Monitoring bacterial community structure and variability in time scale in full-scale anaerobic digesters

Using a high-throughput pyrosequencing technology, this study assessed bacterial community structure and time-scale variability in great detail in seven full-scale anaerobic digesters operated variously in terms of influent substrate, digestion temperature, and reactor configuration. Pyrosequencing generated a total of 83,774 sequence reads from 40 digester sludge samples collected monthly for six months. The highest number of sequence reads were detected within Proteobacteria (20.5%), followed by those within Bacteroidetes (19.7%), Firmicutes (17.8%), and Chloroflexi (4.8%). The relative composition of bacterial populations was varied within the digesters as well as between the digesters, and the bacterial community structures were mainly influenced by digestion temperature. Detailed bacterial community structures were assessed by analyzing the operational taxonomic units (OTUs) based on 97% sequence similarity, which resulted in a total of 9051 OTUs. Among these, a total of 31 core OTUs were analyzed and inferred phylogenetically, which enabled us to classify the sequences within an unclassified phylum. Unclassified sequences were mostly affiliated with the sequences within Spirochaetes and Firmicutes. Interestingly, numerically dominant novel phylotypes (18% of the total sequence reads) presumably involved in anaerobic digestion within Spirochaetes were identified. Temporal variability was further explored using a non-metric multidimensional scaling ordination which demonstrated that the variability of the bacterial community within the digesters was smaller than between digesters. Correlation analysis demonstrated that digester performance and operational conditions affected the pattern of bacterial community in the ordination. Additionally, a multi-response permutation procedure revealed that the bacterial communities within the digesters were more similar than those belonging to other digesters statistically, demonstrating a patchiness of the digesters in the distribution of bacterial populations. Overall, this study revealed the correlation of bacterial community structure and time-scale variability with digester performance and operating conditions.     

Optimal Carbon Capture and Storage Policies

The IPCC recommends the use of carbon capture and sequestration (CCS) technologies in order to achieve the Kyoto environmental goals. This paper sheds light on this issue by assessing the optimal strategy regarding the long-term use of CCS technologies. The aim is to analyze the optimal CCS policy when the sequestration rate is endogenous, being therefore one specific tool of the environmental policy. We develop a simple growth model to identify the main driving forces that should determine the optimal CCS policy. We show that, under some conditions on the cost of extractions, CCS may be a long-term solution to curb carbon emissions. We also show that over time the social planner will choose to decrease the rate of capture and sequestration. We then derive the decentralized equilibrium outcome by considering the programs of the fossil resource-holder and of the representative consumer. Finally, we determine the optimal environmental policy, i.e. the carbon tax scheme, as well as the dynamics of the fossil fuel price needed to implement it.     

Optimal monitoring and management of a water storage

The aim is to fill a water storage with potable water of a given quality, for subsequent treatment and distribution to a water conveying system. During a given period, a set of several pumping stations is working to deliver water from different sources at different locations. A multi-stage control process is considered whereby the total pumping time is divided into short sampling intervals. The intensity of pumping as a function of time is the control variable. It is assumed that there exists a reliable forecast of every pollutant as a function of time and water source. The amount of the pollutants are constrained in the final mass of water in the storage. The mass of water at the end of the operation period should be maximized. A linear programming (LP) model of the problem is described, and an algorithm of the reduction of its dimensionality is presented. An illustrative example is shown. A short conference version of this paper has been presented at 14th IEEE Mediterranean Conference on Control Automation, June 28–30 2006, Polytechnical University of Ancona, Ancona, Italy.     

Optimal Control Models and Elicitation of Attitudes towards Climate Damages

This paper examines the consequences of various attitudes towards climate damages through a family of stochastic optimal control models (RESPONSE): cost-efficiency for a given temperature ceiling; cost-benefit analysis with a pure preference for current climate regime and full cost-benefit analysis. The choice of a given proxy of climate change risks is actually more than a technical option. It is essentially motivated by the degree of distrust regarding the legitimacy of an assessment of climate damages and the possibility of providing in due time reliable and non controversial estimates. Our results demonstrate that (a) for early decades abatement, the difference between various decision-making frameworks appears to matter less than the difference between stochastic and non stochastic approach given the cascade of uncertainty from emissions to damages; (b) in a stochastic approach, the possibility of non-catastrophic singularities in the damage function is sufficient to significantly increase earlier optimal abatements; (c) a window of opportunity for action exists up to 2040: abatements further delayed may induce significant regret in case of bad news about climate response or singularities in damages.     

