Effluent Sediment Research Articles

Ti-containing NPs in raw water and their removal with conventional treatments in four water treatment plants in Taiwan.

The ingestion of Ti-containing nanoparticles from drinking water has emerged as a concern in recent years. This study therefore aimed to characterize Ti-containing nanoparticles in water samples collected from four water treatment plants in Taiwan and to explore the challenges associated with measuring them at low levels using single particle-inductively coupled plasma mass spectrometry. Additionally, the study sought to identify the most effective processes for the removal of Ti-containing nanoparticles. For each water treatment plant, two water samples were collected from raw water, sedimentation effluent, filtration effluent, and finished water, respectively. Results revealed that Ti-containing nanoparticles in raw water, with levels at 8.69μg/L and 296.8 × 103 particles/L, were removed by approximately 35% and 98%, respectively, in terms of mass concentration and particle number concentration, primarily through flocculation and sedimentation processes. The largest most frequent nanoparticle size in raw water (112.0 ± 2.8nm) was effectively reduced to 62.0 ± 0.7nm in finished water, while nanoparticles in the size range of 50-70nm showed limited changes. Anthracite was identified as a necessary component in the filter beds to further improve removal efficiency at the filtration unit. Moreover, the most frequent sizes of Ti-containing nanoparticles were found to be influenced by salinity. Insights into the challenges associated with measuring low-level Ti-containing nanoparticles in aqueous samples provide valuable information for future research and management of water treatment processes, thereby safeguarding human health.

Mass flow and consumption calculations of pharmaceuticals in sewage treatment plant with emphasis on the fate and risk quotient assessment

In Egypt, pharmaceuticals consumption increased dramatically owing to the population growth and the unrestricted sale manner. Accordingly, the occurrence and fate of nine common pharmaceutical active compounds (PhACs) were scrutinized at a sewage treatment plant (STP) in Giza, Egypt. The levels of these PhACs were assessed in different the wastewater treatment stages and dewatered sludge phase using high-performance liquid chromatography coupled with photodiode arrays detector. The average concentrations of the total PhACs detected in influent, primary sedimentation effluent (PSE) and final effluent (FE) were 227, 155 and 89 µg L−1, respectively. The overall removal efficiency of the individual PhACs ranged from 18 to 72% removal. The occurrence trend revealed that biodegradation and adsorption are the concurrently removal mechanisms of the studied PhACs. The overall consumption per day in West of Greater Cairo was estimated based on influent concentration of STP. Sulfamethoxazole, paracetamol and diclofenac were detected with the highest levels in the influent of STP, PSE and FE as well as in the dewatered sludge. Furthermore, the high concentrations of these compounds in the sludge confirm the adsorption pathway removal of theses PhACs. The risk quotient (RQ) assessment for the detected PhACs in FE is greatly higher than the predicted non-effect concentration (PNEC). Conclusively, the FE of STP is considered a risky source for PhACs in adjacent surface water.

Isolation and Molecular Identification of Antibacterial-Producing Actinomycetes against Pathogenic Pathogens from Industrial Effluent Sediments of the Maragheh Glass Factory: A Laboratory Study

Isolation and Molecular Identification of Antibacterial-Producing Actinomycetes against Pathogenic Pathogens from Industrial Effluent Sediments of the Maragheh Glass Factory: A Laboratory Study

Effluent microscopy is a useful adjuvant diagnostic tool in peritoneal dialysis-associated peritonitis.

Infectious complications are the leading cause of technical failure in peritoneal dialysis (PD); however, targeted anti-infective therapy is not feasible at the onset, as effluent cultures take days and may be inconclusive. Although recommended by the guidelines, divergent positivity rates of Gram-stained effluent microscopy question the value of its usefulness. This study aimed to evaluate if microscopy of cell types serves as an additional and timely diagnostic approach. This single-center retrospective analysis included prevalent PD patients (n=250) between 2007 and 2017. Automated quantitative cell count, cytological analysis of Hemacolor and Gram-stained effluent sediment, and effluent cultures were conducted during peritonitis episodes. We calculated the rate of peritonitis, positivity rate of effluent cultures, and effluent microscopy. There were 155 at-risk cases of peritonitis in 662.7 years during the observation period. The culture positivity rate was 73.5%. In neutrophilic culture-negative peritonitis (CNP), effluent Gram staining yielded the identification of the microbial species in 51.6% cases. In 24.4% of CNP, effluent microscopy showed eosinophilic peritonitis, which occurred with less initial effluent leucocytes and showed better PD survival. In PD-associated peritonitis, Gram-stained dialysate with effluent microscopy supplements culture results in CNP. Hemacolor staining is crucial for differentiating eosinophilic peritonitis, showing a divergent clinical course and outcome.

