2017 Vol. 7, No. 3

Display Method:
Simulation of impact of black carbon aerosol on regional climate change in typical industries
ZHENG Huihui, SHI Huading, CHEN Lirong, GAO Qingxian, GUAN Panbo, ZHANG Qiang
2017, 7(3): 255-261. doi: 10.3969/j.issn.1674-991X.2017.03.037
Abstract(1153) PDF(9491KB)(928)
Abstract:
Black carbon aerosol is an important component of atmospheric aerosols, which has a strong absorption effect on the solar shortwave radiation and infrared radiation, and has a great impact on the regional climate. Using the Regional Climate Model Version 3 (RegCM3) and combined with self-established black carbon emissions inventory, the variation of solar radiative forcing by black carbon aerosols emitted from industry, transportation, and residential sectors in 2013 was simulated, and the climate effects of black carbon aerosol emissions from different sectors analyzed. It was shown that the black carbon aerosols were mainly distributed in the North China, Central Plains, Yangtze River Delta, Pearl River Delta and Chengdu-Chongqing region, showing obvious seasonal changes, with higher emissions in winter and spring than in summer. Among the regions, Shandong Province and Hebei Province had the biggest emissions. The emissions of the three typical sectors were in the order of residential sources>industrial sources>transportation source. The black carbon aerosol increased the surface absorption of solar radiation and caused climate effect of raising the temperature of the North China, Central Plains and Yangtze River Delta, and decreasing the temperature of Sichuan-Chongqing region and Pearl River Delta. However, the resulted change of rainfall was little, which may be related to poor simulation function of the model.
Dynamics of atmospheric ammonia concentrations over representative agricultural region in Beijing
DONG Jing, SUN Changhong, WANG Yonggang, WANG Xu, LI Mingwei, WU Juanli
2017, 7(3): 262-267. doi: 10.3969/j.issn.1674-991X.2017.03.038
Abstract(1046) PDF(2396KB)(985)
Abstract:
The spatial-temporal variability of ammonia in the atmosphere over representative agricultural region in Beijing during 2015 was monitored. The results showed that the livestock farm and fertilizer factory are both the most important ammonia sources in agricultural region, with the highest ammonia concentrations reaching 3.52 and 4.27 mg/m 3 at the downwind of the fence line, respectively. The ammonia concentrations at agricultural region presented significant difference between seasons as well as day and night, which were higher in summer and autumn, and lower in winter and spring, meanwhile higher at afternoon and lower at night. During the daytime, the ammonia concentrations present descending order at fertilizer factory, livestock farm, cropland, avenue, residential district, and forest land. At night, the ammonia concentrations were still high at fertilizer factory and livestock farm, but the affected scope was significantly reduced, while the ammonia concentrations obviously decreased at cropland, residential district, and avenue. The ammonia concentrations at residential district in the agricultural region were much lower than the Emission Standards for Odor Pollutants, and would not affect human health.
Emission characteristics and control status of fine particles emitted from coal-fired boilers
WU Yafeng, CHEN Jianhua, ZHONG Lianhong, ZHANG Guoning
2017, 7(3): 268-277. doi: 10.3969/j.issn.1674-991X.2017.03.039
Abstract(1259) PDF(1594KB)(1500)
Abstract:
Coal-fired boiler is one of the primary sources of ambient fine particulate matter in China in terms of source apportionment. In order to understand the emission characteristics and control status of fine particles emitted from coal-fired boilers, some relevant research findings both at home and abroad were summarized systematically, including the size distribution characteristics, component characteristics, emission forms and possible influencing factors of the fine particles. The removal efficiency of fine particles of current dedustors for the flue gas from coal-fired boilers as well as corresponding technical improvements on the dedustors was reviewed. Recent management situation of stationary pollution sources and sampling methods of fine particles both at home and abroad were summarized. Aiming at existing deficiency of research and management, several suggestions are proposed. Firstly, the research should be strengthen on the size distribution characteristics and formation mechanism of fine particles generated and emitted from coal-fired boilers from the point of view of source control, targeting the reduction of the emission of primary condensable particles and the precursors of secondary fine particles. Secondly, the study on component characteristics of fine particles from local coal-fired boilers should be strengthened. Thirdly, the development of efficient dedusting technologies should be accelerated, especially focusing on the affordable control technologies of fine particles for industrial coal-fired boilers. Fourthly, great attention should be paid to the study and management policy of the number concentration of fine particles and superfine particles. Finally, it is suggested that the standard sampling methods and emission limit of fine particles from stationary sources should be formulated by relevant administrative departments.
