(national environmental protection water pollution control engineering technology; Zhejiang Hangzhou Center 3 10007)
In order to solve the problem of poor biochemical treatment effect of printing and dyeing wastewater, the biochemical treatment process of printing and dyeing wastewater by compound hydrolytic acidification/suspended biofilter was developed, and on this basis, special decolorizing bacteria were added for biological enhanced decolorization treatment. The results show that under stable operation conditions, the chromaticity removal rate is increased by 10% ~20%, the total chromaticity removal rate is over 80%, and the COD removal rate is about 90%. It can be seen that it is feasible to improve the decolorization ability of biochemical treatment by biological enhancement technology. Keywords: printing and dyeing wastewater; Compound hydrolytic acidification; Suspended biological filter; To bleach.
China Library Classification Number: X703 Document Identification Number: C Document Number:1000-4602 (2010) 23-0091-03.
Printing and dyeing wastewater is difficult to be treated by traditional biological methods because of its complex composition and poor biodegradability. Therefore, developing new processes and technologies to improve the biodegradation efficiency is the research focus of printing and dyeing wastewater treatment [1~4]. The effect of biological treatment depends on the activity and quantity of effective microorganisms. Bioaugmentation technology can increase the concentration of effective microorganisms, enhance the degradation ability of refractory pollutants and improve the degradation rate by introducing microorganisms with specific functions into the biological treatment system [5].
Composite anaerobic reactor (AHR) is the third generation hydrolytic anaerobic reactor developed on the basis of the second generation reactor. The lower part of AHR reactor is high-concentration granular sludge, and the upper part is a filter material layer composed of filler and attached biofilm. The combination of the two greatly improves the effective volume of the reactor, reduces sludge loss and improves the treatment efficiency [6]. Suspended biological filter adopts suspended biological filler, which has good adsorption and net capture effect on microorganisms, can effectively reduce the loss of microorganisms, and has broad application prospects [7]. In this paper, the composite hydrolytic acidification/suspended biofilter is selected as the biochemical treatment process, and special decolorizing bacteria are added on this basis. At the same time, the pulse water distribution technology is adopted, which strengthens the contact between wastewater and microorganisms in the process of water distribution, improves the mass transfer efficiency, and does not increase additional operating costs. The process was applied to the actual pilot test of printing and dyeing wastewater treatment, and good treatment results were obtained.
1 materials and methods
1. 1 wastewater quality and bacteria
The wastewater comes from the regulating tank of a cotton printing and dyeing enterprise in Shaoxing. The wastewater has complex components, high pollutant concentration and poor biodegradability. The wastewater contains reactive dyes, vat dyes, direct dyes and other dyes and additives, the pH value is 12~ 14, and the water temperature is about 40℃. In order to ensure the stability of inlet water quality, time delay relay is used to control the lift pump to collect water once every 1 h, and its comprehensive water quality is as follows: COD is 1 000~2 800 mg/L, BOD5 is 300~500 mg/L, SS is 150~200 mg/L, and chroma is. Inoculated sludge is taken from the sludge concentration tank of Shaoxing Sewage Treatment Plant. Specific strains are highly efficient decolorizing strains screened and separated from printing and dyeing wastewater and activated sludge from industrial wastewater treatment plants, which have good decolorizing effect on printing and dyeing wastewater [7].
1.2 testing device and method
The pilot plant adopts a series process of compound hydrolysis (A)/ suspended biofilter (O) (see figure 1), and the wastewater is pumped from the regulating tank to the storage tank by time delay relay control lift pump. The wastewater in different time periods is evenly distributed in the storage tank, and the pH value is adjusted to ≤ 10 and then pumped into the pulse water distributor. After the latter stores water for 3~5 min, it instantly distributes water to the bottom of the hydrolytic acidification tank, fully contacts with anaerobic bacteria and facultative bacteria, and decomposes insoluble particles into soluble substances, and macromolecules into micromolecules, thus improving the biodegradability of wastewater, laying a foundation for subsequent aerobic treatment, and at the same time destroying the chromophore of dyes and removing the chromaticity of wastewater. The effluent from stage A overflows to stage O, where the filler fully contacts with the oxygen-containing wastewater, and the organic matter in the wastewater is removed by the metabolism of microorganisms on the biofilm.
