Microbial reductive dechlorination of hexachloro-1,3-butadiene in a methanogenic enrichment culture

Sequential reductive dechlorination of hexachloro-1,3-butadiene (HCBD) was achieved by a mixed, methanogenic culture enriched from a contaminated estuarine sediment. Both methanol and lactate served as carbon and electron sources. Methanol was stoichiometrically converted to methane, whereas lactate was fermented to propionate and acetate and then to methane. Lactate and propionate fermentation, as well as methanogenesis were not inhibited at 0.4 mg HCBD/l, the normal enrichment culture HCBD feeding level. At a higher initial HCBD level of 1.5 mg HCBD/l, propionate fermentation and acetoclastic methanogenesis were inhibited while, after a lag time, enhanced HCBD dechlorination rates were observed. While lactate fermentation was not inhibited at high concentrations (>25 mM) of 2-bromoethanesulfonate (BES), both propionate fermentation and methanogenesis were completely inhibited, although the HCBD dechlorination rate was not affected. Therefore, methanogens were not likely responsible for the observed dechlorination of HCBD in the enrichment culture. The predominant HCBD dechlorination products were isomers of tri- and dichloro-1,3-butadiene. Traces of a monochloro-1,3-butadiene isomer were also detected. Although extensive dechlorination of HCBD was achieved by the enrichment culture, the detoxification efficiency of this process remains unclear because the potential inhibitory effect of the HCBD transformation products is unknown.     

Fate and effect of the antioxidant ethoxyquin on a mixed methanogenic culture

The potential inhibitory effect of ethoxyquin, an antioxidant commonly used as a preservative in the food processing industry (e.g., for stabilizing dissolved air flotation residuals), was evaluated at concentrations up to 300 mg/L using a mixed, mesophilic (35 degrees C) methanogenic culture and dextrin, peptone and methanol as the carbon source. A batch assay conducted with a range of ethoxyquin concentrations did not result in any inhibition up to an ethoxyquin concentration of 75 mg/L, but severe inhibition of methanogenesis was observed at concentrations higher than 150 mg/L. Ethoxyquin addition to a batch reactor with the same mixed, methanogenic culture, at ethoxyquin concentrations gradually increasing over 100 days, resulted in a transient and a complete inhibition of methanogenesis at ethoxyquin concentrations of 150 and 300 mg/L, respectively. Acidogens were not significantly impacted, whereas aceticlastic and methanol degrading methylotrophic methanogens were impacted the most. Acclimation of the methanogenic culture to ethoxyquin was not observed over an incubation period of more than 100 days. Long-term (>100 days) incubation at sub-inhibitory ethoxyquin concentrations did not result in ethoxyquin biotransformation. Similarly, ethoxyquin biotransformation was not evident over an 8-day aeration period in a laboratory-scale activated sludge reactor operated under fully aerobic conditions. Ethoxyquin phase distribution tests conducted with the mixed, methanogenic culture at 1.61 g/L volatile solids concentration and nominal ethoxyquin concentrations equal to or higher than 300 mg/L resulted in solid phase/liquid phase ethoxyquin ratios equal to or higher than 1.0. The combined effect of ethoxyquin recalcitrance under anaerobic conditions along with its phase distribution, which favors biosolids, will result in ethoxyquin accumulation in anaerobic treatment systems used by the food processing industry. Such accumulation may pose concerns relative to inhibitory effects in these treatment systems and the disposal of ethoxyquin-bearing biosolids.     

Fate and effect of quaternary ammonium compounds on a mixed methanogenic culture

The potential inhibitory effect of four quaternary ammonium compounds (QACs) and Vigilquat, a commercial sanitizer which is a mixture of the four QACs, was investigated at concentrations up to 100 mg/L using a mixed, mesophilic (35 degrees C) methanogenic culture. Dextrin and peptone were used as the carbon and energy sources. A batch assay conducted at a range of QAC concentrations showed that QACs were inhibitory to methanogens at and above 25 mg/L. Methanogenesis was more susceptible to QAC inhibition than acidogenesis. Adsorption of QACs on biomass was successfully simulated with the Freundlich isotherm equation. The inhibitory effect of Vigilquat on the mixed methanogenic culture was also investigated in a batch reactor fed with dextrin and peptone. Methanogens were inhibited when the total QAC concentration reached 30 mg/L and volatile fatty acids (VFAs) accumulated. However, methane production recovered in 57 days of incubation, and all VFAs were consumed, suggesting that a prolonged incubation period is necessary for the methanogens to overcome the transient inhibition at a relatively low QAC concentration. None of the QACs tested in this study was biodegraded under methanogenic conditions.     

