Approche pour l'identification des causes de la mauvaise décantation des solides biologiques

Les procédés d'épuration biologique à culture libre (boues activées) comprennent habituellement un décanteur qui permet de concentrer les solides biologiques en vue de leur recirculation en tête du réacteur biologique. Lorsque ce décanteur fonctionne mal on observe une perte de solides biologiques (SB), ce qui se traduit par une augmentation de la concentration des matières en suspension (MES) dans l'effluent du décanteur secondaire et par une baisse des performances du procédé d'épuration. Lorsque la concentration de MES dans l'effluent du décanteur secondaire est trop élevée on mesure l'indice de volume des boues (IVB). Un IVB faible indique que les solides biologiques ont de bonnes caractéristiques de décantation de sorte que la cause de la mauvaise efficacité du décanteur est d'ordre physique et peut être identifiée facilement. Lorsque l'IVB est élevé, la mauvaise décantation est alors causée par un désordre de l'écosystème qui se traduit le plus souvent par une croissance excessive d'organismes filamenteux. Les causes et les solutions d'un tel problème sont alors difficiles à identifier. Pour ce travail, les auteurs ont réalisé une importante revue bibliographique dont les résultats sont présentés sous la forme d'un cheminement critique (fig. 1). Dans cette figure, les cases numérotées de 1 à 48 sont liées par des énoncés logiques. Ainsi, en répondant à des questions simples, il est possible de cheminer dans la figure 1 et d'identifier les causes les plus probables du déséquilibre microbiologique ainsi que les solutions qui ont déjà été apportées avec succès. De plus les auteurs ont associé à chaque case une fiche technique (portant le même numéro que la case) sur laquelle sont présentées des explications et la liste des références consultées.Activated sludge is a microbiological aerated sewage treatment process which includes a secondary clarifier to separate the treated effluent from the biological solids. Part of the concentrated solids is recirculated to maintain an adequate concentration of mixed liquor suspended solids (MLSS) In the aerated basin. When the secondary clarifier malfunctions, some biological solids are lost to the effluent : the process efficiency drops and the concentration of suspended solids (SS) increases. When the SS in the effluent is too high the sludge volume index (SVI) must be measured. A low SVI means that the biological solids have good sedimentation characteristics : the problem is thon physical in nature and is easily identified. When the SVI is high, the problem is due to a disturbance of the microbiological ecosystem, which is at the origin of excessive filamentous organism growth. The origins and solutions of such a problem are much harder to find. To this end the authors proceeded with an important review of the literature, the results of which are summarized through a critical path, in figure 1. Files from 1 to 48 are linked by logical statements in such a way that by answering simple questions, one can proceed through the files and identify the must probable cause of the biological disturbance as well as the solution which has already proven successful. Furthermore, the authors have linked each file to a technical file which bears the same number and on which an explanation and references are found.Before proceeding with figure 1 to identify a problem in real life, one must obtain information, resulting from an analysis and observations, with regard to plant effluent, primary clarifier effluent and activated sludge characteristics, including the MLSS concentration. One must also know the chemical oxygen demand (COD), the soluble and total biochemical oxygen demand (BOD5), as well as the nitrogen and phosphorus concentrations in the plant influent. Furthermore, one must also be told of the presence of toxic material or industrial wastes in the sewage and of the fraction of pollution load which is in the form of particulates. Whether sudden changes in the quality of the plant influent have occurred is worth knowing. The concentration of oxygen or hydrogen sulfide in the primary clarifier is also important. One must also gather data related to the activated sludge treatment itself : type of reactor (completely mixed or plug flow), mixed liquor volatile suspended solids (MLVSS) concentration, dissolved oxygen concentration, rate of oxygen uptake and pH. Finally, the results of a microbiological analysis of the sludge are very useful.To illustrate the use of figure 1, let us say that we have the following data :a) Many filamentous microorganisms are present in the MLSS, in particular Microthrix parvicella, type 0092, and Thiothrix sp;b) The rate of dissolved oxygen uptake is 12 mg O2/g of SS - h;c) The rate of COD removal is 0,48 Kg/Kg of SS -d;d) There are no toxic substances in the plant influent;e) There are no abrupt changes in plant influent quality;f) The pHs of the plant influent and of the MLSS are 7,0 and 6,8 respectively;g) The ammonia nitrogen concentration of the plant influent is 1,2 mg/L (N);h) The phosphorus concentration of the plant influent is 4,4 mg/L (P);i) The total and soluble BOD5 concentrations of the plant influent are 400 and 80 mg/L respectively.With this information, we are ready to proceed through figure 1. From file one, one goes to file 2, since the rate of oxygen uptake is sufficient. Otherwise, we would have proceeded to file 32. The reactor being completely mixed, the next step is file 3, where it is said that, because of the low soluble BOD5 concentration one must go to file 9, where we find a fast of filamentous microarganisms which may be responsible for the disturbance. Since two of these microorganisms are effectively present in the mixed liquor suspended solids (MLSS), Microthrox parvicella and type 0092, we are invited to go to file 35, where it is stated that someone has already solved a similar problem by creating a modified contact zone to increase the substrats (organic matter) concentration around the microbiological flocs. The third filamentous microorganism is not identified in file 9. As a second possibility one may assume, in file 2. That the mixing is not complete, which is often the case. With the help of information and results of analyses already available, we proceed, through file 4, 14, 15 and 16, to file 20 where Thiothrixsp is included in the microorganisms listed. File 20 is linked to file 41, where it is said that the controlled addition of nitrogen in the plant influent has already been used to solve this type of problem.The critical path presented in this article is the result of an elaborate study. It may be used as a tool to identify the causes of bad biological flocs sedimentation in the secondary clarifier and select solutions that have already been used successfully

