BAF process for the latest information

BAF treatment of municipal wastewater construction and operation experience Abstract: Aerated biofilter in the design and construction process of backwashing, aeration, filter media selection and other multiple issues, respectively, combined with the author's practical experience, discusses the aeration of biofilter design and construction of the precautions for the design of the process for reference. So that the mature design of the aeration biofilter process as soon as possible to promote and apply, to avoid blindly applying the design manual or due to the lack of practical experience caused by the process of hidden dangers. The end of the article on the application of the process in Wenzhou, Zhejiang Province, a brief introduction for reference by the majority of colleagues. Aerated biofilter originated from Deliman's V-shaped filter, Deliman will be aeration biofilter applied to the Dalian Malanhe Wastewater Treatment Plant. Because of its advanced technology and technical ingenuity, and then quickly in the country and other places to be widely used. According to the results of preliminary statistics, the national application of aeration biofilter as sewage (depth) treatment of 10,000 tons of sewage treatment plant has been more than 30, with a total treatment capacity of more than 100 × 104m3 / d. According to the results of the research, the design and construction of the process is summarized as follows: 1 pre-treatment of aeration biofilter, according to the characteristics of the process of aeration biofilter, the sewage should be strengthened into the filter tank Pre-treatment to avoid clogging the filter head or filter media layer. Dalian, Shenyang and other places pre-treatment using SEDIPAC?0?3 3D (S3D for short), including aeration sand, air flotation and oil removal and inclined tube sedimentation of three parts [1]; while Xinhui, Guangdong, Jiangmen, the use of hydrolysis acidification, is actually between hydrolysis acidification and high-efficiency sedimentation tanks between the primary sedimentation tanks, the bottom of the region of hydrolysis, the upper part of the realization of the mud-water separation; other such as diatom concentrate, wetland bed pre-treatment process, the purpose of the Theoretically, the wastewater entering the filter tank is not a floating or suspended material. Theoretically, the sewage into the filter tank should not contain plastic pieces and other floating matter, so as not to enter the filter tank water distribution area caused by the blockage of the filter head, for this reason, some sewage treatment plants in the filter tank into the water distribution channel set up a fine grille, grid gap of 2mm (or less). Pretreatment effluent suspended solids (SS) concentration to a large extent to determine the backwash cycle of the filter, found in the operation of the practice, into the filter tank sewage carries too much suspended solids, the filter tank backwash cycle will even be shortened to less than 12h, and will affect the next level of the filter tank and even the water; ammonia and soluble pollutants in high concentrations, but the suspended solids (SS) lower sewage into the filter tank, the filter tank effluent water quality is very good! 2 filter plate construction quality on the application of aeration biofilter effect of the core part of the construction of the filter tank is the construction of the water distribution area, including water distribution and gas distribution chamber, support beams, filter plates, etc. construction, which is also to the installation of the filter plate up to the design level tolerance is the most difficult to achieve. General each filter plate (about 1m2) of the level of tolerance for ± 1mm, a single pool of filter plate level of tolerance for ± 5mm, the same group of filter pool filter plate level of tolerance for ± 10mm. filter plate level requirements are very high, the construction is difficult, the workload is large and relatively cumbersome, the actual construction of the construction unit to achieve this requirement is very difficult. In view of this, should cause the design and construction unit attaches great importance to the construction of the degree of care, construction of new methods, new materials should be invested in the application of more energy. In the filter pond filter plate cast-in-place or prefabricated parts of the construction, should control the positioning of the embedded parts, do a good job of controlling the level, can not be rushed to meet the deadline and affect the quality of the project (including construction accuracy). As the filter head (cap), aeration system construction must wait until after the installation of the filter plate can be constructed, so the level of the filter plate with or without a direct impact on the level of the filter head, aeration system. And the filter head, aeration system level