Prognostic significance of peritoneal dialysis effluent mitochondrial DNA level

BackgroundMitochondrial DNA (mtDNA) resembles bacterial DNA and potentially triggers local and systemic inflammation. We evaluate the prognostic implications of PD effluent mtDNA level in peritoneal dialysis (PD) patients. MethodsWe measured mtDNA in the PD effluent (PDE) sediment and supernatant of 168 incident PD patients. All patients were followed for hospitalization, technique and overall survival. ResultsThe median PD effluent supernatant and sediment mtDNA levels were 255.4 unit (interquartile range [IQR] 157.5–451.3) and 201.6 unit (IQR 147.8–267.3), respectively. Serum C-reactive protein level closely with PDE sediment mtDNA level (r = 0.471, p < 0.001) and less with supernatant mtDNA level (r = 0.156, p = 0.044). PDE supernatant mtDNA level correlates with dialysate-to-plasma creatinine ratio at 4 h (D/P4) (r = 0.361, p < 0.001) but not with any clinical outcome. PDE sediment mtDNA was an independent predictor of technique survival (p = 0.011) and the duration of hospitalization (p = 0.044) after adjusting for clinical confounding factors. ConclusionsPDE sediment mtDNA level significantly correlated with systemic inflammation, while PDE supernatant mtDNA level correlated with peritoneal transport. PDE sediment mtDNA level also independently predicted technique survival and duration of hospitalization. The mechanism of the different implications between PDE sediment and supernatant mtDNA levels deserves further investigations.

Effects of different types of nutrient effluent from shrimp ponds on the seedling growth of Kandelia obovata

Extensive shrimp ponds are located next to the landward edges of most of mangrove forests in China. A shrimp pond may influence mangroves by (1) routine effluent between pond and tide, and (2) dredging effluent from pond-dredging at least once a year. Our study consisted of two experiments to study the effects of these two effluents on the seedling growth of Kandelia obovata. One experiment simulated the effects of routine effluents. The other simulated four sedimentation thicknesses (0 cm, 2 cm, 4 cm, 8 cm) over mangrove soils by dredging effluent from pond-dredging, and revealed the cumulative effects of dredging effluents on K. obovata. At each of the three fixed salinities, i.e., 5, 15 and 25, routine effluent did not result in significant differences in each of the measured growth parameters of K. obovata seedlings. However, effects of dredging effluent on seedling growth of K. obovata were related with sedimentation thickness. Most growth parameters showed maximum values at sedimentation thickness 4 cm. The data indicated that K. obovata accelerated its growth under moderate sedimentation thicknesses and it was tolerant and adaptable to shrimp pond-cleaning effluent sediments up to about 8 cm in our experiment.

Investigating sources and sinks of N2O expression from freshwater microbial communities in urban watershed sediments

Wastewater treatment plants (WWTPs) serve as point-source inputs for a variety of nutrients often dominated by nitrogenous compounds as a result of anthropogenic influence. These effluents can impact biogeochemical cycles in freshwater estuaries, influencing microbial communities in both the water and sediment compartments. To assess the impact of point source nutrients, a transect of sediment and pore water samples were collected from 4 locations in the Little River Sub-watershed including locations above and below the Little River Pollution Control Plant (LRPCP). Variation in chemistry and microbial community/gene expression revealed significant influences of the effluent discharge on the adjacent sediments. Phosphorus and sulfur showed high concentrations within plume sediments compared to the reference sediments while nitrate concentrations were low. Increased abundance of denitrifiers Dechloromonas, Dok59 and Thermomonas correlating with increased expression of nitrous-oxide reductase suggests a conversion of N2O to N2 within the LRPCP effluent sediments. This study provides valuable insight into the gene regulation of microbes involved in N metabolism (denitrification, nitrification, and nitrite reduction to ammonia) within the sediment compartment influenced by wastewater effluent.

Performance improvement of raw water pretreatment process with pre-inoculation biofilm: feasibility and limiting factors.