Developments of bacterial population and methanogenic activity in a laboratory-scale landfill bioreactor

Sludge was taken from laboratory-scale simulators of a landfill bioreactor (LFBR) treating the organic fraction of municipal solid wastes (OFMSW) over a period of 1 year. Population densities of acetogens, hydrogen- and acetate-utilizing methanogens and the specific methanogenic activity (SMA) on degrading butyrate, propionate, acetate and formate were measured. The results indicate that the Gompertz equation is a suitable model for describing the growth data of acetogens, hydrogen- and acetate-utilizing methanogens. The development of SMAs can be systematically described by a simple mathematical equation derived from the Gompertz equation. The measurements of bacterial population growth and methanogenic activity reveal that the SMA of acetate is an ultimate indicator for monitoring the OFMSW decomposition. Leachate recycling can stimulate the carbon flow from hydrolysis/fermentation through the hydrogen/acetate toward methane. A moisture content of 75% is suggested to be an initial rapid decomposition threshold for the anaerobic organic refuse mineralization in a landfill bioreactor.     

Sulfide-induced nitrate reduction in the sludge of an anaerobic digester of a zero-discharge recirculating mariculture system

The anaerobic digester is a vital component in a zero-discharge mariculture system as therein most of the organic matter is mineralized and nitrogen-containing compounds are converted to gaseous N₂. Although denitrification is a major respiratory process in this nitrate-rich treatment stage, also sulfate respiration takes place and may cause undesirable high sulfide concentrations in the effluent water. To examine the effect of sulfide on nitrate reduction, in situ depth profiles of inorganic nitrogen and sulfur compounds were determined. Additionally, nitrate reduction was examined as a function of ambient sulfide concentrations in sludge collected from different locations in the anaerobic reactor. Depth profiles showed high concentrations of nitrate and low concentrations of sulfide and ammonia in the aqueous layer of the reactor. A sharp decrease of nitrate and an increase in sulfide and ammonia concentrations was measured at the water-sludge interface. Nitrate reduction was highest in this interface zone with rates of up to 8.05 ± 0.57 μmol NO₃⁻ h⁻¹ g_(sludge)⁻¹. Addition of sulfide increased the nitrate reduction rate at all sludge depths, pointing to the important role of autotrophic denitrification in the anaerobic reactor. Dissimilatory nitrate reduction to ammonia (DNRA) was found to be low in all sludge layers but was enhanced when sludge was incubated at high sulfide concentrations. Although nitrate reduction rates increased as a result of sulfide addition to sludge samples, no differences in nitrate reduction rates were observed between the samples incubated with different initial sulfide concentrations. This as opposed to sulfide oxidation rates, which followed Michaelis-Menten enzymatic kinetics. Partial oxidation of sulfide to elemental sulfur instead of a complete oxidation to sulfate, could explain the observed patterns of nitrate reduction and sulfide oxidation in sludge incubated with different initial sulfide concentrations.     

Fungal and bacterial mediated denitrification in wetlands: Influence of sediment redox condition

Fungal and bacterial denitrification rates were determined under a range of redox conditions in sediment from a Louisiana swamp forest used for wastewater treatment. Sediment was incubated in microcosms at 6 Eh levels (−200, −100, 0, +100, +250 and +400 mV) ranging from strongly reducing to moderately oxidizing conditions. Denitrification was determined using the substrate-induced respiration (SIR) inhibition and acetylene inhibition methods. Cycloheximide (C₁₅H₂₃NO₄) was used as the fungal inhibitor and streptomycin (C₂₁H₃₉N₇O₁₂) as the bacterial inhibitor. At Eh values of +250 mV and +400 mV, denitrification rates by fungi and bacteria were 34.3-35.1% and 1.46-1.59% of total denitrification, respectively, indicating that fungi were responsible for most of the denitrification under aerobic or weakly reducing conditions. On the other hand, at Eh −200 mV, denitrification rates of fungi and bacteria were 17.6% and 64.9% of total denitrification, respectively, indicating that bacteria were responsible for most of the denitrification under strongly reducing conditions. Results show fungal denitrification was dominant under moderately reducing to weakly oxidizing conditions (Eh > +250 mV), whereas bacterial denitrification was dominant under strongly reducing condition (Eh < −100 mV). At Eh values between −100 to +100 mV, denitrification by fungi and bacteria were 37.9-43.2% and 53.0-51.1% of total denitrification, respectively, indicating that both bacteria and fungi contributed significantly to denitrification under these redox conditions. Because N₂O is an important gaseous denitrification product in sediment, fungal denitrification could be of greater ecological significance under aerobic or moderately reducing conditions contributing to greenhouse gas emission and global warming potential (GWP).     

