Unraveling the role of feed temperature and cross-flow velocity on organic fouling in membrane distillation using response surface methodology

Understanding the role of operating condition on fouling development in membrane distillation (MD) is critical for the further optimization of MD technology. In this study, organic fouling development in MD was investigated varying the feed inlet temperature from 35 to 65 degrees C and the cross-flow velocity from 0.21 to 0.42 m/s. The fouling layer thickness was estimated at the end of each experiment non-invasively with optical coherence tomography. The set of experiments was mined to model the initial flux decline, the near-stable flux, and the final foulant thickness responses by central composite design, a useful response surface methodology (RSM) tool. The results indicated a linear increment of the fouling thickness by increasing the feed inlet temperatures. Overall, the feed inlet temperature governed both the initial flux decline and the fouling deposition. The benefits in water productivity obtained by increasing the feed temperature were always offset by higher fouling deposition. Higher cross-flow velocities showed a positive effect on the initial flux, which however translated in larger values of the initial flux decline rate. On the other hand, the higher shear stress contributed to a decrease of the final steadystate fouling layer thickness. The proposed approach was proven to be a valuable tool to assess the role of the operating conditions on fouling and process performance in MD

Spatially resolved generation profiles for building, land and water-bound PV: a case study of four Dutch energy transition scenarios

Alongside a transition from steerable and centralized traditional electricity generation to intermittent and more decentralized renewable electricity generation from solar panels and wind turbines, Dutch energy transition scenarios project a widespread deployment of heat pumps and electric vehicles towards 2050. While clearly contributing to the decarbonization of the Dutch energy system, these developments impose challenges regarding electricity supply-demand mismatch and grid congestion. Spatially resolved electricity demand and supply profiles are required to gain a better insight into where and when such problems are likely to occur within the different scenarios. The present paper focuses on Dutch solar energy supply and features the construction of geodatabases of scenario-specific, spatially resolved electricity generation profiles for building, land and water-bound PV. Country-level PV capacities are geographically distributed based on spatial variance in roof PV potential and availability of suitable land and water use areas. Corresponding electricity generation profiles are constructed using historical meteorological measurements, a diffuse fraction model and a anisotropic transposition model. Empirically found performance ratio profiles are applied to account for a multitude of performance loss factors, including shading, dust and inverter efficiency. In 2050, building-bound capacity is projected to show only limited overlap with both land-bound and water-bound PV capacity. On the other hand, regions with considerable water-bound PV capacity also tend to show considerable land-bound PV capacity. Compared to the present-day situation, yearly country-level PV electricity generation is projected to be a factor 18.5, 15.7, or 7.7 higher in 2050 when respectively following the Regional, National or International Steering scenarios.</p

Does self-evaluation of CAP quality lead to improvements in assessment and curriculum

