硝酸盐还原条件下Fe0/厌氧微生物联合体系降解2,4,6-三氯酚

本文采用间歇试验,对硝酸盐还原条件下Fe0/厌氧微生物联合体系降解2,4,6-三氯酚(2,4,6-TCP)进行了研究。考察了不同硝酸盐浓度下,体系中pH、硝酸盐浓度以及硝酸盐还原活性的变化情况。结果表明:当2,4,6-TCP初始浓度为20mg/L时,硝酸盐对Fe0/厌氧微生物联合体系降解2,4,6-三氯酚具有明显的抑制作用;且随着硝酸盐浓度的升高,2,4,6-TCP的去除率降低,硝酸盐还原活性升高;体系先发生硝酸盐还原再进行2,4,6-TCP还原脱氯。     

不同电子供体对2,4-二氯酚还原脱氯的影响

以葡萄糖、乙酸钠、Fe0、Fe0 葡萄糖、Fe0 乙酸钠作为电子供体,接种未驯化厌氧混合菌,考察2,4-二氯酚(2,4-DCP)的还原脱氯特性及Fe0作为电子供体的最佳作用条件与持续性特征.结果表明:与葡萄糖的作用相比,Fe0 葡萄糖可有效提高目标物脱氯效果;乙酸钠、Fe0及Fe0 乙酸钠均为有效电子供体,其中Fe0作为电子供体时目标物脱氯效果最佳,最佳作用条件为初始pH8.0,Fe0投加量2.0 g/L,4-CP为其主要脱氯中间产物;Fe0可持续供给2,4-DCP还原脱氯所需电子,而乙酸钠不断消耗后其脱氯效果与Fe0作为电子供体有明显差距.     

零价铁对2,4-二氯酚生物还原脱氯的影响研究

采用间歇试验, 接种驯化两月的厌氧混合微生物, 考察厌氧体系中添加零价铁(Fe0)对2,4-二氯酚(2,4-DCP)生物还原脱氯效果的影响, 并对影响“Fe0+微生物”体系的一些因素进行了探索。结果显示：与零价铁或微生物的单独作用相比, “Fe0+微生物”体系能够有效促进2,4-DCP的脱氯反应, 最佳Fe0投加量和微生物接种量分别为0.5 g/L和376.2 mgVSS/L; 初始pH = 8.0对2,4-DCP的转化效果最好, 偏酸性环境不利于污染物转化; 微生物接种量与铁用量之间有一适宜比例, 一定范围内增加微生物接种量可催生出更多可降解污染物的酶或酶系, 提高2,4-DCP的降解效果。     

零价铁对2,4-二氯酚生物还原脱氯的影响研究

采用间歇试验,接种驯化两月的厌氧混合微生物,考察厌氧体系中添加零价铁（Fe^0）对2,4-二氯酚（2,4-DCP）生物还原脱氯效果的影响,并对影响“Fe^O＋微生物”体系的一些因素进行了探索。结果显示：与零价铁或微生物的单独作用相比,“Fe^O＋微生物”体系能够有效促进2,4-DCP的脱氯反应,最佳Fe^O投加量和微生物接种量分别为0.5g／L和376.2mgVSS／L;初始pH=8.0对2,4-DCP的转化效果最好,偏酸性环境不利于污染物转化;微生物接种量与铁用量之间有一适宜比例,一定范围内增加微生物接种量可催生出更多可降解污染物的酶或酶系,提高2,4-DCP的降解效果。     

1,2,3-三氯丙烷降解机制与污染场地修复技术研究进展

1,2,3-三氯丙烷(1,2,3-trichloropropane,1,2,3-TCP)是一种人工合成的脂肪族氯代烃,在工、农业生产中得到广泛应用。1,2,3-TCP作为环氧氯丙烷工业生产的中间产物,可作为前体物质用于生产土壤熏蒸剂、有机溶剂等。因其环境持久性、迁移性和生态毒性,国内外机构逐渐开始关注该有机氯污染物的环境归趋、生态健康风险和环境管控。当前,1,2,3-TCP污染物的降解与场地修复仍然是研究热点,但是对于1,2,3-TCP降解转化机制尚缺乏深入研究与总结。鉴于此,文中在讨论1,2,3-TCP的来源、环境污染、生态效应及物理化学降解方法与技术等的基础上,进一步综述了1,2,3-TCP的微生物降解与修复机制(如好氧共代谢降解、厌氧降解等);重点讨论了地下水等厌氧环境中1,2,3-TCP的厌氧微生物降解转化途径与机制,并从热力学角度论证了厌氧条件下1,2,3-TCP作为电子受体被有机卤呼吸微生物利用并降解的可行性;最后,对1,2,3-TCP污染场地原位生物修复进行了总结并对未来研究发展方向进行了展望。     

