Mutagenicity of anaerobic fenitrothion metabolites after aerobic biodegradation

Previous studies have revealed that the mutagenicity of fenitrothion increases during anaerobic biodegradation, suggesting that this insecticide's mutagenicity could effectively increase after it pollutes anaerobic environments such as lake sediments. To investigate possible changes to the mutagenicity of fenitrothion under aerobic conditions after it had already been increased by anaerobic biodegradation, batch incubation cultures were maintained under aerobic conditions. The mutagenicity, which had increased during anaerobic biodegradation, decreased under aerobic conditions with aerobic or facultative bacteria, but did not disappear completely in 22 days. In contrast, it did not change under aerobic conditions without bacteria or under continued anaerobic conditions. These observations suggest that the mutagenicity of anaerobically metabolized fenitrothion would not necessarily decrease after it arrives in an aerobic environment: this would depend on the presence of suitable bacteria. Therefore, fenitrothion-derived mutagenic compounds may pollute the water environment, including our drinking water sources, after accidental pollution of aerobic waters. Although amino-fenitrothion generated during anaerobic biodegradation of fenitrothion was the principal mutagen, non-trivial contributions of other, unidentified metabolites to the mutagenicity were also observed.     

The effect of cyclic aerobic-anoxic conditions on biodegradation of benzoate.

The response of a mixed microbial culture to cyclic aerobic and anoxic (denitrifying) conditions was studied in a chemostat with a 48-hour hydraulic residence time receiving a feed containing benzoate and pyruvate. When the cyclic conditions were 3-hour aerobic and 9-hour anoxic, the bacteria-degraded benzoate aerobically via the catechol 2,3-dioxygenase (C23DO) pathway. The quantity of C23DO remained constant throughout the anoxic period but decreased during the initial portion of the aerobic period before returning to the level present in the anoxic period. Anoxic biodegradation of benzoate was via benzoyl-CoA reductase, which remained constant regardless of the redox condition. The aerobic benzoate uptake capability (AeBUC) of the culture increased during the aerobic period but decreased during the anoxic period. The anoxic benzoate uptake capability (AnBUC) exhibited the opposite response. When the cycle was 6-hour aerobic and 6-hour anoxic, aerobic biodegradation of benzoate proceeded via the protocatechuate 4,5-dioxygenase (P45DO) pathway. The P45DO activity decreased early in the aerobic period, but then increased to the level present during the anoxic period. The level of benzoyl-CoA reductase was constant throughout the cycle. Furthermore, AeBUC and AnBUC responded in much the same way as in the 3/9-hour chemostat. During a 9-hour aerobic and 3-hour anoxic cycle, the culture synthesized both P45DO and C23DO, with the former having significantly higher activity. Unlike the other two cycles, AeBUC changed little during the aerobic period, although AnBUC decreased. The culture was well-adapted to the cyclic conditions as evidenced by the lack of accumulation of either substrate during any cycle tested. This suggests that cyclic aerobic-anoxic processes can be used in industrial wastewater-treatment facilities receiving significant quantities of simple aromatic compounds like benzoate. However, the results showed that the kinetics of benzoate degradation were different under aerobic and anoxic conditions, a situation that must be considered when modeling cyclic bioreactors receiving aromatic compounds.     

Correlation analysis of major control factors for the formation and stabilization of aerobic granule

In recent years, aerobic granular sludge technology has demonstrated significant advantages in areas such as the sludge–water separation, residual sludge minimization, simultaneous biological nitrogen and phosphorus removal, and toxic organic compounds degradation in biological wastewater treatment. However, the critical control factors and their relation during sludge granulation have not been revealed indeed, and the stability of aerobic granular sludge is still not good. The Gray’s correlation analysis was used to investigate the relationship of aerobic granular characteristics and control factors in the study. Results showed that the organic loading rate, hydraulic shear stress, and sludge settling time were the major factors affecting the aerobic sludge granulation, and the associated regulating strategy was important for the stabilization of granular sludge system. Based on above results, the mechanism of aerobic sludge granulation was proposed, and it was expected to favor the application of aerobic granular sludge technology.     

