Removal effect and cause analysis of micro-polluted water by biological ceramsite for sewage treatment

With the rapid development of industry and agriculture, the harmful substances in the water have increased year by year. Especially since the 1960s, drinking water sources have deteriorated in many areas. At the same time, with the advancement of water quality analysis technology, trace amounts in source water and drinking water. Pollutants are constantly being detected, and these have placed new and higher requirements on the treatment of drinking water.


1. Characteristics of micro-polluted water sources

  At present, the characteristics of drinking water are contaminated. The content of organic matter is high, and the content of ammonia nitrogen is high. The oxygen-depleting substances such as ammonia nitrogen in water consume a large amount of dissolved oxygen in water, which directly affects the color and turbidity of tap water.

   At present, according to the different ways of removing pollutants, the pretreatment of micro-polluted water can be divided into oxidation method and adsorption method, and oxidation method can be further divided into chemical oxidation method and biological oxidation method. As a kind of biological oxidation method, biological ceramsite has received extensive attention in recent years due to its excellent treatment effect on micro-polluted water.

2. Characteristics of ceramsite

  Taking Yeyan ceramsite as an example, the ceramsite is made of leaf rock ore. After being crushed, it is melted at a high temperature of about 1200 °C, expanded into spherical ceramsite of 5 to 40 mm, and then sieved after crushing. The leaf rock ceramsite shell is dark red, the skin is hard, the interior is lead gray, and the pores are light and porous. The surface of the ceramsite is rough and irregular, and there are many holes with large pore diameters, which are not connected to each other. Since the surface of the ceramsite is mainly a hole having an opening larger than 0.5 μm, the diameter of the bacteria is 0.5 to 1.0 μm. Thus, this structure of ceramsite is very advantageous for microorganisms.

3. Removal of micro-polluted water by bioceramics

  In bioceramic reactors, temperature has a certain effect on the removal of organic matter. In general, the removal rate in winter is 10% to 20% lower than in summer.

  When the water temperature is close to 10 °C, the removal rate of CODMn increases to about 18%, which has little difference with the removal effect at normal temperature. This is because, on the one hand, the decrease in water temperature reduces the activity of microorganisms, and on the other hand, the microorganisms in the bioceramic reactor are in a oligotrophic environment, and the bioceramics can still provide sufficient microbial biomass relative to the organic matter in the water. Therefore, in a certain low temperature range, the negative effects caused by the decrease in microbial activity due to the decrease in water temperature can be offset.

  At low temperatures, temperature has a significant effect on the removal efficiency. Experiments have shown that when the water temperature is between 5 °C and 10 °C, the removal rate of CODMn is between 11% and 23%. When the water temperature is lower than 5 °C, the removal rate of CODMn is between 5% and 12%; At °C, the removal rate of CODMn is only about 6%. This is also the reason why the removal effect of bioceramics is significantly reduced in the two months when the temperature* is low, in December and January. In January and December, the water temperature was below 2 °C for most of the time. At this temperature, the activity of microorganisms was further reduced, and the amount of microorganisms in the bioceramic system also decreased.

  Therefore, in actual operation, attention should be paid to the operation and management of the subsequent processes to ensure the quality of the effluent.

3.12 Removal of organic matter of different molecular weight by bioceramics

  The bioceramic filter has different removal effects on organic substances with different molecular weights. The experimental results show that the bioceramic filter has a good effect on the removal of organic matter with molecular weight greater than 10000, which can reach more than 60%; the molecular weight is between 1000 and 4000. The organic matter between the two, the biological filtration removal effect has also reached 50%; the organic matter with a molecular weight of less than 1000 is also removed, the removal rate is about 10%; and for organic substances with a molecular weight between 4000 ~ 10000, the content is not Reduced, but there is a partial increase.

