Effect Of Hydraulic Retention Time Research Articles

Optimization of Calcium Fluoride Crystallization Process for Treatment of High-Concentration Fluoride-Containing Semiconductor Industry Wastewater.

This study utilized a fluidized bed reactor (FBR) for fluoride removal from high-concentration fluoride-ion-containing simulated semiconductor industry wastewater and recovered high-purity CaF2 crystals. The effects of hydraulic retention time (HRT), pH, Ca2+ to F- ratio, upflow velocity, seed size and seed bed height were investigated by performing lab-scale batch experiments. Considering fluoride removal and CaF2 crystallization efficiency, 5 h HRT, pH 6, seed height of 50 cm and [Ca2+]/[F-] ratio of 0.55 (mol/mol) were found to be optimum. The effect of the interaction between the important process parameters on fluoride removal was further analyzed using response surface methodology (RSM) experimental design. The results showed that all the individual parameters have a significant impact (p = 0.0001) on fluoride removal. SEM-EDX and FTIR analysis showed the composition of the crystals formed inside FBR. HR-XRD analysis confirmed that the crystalline structure of samples was mainly CaF2. The results clearly demonstrated the feasibility of silica seed material containing FBR for efficient removal and recovery of fluoride as high-purity calcium fluoride crystals.

WITHDRAWN: Effects of hydraulic retention time and cultivation on nutrients removal and biomass production in wastewater by membrane photobioreactor: modeling and optimization by machine learning and response surface methodology

Discharge of excess nutrients in wastewater can potentially cause eutrophication and poor water quality in the aquatic environment. A new approach of nutrients removal in wastewater is by utilizing microalgae which grow by absorbing CO2 from air. Furthermore, the use of membrane photo-bioreactor (MPBR) that combines membranes and photo-bioreactor has emerged as a novel wastewater treatment method. This research sought to model, forecast, and optimize the behavior of dry biomass, dissolved inorganic nitrogen (DIN), and dissolved inorganic phosphorus (DIP) in MPBR by response surface methodology (RSM) and artificial neural network (ANN) algorithms, which saved time and resources of experimental work. The independent variables that have been used for modeling were hydraulic retention time (HRT) and cultivation. For this purpose, the dry biomass of algal production, DIN and DIP behavior were modeled by RSM and ANN algorithms, to identify the optimum mode of processing. RSM modeling has shown good agreement with experimental data. According to RSM optimization, the optimum mode for DIN and DIP occurred at 1.15 days of HRT and 1.92 days of cultivation. The ANN showed better performance than the RSM model, with the margin of deviation being less than 10%. Furthermore, the ANN algorithm showed higher accuracy than RSM method in predicting the dry biomass, DIN and DIP behavior in MPBR.

Effect of hydraulic retention time on sulfide production with sludge from hydrothermal vent sediments and its utilization on the removal of Cu, Zn, and Al

The present work aimed to evaluate the production of sulfide through the application of different hydraulic retention times (HRT) and different sulfate loading rates in an up-flow anaerobic sludge blanket (UASB) reactor utilizing acetate-butyrate as electron donors and the coupling of the reactor to a crystallizer to remove metals. The sulfidogenic sludge for the UASB was generated from hydrothermal vent sediments and this was operated at room temperature (18-22 ºC). The sulfate reduction process was linked to the precipitation of Cu2+, Zn2+ and Al3+ in a crystallizer coupled to the UASB reactor (two-stage system) to avoid the toxicity of the metals to the sludge. The concentration of dissolved sulfide increased with the HRT up to 312.9 mg HS–/L at 3 d of HRT. As the sulfate loading rate was increasing, the maximum sulfide concentration obtained was of 376.8 mg HS–/L at 500 mg SO4–2/L/d (1500 mg/L), whereas the concentration of Cu2+, Zn2+ and Al3+ was up to 150, 100, and 100 mg/L, respectively. The removal efficiencies of Cu2+, Zn2+, and Al3+ were higher than 98% when they were fed separately. When a mixture of metals was added, the removal efficiency was close to 80%. Recovery of metals was lower than 57% in all cases. The sulfide production was supported with acetate-butyrate, being the former commonly accumulated because of the oxidation of higher organic compounds; in this case, its utilization sustained sulfate reduction. This process could be controlled by parameters such as HRT and sulfate loading rate to improve the performance of the bioreactor in the treatment of the effluents contaminated with metals in a two-stage system.

