Basic Knowledge of Sewage Treatment
26. What is Sludge Index?
Sludge index (SVI) : refers to the volume per gram of dry sludge occupied by the mixed liquid at the outlet of the aeration tank after standing and settling for 30min, measured in mL.
The low SVI value indicates that the mud particles are small and compact, there are many inorganic substances, and lack of activity and adsorption capacity. If the SVI value is too high, it indicates that the sludge is difficult to settle and separate, and is about to expand or has expanded. Therefore, it is necessary to find out the cause and take measures.
27. What are sludge bulking, disintegration, decay, buoyancy and foam?
Sludge swelling: when the sludge deteriorates, the sludge is not easy to precipitate, the SVI value is increased, the structure of the sludge is loose, the volume is expanded, the moisture content is increased, the clarifying liquid is less, and the color is also different.
Sludge disintegration: The treatment water quality is turbidity, the sludge turbulence is fine, the treatment effect is bad, etc.
Sludge decay: in the secondary sedimentation tank, it is possible to produce anaerobic fermentation and gas due to long-term retention of sludge, resulting in the phenomenon of large sludge floating.
Sludge floating: sludge in the secondary sedimentation tank is block floating phenomenon. Foam problem: Foam in aeration tank is mainly caused by the presence of a large number of synthetic washing or other foaming substances in sewage.
28. What is the activated sludge growth curve?
Activated sludge microorganism is a mixed population of multiple strains, and its growth law is relatively complex, but its growth curve can also be used to represent a certain law. The curve shows the multiplication and decay law of the number of microorganisms over time when environmental conditions such as temperature and dissolved oxygen meet the growth requirements of microorganisms and there is a certain amount of initial microbial inoculation, after a full infusion of nutrients.
The change of activated sludge growth rate is mainly caused by the ratio of nutrients or organic matter to microorganisms (usually expressed as F/M). F/M value is also an important factor affecting the degradation rate of organic substrates, the rate of oxygen utilization, the coagulation and adsorption performance of activated sludge. There are four stages of activated sludge growth curve: adaptation period, logarithmic growth period, deceleration growth period (maximum biomass) and endogenous respiration period (the best water quality treatment effect).
29. activated sludge purification is divided into several processes?
Activated sludge purification of wastewater is accomplished in three stages:
In the first stage, the wastewater is purified mainly by adsorption of activated sludge. The adsorption process is very rapid, usually within 30min, BOD5 removal rate can be up to 70%. At the same time, it also has partial oxidation, but adsorption is the main effect.
The second stage, also known as the oxidation stage. It is mainly to continue to decompose the organic matter adsorbed and absorbed in the pre-oxidation stage, while continuing to adsorb some residual dissolved substances.
The third stage is the mud-water separation stage. In this stage, activated sludge is precipitated and separated in a secondary sedimentation tank. Both anabolism and catabolism of microorganisms can remove organic pollutants from sewage, but the products are different.
30. What are the characteristics of the secondary sedimentation tank?
The characteristics of the secondary sedimentation tank: in the function of the characteristics, in addition to the separation of mud and water, but also for sludge concentration, and because of the change of water quality, water quantity, but also temporary storage of sludge.
31. What is slow sewage filtration system?
Slow percolation of sewage is the function of allowing sewage to pass slowly through the soil and purify the sewage due to natural percolation and filtration. Suitable for soil with good water permeability and low evaporation and humid climate.
32. What is the rapid sewage filtration system?
Suitable for soil with very good permeability. Such as sandy soil, gravel sand and so on. After reaching the surface of the fast percolation field, the sewage tank soon penetrates into the ground and finally enters the groundwater layer.
33. How many stages are there in an anaerobic reaction? What are they?
Anaerobic reaction is divided into three stages:
The first stage is the decomposition of organic matter into fatty acids and their products under the action of hydrolysis and fermentation bacteria.
The second stage is the production of H and acetic acid which is further converted by bacteria into H, carbon dioxide and acetic acid.
The third stage is the methane fermentation stage (alkaline fermentation stage) through the action of two different groups of methanogens, one group converts H2 and carbon dioxide into methane, and the other group deactivates acetic acid to produce methane.
34. What is two-phase digestion?
Two-phase digestion is the separation of the acid - and methane-producing stages of anaerobic digestion of organic substrates.
35.what is the material composition of sludge?
The composition of substances in sludge can be divided into organic sludge and inorganic sludge.
According to the source of sludge, it can be divided into primary precipitation sludge, residual activated sludge, humus sludge, cooked sludge and chemical sludge.
36. What moisture does the sludge contain?
The water contained in sludge is divided into four categories: intergranular water, capillary water, sludge particle adsorption water and internal water. Removal methods: gravity, air flotation, centrifugation.