六氯-1,3-丁二烯的微生物降解研究进展

六氯-1,3-丁二烯(hexachlorobutadiene,HCBD)是一种有毒有害的脂肪族氯代烃,曾经作为杀虫剂、除草剂、变压器油和传热流体等化学工业产品的重要成分被广泛应用于生产生活。HCBD因满足《关于持久性有机污染物的斯德哥尔摩公约》中风险筛选标准(如毒性、持久性、远距离环境迁移和生物累积性等),缔约方于2015年第七次会议中将其增列为持久性有机污染物,2017年又将其列入该公约的附件Ｃ以控制其环境排放量。目前关于HCBD的环境归趋仍是研究热点,但是对于HCBD的微生物降解转化机制尚缺乏深入研究。鉴于此,本文重点回顾并讨论了地下水、底泥等厌氧环境中已报道的HCBD微生物降解转化途径、速率及机制,并从热力学角度阐述HCBD及其降解产物作为电子受体通过还原性脱氯反应被厌氧脱卤微生物代谢转化的可行性。最后,本文根据现有研究结果,提出微生物厌氧降解HCBD的研究展望,包括多组学技术解析HCBD降解功能菌群结构和潜在互作机制、HCBD厌氧降解微生物的分离与纯化,以及HCBD厌氧降解菌剂的开发与污染场地原位生物修复应用等。     

脱卤单胞菌属在厌氧降解有机氯化物及污染场地修复应用中的研究进展

脱卤单胞菌 Dehalogenimonas 是绿弯菌门 (Chloroflexi) 脱卤球菌纲 (Dehalococcoidia) 的一个属。脱卤单胞菌属目前包含 Dehalogenimonas lykanthroporepellens、Dehalogenimonas alkenigignens 和 Dehalogenimonas formicexedens 这 3 个已正式命名的物种,其成员均为严格厌氧的专性有机卤呼吸细菌,利用氢气和甲酸作为电子供体,以氯代烷烃 (例如 1,2,3-三氯丙烷、1,2-二氯丙烷和 1,2-二氯乙烷) 作为电子受体,通过介导还原性脱氯反应获得能量进行生长。我国污染场地地下水中氯代烷烃等有机氯污染较为突出,脱卤单胞菌的产能方式使其在污染场地原位修复中具有重要的应用价值。新近发现的 WBC-2 菌株和"Candidatus Dehalogenimonas etheniformans" GP 菌株可以脱氯降解某些氯代烯烃,其中 GP 菌株能够将一氯乙烯完全脱氯至乙烯,拓展了有限的一氯乙烯脱氯菌种资源,丰富了脱卤单胞菌的生态学功能。文中围绕脱卤单胞菌属的生理生化特性、生态功能及基因组信息进行综述,旨在为污染场地有机氯污染物的清理及工程实施提供理论指导。     

不同价态铁元素对厌氧微生物降解2,4,6-三氯酚的影响

【目的】考察初始pH值为5.0?10.0时, 不同价态铁元素(Fe0、Fe2+和Fe3+)对厌氧微生物降解2,4,6-三氯酚(2,4,6-TCP)的影响。【方法】采用间歇试验, 接种驯化3个月的厌氧污泥, 向其中分别投加Fe0、Fe2+和Fe3+, 测定体系中2,4,6-TCP浓度、pH值、铁离子浓度和微生物脱氢酶活性。【结果】“Fe0/Fe2+/Fe3+-微生物”体系对2,4,6-TCP的降解效率, 在初始pH值为中性偏酸性时, “Fe2+-微生物”体系>“Fe0-微生物”体系>“Fe3+-微生物”体系; 而当初始pH值为碱性时, “Fe0-微生物”体系>“Fe2+-微生物”体系>“Fe3+-微生物”体系; “Fe0/Fe2+/Fe3+-微生物”三种体系均有调节pH值的能力, 其中“Fe0-微生物”体系调节能力最强; 在不同初始pH值条件下不同价态铁元素对厌氧微生物活性的影响结果与其对2,4,6-TCP的影响规律基本相同。【结论】不同价态铁元素对厌氧微生物降解2,4,6-TCP的影响与初始pH值、体系实时pH值和铁元素价态及浓度等因素有关。     

