bluuebunny/crossref_metadata_2025 huggingface dataset:
Issues and Challenges of Chemical Mechanical Polishing for Nano-scale Memory Manufacturing
Authors: Ryu Choon Kun , Shin Jonghan , Park Hyungsoon , Kwak Nohjung , Hong Kwon , Park Sungki
Published: March 2010

As the design rule of memory devices is scaled down to nanoscale, the number of the CMP process has increased considerably due to the complexity of integration scheme. The CMP for isolation has increased significantly because the isolation process of metal contact plugs and damascene metallization at nanoscale has been successfully enabled by the CMP. The CMP selectivity, which depends strongly on the chemistry of the slurry, must be tuned for the various new materials. Recently, in order to get over the limitation in lateral shrinkage of the memory device, several emerging applications have been investigated extensively. A vertical integration needs the new CMP process such as high removal rate Cu CMP. Next generation memories need the CMP process for new materials such as GeSbTe, conductive oxide, and magnetic materials. Since any nano-size scratch will be a killer defect at the nanoscale memory, both the CMP equipment and the consumables must be maintained with tighter degree of control specifications.
Role of Phosphoric Acid in Copper Electrochemical Mechanical Planarization Slurries
Authors: Aksu Serdar
Published: March 2010

In this paper, the electrochemical behavior of copper in aqueous solutions containing phosphoric acid (H3PO4) is investigated to elucidate the role of H3PO4 in the Cu ECMP slurries. Aqueous solubility and potential-pH diagrams were constructed for copper-phosphate-water system. Good correlations were found between the diagrams and the experimental polarization data. It was found that H3PO4 might not able to sufficiently increase the solubility of copper alone. A complexing agent is needed to ensure the high solubility of copper, especially as the slurry pH and dissolved copper concentration increase. Specific conductance measurements revealed that phosphoric acid was the key constituent responsible for increasing the conductivity of the ECMP electrolyte. In situ electrochemical polarization experiments showed that the planarization mechanism during the ECMP process was similar to that observed in conventional copper CMP.
CMP for High Mobility Strained Si/Ge Channels
Authors: Sawano Kentarou , Shiraki Yasuhiro , Nakagawa Kiyokazu
Published: March 2010

Si/Ge heterostructures are one of the most promising performance boosters for next generation CMOS circuits. Lattice mismatch between Si and Ge enables us to manipulate lattice strain, that is, strain engineering is possible. The strain highly alters band structures and gives rise to band splitting and/or effective mass reduction, which brings significant mobility enhancement of the carriers in the strained channel.

High mobility channels such as strained-Si and strained-Ge can be formed on strain-relaxed SiGe buffer layers called SiGe virtual substrates (VS). Since the property of the SiGe VS directly affects that of the overgrown channel layer, creating high-quality SiGe VS is highly required to obtain high performance devices. One critical problem is a very large surface roughness arising on the SiGe VS. So-called crosshatch pattern appears on the surface, irrespective of growth methods. Since strain field coming from the underlying misfit dislocation arrays is responsible for this roughness formation, it is very difficult to create a roughness-free surface.

To overcome this problem, we employed chemical mechanical planarization (CMP) for the purpose of eliminating the roughness. Since CMP is established technology for Si wafer production, it is reasonably applicable to SiGe. Adopting the similar process as Si CMP, we demonstrated that an initial roughness of larger than 10 nm was reduced considerably down to less than 1 nm.

Post-CMP cleaning is an additional issue of great importance for regrowth of device channel structures. We found that the roughness increased during post-CMP cleaning process due to laterally nonuniform etching rate of the SiGe surface. To overcome this, we optimized the cleaning procedure, especially cleaning solution, and successfully obtained very smooth surface with RMS roughness of less than 0.4 nm, the lowest value ever obtained for SiGe surfaces.

The planarized SiGe VS was applied to strained channel structures. Strained Si modulation doped structure was fabricated on the planarized SiGe VS with a Ge concentration of 30 %. The electron Hall mobility obtained from the structure with CMP was 4 times higher than the reference structure without CMP, which is a clear evidence that the roughness-related carrier scattering can be well suppressed by the planarization. Strained Ge channel modulation doped structure was also fabricated on the SiGe VS with much higher Ge concentration (65 %). Although the roughness was much larger than 10 nm due to the high Ge concentration, the surface smoothness less than 1 nm was obtained by CMP. As a result, hole mobility enhancement factor over the reference sample without CMP was found to reach as high as 8 at low temperature and 1.8 at room temperature. These results clearly indicate that CMP is very promising technology for high performance strained Si/Ge based CMOS circuit.
Implant Bone Rings. One-Stage Three-Dimensional Bone Transplant Technique: A Case Report
Authors: Stevens Mark R. , Emam Hany A. , Alaily Mahmoud E. L. , Sharawy Mohamed
Published: March 2010