好氧颗粒污泥的形成过程、形成机理及相关研究

利用SBR和优势混合菌对造纸废水进行处理,在此过程中驯化出好氧颗粒污泥,对好氧颗粒污泥的形成过程、形成机制等进行研究发现,好氧颗粒污泥的形成经历了细菌增殖、絮状体形成、絮状体聚合、凝絮体形成和好氧颗粒污泥形成五个阶段;其形成至少有菌丝缠绕、小块污泥互相联合、吸附和连接四种机制。优势混合菌的加入,是好氧颗粒污泥之所以能够形成的关键因素。     

The emission of volatile compounds during the aerobic and the combined anaerobic/aerobic composting of biowaste

Two different biowaste composting techniques were compared with regard to their overall emission of volatile compounds during the active composting period. In the aerobic composting process, the biowaste was aerated during a 12-week period, while the combined anaerobic/aerobic composting process consisted of a sequence of a 3-week anaerobic digestion (phase I) and a 2-week aeration period (phase II). While the emission of volatiles during phase I of the combined anaerobic/aerobic composting process was measured in a full-scale composting plant, the aerobic stages of both composting techniques were performed in pilot-scale composting bins. Similar groups of volatile compounds were analysed in the biogas and the aerobic composting waste gases, being alcohols, carbonyl compounds, terpenes, esters, sulphur compounds and ethers. Predominance of alcohols (38% wt/wt of the cumulative emission) was observed in the exhaust air of the aerobic composting process, while predominance of terpenes (87%) and ammonia (93%) was observed in phases I and II of the combined anaerobic/aerobic composting process, respectively. In the aerobic composting process, 2-propanol, ethanol, acetone, limonene and ethyl acetate made up about 82% of the total volatile organic compounds (VOC)-emission. Next to this, the gas analysis during the aerobic composting process revealed a strong difference in emission profile as a function of time between different groups of volatiles. The total emission of VOC, NH₃ and H₂S during the aerobic composting process was 742 g ton^-1 biowaste, while the total emission during phases I and II of the combined anaerobic/aerobic composting process was 236 and 44 g ton^-1 biowaste, respectively. Taking into consideration the 99% removal efficiency of volatiles upon combustion of the biogas of phase I in the electricity generator, the combined anaerobic/aerobic composting process can be considered as an attractive alternative for aerobic biowaste composting because of its 17 times lower overall emission of the volatiles mentioned.     

Combined anaerobic/aerobic digestion: effect of aerobic retention time on nitrogen and solids removal

A combined anaerobic/aerobic sludge digestion system was studied to determine the effect of aerobic solids retention time (SRT) on its solids and nitrogen removal efficiencies. After the anaerobic digester reached steady state, effluent from the anaerobic digester was fed to aerobic digesters that were operated at 2- to 5-day SRTs. The anaerobic system was fed with a mixture of primary and secondary sludge from a local municipal wastewater treatment plant. Both systems were fed once per a day. The aerobic reactor was continuously aerated with ambient air, maintaining dissolved oxygen level at 1.1 +/- 0.3 mg/L. At a 4-day or longer SRT, more than 11% additional volatile solids and 90% or greater ammonia were removed in the aerobic digester, while 32.8 mg-N/L or more nitrite/nitrate also was measured. Most total Kjeldahl nitrogen removal was via ammonia removal, while little organic nitrogen was removed in the aerobic digester.     

The digestibility of waste activated sludges.