and filter backwash (mainly gas washing), aeration is closely related to the filter plate high gas volume, filter plate low gas volume or even no gas, filter head assembly must be tested on the filter backwash effect, backwash effect does not meet the design requirements, assembled to fill the seam filter plate must be on the filter cap, filter plate seams to deal with the whole cast-in-situ filter must be adjusted to adjust the level of the filter rod. 3 aeration, the selection of aeration materials on the aeration of biological filtration effect of the operation of the filter plate level, the level of aeration pipe, the size of the gas volume (gas-water ratio) and other factors tend to affect the uniformity of the aeration of the filter. Uneven aeration will lead to a reduction in the actual use of the filter media volume, the actual load of the filter media layer is high, which in turn affects the filter water indicators, but also reduces the utilization of oxygen. Aeration materials have a single pore membrane aerator, tube microporous aerator, disk microporous aerator, perforated tube, filter head aeration, etc., on the aeration effect using a single pore membrane aerator aeration effect is better, as long as the design and construction of a reasonable and even can be done to 1:1 gas supply to make the 200m2 (refers to the total area of the multi-grid filter) filter pool surface cloth gas is basically uniform. In Sichuan, Liaoning and other places in the second filter using filter head aeration, said to be more successful, because there is no application of filter head aeration of personal experience, it is not good to make too many comments here, but one thing is certain, the use of filter head aeration on the level of the filter plate requirements are quite high, otherwise it is difficult to achieve uniform aeration. Suggested in the filter pool assembly support layer, must do a good job of construction organization, to prevent pebbles smashed filter cap or aerator, assembly of a good support layer, must be on the aeration uniformity, backwash uniformity of the test, failing to meet the requirements must be reworked, can not exist in a fluke. Aeration mode has a blower to 1 filter pool gas supply (i.e., a drag a), there is also a blower (or more blower **** 1 main pipeline to the outside gas supply) to a number of filter pool gas supply (i.e., a drag more). Due to the level of installation and the impact of different filtration tanks intercepting different amounts of pollution, a tow more aeration there is a risk of uneven aeration, the use of a tow a (or a tow two) for a better choice, each fan can be set up with a frequency converter to adjust the size of the gas volume. Aeration fan should be used Roots blower, fan water cooling, the body of both sides with gear oil running more smoothly.4 The importance of optimizing the design of backwash with the prolongation of the operating time, the filtration tank intercepts a large increase in the amount of water quality may be accompanied by a deterioration in the water quality, at this time should be filtered for backwashing. Backwash design and construction is reasonable on the operating effect of the aeration biofilter is critical, the following factors should be considered in the design: ① Select the appropriate filter plate opening rate. Openings such as the design of small will lead to increased resistance to backwashing, if serious, may damage the filter plate; openings too large can not form a stable and suitable air cushion layer, will result in uneven backwashing; ② selection of suitable filter backwash air distribution system, such as filter tank area is large, it is recommended to set up a backwash air distribution room (there are corresponding design specifications, I will not go into detail here), but air distribution room in the structural processing, especially construction When more trouble, so there are a considerable number of aeration biofilter project are arranged in the lower part of the filter perforated pipe, and even backwash inlet pipe directly into the filter water distribution area (i.e., the lower part of the filter plate space), have achieved success, but should be cautious (there are some individual project applications are unsuccessful); ③ Select the appropriate intensity of the backwash, according to the value of the design parameters of the Dalian Malan River and our experience in the actual operation of the data obtained According to the design parameters of Dalian Malanhe and our experience data obtained in actual operation, the backwashing intensity of the filter tank should be large, and it is recommended to take the value in the range of 60-90 m/h intensity to achieve the effect of scrubbing the filter media and the micro-expansion of the filter media, and the moderate intensity of the water washing can be used. ④ should be considered in the design of the backwash before the rapid