Anaerobic treatment of low-strength municipal wastewater by a two-stage pilot plant under psychrophilic conditions

A two-stage anaerobic treatment pilot plant was tested for the treatment of raw domestic wastewater under temperatures ranging from 21 to 14 degrees C. The plant consisted of a hydrolytic upflow sludge bed (HUSB) digester (25.5m3) followed by an upflow anaerobic sludge blanket (UASB) digester (20.36m3). The hydraulic retention time (HRT) varied from 5.7 to 2.8h for the first stage (HUSB digester) and from 13.9 to 6.5h for the second stage (UASB digester). Total suspended solids (TSS), total chemical oxygen demand (TCOD), and biochemical oxygen demand (BOD) removals ranged from 76% to 89%, from 49% to 65%, and from 50% to 77%, respectively, for the overall system. The percentage of influent COD converted to methane was 36.1%, the hydrolysis of influent volatile suspended solids (VSS) reached 59.7% and excess biomass was 21.6% of the incoming VSS. Plant performance was influenced by the wastewater concentration and temperature, yet better results were obtained for influent COD higher than 250mg/l.     

Ammonia oxidizing bacteria community dynamics in a pilot-scale wastewater treatment plant

Background

Chemoautotrophic ammonia oxidizing bacteria (AOB) have the metabolic ability to oxidize ammonia to nitrite aerobically. This metabolic feature has been widely used, in combination with denitrification, to remove nitrogen from wastewater in wastewater treatment plants (WWTPs). However, the relative influence of specific deterministic environmental factors to AOB community dynamics in WWTP is uncertain. The ecological principles underlying AOB community dynamics and nitrification stability and how they are related are also poorly understood.

Methodology/Principal Findings

The community dynamics of ammonia oxidizing bacteria (AOB) in a pilot-scale WWTP were monitored over a one-year period by Terminal Restriction Fragment Length Polymorphism (T-RFLP). During the study period, the effluent ammonia concentrations were almost below 2 mg/L, except for the first 60 days, indicting stable nitrification. T-RFLP results showed that, during the test period with stable nitrification, the AOB community structures were not stable, and the average change rate (every 15 days) of AOB community structures was 10%±8%. The correlations between T-RFLP profiles and 10 operational and environmental parameters were tested by Canonical Correlation Analysis (CCA) and Mantel test. The results indicated that the dynamics of AOB community correlated most strongly with Dissolved Oxygen (DO), effluent ammonia, effluent Biochemical Oxygen Demand (BOD) and temperature.

Conclusions/Significance

This study suggests that nitrification stability is not necessarily accompanied by a stable AOB community, and provides insight into parameters controlling the AOB community dynamics within bioreactors with stable nitrification.     

Bacterial community dynamics in a functionally stable pilot-scale wastewater treatment plant

To determine whether functional stability was correlated with a stable microbial community structure in a functionally stable pilot-scale wastewater treatment plant, bacterial communities in the system were monitored over a one-year period. Bacterial community dynamics was characterized by the terminal restriction fragment length polymorphism (T-RFLP) of 16S rRNA genes. During the study period, the effluent BOD concentrations were very stable, with the average BOD concentration below 10 mg/L. The effluent TN concentrations were always below 20 mg/L, except for the first 40 days. T-RFLP results showed that, during the test period, the bacterial community structures were not stable, with an average change rate (every 15 days) of 20.4% ± 11.2%. Based on Lorenz distribution curves, it was observed that 20% of the species corresponded with 40-77% of cumulative relative abundances. Results clearly revealed that, in the pilot-scale wastewater treatment plant, functional stability did not correlate with stable bacterial communities.     