How Intense Policy Demanders Shape Postreform Politics: Evidence from the Affordable Care Act

The implementation of the Affordable Care Act (ACA) has been a politically volatile process. The ACA\u27s institutional design and delayed feedback effects created a window of opportunity for its partisan opponents to launch challenges at both the federal and state level. Yet as recent research suggests, postreform politics depends on more than policy feedback alone; rather, it is shaped by the partisan and interest-group environment. We argue that “intense policy demanders” played an important role in defining the policy alternatives that comprised congressional Republicans\u27 efforts to repeal and replace the ACA. To test this argument, we drew on an original data set of bill introductions in the House of Representatives between 2011 and 2016. Our analysis suggests that business contributions and political ideology affected the likelihood that House Republicans would introduce measures repealing significant portions of the ACA. A secondary analysis shows that intense policy demanders also shaped the vote on House Republicans\u27 initial ACA replacement plan. These findings highlight the role intense policy demanders can play in shaping the postreform political agenda

A method addressing signal occlusion by scene objects to quantify the 3D distribution of forest components from terrestrial lidar

SilviLaser 2015, La Grande Motte, FRA, 28-/09/2015 - 30/09/2015International audienceEstimating exact 3D distribution of canopy components using terrestrial lidar in forest is limited by signal occlusion. We propose a method to address this limitation: it uses voxels, beam returns and beam propagation through the scene. The proposed method was validated using simulated forest scenes and a lidar simulator

Enhanced heterogeneously catalyzed Suzuki–Miyaura reaction over SiliaCat Pd(0)

The SiliaCat Pd(0) solid catalyst can be efficiently employed in the Suzuki–Miyaura cross-coupling of an ample variety of haloarenes, including economically viable chloroarenes. The catalyst can be extensively recycled without loss of activity and with low leaching of valued palladium, opening the route to widespread utilization of the method to afford high yields of biaryls devoid of contaminating by-products

Impact of ultraviolet radiation on marine crustacean zooplankton and ichthyoplankton: a synthesis of results from the estuary and Gulf of St. Lawrence, Canada