Laboratory digestion studies using waste activated sludges (WAS) were conducted to compare the digestion performance between anaerobic and aerobic processes. Nine samples of WAS from seven wastewater treatment plants were collected and batch-digested under both anaerobic and aerobic conditions for 30 days at 25 degrees C. The cation content of wastewater (both floc and solution phases) and solution biopolymer (protein and polysaccharide) was measured before and after digestion and compared with volatile solids destruction data. The study revealed that each digestion process was associated with a distinct biopolymer fraction, which accounted for differences in volatile solids reduction under anaerobic and aerobic conditions. The anaerobic digestion data showed strong correlations between soluble protein generation, ammonium production, percent volatile solids reduction, and floc iron (Fe). These data suggest that the amount of volatile solids destroyed by anaerobic digestion depends on the Fe content of floc. In aerobic digestion, polysaccharide accumulated in solution along with calcium and magnesium. For aerobic digestion, correlations between divalent cation release and the production of inorganic nitrogen were found. This implies that divalent cation-bound biopolymer, thought to be lectin-like protein, was the primary organic fraction degraded under aerobic conditions. The results of the study show that the cation content in wastewater is an important indicator of the material that will digest under anaerobic or aerobic conditions and that some of the volatile solids will digest only under either anaerobic or aerobic conditions.     

Ultrasound and ozone assisted biological degradation of thermally pretreated and anaerobically pretreated distillery wastewater

The present work is aimed at increasing the overall efficiency of the treatment process of distillery spent wash using a combination of different treatment techniques. Initially the effluent samples were subjected to Thermal Pretreatment (TPT-DW) and anaerobic treatment (ANA-DW). Advanced oxidation techniques, viz., Ultrasound (US) and Ozone were then used for further COD reduction followed by the conventional aerobic oxidation using mixed microbial consortium. Pretreatment of TPT-DW with US and Ozone (as stand alone techniques) enhanced the subsequent aerobic oxidation rate. For US treated sample, a maximum of 13% COD reduction was attained at the end of 48 h of aerobic oxidation, while for the ozone treated effluent a maximum of 45.6% COD reduction was obtained as compared to mere 1.8% COD reduction for the control (TPT-DW directly subjected to aerobic oxidation) indicating a 25 times increase in the rate of aerobic biodegradation of ozonated sample. Anaerobically treated effluent sample (ANA-DW) could be successfully treated aerobically. In this case, however, the use of advanced oxidation techniques did not result in any synergistic effects. The rate of the aerobic oxidation was slightly higher for the control (ANA-DW directly subjected to aerobic oxidation) as compared to the sample pretreated using ultrasound or ozonation. TOC analysis revealed that between the two pretreatments studied, ozone was found to be superior over US as it led to both COD as well as TOC reduction during the aerobic oxidation step for ANA-DW effluent stream.     

Modeling of vapor intrusion from hydrocarbon-contaminated sources accounting for aerobic and anaerobic biodegradation

A one-dimensional steady state vapor intrusion model including both anaerobic and oxygen-limited aerobic biodegradation was developed. The aerobic and anaerobic layer thickness are calculated by stoichiometrically coupling the reactive transport of vapors with oxygen transport and consumption. The model accounts for the different oxygen demand in the subsurface required to sustain the aerobic biodegradation of the compound(s) of concern and for the baseline soil oxygen respiration. In the case of anaerobic reaction under methanogenic conditions, the model accounts for the generation of methane which leads to a further oxygen demand, due to methane oxidation, in the aerobic zone. The model was solved analytically and applied, using representative parameter ranges and values, to identify under which site conditions the attenuation of hydrocarbons migrating into indoor environments is likely to be significant. Simulations were performed assuming a soil contaminated by toluene only, by a BTEX mixture, by Fresh Gasoline and by Weathered Gasoline. The obtained results have shown that for several site conditions oxygen concentration below the building is sufficient to sustain aerobic biodegradation. For these scenarios the aerobic biodegradation is the primary mechanism of attenuation, i.e. anaerobic contribution is negligible and a model accounting just for aerobic biodegradation can be used. On the contrary, in all cases where oxygen is not sufficient to sustain aerobic biodegradation alone (e.g. highly contaminated sources), anaerobic biodegradation can significantly contribute to the overall attenuation depending on the site specific conditions.     