R-2-氯丙酸脱卤酶的定向进化

通过易错PCR手段将R-2-氯丙酸脱卤酶定向进化,并使用基于Cl-浓度显色反应的高通量筛选得到有效突变子库,发现突变子DehDIV-G2和DehDIV-E7的酶比活力分别提高25.2%和38.7%。通过SYBYL对酶与底物进行分子对接显示,DehDIV-G2的活化能下降0.961 4 kJ/mol,DehDIV-E7的活化能下降2.549 8 kJ/mol。由于酶和底物R-2-氯丙酸的活化能下降,亲和能力提高,从而提高酶的比活力。     

球形红细菌厌氧降解邻二氯苯及其机理研究

研究分析光合细菌球形红细菌在厌氧光照条件下降解邻二氯苯的条件和机理.结果表明,在厌氧光照条件下球形红细菌的最佳生长和对邻二氯苯的最佳降解条件为:pH 7.0,温度为30℃,接种量10%.在最佳条件下,邻二氯苯的去除率可达90%以上;其降解中间产物主要有氯苯、4-羟基苯甲酸;根据降解产物的分析,推断球形红细菌降解邻二氯苯的机理主要是按照先脱掉一个氯原子生成氯苯,然后氯苯进一步脱氯并通过4-羟基苯甲酸的代谢途径开环进行.     

Anaerobic/aerobic conditions and biostimulation for enhanced chlorophenols degradation in biocathode microbial fuel cells

Anaerobic/aerobic conditions affected bacterial community composition and the subsequent chlorophenols (CPs) degradation in biocathode microbial fuel cells (MFCs). Bacterial communities acclimated with either 4-chlorophenol (4-CP) or 2,4-dichlorophenol (2,4-DCP) under anaerobiosis can degrade the respective substrates more efficiently than the facultative aerobic bacterial communities. The anaerobic bacterial communities well developed with 2,4-DCP were then adapted to 2,4,6-trichlorophenol (2,4,6-TCP) and successfully stimulated for enhanced 2,4,6-TCP degradation and power generation. A 2,4,6-TCP degradation rate of 0.10 mol/m³/d and a maximum power density of 2.6 W/m³ (11.7 A/m³) were achieved, 138 and 13 % improvements, respectively compared to the controls with no stimulation. Bacterial communities developed with the specific CPs under anaerobic/aerobic conditions as well as the stimulated biofilm shared some dominant genera and also exhibited great differences. These results provide the most convincing evidence to date that anaerobic/aerobic conditions affected CPs degradation with power generation from the biocathode systems, and using deliberate substrates can stimulate the microbial consortia and be potentially feasible for the selection of an appropriate microbial community for the target substrate (e.g. 2,4,6-TCP) degradation in the biocathode MFCs.     

Reductive dechlorination of 2-chlorophenol in a hydrogenotrophic, gas-permeable, silicone membrane bioreactor

A gas-permeable silicone membrane bioreactor was used to cultivate the biofilm under hydrogenotrophic condition for reductive dechlorination of 2-chlorophenol (2-CP). The anaerobic sludge obtained from a swine wastewater treatment plant was immobilized by polyvinyl alcohol (PVA) so as to form a biofilm on the surface of the silicone tube. After acclimating for about 4 months, the bioreactor showed a high dechlorinating performance. Under the condition of continuous feeding with 2-CP at 25 mg/l and the hydraulic retention time of 15 h, the 2-CP removal efficiency reached 92.8% (2-CP decay rate: 0.67 g/m² d of surface area of silicone tube). H₂ was used as electron donor for dechlorinating 2-CP, and produced the dechlorinating intermediate, phenol. Both nitrate and sulfate played important roles in inhibiting 2-CP dechlorination through different biological mechanisms. Nitrate can be easily utilized as an electron acceptor by the biofilm, while sulfate cannot. Results of this study demonstrated that nitrate competed with 2-CP as the electron acceptor, while sulfate retarded the activity of hydrogen-dechlorinating bacteria and thus inhibited the 2-CP dechlorination.     