Investigation of the geometry of an electrochemical reactor in order to minimize the operational energy cost in the treatment of cosmetic effluents

Low biodegradability and high toxicity are common characteristics of cosmetic effluent. They have stimulated the application, development, and improvement of advanced technologies, such as electrocoagulation (EC). In this sense, this study aimed to optimize the treatment conditions of operational parameters considering the theoretical energetic operational cost of the treatment of cosmetic effluents through a new design of a cylindrical electrochemical reactor in continuous upward flow (CER-CUF). The effects of hydraulic retention time (HRT), electrical current density (j), and electrical conductivity on COD removal, turbidity, and residual Al concentration were investigated using a Central Composite Rotational Design (CCRD). The COD and turbidity removal efficiencies were 61.96 % and 44.71 %, respectively, with a total operating cost of 0.258 US$ m−3 to treat the effluent cosmetic under optimized conditions (HRT:5 min/j: 5 mA cm−2 and EC:2000.00 μS cm−1) in CER-CUF. These results contribute to advancing of knowledge about electrocoagulation technology and the possibility of full-scale application, in addition to encouraging the use of CER-CUF for treating effluents from the cosmetic industry.

Regulation of hydraulic retention time on caproic acid production via two-phase anaerobic fermentation of Chinese cabbage waste with autopoietic electron donors

The effects of hydraulic retention time (HRT) on the performance of two-phase anaerobic fermentation for caproic acid production from Chinese cabbage waste (CCW) were investigated. In the electron donor phase, yeast was inoculated to achieve efficient autopoietic ethanol, providing electron donors for the chain elongation process. Shorter HRT led to drastic fluctuations in microorganisms, thus resulting in lower acid yields at HRT of 6 days. At HRT of 10 days, the balanced collaboration of various key bacteria avoided the accumulation of intermediate by-products, and the caproic acid production reached 4660 mg COD/L, which was 119.5% and 154.8% higher than that at HRTs of 6 and 14 days, respectively. At HRT of 14 days, the low ethanol loading rate resulted in ethanol excessive-oxidation to acetic acid. Acetic acid accounted for 41.5% of the total product, while the selectivity of caproic acid was only 15.3%. The main contributor to the production process of caproic acid was Caproiciproducens, while the Ruminalococcaceae also played a role in the process. This study provided a theoretical basis for the efficient production of caproic acid through continuous fermentation with autopoietic electron donors.

Enhancing kitchen waste minimization and energy generation at 20 °C: a psychrophilic anaerobic co‐digestion study

AbstractBackgroundIn developing countries, anaerobic digestion still represents an emerging technology for solid waste management, despite the great energy potential of methane in biogas for heating purposes, especially in low‐temperature regions. This research evaluated the effect of hydraulic retention time (40–120 days) on the anaerobic co‐digestion of 35% w/w waste activated sludge and 65% w/w organic kitchen waste at a low temperature (20 °C). The anaerobic co‐digestion was conducted in five 11‐L semicontinuous anaerobic digesters. Additionally, the expected energy production from organic kitchen waste was calculated.ResultsThe specific methane yield (SMY) ranged from 0.20 to 0.27 LCH4 g‐VSadd−1, comparable to the SMY reported for meso‐ and thermophilic anaerobic digestion. Moreover, the expected energy production was 1.06 MJ day−1 of equivalent liquefied petroleum gas, which could satisfy ≤6.6% of the daily water heating requirements of an average Mexican household. The hydraulic retention time in the range of 60–120 days did not seem to significantly affect the performance of the digesters.ConclusionsThese digesters could easily be installed in low temperature regions for domestic use. The waste activated sludge substrate can be replaced with other nitrogen‐rich substances for indoor use. The data shown in this research set the basis for further investigations and domestic applications. © 2023 Society of Chemical Industry (SCI).