Analysis of climate change impact on air pollution potential in Shaanxi
JIANG Quan, CAO Yingxue, YANG Jianjun
2017, 7(3): 278-284. doi: 10.3969/j.issn.1674-991X.2017.03.040
Abstract:
The potential of atmospheric diffusion was analyzed, and the atmospheric diffusion model used to simulate the atmospheric diffusion potential for different years and seasons and for different climate and short-term climate change situations, so as to evaluate the influence of short-term climate change or regional climate change on the air pollution potential and atmospheric environment. According to the simulation results of climate change potential in 1999-2009, the climate change in north of Shaanxi and south of Shaanxi showed the trend of annually decelerating air pollution diffusion forms, with yearly increase rate of the average concentration being 1.38% and 0.29%, respectively. Central of Shaanxi showed more favorable atmospheric diffusion potential for pollutant diffusion, with the maximum sulfur dioxide concentration decreasing by 3.59% yearly.
Study on carrier optimum filling ratio of two-stage MBBR for treatment of reverse osmosis concentrate from high-quality water reclamation of WWTP effluent
CHENG Zirui, JIANG Yunchao, WANG Haiyan, LI Peixian, HANG Qianyu, LI Li, YANG Yanyan, ZHONG Zhen
2017, 7(3): 285-292. doi: 10.3969/j.issn.1674-991X.2017.03.041
Abstract(1106) PDF(2576KB)(1069)
Abstract:
A pilot nitrosation-denitrification two-stage moving bed bio-film reactor (MBBR) was developed for the advanced nitrogen removal of high N H 4 + -N and salinity reverse osmosis concentrate, which was produced from the high-quality water reclamation of wastewater treatment plant (WWTP) effluent. The removal effect of N H 4 + -N, N O 3 - -N, CODCr and other pollutants was compared under carrier filling ratio (FR) of 51%, 42% and 32%, respectively. The results showed that the average N H 4 + -N removal rate was 67.0%±4.0%, 71.3%±8.9% and 73.2%±6.1%, when the FR was 51%, 42% and 32% in the nitrosation MBBR, and the optimal FR was 32%. In the denitrification MBBR, the average N O 3 - -N removal rate was 73.1%±4.2%, 63.7%±9.4% and 64.9%±10.4%, when the FR was 51%, 42% and 32% respectively. Taking account of economical availability, 32% was selected as the optimum FR.
Pilot-scale treatment of pharmaceutical comprehensive wastewater by ABR-CASS fed with different batches of influent
LIAO Miao, FAN Yadong, LIU Shiyue, WEI Jian, LIU Yang, ZENG Ping
2017, 7(3): 293-299. doi: 10.3969/j.issn.1674-991X.2017.03.042
Abstract(1322) PDF(1522KB)(1070)
Abstract:
A pilot-scale anaerobic baffled reactor-cyclic activated sludge system (ABR-CASS) reactor was employed to treat three batches of pharmaceutical wastewater from the same pharmaceutical factory. ABR and CASS showed different treatment capabilities to the wastewater. The ABR was almost hardly affected by the components from different batches of pharmaceutical wastewater. However, the influence to CASS was great. CASS could run stably with sludge loading of 0.012 kg COD/(kg MLSS·d) when fed with the first batch of ABR effluent. For the whole system, the overall efficiencies of COD and NH3-N were 92.54% and 95.77%, separately. However, CASS could not endure the wastewater when fed with the third batch of ABR effluent. GC-MS analysis showed that the toxic compounds of tributylamine and p-methyl phenol from the third batch of ABR effluent might be the main factors caused the crash of CASS. To guarantee stable operation of the whole ABR-CASS system, the elimination capability of ABR on influent key toxic compounds should be concerned to provide suitable influence for CASS operation.
