Inhibition of Biogas Production by Alkyl Benzene Sulfonates (LAS) in a Screening Test for Anaerobic Biodegradability

The effect of the inoculum source on the digestion of linear alkylbenzene sulfonates (LAS) under anaerobic conditions has been investigated. The potential for primary and ultimate LAS biodegradation of anaerobic sludge samples obtained from wastewater treatment plants (WWTPs) of different geographical locations was studied applying a batch test system. It was found that only 4–22% of the LAS added to the batch anaerobic digesters was primarily transformed suggesting a poor primary degradation of the LAS molecule in anaerobic discontinuous systems. Regarding ultimate biodegradation, the addition of LAS to the batch anaerobic digesters caused a reduction on the extent of biogas production. Significant differences in the inhibition extent of the biogas production were observed (4–26%) depending on the sludge used as inoculum. Effect of the surfactant on the anaerobic microorganisms was correlated with its concentration in the aqueous phase. Sorption of LAS on anaerobic sludge affects its toxicity by depletion of the available fraction of the surfactant. LAS content on sludge was related to the total amount of calcium and magnesium extractable ions. The presence of divalent cations promote the association of LAS with anaerobic sludge reducing its bioavailability and the extent of its inhibitory effect on the biogas production.     

Biodegradation of nonylphenol ethoxylates by Bacillus sp. LY capable of heterotrophic nitrification

Biodegradation of nonylphenol ethoxylates (NPEOs) by Bacillus sp. LY, with heterotrophic nitrification ability was investigated. The results showed that NPEOs were readily degraded by Bacillus sp. LY with more than 80% of the total NPEOs being removed within 7 days. Heterotrophic nitrogen removal occurred simultaneously during the biodegradation period of NPEOs. NPEOs were biodegraded through a nonoxidative pathway, through which NPEOs were degraded via sequential removal of ethoxyl units to the nonylphenol. To the authors' knowledge, it is the first report on the biodegradation of NPEO contaminants by a microorganism capable of heterotrophic nitrogen removal.     

竹炭固定化微生物对水中壬基酚的降解效率

竹炭是一种优质生物质炭,不仅比表面积大,孔隙发达,而且机械强度高,是微生物固定化载体的最佳选择之一.本文采用正交试验确定了竹炭固定化微生物的最佳制备条件,对比了竹炭固定菌和游离菌对水中类雌激素壬基酚的降解效果,并考察了竹炭固定菌的重复利用性.结果表明:固定化后降解菌大量地附着在竹炭表面及内部孔隙中,其最佳制备条件为温度30℃、pH=7、竹炭粒径35目.壬基酚的降解符合一级动力学方程,在不同的壬基酚初始浓度下(30、50、80、100 mg·L^-1),竹炭固定菌对壬基酚的7 d降解率分别为100%、75.3%、67.3%和78.7%,显著优于游离菌(54.2%、51.5%、30.6%和23.5%).经过8轮重复利用后,竹炭固定菌对壬基酚的降解率仍可达到36.5%,而此时游离菌的降解率仅为8.9%,说明竹炭固定菌具有长期可重复利用性,在去除废水有机污染物中具有较好的工程应用前景.     

A Hazard Assessment of Aggregate Exposure to Nonylphenol and Nonylphenol Mono- and Di-ethoxylates in the Aquatic Environment

The most commonly detected environmental metabolites of nonylphenol ethoxylates (NPE) are nonylphenol monoethoxylate (NPE1), nonylphenol diethoxylate (NPE2), nonylphenol ether carboxylates (NPEC), and nonylphenol (NP). Since NPEC have relatively low toxicity, the most relevant NPE metabolites for conducting an aggregate hazard assessment are NP, NPE1, and NPE2. Recent studies support the validity of the U.S. Environmental Protection Agency (2005) chronic water quality criteria (WQC) for NP in freshwater and saltwater environments; thus, these criteria were used as reference values in the aggregate hazard assessment. The toxic equivalency approach was used to assess the aggregate hazard of NP, NPE1, and NPE2. A review of relevant studies indicated that the toxic equivalency factor (TEF) for NPE1 and NPE2 approximated 0.37, which supported the use of the more conservative TEF value of 0.50 used by Environment Canada (2001) for NPE1 and NPE2. The interaction of toxicities between NP, NPE1, and NPE2 is assumed to be additive based on a review of the current literature and the shared mechanism of action of these compounds. The data support previous findings that there is a low likelihood that aggregate NP-equivalent concentrations of NPE and its metabolites in U.S. waters will exceed the national chronic WQC for NP.     

