Réduction de la production de boues activées

RÉSUMÉ Les procédés biologiques par boues activées pour le traitement secondaire des eaux usées génèrent des quantités importantes de boues en excès. Plusieurs procédés biologiques, physiques et chimiques sont envisagés pour la réduction de la production de boues. Les procédés Cannibal® et d’ozonation des boues sont efficaces pour la réduction de la production de boues. Les mécanismes de réduction de la production de boues de ces procédés demeurent toutefois mal connus. Une meilleure compréhension des mécanismes de ces procédés permettrait d’optimiser leur conception et leur application. L’objectif général de cette thèse était de déterminer les mécanismes de réduction de la production de boues activées par les procédés opérés à des temps de rétention de boues (TRB) très élevés et d’ozonation des boues. La dégradabilité des matières particulaires non biodégradables a été considérée pour des TRB conventionnels, élevés et très élevés et suite à l’ozonation des boues. Des essais de rétention complète des boues en bioréacteur à membrane (BRM) de taille démonstration alimenté par des eaux usées réelles, en alternance avec des périodes de famine, ont permis de déterminer les paramètres stoechiométriques et cinétiques associés à la production de boues sur une grande plage de taux de charge (food to microorganism ratio; F/M) et de TRB. Deux jeux de paramètres fréquemment employés en pratique pour la conception de centres de récupération des ressources en eaux (CRRE, le nouveau terme pour désigner les stations d’épuration STEP) en Amérique du Nord ont été comparés pour la calibration de la production de boues des essais à rétention complète en termes de demande chimique en oxygène (DCO), de matières volatiles en suspension (MVES) et de biomasse active (XH).----------ABSTRACT The secondary treatment of wastewaters by the activated sludge process generates large quantities of excess sludge. Many biological, physical and chemical processes are being studied to reduce excess sludge production. The Cannibal® and the sludge ozonation processes are two promising sludge reduction processes. The mechanisms involved in the sludge reduction by these processes remains not well understood. A better knowledge of the mechanisms involved in these processes would allow to improve their design and implementation. The general objective of this thesis was to determine the mechanisms for the reduction of excess sludge production from the activated sludge in processes operated at a very long sludge retention time (SRT) and from the sludge ozonation process. Complete sludge retention experiments were conducted in a demonstration scale membrane bioreactor (MBR) fed with a real municipal wastewater and subjected to growth and famine periods to determine the stoichiometric and kinetic parameters related to sludge production over wide-ranging loading rates (food to microorganism ratio; F/M) and SRTs. The default model parameter values (YH, bH and ƒ) from two well-accepted models were compared to determine which parameter set better fitted the COD, VSS and active biomasse accumulation. These two models were selected because of their broad application by practitioners in water resource recovery facilities (WRRFs, the new designation for wastewater treatment plant, WWTPs) design and very similar sludge production and oxygen demand predictions despite dissimilar default parameter values, but different active biomass proportions

Effect of Tree Form on the Productivity of a Cut-to-Length Harvester in a Hardwood Dominated Stand

It is commonly accepted that tree form has an impact on the productivity of single-grip harvesters. However, it remains unclear, which elements of tree form are significant and to what degree they impact harvesting productivity. This is of particular importance in hardwood dominated stands, where hardwood trees often exhibit complex and variable stem and crown architecture that can complicate and prolong the processing phase. With the development of specialized harvesting heads, hardwoods, which were mostly subject to motor-manual operations, are now increasingly being cut and processed with fully mechanized harvesting systems. The goal of this pilot project was to determine the effect of tree form on the productivity of mechanized cut-to-length harvesting. A time and motion study of a single-grip harvester, operating in a hardwood dominated stand, suggests that the presence of a fork or a large branch on the main stem can reduce machine harvesting productivity by 15 to 20%

Mechanisms for Reduced Excess Sludge Production in the Cannibal Process

Reducing excess sludge production is increasingly attractive as a result of rising costs and constraints with respect to sludge treatment and disposal. A technology in which the mechanisms remain not well understood is the Cannibal process, for which very low sludge yields have been reported. The objective of this work was to use modeling as a means to characterize excess sludge production at a full-scale Cannibal facility by providing a long sludge retention time and removing trash and grit by physical processes. The facility was characterized by using its historical data, from discussion with the staff and by conducting a sampling campaign to prepare a solids inventory and an overall mass balance. At the evaluated sludge retention time of 400 days, the sum of the daily loss of suspended solids to the effluent and of the waste activated sludge solids contributed approximately equally to the sum of solids that are wasted daily as trash and grit from the solids separation module. The overall sludge production was estimated to be 0.14 g total suspended solids produced/g chemical oxygen demand removed. The essential functions of the Cannibal process for the reduction of sludge production appear to be to remove trash and grit from the sludge by physical processes of microscreening and hydrocycloning, respectively, and to provide a long sludge retention time, which allows the slow degradation of the “unbiodegradable” influent particulate organics (XU,Inf) and the endogenous residue (XE). The high energy demand of 1.6 kWh/m3 of treated wastewater at the studied facility limits the niche of the Cannibal process to small- to medium-sized facilities in which sludge disposal costs are high but electricity costs are low

