in recent years, with the national and local attention to pollution control, the national standards for sewage treatment are more stringent. the pollutant discharge standards for municipal sewage treatment plants (gb18918-2002) are being adjusted. local standards have been issued in many areas, such as beijing and anhui province. however, the main indicators of effluent from municipal sewage treatment plants in these areas have begun to be better than those in other areas. construction and operation of class a standard of pollutant discharge standard for urban sewage treatment plant. high standard sewage treatment plants mainly require stricter control of organic matter, nitrogen and phosphorus, which should focus on the establishment of advanced treatment processes in construction or revamping, especially the application of denitrification filters.
denitrification filter, as its name implies, is a filter with denitrification function as well as ordinary filter function, which can further remove total nitrogen in deep treatment. it is the most important structure in advanced treatment of high standard sewage treatment plant. according to its structure, operation mode and filter material, it can be divided into many types. in this paper, the active sand filter, denitrifying biological filter and denitrifying deep bed filter are compared and analyzed.
1. brief introduction of technology
(1) activated sand filter
activated sand filter is a kind of high efficiency filter which integrates coagulation, clarification and filtration. the filter is an upward quicksand filter, which is continuously backwashed during operation. raw water enters the inside of the filter through the intake pipe and is evenly distributed by the water distributor. after that, the raw water is discharged to the reverse flow filter material layer side by side. in this process, the raw water is filtered, and the content of pollutants in the water decreases. at the same time, denitrification by membrane-forming microorganisms on the filter material is used to remove nitrogen. with the increase of pollutant content in sand, the pollutant content in the lower layer of filter material is higher than that in the upper layer. the air lift pump located in the center of the filter lifts the bottom sand filter material to the sand washer at the top of the filter for cleaning under the action of the air compressor. the filter sand is cleaned and returned to the filter bed. at the same time, the pollutants produced by the cleaning are discharged.
(2) denitrification biofilter
denitrification biological filter (dnbf) is an improved filter process based on biological aerated filter. at present, there are three types of denitrifying biofilters on the market: biocarbone developed by otv, biofor developed by deliman and biostyr developed by kruger, denmark. in our country, denitrification biofilter is seldom used, and only some cases have been put into operation, which needs further research, development and utilization.
the main working principle of this process is filtration, adsorption and bio-metabolism. specifically, the filler in the filter is used as the carrier to form anoxic environment inside the filter. it is the filter material that indicates a large number of bio-membranes of water quality. when the sewage flows through, the bio-metabolism, bioflocculation, physical adsorption and retention of bio-membranes and fillers with high concentration of active microorganisms in the bio-membranes attached to the filter material and the physical retention of bio-membranes and fillers are utilized. the graded predation of food chain along the direction of water quantity in the reactor can realize denitrification and denitrification and other pollutants removal efficiently.
(3) denitrification deep bed filter
denite deep bedtm filter (denitrification deep bed tm filter) is a treatment process of sts water group, which combines biological denitrification and filtration functions. deep-bed denitrification filter is developed on the basis of traditional v-type filter. quartz sand with special specifications and shapes is used as film-forming medium for denitrifying organisms. at the same time, deep-bed is an excellent removal structure for nitric acid nitrogen (no3-n) and suspended solids. the medium has a good effect of suspended solids interception. in the backwashing period, the filter area per m2 can ensure the interception of solid suspended solids (> 7.3 kg). the characteristics of high solid load greatly prolong the filter cycle, reduce the number of backwash, and can easily cope with abnormal conditions such as peak flow or sludge bulking in treatment plants.
2. comprehensive evaluation
activated sand filter can remove ss, tp and tn at the same time, so that the effluent indexes of ss, tp and tn can reach the first a standard. the filter head is small, less than 1.2m, and the cost of material replacement is low. however, the investment is high, and the control of filter backwashing is inferior to that of denitrifying biological filter and deep bed filter.
the structure of denitrifying biological filter is slightly different from that of denitrifying deep bed filter. the technical parameters are very close, the filtering effect is good and the operation effect is reliable. ss, tp and tn can be removed at the same time. however, the filtration speed is low, the investment in civil engineering is large, the head loss is large, the power consumption is increased, and the management operation is complex.
3. conclusions and suggestions
by comparing the design parameters, indexes and advantages and disadvantages of the three filters, it can be seen that the three filters have better treatment effects on ss, tp and tn, and provide technological guarantee for the removal of total nitrogen in the upgrading of new sewage treatment plants with high standard discharge or existing sewage treatment plants, especially for the upgrading of sewage treatment plants with poor biological denitrification effect. building is very important.
it is suggested that the design institute should fully consider the combination of denitrification filter and other secondary biological treatment processes in the process of designing high discharge standard wastewater treatment plants to effectively improve the treatment efficiency of each treatment process; the operating units of wastewater treatment plants should adjust the process characteristics of various filters, and in order to give full play to denitrification and denitrification function, it is necessary to successfully hang the membrane on the filter material of denitrification filter. controlling the type and dosage of carbon source, we should not only ensure denitrification and denitrification, but also prevent codcr from exceeding the standard of effluent, strengthen operation management and ensure the stability of operation.
source: polaris water treatment network
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