sewage water quality
ss: solid suspended solids, usually in mg/l. generally refers to: filter paper should be filtered water, the filter retentate at 105 °c temperature after drying a constant weight of solid mass. cod: chemical oxygen demand, general unit mg/l.
the principle of cod measurement is: using strong oxidants (china's legal use of potassium dichromate), under acidic conditions, the oxidation of organic matter into co2 and h2o consumption of oxygen, known as the chemical oxygen demand. with codcr, generally expressed as cod.
advantages of cod: it can accurately represent the content of organic matter in the sewage. the determination time is only a few hours and it is not affected by the water quality. the greater the chemical oxygen demand, the more serious the pollution of the water body by organic matter.
bod: bod, generally mg/l. the amount of dissolved oxygen consumed by the decomposition of organic pollutants by microorganisms. nh3-n: ammonia nitrogen, general unit mg/l. ammonia nitrogen refers to nitrogen in the form of free ammonia (nh3) and ammonium ions (nh4 ) in water. tp: total phosphorus, general unit mg/l. the phosphorus compounds in sewage can be divided into organic phosphorus and inorganic phosphorus. number of coliform bacteria: the number of coliform bacteria contained in each litre of water, measured in liters per litre.
total bacteria: the total number of coliform bacteria, pathogens, viruses, and other bacteria, expressed as the total number of bacterial colonies per milliliter of water sample.
common basic concepts
anaerobic: in the biological treatment of sewage, there is no dissolved oxygen nor nitrate-like environmental conditions. dissolved oxygen is below 0.2mg/l. anoxic: in the biological treatment of sewage, there is an environmental condition in which there is not enough dissolved oxygen or dissolved oxygen, but there is nitrate nitrogen. dissolved oxygen is about 0.2-0.5 mg/l. aerobic: in the biological treatment of sewage, there is dissolved oxygen or a combination of nitrate nitrogen. dissolved oxygen is above 2.0mg/l.
aeration: the process of forcing only the oxygen in the air into a specific process in the liquid. its purpose is to obtain enough dissolved oxygen. in addition, aeration can prevent the suspension from sinking, and strengthen the contact of organic matter in the tank with microorganisms and dissolved oxygen, so as to ensure the oxidative decomposition of organic matters in the sewage by microorganisms in the tank under the condition of sufficient dissolved oxygen.
activated sludge: sludge-like floe formed from various organisms such as bacteria, fungi, protozoa and metazoa, and inorganic substances such as metal hydroxides. good adsorption, flocculation, biological oxidation and biosynthetic properties.
activated sludge process: a wastewater treatment method that removes organic pollutants in sewage by using the action of activated sludge in the agglutination, adsorption, oxidation, decomposition and precipitation of sewage.
biofilm method: a wastewater treatment method in which wastewater is contacted with a biofilm grown on the surface of a fixed support, and a biofilm is used to degrade or convert organic contaminants in the waste water.
air flotation: air flotation is the introduction of a large number of micro-bubbles in the water to attach it to suspended particles, resulting in a density less than that of water. it is floated on the water surface using the buoyancy principle to obtain a solid-liquid separation method. the micro-bubbles are generated by aeration and dissolved gas.
coagulation: the purpose of coagulation is to add some chemicals (coagulants or coagulants) to the water, so that colloidal particles that are difficult to precipitate in water can polymerize with each other and grow to a natural degree. this method is called mixing. condensate precipitation.
filtration: in the process of water treatment, filtration generally refers to the process of trapping suspended substances in water with granular fillers such as quartz sand, so that the water can be clarified. the main function of filtration is to remove suspended or colloidal substances in water. in particular, it can effectively remove the smiling particles and bacteria that can not be removed by precipitation technology, and also have a certain degree of removal effect on cod and bod.
precipitation: the process of gravity sedimentation to remove suspended solids in water by using the density difference between suspended matter and water.
common drugs
pac: polyaluminum chloride
caustic soda: naoh hydrated lime: ca(oh)2
quicklime: caopam: polyacrylamide
soda ash: na2co3
sewage treatment method
1. activated sludge method
traditional activated sludge process (commonly referred to as aerobic wastewater process).
2, a/o
a/o is the abbreviation of anoxic/oxic. its advantage is that in addition to degrading organic pollutants, it also has a certain function of nitrogen and phosphorus removal. it is the pretreatment of anaerobic hydrolysis technology for activated sludge. therefore, the a/o method is an improved activated sludge method. the
fundamental:
the a/o process connects the anoxic segment of the anterior segment and the aerobic segment of the posterior segment in series. the a segment do (dissolved oxygen) is not more than 0.2 mg/l, and the o segment do = 2 to 4 mg/l. the anoxic heterotrophic bacteria hydrolyze starch, fiber, carbohydrates and other suspended contaminants and soluble organic matter in the wastewater into organic acids, which break down organic macromolecules into small-molecule organics. insoluble organic matter is converted into soluble organic compounds. the product of anoxic hydrolysis enters the aerobic tank for aerobic treatment, improves the biodegradability of the sewage, and improves the efficiency of oxygen; in the anoxic section heterotrophic bacteria ammoniates protein, fat and other contaminants (organic chain n or ammonia in the amino acid) free ammonia (nh3, nh4 ). under sufficient oxygen conditions, the nitrification of the autotrophic bacteria oxidizes nh3-n(nh4 ) to no3-, and returns to a-pool through reflux control. under the condition of oxygen, the denitrification of the heterotrophic bacteria will return no3- to the pool a through the reflux control. under the condition of hypoxia, the denitrification of the heterotrophic bacteria will reduce no3- to molecular nitrogen (n2). n, o in the ecological cycle, the realization of harmless treatment of sewage.