Technological developments and computerisation influence many jobs. The goal of this study is to identify to what extent employees need an increased and/or different understanding of science and technology to function in their jobs than is currently taught in schools. Whereas previous research tended to focus on very general skills (e.g., problem solving, communication) or long detailed lists of content knowledge, the focus of this study is on competences such as modelling and visualising. Companies most influenced by technological developments were selected in cooperation with National Centres of Expertise on vocational education. They were asked in which companies (1) more and/or different scientific and technological competences, and (2) creativity and flexibility are required. We focused on jobs at the level of senior secondary vocational education, as these jobs are most prone to being outsourced or taken over by computers. Employees working in the different companies were asked what knowledge and skills they use during their work, for example when working with machines and computers. Preliminary results show the influence of technological developments on almost all jobs. Required knowledge and skills are for example: data-analysis, the use of graphs and thinking beyond one's own job. The need for flexibility, creativity and insight in ‘black boxes' seems to depend on the level of education. Theory and aimsThe increased use of information- and communication technology and the influence of scientific and technological developments have caused many countries to redefine the key competences for adequately functioning professionals. This study specifically focuses on the needs of future employees: what competences in the domains of science and technology do they need to function adequately in their jobs, now and the future?Previous studies tend to focus on very general skills such as problem solving and communication (e.g., Holbrook &amp; Rannikmae, 2007), which do not provide any specification of what should be taught. Other studies provide long and detailed lists of content to be taught in schools (e.g., AAAS, 1993). These lists run the risk of quickly becoming outdated as the amount of technical information is doubling every two years (Binkley et al., 2010). This begs the question whether we can identify competences that are general in the sense that we may expect them to stay valuable for a long time, but at the same time not too general to offer directions for curricula. This study tries to answer this question by interviewing employees in companies that are subject to technological developments. In the literature, two domains provide input to this study. First, a number of studies focus on 21st century-skills, lifelong learning competences, or key skills. For example, Binkley et al. (2010) analysed curriculum and assessment frameworks around the world, and identified ten competences, including creativity, critical thinking and ICT literacy. Voogt and Pareja-Roblin (2010) and Dede (2009) reviewed different reports about 21st century skills, generally relying on private/business initiatives. These reports mention skills such as communication, ICT literacy, social awareness, and creativity. Problematic is, however, that explicit links to educational levels are missing and the educational community hardly participates in this debate. These reports thus provide little direction with regard to the content of education. Second, we reviewed the literature about knowledge and skills used in the workplace. Here, hardly any studies exist on the use of science and technology at the workplace. There are, however, studies on mathematics that are general enough to be useful for science and technology as well (e.g., Bakker et al., 2006; Pozzi et al., 1998). These studies show the importance of: (1) knowing what processes are ‘hidden' in computers or machines, and (2) analysing relationships between variables, based on quantitative data. Data and MethodsParticipantsThe context of this study was vocational education in the Netherlands, preparing students for a job at levels ranging from assistant worker to middle management. This middle-level job was chosen, as it is likely to be most affected by technological changes, while employees are not specifically educated in this domain (Levi &amp; Murnane, 2005). To identify companies most influenced by technological developments, interviews were conducted with National Centres of Expertise, who develop national qualification profiles for the different branches. Six interviews were conducted with representatives from: animal and plant care, car mechanics, audician/optician, graphical design, commercials/presentation, and nursing/care. Seven interviews were conducted with employees of these branches: a farmer using robots, employees of Ford cards, a company developing logistical systems, an ICT desk, an outsourcing company, and an audician. In November/December 2010, more interviews will be conducted in different branches, and nursing specifically. InterviewsRepresentatives of the branches were asked to describe developments with regard to: (1) the amount of science and technology, (2) the content of science and technology, and (3) flexibility and creativity needed to function on the job. Depending on their function, the employees were asked:- what kind of machines and computer programs they work with;- if they need to know the ‘invisible processes' inside;- how they are trained to work with new machines and computers;- what they do in case of an unexpected outcome or problem.All participants were asked to describe job situations in which scientific and technological knowledge and skills are used. Preliminary resultsFull results, including the remaining interviews and more examples from concrete job situations, are presented at the conference.- Required knowledge and skills: most employees need some basic knowledge of science and technology. For example, audicians need knowledge of the auditory organs.- Flexibility and creativity: at lower levels, employees are not expected to suggest improvements or solve non-standard problems. An exception is ‘defence/tank' mechanics. They need to know the exact working of tank engines, enabling creativity in emergencies.- Insight in black boxes: opinions seem to differ here. In general, employees can work with machines without knowing ‘what is going on inside'. For example, graphical designer can use software to make sketches without knowing how colours mix. Theoretical and educational significance. Most jobs seem to be influenced by computerisation and technology, leading to changed requirements in terms of knowledge and skills, creativity and insight in black boxes. The identification of these changed requirements could guide curriculum adaptations, better preparing young people for their future jobs. More research seems warranted on the use of science and technology at the workplace (following studies on mathematics). This study is a first step in this direction

Silt density index and modified fouling index relation, and effect of pressure, temperature and membrane resistance

Particulate matter present in feed water of reverse osmosis and nanofiltration membrane elements tends to deposit on the membrane surface and spacers. This type of fouling results in permeate flux decline, loss of product quality and membrane damage. To characterize the fouling potential of RO feed water the Silt Density Index (SDI) and the Modified Fouling Index (MFI0.45) are commonly applied. SDI is applied worldwide for many years on a routine basis by operators since it is a simple and cheap test. Unfortunately, the SDI has several deficiencies e.g. it is not based on any filtration mechanism, has no linear relation with particulate matter and is not corrected for temperature, pressure and membrane resistance. This might explain the frequently reported erratic results obtained in practice, e.g. water treated with ultrafiltration showed in several cases high SDI values, which could not be attributed to failures of the UF membrane elements or systems. To overcome these deficiencies the MFI0.45 has been developed. This test is based on the occurrence of cake filtration during a substantial part of the test, has a linear relation with particulate matter content, and is corrected for pressure and temperature. However the manual procedure of measuring an MFI0.45 is somewhat more complicated and for this reason less suitable for application on a routine basis in practice. Fully automated equipment, measuring SDI and MFI0.45 at the same time is on the market. In this study a mathematical relation between SDI and MFI0.45 has been successfully developed, assuming that cake filtration is the dominant filtration mechanism during the tests. Based on the developed mathematical relation and experiments with an artificial colloidal suspension of aluminum oxide spheres (0.6 μm) as model water, it could be demonstrated that the SDI depends on pressure, temperature and membrane resistance. The effect of temperature and membrane resistance explains to a large extent the erratic results from the field. It is recommended to correcting SDI for temperature and membrane resistance and/or to making the guideline formulated by ASTM for the allowable range of membrane resistances much more stringent