Gas-transfer membranes have been successfully deployed as efficient aeration devices in wastewater treatment. There is an increasing interest in using such membrane technology in industrial ...biotechnology. This study proposes membrane bioreactors as a novel bioreactor setup for polyhydroxybutyrate (PHB) production using Cupriavidus necator, whereby gas-transfer membranes are used for aeration. A proof-of-concept membrane bioreactor was built by combining a 50 ml centrifuge tube with hollow fiber membrane bundles. Different numbers and length of polydimethylsiloxane (PDMS) hollow fiber membranes were used to create membrane bundles with varying specific surface areas for oxygen transfer. In batch mode, a maximum biomass concentration of 10.3 g/L, which corresponds to a yield of 0.67 g biomass/g substrate, was achieved with 250 m2/m3 as the specific surface area of the membranes and 40 rpm as the liquid recirculation rate. Two different fed-batch modes were investigated to induce PHB production by applying nitrogen source limitation via fill-and-draw and two-step feeding strategies. A PHB level of 22% was obtained with fill-and-draw feeding by supplying 0.25 g/L NH4Cl after initial cultivation. Results indicate that membrane bioreactors are promising for C. necator cultivation, but further research is needed to enhance the PHB productivity.
•A novel gas-transfer membrane bioreactor was developed for microbial fermentation.•Various operating parameters were tested in batch for maximizing microbial growth.•Two different fed-batch operation modes were investigated for PHB production.•Membrane bioreactors has shown promising results to cultivate Cupriavidus necator.
•ANN outnumbered other standalone AI models (single models) applied to WWTPs.•Hybrid models were relatively more accurate than the standalone models.•Most of hybrid models were classified as ...CI-metaheuristic models.•FL was the most suitable model for the incomplete data sets.•Despite recent developments, industrial deployment is lacking.
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.
The membrane aerated biofilms reactor (MABR) is an emerging technology in wastewater treatment with particular advantages including high rate nitrification, and very high oxygen transfer ...efficiencies. In this study a synthetic feed water incorporating tetracycline (TC) was investigated in a MABR. Simultaneous removal of ammonium and tetracycline (TC) in the reactor, formation of TC transformation products (TPs), and microbial community analysis in the biofilm growing on the membrane were performed. A range of TC and ammonium loading rates and the effect of different intra-membrane oxygen pressures were on treatment performance were systematically investigated. Successful nitrification and TC degradation were achieved with the highest TC removal (63%) obtained at a HRT of 18 h HRT and 0.41 bar gas pressure. It has shown that different operating conditions (HRT and gas pressure) do not cause a significant change in ammonium removal. The concentration of TPs such as ETC, EATC, and ATC was determined to be at the ppb level. Molecular results showed that MABR reactor was mainly dominated by β-proteobacteria. The relative abundance of this group decreased in parallel with the increasing ammonium and TC loading.
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•Simultaneous nitrification and TC oxidation in the MABR were effectively achieved.•TC and ammonium flux increased with the increase of O2 pressure and loading rates.•The β-proteobacteria were the most dominant bacterial phylum in the MABR biofilm.•The transformation products of TC were determined as ETC, ATC and EATC.
•Membrane aerated biofilm reactor accomplished simultaneous nitrification and OTC oxidation.•Fluxes of both pollutants increased significantly with an increase in their loading rates and O2 ...pressure.•OTC in the removed fraction were completely mineralized to end-products by the aerobic biofilm.•Molecular diversity within the biofilm changed depending on the OTC concentration.
Pharmaceuticals in waterbodies are a growing concern due to their extensive uses and adverse effects on aquatic life. Oxytetracycline (OTC) is one of tetracycline antibiotic group used for treatment of animals and humans. This study evaluates the simultaneous oxidation of OTC and ammonium under autotrophic nitrifying conditions by using a membrane aerated biofilm reactor (MABR) as it provides an appropriate environment for the antibiotic-degrading bacteria. The results showed that MABR achieved fluxes of 1.62 mg OTC/m2.d and 1117 mg N/m2.d while the fluxes of O2 (JOTC-O2) utilized for OTC and NH4-N (JNH4-N-O2) oxidation were calculated to be 2.94 and 5105 mg O2/m2.d, respectively. Three transformation products, 4-Epi-OTC, α-Apo-OTC and β-Apo-OTC, were identified and measured at ppb levels. The biofilm community comprised of Bacteria environmental samples, b-proteobacteria, CFB group bacteria, g-proteobacteria, d-proteobacteria and a-proteobacteria.
•Demand response (DR) in energy systems and industrial process models is reviewed.•Integrated models with a detailed process and system representation are limited.•To date, none of the reviewed DR ...models explores the energy-water nexus.•Demand flexibility sources from wastewater treatment plants (WWTPs) are presented.•Lack of modelling tools causes underutilisation of demand flexibility by WWTPs.
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.
