Biofilm characteristics for providing resilient denitrification in a hydrogen-based membrane biofilm reactor.

In a hydrogen-based membrane biofilm reactor (H2-MBfR), the biofilm thickness is considered to be one of the most important factors for denitrification. Thick biofilms in MBfRs are known for low removal fluxes owing to their resistance to substrate transport. In this study, the H2-MBfR was operated under various loading rates of oxyanions, such as NO3-N, SO4-S, and ClO4- at an H2 flux of 1.06 e- eq/m2-d. The experiment was initiated with NO3-N, SO4-S, and ClO4- loadings of 0.464, 0.026, and 0.211 e- eq/m2-d, respectively, at 20 °C. Under the most stressful conditions, the loading rates increased simultaneously to 1.911, 0.869, and 0.108 e- eq/m2-d, respectively, at 10 °C. We observed improved performance in significantly thicker biofilms (approximately 2.7 cm) compared to previous studies using a denitrifying H2-MBfR for 120 days. Shock oxyanion loadings led to a decrease in total nitrogen (TN) removal by 20 to 30%, but TN removal returned to 100% within a few days. Similarly, complete denitrification was observed, even at 10 °C. The protective function and microbial diversity of the thick biofilm may allow stable denitrification despite stress-imposing conditions. In the microbial community analysis, heterotrophs were dominant and acetogens accounted for 11% of the biofilm. Metagenomic results showed a high abundance of functional genes involved in organic carbon metabolism and homoacetogenesis. Owing to the presence of organic compounds produced by acetogens and autotrophs, heterotrophic denitrification may occur simultaneously with autotrophic denitrification. As a result, the total removal flux of oxyanions (1.84 e- eq/m2-d) far exceeded the H2 flux (1.06 e- eq/m2-d). Thus, the large accumulation of biofilms could contribute to good resilience and enhanced removal fluxes.

Investigation of critical sludge characteristics for membrane fouling in a submerged membrane bioreactor: Role of soluble microbial products and extracted extracellular polymeric substances.

Membrane bioreactors (MBRs) are considered a promising tool for resource recovery in wastewater treatment. Nevertheless, membrane fouling is an inevitable phenomenon that deteriorates the MBR performance. Although many studies have attempted to elucidate the effect of sludge characteristics on MBR fouling, they posed certain limitations. Most of the previous studies focused on the initial sludge or employ the results of short-term batch tests without long-term transmembrane pressure (TMP) profiles in the interpretation of fouling behaviors. This study was conducted considering these limitations to determine the sludge characteristics most closely related to long-term TMP profiles and to identify their role in fouling behaviors. In long-term TMP profiles, critical time (tc; time to TMP jump) and fouling rates (the increase in the TMP slope) were used as fouling indexes, which were used to correlate with average values of sludge characteristics before and after experiments. According to the results, the concentration of the total soluble microbial product (SMP) and extracted extracellular polymeric substance (eEPS) in sludge significantly increased by 1.9 times and up to 28 times after experiment. The increase in the SMP and eEPS caused early TMP jumps and resulted in low-fouling rates by increasing particle size. Owing to the increase in the SMP and eEPS concentration, the origin of fouling potential was shifted from suspended solids to colloids and soluble materials. Fouling resistance caused by soluble material increased by up to 11.38 times.

Development of a new method to evaluate critical flux and system reliability based on particle properties in a membrane bioreactor.

Membrane fouling occurs when the operating flux exceeds a certain point (i.e., critical flux). Critical flux has therefore been widely adopted to determine the initial operating flux in membrane bioreactor (MBR) processes. The flux steeping method currently used to measure the critical flux is time-consuming and uneconomical. This study was conducted to develop a novel approach for the evaluation of critical flux. Given that particle fouling is dominant during the initial fouling stage, we hypothesized that particle properties may be closely related to critical flux. A critical flux prediction model with an R2 of 0.9 was therefore derived, which indicates that particle properties regulate critical flux. The results imply that most of the fouling potential during the early stages of operation is caused by SS, and that the formation of cakes that comprise large particles is the dominant fouling mechanism. The new method proposed in this study reduced the measurement cost and time to evaluate critical flux by 3.5-and 8 times, respectively, compared to the flux-stepping method. In terms of practical application, the applicability of the model equation was identified by system reliability analysis, which indicates that the system failure increases significantly as the standard deviation of the variables increases. This study demonstrated that the prediction of critical flux and system reliability can be achieved through particle characteristic measurement. A similar approach is expected to be employed in real MBR plants as an economical and convenient fouling control strategy to solve problems involving resource shortages.

Synergistic control of membrane biofouling using linoleic acid and sodium hypochlorite.

