Wuxi Highness Technology Co., Ltd

 

Biological nitrogen removal processes such as A / O are considered to be one of the most cost-effective methods of wastewater denitrification. However, the reclaimed sludge after nitrification in the conventional A / O process is first returned to the denitrification tank (pool A) and then into the nitrification tank (O pool), resulting in very similar sludge types in sections A and O, nitrifying bacteria and The denitrification bacteria are difficult to completely separate, and reflux to the A section of the reflux containing a lot of dissolved oxygen, will also have an adverse effect on denitrification denitrification, denitrification efficiency of denitrification is difficult to more than 70%.

 

In order to solve the above problems, the author uses the nitrification solution into the sedimentation tank from the sedimentation tank to the A pool, the sludge from the original pool to the pool to return to the O pool; and with independent intellectual property rights of the new integrated A / O biofilm reactor, it is expected that the nitrification and denitrification processes occur simultaneously and efficiently in different reactors, respectively, in the macro environment. In view of the characteristics of the water quality of printing and dyeing wastewater and the emission requirements of ammonia nitrogen, the starting process of the integrated A / O reactor was studied in order to explore the effect of the process on the removal of organic carbon and ammonia The

 

Test Materials and Methods

 

1.1 Test device

 

The integrated A / O unit consists of the bottom A pool and the top O pool, see Figure 1. For ease of processing, the device uses a square cone structure, the size of 500 mm × 500 mm. A pool height 350 mm, effective volume 20 L, O pool height 600 mm, effective volume 60 L. The A pool is a spherical suspension filler with volcanic rock as the microbial carrier, and the O pool is filled with spherical suspension packing of the combination filler and volcanic rock. A / O follow-up sedimentation tank effective volume 12L.

 

 

 

Figure 1 Test device

 

Dyeing wastewater is pretreated by coagulation and hydrolysis and acidification. It is stored in waste water pool, then enters the pool through the lift pump, degrades some organic matter and ammonia nitrogen, and the influent water is controlled by flow meter. A pool of water from bottom to top into the O pool, in the degradation of most of the organic matter at the same time, the water into the annular sedimentation tank for mud separation. A portion of the separated supernatant was returned to the A pool as a nitrogen source for denitrification and the other was discharged as a final effluent. The sludge in the sedimentation area will return to the O pool along the backflow of the sludge recirculation zone by its own gravity and participate in the degradation process.

 

1.2 Wastewater quality

 

The simulated wastewater used in the test consisted of the addition of various dyes and chemical reagents to a small amount of domestic sewage (about 20% by volume).

 

 

 

The water quality of the wastewater after coagulation and hydrolysis was: COD 180 ~ 225 mg / L, BOD5 73 ~ 93 mg / L, pH was 7.6 ~ 8.2, chroma 85 ~ 107 times, TP 4 ~ 6 mg / L, ammonia nitrogen 20.4 ~ 25.6 mg / L.

 

1.3 filler characteristics and specifications

 

The packing in the A / O reactor is mainly spherical suspension packing (150 mm) and combined packing (200 mm), purchased from Yixing Chenxiang Environmental Protection Equipment Factory. Spherical suspension filler material for the polypropylene, the specific surface area of ​​380 ~ 800 m2 / m3, porosity> 99%, the relative density of 0.93. The rings and fiber bundles of the composite fillers are polyethylene and polyester filaments, with a unit diameter of 80 mm and a beam spacing of 20 mm. Suspension filler filled with volcanic rock mass (origin of Inner Mongolia), filling 70% to 80%, particle diameter of 3 ~ 5 cm. Volcanic rocks are red and dark brown irregular particles, its hydrophilic and strong, is conducive to microbial attachment.

 

1.4 Inoculation of sludge

 

A / O reactor inoculation of sludge using Suzhou High-tech Zone, the first sewage treatment plant concentrated pool of concentrated sludge, inoculation volume of about 40% of the total volume of 50%. The sludge is brown and flocculent, and the sedimentation performance is better. The MLSS and MLVSS of the inoculated sludge were 34.2 and 21.6 g / L, respectively.

 

1.5 Analysis of the project

 

The test uses continuous access to water. COD was determined by standard potassium dichromate method. Ammonia nitrogen was determined by spectrophotometric method. The TP was determined by modified ammonium molybdate spectrophotometry [4]. SS was determined by standard weight method. SV30 was measured by sedimentation method. PHS-25 pH meter (Shanghai Instrument Electric Science Instrument Co., Ltd.) determination, DO determination using JPB-607A portable dissolved oxygen meter (Shanghai Lei magnetic instrument factory).