The initial formation of biofilm and the removal performance of pollutants in biological pretreatment process forpolluted raw water were limited due to the oligotrophic niche in raw water. In this study, the feasibility of using pre-inoculation biofilm formed under nutrients enhanced condition for polluted raw water treatment was analyzed in nine batch reactors. Results showed that the pollutants removal performance of biofilm was improved under nutrients enhanced conditions. Ammonia oxidation rate (AOR) was exponentially increased with the increasing in NH4+-N levels, and organic matter removal rate (ORR) was positively related to the initial total organic carbon (TOC) concentration. The biofilm formation and microbial diversity were further improved via adding more substrates, seeding river sediment and feeding effluent from a mature biofilm reactor. However, the biofilm formed under higher substrate conditions had higher half-saturation constant values (K S) to both NH4+-N and TOC, which decreased AOR and ORR values when it was used to treat polluted raw water. The reduction percentage of AOR and ORR showed logarithmic growth modes with the increase in K S values. Fortunately, improvement of nutrients flux via accelerating influent replacement could enhance the start-up performance effectively and decrease the operation risk introduced by the changes in substrate affinity.

Particle size distribution and property of bacteria attached to carbon fines in drinking water treatment

The quantitative change and size distribution of particles in the effluents from a sand filter and a granular activated carbon (GAC) filter in a drinking water treatment plant were investigated. The average total concentration of particles in the sand filter effluent during a filter cycle was 148 particles/mL, 27 of which were larger than 2 µm in size. The concentration in the GAC effluent (561 particles/mL) was significantly greater than that in the sand filter effluent. The concentration of particles larger than 2 µm in the GAC filter effluent reached 201 particles/mL, with the amount of particles with sizes between 2 µm and 15 µm increasing. The most probable number (MPN) of carbon fines reached 43 unit/L after six hours and fines between 0.45 µm and 8.0 µm accounted for more than 50%. The total concentration of outflowing bacteria in the GAC filter effluent, 350 CFU (colony-forming units)/mL, was greater than that in the sand filter effluent, 210 CFU/mL. The desorbed bacteria concentration reached an average of 310 CFU/mg fines. The disinfection efficiency of desorbed bacteria was lower than 40% with 1.5 mg/L of chlorine. The disinfection effect showed that the inactivation rate with 2.0 mg/L of chloramine (90%) was higher than that with chlorine (70%). Experimental results indicated that the high particle concentration in raw water and sedimentation effluent led to high levels of outflowing particles in the sand filter effluent. The activated carbon fines in the effluent accounted for a small proportion of the total particle amount, but the existing bacteria attached to carbon fines may influence the drinking water safety. The disinfection efficiency of desorbed bacteria was lower than that of free bacteria with chlorine, and the disinfection effect on bacteria attached to carbon fines with chloramine was better than that with only chlorine.

Sequential ozone advanced oxidation and biological oxidation processes to remove selected pharmaceutical contaminants from an urban wastewater

Sequential treatments consisting in a chemical process followed by a conventional biological treatment, have been applied to remove mixtures of nine contaminants of pharmaceutical type spiked in a primary sedimentation effluent of a municipal wastewater. Combinations of ozone, UVA black light (BL) and Fe(III) or Fe3O4 catalysts constituted the chemical systems. Regardless of the Advanced Oxidation Process (AOP), the removal of pharmaceutical compounds was achieved in 1 h of reaction, while total organic carbon (TOC) only diminished between 3.4 and 6%. Among selected ozonation systems to be implemented before the biological treatment, the application of ozone alone in the pre-treatment stage is recommended due to the increase of the biodegradability observed. The application of ozone followed by the conventional biological treatment leads high TOC and COD removal rates, 60 and 61%, respectively, and allows the subsequent biological treatment works with shorter hydraulic residence time (HRT). Moreover, the influence of the application of AOPs before and after a conventional biological process was compared, concluding that the decision to take depends on the characterization of the initial wastewater with pharmaceutical compounds.

기존하수처리장에서 자성체 이온교환수지를 이용한 하수처리공정 적용가능성 평가

The optimal removal efficiency to develop wastewater treatment system using the magnetic ion exchange resin. The secondary sedimentation effluent of wastewater in W wastewater treatment plant located in Gyeong-gi Province was used as the influent. To compare the sedimentation effluent reacted with the magnetic ion exchange resin to the influent, the concentrations of CODmm, TN, NO<SUB>3--</SUB>N and TP were measured. The flux of the influent and HRT were set to 250 mL/min, 10 min, respectively, and BVTR has adjusted to 200, 150, 100. The removal efficiency of CODmn, TN, NO<SUB>3--</SUB>N and TP in the 200 BVTR from 71%, 40.37%, 46.34%, 42.03%, 150 BVTR from 55.22%, 37.83%, 50.38% 41.6% and 100 BVTR from 74%, 59.15%, 79.94%, 79.16%, respectively. The results on 200 BVTR, 150 BVTR, 100 BVTR tests show that 100 BVTR is the optimal factor capable of the highest rate of rejection of the organic material.