Biofouling is a major operational problem in the reverse osmosis (RO) process, affecting the membrane performance. Although sodium hypochlorite (NaOCl) is used to chemically clean the biofouled membranes, high concentrations of NaOCl cause morphological and chemical damage to the RO membrane. The objective of this study is to enhance chemical cleaning efficiency by combining with a dispersion agent (linoleic acid, LA) that does not harm the RO membrane, to overcome the disadvantages of NaOCl. Biofilm cells were initially dispersed with LA treatment and biofouled layers were subsequently cleaned using NaOCl at low concentration. The optimized combination resulted in 3.9-4.4 times higher flux recovery efficiency than that with individual treatments. Furthermore, the combination decreased the volume and thickness of the biofilm as well as the amount of extracellular polymeric substances. Taken together, the combined treatment of LA and NaOCl significantly improves RO biofouling control.

Effect of broad-spectrum biofilm inhibitor raffinose, a plant galactoside, on the inhibition of co-culture biofilm on the microfiltration membrane.

A membrane bioreactor (MBR) integrates process such as membrane filtration and biological treatment of activated sludge. However, organic, inorganic and biological matters cause membrane fouling, which seriously affects membrane performance. The goal of this study was to evaluate the biofouling inhibition capacity of raffinose during the MBR process. The results showed that 0-1,000 µM raffinose significantly reduced the formation of the P. aeruginosa and S. aureus co-culture biofilm by about 25-52 % in a concentration-dependent manner. In addition, the effect of raffinose on the microfiltration membrane biofilm was tested in a flow reactor and lab-scale MBR unit. The results showed that the co-culture biofilm and transmembrane pressure were decreased by raffinose treatment compared to those by furanone C-30 treatment. These results clearly demonstrated that raffinose, broad-spectrum biofilm inhibitor, inhibits biofilm formation in mixed cultures and could be used to mitigate biofouling in MBR processes.

Modeling the early temporal dynamics of viral load in respiratory tract specimens of COVID-19 patients in Incheon, the Republic of Korea.

OBJECTIVE: To investigate the duration and peak of severe acute respiratory syndrome coronavirus 2 shedding as infectivity markers for determining the isolation period. METHODS: A total of 2,558 upper respiratory tract (URT) and lower respiratory tract (LRT) specimens from 138 patients with laboratory-confirmed coronavirus disease were analyzed. Measurements of sequential viral loads were aggregated using the cubic spline smoothing function of a generalized additive model. The time to negative conversion was compared between symptom groups using survival analysis. RESULTS: In URT samples, viral RNA levels peaked on day 4 after symptom onset and rapidly decreased until day 10 for both E and RdRp genes, whereas those in LRT samples immediately peaked from symptom onset and decreased until days 15.6 and 15.0 for E and RdRp genes, respectively. Median (interquartile range) time to negative conversion was significantly longer in symptomatic (18.0 [13.0-25.0] days) patients than in asymptomatic (13.0 [9.5-17.5] days) patients. The more types of symptoms a patient had, the longer the time to negative conversion. CONCLUSIONS: The viral load rapidly changes depending on the time after symptom onset; the viral shedding period may be longer with more clinical symptoms. Different isolation policies should be applied depending on disease severity.

Fouling development in direct contact membrane distillation: Non-invasive monitoring and destructive analysis.

Fouling development in direct contact membrane distillation (DCMD) for seawater desalination was evaluated combining in-situ monitoring performed using optical coherence tomography (OCT) together with destructive techniques. The non-invasive monitoring with OCT provided a better understanding of the fouling mechanism by giving an appropriate sampling timing for the membrane autopsy. The on-line monitoring system allowed linking the flux trend with the structure of fouling deposited on the membrane surface. The water vapor flux trend was divided in three phases based on the deposition and formation of different foulants over time. The initial flux decline was due to the deposition of a 50-70 nm porous fouling layer consisting of a mixture of organic compounds and salts. Liquid chromatography with organic carbon detection (LC-OCD) analysis revealed the abundance of biopolymer in the fouling layer formed at the initial phase. In the second phase, formation of carbonate crystals on the membrane surface was observed but did not affect the flux significantly. In the last phase, the water vapor flux dropped to almost zero due to the deposition of a dense thick layer of sulfate crystals on the membrane surface.

Economic Evaluation of a Hybrid Desalination System Combining Forward and Reverse Osmosis.

This study seeks to evaluate the performance and economic feasibility of the forward osmosis (FO)-reverse osmosis (RO) hybrid process; to propose a guideline by which this hybrid process might be more price-competitive in the field. A solution-diffusion model modified with film theory was applied to analyze the effects of concentration polarization, water, and salt transport coefficient on flux, recovery, seawater concentration, and treated wastewater of the FO process of an FO-RO hybrid system. A simple cost model was applied to analyze the effects of flux; recovery of the FO process; energy; and membrane cost on the FO-RO hybrid process. The simulation results showed that the water transport coefficient and internal concentration polarization resistance are very important factors that affect performance in the FO process; however; the effect of the salt transport coefficient does not seem to be large. It was also found that the flux and recovery of the FO process, the FO membrane, and the electricity cost are very important factors that influence the water cost of an FO-RO hybrid system. This hybrid system can be price-competitive with RO systems when its recovery rate is very high, the flux and the membrane cost of the FO are similar to those of the RO, and the electricity cost is expensive. The most important thing in commercializing the FO process is enhancing performance (e.g.; flux and the recovery of FO membranes).