The total effective volume of the compound hydrolytic acidification tank is 2 m3, the volume of the filling area is 1m3, and the cubic suspended biological filler with the filling volume of1cm×1cm ×1cm. The effective volume of suspended biofilter is 1.m3, and the packing size is 2 cm×2 cm×2 cm.
1.3 sampling and analysis methods
Take the influent of combined process, effluent from pool A and effluent from pool O regularly, and analyze the changes of COD, chromaticity and pH value. COD: potassium dichromate method; BOD5: microbial membrane method; PH: portable PH meter; Chromaticity: dilution multiple method.
2 Results and discussion
2. 1 Effect of biological enhancement on COD and chroma removal
The removal effects of COD and chromaticity by the system before and after bio-enhanced decoloration were investigated (see Figure 2). In the stable operation stage, the retention time in the A stage is 14 h and the retention time in the O stage is10.5 h. The pilot plant is divided into two stages: the first stage without adding decolorizing bacteria (18~34d), the second stage with enhanced treatment of decolorizing bacteria (35~52 d), and the first five days are the film forming stage.
As can be seen from Figure 2, during the pilot test, the influent COD concentration fluctuated greatly. The COD concentration of aerobic effluent is basically stable at about 65438 0.50 mg/L before biological enhancement, and it is stable at about 65438 0.00 mg/L after enhanced, slightly lower than that before enhanced. The influent chromaticity is 300 ~ 1 0,000 times, and the aerobic effluent chromaticity is gradually reduced from 1 10~ 180 times to less than 100 times after enhanced decoloration.
After adding decolorizing bacteria, the COD removal rate did not change obviously, and the chromaticity removal rate increased from about 70% to over 80%, with the highest reaching 90%. It can be seen that decolorizing bacteria can effectively improve the removal rate of chromaticity by biochemical system, but have no obvious promotion effect on COD removal.
2.2 Mechanism Analysis of Bioenhanced Decolorization
Fig. 3 is the change curve of COD and chromaticity removal rate of the system before and after biological enhanced decoloration in A and O stages.
As can be seen from Figure 3, the removal rate curves of COD and chromaticity basically coincide when decolorizing bacteria are not added in Grade A, but the decolorization rate is improved after decolorizing bacteria are added, and the removal rate curves of COD and chromaticity are separated. This is because when decolorizing bacteria are not added, the removal of Grade A COD is mainly achieved by removing insoluble SS [6,8], and the concentration of SS is proportional to the apparent chromaticity, so the removal rates of COD and chromaticity basically coincide; After adding decolorizing bacteria, because decolorizing bacteria can't use dye molecules as direct carbon sources, they can only destroy their chromophoric groups and reduce them to aniline compounds, and then mineralize these substances through aerobic process, so that the decolorization rate curve is separated from the COD removal rate curve, which reduces the dependence of decolorization rate on ss removal rate.
It can also be seen from Figure 3 that the decolorization rate of O stage has not changed obviously before and after bio-enhanced decolorization, but the removal rate of COD has increased slightly, which is consistent with the speculation that decolorizing bacteria decompose dyes into aniline compounds and then degrade them through aerobic process. At the same time, it also reflects that the proportion of residual dyes in wastewater to total COD concentration is low, which is also in line with the characteristics of printing and dyeing wastewater.
3 Conclusion
① Composite hydrolytic acidification/suspended biofilter was used as biochemical treatment process, and special microbial strains were added on this basis. At the same time, pulse water distribution technology is adopted. When the retention time of phase A is 14 hour, the retention time of phase O is 10 hour. After 5 h, the removal rates of chromaticity and COD were above 80% and 90% respectively.
② After bio-enhanced decolorization, the decolorization rate of the system increased by 10%~20%. The decolorizing bacteria can't use dyes as direct carbon sources, but can only reduce and decompose them into aniline compounds, and then mineralize them through aerobic process, so the removal rate of COD has not been significantly improved.
③ Using bio-enhanced decolorization technology can effectively improve the decolorization rate of biochemical treatment, effectively reduce the cost of advanced treatment, and lay a foundation for the resource utilization of wastewater.
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