Study on Adjustable Head Fall Mixer with Grids

The performance of adjustable head fall mixer is studied in a pilot experiment. Experimental results indicate that the dispersal efficiency increases with the space between grids and mixing pipe, which could be up to 96%. When the flow rate increases more than 31%, the dispersal efficiency decreases a little but still above 96%. It is demonstrated that special coagulant injection head makes significant contribution to improving the mixer efficiency. The almost same turbidity of sedimentation effluent could be achieved with less coagulant, thus 30% chemical can be saved. Dissolved oxygen increases 2.5 mg/L in the mixing unit, which will benefit the following processes.

Some ozone advanced oxidation processes to improve the biological removal of selected pharmaceutical contaminants from urban wastewater

Removal of nine pharmaceutical compounds—acetaminophen (AAF), antipyrine (ANT), caffeine (CAF), carbamazepine (CRB), diclofenac (DCF), hydrochlorothiazide (HCT), ketorolac (KET), metoprolol (MET) and sulfamethoxazole (SMX)—spiked in a primary sedimentation effluent of a municipal wastewater has been studied with sequential aerobic biological and ozone advanced oxidation systems. Combinations of ozone, UVA black light and Fe(III) or Fe3O4 constituted the chemical systems. During the biological treatment (hydraulic residence time, HRT = 24 h), only AAF and CAF were completely eliminated, MET, SMX and HCT reached partial removal rates and the rest of compounds were completely refractory. With any ozone advanced oxidation process applied, the remaining pharmaceuticals disappear in less than 10 min. Fe3O4 or Fe(III) photocatalytic ozonation leads to 35% mineralization compared to 13% reached during ozonation alone after about 30-min reaction. Also, biodegradability of the treated wastewater increased 50% in the biological process plus another 150% after the ozonation processes. Both untreated and treated wastewater was non-toxic for Daphnia magna (D. magna) except when Fe(III) was used in photocatalytic ozonation. In this case, toxicity was likely due to the ferryoxalate formed in the process. Kinetic information on ozone processes reveals that pharmaceuticals at concentrations they have in urban wastewater are mainly removed through free radical oxidation.

Uptake of 210Po by aquatic plants of a fresh water ecosystem around the uranium mill tailings management facility of Jaduguda, India

Purpose: The present study was designed to investigate the uptake of Polonium-210 (210Po) by aquatic plants growing in a fresh water ecosystem around the tailings management facility of the uranium industry of Jaduguda, India. Evaluation of the activity concentration of 210Po in aquatic plants, the concentration ratio of 210Po from substrate to plants and the relationship of 210Po with other stable elements were major objectives of the investigation.Materials and methods: Based on the habitat, three types of plant were collected and analyzed for 210Po activity estimation. Along with aquatic plants, effluent, surface water and bottom sediment were also collected and analyzed for 210Po activity content. From the acid solution 210Po was electrodeposited on brightly polished silver discs and counted for alpha activity in an alpha counter.Results: The highest 210Po activity concentration (4884 Bq kg−1 fresh weight) was found in filamentous algae from residual water of the tailings pond. For sediment-rooted plants, a significant positive correlation (r = 0.91, p < 0.0001) was observed between plant and sediment activity concentration of 210Po.Conclusions: For all of the three different groups of plants studied, highly significant correlations were observed between activity concentration of 210Po and Cu with the significance level variation between 0.00–0.05 (both for linear and log transformed data).

Treatment of low-turbidity source water by permanganate pre-oxidation: In situ formed hydrous manganese dioxide as filter aid

This pilot study investigated the effects of in situ formed manganese dioxide (in situ δMnO2), produced from KMnO4 reduction, on the removal efficiency for turbidity and particles and the run length of filters through this pilot-scale study. The sedimentation effluent showed an insignificant difference in turbidity but a remarkable decrease in particle concentration after dosing KMnO4. The residual particle concentration decreased from 1504units/mL to 359, 302, 164units/mL in the anthracite filter effluent and from 994units/mL to 219, 134, 99units/mL in the granular activated carbon (GAC) effluent at KMnO4 dosages of 0.2, 0.3, and 0.4mg/L respectively. However, this effect was achieved at the expense of a rapid increase of water head loss (WHL), and the average run length decreased from 70h to 54, 52, and 48h accordingly. After dosing KMnO4 at 0.2, 0.3, and 0.4mg/L, the contributive ratios of the uppermost 200mm layers on WHL increased from 68.5% to 81.9%, 76.0%, and 82.2%, respectively.

