Effect of dilution rate on dynamic and steady-state biofilm characteristics during phenol biodegradation by immobilized Pseudomonas desmolyticum cells in a pulsed plate bioreactor

Continuous pulsed plate bioreactor (PPBR) was used for phenol biodegradation. Pseudomonas desmolyticum cells immobilized on granular activated carbon was used. Dynamic and steady state biofilm characteristics depend on dilution rate (DR). Lower DR favour phenol degradation and uniform, thick biofilm formation. Exo polymeric substance production in biofilm are favoured at lower dilution rates. Pulsed plate bioreactor (PPBR) is a biofilm reactor which has been proven to be very efficient in phenol biodegradation. The present paper reports the studies on the effect of dilution rate on the physical, chemical and morphological characteristics of biofilms formed by the cells of Pseudomonas desmolyticum on granular activated carbon (GAC) in PPBR during biodegradation of phenol. The percentage degradation of phenol decreased from 99% to 73% with an increase in dilution rate from 0.33 h?1 to 0.99 h?1 showing that residence time in the reactor governs the phenol removal efficiency rather than the external mass transfer limitations. Lower dilution rates favor higher production of biomass, extracellular polymeric substances (EPS) as well as the protein, carbohydrate and humic substances content of EPS. Increase in dilution rate leads to decrease in biofilm thickness, biofilm dry density, and attached dry biomass, transforming the biofilm from dense, smooth compact structure to a rough and patchy structure. Thus, the performance of PPBR in terms of dynamic and steady-state biofilm characteristics associated with phenol biodegradation is a strong function of dilution rate. Operation of PPBR at lower dilution rates is recommended for continuous biologic treatment of wastewaters for phenol removal.     

Al(III)对糖浆溶液中有机还原物质还原六价铬的影响

通过批实验研究了Al(III)对糖浆溶液化学还原六价铬反应的影响,揭示了不同条件下Al(III)对六价铬还原反应动力学的影响.结果表明:Al(III)能够促进糖浆溶液还原六价铬反应进行;其作用机制是Al(III)与糖浆溶液中有机还原物质及Cr(VI)反应形成三者的络合物,降低糖浆中多酚等有机还原物质还原Cr(VI)的反应活化能,提高六价铬还原反应速率.Al(III)存在时,该六价铬还原反应符合准一级动力学反应; pH 2.0,2.5,3.0,3.5时,添加Al(III)的实验组中六价铬反应速率常数比对应的空白对照组中反应速率常数分别增加了0.0251,0.0139,0.0058, 0.0048h-1.添加Al(III)前后反应体系中六价铬还原的反应活化能(Eа)分别为66.38,62.80kJ/mol.当糖浆浓度不足时,Al(III)能够提高糖浆溶液还原六价铬的反应去除率.     

Fe3+对反硝化系统除磷效果及微生物产物的影响

铁盐常作为化学药剂来辅助城市污水处理厂的生物除磷. 利用间歇试验考察投加不同ρ(FeCl₃)时反硝化除磷系统中污染物的去除效果以及EPS(胞外聚合物)、PHA(聚羟基脂肪酸酯)、糖原的形成与转化,并通过分析胞内Fe3+含量来解析Fe3+对反硝化除磷系统的影响. 结果表明:①Fe3+投加量(以ρ计)<10 mg/L时,系统中PO₄3-P的去除率由未投加时的88.4%升至100%;Fe3+投加量>10 mg/L时,PO₄3-P的去除率随Fe3+投加量的增加而缓慢降至84.4%(Fe3+投加量为25 mg/L时). ②Fe3+投加量(10 mg/L)较低时,会增加污泥中w(总EPS);但由于Fe3+会与EPS中的羟基、氨基等官能团发生络合反应,导致Fe3+投加量(>10 mg/L)较高时可检出的w(总EPS)降低. ③投加Fe3+对厌氧段内w(PHA)、w(糖原)的变化及生物释磷的抑制作用影响不大,但Fe3+投加量(>10 mg/L)较高时对缺氧段NO₃--N的生物利用、生物吸磷作用以及PHA和糖原的转化速率有明显的抑制作用. ④缺氧阶段末胞内Fe3+含量(以w计)增加144%(Fe3+投加量为25 mg/L时),说明抑制作用主要是因为缺氧段Fe3+随细胞吸磷作用一并进入胞内,直接影响生物酶活性.      