Impact of prehybridization PCR amplification on microarray detection of nitrifying bacteria in wastewater treatment plant samples

A gel-based microarray that included a set of 26 oligonucleotide probes targeting all nitrifying bacteria at varying levels of specificity suggested the presence of targeted microorganisms when hybridized to RNA isolated from a wastewater treatment plant, but could not discriminate between perfectly matched and mismatched sequences due in part to low signal intensity. To enhance sensitivity and improve discrimination, polymerase chain reaction was used to selectively amplify the 16S rRNA genes of specific nitrifier groups. RNA transcribed from these DNA templates was hybridized to the microarray and thermal dissociation analysis was used to characterize the specificity of hybridization. Amplification with Nitrospira-specific primers resulted in the selective amplification of this target group, confirmed by both a significant increase in signal intensity and a melting profile identical to the reference RNA. In contrast, Nitrobacter was not detected in the environmental samples with probe Nbac1000 despite pre-amplification with Nitrobacter-specific primers, indicating the absence of strains containing this Nitrobacter-specific sequence. Pre-amplification using primers specific for beta-Proteobacterial ammonia-oxidizing bacteria resulted in a significant increase in signal intensity for probe Nso190, but melting profiles for probe Nso190 showed a slight deviation between amplified RNA and the reference microorganism, suggesting that the amplification products contained some sequences that varied by a single nucleotide difference in the probe target region.     

有色环境噪音对空间异质种群动态同步性的影响

随着种群动态和空间结构研究兴趣的增加,激发了大量的有关空间同步性的理论和实验的研究工作。空间种群的同步波动现象在自然界广泛存在,它的影响和原因引起了很多生态学家的兴趣。Moran定理是一个非常重要的解释。但以往的研究大多假设环境变化为空间相关的白噪音。越来越多的研究表明很多环境变化的时间序列具有正的时间自相关性,也就是说用红噪音来描述更加合理。因此,推广经典的Moran效应来处理空间相关红噪音的情形很有必要。利用线性的二阶自回归过程的种群模型,推导了两种群空间同步性与种群动态异质性和环境变化的时间相关性(即环境噪音的颜色)之间的关系。深入分析了种群异质性和噪音颜色对空间同步性的影响。结果表明种群动态异质性不利于空间同步性,但详细的关系比较复杂。而红色噪音的同步能力体现在两方面:一方面,本身的相关性对同步性有贡献;另一方面,环境变化时间相关性可以通过改变种群密度依赖来影响同步性,但对同步性的影响并无一致性的结论,依赖于种群的平均动态等因素。这些结果对理解同步性的机理、利用同步机理来制定物种保护策略和害虫防治都有重要的意义。     

Diversity and dynamics of Archaea in an activated sludge wastewater treatment plant

ABSTRACT: BACKGROUND: The activated sludge process is one of the most widely used methods for treatment of wastewater and the microbial community composition in the sludge is important for the process operation. While the bacterial communities have been characterized in various activated sludge systems little is known about archaeal communities in activated sludge. The diversity and dynamics of the Archaea community in a full-scale activated sludge wastewater treatment plant were investigated by fluorescence in situ hybridization, terminal restriction fragment length polymorphism analysis and cloning and sequencing of 16S rRNA genes. RESULTS: The Archaea community was specialized and dominated by Methanosaeta-like species. During a 15 month period major changes in the community composition were only observed twice despite seasonal variations in environmental and operating conditions. Water temperature appeared to be the process parameter that affected the community composition the most. Several terminal restriction fragments also showed strong correlations with sludge properties and effluent water properties. The Archaea were estimated to make up 1.6-% of total cell numbers in the activated sludge and were present both as single cells and colonies of varying sizes. CONCLUSIONS: The results presented here show that Archaea can constitute a constant and integral part of the activated sludge and that it can therefore be useful to include Archaea in future studies of microbial communities in activated sludge.     

Effects of herbivory and plant conditioning on the population dynamics of spider mites

Plants vary in their resistance to tetranychid spider mites, and this can have profound effects on spider-mite population dynamics. Such variation can be attributable to many factors. In this review, however, we focus on how previous or concurrent feeding by phytophagous hervivores influences expression of plant resistance to spider mites.Induced resistance is a change in the host plant in response to extrinsic stimuli, resulting in reduced host suitability for the population growth of spider mites. We begin our review by summarizing the different ways in which spider mites and plants interact to produce induced resistance-like phenomena. We then discuss a number of hypotheses which address the mechanisms underlying induced resistance and end by suggesting agricultural applications. Although the potential use of induced resistance to manage spider mites is apparent, progress in this area will depend on a better understanding of the mechanisms involved and their associated costs and benefits to the plant.     