Enhanced phosphorus removal from biological secondary effluent using denitrifying phosphorus-removal granular sludge

With the phosphorus discharge standard getting more stringent, it is imperative to enhance phosphorus removal from biological secondary effluent (BSE) of wastewater treatment plants (WWTPs). This study proposed a semi-continuous process for enhanced phosphorus removal from BSE using denitrifying phosphorus-removal granular sludge (DPGS) in a fluidized reactor operating under the alternative anaerobic/anoxic mode. This study investigated the effects of hydraulic retention time (HRT) and treating volume of BSE on the enhanced phosphorus removal performance of this process. At the appropriate HRT and treating volume of BSE, this process reduced the total phosphorus of practical BSE from 0.54 to 0.14 mg/L with an average removal efficiency of 74.5 % and removed 2.1 mg/L nitrate in 95 days. Removed phosphorus from practical BSE was concentrated into a small volume of water via the anaerobic phosphorus release and anoxic phosphorus uptake of denitrifying phosphorus-accumulating organisms (DPAOs) in DPGS, which was conducive for phosphorus recovery via chemical precipitation. The metagenomic analysis reveals that the relative abundance of DPAOs in DPGS increased while that of denitrifying glycogen-accumulating organisms decreased during 95 days of operation. This study provides a more cost-efficient and eco-friendly process for WWTPs to enhance phosphorus removal from BSE and phosphorus recycling.

Co-digestion of solid-liquid waste from citrus agroindustrial: Effect of hydraulic retention time and organic loading rate on H2 production in a long-term continuous operation leach bed reactor

The Leach Bed Reactor (LBR) application is a promising alternative for the anaerobic digestion of solid waste and wastewater. In this study, the LBR was continuously operated for 160 days in four different phases, for co-fermentation of solid and liquid waste from the citrus agroindustry, at 37 °C, evaluating the effect of hydraulic retention time (HRT) and organic loading rate (OLR). The maximum volumetric hydrogen production (VHPR) was observed at an HRT of 12h (958.3 mLH2.L-1.d-1); however, the highest hydrogen yield (HY) was identified at an HRT of 24h (104.9 mLH2.g-1CHO). Based on the metabolic characteristics of microorganisms identified in higher relative abundance, by 16S rRNA sequencing, such as Lactobacillus, Caproicoproducens, Bifidobacterium, Olsenella, and Solobacterium, an occurrence of chain elongation pathways in the production of butyric and caproic acids was inferred, with hydrogen production resulting from the lactic acid oxidation. The maximum electricity production potential of 16.3 kWh.m-3 liquor was estimated.

The effect of hydraulic retention time on stabilisation unit in anaerobic – contact stabilisation (A-CST) for treating palm oil mill effluent

The increased use of palm oil in Indonesia has triggered an increase in the quantity of Palm Oil Mill Effluent (POME). The contents of Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Suspended Solid (TSS), as well as oils and grease in palm oil mill effluent, need to be reprocessed, in accordance with the provisions of the Ministry of Environment Regulation No. 5 of 2014, concerning Wastewater Quality Standards, before being discharged into water bodies. In this study, a modification of the treatment unit involving the integration of suspended growth and attached growth in anaerobic and aerobic processes, known as Anaerobic – Contact Stabilisation (A-CST) unit, was conducted to reduce the high concentration of organic matter in POME. This modification can shorten the detention time and reduce the land usage for treatment. The objective of this research was to analyse the performance of the modified A-CST system, based on variations in the detention time and modelling the estimation of biokinetics under unsteady-state conditions, through numerical analysis, statistical tests, and model validation. The research focused on the stabilisation unit, with variations in Hydraulic Retention Time (HRT) of 6 hours, 5 hours, and 4 hours. The results of this study revealed that, the highest percentage of removal was obtained at an HRT variation of 6 hours, with a COD 88%.

Effect of hydraulic retention time on the performance of sequencing batch reactor under combined stress of ibuprofen and ciprofloxacin

The impacts of changes in hydraulic retention time (HRT) on nitrogen elimination, the activity of sludge and the structure of microbial communities in a sequencing batch reactor under the joint stress of ibuprofen (IBP) and ciprofloxacin (CIP) were investigated. Under the combined stress of IBP (belonged to nonsteroidal anti-inflammatory drugs) and CIP (belonged to antibiotics), the elimination level of ammonia nitrogen, chemical oxygen demand, and the rate of specific ammonia oxidation, specific nitrite oxidation, specific nitrate reduction in activated sludge declined with the shortening of HRT. Under the joint stress of IBP and CIP, the content of polysaccharide (PS) and protein (PN) together with the ratio of PN to PS in the extracellular polymeric substances grew with the shortening of HRT, and the content of aromatic proteins increased significantly, which indicated that aromatic proteins were the major protective response substances to the shortening of HRT. Under the joint stress of IBP and CIP, with the reduction of HRT, and the reduction rate of relative abundance of nitrifying bacteria was more evident than that of denitrifying bacteria. This exploration gives novel thoughts for understanding the impacts of HRT on biological nitrogen removal of wastewater under combined stress of IBP and CIP.