precipitation, aeration biofilter piping system is more complex, but the rapid precipitation pipeline settings are very important. At present, the domestic application of aeration biofilter project, in addition to the Jiuquan wastewater treatment plant are upward-flow aeration biofilter, the filter work interception of suspended solids in the water distribution area and most of the lower filter layer space, these substances due to the upper layer of the filter layer of the obstruction, it is not easy to drain from the backwash drainage excluded, but on the contrary, it is easy to drain from the venting pipe (i.e., rapid descending water pipeline). Therefore, it is recommended that before backwashing, the use of electric emptying drain about 1/5 of the pool capacity of water, and then backwashing, backwashing effect is good. Of course, the level of the filter plate on the impact of backwashing is critical, has been mentioned, will not repeat here. Generally speaking, the filter put into operation in the early stage (refers to the operation soon or in the debugging period), due to the amount of biofilm is not much, aeration and backwash resistance is small, backwash intensity should be small. With the prolongation of the filter put into use time, microbial attachment ability to enhance the amount of microorganisms increase, backwash difficulty will increase, then should extend the backwash time or take other measures to make the backwash effect is guaranteed. Backwashing time, using the design parameters of the feed water for 15min or less, but the feedback from the actual operation of the situation is not optimistic, Dalian, Xinhui, Cixi backwash time are more than 20min, up to 50min. so the design considerations in the 15-40min, and consider the filter backwash on other filter tank load impact and loss of backwash water! 5 aeration biofilter filter media selection filler as a carrier for microbial growth, in the aeration biofilter and added a new meaning: filter media. Both for the survival of microorganisms to provide a carrier function, but also has a general filter process filtration function. Therefore, the choice of filter media is critical to the normal and stable operation of the aeration biofilter [2].5.1 Selection of filter media particle size Aerated biofilter filter media particle size is generally in the range of 2 to 8 mm. in order to achieve the purpose of denitrification, some aeration biofilter will be divided into two areas of the filter media layer, the lower part of the anoxic zone, the upper part of the aerobic zone; and even some filters throughout the filter media layer for anoxic operation, the treated effluent reflux introduction of NO- 3-N denitrification denitrification, the filter media is not suitable for the treatment of nitrogen dioxide, but for the treatment of nitrogen oxide. 3-N denitrification denitrification, Guangdong Jiangmen Fengle Wastewater Treatment Plant, a denitrification filter DN pool that is this type. This type of filter pool selection of filter media particle size should be large, generally between 5 to 8mm is good. Multi-stage aerobic filtration tank particle size range selection: a filter tank to consider the need for sufficient dirt space, the particle size of 4 to 6mm, two filter tanks to take 2 to 5mm better, as long as the backwash can meet the requirements and backwash is not too frequent, it is recommended to take a small particle size to get better results. 5.2 Characteristics of the filter media selection of good aeration of the biological filter tank filter media and its hardness (strength) must meet the requirements, otherwise the filter media in the filter tank, wear and tear, breakage, will be filled with filter media. Wear and tear, breakage, will fill the filter gap, reduce the dirt space and cause backwashing difficulties. At present, the domestic application of more ceramic filter media, relative to other lightweight filter media, the type of filter media accumulation capacity is larger, not easy to expand the backwash loose, on the one hand, resulting in filter cleaning is difficult to meet the requirements, on the other hand, resulting in the backwash water consumption, gas consumption, time-consuming to increase. The surface of the filter media should be rough and porous, the surface is not glazed bright, in the case of other indicators are guaranteed, the larger the surface area, the better, which is more conducive to hanging film and improve biomass. Specific surface area of low filter media put into use will make the biomass in the filter tank to improve the restrictions on the treatment of water quality. It is recommended that the filter media selection to increase the control of the above aspects, as for other types of indicators can be selected according to the actual needs and filter media manufacturers recommended parameters discretion.6 Biological phase characteristics of aeration biofilter