R-plasmid transfer in a wastewater treatment plant.

Enteric bacteria have been examined for their ability to transfer antibiotic resistance in a wastewater treatment plant. Resistant Salmonella enteritidis, Proteus mirabilis, and Escherichia coli were isolated from clinical specimens and primary sewage effluent. Resistance to ampicillin, chloramphenicol, streptomycin, sulfadiazine, and tetracycline was demonstrated by spread plate and tube dilution techniques. Plasmid mediation of resistance was shown by ethidium bromide curing, agarose gel electrophoresis, and direct cell transfer. Each donor was mated with susceptible E. coli and Shigella sonnei. Mating pairs (and recipient controls) were suspended in unchlorinated primary effluent that had been filtered and autoclaved. Suspensions were added to membrane diffusion chambers which were then placed in the primary and secondary setting tanks of the wastewater treatment plant. Resistant recombinants were detected by replica plating nutrient agar master plates onto xylose lysine desoxycholate agar plates that contained per milliliter of medium 10 micrograms of ampicillin, 30 micrograms of chloramphenicol, 10 micrograms of streptomycin, 100 micrograms of sulfadiazine, or 30 micrograms of tetracycline. Mean transfer frequencies for laboratory matings were 2.1 X 10(-3). In situ matings for primary and secondary settling resulted in frequencies of 4.9 X 10(-5) and 7.5 X 10(-5), respectively. These values suggest that a significant level of resistance transfer occurs in wastewater treatment plants in the absence of antibiotics as selective agents.     

生境片断化对濒危植物景东翅子树种群结构与动态的影响

生境的破坏及其片断化是生物多样性丧失的主要原因, 了解生境片断化对植物种群动态的影响十分必要。本文比较分析了不同大小生境片断(5 ha和15 ha)和连续森林中濒危植物景东翅子树(Pterospermum kingtungense)种群的结构与动态, 目的是明确影响景东翅子树种群动态的关键生活史阶段及其种群保护的目标, 为濒危植物种群保护和管理策略的制定提供科学依据。在上述3种生境中分别设立3个50 m × 100 m的1.5 ha固定样地, 调查景东翅子树所有个体的胸径(其中幼苗和幼树为地径)和高度、个体的存活及幼苗的补充情况。基于上述统计参数, 建立预测种群动态的Lefkovitch矩阵模型, 同时应用矩阵模型的弹性分析方法量化种群统计参数对种群增长率的相对贡献。结果表明: (1)在5 ha和15 ha生境片断及连续森林各1.5 ha的样地中, 2018年首次调查到景东翅子树的个体数分别为34、82和88株, 2019年复查时的个体数分别为33、82和87株。3种生境中景东翅子树种群的年龄结构均以幼树为主, 但5 ha生境片断森林缺乏幼苗和大树(包括成树和亚成树), 而15 ha生境片断森林幼苗较丰富。(2)在3种生境中景东翅子树种群的增长率等于1 (15 ha生境片断)或趋近于1 (5 ha生境片断和连续森林), 说明不同生境中的景东翅子树种群比较稳定, 这主要是因为其各生活史阶段的存活率均较高。(3)景东翅子树成树和亚成树阶段的存活率对种群增长率的贡献最大, 是影响其种群动态的关键生活史阶段。因此对于大树(包括成树和亚成树)的保护是极度濒危植物景东翅子树种群维持的关键。研究结果揭示小生境片断降低了景东翅子树种群的数量, 改变了种群的结构, 但对种群动态的影响效应尚未显现。因此对于这些小生境片断中濒危植物种群的保护和恢复是可行的, 也是有价值的。     

Performance of and methanogenic communities involved in an innovative anaerobic process for the treatment of food wastewater in a pilot plant

In this study, dual-cylindrical anaerobic digesters were designed and built on the pilot plant scale for the improvement of anaerobic digestion efficiency. The removal efficiency of organics, biogas productivity, yield, and microbial communities was evaluated as performance parameters of the digester. During the stable operational period in the continuous mode, the removal efficiencies of chemical oxygen demand and total solids were 74.1 and 65.1%, respectively. Biogas productivities of 63.9 m³/m³-FWW and 1.3 m³/kg-VS_removed were measured. The hydrogenotrophic methanogen orders, Methanomicrobiales and Methanobacteriales, were predominant over the aceticlastic methanogen order, Methanosarcinaceae, probably due to the tolerance of the hydrogenotrophs to environmental perturbation in the field and their faster growth rate compared with that of the aceticlastics.     

