Abushaban, Almotasembellah; Salinas-Rodriguez, Sergio G.; Mangal, Muhammad Nasir; Mondal, Subhanjan; Goueli, Said A.; Knezev, Aleksandra; Vrouwenvelder, Johannes S.; Schippers, Jan C.; Kennedy, Maria D.(Desalination, Elsevier BV, 2018-12-06)[Article]
A direct method for measuring adenosine-triphosphate (ATP) in seawater was developed recently, in which commercial reagents are added directly to seawater. However, calibration is required if seawater quality changes (such as changes in salinity, pH, Mg, Fe) as the seawater matrix interferes with ATP measurement. In this research, a 0.1 μm filtration process is introduced to eliminate such interferences. In addition, a filter rinsing step with sterilized artificial seawater is proposed to eliminate interference of free ATP. The ATP-filtration method is fast (<5 min), reproducible (VC = 7%), six times more sensitive than the direct ATP-method and correlates (R = 0.72, n = 100) with intact cell concentration. Microbial ATP concentration measured using the ATP-filtration method and the ATP-direct method were comparable. Microbial ATP measured along the treatment train of a full-scale seawater reverse osmosis (SWRO) plant decreased from 530 in the raw seawater to 10 ng-ATP/L after pre-treatment and to 0.5 ng-ATP/L in the SWRO permeate. The method was also applied to monitor bacterial growth potential (BGP) across the pre-treatment train of a (pilot) seawater desalination plant, where the removal of BGP through the media filtration and ultrafiltration was 44% and 7%, respectively.
Sanawar, Huma; Pinel, I.; Farhat, Nadia; Bucs, Szilard; Zlopasa, J.; Kruithof, J.C.; Witkamp, Geert Jan; van Loosdrecht, Mark C.M.; Vrouwenvelder, Johannes S.(Water Research X, Elsevier BV, 2018-10-15)[Article]
Chemical cleaning is routinely performed in reverse osmosis (RO) plants for the regeneration of RO membranes that suffer from biofouling problems. The potential of urea as a chaotropic agent to enhance the solubilization of biofilm proteins has been reported briefly in the literature. In this paper the efficiency of urea cleaning for RO membrane systems has been compared to conventionally applied acid/alkali treatment. Preliminary assessment confirmed that urea did not damage the RO polyamide membranes and that the membrane cleaning efficiency increased with increasing concentrations of urea and temperature. Accelerated biofilm formation was carried out in membrane fouling simulators which were subsequently cleaned with (i) 0.01M sodium hydroxide (NaOH) and 0.1M hydrochloric acid (HCl) (typically applied in industry), (ii) urea (CO(NH2)2) and hydrochloric acid, or (iii) urea only (1340 g/Lwater). The pressure drop over the flow channel was used to evaluate the efficiency of the applied chemical cleanings. Biomass removal was evaluated by measuring chemical oxygen demand (COD), adenosine triphosphate (ATP), protein, and carbohydrate content from the membrane and spacer surfaces after cleaning. In addition to protein and carbohydrate quantification of the extracellular polymeric substances (EPS), fluorescence excitation−emission matrix (FEEM) spectroscopy was used to distinguish the difference in organic matter of the remaining biomass to assess biofilm solubilization efficacy of the different cleaning agents. Results indicated that two-stage CO(NH2)2/HCl cleaning was as effective as cleaning with NaOH/HCl in terms of restoring the feed channel pressure drop (>70% pressure drop decrease). One-stage cleaning with urea only was not as effective indicating the importance of the second-stage low pH acid cleaning in weakening the biofilm matrix. All three chemical cleaning protocols were equally effective in reducing the concentration of predominant EPS components protein and carbohydrate (>50% reduction in concentrations). However, urea-based cleaning strategies were more effective in solubilizing protein-like matter and tyrosine-containing proteins. Furthermore, ATP measurements showed that biomass inactivation was up to two-fold greater after treatment with urea-based chemical cleanings compared to the conventional acid/alkali treatment. The applicability of urea as an alternative, economical, eco-friendly and effective chemical cleaning agent for the control of biological fouling was successfully demonstrated.