A variety of techniques and materials has been used to provide the structural base of bone and soft tissue support for dental implants. Alveolar bone augmentation techniques include different surgical approaches such as guided bone regeneration, onlay grafting, interpositional grafting, distraction osteogenesis, ridge splitting, and socket preservation. In the case presented, a technique was used to augment the alveolar bone three-dimensionally with autologous “bone rings” and immediate implant placement in a 1-stage procedure following teeth extraction. Bone rings (circular osteotomies) were outlined at the symphysis area using trephine burs, and a central osteotomy for implant placement was done before its removal. The rings were then removed and sculptured to fit the extraction socket; this was followed by screwing the implant through the ring, gaining its primary stability from the prepared basal bone.
Interim Endodontic Therapy for Alveolar Socket Bone Regeneration of Infected Hopeless Teeth Prior to Implant Therapy
Authors: Rass Marwan Abou
Published: March 2010

The immediate placement of implants in the fresh extraction sockets of infected teeth with periradicular and periapical lesions is contraindicated because of both the infection and the loss of architecture required for proper implant placement. There are 4 approaches for implant replacement of a hopeless tooth with lesions: (1) extraction and delayed implant placement; (2) extraction, debridement, guided bone regeneration (GBR), guided tissue regeneration (GTR), and delayed implant placement; (3) extraction, intrasocket debridement, and immediate implant placement; or (4) extraction, debridement, GBR, GTR, and simultaneous implant placement. The extraction of such hopeless teeth often results in large bone and soft tissue defects that are difficult to repair. This article introduces an alternative approach: interim endodontic implant site preparation, defined as a transitional, surgical, or nonsurgical endodontic treatment to regenerate the hopeless tooth bone defects and prepare the site for proper implant placement. This article describes 3 distinct interim endodontic protocols used to manage 5 patients, all of whom had severely infected hopeless teeth with large lesions and were treatment planned for implant replacement: the first, interim nonsurgical endodontic treatment to restore the normal anatomy of the infected hopeless tooth; the second, interim surgical endodontics on the hopeless tooth with preexisting endodontic treatment to regenerate apical bone for primary implant stability, thus avoiding the involvement of the maxillary sinus and other critical anatomic structures; and the third, interim surgical endodontics on the hopeless tooth with preexisting endodontic treatment to confine the size of the osseous defect and simplify the GBR and GTR procedures. The outcome of interim endodontic treatment on these 5 patients demonstrated that tooth extraction would have been a less predictable approach. The interim treatment changed the overall direction of the patients' dental care. When treated, these hopeless teeth served many preventive, biologic, and esthetic functions. The infections of the alveolar sockets were eliminated, the alveolar bone defects were repaired through normal bone regeneration, and sockets anatomies were maintained or restored. Furthermore, the patients were spared maxillary sinus surgery and the possible complications resulting from major GBR and GTR procedures. In summary, the interim treatment facilitated tooth extraction and immediate implant placement.
Histologic Analysis of the Oral Mucosa Lining Osseointegrated Implant Cover Screws: A Study in Humans
Authors: Nahas André Alan , Dechichi Paula , de Magalhães Denildo , Vieira Andreia Espíndola
Published: March 2010

Osseointegrated dental implants are inserted into the alveolar ridge, and for them to function as tooth replacements, the surrounding tissues need to adapt to them. Just as with teeth, dental implants traverse the oral mucosa and have access to the contaminated environment of the oral cavity. Therefore, periodontal and peri-implant tissues are important for establishing a protective barrier. The aim of the present study was to perform a histologic analysis of the mucosa surrounding osseointegrated implant cover screws. For this study, 17 mucosal specimens were obtained from 12 patients during the second surgical session for implant exposure to the oral environment. After histologic preparation, specimens were sectioned perpendicularly to the mucosal surface to a thickness of about 3 µm, stained with 1% toluidine blue, and examined under light microscopy. All specimens showed a keratinized, stratified, squamous epithelium with well-defined strata. In the lamina propria, unorganized dense connective tissue was noted in the reticular layer, and in 4 samples, a chronic inflammatory infiltrate was seen in this region. The papillary layer presented tall connective papillae consisting of loose connective tissue. The results of this study confirm the hypothesis that the mucosa that conceals osseointegrated implant cover screws has the same morphologic characteristics as the alveolar masticatory mucosa. Furthermore, clinical conditions of normality in peri-implant tissues may not coincide with situations of histologic normality.
Use of Ultrasound in the Management of Thyroid Cancer
Authors: Lew John I. , Solorzano Carmen C.
Published: March 2010

The use of ultrasound for thyroid cancer has evolved dramatically over the last few decades. Since the late 1960s, ultrasound has become essential in the examination of the thyroid gland with the increased availability of high-frequency linear array transducers and computer-enhanced imaging capabilities of modern day portable ultrasound equipment in a clinic- or office-based setting. As a noninvasive, rapid, and easily reproducible imaging study, ultrasound has been demonstrated to have a broadened utility beyond the simple confirmation of thyroid nodules and their sizes. Recently, office-based ultrasound has become an integral part of clinical practice, where it has demonstrated overwhelming benefits to patients being evaluated and treated for thyroid cancer. Ultrasound has become useful in the qualitative characterization of thyroid nodules based on benign or malignant features. On the basis of such classifications and the relative risk for thyroid malignancy, the need for ultrasound-guided fine-needle aspiration, preoperative and intraoperative staging, lymph node mapping, and the extent of surgery can subsequently be determined. Furthermore, ultrasound has additional value in the surveillance of patients treated for thyroid cancer.
Ship impact on offshore minimum-structure platforms
Authors: Grewal G. S. , Lee M. M. K.
Published: March 2010