Effect of hydrothermal and anaerobic digestion on dissolution of carbon,nitrogen and phosphorus in sludge
WANG Zaizhao, JIA tongtong, WANG Jiaoqin, GONG Lei
2017, 7(3): 300-305. doi: 10.3969/j.issn.1674-991X.2017.03.043
Abstract(1031) PDF(1780KB)(1105)
Abstract:
The influence of hydrothermal pretreatment temperature and anaerobic digestion on the dissolution of carbon, nitrogen and phosphorus in sludge was studied. The results showed that the higher the hydrothermal pretreatment temperature was more favorable to the dissolution of carbon, nitrogen and phosphorus. When the hydrothermal pretreatment temperature was 200 ℃, the dissolution rate of SCODCr improved by 5.9 times compared with the raw sludge, the rate of NH3-N and TN improved by 7.2 and 8.7 times, and the rate of P O 4 3 - and TP improved by 0.2 and 6.1 times, respectively. After the anaerobic digestion, the carbon and phosphorus content in sludge decreased, while the nitrogen content increased. The cumulative methane production was related to the hydrothermal treatment temperature; when the hydrothermal temperature was 160 ℃, the cumulative methane production was up to 12 223 L/mg-CO D C H 4 , increased by 14.5 times than that of the raw sludge. According to the experimental results, strategy for recovering nitrogen and phosphorus from the hydrothermal and anaerobic digestion sludge was proposed, including adding some magnesium source after hydrothermal pretreatment so as to recover phosphorus, and adding some adsorbent to adsorb the nitrogen during the dissolution of anaerobic digestion. It was also proposed that while recycling the nitrogen and phosphorus in sludge, the cumulative methane production in anaerobic digestion should be improved through water and thermal process.
Research progress of preparation of sewage sludge-based carbonaceous adsorbents and their adsorption characteristics
XIN Wang, SONG Yonghui, ZHANG Yadi, DUAN Lijie, PENG Jianfeng, LIU Ruixia
2017, 7(3): 306-317. doi: 10.3969/j.issn.1674-991X.2017.03.044
Abstract(1226) PDF(1817KB)(1344)
Abstract:
With the extensive construction and operation of urban sewage treatment plant, massive excess sludge has brought great pressure to the water industry and environmental protection. The safe disposal and resource utilization of sewage sludge have been the hot issues in the field of environmental protection. The preparation of sludge-based carbons from carbonizing excess sludge at high temperature is one of the important directions of sewage sludge recycling, safe disposal and environmental remediation. The main methods include direct carbonization, chemical activation, catalytic activation, and carbon source addition, etc. The characteristics of various preparation methods and the properties of the product were summarized firstly, and the adsorption performance of organic pollutants and heavy metals in aqueous phase and the adsorption mechanisms were analyzed. Then the main research directions of preparation of activated carbons from pyrolytic sludge were proposed. Finally the outlook of excess sewage pyrolysis disposal was given from the perspectives of energy recovery, special industrial sludge and waste resource utilization.
Chlorine element migration in gasification process of oily sludge-coal water slurry
YANG Dongyuan, HU Guangfa, QI Yonghong, WANG Yan, YAO Bin
2017, 7(3): 318-322. doi: 10.3969/j.issn.1674-991X.2017.03.045
Abstract(1028) PDF(1029KB)(962)
Abstract:
Based on an analysis of the chemical composition and characteristics of oily sludge produced from Ordos basin oilfield and the gasification ash & ash water after mixing with coal water slurry, the chlorine migration in the gasification process of oily sludge-coal water slurry was studied. The results showed that the oily sludge mix ratio is 5% (wt) in the whole slurry, and the ash water composition is basically identical with common coal water slurry. The chlorine in oil sludge-coal water slurry is mainly migrated into ash water during gasification process, with little into the coarse slag and fine dregs. By gasification reaction the chlorine in oily sludge mainly transfers into hydrochloric acid, and no dioxins are formed in the gaseous phase.
