| Sewage contains a large number of carbon sources(organic matter).If it is converted into energy for use,it has important significance for reducing sewage treatment energy consumption,decreasing carbon emissions and realizing energy self-sufficiency in sewage treatment plants.Due to the low concentrations of carbon sources in sewage,it is difficult to directly use its productivity economically and efficiently.Therefore,the efficient concentration and capture of carbon sources in sewage is a key step to realize its energy utilization.The high load bioflocculation membrane reactor which is combined with bioflocculation and membrane separation can not only avoid the negative impact of the introduction of additional chemicals,but also achieve efficient capture of organic matter and effective mitigation of membrane pollution.It has become a very attractive technology for concentration and capture of sewage carbon sources.However,at present,there are still some problems in this technology,such as the parameters of reactors with different configurations and different treatment objects need to be further optimized;The influence mechanism of temperature on the efficiency of the reactor in capturing sewage carbon sources is not clear;The membrane fouling control technology of the reactor needs to be further developed.In this paper,a cylindrical structure of high loaded biolflocculation membrane reactor(HLB-MR)was constructed by using hollow fiber ultrafiltration membrane module with small membrane pore size(0.03μm),and carried out research around the above-mentioned unsolved scientific problems.The specific research contents and conclusions are as follows:First,the sludge retention time(SRT)of the HLB-MR is optimized and its influence mechanism is analyzed.The results show that: under the short SRT condition of 0.2d,0.6d and 1.0d,with the increase of SRT,the content of extracellular polymer substance(EPS)in the HLB-MR gradually increases,and more EPS and metal ions(calcium,magnesium,iron)form bridges,which enhanced the bioflocculation effect of colloidal organic matter,and the membrane fouling in the reactor is gradually reduced.But the mineralization rate of organic matter gradually increases,and the capture efficiency of organic matter gradually decreases.From the comprehensive comparison of organic matter recovery effect and membrane fouling control,it is determined that SRT of 0.6d is the better control parameter for HLB-MR.Under these conditions,the flocculation efficiency of colloidal COD is as high as 90%,and the degree of membrane fouling is relatively light;the recovery rate of total COD can be as high as over 80%.With the change of SRT,the microbial community structure in the HLB-MR has changed significantly;Acinetobacter and norank＿f＿norank＿o＿Saccharimonadales are dominant species in the supernatant,which may cause greater membrane fouling.Ornithinibacter,Trichococcus,and norank＿f＿norank＿o＿norank＿c＿Actinobacteria are the dominant species in the sediment,which may have a better effect on promoting bioflocculation.Besides the optimization of SRT parameters,the dissolved oxygen(DO)parameters are also optimized and analyse its influence mechanism.The results show that: when the DO concentration of the HLB-MR is controlled at 1～2mg/L and 6～8mg/L,the DO concentration increases,the EPS content in the reactor increases,the more EPS and metal ions(magnesium,aluminum)form bridges,which enhances the bioflocculation effect of colloidal organic matter and improves the capture efficiency of organic matter.However,the membrane fouling of the reactor has gradually increased.The higher viscosity of the concentrate,the higher content of EPS-polysaccharide in the supernatant,and the higher proportion of fine particles(0～1μm)in the concentrate in the high DO concentration reactor may all be the main reasons for the aggravation of membrane fouling.In view of the fact that when the DO is 1～2mg/L,the reactor can still achieve a flocculation efficiency of 83% and an organic matter capture efficiency of more than 70%.From the comprehensive comparison of organic matter recovery,membrane pollution control and operating cost,it is determined that the DO concentration is 1～2mg/L is the better control parameter of HLB-MR.The microbial communities of the concentrate sediment and supernatant in the two HLB-MRs with different DO concentrations are significantly different,and the microbial community of the sediment is more similar to that of the influent.With the increase of DO concentration,the relative abundance of Actinobacteria and Saccharibacteria in the sediment of the reactor increases,which may promote biolocculation.On the basis of optimization of process parameters,according to the water temperature characteristics of sewage in different regions and seasons in my country,three typical temperatures of 8℃,15℃ and 25℃ are selected.From the perspective of temperature adaptability,the efficiency and mechanism of the HLB-MR for capturing sewage carbon sources are studied.The results show that: With the increase of temperature,the capture efficiency of organic matter in the HLB-MR gradually increases,but at low temperature(8°C)conditions,HLB-MR can still recover at least 65% of the influent COD.At the three temperatures,the biological flocculation efficiency of the HLB-MR is positively correlated with the amount of EPS secreted by microorganisms and the cations(sodium,calcium and aluminum)taken up in the sludge matrix.The flocculation efficiency is the highest at 15°C.The poor bioflocculation effect at low temperature(8℃)is related to the increase of liquid viscosity and the decrease of the diffusion velocity of sub-micron particles caused by irregular Brownian motion.The reason for the poor flocculation effect under high temperature(25℃)may be the disintegration of sludge flocs.Under the temperature conditions of 15°C and 25°C,the HLB-MR is suitable for capturing and recycling the carbon source in sewage,and the membrane fouling is lighter,which can ensure the continuous and stable operation of the system.However,too low temperature(8°C)has a negative effect on the COD removal effect,organic matter recovery effect,biological flocculation effect and membrane fouling of the HLB-MR.Measures such as increasing SRT,increasing aeration intensity,adding powdered activated carbon,enhancing backwashing or reducing membrane flux(increasing membrane area)can be used to overcome the adverse effects of temperature reduction during the cold season in cold regions.Finally,starting from the control of membrane fouling,on the basis of the original HLB-MR,a low-intensity ultrasound intermittent off-line radiation concentrate recirculation system was added to construct an ultrasound-assisted HLB-MR and carry out research.The results show that: ultrasonic radiation has little effect on the COD removal efficiency,organic matter capture efficiency and biological flocculation effect of the HLB-MR,but the membrane fouling of the ultrasound-assisted HLB-MR is effectively alleviated.This is mainly due to the fact that the decrease in the viscosity of the concentrate,the bound EPS and the colloidal organic content of the supernatant in the ultrasonic-assisted reactor has a greater positive effect than the negative effect caused by the size reduction of sludge flocs.The ultrasonic-assisted HLB-MR process upgrade system was constructed by integrating the advantages of ultrasonic effectively cleaning pollution and changing the characteristics of concentrate,which can effectively ensure the stability of the system and further improve the subsequent resource recovery rate of the captured concentrate.Ultrasonic radiation can cause significant changes in the microbial community structure in the HLB-MR.Neisseriaceae and norank＿o＿＿HTA4,which tend to exist in the form of floating,are easier to separate from the inside and surface of the floc,which may cause serious membrane fouling.The dominant bacteria such as Comamonadaceae and Intrasporangiaceae in the sediment may play a better flocculation effect.The research results of this paper can lay a theoretical foundation for the engineering application of HLB-MR,provide a feasible process for the key carbon source separation unit in sewage recycling and energy conversion.It has a positive role in promoting the transformation of wastewater treatment plants to the direction of energy balance or "carbon neutral" operation. |
PDF Full Text Request