Effect of antecedent conditions and fixed rock fragment coverage on soil erosion dynamics through multiple rainfall events

The effect of antecedent conditions and specific rock fragment coverage on precipitation-driven soil erosion dynamics through multiple rainfall events was investigated using a pair of 6-m × 1-m flumes with 2.2% slope. Four sequential experiments – denoted E1, E2, E3 and E4, involved 2-h precipitation (rates of 28, 74, 74 and 28 mm h-1, respectively) and 22 h without rainfall – were conducted. In each experiment, one flume was bare while the other had 40% rock fragment coverage. The soil was hand-cultivated and smoothed before the first event (E1) only, and left untouched subsequently. Sediment yields at the flume exit reached steady-state conditions over time scales that increased with sediment size. Experiments were designed such that both steady and non-steady effluent sediment yields were reached at the conclusion of E1. Results from subsequent experiments showed that short-time soil erosion was dependent on whether steady-state erosion was achieved during the preceding event, although consistent steady-state effluent sediment yields were reached for each sediment size class. Steady-state erosion rates were, however, dependent on the rainfall intensity and its duration. If steady-state sediment yields were reached for a particular size class, that class’s effluent sediment yield peaked rapidly in the next rainfall event. The early peak was followed by a gradual decline to the steady-state condition. On the other hand, for size classes in which steady state was not reached at the end of the rainfall event (i.e., E1), in the following event (E2), the sediment yields for those classes increased gradually to steady state, i.e., the sharp peak was not observed. The effect of rock fragment cover (40%) on the soil surface was also found to be significant in terms of the time to reach steady state, i.e., their presence reduced the time for steady conditions to be attained. Effluent sediment yields for the bare and rock fragment-covered flumes (E1) showed steady conditions were reached for the latter, in contrast to the former. We used the Hairsine-Rose (H-R) model to simulate the experimental data as it explicitly models soil particle size classes. Experiments E1 and E2 involved soil compaction by raindrops, and in this case the model predictions were found to be unsatisfactory. However, compaction was effectively completed by the end of experiment E2, and the model provided reasonable predictions for experiments E3 and E4.

Evaluation of a laboratory-scale bioreactive in situ sediment cap for the treatment of organic contaminants

The development of bioreactive sediment caps, in which microorganisms capable of contaminant transformation are placed within an in situ cap, provides a potential remedial design that can sustainably treat sediment and groundwater contaminants. The goal of this study was to evaluate the ability and limitations of a mixed, anaerobic dechlorinating consortium to treat chlorinated ethenes within a sand-based cap. Results of batch experiments demonstrate that a tetrachloroethene (PCE)-to-ethene mixed consortium was able to completely dechlorinate dissolved-phase PCE to ethene when supplied only with sediment porewater obtained from a sediment column. To simulate a bioreactive cap, laboratory-scale sand columns inoculated with the mixed culture were placed in series with an upflow sediment column and directly supplied sediment effluent and dissolved-phase chlorinated ethenes. The mixed consortium was not able to sustain dechlorination activity at a retention time of 0.5 days without delivery of amendments to the sediment effluent, evidenced by the loss of cis-1,2-dichloroethene ( cis-DCE) dechlorination to vinyl chloride. When soluble electron donor was supplied to the sediment effluent, complete dechlorination of cis-DCE to ethene was observed at retention times of 0.5 days, suggesting that sediment effluent lacked sufficient electron donor to maintain active dechlorination within the sediment cap. Introduction of elevated contaminant concentrations also limited biotransformation performance of the dechlorinating consortium within the cap. These findings indicate that in situ bioreactive capping can be a feasible remedial approach, provided that residence times are adequate and that appropriate levels of electron donor and contaminant exist within the cap.