The objectives of the research program reported upon here were (1) to measure ambient levels of UV radiation and determine whichvariables most strongly affected its attenuation in the waters of the estuary and Gulf of St. Lawrence, Canada; and (2) to investigate the potential direct impacts of W radiation on species of crustacean zooplankton and fish whose early life stages are planktonic. In this geographic region, productivity-determining biophysical interactions occur in the upper 0 to 30 m of the water column. Measurements of the diffuse attenuation coefficients for ultraviolet-B radiation (W-B, 280 to 320 nm) at various locations in this region indicated maximum 10% depths (the depth to which 10% of the surface energy penetrates at a given wavelength) of 3 to 4 m at a wavelength of 310 nm. Organisms residing in this layer-including the eggs and larvae of Calanus finmarchicus and Atlantic cod Gadus morhua-are exposed to biologically damaging levels of W radiation. As a result of these physical and biological characteristics, this system offered a relevant opportunity to assess the impacts of UV on subarctic marine ecosystems. Eggs of C. finmarchicus were incubated under the sun, with and without the W-B and/or UV-A (320 to 400 nm) wavebands. W-exposed eggs exhibited low percent hatchmg compared to those protected from W : W radiation had a strong negative impact on C. finmarchicus eggs. Further, percent hatching in W-B-exposed eggs was not significantly lower than that in eggs exposed to UV-A only: under natural sunlight, UV-A radiation appeared to be more detrimental to C. finmarchicus embryos than was UV-B. In analogous experiments with Atlantic cod eggs, exposure to UV-B produced a significant negative effect. However, UV-A had no negative effect on cod eggs. Additional experiments using a solar simulator (SS) revealed high wavelength-dependent mortality in both C. finmarchicus and cod embryos exposed to UV. The strongest effects occurred under exposures to wavelengths below 312 nm. At the shorter wavelengths (<305 nm) UV-B-induced mortality was strongly dose-dependent, but (for both C. finmarchicus and cod) not significantly influenced by dose-rate. Thus, at least within the limits of the exposures under which the biological weighting functions (BWFs) were generated, reciprocity held. The BWFs derived for UV-B-induced mortality in C. finmarchicus and cod eggs were similar in shape to the action spectrum for UV-B effects on naked DNA. Further, the wavelengthdependence of DNA damage was similar to that for the mortality effect. These observations suggest that W-induced mortality in C. finmarchicus and cod eggs is a direct result of DNA damage. There was no evidence of a detrimental effect of UV-A radiation in these SS-derived results. A mathematical model that includes the BWFs, vertical mixing of eggs, meteorological and hydrographic conditions, and ozone depletion, indicates that W-induced mortality in the C. finmarchicus egg population could be as high as 32.5 %, while the impact on the cod egg population was no more than 1.2%. Variability in cloud cover, water transparency (and the variables that affect it), and vertical distribution and displacement of planktonic organisms within the mixed layer can all have a greater effect on the flux of UV-B radiation to which they are exposed than will ozone layer depletion at these latitudes. Our observations indicate that C, finmarchicus and cod eggs present in the first meter of the water column (likely only a small percentage of the total egg populations) are susceptible to W radiation. However, although exposure to UV can negatively impact crustacean zooplankton and ichthyoplankton populations, these direct effects are likely minimal within the context of all the other environmental factors that produce the very high levels of mortality typically observed in their planktonic early life stages. The impact of indnect effects-which may well be of much greater import-has yet to be evaluated

An examination of the temporal and geographical patterns of psychiatric emergency service use by multiple visit patients as a means for their early detection

<p>Abstract</p> <p>Background:</p> <p>Frequent users of the psychiatric emergency service (PES) place a heavy burden upon the mental health care delivery system. The aim of this study was to identify distinct temporal or geographical patterns of PES use by these patients as potential markers for their early detection.</p> <p>Methods:</p> <p>Diagnostic profiles were obtained for patients making an intermediate (4 to 10) or a high (11 or more) number of visits to a general hospital PES in Montreal (Canada) between 1985 and 2004. Between-group comparisons were made with regards to several parameters. These included the time intervals between consecutive visits, visit clustering (single, repeating, and the time interval to the first cluster) and visits made to three other services where data was similarly acquired from 2002 to 2004.</p> <p>Results:</p> <p>The two multiple visit groups differed with regards to diagnostic profiles and actual time between consecutive visits (significantly shorter in patients with 11 or more visits). Patients with 11 or more visits were more likely to have a single cluster (3 or more visits/3 months) or repeating clusters (4 visits/3 months) in their patterns of use. Personality disorders were more prevalent in patients with single clusters as they were, along with schizophrenia, in those with repeating clusters. In addition, clusters were found to occur sufficiently early so as to be potentially useful as markers for early detection. Ten percent of those with 11 or more visits and 16% of those with an intermediate number of visits frequented at least one other PES. A small number of patients, primarily those with substance abuse, made over 50% of their visits to other services.</p> <p>Conclusion:</p> <p>Temporal and geographical patterns of use differed significantly between the multiple visit groups. These patterns, combined with distinct diagnostic profiles, could potentially lead to the more rapid identification and treatment of specific sub-groups of multiple visit patients.</p