Khan, Babar Khalid; Fortunato, Luca; Leiknes, TorOve(Enzyme and Microbial Technology, Elsevier BV, 2018-10-05)[Article]
Membrane-based filtration technologies have seen rapid inclusion in a variety of industrial processes, especially production of drinking water by desalination. Biological fouling of membranes is a challenge that leads to increased costs from efficiency reductions, membrane damage and ultimately, membrane replacement over time. Such costs can be mitigated by monitoring and optimizing cleaning processes for better prognosis. Monitoring bacterial accumulation in situ can therefore advance understanding of cleaning efficiency. A fluorescence-based sensor for early biofouling detection capable of measuring extracellular enzyme activity was developed and tested in a lab-scale seawater reverse osmosis (SWRO) biofouling model for use in monitoring bacterial accumulation proximal to the surface of a membrane. We tracked bacterial biomass accumulation rapidly and non-invasively using exogenously applied fluorogen-substrates and corroborated with optical coherence tomography imaging of the membrane surface in real-time. The selected fluorogen and fluorogen-substrate were characterized and down selected by high throughput screening in vitro for compatibility in seawater and profiled over relevant Red Sea desalination parameters (pH and temperature). This approach demonstrates the practicality of prototyping an early-detection biofouling sensor in membrane based processes, such as seawater desalination, using extracellular enzyme activity as a measure of bacterial abundance.
Membrane distillation (MD) process technology is swiftly moving to industrial prototyping where efficient scale-up calculations are crucial to shorten product development cycle. The aim of this numerical investigation is to suggest the best modeling strategy that will enable to innovate; modify or check new direct contact MD (DCMD) module designs or operation in a timely manner. Two main modeling strategies are presented, namely convective and conjugate approaches. For a given flat module, it is shown that replacing the permeate side by a modified convection boundary condition that accounts for every known resistance to heat transfer gives similar results in the feed side as a coupled conjugate approach where the membrane, with a modified thermal conductivity, is part of the computational domain. The two methods are compared for different module lengths in terms of permeate flux and temperature distribution. Simulation time reports show the important gain in CPU time when using the convective approach while retaining desired calculation accuracy during scale-up. Furthermore, investigations were carried out to assess the effect of 3D inlet and outlet effects. Results for a laboratory scale module suggest that the convective approach can be safely used during early design stages and scale-up of single modules in the range of high permeate fluxes, while the conjugate approach has to be used for an accurate prediction of permeate temperatures needed in heat recovery strategy and equipment design.
Summary The energy efficiency in solar steam generation by 2D photothermal materials has approached its limit. In this work, we fabricated 3D cylindrical cup-shaped structures of mixed metal oxide as solar evaporator, and the 3D structure led to a high energy efficiency close to 100% under one-sun illumination due to the capability of the cup wall to recover the diffuse reflectance and thermal radiation heat loss from the 2D cup bottom. Additional heat was gained from the ambient air when the 3D structure was exposed under one-sun illumination, leading to an extremely high steam generation rate of 2.04 kg m−2 h−1. The 3D structure has a high thermal stability and shows great promise in practical applications including domestic wastewater volume reduction and seawater desalination. The results of this work inspire further research efforts to use 3D photothermal structures to break through the energy efficiency limit of 2D photothermal materials.
Ahmed, Elaf; Kalathil, Shafeer; Shi, Le; Alharbi, Ohoud; Li, Renyuan; Zaouri, Noor A.; Wang, Peng(Journal of Saudi Chemical Society, Elsevier BV, 2018-02-21)[Article]
Ultra-small nanoparticles (USNPs) of noble metals have a great potential in a variety of applications due to their high surface areas and high reactivity. This works employed electrochemically active biofilms (EABs) composed of a single bacterium strain of Shewanella loihica PV-4 and successfully synthesized USNPs of noble metal Au, Pd, and Pt. The synthesized USNPs had a size range between 2 and 7 nm and exhibited excellent catalytic performance in dye decomposition. The results of this work shine lights on the use of EABs in nanoparticle synthesis.
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