This paper presents the findings of a numerical investigation into the vulnerability of the topsides safety systems to strong vibrations caused by a ship impact. Three minimum structures and a jacket platform have been considered in order to compare the magnitude of responses that could be expected for a range of ship impacts. The study has identified important operational issues that should be addressed when determining to what extent the resulting vibrations exceed equipment operating limits, or present a risk to personnel in their working environment. At present, the guidance for engineers with regard to dynamic response is only given for protecting installations against earthquakes, even though a ship impact can be much stronger and have more severe consequences. The acceleration spectrum has been used in order to generate acceleration spectra in a similar way to the approach adopted by the nuclear industry. This was done so that critical safety equipment could then be specified to withstand the vibrations which could arise from all forms of shock loading.
Modelling of reinforced concrete structures in fire
Authors: Huang Z.
Published: March 2010

In this paper a robust finite-element procedure is presented for three-dimensional modelling of reinforced concrete structures under fire conditions. In this non-linear procedure a reinforced concrete building is modelled as an assembly of finite plain beam–column and slab elements, reinforcing steel bar elements and bond-link elements. Both material and geometric non-linearities are considered in the model. To consider the effects of concrete spalling on the thermal and structural behaviours of concrete structures under fire conditions, a ‘void layer' and ‘void segment' are introduced to represent the spalled-concrete part within concrete slabs, beams and columns. A critical temperature is used as the concrete spalling criterion. These developments enable the model to simulate quantitatively the effects of concrete spalling on both the thermal and structural behaviours of reinforced concrete structures in fire. A series of analyses are also conducted on a generic reinforced concrete building. The results indicate that, under fire conditions, the structural behaviour of isolated members with the concrete spalled is very different compared with the behaviour exhibited when embedded within a building. The influence of bond conditions between concrete and reinforcing steel bars on the fire resistance of structural members is significant. The global structural fire resistance of the reinforced concrete building is significantly affected by the concrete spalling on their members, in which the most important member is floor slabs.
Modelling wave deformation due to submerged breakwaters
Authors: Kriezi E. , Karambas T.
Published: March 2010

The present paper presents an experimental and numerical study of partial wave reflection and transmission for monolithic rectangular submerged breakwaters located in the nearshore region. The study is based on large-scale experiments that have been conducted in Universitat Politecnica de Catalunya, Laboratory de Ingeneria Maritima in Spain. Both irregular and regular waves are tested under breaking and non-breaking conditions. The experimental findings confirmed that the wave breaking due to the presence of the structure is a main energy dissipation mechanism which significantly affects wave transmission. The numerical approach of the problem is based on a higher-order Boussinesq type of equations for breaking and non-breaking waves with improved linear dispersion characteristics. The energy loss due to eddy motions near the sharp corners of the structure is introduced in the model by using a hydraulic loss formula. The breaking criterion proposed by Okamoto and Basco was introduced in the numerical model. The comparison between model results and experimental data shows that the model is able to describe breaking and non-breaking wave deformation passing over a submerged breakwater
The time evolution of scour around offshore structures
Authors: Harris J. M. , Whitehouse R. J. S. , Benson T.
Published: March 2010

This paper describes the development of an engineering model to predict the development of scour evolution through time around an offshore structure under current, wave and combined wave–current flows. The model has been tested against a range of data as well as being run for idealised tests. From the results of these tests issues with respect to scour prediction have been highlighted. In particular, the initial growth rate of scour appears to be too rapid based on the large-scale laboratory tests and tidal field data against which the model has been compared. Application of the model to a field-scale study has been completed which shows that in shallow water depths storm waves dominate the scour process. In deeper water depths, currents generally dominate even under storm conditions, although this will be dependent on the wave height and period and the actual water depth. The scour time evolution predictor (Step) model can be applied to scour assessment studies where there is a requirement to have an indication of the time-history of scour. The model clearly has a role in offshore wind turbine studies, but it is not limited to this sector and can be applied to bridge scour situations or other situations where scouring around monopile structures is an issue. Furthermore, if the scour at other types of structures or objects needs to be evaluated then provided the equilibrium scour depth and time-scale functions are available these can be implemented within the framework of the Step model.
A review of coastal risk management in the UK
Authors: Pontee N. I. , Parsons A.
Published: March 2010

