Pascal Saikaly

Membrane surface hydrophilic modification has always been considered to mitigating biofouling in membrane bioreactors (MBRs). Four hollow-fiber ultrafiltration membranes (pore sizes ∼0.1 μm) differing only in hydrophobic or hydrophilic surface characteristics were operated at a permeate flux of 10 L/m(2) h in the same lab-scale MBR fed with synthetic wastewater. In addition, identical membrane modules without permeate production (0 L/m(2) h) were operated in the same lab-scale MBR. Membrane modules were autopsied after 1, 10, 20 and 30 days of MBR operation, and total extracellular polymeric substances (EPS) accumulated on the membranes were extracted and characterized in detail using several analytical tools, including conventional colorimetric tests (Lowry and Dubois), liquid chromatography with organic carbon detection (LC-OCD), fluorescence excitation - emission matrices (FEEM), fourier transform infrared (FTIR) and confocal laser scanning microscope (CLSM). The transmembrane pressure (TMP) quickly stabilized with higher values for the hydrophobic membranes than hydrophilic ones. The sulfonated polysulfone (SPSU) membrane had the highest negatively charged membrane surface, accumulated the least amount of foulants and displayed the lowest TMP. The same type of organic foulants developed with time on the four membranes and the composition of biopolymers shifted from protein dominance at early stages of filtration (day 1) towards polysaccharides dominance during later stages of MBR filtration. Nonmetric multidimensional scaling of LC-OCD data showed that biofilm samples clustered according to the sampling event (time) regardless of the membrane surface chemistry (hydrophobic or hydrophilic) or operating mode (with or without permeate flux). These results suggest that EPS composition may not be the dominant parameter for evaluating membrane performance and possibly other parameters such as biofilm thickness, porosity, compactness and structure should be considered in future studies for evaluating the development and impact of biofouling on membrane performance.

Electrically conductive, graphene-coated, hollow-fiber porous membranes were used as cathodes in anaerobic electrochemical membrane bioreactors (AnEMBRs) operated at different applied voltages (0.7 and 0.9 V) using a new rectangular reactor configuration compared to a previous tubular design (0.7 V). The onset of biofouling was delayed and minimized in rectangular reactors operated at 0.9 V compared to those at 0.7 V due to higher rates of hydrogen production. Maximum transmembrane pressures for the rectangular reactor were only 0.10 bar (0.7 V) or 0.05 bar (0.9 V) after 56 days of operation compared to 0.46 bar (0.7 V) for the tubular reactor after 52 days. The thickness of the membrane biofouling layer was approximately 0.4 μm for rectangular reactors and 4 μm for the tubular reactor. Higher permeate quality (TSS = 0.05 mg/L) was achieved in the rectangular AnEMBR than that in the tubular AnEMBR (TSS = 17 mg/L), likely due to higher current densities that minimized the accumulatio...

Membrane biofouling is a complex process that involves bacterial adhesion, extracellular polymeric substances (EPS) excretion and utilization, and species interactions. To obtain a better understanding of the microbial ecology of biofouling process, this study conducted rigorous, time-course analyses on the structure, EPS and microbial composition of the fouling layer developed on ultrafiltration membranes in a nitrification bioreactor. During a 14-day fouling event, three phases were determined according to the flux decline and microbial succession patterns. In Phase I (0-2 days), small sludge flocs in the bulk liquid were selectively attached on membrane surfaces, leading to the formation of similar EPS and microbial community composition as the early biofilms. Dominant populations in small flocs, e.g., Nitrosomonas, Nitrobacter, and Acinetobacter spp., were also the major initial colonizers on membranes. In Phase II (2-4 d), fouling layer structure, EPS composition, and bacterial...