高寒森林不同生境对凋落叶分解灰分动态的影响

灰分是凋落叶的重要组成部分,其浓度直接关系到凋落叶的分解过程及有机组分的动态特征,且可能受生境和分解时期的影响,然而有关凋落叶分解过程中灰分动态的研究鲜有报道。采用凋落袋法,以岷江上游高寒森林4种代表性植物康定柳(Salix paraplesia)、高山杜鹃(Rhododendron lapponicum)、方枝柏(Sabina saltuaria)和四川红杉(Larix mastersiana)凋落叶为研究对象,研究了高寒森林凋落叶在3种不同环境条件下(林下、溪流、河岸带)分解过程中灰分的动态特征。结果表明,灰分量随凋落叶的分解整体呈现降低的趋势,且不同环境条件和不同物种之间存在明显的差异。与之相反,经过两年的分解,除溪流中康定柳凋落叶灰分浓度略有下降外(-0.99%),林下和河岸带中康定柳凋落叶及其它物种凋落叶中灰分浓度在所有环境条件下均表现出了增加的趋势(5.86%—72.15%)。凋落叶分解过程中灰分浓度变异量在不同分解时期存在明显或显著的差异,且受物种和环境因子的调控。这些结果表明,传统上认为凋落叶分解过程中灰分浓度比较稳定的观点是不准确的,且以凋落叶分解过程中灰分浓度不变的前提下采用无灰分质量损失(ash free mass loss)而计算凋落叶质量损失的方法存在一定的不准确性。研究为认识凋落叶分解过程中灰分的动态特征及凋落叶质量损失的测定方法提供了一定的参考。     

Visibility of the environmental noise modulating population dynamics

Characterizing population fluctuations and their causes is a major theme in population ecology. The debate is on the relative merits of density-dependent and density-independent effects. One paradigm (revived by the research on global warming and its relation to long-term population data) states that fluctuations in population densities can often be accounted for by external noise. Several empirical models have been suggested to support this view. We followed this by assuming a given population skeleton dynamics (Ricker dynamics and second-order autoregressive dynamics) topped off with noise composed of low- and high-frequency components. Our aim was to determine to what extent the modulated population dynamics correlate with the noise signal. High correlations (with time-lag -1) were observed with both model categories in the region of stable dynamics, but not in the region of periodic or complex dynamics. This finding is not very sensitive to low-frequency noise. High correlations throughout the entire range of dynamics are only achievable when the impact of the noise is very high. Fitted parameter values of skeleton dynamics modulated with noise are prone to err substantially. This casts doubt as to what degree the underlying dynamics are any more recognizable after being modulated by the external noise.     