A/O-膜生物反应器和A~2O系统中有机物分子量分布的对比研究

采用凝胶过滤色谱(GPC)对A/O-膜生物反应器(A/O-MBR)和A2O系统中有机物分子量分布进行了对比研究.结果表明,A/O-MBR系统中由进水到好氧滤液的有机物分子量分布依次变宽,其趋势恰好与A2O系统相反;A/O-MBR好氧滤液的有机物分子量分布远宽于A2O好氧滤液.A/O-MBR好氧滤液中重均分子量(Mw)＞107 u的有机物占总有机物质量的3.4%,表明正是由于膜的截留作用导致这类大分子有机物在MBR中的累积,而无法像A2O系统一样随出水流走;A/O-MBR系统各段污泥混合液的胞外聚合物(EPS)的分子量分布较分散,说明A/O-MBR系统中微生物新陈代谢产物多,并在膜的截留作用下最终造成了这些产物在膜表面大量的沉积.     

活性污泥胞外聚合物提取方法研究

考察4种方法(蒸气法、EDTA法、NaOH法和搅拌法)对3种活性污泥(可乐厌氧活性污泥、可乐好氧活性污泥和市政污水污泥)胞外聚合物的提取效率,对比分析了各提取方法对不同样品提取所得胞外聚合物的组成影响,结果表明,EDTA法提取多糖的效率最高,提取市政污水污泥、可乐好氧活性污泥和可乐厌氧活性污泥胞外聚合物糖分别在8.3、16.7和9.7 mg/g VSS左右;NaOH提取蛋白质的效率最高,提取市政污水污泥、可乐好氧活性污泥和可乐厌氧活性污泥胞外聚合物蛋白质分别为:3.15、0.55和5.57 mg/g VSS.对于3种不同种类污泥,EDTA法提取EPS总量效率最高,分别为市政污水污泥10.7 mg/g VSS、可乐好氧活性污泥16.8 mg/g VSS和可乐厌氧活性污泥9.97 mg/g VSS,分别比效率最低的搅拌法高出5倍、5倍和3倍.     

颗粒污泥与絮状污泥处理垃圾渗滤液的耐盐性能比较

通过批次实验系统研究了好氧颗粒污泥和絮状污泥处理垃圾渗滤液时的耐盐性能。实验结果表明,进水含盐量小于10 000 mg/L时,实验所用好氧颗粒污泥和絮状污泥的有机物去除能力、沉降性能、污泥活性基本上不受进水含盐量变化的影响。当进水含盐量大于10 000 mg/L时,随着进水含盐量的增大,絮状污泥的污泥沉降指数(SVI)快速减小,污泥活性及去除有机物的能力下降;相比而言,好氧颗粒污泥沉降性能更为稳定,SVI基本维持在30 mL/g左右,污泥活性及去除有机物的能力缓慢下降。当进水含盐量重新降低时,好氧颗粒污泥沉降性能变化不大,污泥活性及去除有机物的能力恢复迅速;而絮状污泥沉降性能变差,污泥活性及去除有机物的能力仍受较大抑制。     

The role of SBR mixed liquor volume exchange ratio in aerobic granulation

Four sequencing batch reactors (SBR) were operated at different volume exchange ratios of 20-80%. Results showed that a rapid aerobic granulation could be achieved in SBR run at high volume exchange ratios, and the characteristics of mature aerobic granules in terms of mean size, SVI, granule fraction, EPS and calcium content were all closely related to the volume exchange ratio applied to SBR. To interpret the role of volume exchange ratio in aerobic granulation, a concept of minimum settling velocity of bioparticles was proposed, which is the function of both settling time and volume exchange ratio. It was further demonstrated that the effect of volume exchange ratio on aerobic granulation in SBR would be realized through selecting the minimum settling velocity of bioparticles. In fact, the minimum settling velocity would serve as a major selection pressure exerted on bioparticles. It appeared from this study that the production of EPS was stimulated significantly by high volume exchange ratio, which was associated with marketable accumulation of calcium ion in aerobic granulation. It is expected that this study may offer insights into the mechanism of aerobic granulation.     