  In the bioceramic filter, although the hydraulic retention time is short, the specific surface area of the biofilm is large, and the extracellular polymer contains a viscous substance such as polysaccharide, which can form a similar chemical flocculation effect, and has a macromolecular organic substance in the water. Strong adsorption and coagulation ability, so that it is adsorbed and retained by the biofilm on the filler in the reactor, thus forming a better removal effect on organic matter with larger molecular weight. In the biological treatment process, microbial extracellular enzymes can decompose larger molecular organic matter into smaller molecular organic matter, and decompose part of low molecular organic matter into carbon dioxide and water in order to maintain the material and energy needs of the microorganism's own growth and metabolism. Medium and small molecular weight (molecular weight in the range of 1000 to 4000) organic matter also has a good removal rate. For the phenomenon that the organic matter content of molecular weight between 4000 and 10000 is partially increased, this does not mean that the bioceramic filter has no removal effect on the organic matter in the interval, possibly because the microorganism decomposes some organic matter having a molecular weight of more than 1000 into the interval. Organic matter, which causes an increase in the organic content of this part. Biofiltering therefore removes hydrophilic small and medium molecules as well as colloidal and macromolecular organics.

  When the load is basically constant, the aeration time is longer, and the corresponding removal rate is also high. When the residence time is very short, that is, when the filtration speed is high, it basically only plays a filtering role, and the removal rate of organic matter is not obvious. . When the residence time exceeds 1 h, the COD removal rate is not greatly improved. It can be seen that the residence time of the aeration zone is preferably 1 h.

4. Removal of ammonia nitrogen

  The removal of ammonia nitrogen, biological ceramsite filter as a drinking water source water pretreatment is very good, the removal rate of ammonia nitrogen at room temperature can reach more than 80%, even under low temperature conditions (0 ~ 14 ° C), there are High removal rate. In normal operation, bioceramics have a good removal rate of ammonia nitrogen. The bioceramic pretreatment process is an effective method for removing ammonia nitrogen from micro-polluted source water.

Under low temperature conditions, the bioceramic reactor still has a good removal effect on ammonia nitrogen in the influent water, even with a removal rate of more than 65% at very low water temperatures close to 0 °C, and the bioceramic reactor effluent during the test. Ammonia nitrogen is less than 0.5 mg/L.

4.1 For low temperature conditions, the bioceramic filter still has a high removal effect.

 (1) Among the autotrophic nitrifying bacteria, Nitrosomonas and Nitrosococcus are suitable for growth in the range of 2 to 40 ° C, and Nitrobacter is also suitable for growth in the range of 5 to 40 ° C. Therefore, It has certain adaptability to temperature, and among the dominant strains isolated from the bioceramic filter under low temperature conditions (<5 °C), Pseudomonas has an advantage, of which 29 have pseudo-single cells described in detail. Among the strains, five species were found to grow at 4 ° C or below, and they can also grow in nutrient-poor environments. Therefore, the removal effect of microorganisms on ammonia nitrogen under low temperature conditions is ensured.

  2) It can be seen from the Monoud formula that, when the temperature drops, although the rate of degradation of the ammonia matrix by the nitrifying bacteria decreases with the decrease of temperature, that is, the μmax in the formula decreases, but the saturation coefficient Ks also follows the temperature. Decline and fall. Therefore, the affinity of the nitrifying bacteria for ammonia nitrogen is enhanced, and the rate of utilization of the substrate by the nitrifying bacteria can be maintained at a certain level. At the same time, the rate of self-oxidative decomposition of nitrifying bacteria decreases with decreasing temperature, indicating that it can grow and multiply with less energy at the bottom water temperature.

  3) According to the study by MaCarty et al., in order to maintain the steady state operation of the biofilm, it is necessary to keep the organic matter in the water with a small concentration of Smin. When the temperature is low, the low concentration of the ammonia nitrogen in the effluent is also lower, and at the temperature. After rising, the low concentration of ammonia nitrogen in the effluent also rises. Therefore, the bioceramic filter can maintain a high removal rate under low temperature conditions.

5. Treatment effect on turbidity

 There are many factors for the formation of turbidity in water. Secondary pollution of sediments, suspended solids, pipelines, etc., colloids, microbial communities and some organic matter can produce turbidity. The bioceramic filter has a good removal effect on turbidity, and the removal rate is basically maintained between 70% and 90%, which is less affected by the water temperature.