 

1.6 test run process

 

The sludge is added to the reactor, the first period of a week of sludge recovery process, the process of using domestic sewage as raw water for boring, a week after the start of the process. The whole process was carried out at room temperature (about 18 ~ 27 ℃), divided into four stages: the first stage of sludge culture and domestication, this stage of water COD load control in 0.5 kg / (m3 ˙ d) The time of 28 d; in the second stage gradually increase the water load, which pool pool gradually increased to 1.1 kg / (m3 ˙ d), O pool increased to 0.27 kg / (m3 ˙ d), this stage of operation time 26 d; Three and fourth stages of the impact load test, the duration of 16 d.

 

2 Results and discussion

 

2.1 COD removal effect

 

The removal efficiency of COD by A / O reactor is shown in Fig. In the first stage, when the raw water was pretreated into the A pool, the effluent COD of the A pool did not fall in the two weeks, and the COD degradation rate of the O pool reached 20% in the first weekend. From the beginning of the third week, A pool of effluent COD began to decline. At the end of the first stage, the degradation rate of COD increased gradually and exceeded 20%, and the degradation rate of COD was close to 50%, and the average was more than 40%. In the second stage, the degradation efficiency of COD in wastewater was better than that of A / O system, and the effluent COD showed a decreasing trend. At the end of the second stage, the degradation rate of COD in pool A and O pool reached 25% and 55% respectively, and the average COD of effluent was 150, 66 mg / L, and the removal rate of COD was 67.6%. Indicating that the inoculation of sludge gradually adapt to the preparation of printing and dyeing wastewater quality. In the third stage of the A / O system for short-term impact load test. At this stage, the average influent COD of the system is 305.9 mg / L, and the effluent COD of pool A and O pool increases. The average removal rates of COD and COD were 32.8% and 37.1%, respectively, and the average COD of effluent was 205.4 and 128.7 mg / L, respectively. The fourth stage reduces the influent COD to 210.4 mg / L. At this stage, the average removal rate of COD in pool A and O pool was opposite, and pool A dropped to 29.1% and O pool increased to 52.7%.

 

 

 

Figure 2 COD removal rate at different stages of A / O reactor

 

The experimental results show that the new integrated A / O reactor has better ability to degrade the organic matter from the printing and dyeing wastewater. During normal operation, the removal rate of COD in A / O reactor is more than 65%. At the stage of shock load, the removal rate of COD is 62.3%.

 

2.2 ammonia removal effect

 

Ammonia removal is a test of the advantages and disadvantages of the integrated A / O system. Sedimentation tank effluent back to the A pool for denitrification denitrification, while A pool using the membrane method is the characteristics of the process. The original O pool effluent back to the sedimentation tank by the return of water can bring the following benefits:

 

(1) low dissolved oxygen in the solution, is conducive to ensuring A pool of hypoxic environment;

 

(3) A / O two pool of sludge on the habitat of microbial dominant population is obvious, the activity is high, so the activity of the microbial biomass is significantly increased, , Without changing or even improve the denitrification rate of the case, from the sedimentation tank effluent reflux of nitrification is expected to reduce, can save a certain power consumption.

 

Ammonia nitrogen in the A pool changes shown in Figure 3 (a). In the first stage, with the acclimation of sludge culture and the adaptation to the water quality, the ammonia nitrogen in the effluent effluent decreased rapidly. At the end of the first stage, the removal rate of ammonia nitrogen was close to 80%, with an average of 32.5%. The removal rate of ammonia nitrogen increased slowly and exceeded 90%, with an average of 86.7%, at 20 ~ 25 mg / L. After the two shock load stages, the influent ammonia nitrogen was close to 30 mg / L, and the removal rate of the pool was decreased, but the effluent ammonia nitrogen exceeded the expected value of 5.7 mg / L. In addition, from the test process, O pool on ammonia nitrogen also have a certain removal effect, as shown in Figure 3 (b) below. The removal rate of ammonia nitrogen in the first stage O pool is close to 10%, and the second stage reaches 18%. In the shock load stage and the A pool, the removal rate of Ammonia nitrogen in O pool was increased to 25.8% of the mean.

 

The DO in the A / O system is continuously monitored. In the longitudinal section of the A pool, DO showed a different distribution of the law, the whole from the bottom up (along the direction of rising water) gradually reduced trend. However, due to the small volume of the reactor, DO maintained at 0.4 ~ 0.8 mg / L, basically meet the conditions of hypoxia denitrification. The results of DO monitoring in O pool show that the DO of the whole O pool is basically distributed in the longitudinal section, and the average of the DO in the cross section is 1 mg / L.