不同结构芳香酸对厌氧颗粒污泥特性与微生物群落的影响

以苯甲酸（BA）、邻苯二甲酸（PA）、连苯三甲酸（HA）、1-萘甲酸（1NA）为研究对象,探究了不同结构芳香酸对厌氧颗粒污泥理化特性与微生物群落的影响.结果表明,在40 d的接触实验中,1NA实验组对溶解性化学需氧量（SCOD）的去除率为86.09%,与空白对照组相比降低了7%.4个实验组污泥疏松胞外聚合物（LB-EPS）和紧密胞外聚合物（TB-EPS）中多糖含量分别比对照组高0.30~1.28、0.19~1.03 mg·g^-1,蛋白含量分别提高了0.025~0.326、0.007~0.171 mg·g^-1.在LB-EPS三维荧光（EEM）光谱中,HA和1NA实验组中出现了类腐殖酸物质荧光峰,且辅酶F₄₂₀峰强度有所降低.对于酶活性而言,HA、1NA实验组乙酸激酶相对活性比对照组减少了65.26%、6.93%.通过高通量测序发现,对照组与实验组中的优势菌群均为Proteobacteria、Chloroflexi和Firmicutes.HA与1NA的加入降低了Actinobacteria的相对丰度,提高了Bacteroidetes和Synergistetes的相对丰度.对于古细菌而言,Methanothrix在对照组与实验组中为优势种属,其相对丰度达到49.95%~80.40%;但实验组Methanothrix的相对丰度减少了10.69%~30.45%,且1NA实验组尤为明显;而1NA的加入提高了Methanospirillum的相对丰度,达到34.08%.同时,细菌和古细菌代谢通路预测表明,其主要功能组为代谢、遗传信息处理、环境信息处理和细胞过程,芳香酸使得厌氧颗粒污泥中氨基酸的代谢功能有所增强.     

植物修复土壤重金属污染中外源物质的影响机制和应用研究进展

重金属进入土壤后难以被降解,并通过食物链在生物体内富集,长此以往会导致中毒、癌症、畸形、突变,严重影响了人类生产活动及地球生态系统的稳定。植物修复技术是一种经济有效的重金属污染修复技术,其依靠超富集植物强大的自身抗性机制,从土壤中提取或稳定重金属,达到污染治理的目的。然而修复土壤重金属污染的超富集植物通常生长缓慢、生物量低,其抗性机制也会受到植物本身对重金属胁迫的阈值限制,当胁迫超过这个阈值,植物修复的效率就会大大降低甚至失去修复功能。文章在解析植物重金属相互作用机制的基础上,综述了添加外源物质对重金属毒害植物的缓解效应以及其在强化植物修复土壤重金属污染中的应用研究进展;介绍了应用外源物质调控植物吸收转运重金属的3种途径,分别为提高土壤重金属生物利用度、促进植物生长以及增强植物耐性。提出了应用外源物质作为强化植物修复措施的潜力及今后的研究方向,其未来的研究应着重于以下方面:明确外源物质的应用浓度、时期、方式与植物吸收转运重金属之间的关系;从植物内源激素及信号分子间的互作、抗逆基因表达、内生及根际微生物等不同层面上揭示外源物质对植物积累重金属的调控机理;开展外源物质与其他植物修复强化技术的联合应用研究。这些研究可为土壤重金属污染的植物修复技术及其强化措施研究提供科学依据,同时也对植物修复工程技术的发展实践具有一定的指导意义。     

Rapid control of black and odorous substances from heavily-polluted sediment by oxidation: Efficiency and effects