An Ecological Risk Assessment of Nonylphenol and Its Ethoxylates in the Aquatic Environment

Nonylphenol ethoxylates (NPEs) are a group of surfactants that are widely used for industrial, commercial, institutional and household purposes in Canada. Ethoxylation of nonylphenol (NP) occurs upon reaction with ethylene oxide, producing NPEs, although NP is also used in the production of the antioxidant tris(nonylphenol)phosphite. NP and NPEs are not produced naturally, and the primary route of environmental exposure to NP and NPEs is via textile mill, pulp and paper mill and municipal wastewater treatment plant effluents. NPEs occur as complex mixtures and are described by the average ethoxylate chain length, which ranges from 1 to 100. The environmental fate of NPEs is strongly dependent on the effluent and, the degree and type of treatment to which the effluent is subjected. An ecological risk assessment was performed to determine if exposure to NP and NPEs results in effects on the Canadian environment, based on current use patterns. The Canadian ecological risk assessment found that adverse effects on aquatic organisms are likely, although assumptions were made with respect to appropriate dilution factors.     

硝酸盐还原促进毒害性有机污染物降解的研究进展

大量具有高毒性、持久性和生物蓄积性的有机污染物被排放到环境中,对生态环境和人类健康造成了严重威胁。近年来,利用硝酸盐作电子受体在厌氧条件下降解毒害性有机污染物,已取得一定的进展。本文综述了硝酸盐还原体系中几种典型毒害性有机污染物(多环芳烃、单环或杂环芳烃类有机物及卤代有机物)的厌氧降解研究进展。在此基础上,提出了硝酸盐还原促进毒害性有机污染物降解研究中存在的主要问题及其在加速污染环境净化方面的应用前景。     

含易降解有机质时对苯二甲酸(TA)厌氧降解动力学

含易降解有机物的对苯二甲酸有机废水在厌氧处理时,其中的易降解有机质通过甲烷发酵被优先利用,其中间代谢物对对苯二甲酸的降解有抑制作用,同时,对苯二甲酸自身的降解也存在底物抑制现象。本文建立了有易降解有机质存在时对苯二甲酸厌氧降解的抑制动力学模型方程：q=q_max SS+Ks[1+(I-0.86)/K_I,s,并利用非线性回归,确定了模型参数q_max=1972.0mgTA/gVSS·d;K_s=20.2844gTA/L;K_I,I=2.041gCOD/L;K_I,s=0.0108 gTA/L,实验数据对该动力学方程能较好拟合。在此基础上提出两段厌氧处理新工艺。     

铁还原菌降解石油烃的研究进展

铁还原菌是指能够利用细胞外Fe(III)作为末端电子受体,通过氧化有机物将Fe(III)还原为Fe(II)微生物的总称。铁还原作用广泛存在于土壤、河流、海洋、地表含水层以及高温高压的地下深部油藏。在厌氧或兼性厌氧条件下,Fe(III)还原耦合有机物的降解,对铁、碳元素的生物地球化学循环具有重要意义。本文介绍了铁还原菌的多样性和铁还原作用机理,综述了铁还原菌在石油烃降解方面的研究进展。此外,还总结了铁还原菌在生物修复中的潜在作用,并对未来的研究方向进行了展望。     

Degradation ofortho-chlorophenol,para-chlorophenol, and 2,4-dichlorophenoxyacetic acid by the bacterial community of anaerobic sludge