Risk ranking technology method on groundwater pollution of contaminated sites
YANG Yu, LIAN Xinying, MA Zhifei, XU Xiangjian, JIANG Yonghai, PENG Xing, XI Beidou
2017, 7(3): 323-331. doi: 10.3969/j.issn.1674-991X.2017.03.046
Abstract(1007) PDF(819KB)(1078)
Abstract:
Referring to the risk ranking methodology of groundwater contamination both at home and abroad and based on the comprehensive analysis on the key points of the groundwater pollution risk in the contaminated sites, the analytic hierarchy process was applied to establish the risk ranking index system on groundwater pollution of contaminated sites from three aspects, i.e. the contaminated sites properties, the groundwater inherent vulnerability in the contaminated sites region and the characteristics of the groundwater protection target. The risk ranking index system consists of 17 indicators. Based on the survey on contaminated sites and the physical and chemical properties of 159 typical pollutants, the risk level for each indicator was ranked. The total risk index was calculated by multiplying the individual risk indicators, and the method of groundwater pollution of contaminated sites was established by applying the clustering analysis. The method can effectively avoid the subjectivity of index weight calculation, and ide.pngy the main factors that lead to the risk. The results showed that the risk of groundwater pollution of contaminated sites could be divided into 3 levels, i.e. the risk value less than 5 (Level 1), between 5 and 15 (Level 2) and greater than 15 (Level 3). By applying the risk assessment system in a hazardous waste landfill, it was shown that the landfill had a potential risk of Level 3, and the properties of the contaminated sites, especially the characteristic pollutant was the main factors that caused the groundwater environmental risk.
Influence of Phragmites australis carbon dosage on enhanced nitrogen removal start-up of pilot-scale surface flow constructed wetland
ZHANG Hengliang, ZHU Tiequn, WANG Haiyan, CHU Zhaosheng, HANG Qianyu, HOU Zeying
2017, 7(3): 332-339. doi: 10.3969/j.issn.1674-991X.2017.03.047
Abstract(1112) PDF(1994KB)(1020)
Abstract:
Slow-released plant carbon, Phragmites australis pieces, was added to the surface flow constructed wetland (SFW) to enhance the denitrification nitrogen removal of the low C/N ratio agricultural runoff. The characteristics of the simulated agricultural runoff were as follows: (8.00±1.00)mg/L N O 3 - -N, (9.00±1.00)mg/L TN, (0.70±0.10)mg/L N H 4 + -N, 0.01mg/L N O 2 - -N and (1.00±0.05)mg/L TP. Three pilot-scale SFWs were designed for experiment as follows: the blank SFW without Phragmites australis pieces dosage, 1 # SFW with 1/4 areal proportion of Phragmites australis pieces to enhanced denitrification wetland and 2 # SFW with 1/2 areal proportion of Phragmites australis pieces to enhanced denitrification wetland. A 40-day start-up operation was carried out in static mode. The results showed that the N O 3 - -N removal efficiency increased gradually to 84.2%, 89.1% and 97.8% on the 18 th, 18 th and 7 th day for the blank, 1 # and 2 # SFW respectively, while their TN removal efficiency gradually increased to 75.1%, 79.4% and 90.0% on the 15 th, 15 th and 7 th day in the early stage (1-18 d). The N O 3 - -N was added to (8.00 ± 1.00) mg/L when it was almost completely consumed on the 18 th day. In the latter stage (19-40 d), the N O 3 - -N removal gradually increased to 78.0%, 92.2% and 95.8% on the 40 th, 37 th and 35 th day for the blank, 1 # and 2 # SFW respectively, while their TN removal efficiency increased gradually to 71.4%, 75.2% and 77.1% accordingly. The start-up period of SFW could be greatly shortened by adding Phragmites australis pieces as carbon source, and 2 # SFW started with the higher speed. Moreover, the N O 3 - -N and TN removal rates of 2 # SFW were also higher than those of 1 # and the blank SFWs. It was indicated that the higher-speed start-up and better nitrogen removal efficiency could be obtained for SFW with more Phragmites australis pieces carbon dosage.
Characteristics and potential ecological risk assessment of heavy metals pollution in sediment of Huiji River
YANG Weihong
2017, 7(3): 340-347. doi: 10.3969/j.issn.1674-991X.2017.03.048
Abstract(1171) PDF(1456KB)(978)
Abstract:
The contents of heavy metals, including Cu, Zn, Pb, Cd and Cr, in the sediments of 8 sections in the Huiji Rriver were analyzed for the last continuous five years. The single factor pollution index, integrated pollution index, geoaccumulation index and potential ecological risk index were adopted to evaluate the potential risk of the heavy metal pollution. The monitoring results indicated that the sediments from 8 monitoring sections had been polluted to different degree except that from Sunlitang bridge section which was at the upstream of Huiji river, while the sediment from Pitun bridge showed the highest pollution risk, at the severity level of severe pollution.The comprehensive pollution indices suggested that the river was under heavy pollution by Cd, light pollution by Cu and Pb, slight pollution by Zn and no pollution by Cr. The comprehensive pollution indices of most sediment ranged from 0.55 to 1.89, except 6.74 for Pitun bridge section. The geoaccumulation indices suggested that the most severe pollution was caused by Cd, which leaded to a high Igeo at 3.50, referred to heavy pollution. The river was still under moderate pollution by Cu and Pb, light pollution by Zn. The potential ecological risk indices suggested that the river was under high risk of Cd pollution and low risk of other four heavy metals pollution. The comprehensive potential ecological risk was high, which is pecked at 2 233.50 in the Pitun bridge section, mainly because of the high cadmium concentration in the sediment.