ABSTRACT A novel model for activated sludge sewage treatment was developed to predict exploitative competition of six heterotrophic bacterial species competing for three complementary growth limiting substrates using the non-interactive Monod equation. The central hypothesis of the model is that in a multi-species/substrate system the number of coexisting bacterial species, N, exceeds the number of limiting resources, K, available for them. The explanation for this is that for certain species combinations, the dynamics of the competition process generate non-equilibrium conditions and oscillations, and these oscillations in bacterial community structure allow the coexistence of greater number of species than the number of limiting substrates (N>K). This result is a direct contradiction of an existing activated sludge competition theory, “the principle of competitive exclusion,” which states that the competition process results in equilibrium conditions, which allow only N≤K species to coexist. The model was used to investigate the effect of varying solids retention times (SRT) and hydraulic retention time (HRT) values on the species diversity using the conventional, completely mixed activated sludge configuration. The results of model simulations showed that for a certain range of solids retention times (SRT = 2.6-5.6 days) the competition of six microbial species for three growth limiting substrates produces oscillations within the structure of the bacterial community allowing for the sustained growth of the six species on the three substrates. Also, the model simulations showed that low SRT values (2.3-2.5 days) act as a strong selective pressure reducing the diversity of the bacterial species through the mechanism of washout. At high SRT values (5.7-30 days), the competitive exclusion principle dominates and the diversity of the microbial community is reduced such that N ≤ K. The results of this model are of general importance for the design and operation of activated sludge systems demonstrating robust performance due to the presence of a diverse community of microorganisms. By developing a model to predict the diversity of the microbial community based upon operating conditions, we are providing a first step in the development of a system of rules-based design that maximizes the diversity of the microbial community in activated sludge systems.

ABSTRACT A comprehensive and simplified floc model describing resource competition was developed to evaluate the impact of bioreactors operating parameters and key characteristic of flocs on bacterial species dynamics and oscillation patterns. It described competition among six aerobic heterotrophs for three complementary growth–limiting nutrients in activated sludge flocs, and incorporates the effects of diffusion limitations and floc propagation. This model was an extension of a previously reported biofilm model. Simulation results showed that at certain values of solid retention time (SRT), competition of species favored sustained oscillations in the abundances of species for fully penetrated flocs. Comparison of the dispersed-growth process, the biofilm, and the suspended flocs showed that the oscillation growth pattern of species was not only a function of competition, but also depended on key physical characteristics of the ecosystem. The significance of the current study was that it was the first to examine the relationship between operating parameters, characteristic of flocs, and bacterial species dynamics in activated sludge system, and advanced the understanding of realistic biological treatment process.

ABSTRACT The objective of this study was to test the hypothesis that the selection of the solids retention time (SRT) for a suspended growth activated sludge wastewater treatment systems influences the level of biodiversity of the bacterial community. This hypothesis was tested using an ecologybased mechanistic model, laboratory-scale activated sludge bioreactors, and molecular biology tools. Simulation results demonstrated that bioreactors operated with an SRT of 2 days supported a more diverse bacterial community as compared to bioreactors operated with an SRT of 8 days. Six laboratory-scale bioreactors were operated in parallel at an SRT of 2 days or an SRT of 8 days, and samples of mixed liquor were removed to determine the level of biodiversity of the bacterial community using terminal-restriction fragment length polymorphism (T-RFLP) targeting 16S ribosomal RNA genes. Results from T-RFLP analyses confirmed simulation results suggesting that bioreactors operated at an SRT of 2 days have an increase in the number of different types of bacteria. This result is significant because ecology theory suggests that ecosystems with a greater number of different types of organisms have an increased capability to successfully withstand perturbation. Thus, we conclude that future work should test the hypothesis that operating conditions of bioreactors influence the level of biodiversity of the bacterial community resulting in systems with an enhanced capability to withstand toxic shock loads.

The combination of flow cytometry (FCM) and 16S rRNA gene pyrosequencing data was investigated for the purpose of monitoring and characterizing microbial changes in drinking water distribution systems. High frequency sampling (5 min intervals for 1 h) was performed at the outlet of a treatment plant and at one location in the full-scale distribution network. In total, 52 bulk water samples were analysed with FCM, pyrosequencing and conventional methods (adenosine-triphosphate, ATP; heterotrophic plate count, HPC). FCM and pyrosequencing results individually showed that changes in the microbial community occurred in the water distribution system, which was not detected with conventional monitoring. FCM data showed an increase in the total bacterial cell concentrations (from 345 ± 15 × 10(3) to 425 ± 35 × 10(3) cells mL(-1)) and in the percentage of intact bacterial cells (from 39 ± 3.5% to 53 ± 4.4%) during water distribution. This shift was also observed in the FCM fluorescence fing...