This paper reviews the approaches that have been developed in the UK in order to deliver sustainable policies for managing risks from coastal erosion and flooding. One of the most important facilitators has been the adoption of a strategic framework at a national scale. This framework involves several scales of plans (shoreline management plans and strategy plans) as well as schemes. The recognition that funding sources are finite, and therefore need to be spent wisely, has also encouraged the development of more sustainable schemes. This has necessitated the development of a national appraisal methodology under which only the highest priority schemes achieve central government funding. The government also funds a national research programme to support flood and coastal erosion risk management. This paper gives examples of some of the outputs of this programme, which have included studies that have led to an improved understanding of coastal processes, coastal evolution, and risk levels, as well as the development of national data sets and management tools. The paper suggests some further improvements that could be made to the research programme. The discussion focuses on the likelihood of increasing choice of ‘managed realignment’ and ‘no active intervention’ policies in the future, their potential unpopularity with local stakeholders, and the current work under way to deal with these issues. The paper concludes with some thoughts on the priorities for coastal management over the next decade.
Effects of Menstrual Cycle on Periodontal Health and Gingival Crevicular Fluid Markers
Authors: Becerik Sema , Özçaka Özgün , Nalbantsoy Ayşe , Atilla Gül , Celec Peter , Behuliak Michal , Emingil Gülnur
Published: March 2010

Background: Fluctuations in sex steroid hormones, which are also noticeable through the menstrual cycle of women, may impact periodontal health. The aim of this study is to evaluate the effect of hormonal changes occurring in the menstrual cycle on gingival inflammation and the gingival crevicular fluid (GCF) levels of interleukin 6 (IL‐6), prostaglandin E2 (PGE2), tissue plasminogen activator (t‐PA), and plasminogen activator inhibitor‐2 (PAI‐2).

Methods: Twenty‐five gingivitis patients and 25 periodontally healthy subjects having regular menstrual cycles were seen at menstruation (ME) (1 to 2 days of menstruation), ovulation (OV) (12 to 14 days), and premenstrual phases (PM) (22 to 24 days). GCF and saliva samples were collected and clinical parameters including plaque index and bleeding on probing were recorded at each menstrual phase. Salivary estrogen and progesterone levels were analyzed to determine exact menstrual cycle days. GCF levels of IL‐6, PGE2, t‐PA, and PAI‐2 were measured by enzyme‐linked immunosorbent assay.

Results: The percentages of sites with bleeding on probing were significantly higher in ME (60.85 ± 18.36) and OV (58.92 ± 25.04) than in the PM (40.12 ± 20.10) phase in the gingivitis group (P <0.001; repeated measures analysis of variance), whereas it was similar for all phases in the healthy group (P >0.05; repeated measures analysis of variance). GCF levels of IL‐6 were significantly elevated in gingivitis patients compared to healthy subjects in all phases (P = 0.004, P = 0.041, and P = 0.046 for ME, OV, and PM, respectively; Mann‐Whitney U test). GCF levels of IL‐6, PGE2, t‐PA, and PAI‐2 were unchanged in different menstrual phases in both groups (P >0.05; Friedman test).

Conclusion: The present study suggests that changes in the sex steroid hormones during menstrual cycles might have a limited effect on the inflammatory status of gingiva, but GCF cytokine levels were not affected.
A Behavioral Economics Perspective on Tobacco Taxation
Authors: Cherukupalli Rajeev
Published: March 2010

Economic studies of taxation typically estimate external costs of tobacco use to be low and refrain from recommending large tobacco taxes. Behavioral economics suggests that a rational decision-making process by individuals fully aware of tobacco's hazards might still lead to overconsumption through the psychological tendency to favor immediate gratification over future harm. Taxes can serve as a self-control device to help reduce tobacco use and enable successful quit attempts. Whether taxes are appropriately high depends on how excessively people underrate the harm from tobacco use and varies with a country's circumstances. Such taxes are likely to be more equitable for poorer subgroups than traditional economic analysis suggests, which would strengthen the case for increased tobacco taxation globally.
Changing Patterns in Health Behaviors and Risk Factors Related to Cardiovascular Disease Among American Indians and Alaska Natives
Authors: Jernigan Valarie Blue Bird , Duran Bonnie , Ahn David , Winkleby Marilyn
Published: March 2010

Objectives. We assessed changes in cardiovascular disease–related health outcomes and risk factors among American Indians and Alaska Natives by age and gender.

Methods. We used cross-sectional data from the 1995 to 1996 and the 2005 to 2006 Behavioral Risk Factor Surveillance System. The respondents were 2548 American Indian and Alaska Native women and men aged 18 years or older in 1995–1996 and 11 104 women and men in 2005–2006. We analyzed the prevalence of type 2 diabetes, obesity, hypertension, cigarette smoking, sedentary behavior, and low vegetable or fruit intake.

Results. From 1995–1996 to 2005–2006, the adjusted prevalence of diabetes among American Indians and Alaska Natives increased by 26.9%, from 6.7% to 8.5%, and obesity increased by 25.3%, from 24.9% to 31.2%. Hypertension increased by 5%, from 28.1% to 29.5%. Multiple logistic models showed no meaningful changes in smoking, sedentary behavior, or intake of fruits or vegetables. In 2005–2006, 79% of the population had 1 or more of the 6 risk factors, and 46% had 2 or more.