Effect of hydraulic retention time on biological nutrients removal in an anaerobic membrane bioreactor treating low-strength drain wastewater

This work compares the nutrients removal efficiency of an anaerobic membrane bioreactor (AnMBR) treating low-strength drain wastewater (total chemical oxygen demand CODt of 157.09 ± 34.83 mg/L) at two different hydraulic retention times (HRTs). Because nutrients removal is poor in anaerobic systems, longer HRTs of 4 days and 3 days were opted for in this study. AnMBR performance was superior at 3 day HRT with removal efficiencies of 53.32 ± 4.83 % (CODt), 88.60 ± 19.04 % (ammonia-nitrogen, NH4+-N), and 63.65 ± 4.90 % (phosphate, PO43−) with higher permeate flux of around 6.6 L/m2 h. The possible reason for achieving better nutrients removal at 3 day HRT could be enough food and adequate contact time experienced by the microorganisms. Therefore, longer yet sufficient HRT can be an approach for improved nutrients removal in an AnMBR treating low-strength wastewater.

Comparison of aerobic and anoxic-oxic sequential batch reactors for treating textile wastewater

ABSTRACT The discharge of untreated textile dyeing wastewater containing azo dyes has significant ecological consequences. The incomplete biodegradation of these dyes can produce harmful and carcinogenic aromatic amines (AAs), which pose a threat to the environment. This study evaluates the treatment of real textile dyeing wastewater containing azo dyes by two different systems: an anoxic sequential batch reactor (A/O-SBR) and an aerobic sequential batch reactor (A-SBR). The effects of hydraulic retention time (HRT) on both systems were investigated in terms of chemical oxygen demand (COD), total nitrogen (TN), color, and AAs removal. Ranging between 85% and 92%, the COD removal efficiency was almost similar in the A/O-SBR and A-SBR systems, suggesting that the aerobic phase is primarily responsible for COD removal. However, A/O-SBR showed higher removal of color (90%) than A-SBR (75%) due to the presence of an anoxic phase. HRT has a significant impact on color removal in both systems. However, there was no significant effect on COD removal when HRT exceeded 12 h. According to LC-MS/MS analysis, increasing the HRT from 12 h to 24 h increased the AAs concentration in the anoxic phase, from 253 ng/L to 261 ng/L and slightly decreased the AAs concentration in the aerobic phase from 107 ng/L to 102 ng/L. This resulted in an overall improvement in both dye and AAs removal. The presence of aerobic phase in A/O-SBR and A-SBR demonstrates strong AAs removal capacity. GC-MS/MS analysis indicated that as the HRT of A/O-SBR and A-SBR increased, the number of by-products increased.

Effects of hydraulic retention time and influent nitrate concentration on solid-phase denitrification system using wheat husk as carbon source.

Solid-phase denitrification shows promise for removing nitrate (NO3--N) from water. Biological denitrification uses external carbon sources to remove nitrogen from wastewater, among which agriculture waste is considered the most promising source due to its economic and efficiency advantages. Hydraulic retention time (HRT) and influent nitrate concentration (INC) are the main factors influencing biological denitrification. This study explored the effects of HRT and INC on solid-phase denitrification using wheat husk (WH) as a carbon source. A solid-phase denitrification system with WH carbon source was constructed to explore denitrification performance with differing HRT and INC. The optimal HRT and INC of the wheat husk-denitrification reactor (WH-DR) were 32 h and 50 mg/L, respectively. Under these conditions, NO3--N and total nitrogen removal rates were 97.37 ± 2.68% and 94.08 ± 4.01%, respectively. High-throughput sequencing revealed that the dominant phyla in the WH-DR operation were Proteobacteria, Bacteroidetes, and Campilobacterota. Among the dominant genera, Diaphorobacter (0.85%), Ideonella (0.38%), Thiobacillus (4.22%), and Sulfurifustis (0.60%) have denitrification functions; Spirochaeta (0.47%) is mainly involved in the degradation of WH; and Acidovorax (0.37%) and Azospira (0.86%) can both denitrify and degrade WH. This study determined the optimal HRT and INC for WH-DR and provides a reference for the development and application of WH as a novel, slow-release carbon source in treating aquaculture wastewater.