The bacterial community of anaerobic sludge could degradeo-chlorophenol,p-chlorophenol, and 2,4-dichlorophenoxyacetic acid at concentrations as high as 100 mg/l. The time needed for the degradation of a given chlorinated phenol derivative increased 1.5- to 2-fold upon a twofold increase in its concentration (from 50 to 100 mg/l). The duration of the adaptation period depended on the compound studied and on its concentration. The degradation of 2,4-dichlorophenoxyacetic acid proceeded via 2,4-dichlorophenol andp-chlorophenol as intermediates; the degradation ofo-chlorophenol occurred with the formation of phenol. The dynamics ofp-chlorophenol degradation and chloride ion accumulation were studied.     

Kinetics of Polycyclic Aromatic Hydrocarbon (PAH) Degradation in Long-term Polluted Soils during Bioremediation

Bioremediation experiments with ten different soil samples from former industrial sites which were long-term polluted with polycyclic aromatic hydrocarbons (PAHs) were carried out using outdoor pot trials. The degradation of 15 PAHs according to the US EPA was investigated for 168 weeks through repeated soil sampling and determination of the total PAH concentration. On average, degradation was largest for acenaphthene (88%; 63 to 99%) and smallest for anthracene (22%; no significant degradation to 89%). For most of the PAH single substances, degradation kinetics were characterised by a first initial phase of fast degradation. In a subsequent second phase, degradation diminished and residual PAH concentrations were approached within 168 weeks, resulting in a similar PAH pattern in the ten soil samples. Degradation kinetics was calculated through the selection of the appropriate differential rate equation from a set of seven equations. Kinetics of PAH degradation was best fitted by single and two coupled first order exponential equations with median R2 of 0.71 (0.01 to 1.00). Degradation rate constants of the rapid phase (k ₁) ranged from 0.05×10⁻² week⁻¹ for benzo[k]fluoranthene to 18.3 week⁻¹ for naphthalene and for the subsequent slow degradation phase (k ₂) they ranged from 0.01×10⁻² week⁻¹ for benzo[a]anthracene to 2.3×10⁻² week⁻¹ for fluoranthene. Degradation was governed by desorption and diffusion processes of different rates, while microbial activity did not influence the kinetics. Median disappearance times (DT₅₀) ranged from 6.1 weeks for naphthalene to 522 weeks for benzo[k]fluoranthene. With the exception of the 6-ring PAHs dibenzo[ah]anthracene and indeno[1,2,3-cd]pyrene, this sequence followed the PAHs’ degree of condensation. The total initial PAH concentration and the residual concentration were correlated with R2 of 0.69, with larger initial PAH concentrations leading to larger residual concentrations and degradation rates.     

城市污泥生物好氧发酵对有机污染物的降解及其影响因素

分析了国内部分城市脱水污泥中几种主要有机污染物浓度,PAHs含量为1.156—34.940mg/kg,PCBs含量为0—115.730mg/kg;PCDD/Fs含量为9.530—22.900 ngTEQ/g干泥,NP含量为177.000mg/kg。提出要实现污泥安全、环保的土地利用,可采用生物好氧发酵技术降解污泥中的有机污染物,降低污泥在土地利用时有机污染物带来的环境风险。同时通过优化污泥生物好氧发酵控制条件:C/N值范围为25∶1—40∶1,温度在30—55℃,氧气浓度5%—15%,强制通风量控制在1.5—2.0m3.min-1.t-1(干泥)左右,pH6—9,混料含水率为50%—65%,经生物好氧发酵后的污泥施用土地,可以大大降低污泥在土地利用时的环境风险,避免污泥资源化利用带来的二次污染问题。     

Polycyclic Aromatic Hydrocarbon (PAH) Degradation Coupled to Methanogenesis

Baltimore Harbor (Baltimore, MD) sediments were utilized to initiate anaerobic enrichment cultures with polycyclic aromatic hydrocarbons (PAHs) in the absence of supplementary electron acceptors. Cultures amended with naphthalene and phenanthrene exhibited sustained, transferable degradation of the PAHs. Bromoethanesulfonic acid, a selective inhibitor of methanogenesis, inhibited the degradation of 200 μm naphthalene and phenanthrene; molecular characterization based on 16S rRNA sequences confirmed that methanogenic Archaea were eliminated, thus providing evidence that methanogenesis is involved in the degradation pathway. Revisions requested 16 November 2005; Revisions received 14 December 2005     

Formation of metabolites during biodegradation of linear alkylbenzene sulfonate in an upflow anaerobic sludge bed reactor under thermophilic conditions.