Bioavailability of dissolved free amino acids to alga Selenastrum capricornutum
ZHAI Tianen, HUO Shouliang, ZHANG Jingtian, XI Beidou, XIAO Zhe
2017, 7(3): 348-356. doi: 10.3969/j.issn.1674-991X.2017.03.049
Abstract(1146) PDF(2322KB)(766)
Abstract:
In order to understand the incubation process of algae on the low concentrations of dissolved free amino acids (DFAA), the growth of Selenastrum capricornutum was studied in the laboratory. Six individual amino acids, i.e. serine, aspartic acid, glutamic acid, glycine, alanine and arginine, were used as the sole and mixed nitrogen sources for algal incubation under axenic conditions. The results showed that algae were able to utilize various amino acids for growth; meanwhile, algae could spread different amino acids in the incubation. DFAA concentration decreased with up to 90% in the 2 days, while the cells number of algae reached to the maximum in the 6-8 days, meaning that the growth of algae cell number lags behind the decrease of the of DFAA content. In the individual amino acids experiments, rank order of the use of amino acid was: arginine>alanine>glutamic acid>aspartic acid>serine>glycine. In the mixed amino acids experiments, the cell proliferation rate of algae was significantly higher than that of individual amino acid group; meanwhile with the increase of mixed amino acid concentration, the maximum number of algal cells was also increased. Selenastrum capricornutum can also release other kinds of amino acids in the use of the individual amino acid, among them, the main release amino acids are aspartic acid and glycine. Algae could use amino acid rapidly in the lack of inorganic nitrogen condition, which provided a theoretical basis to illustrate dissolved organic nitrogen promotes algae growth.
Research progress of chloroanisoles pollutants in the environment
REN Min, ZHAO Gaofeng, WANG Xiaoyan, ZHAO Xiaohui, LI Kun, ZHAGN Panwei, LIU Qiaona, ZHAO Dandan, LI Dongjiao
2017, 7(3): 357-365. doi: 10.3969/j.issn.1674-991X.2017.03.050
Abstract(1445) PDF(905KB)(1221)
Abstract:
Chloroanisoles(CAs) are common odorous substances in wine and drinking water needing to be removed. CAs exist in different media in different parts of the world. They are often reported as off-flavor compounds which produce an earthy and musty flavors and odors in wine and drinking water, and are mainly from the degradation products of pentachlorophenols (PCP) and sodium salts. CAs have the properties of strong durability and long-range transport properties as POPs, especially the properties of reproductive toxicity and neurotoxicity. However, there are no standard methods for the determination of CAs in the world. Two kinds of CAs, 2,4,6-Trichloroanisole (TCA) and Pentachloroanisole (PCA), were studied, of which TCA has the lowest odor threshold and PCA has the highest toxicity. The source and distribution, production mechanism, metabolic transformation, toxic effects, detection and removal methods of CAs were discussed. To conclude, CAs are widely distributed with certain toxic effects. In the future, further study on the environmental migration, transformation laws and toxicology of CAs should be strengthened.