Continuous dark fermentation by industrial food wastewater: the effect of hydraulic retention time on hydrogen production and microbial variation

Continuous dark fermentation by industrial food wastewater: the effect of hydraulic retention time on hydrogen production and microbial variation

Effect of Hydraulic retention time on performance of anaerobic membrane bioreactor treating slaughterhouse wastewater

Slaughterhouse wastewater is a major environmental concern in many Vietnamese cities due to its high organic content and unpleasant odor. This study aimed to evaluate performance of a submerged flat sheet Anaerobic membrane bioreactor (AnMBR) system at different hydraulic retention time (HRT, 8–48 h) treating wastewater from a slaughterhouse in Hanoi City (Vietnam) at ambient temperature. The wastewater characteristics were as follows: chemical oxygen demand (COD) of 910 ± 171 mg/L; suspended solids (SS) of 273 ± 139 mg/L; and total nitrogen (T-N) of 115 ± 31 mg/L. The AnMBR system achieved high removal efficiencies for SS (99%) and COD (>90%) at an optimum HRT of 24 h. The biomethane yield reached 0.29 NL CH4/g CODinf. Importantly, the system maintained stable operation without flux decay and membrane fouling. HRT longer than 24 h could offer the better effluent quality without an increase in transmembrane pressure (TMP); however, it led to a lower methane production rate. Shorter HRT of 8–12 h caused a high TMP over −10 kPa, posing a risk for membrane fouling and biomass loss during cleaning, thus resulting in a low methane production. Our results suggest that AnMBR can be a reliable technology for wastewater treatment, reuse and energy recover from slaughterhouse wastewater in Vietnam and other similar climate countries.

Continuous lactate-driven dark fermentation of restaurant food waste: Process characterization and new insights on transient feast/famine perturbations

The effect of hydraulic retention time (HRT) on the continuous lactate-driven dark fermentation (LD-DF) of food waste (FW) was investigated. The robustness of the bioprocess against feast/famine perturbations was also explored. The stepwise HRT decrease from 24 to 16 and 12 h in a continuously stirred tank fermenter fed with simulated restaurant FW impacted on hydrogen production rate (HPR). The optimal HRT of 16 h supported a HPR of 4.2 L H2/L-d. Feast/famine perturbations caused by 12-h feeding interruptions led to a remarkable peak in HPR up to 19.2 L H2/L-d, albeit the process became stable at 4.3 L H2/L-d following perturbation. The occurrence of LD-DF throughout the operation was endorsed by metabolites analysis. Particularly, hydrogen production correlated positively with lactate consumption and butyrate production. Overall, the FW LD-DF process was highly sensitive but resilient against transient feast/famine perturbations, supporting high-rate HPRs under optimal HRTs.

Influence of Electrodes Configuration on Hydraulic Characteristics of Constructed Wetland–Microbial Fuel Cell Systems Using Graphite Rods and Plates as Electrodes

Constructed wetland–microbial fuel cell coupling systems (CW–MFCs) have received significant academic interest in the last decade mainly due to the promotion of MFCs in relation to pollutants’ degradation in CWs. Firstly, we investigated the effect of hydraulic retention time (HRT) and electrode configuration on the flow field characteristics of CW–MFCs using graphite rods and plates as electrodes, as well as the optimization of electrode configuration using computational fluid dynamics (CFD) numerical simulation. The results showed that: (1) the apparent HRT was the most influential and decisive factor, with a contribution of over 90% for the average HRT of CW–MFCs; (2) anode spacing was the most influential factor for the hydraulic performance of CW–MFCs, with contributions of over 50% for water flow divergence and hydraulic efficiency (λ) and over 45% for effective volume ratio (e); (3) anode size was significant for e and λ, with a contribution of over 20%; (4) cathode position and cathode size had no statistically significant effect on the hydraulic performance of CW–MFCs. It was mainly through the blocking of water flows, flows around, compressing water flow channels and boundary layer separation that the MFC electrodes influenced the hydraulic characteristics of the flow field in CW–MFCs. Optimizing the flow field by optimizing the electrode configuration helped to facilitate electricity generation and pollutants’ removal in CW–MFCs. This study offers a scientific reference for improving the hydraulic performance of CW–MFCs, and it also provides a new research perspective for improving the wastewater treatment and electricity production performance of CW–MFCs.

