Biopolymer fouling in dead-end ultrafiltration of treated domestic wastewater

Ultrafiltration (UF) is considered as a suitable treatment process after conventional wastewater treatment to produce reuse water. Nevertheless, fouling affects the performance of UF to a large extent. As biopolymers (mostly macro polysaccharide-like and protein-like molecules) have been identified as major foulants affecting the filterability of water in dead-end UF, the present study focuses on investigating the reversibility of biopolymer fouling occurring at different biopolymer mass loads to the membrane and under different compression conditions. UF-membrane stirred cell tests using five cycles show that filtering treated domestic wastewater leads to a significant permeability reduction due to the accumulation of biopolymers on the membrane surface and/or in the membrane pores. Although they can be removed by hydraulic backwashing, an increased mass load of biopolymers reduces the removal efficiency. This correlation was verified using a UF pilot plant filtering treated wastewater (secondary effluent or slow sand filtrate). The effect of biopolymer fouling layer deformation on its reversibility was studied using multi-cycle membrane filtration tests under different filtration pressures. The results showed that higher filtration pressures result in more compact biopolymer fouling which is more difficult to be hydraulically backwashed. This phenomenon was also confirmed by pilot-scale UF experiments.     

Application of ceramic membranes with pre-ozonation for treatment of secondary wastewater effluent

Membrane fouling is an inevitable problem when microfiltration (MF) and ultrafiltraion (UF) are used to treat wastewater treatment plant (WWTP) effluent. While historically the use of MF/UF for water and wastewater treatment has been almost exclusively focused on polymeric membranes, new generation ceramic membranes were recently introduced in the market and they possess unique advantages over currently available polymeric membranes. Ceramic membranes are mechanically superior and are more resistant to severe chemical and thermal environments. Due to the robustness of ceramic membranes, strong oxidants such as ozone can be used as pretreatment to reduce the membrane fouling. This paper presents results of a pilot study designed to investigate the application of new generation ceramic membranes for WWTP effluent treatment. Ozonation and coagulation pretreatment were evaluated to optimize the membrane operation. The ceramic membrane demonstrated stable performance at a filtration flux of 100 gfd (170 LMH) at 20 °C with pretreatment using PACl (1 mg/L as Al) and ozone (4 mg/L). To understand the effects of ozone and coagulation pretreatment on organic foulants, natural organic matter (NOM) in four waters - raw, ozone treated, coagulation treated, and ozone followed by coagulation treated wastewaters - were characterized using high performance size exclusion chromatography (HPSEC). The HPSEC analysis demonstrated that ozone treatment is effective at degrading colloidal NOMs which are likely responsible for the majority of membrane fouling.     

Identification of effluent organic matter fractions responsible for low-pressure membrane fouling

Anion exchange resin (AER), powder activated carbon (PAC) adsorption and ozonation treatments were applied on biologically treated wastewater effluent with the objective to modify the effluent organic matter (EfOM) matrix. Both AER and PAC led to significant total organic carbon (TOC) removal, while the TOC remained nearly constant after ozonation. Liquid Chromatography-Organic Carbon Detection (LC-OCD) analysis showed that the AER treatment preferentially removed high and intermediate molecular weight (MW) humic-like structures while PAC removed low MW compounds. Only a small reduction of the high MW colloids (i.e. biopolymers) was observed for AER and PAC treatments. Ozonation induced a large reduction of the biopolymers and an important increase of the low MW humic substances (i.e. building blocks).Single-cycle microfiltration (MF) and ultrafiltration (UF) tests were conducted using commercially available hollow fibres at a constant flux. After reconcentration to their original organic carbon content, the EfOM matrix modified by AER and PAC treatments exhibited higher UF membrane fouling compared to untreated effluent; result that correlated with the higher concentration of biopolymers. On the contrary, ozonation which induced a significant degradation of the biopolymers led to a minor flux reduction for both UF and MF filtration tests. Based on a single filtration, results indicate that biopolymers play a major role in low pressure membrane fouling and that intermediate and low MW compounds have minor impact. Thus, this approach has shown to be a valid methodology to identify the foulant fractions of EfOM.     

Effects of floc aluminum on activated sludge characteristics and removal of 17-α-ethinylestradiol in wastewater systems

The effects of floc aluminum (Al) on activated sludge performance and 17-α-ethinylestradiol (EE2) removal were studied using bench-scale activated sludge systems. The results showed that higher Al-fed activated sludge led to better settling, dewatering, and effluent quality with better EE2 removal. EE2 concentrations in the effluent revealed correlations with effluent suspended solids and large particulate/colloidal effluent biopolymer (protein + polysaccharide). Furthermore, a significant correlation existed between effluent proteins and EE2 for all size fractions, indicating that hydrophobic proteinaceous colloids provide binding sites for EE2 and washout together into the effluent. These results suggest that aluminum plays a crucial role in bioflocculation of activated sludge and the efficacy of flocculation influences the removal of endocrine disrupting compounds (EDCs) from wastewater treatment systems.     