Biodegradation of linear alkylbenzene sulfonate (LAS) was shown in an upflow anaerobic sludge blanket reactor under thermophilic conditions. The reactor was inoculated with granular biomass and fed with a synthetic medium and 3 micromol/L of a mixture of LAS with alkylchain length of 10 to 13 carbon atoms. The reactor was operated with a hydraulic retention time of 12 h with effluent recirculation in an effluent to influent ratio of 5 to 1. A sterile reactor operated in parallel revealed that sorption to sludge particles initially accounted for a major LAS removal. After 8 days of reactor operation, the removal of LAS in the reactor inoculated with active granular biomass exceeded the removal in the sterile reactor inoculated with sterile granular biomass. The effect of sorption ceased after 185 to 555 h depending on the LAS homologs. 40% of the LAS was biodegraded, and the removal rate was 0.5 x 10(-6) mol/h/mL granular biomass. Acidified effluent from the reactor was subjected to dichloromethane extraction followed by gas chromatography/mass spectrometry. Benzenesulfonic acid and benzaldehyde were detected in the reactor effluent from the reactor with active granular biomass but not in the sterile and unamended reactor effluent. Benzenesulfonic acid and benzaldehyde are the first identified degradation products in the anaerobic degradation of LAS.     

Benzene Degradation at a Site Amended with Nitrate or Chlorate

Aromatic hydrocarbons are widespread in nature and often contribute to the pollution of soils, sediments, and groundwater. The contamination of soil with mobile aromatic compounds, generally termed BTEX (benzene, toluene, ethylbenzene, xylene) is observed at many industrial sites, especially those associated with the petrochemical industry. In situ bioremediation of sites that are contaminated with BTEX can be applied both aerobically and anaerobically. The use of anaerobic in situ bioremediation is advantageous because supply of oxygen is not needed. Nevertheless, anaerobic in situ bioremediation is less commonly used for BTEX contaminated sites. This paper describes push-pull experiments in order to stimulate the degradation of benzene by the addition of nitrate or chlorate. Deuterated benzene was subjected with nitrate-amended groundwater to the aquifer, and the mineralization was traced by the enrichment of deuterium in the groundwater. Nitrate can be used as electron acceptor, and the addition of nitrate at a site in The Netherlands resulted in partial degradation of benzene. This was demonstrated by comparing various push-pull experiments, benzene concentration measurements, stable isotope analyses of benzene and water, and modeling. Chlorate can be used for the in situ production of oxygen, followed by degradation of benzene with oxygen as electron acceptor. The addition of chlorate at the site resulted in the complete removal of benzene demonstrating a complete degradation within 4 weeks. A pull phase was not needed during this run.     

Phytoremediation of organic contaminants in soils

Soil pollution, a very important environmental problem, has been attracting considerable public attention over the last decades. Unfortunately, the enormous costs associated with the removal of pollutants from soils by means of traditional physicochemical methods have been encouraging companies to ignore the problem. Phytoremediation is an emerging technology that uses plants to clean up pollutants in the environment. As overwhelmingly positive results have become available regarding the ability of plants to degrade certain organic compounds, more and more people are getting involved in the phytoremediation of organic contaminants. Phytoremediation of organics appears a very promising technology for the removal of these contaminants from polluted sites.     