the main process disadvantages:
in the anoxic tank, the organic carbon in the sewage is used by the denitrifying bacteria, which can reduce the organic load of the subsequent aerobic tank. the alkalinity produced by the denitrification reaction can compensate for the alkalinity requirement of the nitrification reaction in the aerobic tank. . after the aerobics are in the anoxic tank, the organic contaminants remaining in the denitrification can be further removed and the quality of the effluent can be improved.
the removal rate of bod5 is relatively high, which can reach 90-95%, but the effect of nitrogen and phosphorus removal is slightly poor, the denitrification efficiency is 70-80%, and the phosphorus removal is only 20-30%. however, due to the relatively simple a/o process and its outstanding features, it is still a relatively common process. the process can also combine an anoxic tank with an aerobic tank, and use a baffle plate in the middle to reduce the construction cost. therefore, this type is favorable to the modification of the existing plug flow type aeration tank.
influencing factors:
a/o process operation process control does not produce sludge swelling and loss, its degradation rate for organic matter is high (90 ~ 95%), the disadvantage is that the effect of nitrogen and phosphorus removal is poor. if the original sewage contains phosphorus concentration<3mg>
1) mlss should generally be above 3000mg/l. below this value, the denitrification effect of the a/o system is significantly reduced. the
2) tkn/mlss loading rate (tkn-kay nitrogen, which refers to the sum of ammonia nitrogen and organic nitrogen in water): this loading rate should be below 0.05 g tkn/(gmlss·d) in the nitration reaction. the
3) bod5/mlss loading rate: in the nitrification reaction, the main factor affecting nitrification is the presence and activity of nitrifying bacteria, since the minimum specific growth rate of autotrophic nitrifying bacteria is 0.21/d; and the minimum of heterotrophic aerobic bacteria the specific proliferation rate was 1.2/d. the former has a much smaller specific growth rate than the latter. to make nitrifying bacteria to survive and predominate, it is required that the sludge age is greater than 4.76d; but for heterotrophic aerobic bacteria, the sludge age is only 0.8d. in the conventional activated sludge process, since the sludge age is only 2 to 4 days, the nitrifying bacteria cannot survive and occupy an advantage, and the nitrification task cannot be completed. to make nitrobacteria grow well, it is necessary to increase the mlss concentration or increase the aeration tank volume to reduce the organic load and increase the sludge age. the sludge loading rate (bod5/mlss) should be less than 0.18kgbod5/kgmlss·d
4) sludge age ts: in order to maintain a sufficient amount of nitrifying bacteria in the nitrification tank to ensure smooth nitrification, the determined sludge age should be 3 times of the generation time of nitrifying bacteria, and the average generation time of nitrifying bacteria is about 3.3d (20). °c) if the winter water temperature is 10°c and the nitrifying bacteria generation time is 10d, the design sludge age should be 30d.
5) total nitrogen concentration of sewage influent: tn should be less than 30mg/l. excessive nh3-n concentration will inhibit the growth of nitrifying bacteria and reduce the denitrification rate to less than 50%. the
6) mixture reflux ratio: the size of r directly affects the denitrification denitrification effect, r increases, and the denitrification rate increases, but r increases to increase power consumption and increase operating costs.
7) anoxic cell bod5/nox--n ratio: h>4 to ensure sufficient carbon/nitrogen ratio, otherwise the denitrification rate drops rapidly; but when entering the nitrification tank bod5 value should be controlled below 80mg/l, when bod5 if the concentration is too high, the heterotrophic bacteria will multiply rapidly and the growth of autotrophic bacteria will be inhibited so that the nitrification reaction will be arrested.
8) dissolved oxygen in the nitrification tank: do> 2mg/l. generally sufficient oxygen supply do should maintain 2~4mg/l to meet the requirements of nitrification and oxygen demand. according to the calculation, oxidation of 1gnh4 requires 4.57g of oxygen.
9) hydraulic retention time: the hydraulic retention time of nitrification is >6h; while the denitrification hydraulic retention time is 2h, the ratio between the two is 3:1, otherwise the denitrification efficiency will drop rapidly. the
10) ph: the nitration process produces hno3 to reduce the ph of the mixture, while nitrifying bacteria are sensitive to ph. the optimum ph for nitration is 8.0-8.4. in order to maintain the appropriate ph, corresponding measures should be taken. the calculation shows that 1 g of ammonia nitrogen ( nh3-n) is completely nitrated and requires approximately 7.1 g of alkalinity (calculated as caco3); the alkalinity (3.75 g alkalinity/gnox--n) produced by the denitrification process can compensate for about half of the alkalinity of the nitration reaction. the optimum ph of the denitrification reaction is 6.5-7.5, and it is unfavorable if it is more than 8 or less than 7. the
11) temperature: nitrification reaction is 20～30°c, and the nitration reaction is almost stopped below 5°c; denitrification reaction is 20～40°c, and the denitrification rate drops rapidly below 15°c. therefore, in the winter, the denitrification sludge age should be increased, the load rate should be reduced, and the hydraulic retention time should be increased to maintain the denitrification rate.
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