Research progress on strengthening phytoremediation technologies for heavy metals contaminated soil
XU Jianfeng, WANG Lei, XIONG Ying, XI Beidou, ZHANG Lieyu, MAO Xuhui, YANG Tianxue, WU Minghong, LI Tongtong
2017, 7(3): 366-373. doi: 10.3969/j.issn.1674-991X.2017.03.051
Abstract(1725) PDF(936KB)(1763)
Abstract:
The traditional remediation technologies of the soil contaminated heavy metals were mainly physical, chemical and biological. The phytoremediation technologies are reliable biological technologies for removing the heavy metal pollution in soil in recent years and become the frontier and hot research areas of resource, environmental and biological sciences internationally. Due to their low cost, wide adaptability and no secondary pollution, the phytoremediation technologies have been widely studied. To screen out or breed suitable plant species which can tolerate and accumulate multiple metals, with fast growth and wide adaptation is of most importance for phytoremediation. The current remediation technologies of heavy metals in soil were summarized. In view of the restriction problems of phytoremediation of heavy metals in soil, the research progress of strengthening phytoremediation technologies were reviewed. The physical, chemical, and biotechnology methods for increasing the plant biomass and heavy metal accumulation were discussed, focusing on the mechanism and application effects of genetic engineering technology, chelate induced technology, root exudates and arbuscular mycorrhizae strengthening phytoremediation, and prospecting future research directions.
Ecological carrying capacity evaluation on exploiting coastline for port construction in Xiamen Bay based on habitat protection
FAN Xiaoshan, HE Ping, JIA Jiao, XU Yaoyao, DONG Jingru
2017, 7(3): 374-381. doi: 10.3969/j.issn.1674-991X.2017.03.052
Abstract(1054) PDF(4883KB)(1772)
Abstract:
The evaluation of ecological carrying capacity is the important reference for optimizing the project plans and promoting the sustainable development of socio-economy and natural environment. However most of the available evaluation methods of ecological carrying capacity are incompetent in project pertinence. The methods are basically used to study the comprehensive and regional resource and environmental problems, but not suitable for assessing the sustainable carrying capacity of natural resource and eco-environment systems for specific types of project construction within the planning area. Taking Xiamen Bay as an example, the RS and GIS technologies were applied and the principle of ecological suitability evaluation used to constitute the evaluation index system and explore the ecological capacity evaluation technique for the coastal port development, based on coastline habitat conservation of important species and in combination of the constraint conditions for the development. The research can enhance the technical supports ability of the evaluation results in improving the project schemes, and promote to reform the ecological capacity evaluation technologies for project plans.
Heating by air-source heat pump for cold climate in Chinese rural regions
PANG Weike, LÜ Lianhong, LUO Hong
2017, 7(3): 382-387. doi: 10.3969/j.issn.1674-991X.2017.03.053
Abstract(933) PDF(1735KB)(1255)
Abstract:
Based on Chinese rural features, a heating way adopting an air-source heat pump (ASHP) for low cold climate that is a novel and pollution-free technique of energy utilization is proposed. The technique is feasible to replace the traditional heating way of dispersed coal combustion. The air-source heat pump is with a stable and reliable design of adding refrigerant for enthalpy increment. The results showed that under the simulated conditions of the evaporation temperature of -30 ℃, condensing temperature of 45 ℃, and ejecting refrigerant ratio of 0.6, its coefficient of performance (COP) is more than 2.25 and the energy efficiency ratio (EER) is more than 1.90 in theory. During its application in practice, the air-source heat pump could heat by warm air or water to meet with different needs. It is projected that about 386 million tons of carbon dioxide, 11.5 million tons of sulfur dioxide, 5.7 million tons of nitrogen oxide and 105 million tons of powder and dust could be decreased annually if the heat pumps are popularized in Chinese countryside. It can serve as an optimal scheme to phase out the traditional heating way in the countryside.
Experimental study on fine particle and dust removal efficiency influenced by low-low temperature electrostatic precipitator
LIU Xiyao, LU Chunmei, CHEN Yong, YANG Ding, HUANG Jinju
2017, 7(3): 388-392. doi: 10.3969/j.issn.1674-991X.2017.03.054
Abstract:
Under simulated operating conditions, new multi-functional testing dust remover and electrical low pressure impactor (ELPI), etc. were used to conduct experiment study on the low-low temperature electrostatic precipitator (ESP) technology for the fine particle (such as PM10, PM2.5, PM1.0) and dust. The results showed that PM10, PM2.5, PM1.0 and dust removal efficiencies were significantly higher at lower inlet flue gas temperatures (67-68 ℃)than that at higher inlet flue gas temperatures (86-89 ℃). At lower inlet flue gas temperatures, as the inlet flue gas flow rate decreased, the extent of increased fine particle and dust removal efficiencies was more significant, which indicated that as inlet flue gas flow rate decreased, the residence time of fine dust in the electrical field extended, thus more convenient to collecting fine particle and dust for low-low ESP.