 

 

 

Figure 3 removal of ammonia nitrogen effect

 

O pool on the removal of ammonia nitrogen can be explained from the following aspects: (1) aerobic O pool with denitrification denitrification effect is due to the addition of volcanic rocks in the pool as a microbial carrier. Volcanic rocks have a unique void structure, easy to microbial enrichment and reproduction. On the surface of the carrier, the habitat of microbes is ideal. However, this ideal survival state makes the biofilm formed on the surface of the carrier thicker, and the inside of the filler has some hypoxia or even anaerobic condition, which provides the condition for denitrification. (2) O reactor, the sludge settling in the recirculation zone will return to the reactor under gravity and re-participate in the degradation process. This part of the sludge contains a certain amount of nitrification solution for the denitrification process to provide nitrate nitrogen; (3) O pool bottom of the aeration process exacerbated the mud and water mixing, so that the sewage pool in the O pool through the sludge recirculation area to form a number of up and down cycles , To a certain extent, can also promote the occurrence of nitrification - denitrification.

 

In addition, for the whole A / O system, in the second stage of normal operation, the ammonia nitrogen of the system was maintained at 2.5 mg / L, which indicated that the integrated A / O reactor had a very good degradation of ammonia nitrogen in the printing and dyeing wastewater Effect, effluent ammonia nitrogen below 5 mg / L, can meet GB 4287-1992 and DB 32 / 1072-2007 standard requirements.

 

2.3 Effect of reflux ratio on ammonia nitrogen treatment

 

During the test period in order to examine the overall performance of the system, nitrification reflux ratio remained at 80%. And then change the reflux ratio to examine its effect on the removal of ammonia nitrogen, the results shown in Table 2.

 

 

 

As can be seen from Table 2, it is advantageous to increase the reflux ratio to the denitrification of the system at reflux ratio <120%. However, when the reflux ratio is increased to 150%, the denitrification efficiency of the A section is decreased and the denitrification efficiency of the O stage is increased, but the total denitrification rate is relatively low. It is concluded that the denitrification rate is mainly due to the short residence time of the reactor. When the backflow increases, the denitrification and nitrification time are obviously shortened, resulting in a significant decrease in denitrification and nitrification efficiency. Table 2 also shows that: reflux ratio of 80% to 120%, to improve the reflux ratio to a certain extent, improve the system denitrification rate, but the increase is not large. The results show that the integrated A / O reactor can improve the denitrification rate and reduce the reflux ratio of nitrification solution, which is energy saving and efficiency.

 

2.4 The effect of reflux ratio on the treatment of organic matter

 

The reflux ratio of nitrification solution also affects the degradation of organic matter in wastewater by A / O system. The effect of different reflux ratio on the removal of organic matter is shown in Table 3. Table 3 shows that increasing the reflux ratio is advantageous for the aerobic removal of organic matter, especially when the reflux ratio is between 100% and 120%, the removal rate of organic matter in the A / O system is close to 80%. However, for the anoxic stage, increasing the reflux ratio does not benefit the degradation of the organism. According to Table 2 and Table 3, it can be seen that for the integrated A / O system, the reflux ratio is too large for denitrification and energy consumption, which is 80% ~ 100%.

 

 

 

(1) After the pretreatment of the printing and dyeing wastewater as the object of treatment, inoculated with the city sewage sludge, and in the pool after adding filler, the integrated A / O reactor can achieve rapid start. (2) At the temperature of 18 ~ 27 ℃, when the influent COD of the system was 205.5 mg / L, the COD volume of the A and O segments was 1.1, 0.27 kg / (m3 · d), the effluent COD was 66.2 mg / L, the degradation rate was 67.6%. (3) The integrated A / O system has a high ability to degrade ammonia nitrogen in simulated printing and dyeing wastewater. At the reflux ratio of 80%, the effluent ammonia nitrogen below 5 mg / L, fully meet the requirements of DB 32 / 1027-2007. (4) The integrated A / O reactor has a good ability to degrade the organic matter and ammonia nitrogen in the waste water while reducing the internal reflux ratio, and the optimum reflux ratio is 80% ~ 100%. (5) The effluent of the reactor sedimentation tank is conducive to maintaining the optimum dissolved oxygen concentration required for the hypoxia stage. Dissolved oxygen at 0.4 ~ 0.8 mg / L, A pool denitrification rate of nearly 90%.