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Silicon carbide ceramic membrane is a high precision microfiltration & ultrafiltration grade membrane separation product made of high purity silicon carbide fine powder through recrystallization sintering technology.
It has high flux, high corrosion resistance, easy cleaning, and long service life.
At present, the highest filtration precision can reach 20nm. It uses unique design and manufacturing processes to combine inert silicon carbide materials and screened non-ceramic materials to form the inherently strong and durable membrane. This guarantees its long term service and durability in harsh environments.
It uses equivalent or lower investment cost compared to organic ultrafiltration membranes to create SIC carbide inorganic ultrafiltration products that are more reliable, easier to operate, and have longer service life, meanwhile, achieve the lowest total life cycle cost in the long time service.
Industrial wastewater generally has special characteristics such as strong acidity and alkalinity, containing organic solvents, etc. Traditional organic membranes are usually difficult to adapt to such harsh and complex conditions; Ceramic membranes, due to their material advantages, can operate stably for a long time in these extreme environments.
● The silicon carbide membrane is produced by recrystallization process, with a sintering temperature of 2400 ℃. During the sintering process, the sintering neck between the silicon carbide aggregates undergoes a phase transition from solid to gas to solid, with an opening rate of over 45%. The formed filter channel has strong connectivity, coupled with the inherent hydrophilicity of the silicon carbide material (contact angle only 0.3 °), resulting in a pure water flux of up to 3200LMH, and is hydrophilic and oleophobic.
● The isoelectric point of the silicon carbide membrane is around pH 3, and the surface of the membrane can maintain being negatively charged over a wide pH range, improving its pollution resistance.
● Excellent chemical stability, capable of working in extreme environments (pH range 1-14); a variety of cleaning plans can be developed based on the characteristics of pollution factors; Oxidants are fully tolerant, including ozone and hydroxyl radicals.
★High flux, 3-10 times compared to organic membranes;
★Small footprint, saving land;
★Water consumption for backwashing is reduced by more than 50%;
★Chemical tolerance, capable of working in pH 0-14 environment, acid and alkali resistant;
★The service life is 2-10 times longer than the organic membranes, lower replacement cost;
★Allow for strict chemical cleaning, high flexibility in cleaning, and the flux is easy to recover after cleaning;
★The performance is easy to recover after pollution and blockage, eliminating the cost of membrane replacement caused by unexpected failures;
★ Low system preprocessing requirements, reducing total system investment and operating costs;
★Higher Pressure differences between membranes allowed, so low temprature source water flux increases;
★No membrane broken problem, and less maintainance required.
Washing and concentration of nano powder
Oil-water separation (oilfield reinjection water, liquid hazardous waste regeneration)
Material separation
Solid liquid separation with high solid content (mine water, biological fermentation broth)
Solid liquid separation in harsh chemical environment (acid purification, nano powder catalyst recovery)
Printing and dyeing wastewater and papermaking and pulp industry wastewater are the main sources of COD (chemical oxygen demand) pollution. Compared with traditional treatment methods, using ceramic membrane ultrafiltration technology to intercept and filter COD and lignin has a higher retention rate, and can also achieve direct recovery and reuse of permeate.
The manufacturing process of photovoltaic cells, including cleaning, etching and coating, produces a large amount of acidic fluoride-containing wastewater due to the use of hydrofluoric acid. China is a major producer of photovoltaic cells, with thousands of enterprises that produce a large amount of acidic fluoride-containing wastewater every day.
The fluoride concentration in the acidic fluoride-containing wastewater of photovoltaic enterprises is generally hundreds to thousands of micrograms per liter, and the pH value is low.
Common treatment technologies include chemical precipitation, ion exchange, adsorption and membrane separation.
Chemical precipitation includes reagent precipitation and electrocoagulation precipitation; adsorption includes biological adsorption, physical adsorption and chemical adsorption; membrane technology includes reverse osmosis, electrodialysis and nanofiltration.
Among these technologies, the most widely used method is calcium fluoride precipitation, which uses CaCl2 and Ca(OH)2 as the main chemical reagents.
These reagents provide Ca 2+ to react with F– to form calcium fluoride flocs in water. The flocs are precipitated as calcium fluoride sludge under the action of coagulants and flocculants.
However, this method has two major limitations: the generated calcium fluoride sludge contains a large amount of heavy metals, which poses a potential risk of serious environmental pollution, and the addition of coagulants and the complex composition of the sludge lead to high treatment costs, making recycling impractical.
In addition, calcium fluoride has high utilization value in the photovoltaic and semiconductor fields and is an extremely scarce and non-renewable resource.