钱塘江海塘与浙江采石文化的关系研究

历史上的大型工程建设往往会对采石文化产生巨大的推动作用。钱塘江海塘的修筑是古代浙江一项伟大的水利工程,该工程的修筑对石材产生了巨大的需求,使浙江采石文化获得了较大的发展,而采石文化的发展也保证了工程的石材供应。如今,将古海塘的保护和旅游开发与区域采石文化结合起来,可以取得较好的效果。     

The synthesis of the dissimilatory nitrate reductase under aerobic conditions in a number of denitrifying bacteria, isolated from activated sludge and drinking water

A number of denitrifying bacteria were isolated from activated sludge and drinking water. These bacteria were tested for the synthesis of the dissimilatory nitrate reductase under aerobic conditions (dissolved oxygen concentration above 4 mg · l⁻¹). The synthesis of this enzyme varied from total repression by oxygen in some bacteria, especially those isolated from drinking water, until a nearly non oxygen-repressed synthesis in other bacteria (strains 15 and N4). The effect of the dissolved oxygen concentration during growth of the bacteria on the synthesis of the dissimilatory nitrate reductase in cells of strain 15 was studied more extensively. A considerable repression of the enzyme synthesis was obtained when the dissolved oxygen concentration was relatively high (approx 15 mg·l⁻¹). Addition of chlorate to the growth medium of strain 15 (using NH⁺₄-N as nitrogen source) also resulted in a serious repression of the nitrate reductase synthesis during aerobic growth (dissolved oxygen above 4 mg·l⁻¹). The dissimilatory nitrate reductase of aerobically grown cells of strains 15 and N4 was found to be mainly localized in the membrane fraction.     

River sediments provide a link between catchment pressures and ecological status in a mixed land use Scottish River system

This study evaluates water quality, suspended and bed sediment, ecological and catchment land use data for 13 catchments of the mixed land use River Dee, NE Scotland, where pollution point sources are limited. Samples were collected at key times of biological activity (early and late summers). Mean river water concentrations were smaller in main stem and upland sites and greater in tributaries where agricultural pressures were greater and were 2-41 microgPO(4)-Pl(-1), 8-58 microg total dissolved Pl(-1) and 1-6 mg l(-1) of suspended particulate matter (SPM). SPM was 7-372 times enriched in biologically available P (BAP; determined using an FeO paper strip method) and 2-122 times in organic C relative to bed sediments. Ratios in river water concentrations of BAP attributed to the SPM (0.1-1.0 microgPl(-1)) to PO(4)-P had the greatest range at baseflow (0.01-0.80) with larger values for low land use intensity catchments. During May chlorophyll a concentrations were related to SPM BAP (p<0.001), but later in summer to PO(4)-P, and there was a corresponding change in the organic composition of SPM observed by IR spectroscopy. SPM concentrations and SPM BAP were better related to intensive grassland land use (p<0.001) than was PO(4)-P concentration (p<0.01) and also predicted abundances of filter feeding macroinvertebrates (p<0.001). Within this river system SPM quantity and composition proved to be an indicator of river biogeochemical functioning and requires further investigation as a potentially sensitive monitoring tool and to increase our understanding of chemical ecological links.     

The relative importance of Lemna gibba L., bacteria and algae for the nitrogen and phosphorus removal in duckweed-covered domestic wastewater