Environmental performance of a municipal wastewater treatment plant

Goal, Scope and Background  Nowadays, every strategy must be developed taking into account the global impact on the environment; if this aspect is forgotten, a change of environmental loads or their effect will be caused and no reduction will be attained. For instance, a wastewater treatment plant (WWIP), which is considereda priori as an ecological treatment system, gives rise to an environmental impact due to its energy consumption, use of chemical compounds, emissions to the atmosphere and sludge production, the post-treatment of which will also have diverse environmental effects. The goal of this study is to evaluate the potential environmental impact corresponding to a municipal WW1P and to identify the hot spots associated with the process. Methods  In this study, the Centre of Environmental Science (CML) of Leiden University methodology has been considered to quantify the potential environmental impact associated with the system under study. A comprehensive analysis of the WWTP was evaluated for the physico-chemical characterisation of the wastewaters as well as the inventory of all the inputs (energy, chemical compounds, ...) and outputs (emissions to air, water, soil and solid waste generation) associated with the global process. Regarding Life Cycle Inventory Assessment, SimaPro 5.0 was used and in particular CML factors (updated in 2002) were chosen for characterisation and normalisation stages. Results and Discussion  A comprehensive inventory of empirical data from water, sludge and gas flows during 2000 and 2001 was obtained. Two impact categories arise due to their significance: eutrophication and terrestrial ecotoxicity. Consequently, the aspects to be minimised in order to reduce the environmental impact of the system are the pollutant load at the watercourse discharge (mainly NH₃, PO₄ ^[3- and COD, even when all of them are below legal limits) and the emissions to soil (mainly Cr, Hg and Zn, even when they are present in low concentrations) when the sludge is used for agricultural application. Conclusions  As far as the environmental impact is concerned, differentiation between humid and dry season is not required as results are practically equal for both situations. Water discharge and sludge application to land have turned out to be the main contributors in the environmental performance of a WWTP. Regarding the former, the removal of nitrogen by means of a nitrification-denitrification system coupled to conventional biological aerobic treatment implies a high environmental impact reduction and, as for the latter, bearing in mind the proposed legislation, heavy metals as well as pathogens are supposed to be the key parameters to define the most adequate treatment strategies for the generated sludge. Recommendations and Outlook  This study can serve as a basis for future studies that can apply a similar policy to a great number of wastewater facilities. Besides, features such as different treatment systems and capacities can provide additional information with the final aim of including the environmental vector in the decision-making process when the operation of a WWTP is intended to be optimised. Moreover, sludge must also be a focus of attention due to the expected increase and its major contribution to the global environmental impact of a WWTP, which can determine other treatment alternatives.     

Antibiotic-resistance profile in environmental bacteria isolated from penicillin production wastewater treatment plant and the receiving river

The antibiotic‐resistance characteristics of bacterial strains in antibiotic production wastewater treatment plants (WWTP) that contain high concentrations of antibiotics are unknown, as are the environmental effects of the discharge of wastewater from such facilities. In this study, 417 strains were individually isolated from the effluent of a WWTP that treated penicillin G production wastewater, as well as from downstream and upstream areas of the receiving river. The minimum inhibition concentrations (MICs) of 18 antibiotics representing seven classes were then determined for each of these strains. Relatively high similarity in the bacterial composition existed between the wastewater and downstream river samples when compared with the upstream sample. High resistance ratios and MIC values were observed for almost all antibiotics in wastewater isolates, followed by strains from downstream river, of which the resistance ratios and levels were still significantly higher than those of upstream strains. The resistance ratios and levels also significantly differed among strains belonged to different species in the penicillin production wastewater effluent and downstream river. In both samples, the resistances to β‐lactam antibiotics were more frequent, with much higher levels, than the other class antibiotics. Then five clinically important resistant genes mainly coding for extended‐spectrum β‐lactamases (ESBLs) were determined for all strains, only bla_TEM‐1 which did not belong to ESBL was detected in 17.3% and 11.0% of strains isolated from wastewater and downstream river respectively. Class I integrons were detected in 14% of wastewater isolates and 9.1% of downstream isolates, and primarily contained gene cassettes conferring resistance to aminoglycoside antibiotics. The unexpectedly high levels of multiple antibiotic resistance in strains from wastewater and downstream river were speculated to be mainly due to multidrug efflux systems.     

Reduction in excess sludge production in a dairy wastewater treatment plant via nozzle-cavitation treatment: Case study of an on-farm wastewater treatment plant

Nozzle-cavitation treatment was used to reduce excess sludge production in a dairy wastewater treatment plant. During the 450-d pilot-scale membrane bioreactor (MBR) operation, when 300 l of the sludge mixed liquor (1/10 of the MBR volume) was disintegrated per day by the nozzle-cavitation treatment with the addition of sodium hydrate (final concentration: 0.01% W/W) and returned to the MBR, the amount of excess sludge produced was reduced by 80% compared with that when sludge was not disintegrated.