Therefore, the development goals of photovoltaic wastewater treatment technology are to minimize by-products, reduce operating costs and improve the recovery efficiency of calcium fluoride.
The chemical crystallization circulating granular fluidized bed (CrystPFB) technology can induce calcium fluoride crystallization in water.
This process not only reduces the concentration of fluoride in water, but also produces higher purity calcium fluoride particles, minimizes the generation of by-products, and its effects and mechanisms have been widely verified.
There have been studies on CrystPFB-induced calcium fluoride crystallization, focusing on fluoride removal, induced crystallization mechanism, and calcium fluoride crystallization kinetics.
However, the fluoride concentration in the studied wastewater is usually between 100 and 300 mg/L, and most studies use laboratory-scale methods.
Some researchers have also applied CrystPFB technology to remove fluoride from rare earth metallurgical wastewater, using calcium and silica as seeds to induce calcium fluoride crystallization, and achieved a recovery rate of more than 90% at an influent concentration of 400 mg/L.
Other researchers have explored the combined effects of chemical precipitation and CrystPFB on high-concentration fluoride-containing wastewater, and compared the effects of chemical precipitation and CrystPFB in treating extremely high-concentration fluoride. It was found that when the fluoride concentration was lower than 450 mg/L, CrystPFB showed the best performance, with a total removal rate of 98%.
In summary, further research on the removal of fluoride from high-concentration industrial wastewater is needed to overcome the limitations of low influent fluoride concentration (<1000 mg/L) and small treatment scale (laboratory scale or small-scale experiments). In particular, acidic fluorine-containing photovoltaic wastewater has complex water quality and is difficult to treat.
When the effluent ammonia nitrogen and COD are normal, the total nitrogen is always high or even exceeds the standard, indicating that the total nitrogen exceeding the standard in the effluent is in the form of nitrate nitrogen, not ammonia nitrogen. At this time, you can consider enhancing the nitrification and denitrification process to convert nitrate nitrogen into nitrogen gas. This type of problem is not common but not complicated for some sewage treatment plants. Sometimes adjusting the parameters can meet the standards.
01 Insufficient carbon source The theoretical C/N ratio required for total nitrogen removal is 2.86, but in actual operation, the C/N (COD: TN) ratio is generally controlled at 4~6, which often means that the total nitrogen removal rate of the water treatment system is low. At this time, the C/N ratio should be 4~6, and the appropriate carbon source should be added. It can be comprehensively considered based on denitrification rate, sludge production, startup speed and nitrite nitrogen accumulation. For example, glucose with a relatively low reaction rate can be added at low concentrations of nitrate nitrogen, and methanol and acetic acid with high reaction rates need to be added at high concentrations of nitrate nitrogen.
02 The reflow ratio is unreasonable. The internal reflow ratio is too low, and the nitrate nitrogen cannot flow back to the anoxic zone. The denitrification reaction cannot proceed normally, resulting in a decrease in the total nitrogen removal efficiency. At this time, under the premise of ensuring the denitrification efficiency, combined with the influence of DO and the relationship between cost performance, the internal reflow ratio can generally be controlled at 200~400%.
03 The working environment of the denitrification pool is destroyed. The DO of the denitrification pool is greater than 0.5, which destroys the anoxic environment, allowing facultative heterotrophic bacteria to preferentially use oxygen for metabolism. Nitrate nitrogen cannot be removed, resulting in an overall increase in TN. If the internal reflow is too large and causes too much DO to be carried, the internal reflow ratio can be adjusted down or the aeration at the internal reflow can be turned down; if the distance between the inlet and the water surface is too high, resulting in falling oxygenation, the height difference should be reduced.
The concentration of ammonia nitrogen is higher than the result of total nitrogen determination
Theoretically, total nitrogen should be higher than ammonia nitrogen, because total nitrogen includes inorganic nitrogen (nitrate nitrogen, nitrite nitrogen, ammonia nitrogen) and various organic nitrogen, but in actual detection work, the ammonia nitrogen content is higher than the total nitrogen. Among them, impure reagent purity, insufficient digestion time, poor quality of experimental water, etc. may be the main reasons for the ammonia nitrogen to be higher than the total nitrogen.
01 The purity of potassium persulfate reagent is not enough. The purity of potassium persulfate reagent is not enough, resulting in a high total nitrogen blank value and a small actual measurement value. The total nitrogen detection and analysis has strict requirements on potassium persulfate reagent. The analytical pure potassium persulfate used in the laboratory requires a nitrogen content of ≤0.0005%. However, due to differences in the quality of reagents produced by different manufacturers and batches, the nitrogen content often does not meet this requirement, resulting in a high total nitrogen blank value and a small actual measurement value. There are only two ways to deal with this situation: purify or replace the reagent. Potassium persulfate with low purity can be purified before use, but due to laboratory conditions and the instability of potassium persulfate to temperatures above 50°C, it is recommended to use high-grade pure reagents or imported potassium persulfate.