To arrive at detailed nutrient balances for duckweed-covered wastewater treatment systems, five laboratory-scale experiments were carried out in shallow (3.3 cm), 1 l batch systems to assess separately the contributions of duckweed itself, attached and suspended bacteria as well as algae to N- and P-removal in domestic wastewater. Depending on the initial concentrations, our duckweed-covered systems removed 120–590 mg N m⁻² d⁻¹ (73–97% of the initial Kjeldahl-nitrogen) and 14–74 mg P m⁻² d⁻¹ (63–99% of the initial total phosphorus) in 3 days. Duckweed (Lemna gibba L.) itself was directly responsible for 30–47% of the total N-loss by uptake of ammonium and, probably dependent on the initial P-concentrations, for up to 52% of the total P-loss. The indirect contribution of duckweed to the total nutrient removal was also considerable and included the uptake (and adsorption) of ammonium and ortho-phosphate by algae and bacteria in the attached biofilm and the removal of N through nitrification/denitrification by bacteria attached to the duckweed. Together these accounted for 35–46 and 31–71% of the total N- and P-loss, respectively. Therefore, approximately of the total N- and P-loss could be attributed to the duckweed mat. The remaining quarter is due to non-duckweed related components: uptake and nitrification/denitrification by algae and bacteria attached to the walls and the sediment of the system (including sedimentation). Other processes, like NH₃-volatilisation, N-fixation and nutrient uptake as well as nitrification/denitrification by suspended microorganisms did not influence the N- and P-balance of our systems, but could become important with increasing water depths and retention times.     

景德镇地域文化与旅游景观街的关系及影响

从地域文化与旅游景观街的概念入手,阐述了景德镇地域文化的特征,着重分析了景德镇地域文化与当地旅游景观街的关系及具体影响,并探讨了其研究意义,进而指导当地旅游景观街的建设。     

自动射流灭火系统在某文化宫的应用

针对文化宫的建筑特点,提出了采用新型图像火灾安全监控系统和自动射流灭火系统,解决其消防问题的方法,并介绍了自射流灭火系统的工作流程、安装技术及实施中的注意事项,以供参考。     

The Singapore buildable design appraisal system: a preliminary review of the relationship between buildability,site productivity and cost.

This paper presents preliminary findings of a study to examine the relationship between site productivity, construction costs and the ‘buildable score’ of a buildable design appraisal system recently developed by the Singapore Construction Industry Development Board. The buildable score for a building is a numerical figure computed by taking into account the level of standardization, simplicity and extent of integrated elements used in the design of a building. The stated objective of the appraisal system is ‘to promote more buildable designs in the industry through assessing the contribution of design to site efficiency and produc6 tivity’. Empirical results from 37 completed building projects provide support for the appraisal system's proposition that ‘a design with a higher buildable score will result in more efficient labour usage in construction and therefore higher site labour productivity’. However, the relationship between construction costs and buildable score is less distinct.     

A study of the relationship between the mixed liquor fauna and plant performance for a variety of activated sludge sewage treatment works

A study of the mixed liquor faunas of 13 activated sludge plants revealed that various taxa were associated with different final effluent BOD (ATU), final effluent ammoniacal-N and mixed liquor suspended solids concentrations, and could be ranked accordingly. Three types of activated sludge plant were identified, including nitrifying and non-nitrifying plants which operated with a high or low sludge loading, and each supported a characteristic mixed liquor fauna. Furthermore, when species associations of the commoner activated sludge taxa were investigated by the minimum spanning tree technique, two discrete assemblages were revealed, which could be interpreted in relation to nitrification. It is suggested that the examination of mixed liquor faunas using these data may yield information about plant performance which would otherwise be difficult to obtain, and that this may be particularly useful in the operation of plants to achieve consistent stable nitrification.     

人地关系视角下河西走廊地域建筑生态文化

分析河西走廊早期生态环境与人文因素的互动关系,为溯源河西地域建筑形态和发展,做有据可依的地域建筑生态文化初步研究,河西走廊地域建筑在其自身的发展过程中,生态环境对于地域建筑的生成、发展及其相互关系,是确定河西走廊地域建筑生态文化指向的根本所在。     

碱激发体系与土聚水泥抗压强度关系的人工神经网络预测

人工神经网络技术由于自组织、自学习、自适应的能力,常被引入灰色系统模型建立、模式识别、目标分类等研究领域.本次研究运用人工神经网络技术,选取土聚水泥碱激发体系中的碱激发剂浓度(COH-)、碱硅摩尔比(M2O/SiO2)和硅摩尔比(Al2O3/SiO2)为预测指标,基于 MATLAB 神经网络工具箱,建立预测方法,对土聚水泥的 28 d抗压强度进行预测.结果表明,预测精度较高.     