Compact secondary treatment train combining a lab-scale moving bed biofilm reactor and enhanced flotation processes

High-rate wastewater processes are receiving a renewed interest to obtain energy positive/efficient water resource recovery facilities. An innovative treatment train combining a high-rate moving bed biofilm reactor (HR-MBBR) with an enhanced flotation process was studied. The two objectives of this work were 1) to maximize the conversion of soluble organics to particulate matter in an HR-MBBR and 2) to maximize the particulate matter recovery from the HR-MBBR effluent by green chemicals to enhance biogas production by anaerobic digestion. To achieve these objectives, lab-scale MBBRs fed with synthetic soluble wastewater were operated at organic loading rates (OLRs) between 4 and 34 kg COD m−3 reactor d−1 corresponding to hydraulic retention times (HRTs) between 6 and 54 min. Colloidal and soluble chemical oxygen demand (COD) removal efficiency in the HR-MBBR increased with HRT to reach a plateau of 85% at an HRT longer than 27 min. Carrier clogging observed at an OLR higher than 16 kg COD m−3 d−1 (HRT < 13 min) resulted in about 23% loss in colloidal and soluble COD removal efficiency. Thus, the recommended parameters were between 22 and 37 min and between 6 and 10 kg COD m−3 d−1 for the HRT and the OLR, respectively, to maximize the conversion of soluble organics to particulate matter. Total suspended solids (TSS) recovery of 58–85% and 90–97% were achieved by enhanced flotation using green and unbiodegradable chemicals, respectively, corresponding to a TSS effluent concentration below 14 and 7 mg TSS/L. Among the synthetic polymers tested, a high molecular weight and low charge density cationic polyacrylamide was found to give the best results with less than 2 mg TSS/L in the clarified effluent (97% TSS recovery). Green chemicals, although performing slightly less for solids separation than unbiodegradable chemicals, achieved a mean TSS concentration of 10 ± 3 mg/L in the clarified effluent

Effect of ozonation on anaerobic digestion sludge activity and viability

The effect of ozonation of anaerobic digested sludge on methane production was studied as a means of increasing the capacity of municipal anaerobic digesters. Ozone doses ranging from 0 to 192 mg O3/g sludge COD were evaluated in batch tests with a bench scale ozonation unit. Ozonation initially, and temporarily, reduced biomass viability and acetoclastic methanogenic activity, resulting in an initial lag phase ranging from 0.8 to 10 days. Following this lag phase, ozonation enhanced methane production with an optimal methane yield attained at 86 mg O3/g COD. Under these conditions, the yield of methane and the rate of its formation were 52% and 95% higher, respectively, than those factors measured without ozonation. A required optimal ozone dose could be feasible to improve the anaerobic digestion performance by increasing the methane production potential with a minimum impact on microbial activity; thus, an optimal ozone dose would enable an increase in the capacity of anaerobic digesters

Ozonation of Primary Sludge and Digested Sludge to Increase Methane Production in a Chemically Enhanced Primary Treatment Facility

The purpose of this research was the investigation of the ozonation of sludge as a method to improve anaerobic digestion performance in a chemically enhanced primary treatment facility. Batch tests were conducted to evaluate the effect of ozonation on the physicochemical characteristics of both primary and digested sludge. Then, the performance of semi-continuous anaerobic digesters in combination with ozone treatment was investigated (pre-ozonation and post-ozonation). Ozonation of primary sludge did not increase the soluble COD nor the biodegradable COD, but resulted in the mineralization of a fraction of the organic matter into CO2. However, the ozonation of anaerobic digested sludge resulted in an increase in soluble COD and biodegradable COD and in a small level of mineralization at the dose of 90 mg O3/g COD. Pre-ozonation of primary sludge was not effective in enhancing the performance of the anaerobic digester. The coupling of ozonation and anaerobic digestion by means of the post-ozonation of digested sludge was found to be effective in improving methane production (+16%), for COD removal efficiency and for the dewaterability of anaerobic digesters compared to the control digester

Increased adipose tissue indices of androgen catabolism and aromatization in women with metabolic dysfunction

