time: 2018-08-01 Origin: Site
Air distribution system
The process air distribution system (oxygen aeration) and the air supply system (backwash aeration) for the combined backwash of air and water.
Process air distribution system: Maintain sufficient dissolved oxygen in the biological aerated filter and maintain high activity of biofilm in the filter. Biological aerated filter generally adopts blast aeration, air diffusion system generally has perforated air pipe air diffusion system and special air diffusion system, the device (EPT) is installed in the air pipe at a certain interval, from the supporting plate about 0.1-0.15 m, air through the diffuser parallel flow filter media layer can be up to 30%. Oxygen utilization rate is not easy to plug.
Backwash system
It is composed of backwash water supply system and backwash air supply system.
Gas-water combined backwashing is used to remove various particles, colloidal contaminants and microbial membranes from the filter during operation. The water distribution and gas distribution of the combined backwash system is realized through a filter plate and a long handle filter fixed on it. During backwashing, the air cushion layer is formed under the backwash air intake and the filter plate, and then the air enters from the air intake hole at the upper end of the long handle filter head, and the backwash water enters from the water intake hole at the lower end of the long handle filter head.
The backwash process is generally divided into three steps: gas washing, gas water simultaneous backwashing and water rinsing. The purpose of gas washing is to loose the filter material layer and expand the filter layer. The gas washing intensity is generally 10~15L/ (m2*S) and the time is 5min. The purpose of air-water simultaneous backwashing is to flush out suspended solids and aged biofilm from the filter material. The washing intensity is 5.0-8.5 L/(m2*S) and the time is 5-8 minutes. The purpose of water rinsing is to rinse out the suspended matter and the aged biofilm on the upper surface of the filter material for 5-8 minutes. The expansion rate of the filter layer is about 10%.
Effluent system
The effluent system can be divided into two types: the surrounding weir or the single weir. In large and medium-sized sewage treatment plants, unilateral weir is usually used to discharge water, and the outlet of the weir is designed as a 60 degree slope to reduce the outflow velocity. A grid shaped stabilizer plate is arranged at the outlet of the outlet of the water outlet to intercept the filter material brought out by the water during backwashing.
Factors affecting the treatment effect of biological aerated filter
Water temperature
Water temperature is the main reason that affects the growth and metabolic activity of microorganisms. The metabolic activity of most microorganisms increases with the increase of temperature and decreases with the decrease of temperature. According to the Airheniuslls formula, the biochemical reaction rate will be doubled as the temperature does not drop by 10 degrees. The suitable temperature for bacteria to grow and reproduce is between 25 and 35 degrees Celsius. Therefore, the treatment effect of BAF is the best in summer when the temperature is high, but in winter when the water temperature is low, the activity of biofilm is inhibited, the treatment effect is affected, and the quality of effluent is poor.
PH and alkalinity
The growth and reproduction of microorganisms are closely related to the pH value of sewage. The change of pH value may cause the change of cell membrane charge, and then affect the absorption of organic matter by microorganisms and the activity of enzymes in the process of microbial metabolism. For aerobic microorganisms, the pH value of influent is more suitable between 6.5~8.5. Nitrification is an alkali-consuming process. The optimum pH range is 7.0-8.5, which is beyond the optimum range. The activity of nitrifying bacteria decreases sharply and the removal rate of ammonia nitrogen decreases.
Hydraulic load
The hydraulic load directly affects the residence time of sewage in the filter. The smaller the hydraulic load, the longer the hydraulic residence time, the better the treatment effect, and vice versa. However, the turbulence of water flow can accelerate the renewal of biofilm, mass transfer in the filter and the utilization of dissolved oxygen, and the small hydraulic load will lead to the clogging of filter media. Therefore, the hydraulic load is usually 0.5~1.5m3/ (m2*h) in operation.
Dissolved oxygen
It is an important factor affecting biofilm growth and effluent effect. Oxygen demand is an important index of process control in aerobic treatment process. 4~6mg/L is suitable for treating dissolved oxygen in water. When DO is lower than 2mg/L, the life activity of aerobic microorganisms is limited, which reduces the rate of organic matter oxidation and ammonia nitrogen conversion. Therefore, the control of aeration rate is particularly important, aeration rate is large, dissolved oxygen in the filter is high, improve the aerobic microorganism oxidation decomposition rate of organic matter, at the same time, the shear force generated by the air flow is conducive to the aging of biofilm shedding.
Daily operation management
Daily monitoring indicators include water temperature, pH, DO, CODCr and BOD5. In addition, biomicroscopic examination should be carried out in time, and the working condition of biofilm should be judged according to the water quality index, and the operating parameters should be adjusted accordingly.
