Now showing 1 - 10 of 51
  • Publication
    The Triple Bottom Line for Efficiency: Integrating Systems Within Water and Energy Networks
    Energy and water have been integrated throughout most of modern history, and that linkage will continue into the future, not only in the physical infrastructure but also through digital infrastructure (e.g., the Internet of Things). The term energy-water nexus is quickly expanding to refer to more than simply water used for energy production and energy used for water treatment and transport. Just as the energy grid is changing-becoming more flexible and resilient and providing energy-efficiency gains-the water network is also changing. The integration of these two systems can provide optimization and opportunities that would not otherwise be possible. This integration of "electrons and molecules" is being enabled by advances in Internet connectivity and wireless communications, so that energy in all its forms can be employed most effectively by end users to optimize efficiency, reliability, security, economics, and environmental performance.
      28Scopus© Citations 11
  • Publication
    A physical impact of organic fouling layers on bacterial adhesion during nanofiltration
    Organic conditioning films have been shown to alter properties of surfaces, such as hydrophobicity and surface free energy. Furthermore, initial bacterial adhesion has been shown to depend on the conditioning film surface properties as opposed to the properties of the virgin surface. For the particular case of nanofiltration membranes under permeate flux conditions, however, the conditioning film thickens to form a thin fouling layer. This study hence sought to determine if a thin fouling layer deposited on a nanofiltration membrane under permeate flux conditions governed bacterial adhesion in the same manner as a conditioning film on a surface. Thin fouling layers (less than 50 μm thick) of humic acid or alginic acid were formed on Dow Filmtec NF90 membranes and analysed using Atomic Force Microscopy (AFM), confocal microscopy and surface energy techniques. Fluorescent microscopy was then used to quantify adhesion of Pseudomonas fluorescens bacterial cells onto virgin or fouled membranes under filtration conditions.It was found that instead of adhering on or into the organic fouling layer, the bacterial cells penetrated the thin fouling layer and adhered directly to the membrane surface underneath. Contrary to what surface energy measurements of the fouling layer would indicate, bacteria adhered to a greater extent onto clean membranes (24 ± 3% surface coverage) than onto those fouled with humic acid (9.8 ± 4%) or alginic acid (7.5 ± 4%). These results were confirmed by AFM measurements which indicated that a considerable amount of energy (10−7 J/μm) was dissipated when attempting to penetrate the fouling layers compared to adhering onto clean NF90 membranes (10−15 J/μm). The added resistance of this fouling layer was thusly seen to reduce the number of bacterial cells which could reach the membrane surface under permeate conditions. This research has highlighted an important difference between fouling layers for the particular case of nanofiltration membranes under permeate flux conditions and surface conditioning films which should be considered when conducting adhesion experiments under filtration conditions. It has also shown AFM to be an integral tool for such experiments.
    Scopus© Citations 22  431
  • Publication
    Modelling demand response with process models and energy systems models: Potential applications for wastewater treatment within the energy-water nexus
    A promising tool to achieve more flexibility within power systems is demand response (DR). End users in many strands of industry have been subject to research regarding the opportunities for implementing DR programmes. We review recent DR modelling approaches in the realm of energy systems models and industrial process models. We find that existing models over- or underestimate the available DR potential from an industrial end user for two main reasons. First, the interaction between power system operation and industrial process operation caused by DR is not taken into account. Second, models abstract from critical physical process constraints affecting the DR potential. To illustrate this, we discuss the wastewater treatment process as one industrial end user within the energy-water nexus, for which the lack of suitable modelling tools is affecting the accurate assessment of the DR potential. Case studies indicate the potential for wastewater treatment plants to provide DR, but no study acknowledges the endogeneity of energy prices which arises from a large-scale utilisation of DR. Therefore, we propose an integrated modelling approach, combining energy system optimisation with the level of operational detail in process simulation models. This will yield a higher level of accuracy regarding the assessment of DR potential from a specific process, such as wastewater treatment.
      26Scopus© Citations 47
  • Publication
    The role of cell-surface interactions in bacterial initial adhesion and consequent biofilm formation on nanofiltration/reverse osmosis membranes
    Until recently, the realization that membrane biofouling during nanofiltration (NF) and reverse osmosis (RO) processes is an unavoidable occurrence, has led to a paradigm shift in which biofouling management approaches rather than biofouling prevention are now being considered. To implement this new concept, it is crucial to understand the fundamentals of cell-surface interactions during bacterial adhesion, a prerequisite to biofouling of membranes. As such, with membrane biofouling already being widely studied and documented, greater attention should be given to the factors involved in the initial bioadhesion onto membranes during NF/RO processes. This review focuses on the interactions between bacterial cells and NF/RO membranes, emphasizing the mechanisms of bacterial adhesion to NF/RO membranes with particular reference to the effects of micro-environmental conditions experienced at the membrane interface, such as feed-water composition, hydrodynamics, permeate flux and conditioning layers. This review also discusses membrane surface properties and how it relates to bacterial adhesion as well as latest advancements in antibacterial membranes, identifying areas that need further investigation.