The cooling and heating potential of an earth tube system in buildings

A new module was developed for and implemented in the EnergyPlus program for the simulation of earth tubes. The model was validated against and showed good agreement with both theoretical and experimental data. Using the new module, a parametric analysis was carried out to investigate the effect of pipe radius, pipe length, air flow rate and pipe depth on the overall performance of the earth tube under various conditions during cooling season. Pipe length and pipe depth turned out to affect the overall cooling rate of the earth tube, while pipe radius and air flow rate mainly affect earth tube inlet temperature. The cooling and heating potential of earth tubes in four different locations were also investigated. Whether or not an earth tube is beneficial turned out to be heavily dependent on the climate of the location.     

The importance of the relationship between scale and process in understanding long-term DOC dynamics

Concentrations of dissolved organic carbon have increased in many, but not all, surface waters across acid impacted areas of Europe and North America over the last two decades. Over the last eight years several hypotheses have been put forward to explain these increases, but none are yet accepted universally. Research in this area appears to have reached a stalemate between those favouring declining atmospheric deposition, climate change or land management as the key driver of long-term DOC trends. While it is clear that many of these factors influence DOC dynamics in soil and stream waters, their effect varies over different temporal and spatial scales. We argue that regional differences in acid deposition loading may account for the apparent discrepancies between studies. DOC has shown strong monotonic increases in areas which have experienced strong downward trends in pollutant sulphur and/or seasalt deposition. Elsewhere climatic factors, that strongly influence seasonality, have also dominated inter-annual variability, and here long-term monotonic DOC trends are often difficult to detect. Furthermore, in areas receiving similar acid loadings, different catchment characteristics could have affected the site specific sensitivity to changes in acidity and therefore the magnitude of DOC release in response to changes in sulphur deposition. We suggest that confusion over these temporal and spatial scales of investigation has contributed unnecessarily to the disagreement over the main regional driver(s) of DOC trends, and that the data behind the majority of these studies is more compatible than is often conveyed.     

Effect of temperature and disinfection strategies on ammonia-oxidizing bacteria in a bench-scale drinking water distribution system

The establishment of ammonia-oxidizing bacteria (AOB), a group of autotrophic microorganisms responsible for nitrification in chloraminated distribution systems, was studied in a bench-scale distribution system. The potential significance of temperature and disinfectant residual associated with chloramination in full-scale drinking water distribution systems was assessed. Biofilm development was primarily monitored using AOB abundance and nitrite concentrations. The bench-scale system was initially operated under typical North American summer (22 degrees C) and fall (12 degrees C) temperatures, representing optimal and less optimal growth ranges for these microorganisms. Additional experimentation investigated AOB establishment at a suboptimal winter distribution system temperature of 6 degrees C. The effect of chloramine residual on AOB establishment was studied at higher (0.2-0.6mg/L) and lower (0.05-0.1mg/L) ranges, using a 3:1 (w/w) chlorine:ammonia dosing ratio. Conditions were selected to represent those typically found in a North American distribution system, in areas of low flow and longer retention times, respectively. Finally, the effect of a free chlorine residual on an established nitrifying biofilm was briefly examined. Results clearly indicate that AOB development occurs at all examined temperatures, as well as at selected monochloramine residuals. The maintenance of a disinfectant residual was difficult at times, but was more inhibitory to the nitrifying biofilm than the lower temperature. It can be concluded from the data that nitrification may not be adequately inhibited during the winter months, which may result in more advanced stages of nitrification the following season. Free chlorination can be effective in controlling AOB activity in the short term, but may not prevent reestablishment of a nitrifying biofilm upon return to chloramination.     

Model system of bulking and flocculation in mixed culture of Sphaerotilus sp. and Pseudomonas sp. for dissolved oxygen deficiency and high loading

A mixed continuous culture system was made up as a model for bulking and flocculation phenomena of the activated sludge to study the effect of dissolved oxygen (DO) deficiency and the effect of high organic loading. The system consisted of a floc forming bacterium and a filamentous bacterium which were isolated from the activated sludge and were identified as Pseudomonas sp. and Sphaerotilus sp., respectively. Sphaerotilus sp. had potential to cause a filamentous bulking phenomenon on the activated sludge. It was observed that the filamentous microorganism showed three kinds of growth form, filamentous form, pellet form and dispersed form, and that the floc former showed two kinds of growth form, good floc form and dispersed form. In the model system, these changes of growth form of two microorganisms, which could be thought as the cause of settling characteristics changes, depended on the DO level and the dilution rate (as a substitution for organic loading). The DO level also influence the aggregative ability of each microorganism and the maximum oxygen uptake rate, Q_O2max, of filamentous microorganism. The proportions of both microorganisms in model system were inverted reversibly by the DO level or the dilution rate changes.