The combined influence of distance and neighbourhood deprivation on Emergency Department attendance in a large English population: a retrospective database study

YesThe frequency of visits to Emergency Departments (ED) varies greatly between populations. This may reflect variation in patient behaviour, need, accessibility, and service configuration as well as the complex interactions between these factors. This study investigates the relationship between distance, socio-economic deprivation, and proximity to an alternative care setting (a Minor Injuries Unit (MIU)), with particular attention to the interaction between distance and deprivation. It is set in a population of approximately 5.4 million living in central England, which is highly heterogeneous in terms of ethnicity, socio-economics, and distance to hospital. The study data set captured 1,413,363 ED visits made by residents of the region to National Health Service (NHS) hospitals during the financial year 2007/8. Our units of analysis were small units of census geography having an average population of 1,545. Separate regression models were made for children and adults. For each additional kilometre of distance from a hospital, predicted child attendances fell by 2.2% (1.7%-2.6% p<0.001) and predicted adult attendances fell by 1.5% (1.2% -1.8%, p<0.001). Compared to the least deprived quintile, attendances in the most deprived quintile more than doubled for children (incident rate ratio (IRR) = 2.19, (1.90-2.54, p<0.001)) and adults (IRR 2.26, (2.01-2.55, p<0.001)). Proximity of an MIU was significant and both adult and child attendances were greater in populations who lived further away from them, suggesting that MIUs may reduce ED demand. The interaction between distance and deprivation was significant. Attendance in deprived neighbourhoods reduces with distance to a greater degree than in less deprived ones for both adults and children. In conclusion, ED use is related to both deprivation and distance, but the effect of distance is modified by deprivation

The Social and Ethical Acceptability of NBICs for Purposes of Human Enhancement: Why Does the Debate Remain Mired in Impasse?

The emergence and development of convergent technologies for the purpose of improving human performance, including nanotechnology, biotechnology, information sciences, and cognitive science (NBICs), open up new horizons in the debates and moral arguments that must be engaged by philosophers who hope to take seriously the question of the ethical and social acceptability of these technologies. This article advances an analysis of the factors that contribute to confusion and discord on the topic, in order to help in understanding why arguments that form a part of the debate between transhumanism and humanism result in a philosophical and ethical impasse: 1. The lack of clarity that emerges from the fact that any given argument deployed (arguments based on nature and human nature, dignity, the good life) can serve as the basis for both the positive and the negative evaluation of NBICs. 2. The impossibility of providing these arguments with foundations that will enable others to deem them acceptable. 3. The difficulty of applying these same arguments to a specific situation. 4. The ineffectiveness of moral argument in a democratic society. The present effort at communication about the difficulties of the argumentation process is intended as a necessary first step towards developing an interdisciplinary response to those difficulties

Testing the application of terrestrial laser scanning to measure forest canopy gap fraction

Terrestrial laser scanners (TLS) have the potential to revolutionise measurement of the three-dimensional structure of vegetation canopies for applications in ecology, hydrology and climate change. This potential has been the subject of recent research that has attempted to measure forest biophysical variables from TLS data, and make comparisons with two-dimensional data from hemispherical photography. This research presents a systematic comparison between forest canopy gap fraction estimates derived from TLS measurements and hemispherical photography. The TLS datasets used in the research were obtained between April 2008 and March 2009 at Delamere Forest, Cheshire, UK. The analysis of canopy gap fraction estimates derived from TLS data highlighted the repeatability and consistency of the measurements in comparison with those from coincident hemispherical photographs. The comparison also showed that estimates computed considering only the number of hits and misses registered in the TLS datasets were consistently lower than those estimated from hemispherical photographs. To examine this difference, the potential information available in the intensity values recorded by TLS was investigated and a new method developed to estimate canopy gap fraction proposed. The new approach produced gap fractions closer to those estimated from hemispherical photography, but the research also highlighted the limitations of single return TLS data for this application