Conclusions. Diabetes, obesity, and hypertension and their associated risk factors should be studied further among urban, rural, and reservation American Indian and Alaska Native populations, and effective primary and secondary prevention efforts are critical.
Spatial distribution of some microbial trophic groups in a plug-flow-type anaerobic bioreactor treating swine manure
Authors: Talbot Guylaine , Roy Caroline S. , Topp Edward , Kalmokoff Martin L. , Brooks Stephen P. J. , Beaulieu Carole , Palin Marie-France , Massé Daniel I.
Published: March 2010

Anaerobic digestion of swine manure is carried out by a consortium of microbial species, including volatile fatty acid (VFA) producers, VFA-degraders and methanogens. The distribution of five phylogenetic groups within a plug-flow-type anaerobic bioreactor consisting of eight serially-connected tanks was examined through the sequential digestion of swine manure. Quantification was carried out using reverse transcription real-time PCR (RT-Q-PCR) assays targeting the 16S rRNA of Clostridium (cluster XIVa), Peptostreptococcus, Syntrophomonas, Methanosaeta, and Methanosarcina spp. The VFA producers Peptostreptococcus spp. and Clostridium spp. were found predominantly in compartments where hydrolysis/acidogenesis took place. The spatial distribution of the aceticlastic methanogens, Methanosaeta and Methanosarcina, within the bioreactor was not correlated with methanogenic activity. In contrast the VFA-degrading genus Syntrophomonas spp. was more abundant in compartments with elevated methanogenic activity. Multivariate statistical analyses of the RT-Q-PCR data have provided new insights into our understanding of how the various trophic groups were distributed within this bioreactor system. While the distribution of clostridia, peptostreptococci and Syntrophomonas corresponded to their known metabolic functions, aceticlastic methanogens were not apparently linked to the methanogenesis stage occurring in latter compartments, suggesting that hydrogenotrophic methanogens were the primary methane generators in this bioreactor. However, aceticlastic methanogens could be involved in compartments related to the hydrolysis/acidogenesis stage.
The effect of co-existing solutes on arsenate removal with hydrotalcite compound
Authors: Kiso Y. , Jung Y. J. , Yamamoto H. , Oguchi T. , Kuzawa K. , Yamada T. , Kim S. S. , Ahn K. H.
Published: March 2010

Hydrotalcite (HTAL-Cl), an inorganic anion exchanger, is of use as an adsorbent for the removal of arsenate (As(V)) in water systems. The adsorption properties of HTAL-Cl for As(V) and the effects of co-existing anions on the As(V) removal performance were investigated in this work. Under the conditions of pH≥4, the adsorption capacity for As(V) gradually decreased with an increase of pH, but As(V) was removed effectively within the range of pH = 5–8. Co-existing anions interfered As(V) removal, and the effect decreased in the order of HPO42− > HCO3− > SO42− > Cl−. In binary solute systems containing phosphate and As(V), the maximum adsorption capacity of HTAL-Cl was 0.95 mmol g−1 for phosphate and 0.65 mmol g−1 for As(V): the total of these values corresponded to the maximum adsorption capacity for As(V) in single solute systems. The adsorption isotherms in these binary solute systems were approximated by the following modified Langmuir equations:

As(V):   qAs=18.7√CAs/1 + 21.5√CP + 12.8√CAs,    phosphate :    qP = 33.1√CP/ 1+ 21.5√CP+  12.8√CAs

The column adsorption experiments showed that the adsorbed As(V) was released by the phosphate adsorption, because phosphate was adsorbed more strongly on HTAL-CL than As(V).
Characteristics of developed granules containing selected decolourising bacteria for the degradation of textile wastewater
Authors: Ibrahim Z. , Amin M. F. M. , Yahya A. , Aris A. , Muda K.
Published: March 2010

Textile wastewater, one of the most polluted industrial effluents, generally contains substantial amount of dyes and chemicals that will cause increase in the COD, colour and toxicity of receiving water bodies if not properly treated. Current treatment methods include chemical and biological processes; the efficiency of the biological treatment method however, remains uncertain since the discharged effluent is still highly coloured. In this study, granules consisting mixed culture of decolourising bacteria were developed and the physical and morphological characteristics were determined. After the sixth week of development, the granules were 3–10 mm in diameter, having good settling property with settling velocity of 70 m/h, sludge volume index (SVI) of 90 to 130 mL/g, integrity coefficient of 3.7, and density of 66 g/l. Their abilities to treat sterilised raw textile wastewater were evaluated based on the removal efficiencies of COD (initial ranging from 200 to 3,000 mg/L), colour (initial ranging from 450 to 2000 ADMI) of sterilised raw textile wastewater with pH from 6.8 to 9.4. Using a sequential anaerobic-aerobic treatment cycle with hydraulic retention time (HRT) of 24 h, maximum removal of colour and COD achieved was 90% and 80%, respectively.
Faecal indicator bacteria in river biofilms
Authors: Balzer M. , Witt N. , Flemming H.-C. , Wingender J.
Published: March 2010