Nitrifying genera in activated sludge may influence nitrification rates

Sequencing batch reactors were acclimated under aerobic and alternating anoxic/aerobic conditions. Greater nitrification rates in the alternating reactor were investigated by comparing environmental conditions. In the alternating reactor, pH, alkalinity, oxygen, and nitrite were higher at the onset of aerobic nitrification. Kinetic studies and batch tests, with biomass developed under aerobic and alternating conditions, revealed that these factors were insufficient to explain the divergent nitrification rates. Nitrifying genera vary in nitrification kinetics and sensitivity to environmental conditions. Nitrosospira and Nitrospira spp. could dominate in aerobic reactors, as they are adapted to low nitrite and oxygen conditions. Nitrosomonas and Nitrobacter spp. are better competitors with abundant substrates and have higher nitrite tolerance, so they could excel under alternating conditions. This theoretical explanation is consistent with the kinetics and environmental conditions in these reactors and argues for using alternating treatment, because the harsh conditions select for populations with inherently faster nitrification rates.     

Roles of ATP-dependent N-acylhomoserine lactones (AHLs) and extracellular polymeric substances (EPSs) in aerobic granulation

Aerobic granules which form through a cell-to-cell self-immobilization process have been intensively studied and developed for wastewater biotreatment. However, the microbiological origin of this phenomenon is still largely unknown. This study investigated the possible role of metabolic energy in the development of aerobic granules. Results showed that aerobic granulation was positively related to ATP-dependent N-acylhomoserine lactones (AHLs) and extracellular polymeric substances (EPSs) production. Inhibited ATP synthesis by a chemical uncoupler, 3,3′,4′,5-tetrachlorosalicylanilide, led to significant reduction of AHLs and EPSs production, which in turn prevented aerobic granulation. This study for the first time demonstrated the involvement of ATP-dependent AHLs in aerobic granulation.     

Sequential anaerobic-aerobic treatment of an aquifer contaminated by halogenated organics: field results

In situ, sequential, anaerobic to aerobic treatment of groundwater removed perchloroethene (PCE, 1.1 microM) and benzene (0.8 microM) from a contaminated aquifer. Neither aerobic nor anaerobic treatment alone successfully degraded both the chlorinated and non-chlorinated organic contaminants in the aquifer. After the sequential treatment, PCE, trichloroethene (TCE), vinyl chloride (VC), chloroethane (CA), and benzene were not detectable in groundwater. Desorption of residual aquifer contaminants was tested by halting the groundwater recirculation and analyzing the groundwater after 3 and 7 weeks. No desorption of the chlorinated contaminants or daughter products was observed in the treated portion of the aquifer. Sequential anaerobic to aerobic treatment was successful in remediating the groundwater at this test site and may have broad applications at other contaminated sites. Over the 4-year course of the project, the predominant microbial environment of the test site varied from aerobic to sulfate-reducing, to methanogenic, and back to aerobic conditions. Metabolically active microbial populations developed under all conditions, demonstrating the diversity and robustness of natural microbial flora in the aquifer.     

Bacterial responses to temperature during aeration of pig slurry

The temperature effect on total anaerobic and aerobic bacterial growth in pig slurry was studied using low level batch aeration treatments. Five bioreactors were built using Plexiglas tubes to perform five temperature treatments (5 degrees C, 10 degrees C, 15 degrees C, 20 degrees C, and 25 degrees C). An airflow rate of 0.129 L/min/L manure was used to aerate manure contained in all reactors. Data showed that temperature had a profound impact on the aerobic counts in pig slurry during the aeration process. When the temperature increased from 15 degrees C to 25 degrees C, the average oxidation-reduction potential decreased from +40 mV to -60 mV, accompanied by a 75% reduction of aerobic bacteria in the manure. At 25 degrees C, the anaerobic counts were consistently higher than aerobic counts for most of days. A quadratic relationship was observed between the aerobic counts and the oxidation-reduction potential with a correlation coefficient of 0.8374. To reduce odor generation potential, the oxidation-reduction potential in the manure should be maintained at +35 mV or higher.     