•Scheduling of reject water in a WRRF was investigated for demand response potential.•Control strategies indicate the potential to reduce peak power demand.•Under time-of-use price tariffs, ...electricity cost savings were achieved.•All scenarios maintained effluent quality at an acceptable standard.
The objective of this paper is to determine the importance of integrating peak demand mitigation and future energy pricing structures for process modelling of conventional water resource recovery facilities (WRRFs) when evaluating energy cost and control strategies. The well-established benchmark simulation model (BSM2) is used to monitor energy usage, and a detailed holistic study of different flow streams is performed in order to establish potential opportunities for flexible control of WRRF energy demand. Secondly, a detailed framework is introduced to optimize scheduling control strategies for the reject water stream while considering peak electricity demand avoidance as well as completing a comprehensive energy cost model based on current and anticipated future energy tariff structures. The reject water scheduling strategies, without other active controls (e.g. aeration), revealed 63.4% average peak demand mitigation and €10,755 cumulative annual energy cost savings on a 100k population equivalent WRRF without a deterioration in effluent quality. Analysis of different reject water scheduling control strategies shows that reject water scheduling can be an effective tool for energy cost optimisation under alternative electricity tariff structures. These strategies also deliver electricity peak demand mitigation.
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The use of gas permeable membranes for bubbleless aeration is of increasing interest due to the energy savings it affords in wastewater treatment applications. However, flow maldistributions are a ...major factor in the impedance of mass transfer efficiency. In this study, the effect of module configuration on the hydrodynamic conditions and gas transfer properties of various submerged hollow fibre bundles was investigated. Flow patterns and velocity profiles within fibre bundles were predicted numerically using computational fluid dynamics (CFD) and the model was validated by tracer-response experiments. In addition, the effect of fibre spacing and bundle size on the aeration rate of various modules was evaluated experimentally. Previous studies typically base performance evaluations on the liquid inlet velocity or an average velocity, an approach which neglects the effect of geometric features within modules. The use of validated CFD simulations provides more detailed information for performance assessment. It was shown that specific oxygen transfer rates declines significantly with increasing numbers of fibres in a bundle. However, the same trend was not observed when the fibre spacing is increased. A correlation was proposed for the prediction of the overall mass transfer coefficient utilizing the local velocity values obtained from the validated CFD model.
•Study of hydrodynamics of membrane modules with different configurations.•Detailed flow field analysis performed using CFD modelling and tracer-response method.•Successful simulation of tracer response curves for various bundles using CFD.•Development of a correlation for prediction of oxygen transfer rate.
Summary
It is now generally accepted that biofouling is inevitable in pressure‐driven membrane processes for water purification. A large number of published articles describe the development of novel ...membranes in an effort to address biofouling in such systems. It is reasonable to assume that such membranes, even those with antimicrobial properties, when applied in industrial‐scale systems will experience some degree of biofouling. In such a scenario, an understanding of the fate of planktonic cells, such as those entering with the feed water, has important implications with respect to contact killing particularly for membranes with antimicrobial properties. This study thus sought to investigate the fate of planktonic cells in a model nanofiltration biofouling system. Here, the interaction between auto‐fluorescent Pseudomonas putida planktonic cells and 7‐day‐old Pseudomonas fluorescens resident biofilms was studied under permeate flux conditions in a nanofiltration cross flow system. We demonstrate that biofilm cell recruitment during nanofiltration is affected by distinctive biofilm structural parameters such as biofilm depth.
The potential of the membrane aerated biofilm reactor (MABR) for high-rate bio-oxidation was investigated. A reaction-diffusion model was combined with a preliminary hollow-fiber MABR process model ...to investigate reaction rate-limiting regime and to perform comparative analysis on prospective designs and operational parameters. High oxidation fluxes can be attained in the MABR if the intra-membrane oxygen pressure is sufficiently high, however the volumetric oxidation rate is highly dependent on the membrane specific surface area and therefore the maximum performance, in volumetric terms, was achieved in MABRs with relatively thin fibers. The results show that unless the carbon substrate concentration is particularly high, there does not appear to be an advantage to be gained by designing MABRs on the basis of thick biofilms even if oxygen limitations can be overcome. Biotechnol. Bioeng. 2008;99: 1361-1373.
Demand response (DR) programmes encourage energy end users to adjust their consumption according to energy availability and price. Municipal wastewater treatment plants are suitable candidates for ...the application of such programmes. Demand shedding through aeration control, subject to maintaining the plant operational limits, could have a large impact on the plant DR potential. Decreasing the aeration intensity may promote the settling of the particulate components present in the reactor mixed liquor. The scope of this study is thus to develop a mathematical model to describe this phenomenon. For this purpose, Benchmark Simulation Model No.1 was extended by implementing a dual-layer settling model in one of the aerated tanks and combining it with biochemical reaction kinetic equations. The performance of this extended model was assessed in both steady-state and dynamic conditions, switching the aeration system off for 1 hour during each day of simulation. This model will have applications in the identification of potential benefits and issues related to DR events, as well as in the simulation of the plant operation where aerated tank settling is implemented.
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