Optimal Space-time Coverage and Exploration Costs in Groundwater Monitoring Networks

A method to determine the optimal subset of stations from a reference level groundwater monitoring network is proposed. The method considers the redundancy of data from historical time series, the times associated with the total distance required to run through the entire monitoring network, and the sum of the times for each monitoring station. The method was applied to a hypothetical case-study consisting of a monitoring network with 32 stations. Cost-benefit analysis was performed to determine the number of stations to include in the new design versus loss of information. This optimisation problem was solved with simulated annealing. Results showed that the relative reduction in exploration costs more than compensates for the relative loss in data representativeness.     

Optimal charges on river effluent from lumped and distributed sources

We propose a modelling framework for the design of a Pigouvian effluent tax, in an environmental management problem implicating several economic agents located in a river basin. The proposed charging system allows for the agents' geographical position relative to the river's sections, at which environmental standards are to be enforced, and takes into account the possible different market structures within which the agents are operating. In particular, we consider industrial agents competing on an oligopolistic market, and a set of farmers acting as price takers on a large market. A regional authority's goal is to induce agents to some sort of cooperation which would result in the satisfaction of the common environmental constraints. The economic process on one side, and the pollution transport and accumulation on the other, constitute two dynamic processes in two different time scales. As the economic process is much slower than the other process we can neglect the latter's transients and concentrate on the time invariant steady state solutions to the transportation equation. The model thus constructed has some noncooperative game and optimal control problem's features with space being the ‘running’ variable. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dissipation studies of fentrazamide (YRC-2388) in soil under anaerobic condition

Dissipation of fentrazamide in soil and water under flooded (anaerobic) conditions was studied. Fentrazamide was applied to soil at 100 g ha(-1). Soil was extracted with 0.1 N HCl?:?acetone (1?:?1 v/v) followed by partition and cleanup with silica SPE. Separation was achieved in an ODS-II column with a mobile phase of acetonitrile?:?water (70?:?30 v/v) and detection at 214 nm. Recovery of fentrazamide varied from 75.2-90.4% and 89.9-97.8% in soil and water, respectively. Fentrazamide dissipated rapidly and fentrazamide residues were not detected after 100 and 35 days of application in soil and water, respectively. Half life in soil and water was 9.06 and 3.66 days, respectively. Dissipation followed monophasic first order kinetics pattern. No fentrazamide was detected in soil, rice grain and rice straw at harvest of crop. Calibration curves for quantification were linear and relative standard deviation (RSD) was 1.78%. LOD for instrument was 0.002 μg mL(-1) and LOQ for methods were 0.005 μg g(-1) for soil and water.     

Monitoring of growth and physiological activities of biofilm during succession on polystyrene from activated sludge under aerobic and anaerobic conditions

The present research work monitored the successive biofilm development and its catabolic role in the degradation of polystyrene (PS). PS material was artificially colonized with biofilm by incubating it with activated sludge under aerobic and anaerobic conditions. Biofilm formation was monitored by gravimetric weight analysis, spectrophotometric absorbance technique, heterotrophic plate count, and scanning electron microscopy under aerobic and anaerobic conditions. The wet weight (1.59 and 1.17 g) and dry weight (0.41 and 0.08 g) of a biofilm showed a significant constant increase under aerobic and anaerobic conditions, respectively, from first till 9 weeks of incubation. Plate count of the selected bacteria (Escherichia coli, Salmonella typhimurium, Shigella dysenteriae, Pseudomonas aeruginosa) considerably declined (90–99 %) in the biofilm after seventh and fifth weeks of incubation under aerobic and anaerobic conditions, respectively, indicating a positive shift from pathogenic to beneficial microbial community. While most probable number index of fecal coliforms and E. coli in the sludge showed more reduction (98 and 99 %) under aerobic as compare to anaerobic conditions (86 and 91 %) after 9 weeks of biofilm formation on PS cubes. Correspondingly, the decreasing levels of chemical oxygen demand and biochemical oxygen demand (up to 73 %) showed signs of sludge digestion. Scanning electron microscope coupled with energy dispersive X-ray spectroscope revealed nature of PS media containing high carbon content. However, biofilm development proved to be involved in the biochemical transformation of the PS medium as indicated by Fourier transform infrared spectroscopy.     