The development of rapid detection assays of cell viability is essential for monitoring the microbiological quality of water systems. Coupling propidium monoazide with quantitative PCR (PMA-qPCR) has been successfully applied in different studies for the detection and quantification of viable cells in small-volume samples (0.25-1.00 mL), but it has not been evaluated sufficiently in marine environments or in large-volume samples. In this study, we successfully integrated blue light-emitting diodes for photoactivating PMA and membrane filtration into the PMA-qPCR assay for the rapid detection and quantification of viable Enterococcus faecalis cells in 10-mL samples of marine waters. The assay was optimized in phosphate-buffered saline and seawater, reducing the qPCR signal of heat-killed E. faecalis cells by 4 log10 and 3 log10 units, respectively. Results suggest that high total dissolved solid concentration (32 g/L) in seawater can reduce PMA activity. Optimal PMA-qPCR standard curves with a 6-log dynamic range and detection limit of 10(2) cells/mL were generated for quantifying viable E. faecalis cells in marine waters. The developed assay was compared with the standard membrane filter (MF) method by quantifying viable E. faecalis cells in seawater samples exposed to solar radiation. The results of the developed PMA-qPCR assay did not match that of the standard MF method. This difference in the results reflects the different physiological states of E. faecalis cells in seawater. In conclusion, the developed assay is a rapid (∼5 h) method for the quantification of viable E. faecalis cells in marine recreational waters, which should be further improved and tested in different seawater settings.

In this study, two experimental sets of data each involving two thermophilic anaerobic digesters treating food waste, were simulated using the Anaerobic Digestion Model No. 1 (ADM1). A sensitivity analysis was conducted, using both data sets of one digester, for parameter optimization based on five measured performance indicators: methane generation, pH, acetate, total COD, ammonia, and an equally weighted combination of the five indicators. The simulation results revealed that while optimization with respect to methane alone, a commonly adopted approach, succeeded in simulating methane experimental results, it predicted other intermediary outputs less accurately. On the other hand, the multi-objective optimization has the advantage of providing better results than methane optimization despite not capturing the intermediary output. The results from the parameter optimization were validated upon their independent application on the data sets of the second digester.

ABSTRACT A new and sustainable modification has been introduced into the conventional solar still, considerably increasing its productivity. This enhancement in the solar still productivity is achieved without forsaking the basic features of the still such as low cost, ease of handling, sustainability, water quality, material availability, low maintenance and space conservation. The introduced modification is in the form of a slowly rotating hollow drum within the still cavity that allows the formation of thin water films, which evaporate rapidly. Several environmental and operational parameters attribute to the optimization of the new still design. Environmental factors refer primarily to weather conditions such as solar intensity, relative humidity, ambient temperature and wind speed and direction. Operational variables include drum speed, brine depth in the basin, cover cooling and other related parameters such as the materials used and the still configuration. The influence of these parameters is discussed and their impact on productivity is investigated in detailed order to identify existing correlations and optimize design and operation of the new system. An error analysis was conducted for all experimental data obtained from this study.

ABSTRACT A microbial osmotic fuel cell (MOFC) has a forward osmosis (FO) membrane situated between the electrodes that enable desalinated water recovery along with power generation. Previous designs have required aerating the cathode chamber water, offsetting the benefits of power generation by power consumption for aeration. An air-cathode MOFC design was developed here to improve energy recovery, and the performance of this new design was compared to conventional microbial fuel cells containing a cation (CEM) or anion exchange membrane (AEM). Internal resistance of the MOFC was reduced with the FO membrane compared to the ion exchange membranes, resulting in a higher maximum power production (43 W/m3) than that obtained with an AEM (40 W/m3) or CEM (23 W/m3). Acetate (carbon source) removal reached 90% in the MOFC; however, a small amount of acetate crossed the membrane to the catholyte. The initial water flux declined by 28% from cycle 1 to cycle 3 of operation but stabilized at 4.1 L/m2/h over the final three batch cycles. This decline in water flux was due to membrane fouling. Overall desalination of the draw (synthetic seawater) solution was 35%. These results substantially improve the prospects for simultaneous wastewater treatment and seawater desalination in the same reactor.