好氧/缺氧消化降解污泥特征分析

为考察好氧/缺氧消化过程中污泥降解的特征，利用2个反应器进行对比试验，研究好氧/缺氧和好氧消化2个过程中VS的去除，pH和碱度变化，消化上清液中COD和氮元素变化等情况。试验结果表明:好氧/缺氧消化能够满足污泥稳定的要求，在常温条件下，消化16 d VS去除率即可达到38.2%，同时比好氧消化节约曝气能耗。好氧/缺氧消化对污泥中总氮的去除率高于传统的好氧消化，达到了36.4%，而且能够降低消化污泥上清液中的氨氮和硝态氮浓度。     

Fate and transformation of naphthylaminesulfonic azo dye Reactive Black 5 during wastewater treatment process

Certain aromatic amines generated by the decolorization of some azo dyes are not removed substantially by conventional anaerobic–aerobic biotreatment. These aromatic amines are potentially toxic and often released in the wastewater of industrial plants. In this study, the fate and transformation of the naphthylaminesulfonic azo dye Reactive Black 5 (RB5) during different phases of a sequencing batch reactor were investigated. The major products of RB5 decolorization during the anaerobic phase include 2-[(4-aminophenyl)sulfonyl]ethyl hydrogen sulfate (APSEHS) and 1-2-7-triamino-8-hydroxy-3-6-naphthalinedisulfate (TAHNDS). During the aerobic phase, APSEHS was hydrolyzed and produced 4-aminobenzenesulfonic acid, which was further degraded via dearomatization. TAHNDS was transformed rapidly via auto-oxidation into TAHNDS_DP-1 and TAHNDS_DP-2, which were not further removed by the activated sludge during the entire 30-day aerobic phase. In contrast, different behaviors of TAHNDS were observed during the anoxic phase. The transformation of TAHNDS was initiated either by deamination or desulfonation reaction. TAHNDS was then converted into 3,5-diamino-4-hydroxynaphthalene-2-sulfonic acid, which was subsequently removed via ring cleavage reaction under aerobic condition. In conclusion, complete degradation of TAHNDS by activated sludge occurs only during anoxic/aerobic processes instead of the conventional anaerobic/aerobic processes.     

Occurrence of carbon monoxide during organic waste degradation

The concentrations of carbon monoxide (CO) and other gases were measured in the emissions from solid waste degradation under aerobic and anaerobic conditions during laboratory and field investigations. The emissions were measured as room temperature headspace gas concentrations in reactors of 1, 30, and 150 L, as well as sucked gas concentrations from windrow composting piles and a biocell, under field conditions. The aerobic composting laboratory experiments consisted of treatments with and without lime. The CO concentrations measured during anaerobic conditions varied from 0 to 3000 ppm, the average being 23 ppm, increasing to 133 ppm when methane (CH4) concentrations were low. The mean/maximum CO concentrations during the aerobic degradation in the 2-L reactor were 101/194 ppm without lime, 486/2022 ppm with lime, and 275/980 ppm in the 150-L reactors. The presence of CO during the aerobic composting followed a rapid decline in O2 concentrations Significantly higher CO concentrations were obtained when the aerobic degradation was amended with lime, probably because of a more extreme depletion of oxygen. The mean/maximum CO concentrations under field conditions during aerobic composting were 95/1000 ppm. The CO concentrations from the anaerobic biocell varied from 20 to 160 ppm. The hydrogen sulfide concentrations reached almost 1200 ppm during the anaerobic degradation and 67 ppm during the composting experiments.