02 Insufficient high-temperature digestion time or poor sealing In practice, once the digestion time of total nitrogen is not sufficient, potassium sulfate will be incompletely converted, resulting in the production of nitrate nitrogen and nitrite nitrogen, which makes the ammonia nitrogen content in sewage significantly higher than the total nitrogen content. In addition, in general, during the experiment, due to limited conditions, the test tubes, digestion cups and other experimental equipment used cannot be absolutely sealed. Therefore, the ammonium ions oxidized during the digestion process are converted into ammonia gas under the action of high temperature and released into the air, resulting in the total nitrogen content of the samples with high ammonia nitrogen content only containing part of the ammonia nitrogen, which is lower than the ammonia nitrogen content.
03 The quality of the experimental water is poor and the ammonia content is relatively high. The ammonia-free water used in the experiment is contaminated and has a relatively high ammonia content, which will result in a high blank value obtained in the experiment. If ammonia is present in the water during configuration, it will affect the determination of total nitrogen. If the water contains nitrogen when preparing the standard solution, the absorbance of the drawn standard curve will be higher than the actual value. In this way, when the water sample is actually tested, the measured value of total nitrogen will be lower than the actual value. Generally, the fresh distilled water can be processed twice and the distillate in the middle can be selected as the experimental water for ammonia nitrogen testing. Of course, it is recommended that laboratories with conditions use ultrapure water.
Why is there no change or even low ammonia nitrogen in influent, but ammonia nitrogen in effluent is always high? In fact, it is common for ammonia nitrogen in effluent to be higher than that in influent in sewage treatment. Generally speaking, if there is no abnormality in ammonia nitrogen in influent but ammonia nitrogen in effluent increases or exceeds the standard, then the nitrification reaction must be inhibited and a certain step in the denitrification process has not been completed.
01 The low dissolved oxygen in the aerobic pool may be caused by the blockage of the aeration head, which cannot be aerated or stirred. Over time, insufficient dissolved oxygen will lower the average level of the entire aerobic pool, causing ammonia nitrogen in effluent to exceed the standard along with COD. Therefore, the aeration system should maintain sufficient aeration volume for a long time, and the operator should regularly check the normal operation of the aeration tank facilities.
02Ammonification is greater than nitrification. Generally, the total nitrogen in wastewater is mainly ammonia nitrogen, while in some specific wastewaters (such as amino acid wastewater), the main component of total nitrogen is organic nitrogen. Organic nitrogen is converted into ammonia nitrogen under the action of ammonifying bacteria, resulting in an increase in ammonia nitrogen in the system. When the organic nitrogen content in the influent is relatively high, if the ammoniation reaction rate is higher than the nitrification reaction rate, the ammonia nitrogen produced will be higher than the ammonia nitrogen nitrified, so the total amount of ammonia nitrogen will also increase, and it will accumulate and mix into the effluent, which is also one of the common reasons why the ammonia nitrogen in the effluent is higher than that in the influent.
03 The introduction of additional nitrogen in the sewage treatment process The ammonia nitrogen in the effluent is higher than that in the influent, which obviously does not conform to the law of conservation of matter. It is very likely that ammonia nitrogen from other aspects is mixed in the sewage treatment process. Excessive addition of external carbon source, incorrect calculation of addition ratio, and use of black PAC rich in ammonia nitrogen will introduce additional nitrogen into the sewage treatment system, making the ammonia nitrogen in the effluent higher than that in the influent.
04 The sludge age is not enough The generation cycle of nitrifying bacteria is longer than that of most aerobic bacteria. If the sludge age is shorter than the generation cycle, the number of nitrifying bacteria may be insufficient, the denitrification efficiency will be reduced, and the ammonia nitrogen will increase. At this time, it is necessary to reduce sludge discharge and increase return flow to extend the sludge age, or add the same type of sludge to find a way to establish a population advantage for nitrifying bacteria. In addition, sludge aging, poisoning, and swelling cause the degradation capacity of biological denitrification after sludge disintegration to be greatly reduced. With the weakening of sludge concentration and biological activity, the ammonia nitrogen removal rate is greatly reduced, making it lower than the original level, and will also cause the ammonia nitrogen in the effluent to be higher than the ammonia nitrogen in the influent.
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