Anaerobic and aerobic biodegradation of chlorophenols using UASB and ASG bioreactors

Chlorophenol degradation was studied by combined anaerobic–aerobic treatments as a single or multi-substrate system. 2,4-Dichlorophenol (2,4-DCP) was degraded to the extent of 52 and 78% in up-flow anaerobic sludge blanket (UASB) and aerobic suspended growth (ASG) reactors respectively, at organic loading rates of 0.18kg/m³/day and hydraulic retention time of 26.4h in the presence of glucose. The UASB represents the dominating facultative anaerobic microbial population. When the effluent from the anaerobic reactor (UASB) was subjected to aerobic treatment on the ASG reactor, 2,4-DCP and COD removals of 86 and 95% respectively were achieved. Aerobic degradation of chlorophenol by acclimated mixed bacterial isolates was found to be sequential: 2-Chlorophenol (2-CP) and 4-CP were degraded first, followed by 2,4-DCP and 2,4,6-Trichlorophenol (2,4,6-TCP) while the contrary was obtained in anaerobic degradation. In anaerobic degradation by acclimated mixed bacterial cells, 2,4-DCP and 2,4,6-TCP were degraded first followed by mono-chlorophenols. The anaerobic/aerobic bioreactors were most efficient when operated in sequence (series) rather than in parallel.     

Effect of pH on the anaerobic dechlorination of chlorophenols in a defined medium

Anaerobic dehalogenation of aromatic compounds is a well-documented phenomenon. However, the effects of operating parameters such as pH have received little attention despite their potential impact on treatment processes using dehalogenating organisms. In this work the effect of pH on the dehalogenation of 2,4,6-trichlorophenol (2,4,6-TCP) was studied using defined media containing one of several non-fermentable buffering agents (MOPS, TRICINE, BICINE, CHES), and no chloride ions. The dechlorination process was followed by monitoring the disappearance of 2,4,6-TCP, as well as the appearance of its dehalogenation products, i.e., 2,4-dichlorophenol (2,4-DCP), 4-chlorophenol (4-CP), and chloride ions. The results indicate that dechlorination occurs only if the pH is within the range 8.0–8.8. The newly formed 2,4-DCP was also dehalogenated in the process. However, even within this pH range dechlorination ceased when all 2,4,6-TCP and 2,4-DCP was converted to 4-CP. Stoichiometric amounts of all dehalogenation products (including chloride) could be recovered at any stage during the process. In addition, the biomass concentration was measured. After an initial lag phase, it appeared that the rate of dechlorination per unit biomass (proportional to the Cl^– concentration divided by the biomass concentration) went through a rapid increase and then remained constant throughout the process. This indicates that the dechlorinating organism(s) either make up the entire population or constitute a stable fraction of it. Correspondence to: P. M. Armenante     

The anaerobic degradation of 3-chloro-4-hydroxybenzoate in freshwater sediment proceeds via either chlorophenol or hydroxybenzoate to phenol and subsequently to benzoate.