    Scopus© Citations 214  1371
  • Publication
    Data to Intelligence: The Role of Data-Driven Models in Wastewater Treatment
    Increasing energy efficiency in wastewater treatment plants (WWTPs) is becoming more important. An emerging approach to addressing this issue is to exploit development in data science and modelling. Deployment of sensors to measure various parameters in WWTPs opens greater opportunities for exploiting the wealth of data. Artificial intelligence (AI) is emerging as a solution for automation and digitalization in the wastewater sector. This review aims to comprehensively investigate, summarize and analyze recent developments in AI methods applied to the modelling of WWTPs. The review shows that among the standalone models, Artificial Neural Networks (ANN) was the most popular model followed by, in descending order: Decision Trees (DT), Fuzzy Logic (FL), Genetic algorithm (GA) and Support Vector Machine (SVM). In the case of incomplete data, FL was the most frequently used method as it uses linguistic expert rules to find an approximation for the missing data. Regarding accuracy and precision, hybrid models demonstrated relatively better performance than the standalone ones. Among these models, the Machine Learning (ML)-metaheuristic, which integrates an AI model with a bioinspired optimization method, was the most preferred type as it was used in more than 45% of the hybrid models. Correlation coefficient (R), Correlation of Determination (R2) and Root Mean Square Error (RMSE) were the frequently used metrics for model performance evaluation. Finally, the review shows that despite recent developments, industrial deployment is still lacking. The industrial application requires close interaction of interested parties, among which research institutes, private sector and public sector play an inevitable role. The future research should focus on mitigating the barriers for more in-depth collaboration of interested parties and finding new paths for more cooperative and harmonized activity of them.
    Scopus© Citations 18  98
  • Publication
    Tracer measurements reveal experimental evidence of biofilm consolidation
    (Wiley, 2007-11-01)
    The ability to simultaneously measure both biofilm thickness and the mass transfer coefficient of an inert tracer through it provides a powerful method to study biofilm development. In this communication previously published data has been collated to interpret global trends in biofilm structure during the transition towards steady-state. It appears that sudden changes in biofilm structure (directly related to the rate of change of biofilm mass transfer resistance) may occur following transitions in rate of biomass production. These observations are consistent with the concept of consolidation, recently introduced into spatially structured biofilm mathematical models to account for structural realignment of the biofilm under dynamic conditions.
      391Scopus© Citations 16
  • Publication
    Investigation of energy and operation flexibility of membrane bioreactors by using benchmark simulation model
    The aims of this study is to investigate operation and energy flexibility of membrane bioreactors for municipal wastewater treatment by mathematical modelling. Compared to conventional active sludge technology, membrane bioreactor has better treatment performance and it can achieve complete retention of solids and very high COD removal. Based on variable electricity price structure, appropriate optimization strategy can save 16% energy cost without violating exiting discharge standards.. The results showed that MBRs have a significant potential to create considerable commercial value by providing energetic flexibility.
      148
  • Publication
    The significance of calcium ions on Pseudomonas fluorescens biofilms – a structural and mechanical study
    The purpose of this study was to investigate the effects of calcium ions on the structural and mechanical properties of Pseudomonas fluorescens biofilms grown for 48 h. Advanced investigative techniques such as confocal laser scanning microscopy and atomic force spectroscopy were employed to characterize biofilm structure as well as biofilm mechanical properties following growth at different calcium concentrations. The presence of calcium during biofilm development led to higher surface coverage with distinct structural phenotypes in the form of a granular and heterogeneous surface, compared with the smoother and homogeneous biofilm surface in the absence of calcium. The presence of calcium also increased the adhesive nature of the biofilm, while reducing its elastic properties. These results suggest that calcium ions could have a functional role in biofilm development and have practical implications, for example, in analysis of biofouling in membrane-based water-treatment processes such as nanofiltration or reverse osmosis where elevated calcium concentrations may occur at the solid–liquid interface.
    Scopus© Citations 34  488
  • Publication
    Performance analysis of a pilot-scale membrane aerated biofilm reactor for the treatment of landfill leachate
    A 60 L membrane aerated biofilm reactor (MABR) was successfully employed to treat landfill leachate, which contained very high concentrations of refractory chemical oxygen demand (COD) and ammonium. Air or pure oxygen was supplied to the bioreactor through polydimethyl siloxane hollow fibre membranes. Over a year of operation with an average hydraulic retention time of about 5 days, and influent ammonium concentrations ranging from 500 to 2500 mg/L, the MABR achieved 80–99% nitrification. Simultaneously, the influent COD concentrations which ranged from 1000 to 3000 mg/L were reduced by approximately 200–500 mg/L. Oxygen transfer rates as high as 35 g O2/m2-day were achieved during the study. By operating at low gas flowrates, high oxygen transfer efficiencies were achieved without any negative impact on oxygen transfer rates. This suggested that the biofilm was not oxygen limited during this study. The very low gas flowrates and the low pressure losses required to move air through the membranes resulted in very high standard aeration efficiencies that exceeded 10 kg O2/kW h. The results indicate that mixing energy far exceeded that required for aeration in this study. Our results suggest that with process optimisation, MABR technology offers a low energy option for effective leachate treatment.
    Scopus© Citations 81  1158
  • Publication
    Oxygen-mediated regulation of biofilm development is controlled by the alternative sigma factor sigma(B) in Staphylococcus epidermidis
    Using a modified rotating-disk reactor to sparge oxygen to Staphylococcus epidermidis cultures, we found that oxygen negatively regulates biofilm development by influencing the activity of {sigma}B. Under anaerobic conditions, increased {sigma}B activity activates icaADBC, which encodes enzymes responsible for polysaccharide intercellular adhesin synthesis, by repressing transcription of the negative regulator icaR.
    Scopus© Citations 33  432