Volumetric Filtration of Rainfall Runoff. I: Event-Based Separation of Particulate Matter

As a unit operation, filtration generally requires flow equalization and primary clarification. This study examines the separation of runoff particulate matter (PM) in a volumetric clarifying filter (VCF). The VCF is a detention/retention vault integrating filtration after sedimentation. A paved source area (1,088m2) directly loaded the vault (4.2m3) with five radial filters (4m2 of filtration surface area). PM separation was examined for 19 runoff events through monitoring of influent and effluent granulometric fractions. During the monitoring phase no maintenance was conducted and subsequent to the 19 events a measured material balance of the sedimentation vault and the radial cartridge filters generated a 94% recovery of PM. During 5 months of monitoring and PM mass, suspended sediment concentration (SSC) was reduced from 334 to 34 mg/L (90% reduction) with effluent sediment (>75μm) of <3 mg/L, settleable of 14 mg/L, suspended PM (<25μm) of 17 mg/L as event mean concentrations; with turbidity reduced from 96 to 23 NTU (76% reduction). Based on separate PM recovery from the vault and filters, 77% of the PM separation was sedimentation in the vault and 23% as filtration. Captured particle-size distributions are heterodisperse with a d50m of 300 μm in the vault and a d50m that ranged from 34 to 63 μm with filter depth. Filter forensics indicated PM capture was nonuniform, with the bottom and middle most heavily loaded by PM as compared to the upper third of the filter. While paired testing of automatic and manual sampling produced similar median effluent SSC, automatic sampling significantly misrepresented the median influent PM as SSC (p⩽α=0.05).

Assessment of human adenovirus removal in a full-scale membrane bioreactor treating municipal wastewater

Human adenoviruses (HAdVs) in wastewater samples taken from four different treatment stages of a full-scale municipal wastewater treatment plant (i.e., incoming raw sewage, primary sedimentation effluent, membrane bioreactor (MBR) influent, and MBR effluent) were quantified by real-time PCR assays to further estimate removal efficiency of the HAdVs. Based on hexon gene sequence comparisons, HAdV species A, C, and F were consistently found in the wastewater samples. In general, all three identified HAdV species were detected in most of the wastewater samples using the real-time PCR assays. Overall HAdV concentrations were rather stable over the entire 8-month study period (January–August, 2008) (approximately 10 6–10 7 viral particles/L of wastewater for the raw sewage and primary effluent; 10 8–10 9 viral particles/L for the MBR influent; and, 10 3–10 4 viral particles/L for the MBR effluent). No significant seasonal differences were noticed for the HAdV abundances. Removal efficiencies of the viral particles in the full-scale MBR process were assessed and showed an average HAdV removal of 5.0 ± 0.6 logs over the study period. The removal efficiencies for F species (average log removal of 6.5 ± 1.3 logs) were typically higher ( p-value <0.05) than those of the other two species (average of 4.1 ± 0.9 and 4.6 ± 0.5 logs for species A and C, respectively). These results demonstrate that the full-scale MBR system efficiently removed most HAdV from the wastewater leaving about 10 3 viral particles/L in the MBR effluent.

The substitution of sand filtration by immersed-UF for surface water treatment: pilot-scale studies

The newly issued National Drinking Water Standard required that turbidity should be lower than 1 NTU, and the substitution of sand filtration by immersed ultrafiltration (immersed-UF) is feasible to achieve the standard. This study aimed to optimise the operational processes (i.e. aeration, backwashing) through pilot scale studies, to control membrane fouling while treating the sedimentation effluent. Results indicated that the immersed-UF was promising to treat the sedimentation effluent. The turbidity was below 0.10 NTU, bacteria and E. coli were not detected in the permeate water. The intermittent filtration with aeration is beneficial to inhibit membrane fouling. The critical aeration intensity is observed to be 60.0 m(3) m(-2) h(-1). At this aeration intensity, the decline rate of permeate flux in one period of backwashing was 1.94% and 7.03% for intermittent filtration and sustained filtration respectively. The different membrane backwashing methods (i.e. aeration 1.5 min, synchronous aeration and water backwashing 2 min, water backwashing 1.5 min; synchronous aeration and water backwashing 3 min, water backwashing 2 min; aeration 3 min, single water backwashing 2 min; synchronous aeration and water backwashing 5 min; single water backwashing 5 min) on the recovery of permeate flux were compared, indicating that the synchronous aeration and water backwashing exhibited best potential for permeate flux recovery. The optimal intensity of water backwashing is shown to be 90.0 L m(-2) h(-1). When the actual water intensity was below or exceeded the value, the recovery rate of permeate flux would be reduced. Additionally, the average operating cost for the immersed UF membrane, including the power, the chemical cleaning reagents, and membrane modules replacement, was about 0.31 RMB/m(3).