To study the anaerobic degradation of the chimera 3-chloro-4-hydroxybenzoate (3-Cl,4-OHB), anaerobic freshwater sediment samples from the vicinity of Athens, Ga., were adapted for the transformation of 4-hydroxybenzoate (4-OHB), 3-chlorobenzoate (3-CB), 2-chlorophenol (2-CP), and 2,4-dichlorophenol (2,4-DCP). In nonadapted samples, both 4-OHB (product of aryl dechlorination) and 2-CP (product of aryl decarboxylation) were observed as intermediates in the transformation of 3-Cl,4-OHB to phenol. The accumulated phenol was subsequently transformed to benzoate, an intermediate in the conversion to methane and CO2. In 4-OHB-adapted samples (i.e., samples adapted for aryl decarboxylation), 2-CP was the first intermediate which was subsequently dechlorinated to phenol. In 3-CB-adapted samples (i.e., samples adapted for meta-chlorobenzoate dehalogenation), 3-Cl,4-OHB was stoichiometrically dechlorinated to 4-OHB. In 2-CP-adapted samples (i.e., samples adapted for ortho-chlorophenol dehalogenation), 4-OHB was the first major intermediate. Furthermore, 3-CB was not dechlorinated in 2-CP-adapted sediment samples, suggesting the possibility that different 3-Cl,4-OHB dechlorinating systems were induced in the 2-CP- and 3-CB-adapted sediments. Adaptation of sediment samples for dechlorination of 2,4-DCP did not lead to adaptation for dechlorination of 3-Cl,4-OHB. However, 3-Cl,4-OHB was dechlorinated to 4-OHB in our stable, sediment-free 2,4-DCP-dechlorinating enrichment, isolated previously from the same environment.(ABSTRACT TRUNCATED AT 250 WORDS)     

The anaerobic degradation of 3-chloro-4-hydroxybenzoate in freshwater sediment proceeds via either chlorophenol or hydroxybenzoate to phenol and subsequently to benzoate.

To study the anaerobic degradation of the chimera 3-chloro-4-hydroxybenzoate (3-Cl,4-OHB), anaerobic freshwater sediment samples from the vicinity of Athens, Ga., were adapted for the transformation of 4-hydroxybenzoate (4-OHB), 3-chlorobenzoate (3-CB), 2-chlorophenol (2-CP), and 2,4-dichlorophenol (2,4-DCP). In nonadapted samples, both 4-OHB (product of aryl dechlorination) and 2-CP (product of aryl decarboxylation) were observed as intermediates in the transformation of 3-Cl,4-OHB to phenol. The accumulated phenol was subsequently transformed to benzoate, an intermediate in the conversion to methane and CO2. In 4-OHB-adapted samples (i.e., samples adapted for aryl decarboxylation), 2-CP was the first intermediate which was subsequently dechlorinated to phenol. In 3-CB-adapted samples (i.e., samples adapted for meta-chlorobenzoate dehalogenation), 3-Cl,4-OHB was stoichiometrically dechlorinated to 4-OHB. In 2-CP-adapted samples (i.e., samples adapted for ortho-chlorophenol dehalogenation), 4-OHB was the first major intermediate. Furthermore, 3-CB was not dechlorinated in 2-CP-adapted sediment samples, suggesting the possibility that different 3-Cl,4-OHB dechlorinating systems were induced in the 2-CP- and 3-CB-adapted sediments. Adaptation of sediment samples for dechlorination of 2,4-DCP did not lead to adaptation for dechlorination of 3-Cl,4-OHB. However, 3-Cl,4-OHB was dechlorinated to 4-OHB in our stable, sediment-free 2,4-DCP-dechlorinating enrichment, isolated previously from the same environment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sequential anaerobic degradation of 2,4-dichlorophenol in freshwater sediments.

2,4-Dichlorophenol (2,4-DCP) was anaerobically degraded in freshwater lake sediments. From observed intermediates in incubated sediment samples and from enrichment cultures, the following sequence of transformations was postulated. 2,4-DCP is dechlorinated to 4-chlorophenol (4-CP), 4-CP is dechlorinated to phenol, phenol is carboxylated to benzoate, and benzoate is degraded via acetate to methane and CO2; at least five different organisms are involved sequentially. The rate-limiting step was the transformation of 4-CP to phenol. Sediment-free enrichment cultures were obtained which catalyzed only the dechlorination of 2,4-DCP, the carboxylation of phenol, and the degradation of benzoate, respectively. Whereas the dechlorination of 2,4-DCP was not inhibited by H2, the dechlorination of 4-CP, and the transformation of phenol and benzoate were. Low concentrations of 4-CP inhibited phenol and benzoate degradation. Transformation rates and maximum concentrations allowing degradation were determined in both freshly collected sediments and in adapted samples: at 31 degrees C, which was the optimal temperature for the dechlorination, the average adaptation time for 2,4-DCP, 4-CP, phenol, and benzoate transformations were 7, 37, 11 and 2 days, respectively. The maximal observed transformation rates for these compounds in acclimated sediments were 300, 78, 2, 130, and 2,080 micromol/liter(-1)/day(-1), respectively. The highest concentrations which still allowed the transformation of the compound in acclimated sediments were 3.1 m/M 2,4-DCP, 3.1 mM 4-CP, 13 mM phenol, and greater than 52 mM benzoate. The corresponding values were lower for sediments which had not been adapted for the transformation steps.     