Biofilms in surface waters primarily consist of allochthonous microorganisms. Under conditions of pollution faecally derived bacteria may interact with these biofilms. Total coliform bacteria, Escherichia coli and intestinal enterococci are used to monitor source water quality, indicating faecal pollution and the possible presence of enteric pathogens. In the present study the occurrence of faecal indicators was investigated in biofilms (epilithic biofilms, sediments) of German rivers. All of the biofilms contained significant concentrations of these bacteria, which were several orders of magnitude lower compared with the total cell number and the number of culturable heterotrophic plate count bacteria indicating that faecal indicator bacteria represented a minor fraction of the whole biofilm communities. The biofilms displayed approximately two orders of magnitude higher concentrations of total coliforms, E. coli and enterococci compared with the overlying water. Identification of coliform and enterococcal isolates from the biofilms revealed the presence of species which are known to be opportunistic pathogens. Overall, the results of the present study show that faecal indicator bacteria can survive in the presence of high cell densities of the authochthonous microflora in epilithic biofilms and sediments, suggesting that these biofilms may act as a reservoir for bacterial pathogens in polluted rivers.
Comparison of single-stage and a two-stage vertical flow constructed wetland systems for different load scenarios
Authors: Langergraber Guenter , Pressl Alexander , Leroch Klaus , Rohrhofer Roland , Haberl Raimund
Published: March 2010

Constructed wetlands (CWs) are known to be robust wastewater treatment systems and are therefore very suitable for small villages and single households. When nitrification is required, vertical flow (VF) CWs are widely used. This contribution compares the behaviour and treatment efficiencies of a single-stage VF CW and a two-stage VF CW system under varying operating and loading conditions according to standardized testing procedures for small wastewater treatment plants as described in the European standard EN 12566-3. The single-stage VF CW is designed and operated according to the Austrian design standards with an organic load of 20 g COD m−2 d−1 (i.e. 4 m2 per person equivalent (PE)) The two-stage VF CW system is operated with 40 g COD m−2 d−1 (i.e. 2 m2 per PE). During the 48 week testing period the Austrian threshold effluent concentrations have not been exceeded in either system. The two-stage VF CW system showed to be more robust as compared to the single-stage VF CW especially during highly fluctuating loads at low temperatures.
The evaluation of benzene and phenol biodegradation kinetics by applying non-structured models
Authors: Trigueros D. E. G. , Módenes A. N. , Espinoza-Quiñones F. R. , Kroumov A. D.
Published: March 2010

The biodegradation kinetics of the aromatic hydrocarbons benzene and phenol as single substrates and as a mixture were investigated through non-structured model analysis. The material balance equations involving the models of Monod and Andrews and representing the biodegradation kinetics of individual substrates in batch mode were numerically solved. Further, utilization of a benzene–phenol mixture was described by applying more sophisticated mathematical forms of competitive, noncompetitive and uncompetitive inhibition models as well as the sum kinetic interactions parameters (SKIP) model. In order to improve the performance of the studied models, some modifications were also proposed. The Particle Swarm Global Optimization method, coded in Maple, was applied to the parameter identification procedure of each model, where the least square method was used as a search statistical criterion. The description of the biodegradation kinetics of a benzene–phenol mixture by the competitive inhibition model was based on the information that the compounds could be catabolized via one metabolic pathway of Pseudomonas putida F1. Simulation results were in good agreement with the experimental data and proved the robustness of the applied methods and models. The developed knowledge database could be very useful in the optimization of the biodegradation processes of different bioreactor types and operational conditions.
Influence of anionic surfactant on the process of electro-Fenton decolorized methyl orange
Authors: Ren B. X.
Published: March 2010

The electro-Fenton process has been shown to be very successful to remove dyes from water. However, the influence of other constituents in dyeing industry wastewater, such as Sodium Dodecyl Sulfate (SDS) surfactants, has not been investigated. In this study, the effect of SDS surfactant on the kinetics of Methyl Orange degradation undergoing Electro-Fenton process was investigated. Results show that Methyl Orange degradation rate decreased as SDS concentration (below Critical Micelle Concentration, CMC) increased, which was attributed to the consumption of hydroxyl radicals (˙OH) by surfactants. The kinetics modeling indicates the reaction was the first-order reaction to Methyl Orange even SDS existing. The pseudo first-order rate constants decreased as SDS concentration increased.
Implications and remediations of DMAEA-Q type polymer hydrolysis in wastewater treatment plants
Authors: Saveyn H. , Curvers D. , Pelicaen J. , Cauwenberghs J. , Thoeye C. , Van der Meeren P.
Published: March 2010

The present paper outlines the impact of hydrolysis occurring in DMAEA-Q type polymers in the dewatering facilities of municipal wastewater treatment plants. Laboratory studies of polymer hydrolysis kinetics were combined with full-scale dewatering experiments to investigate the influence of polymer charge loss on polymer consumption and cake dry matter yields. The results indicate that prolonged polymer storage leads to important charge loss effects, resulting in increased dosage requirements for satisfactory dewatering performance. Fortunately, charge loss effects due to hydrolysis upon polymer storage could be minimized by acidifying the polymer batches. Furthermore, cake dry matter contents obtained from dewatering tests with freshly prepared polymer batches suggested that acidification of the polymer batch also had a beneficial effect on the conditioning efficiency of the polymer solution. The results from this study thus stress the influence of pH on the shelf life and efficiency of polymer solutions in wastewater treatment plants. As a consequence, polymer preparation and storage procedures should be adapted to the polymer consumption pattern and pH of the medium used for polymer batch production.
Aerated biofilter with seasonally varied operation modes for the production of irrigation water
Authors: Meda A. , Cornel P.
Published: March 2010