Abstract Background Body fat distribution is a risk factor for obesity-associated comorbidities, and adipose tissue dysfunction plays a role in this association. In humans, there is a sex difference in body fat distribution, and steroid hormones are known to regulate several cellular processes within adipose tissue. Our aim was to investigate if intra-adipose steroid concentration and expression or activity of steroidogenic enzymes were associated with features of adipose tissue dysfunction in individuals with severe obesity. Methods Samples from 40 bariatric candidates (31 women, 9 men) were included in the study. Visceral (VAT) and subcutaneous adipose tissue (SAT) were collected during surgery. Adipose tissue morphology was measured by a combination of histological staining and semi-automated quantification. Following extraction, intra-adipose and plasma steroid concentrations were determined by liquid chromatography, electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). Aromatase activity was estimated using product-over-substrate ratio, while AKR1C2 activity was measured directly by fluorogenic probe. Gene expression was measured by quantitative PCR. Results VAT aromatase activity was positively associated with VAT adipocyte hypertrophy (p-valueadj &lt; 0.01) and negatively with plasma HDL-cholesterol (p-valueadj &lt; 0.01), while SAT aromatase activity predicted dyslipidemia in women even after adjustment for waist circumference, age and hormonal contraceptive use. We additionally compared women with high and low visceral adiposity index (VAI) and found that VAT excess is characterized by adipose tissue dysfunction, increased androgen catabolism mirrored by increased AKR1C2 activity and higher aromatase expression and activity indices. Conclusion In women, increased androgen catabolism or aromatization is associated with visceral adiposity and adipose tissue dysfunction

Why Delannoy numbers?

This article is not a research paper, but a little note on the history of combinatorics: We present here a tentative short biography of Henri Delannoy, and a survey of his most notable works. This answers to the question raised in the title, as these works are related to lattice paths enumeration, to the so-called Delannoy numbers, and were the first general way to solve Ballot-like problems. These numbers appear in probabilistic game theory, alignments of DNA sequences, tiling problems, temporal representation models, analysis of algorithms and combinatorial structures.Comment: Presented to the conference "Lattice Paths Combinatorics and Discrete Distributions" (Athens, June 5-7, 2002) and to appear in the Journal of Statistical Planning and Inference

Retreat into scientism, paradoxes of transparency, and corruption in education

Um dos sintomas da razão indolente (SANTOS, 2006) é o recuo ao cientificismo, o qual tem sido, particularmente, acentuado nas políticas, cada vez mais hegemônicas, de avaliação, de prestação de contas e de responsabilização. Por isso, um dos objetivos deste texto é o de colocar em causa este aparente consenso cientificista (ou este consenso supostamente transideológico) e fazer uma breve incursão exploratória ao que aqui se designa de paradoxos da transparência. Considera-se que esses paradoxos traduzem a existência de tensões e contradições relativas a uma dimensão central dos discursos políticos e educacionais contemporâneos. Com isso, o artigo pretende dar continuidade a uma linha de pesquisa que tem procurado sublinhar a relevância da necessidade de complexificar e dar maior rigor teórico-conceptual à accountability em educação. Finalmente, tentando abrir caminho para o desenvolvimento de novas articulações e análises, chama-se a atenção para a corrupção na educação cuja complexidade ainda é insuficientemente conhecida e pesquisada, nomeadamente, nas suas relações com as problemáticas da transparência e da accountability. Admite-se que as práticas de corrupção em educação, em muitas situações, são (paradoxalmente) induzidas pela necessidade de dar resposta à governação baseada nos números, nos rankings e nas (supostas) evidências, anulando completamente as expectativas legítimas em torno da transparência dos processos educacionais e das decisões políticas.One symptom of “indolent reason” (SANTOS, 2006) is the retreat into scientism, which is especially marked in the increasingly hegemonic policies surrounding assessment, reporting and accountability. As such, one of the aims of this paper is to call into question this apparent consensus on scientism (a supposedly trans-ideological consensus), and briefly explore what we define as the paradoxes of transparency. These paradoxes are found to reveal the existence of tensions and contradictions concerning a central aspect of current political and educational discourse. In doing so, the article seeks to continue a line of study which has aimed to emphasize the significance of the need for a more complex, and theoretically and conceptually rigorous understanding of accountability in education. Finally, in an attempt to pave the way for further discussion and analysis, attention is drawn to corruption in education, the complex nature of which remains insufficiently understood and studied, notably in terms of its relationship with the problems of transparency and accountability. It is acknowledged that practices of corruption within education are, in many situations, (paradoxically) caused by the need to answer to a system of governance based on numbers, league tables, and (supposed) truths, completely nullifying legitimate expectations about the transparency of educational processes and policy decisions.Trabalho financiado por Fundos Nacionais através da FCT – Fundação para a Ciência e a Tecnologia – no âmbito do Projeto PEst-OE/CED/UI1661/2014.info:eu-repo/semantics/publishedVersio