37. What does mechanical dehydration include?
Mechanical dehydration: vacuum filtration dehydration, pressure filtration dehydration, rolling dehydration, centrifugal dehydration of sludge.
38. What is the purpose of sludge stability?
The purpose of stabilization of sludge is to eliminate the stink and kill pathogenic microorganism in sludge.
39. What is adsorption?
The use of porous solid (such as activated carbon) or floc material (such as polyiron) will be toxic and harmful substances in wastewater adsorption on the surface of solid or floc or micropores, to achieve the purpose of purifying water quality, this treatment method is called as adsorption treatment. The object of adsorption may be an insoluble solid substance or a soluble substance.
40. What are the characteristics of physical adsorption and chemical adsorption?
Physical adsorption characteristics: the adsorption heat is small, low temperature can be carried out, adsorption is reversible, adsorption is basically no selectivity.
Chemical adsorption characteristics: adsorption heat is large, adsorption is irreversible, adsorption is selective.
41. What is resin density?
Resin density: generally refers to wet true density and wet apparent density of two ways of expression. Wet-true density is related to the backwash strength of the resin layer, the expansion rate, and the resin delamination of the mixing bed and bunk bed. Wet-apparent density is used to calculate the amount of wet resin required to fill the ion exchanger.
42. what is the role of water filler?
The role of water spraying filler: the water distribution system splash droplets, after many splashes scattered into small water droplets or water film, increase the contact area of water and air, extend the contact time, so as to ensure the good heat and mass exchange of air and water.
43. What are mixed volatile suspended solids?
Mixed liquid volatile suspended solids (MLVSS) refers to the weight of the volatile substances in the dry sludge contained in the biochemical tank mixed liquid per unit volume. The unit is also mg/L. Since it does not include the inorganic substances in the activated sludge, it can more accurately represent the number of microorganisms in the activated sludge.
44. Why is there surplus sludge produced?
In the process of biochemical treatment, the microorganisms in activated sludge continuously consume the organic matter in the wastewater.
Among the organic substances consumed, some of them are oxidized to provide the energy required for microbial life activities, while the other part of them are used by microorganisms to synthesize new cytoplasm, so as to make microorganisms multiply and reproduce. While microorganisms metabolize, some old microorganisms die, so as to produce residual sludge.
45. What is the needle carbon technology?
Iron carbon treatment method is also known as iron carbon micro-electrolysis method or iron carbon internal electrolysis method, it is an application form of metal iron wastewater treatment technology, iron carbon method as a pretreatment technology to deal with toxic and harmful, high concentration COD wastewater has a unique effect.
46. Why should the pH of the effluent from the neutralization sedimentation tank be adjusted above 9?
Iron carbon discharge water contains a lot of ferrous sulfate, if not removed, it will affect the growth and reproduction of microorganisms in the subsequent biochemical tank.
47, what are the types of air float?
Air buoyancy is divided into: dissolved air buoyancy (vacuum dissolved air buoyancy and pressure dissolved air buoyancy), loose air buoyancy and electrolysis air buoyancy.
48. What is flocculation?
Flocculation is the addition of polymer coagulant in wastewater, polymer coagulant dissolved, will form polymer. The structure of the polymer is linear structure, one end of the line pulls a tiny particle, the other end pulls another tiny particle, which plays the role of bonding bridge between the two particles far apart, so that the particles gradually become larger, and eventually the formation of large particles of flocs (commonly known as alum), accelerating particle settlement.
49. why should waste water with polyiron flocculation adsorption treatment?
The formation of ferric hydroxide flocs in the coagulation process has a good ability to absorb organic matter in wastewater. The experimental data show that after the adsorption of wastewater with ferric flocculation, about 10%-20% of COD in wastewater can be removed, which can greatly reduce the operating burden of the biochemical tank and is conducive to the standard discharge of wastewater treatment.
In addition, polyferric coagulation pretreatment can remove the toxic and inhibitory trace substances in the wastewater, so as to ensure the normal operation of the microorganisms in the biochemical tank. Among many coagulants, the price of polyiron is relatively cheap (25-300 yuan/ton), so the treatment cost is relatively low, more suitable for the pretreatment of process wastewater.
50.why the colloidal particles in waste water is not easy to precipitate naturally?
Many impurities in wastewater with specific gravity greater than 1 suspended matter, large particles, easy to settle suspended matter can be removed by natural sedimentation, centrifugation and other methods.
But the proportion of less than 1, tiny or even invisible suspended particles are difficult to natural settlement, such as colloidal particles are 10-4-10-6mm size of the particles, very stable in water, its settlement speed is very slow, settlement of 1m requires 200 years of farming.