Water reuse for agricultural irrigation can contribute to the conservation of valuable water resources and opens the possibility to reuse the wastewater's nutrients (N and P) at the same time. As irrigation is usually limited to vegetation periods, effluent requirements for treated wastewater may vary seasonally. A process concept for wastewater treatment with variable operation modes for the seasonal production of nutrient-rich irrigation water and nutrient-poor discharge water is proposed. It is shown that a two-step process consisting of organics removal followed by biological aerated filters (biofilters) for nitrogen removal is a promising combination which allows a flexible and seasonally varied operation with a fast re-start of biological nitrification after shut-down periods. To date, there is no commonly accepted practice amongst operators to take biofilters out of service for periods of time while - at the same time - maintaining biological activity to enable a quick start-up. This paper shows that during shut-down periods the activity drop rate is the smallest if the filter bed is maintained flooded and without aeration; then a very quick re-start is possible.
Evaluation of ultrasound technology for the disinfection of process water and the prevention of biofilm formation in a pilot plant
Authors: Lambert N. , Rediers H. , Hulsmans A. , Joris K. , Declerck P. , De Laedt Y. , Liers S.
Published: March 2010

In this study, we investigated the use of ultrasound for the disinfection of process water as an alternative for more traditional techniques, like chlorination and UV-irradiation. A pilot plant was constructed to mimic circulating process water in industrial environments. The disinfection efficiency of ultrasound was assessed and compared to UV-treatment and chlorination. In addition, the operational costs for the different technologies were evaluated. Based on disinfection efficiency and operational costs, the pilot plant experiments indicate that chlorination is the method of preference to treat bacteria in suspension. In the prevention of biofilm formation, the results of UV irradiation and ultrasound are comparable, with a slightly higher energy consumption for the ultrasonic treatment. Finally, the use of ultrasound to prevent biofilms was also evaluated in an industrial environment (case study). The results obtained from the case study are in agreement with the results obtained from the pilot plant study. To our knowledge, this is the first study that evaluates the use of ultrasound technology for prevention of biofilm formation in realistic circumstances as encountered in an industrial environment.
Access to potable water and sanitation in Cameroon within the context of Millennium Development Goals (MDGS)
Authors: Ako Andrew Ako , Shimada Jun , Eyong Gloria Eneke Takem , Fantong Wilson Yetoh
Published: March 2010

Cameroon has been fully engaged with the Millennium Development Goals (MDGs) since their inception in 2000. This paper examines the situation of access to potable water and sanitation in Cameroon within the context of the Millennium Development Goals (MDGs), establishes whether Cameroon is on the track of meeting the MDGs in these domains and proposes actions to be taken to bring it closer to these objectives. Based on analyzed data obtained from national surveys, government ministries, national statistical offices, bibliographic research, reports and interviews, it argues that Cameroon will not reach the water and sanitation MGDs. While Cameroon is not yet on track to meet the targets of the MDGs for water and sanitation, it has made notable progress since 1990, much more needs to be done to improve the situation, especially in rural areas. In 2006, 70% of the population had access to safe drinking water and the coverage in urban centres is 88%, significantly better than the 47% in rural areas. However, rapid urbanization has rendered existing infrastructure inadequate with periurban dwellers also lacking access to safe drinking water. Sanitation coverage is also poor. In urban areas only 58% of the population has access to improved sanitation facilities, and the rate in rural areas is 42%. Women and girls shoulder the largest burden in collecting water, 15% of urban and 18% rural populations use improved drinking water sources over 30 minutes away. Cameroon faces the following challenges in reaching the water and sanitation MDGs: poor management and development of the resources, coupled with inadequate political will and commitment for the long term; rapid urbanization; urban and rural poverty and regulation and legislative lapses. The authors propose that: bridging the gap between national water policies and water services; recognizing the role played by Civil Society Organizations (CSOs) in the attainment of MDGs; developing a Council Water Resource Management Policy and Strategy (CWARMPS); organizing an institutional framework for the water and sanitation sector as well as completion and implementation of an Integrated Water Resources Management (IWRM) plan, would bring Cameroon closer to the water and sanitation MDGs.
An assessment of oxygen transfer efficiency in a gas permeable hollow fibre membrane biological reactor
Authors: Soreanu G. , Lishman L. , Dunlop S. , Behmann H. , Seto P.
Published: March 2010

The clean water oxygen transfer efficiency (OTE) of a full scale non-porous hollow fibre gas permeable (GP) membrane (surface area of 500 m2) was evaluated at inlet air pressures of 1.2, 1.4, and 1.8 atm using two established testing methods. To form a basis of comparison with traditional aeration technologies, additional testing was done with conventional aerators (fine bubble and coarse bubble diffusers) replacing the GP membrane. OTE can be established based on the re-aeration of deoxygenated water or by monitoring the catalytic oxidation of a sodium sulphite (Na2SO3) solution. In this study, OTE values determined by sulphite oxidation (SOTES) were consistently higher than those established during re-aeration (SOTER) suggesting that the chemical reaction was enhancing the mass transfer. The chemical reaction was sufficiently fast in the case of the GP membrane, that the gas phase limited the mass transfer. The GP membrane operating at 1.2 atm had a SOTES of 70.6% and a SOTER of 52.2%.