Mesophilic anaerobic digestion of waste activated sludge in an intermittent mixing reactor: Effect of hydraulic retention time and organic loading rate

An anaerobic digester was operated at mesophilic temperature and with intermittent mixing conditions to treat waste activated sludge. The organic loading rate (OLR) was increased by decreasing the hydraulic retention time (HRT), and the effect on process performance, digestate characteristics and inactivation of pathogens was investigated. The removal efficiency of total volatile solids (TVS) was also measured by biogas formation. The HRT varied from 50 to 7 days, corresponding to OLR from 0.38 to 2.31 kgTVS.m−3.d−1. The acidity/alkalinity ratio remained within stable limits (lower than 0.6) at 50-, 25- and 17-day HRT; due to an imbalance between the production and consumption of volatile fatty acids, the ratio increased to 0.7 ± 0.2 at HRT of 9 days and 7 days. The highest TVS removal efficiencies were 16, 12 and 9%, which were obtained at 50-, 25- and 17 day-HRT, respectively. Intermittent mixing provided solids sedimentation greater than 30% for almost all HRT tested. The highest methane yields (0.10–0.05 m3.kgTVSfed−1.d−1) were obtained when the reactor was operated at a higher HRT (50-17 days). At lower HRT, methanogenic reactions were likely limited. Zinc and copper were the main heavy metals found in the digestate, while the most probable number (MPN) of coliform bacteria remained below 106 MPN.g TVS−1. Neither Salmonella nor viable Ascaris eggs were found in the digestate. In general, increasing the OLR by decreasing the HRT to 17 days under intermittent mixing conditions provided an attractive alternative to treat sewage sludge despite some limitations due to biogas and methane yields.

The Combination of Anaerobic Digestion and Electro-Oxidation for Efficient COD Removal in Beverage Wastewater: Investigation of Electrolytic Cells

The world’s ever-growing population is driving an increased demand for clean water, which makes treating and reusing wastewater an essential practice. In recent years, biological and physicochemical methods have been preferred for wastewater treatment, with combined systems proving particularly effective. In this study, the combination of anaerobic digestion (AD) and electro-oxidation (EO) was investigated as a process for removing chemical oxygen demand (COD) from actual beverage wastewater. The effect of hydraulic retention time (HRT) on AD, electrolysis time, sodium chloride (NaCl) dosage, initial pH, and electro-properties on EO was investigated. At optimum conditions, namely an HRT of 2 days for AD, NaCl concentration of 3 g L−1, 80 min of EO time, natural pH (7.45), and applied voltage of 20 V for EO, the removal efficiency for COD was an impressive 96.47%, with energy consumption and specific energy consumption calculating 177.33 kWh m−3 and 33.79 kWh kgCOD−1, respectively. The amount of by-product gases (CH4 and H2) were also meagerly determined in this study. The results confirm that combining the AD and EO methods is an effective COD removal solution that can benefit the industry, while also offering a sustainable solution to combat water scarcity and meet the growing demand for clean water.

Effect of hydraulic retention time on performances of gravity-driven membrane (GDM) reactor for seawater pretreatment

This study aims to illustrate the effect of hydraulic retention time (HRT) on reactor performance and biofilm characteristics in the gravity-driven membrane (GDM) reactor pretreating seawater. Three GDM reactors were operated in parallel for ~62 days under HRTs of 22 h, 54 h, and 102 h, respectively. The results indicated that the GDM reactors at HRTs of 22 h and 102 h had relatively higher permeate flux and superior permeate quality (especially assimilable organic carbon, AOC) compared to that at HRT of 54 h. Extending HRT benefited to reduce irreversible fouling, but cake layer fouling was maximized at HRT of 54 h. As different HRTs led to significantly dissimilar microbial community structure and cake layer composition, such higher cake layer resistance at HRT of 54 h was attributed to homogenous nature of the biofilm, which contained greater amount of organics and less abundance of Nematoda (dominant predator). Lastly, as increasing ~5-time of HRT (from 22 h to 102 h) improved ~1.5 of permeate flux, a shorter HRT of 22 h was preferable for the GDM reactor in pretreating seawater with regard to treatment productivity and footprint.