Oxidants were proposed to rapidly control black and odorous substances in sediments. NaClO and KMnO₄ had excellent efficiency to remove black and odorous substances. NaClO dramatically accelerated the release of organics, NH₄⁺-N, P, and heavy-metals. Moderate oxidation had a limited effect on microbial communities. NaClO of 0.2 mmol/g was viewed to be the optimum option. The control of black and odorous substances in sediments is of crucial importance to improve the urban ecological landscape and to restore water environments accordingly. In this study, chemical oxidation by the oxidants NaClO, H₂O₂, and KMnO₄ was proposed to achieve rapid control of black and odorous substances in heavily-polluted sediments. Results indicate that NaClO and KMnO₄ are effective at removing Fe(II) and acid volatile sulfides. The removal efficiencies of Fe(II) and AVS were determined to be 45.2%, 94.1%, and 93.7%, 89.5% after 24-h exposure to NaClO and KMnO₄ at 0.2 mmol/g, respectively. Additionally, rapid oxidation might accelerate the release of pollutants from sediment. The release of organic matters and phosphorus with the maximum ratios of 22.1% and 51.2% was observed upon NaClO oxidation at 0.4 mmol/g. Moreover, the introduction of oxidants contributed to changes in the microbial community composition in sediment. After oxidation by NaClO and KMnO₄ at 0.4 mmol/g, the Shannon index decreased from 6.72 to 5.19 and 4.95, whereas the OTU numbers decreased from 2904 to 1677 and 1553, respectively. Comparatively, H₂O₂ showed a lower effect on the removal of black and odorous substances, pollutant release, and changes in sediment microorganisms. This study illustrates the effects of oxidant addition on the characteristics of heavily polluted sediments and shows that chemical oxidants may be an option to achieve rapid control of black and odorous substances prior to remediation of water environments.     

危险货物办理站安全质量评估方法初探

从铁路危险货物的运输现状出发，通过对影响危险货物办理站安全工作质量的因素的分析，探讨了安全质量的评估方法，并提出了一个新的概念──安全管理难度系数，由此建立起安全质量综合评估模型，以实现对危险货物办理站安全工作的全面衡量。     

Specific association of 36Cl with low molecular weight humic substances in soils

Soils initially contaminated with ³⁶Cl in the chloride form were subjected to solid–liquid extractions using a variety of reagents including deionised water and 1 M sodium hydroxide (NaOH). 1 M NaOH was found to result in the greatest recovery of ³⁶Cl from the soils, a result which provided initial evidence that radioactive chlorine became attached to humic substances present naturally within the soils. Deionised water and 1 M NaOH extracts were subjected to analysis involving separation by gel filtration chromatography (GFC). It was found that ³⁶Cl in 1 M NaOH extracts associated preferentially with low molecular weight (LMW) fractions of humic substances whereas, in deionised water extracts, ³⁶Cl appeared to be present exclusively in the chloride form. Previous literature evidence, mainly from highly organic forest soils, suggests that conversion of stable chlorine from chloride to organic forms can occur as a result of biological action. The present paper also presents good evidence for the specific attachment of stable chlorine (³⁷Cl) to a LMW humic fraction, again demonstrated using GFC separation. Current risk assessments of the deep geological disposal of solid radioactive wastes containing ³⁶Cl typically assume a very low degree of sorption based on the notion that the predominant environmental species of radiochlorine is chloride. This paper concludes with a brief discussion on the implications of organochlorine formation in the biosphere for assessment of the radiological impact of deep geological disposal of solid radioactive wastes.     

Concentrations of natural radionuclides in imported mineral substances

Levels of natural radionuclides, such as thorium-232 (232Th), radium-226 (226Ra) and potassium-40 (40K), were determined in about 2,000 samples of imported mineral substances using gamma spectrometry. The maximum concentration levels of 232Th, 226Ra and 40K were 1,260 +/- 54, 13,400 +/- 94 and 1,256 +/- 260 Bq kg(-1), respectively, in zirconium compounds. Due to relatively high concentrations of the above-mentioned radionuclides in some imported mineral substances, the National Radiation Protection Department (NRPD), as the competent authority, has established national limits (900 Bq kg(-1) for 232Th, 1800 Bq kg(-1) for 226Ra and 11,000 Bq kg(-1) for 40K), based on the external exposures, for general importation permits of these materials.