Degradation of 2,4,6-trichlorophenol (2,4,6-TCP) by co-immobilization of anaerobic and aerobic microbial communities in an upflow reactor under air-limited conditions

The co-immobilization and the culture of anaerobic and aerobic communities was tested for the mineralization of 2,4,6-trichlorophenol (2,4,6-TCP). At first, the anaerobic microorganisms (aggregated into granules) were cultivated in an upflow anaerobic sludge blanket (UASB) reactor, in a continuous mode, with glucose, propionate, acetate (COD loading rate = 0.5-2.0 g COD/l per day, ratio 1:1:1) and 2,4,6-TCP (2,4,6-TCP loading rate = 25-278 micromol/l per day) as substrates. 2,4,6-TCP was degraded into 2,4-DCP and 4-CP, but it was not mineralized because of the low degradation rates of 4-CP. Furthermore, the highest loading rates of 2,4,6-TCP (>126 micromol/l per day) caused the inhibition of the strains degrading the propionate. The granules were therefore tested in association with the aerobic community. They were immobilized in kappa-carrageenan/gelatin [2% (w/w) of each polymer] gel beads and cultivated in a reactor, on their own (to test the influence of the gel), and then with the aerobic community, under anaerobic and air-limited conditions, respectively. The results showed that (1) the gel did not influence the activity of the granules, (2) the anaerobic and aerobic communities could be easily co-immobilized in gel beads and cultivated in a reactor, (3) the mineralization of 2,4,6-TCP (2,4,6-TCP loading rate = 10-506 micromol/l per day), its intermediates of degradation and the other substrates [glucose + acetate + propionate (ratio 1:1:1) = COD loading rate = 500 mg COD/l per day] could be obtained under air-limited conditions if the culture parameters were strictly controlled [airflow = 36-48 vvd (volume of air/volume of liquid in the reactor per day), pH value at around 7.5]. Finally, the gel did not retain its structure during the whole culture (263 days) in the air-limited reactor, but the anaerobic and aerobic communities retained their activities and worked together for the mineralization.     

Characterization Studies of an Anaerobic, Pentachlorophenol-Dechlorinating Enrichment Culture

Dechlorination studies were conducted using microbial cultures developed in a fluidized-bed reactor (FBR) that dechlorinates pentachlorophenol (PCP) to 3,4-dichlorophenol (3,4-DCP) and 4-monochlorophenol (4-MCP). Electron donor experiments demonstrated that lactate, propionate, and H₂ can serve as electron donors for chlorophenol (CP) dechlorination in mixed, anaerobic, PCP-enriched cultures. Dechlorination did not proceed in the absence of an electron donor. Acetate, which resulted in little H₂ production, was a poor electron donor. The results of inhibition studies using vancomycin and 2-bromoethanesulfonic acid implicate members of the domain bacteria in the dechlorination of CPs, whereas methanogens do not appear to be involved in dechlorination. Brief heat treatment (80°C for 90 min) of the FBR enrichment cultures implicated endospore formers in the dechlorination of CPs, primarily at the ortho position, where PCP was dechlorinated to 3,4,5-trichlorophenol (3,4,5-TCP) (the sole TCP detected) and subsequently to 3,4-DCP. Both lactate and H₂ served as electron donors in the heat-and oxygen-treated cultures. In contrast, a lactate-fed anaerobic spread-plate enrichment culture exhibited solely meta-dechlorination, where PCP dechlorinated solely to 2,4,6-TCP. The separation of ortho- and meta-specific dechlorination reactions provides evidence that PCP dechlorination in the FBR enrichment culture was catalyzed by at least the following two separate groups of CP-dechlorinating bacteria: one meta-dechlorinating group and one primarily ortho-dechlorinating group.