SOTER for the coarse bubble and fine bubble diffusers were 3.8% and 23.6%, respectively. This is comparable to the manufacturer's values, corrected for depth of 3.4% and 18.3%, respectively. Particularly, the derived OTE values were used to evaluate differences in energy consumption for a conventional treatment plant achieving carbon removal and nitrification. This analysis highlights the potential energy efficiency of GP membranes, which could be considered for the design of the membrane modules.
Nanofiltration for the removal of algal metabolites and the effects of fouling
Authors: Dixon M. B. , Falconet C. , Ho L. , Chow C. W. K. , O'Neill B. K. , Newcombe G.
Published: March 2010

Nanofiltration (NF) has been shown to be an effective way of removing organic micropollutants from drinking water due to its size exclusion properties. A rapid bench scale membrane test unit was utilised to trial six NF membranes to remove the algal metabolites, microcystin, cylindrospermopsin, 2-methylisoborneol (MIB) and geosmin (GSM). Membrane fouling due to the algal metabolites was observed for both charged and neutral metabolites. MIB and GSM were removed effectively by low molecular weight cut-off (MWCO) membranes but less effectively by a higher MWCO membrane. Removal of MIB and GSM by the higher MWCO membrane was improved as the membrane fouled. Microcystin was initially removed to above 90% by tight NF membranes but fouling of several membranes caused decreased percent removals over time. Tight NF membranes afforded removals of 90–100% for cylindrospermopsin, while removal by the higher MWCO membrane was lower but improved with time due to fouling.
Conceptual analysis of the UASB/polishing pond system regarding the removal of surfactants, micropollutants and control of gaseous emissions
Authors: Chernicharo C. A. L. , Aquino S. F. , Sperling M. V. , Stuetz R. M. , Santos L. V. , Mabub M. O. A. , Moreira M. A. , Vasconcelos O. M. S. R. , Glória R. M.
Published: March 2010

A conceptual and integrated analysis of the UASB/Polishing Pond system is presented in relation to the removal of specific constituents not normally covered in the pond's literature, namely surfactants (linear alkylbenzene sulphonate, LAS), micropollutants (phthalates and bisphenol A) and sulfide. Experimental studies carried out on a small full-scale UASB/PP system have shown limited overall removal efficiencies for some constituents (53% to 70% for phthalates and 50% for LAS), but excellent removal levels for bisphenol A (around 99%) and sulfide (no trace concentrations were detected in the second and third ponds of the series). Further research is needed to investigate possible limitations and to identify means to improve the performance of the UASB/PP system.
Modelling of a Catalytic Micro-Reactor Coupling Endothermic Methane Reforming and Combustion
Authors: Vaccaro Salvatore , Malangone Luca , Ciambelli Paolo
Published: March 2010

In this study the mathematical modelling of a catalytic microstructured plate reactor for the production of hydrogen was performed in 2D and 3D geometry. The proposed reacting system uses the heat generated by an exothermic reaction (combustion) to sustain endothermic reforming reactions. Therefore, it pertains to those devices useful for producing the feed for fuel cell system for the remote generation of electrical power. However, because of the compactness of the reacting system it can also be considered in the context of apparatus aiming at process intensification. Within this frame the catalytic contribution of both exothermic and endothermic reactions was modelled considering the classic Langmuir-Hinshelwood surface kinetic theory. The advantage of using a real 3D geometry configuration consists in the possibility of considering the importance of the entering and boundary effects with particular attention to fluid stagnation and heat hot spots. The trade off of such a choice is certainly the huge increase of computing time and/or of the power of the computing facility. With respect to other works performed with similar reactor geometry and reacting systems this does not use simplifying assumptions such as catalyst layers modeled by one-dimensional approach, fully developed laminar flow or transverse heat and mass transfer taken into account through lumped heat and mass transfer coefficients. Results of simulations presented here concentrates on the comparisons between results of: countercurrent (CTC) and concurrent (CNC) flow patterns of the reactant streams; of simulations carried out with 2D and 3D models and of the influence of the thickness of the catalytic layers on the reactor performance. Simulations indicates that CNC flow pattern of reactants streams allows a better performance of the reactor since positive temperature differences between the catalyst layers and the gas in the channels maintain along the whole reactor and, consequently, there are not heat flux inversions, which occur under CTC flow pattern. Results also showed that as concerns an adiabatic reactor, whatever the operating conditions, 2D and 3D models yield substantially the same results. Finally, modelling demonstrated that for a realistic catalyst layer configuration thicknesses larger than 50 µm are useless for enhancing the reactor performance. The feasibility of the model proposed may show its potential in fast and easy implementation of several combustion and reforming fuels so to significantly enhance the performance prediction of real processes.