Optimal Sampling and Problematic Likelihood Functions in a Simple Population Model

Markov chains provide excellent statistical models for studying many natural phenomena that evolve with time. One particular class of continuous-time Markov chain, called birth–death processes, can be used for modelling population dynamics in fields such as ecology and microbiology. The challenge for the practitioner when fitting these models is to take measurements of a population size over time in order to estimate the model parameters, such as per capita birth and death rates. In many biological contexts, it is impractical to follow the fate of each individual in a population continuously in time, so the researcher is often limited to a fixed number of measurements of population size over the duration of the study. We show that, for a simple birth–death process, with positive Malthusian growth rate, subject to common practical constraints, there is an optimal schedule for measuring the population size that minimises the expected confidence region of the parameter estimates. Throughout our exposition of the optimal experimental design, we compare it to a simpler equidistant design, where the population is sampled at regular intervals. This is an experimental design worthy of comparison since it can represent a much simpler design to implement in practice. In order to find optimal experimental designs for our population model, we make use of a combination of useful statistical machinery. Firstly, we use a Gaussian diffusion approximation of the underlying discrete-state Markov process, which allows us to obtain analytical expressions for Fisher’s information matrix (FIM), which is crucial to optimising the experimental design. We also make use of the cross-entropy method of stochastic optimisation for the purpose of maximising the determinant of FIM to obtain the optimal experimental designs. Our results show that the optimal schedule devised by others for a simple model of population growth without death can be extended, for large populations, to the two-parameter model that incorporates both birth and death. For the simple birth–death process, we find that the likelihood surface is also problematic and poses serious problems for point estimation and easily defining confidence regions. A Bayesian approach to inference is proposed as a way in which these problems could be circumvented.     

Optimal Selection of Priority Development Areas Considering Tradeoffs Between Hydrology and Development Configuration

Mixed-integer linear programs are proposed for siting development and conservation areas in watersheds, addressing economic objectives (development perimeter and proximity) and ecological objectives. Links between watershed hydrology and ecology need not be well defined. Parameters for the linear programs are obtained from linearization of the SWAT hydrologic model.     

Optimal Foraging, Institutions and Forest Change: A Case from Nepal

The forest composition we witness today is a productof temporal anthropogenic and nonanthropogenicdisturbances. Scholars from geography, anthropology,and other disciplines have long been aware of theinforming nature of spatial relationships: humanactions in a previous time often leave imprints intoday's landscape. Traditional empirical studies offorest condition typically ignore this type ofinformation and rely on aggregated forest-levelindicators developed from aspatial plot-levelanalyses. This paper conducts a spatial analysis ofone important forest product species, Shorearobusta, in a foraging setting in southern Nepal. Forest plot locations were located using DifferentialGlobal Positioning Systems (DGPS) and were processedusing a Geographic Information System. Three rivalhypotheses of the geographic distribution of Shorea robusta are presented: (1) a pattern of nohuman disturbance, (2) a pattern of open access andoptimal foraging, and (3) a pattern of optimalforaging altered by the geographic configuration ofenforced institutions. Multivariate regression modelsare estimated and optimal foraging patterns areidentified. Statistical tests lend support to thethird hypothesis. Methods such as the ones presentedhere are important if we are to better understand thegeographic implications of institutional design onhuman behavior and the environmental outcomes that result.     

地表水特定项目优化检测技术研究

对地表水中特定项目指标的检测技术进行了优化研究,根据检测目标化合物的结构性质和色谱分析手段的兼容性,对前处理方法和分析手段进行了优化整合,提出了特定项目的解决方案,提高了工作效率,对切实保障饮用水源安全有实际意义.     

International Environmental Agreements: Design of Optimal Transfers Under Heterogeneity

International environmental agreements (IEAs) can coordinate abatement of transboundary pollutants. This paper investigates how heterogeneous countries facing a stock pollutant might structure such an agreement. In particular, we examine how an IEA might be implemented with a set of monetary transfers. The focus is on transfers that are time invariant, linear in emissions, and consistent with budget balance. There is a range of such schemes that would induce efficient emissions. We provide a simple and intuitive characterization of these penalties and describe how specific proposals might be chosen in order to facilitate compliance and implementation. Our proposals are illustrated with a simple example. We show that heterogeneity reduces the scope for penalty schemes to jointly satisfy desirable properties.     