Exposure Analysis of C8- and C9-Alkylphenols,Alkylphenol Ethoxylates,and Their Metabolites in Surface Water Systems within the United States

This study was conducted to develop a statistical understanding of exposures to C8- and C9-alkylphenol ethoxylates (APEO) and their metabolites (APEM) in U.S. surface waters. Concentrations of APEO/APEM (all analytes) in freshwater have been reported by 19 investigations over the past 15 years. Only limited data are available for sediments and marine ecosystems. Based on the frequency of detection in surface waters, 67% of all analytes were below their detection limits. Although maximum reported concentrations varied with time, the average and 90th centile concentrations have remained relatively constant. Examination of frequency distributions for nonylphenol (NP) concentrations indicated that 99% of the levels in fresh surface waters are below the U.S. Environmental Protection Agency's Aquatic Life Ambient Chronic Water Quality Criteria for NP (6.6 μg/L). A conservative evaluation of aggregated NPEO/NPEM concentrations suggested that 97% of the samples contained aggregate NP equivalent concentrations that are also below 6.6 μg/L. These results suggest that on a nationwide basis, the likelihood of surface water concentrations exceeding the chronic USEPA Water Quality Criterion for NP is low.     

Role of sulfate in microbial transformations of environmental contaminants: Chlorinated aromatic compounds

Despite recent progress made in describing microbial transformations that occur under anaerobic conditions, our understanding of the role sulfate‐reducing bacteria may play in the remediation of environmental contaminants is still very limited. The objective of this mini‐review is to summarize what is currently known of the metabolism of chlorinated aromatic compounds in the presence of sulfate. Sulfidogenic processes are discussed with respect to the thermodynamics of haloaromatic oxidation and to their potential use in the in situ bioremediation of hazardous organic wastes. A comprehensive listing is made of anaerobic transformations that involve both halogenated and nonhalogenated monoaromatic substrates by denitrifiers, dissimilatory iron‐reducing bacteria, and methanogenic consortia. In contrast to other anaerobic processes, studies involving sulfate‐mediated metabolism of hazardous organic compounds have been neglected; however, the recent success in defining methanogenic transformations, in particular, has enhanced expectations of defining an analogous role for sulfate‐reducing microbial communities in low redox environments that have become contaminated with hazardous substances.     

Degradation of organic pollutants by methane grown microbial consortia

Microbial consortia were enriched from various environmental samples with methane as the sole carbon and energy source. Selected consortia that showed a capacity for co-oxidation of naphthalene were screened for their ability to degrade methyl-tert-butyl-ether (MTBE), phthalic acid esters (PAE), benzene, xylene and toluene (BTX). MTBE was not removed within 24 h by any of the consortia examined. One consortium enriched from activated sludge (AAE-A2), degraded PAE, including (butyl-benzyl)phthalate (BBP), and di-(butyl)phthalate (DBP). PAE have not previously been described as substrates for methanotrophic consortia. The apparent K_m and V_max for DBP degradation by AAE-A2 at 20 °C was 3.1 ± 1.2 mg l^–1 and 8.7 ± 1.1 mg DBP (g protein × h)^–1, respectively. AAE-A2 also showed fast degradation of BTX (230 ± 30 nmol benzene (mg protein × h)^–1 at 20 °C). Additionally, AAE-A2 degraded benzene continuously for 2 weeks. In contrast, a pure culture of the methanotroph Methylosinus trichosporium OB3b ceased benzene degradation after only 2 days. Experiments with methane mono-oxygenase inhibitors or competitive substrates suggested that BTX degradation was carried out by methane-oxidizing bacteria in the consortium, whereas the degradation of PAE was carried out by non-methanotrophic bacteria co-existing with methanotrophs. The composition of the consortium (AAE-A2) based on polar lipid fatty acid (PLFA) profiles showed dominance of type II methanotrophs (83–92% of biomass). Phylogeny based on a 16S-rRNA gene clone library revealed that the dominating methanotrophs belonged to Methylosinus/Methylocystis spp. and that members of at least 4 different non-methanotrophic genera were present (Pseudomonas, Flavobacterium, Janthinobacterium and Rubivivax).