activated sludge method when a large number of filamentous bacteria breeding, easy solid-liquid separation difficulties, resulting in water entrapment of sludge, resulting in poor quality of the effluent water. In fact, filamentous bacteria have a large specific surface area, good adsorption capacity, survival ability, strong ability to degrade pollutants, just due to the light weight is difficult to achieve solid-liquid sedimentation and separation. The aeration biofilter due to the use of filter (fill) material as a carrier for microbial survival, turning harm into good, so the microbial population in the filter is particularly large, the biofilm floc is rich in filamentous bacteria, long filaments, high density. The following describes the microbial phase of the secondary aerobic biofilter that we observed in the Xinhui wastewater treatment plant for reference: primary filter tank: the bacterial gelatinous mass is bright yellow, filamentous bacteria are abundant, the bellworms, the tired branch worms, the set of cover worms are more, the rotifers and nematodes are less; the secondary filter tank: the filamentous bacteria are abundant, the nematodes are more, the rotifers are less, and the occasional erythromelania is also seen (in the microscope is huge in size). Secondary filtration tank effluent in the sunlight visible to the naked eye small red worms, the water is clear and transparent.7 Aeration biofilter operating effect and backwashing on the filter operating effect of the following Wenzhou Economic and Technological Development Zone Binhai Park sewage treatment plant operating conditions as an example of the operating effect of the aeration biofilter is analyzed. The scale of the project ***5 × 104m3 / d, is running aeration biofilter for its first phase of the project, the treatment capacity of 2 × 104m3 / d, the original water to synthetic leather-based industrial wastewater accounted for a large proportion of the composition of the influent ammonia and nitrogen concentration is higher, considering the aeration of the biofilter has a good performance of nitrification, the process of using diatom concentrate + aeration of the biofilter composite process, part of the filtration tank is divided into two levels: CN The filter is divided into two levels: CN (de-C, part of the nitrification) and N (nitrification), each level of filter with 12 cells, in December 2005, officially put into operation. The treatment effect is shown in Table 1: Table 1 Inlet and outlet water quality indicators mg/L Item CODCr BOD5 NH3-N PO43-P SS Inlet water quality 350 160 60 5 200 Actual outlet water indicators <30 <5 <5 <0.5 <5 As the outlet water is already very clear after pretreatment, the pre-treatment effluent Suspended solids (SS) is less than 40mg / l, backwash cycle is currently controlled in 7-10d. But the initial filtration water quality after backwash is poor, backwash should not be immediately after the water, the current use of backwash after the mulled aeration of 2h in order to improve the quality of the initial filtration water measures, otherwise the impact on the quality of the effluent water is greater.8 Conclusions and recommendations of the aeration biofiltration tank process of the effluent water quality is more stable. The treatment effect is relatively good, low CODCr high NH3-N wastewater treatment effect is better; biomass is large, the completion of the NH3-N nitrification residence time requires only 2 ~ 4h; covers an area of small, plant filter area without odor, as long as the noise standard, can be constructed in the urban areas or suburban areas of the city, saving the pipeline network investment. Aerated biofilter water quality is good, stable operation, with the improvement of the level of automation, the application of aeration biofilter will become more and more widespread. From the application of aeration biofilter, the best choice is to be applied in the depth treatment of micro-pollution source water and sewage, that is, the filter intake for the secondary treatment of water, the reason is mainly because of the pretreatment is difficult to get a good guarantee. If you consider the actual situation in China, the front end of the first level of intensive treatment, the removal of floating matter to be thorough, into the filter tank suspended concentration should be as low as possible, the primary sedimentation tank (high-efficiency sedimentation tank) surface load should be appropriate, and should be as much as possible to consider changes in the amount of water on the pre-system of the impact of the process can make the best use of its strengths and avoid the shortcomings (soluble pollutants, especially ammonia nitrogen, such as the removal of high removal efficiency, but intolerance to the characteristics of the suspended solids), processing Efficiency is given full play, but also more conducive to the popularization and application of the process.