Environmental quality control and environmental games

Conclusion  In this paper we have considered a specific environmental game emphasizing both control-prevention efforts and the propensity to pollute by a firm which adopts a given pollution abatement technology. A random payoff game was constructed and solved under a risk neutral assumption and quadratic utilities for both the firm and the environmental controller. The game thus defined, provides a wide range of interpretations and potential approaches for selecting a control-inspection policies to prevent environmental risks. There are of course many facets to this problem, which could be considered and have not been considered in sufficient depth. For example, more complex control mechanisms and liabilities, the effects of insurance and risk sharing, the application of cooperative efforts and subvention of pollution abatement investments (through tax incentives and their like), etc. have not been considered [5,7]. These are topics for further research. The basic presumption of this paper is that it is very difficult to fully enforce pollution prevention by firms, as a result, some controls are needed to ensure that firms be controlled so that appropriate efforts are carried.     

The potential for anaerobic mineralisation of hydrocarbon constituents of oily drill cuttings from the North Sea seabed

The potential for natural attenuation of hydrocarbons in oily drill cuttings from the seabed beneath a North Sea oil platform was investigated. The study focused on the anaerobic degradation of n-hexadecane, n-octacosane and naphthalene using additions of 14C-labelled analogues to drill cuttings samples and was conducted under realistic seabed conditions (except pressure) over an 11-month period. No mineralisation of naphthalene was detected over this time period and mineralisation of octacosane represented only 0.5-1.5% of the added label. In contrast, mineralisation of hexadecane was 10-49% after 11 months of incubation. Selective inhibition of key functional bacterial groups revealed the key role of both sulfate reduction and methanogenesis in the degradation process. This study demonstrates the potential for natural attenuation of at least some hydrocarbon constituents of oily drill cuttings under realistic environmental conditions and highlights the involvement of a wide functional consortium in the natural attenuation process.     

Optimal Expansion of Water Quality Monitoring Network by Fuzzy Optimization Approach

River reaches are frequently classified with respect to various mode of water utilization depending on the quantity and quality of water resources available at different location. Monitoring of water quality in a river system must collect both temporal and spatial information for comparison with respect to the preferred situation of a water body based on different scenarios. Designing a technically sound monitoring network, however, needs to identify a suite of significant planning objectives and consider a series of inherent limitations simultaneously. It would rely on applying an advanced systems analysis technique via an integrated simulation-optimization approach to meet the ultimate goal. This article presents an optimal expansion strategy of water quality monitoring stations for fulfilling a long-term monitoring mission under an uncertain environment. The planning objectives considered in this analysis are to increase the protection degree in the proximity of the river system with higher population density, to enhance the detection capability for lower compliance areas, to promote the detection sensitivity by better deployment and installation of monitoring stations, to reflect the levels of utilization potential of water body at different locations, and to monitor the essential water quality in the upper stream areas of all water intakes. The constraint set contains the limitations of budget, equity implication, and the detection sensitivity in the water environment. A fuzzy multi-objective evaluation framework that reflects the uncertainty embedded in decision making is designed for postulating and analyzing the underlying principles of optimal expansion strategy of monitoring network. The case study being organized in South Taiwan demonstrates a set of more robust and flexible expansion alternatives in terms of spatial priority. Such an approach uniquely indicates the preference order of each candidate site to be expanded step-wise whenever the budget limitation is sensitive in the government agencies.     

Modelling the Optimal Strategies of Fertiliser Application Using the Game-Theoretic Approach

This paper is a case study which describes the application of game-theoretic approach in resource management with specific emphasis on developing optimal strategies of phosphorus applications for soil fertilisation. The approach adopted allows resource managers to consider not only competitive strategies, which were treated as the Nash equilibrium game solutions, but also strategies which imply cooperation between farmers. These strategies were modelled as the cooperative Pareto optima of the game. The objective function of the game has been developed in order to reflect both economic advantages of phosphorus applications and the environmental losses associated with these applications expressed as dollar values. The paper presents algorithms for finding competitive and cooperative solutions of the game for the particular case when no time scheduling is included in the game parametrisation. The results obtained in the paper showed that the cooperative solutions lead to much lesser environmental impacts than that in the case of non-cooperative strategies.