混凝/砂滤结合GAC/UF法处理洗车废水的研究

采用混凝、沉淀-砂滤-GAC-UF工艺对洗车废水进行回用处理,结果表明该工艺的处理效果良好,出水水质可满足洗车水回用的水质要求。混凝、沉淀、砂滤预处理工艺对浊度、LAS和氨氮的去除效果较好,可大大减轻后续深度处理工艺的负荷,延缓GAC／UF反应器的堵塞进程;GAC单元对LAS的去除率〉70％,是整个系统去除LAS的主要单元;UF单元对浊度的去除率〉90％,是出水浊度的有效控制单元。采用该工艺处理洗车废水并回用,每年可节省费用约1．2万元,经济效益显著。     

Identification and quantification of major organic foulants in treated domestic wastewater affecting filterability in dead-end ultrafiltration

Ultrafiltration (UF) membranes can be used after conventional wastewater treatment to produce particle free and hygienically safe water for reuse. However, membrane fouling affects the performance of UF to a large extent. Stirred cell tests with UF membrane show high flux decline filtering treated domestic wastewater. Investigation on the impact of size fractioned substances indicates that dissolved substances are major foulants affecting water filterability. Dissolved organic substances in feed and permeate samples of the stirred cell tests are analyzed by liquid chromatography with online organic carbon detection (LC-OCD). The resulting chromatograms displayed a significant difference of feed and permeate samples in the range of large molecules identified as biopolymer peak. The substances detected in this peak (mostly macro polysaccharide-like and protein-like molecules) are almost completely retained by UF membranes. Quantified investigation shows that biopolymer concentration influences filterability of corresponding water sample proportionally. The apparent magnitude of delivered biopolymer to membrane has a striking correlation with fouling resistance. The relationship was verified to be reproducible using different water samples. Mechanism analysis demonstrates that based on the delivered biopolymer load to membrane pore blocking or cake/gel fouling is the main fouling mechanism in the present experiment conditions.     

Ultrafiltration of wastewater: effects of particles, mode of operation, and backwash effectiveness

The effects that wastewater quality and mode of operation have on the performance of an asymmetric, hollow fiber, polysulfone, ultrafiltration (UF) membrane with a molecular weight cutoff of 100,000 Daltons were investigated. Performance was assessed through monitoring membrane flux, transmembrane pressure, effluent biochemical oxygen demand, and operational cost of the experimental system while treating filtered secondary, secondary, and filtered primary effluents. Fluxes achieved for filtered secondary (129-173 l/m2 h), secondary (101-158 l/m2 h), and filtered primary (20-41 l/m2 h) effluents were compared to those obtained at three other locations where similar UF systems were operated. A conceptual model of the impact of an insufficient backwash and of operating the UF system at constant flux on membrane performance is presented to explain the differences in fluxes. Employing pre-membrane granular filtration to remove a portion of the problematic particles in secondary effluent prior to UF led to optimal operational conditions. The costs associated with the operation of pre-membrane granular filtration were offset by the increase in production achieved. Although the use of recirculation could increase maintainable flux when treating a concentrated feed (e.g., filtered primary effluent), the associated costs were high. Improved UF performance was found to result from allowing flux to decline naturally, rather than using a constant flux mode of operation. The effluents produced when filtered secondary and secondary effluents were the feeds would be equivalent to an oxidized, coagulated, clarified, and filtered wastewater as per Title 22 California Wastewater Reclamation Criteria.     

Low dose powdered activated carbon addition at high sludge retention times to reduce fouling in membrane bioreactors

The addition of a low concentration of PAC (0.5 g L⁻¹ of sludge, i.e. a dose of 4 mg L⁻¹ of wastewater), in combination with a relatively long SRT (50 days), to improve membrane filtration performance was investigated in two pilot-scale MBRs treating real municipal wastewater. Continuous filterability tests at high flux showed the possibility to run for 18 h at 72 L m⁻² h⁻¹ and 180 h at 50 L m⁻² h⁻¹, while significant fouling occurred without PAC. In addition, measurements of the critical flux showed an increase of 10% for this strategy. Low dosage and high retention time makes it feasible and cost effective. Further advantages with regard to permeate quality and possible micropollutants removal are currently under investigation.     

Occurrence and removal of N-nitrosamines in wastewater treatment plants

The presence of nitrosamines in wastewater might pose a risk to water resources even in countries where chlorination or chloramination are hardly used for water disinfection. We studied the variation of concentrations and removal efficiencies of eight N-nitrosamines among 21 full-scale sewage treatment plants (STPs) in Switzerland and temporal variations at one of these plants. N-nitrosodimethylamine (NDMA) was the predominant compound in STP primary effluents with median concentrations in the range of 5-20 ng/L, but peak concentrations up to 1 μg/L. N-nitrosomorpholine (NMOR) was abundant in all plants at concentrations of 5-30 ng/L, other nitrosamines occurred at a lower number of plants at similar levels. From concentrations in urine samples and domestic wastewater we estimated that human excretion accounted for levels of <5 ng/L of NDMA and <1 ng/L of the other nitrosamines in municipal wastewater, additional domestic sources for <5 ng/L of NMOR. Levels above this domestic background are probably caused by industrial or commercial discharges, which results in highly variable concentrations in sewage. Aqueous removal efficiencies in activated sludge treatment were in general above 40% for NMOR and above 60% for the other nitrosamines, but could be lower if concentrations were below 8-15 ng/L in primary effluent. We hypothesize that substrate competition in the cometabolic degradation explains the occurrence of such threshold concentrations. An additional sand filtration step resulted in a further removal of nitrosamines from secondary effluents even at low concentrations. Concentrations released to surface waters were largely below 10 ng/L, suggesting a low impact on Swiss water resources and drinking water generation considering the generally high environmental dilution and possible degradation. However, local impacts in case a larger fraction of wastewater is present cannot be ruled out.     

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 10⁶-10⁷ viral particles/L of wastewater for the raw sewage and primary effluent; 10⁸-10⁹ viral particles/L for the MBR influent; and, 10³-10⁴ 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 10³ viral particles/L in the MBR effluent.     

Chitosan and metal salt coagulant impacts on Cryptosporidium and microsphere removal by filtration

Maintenance of appropriate chemical pretreatment is a critical component of ensuring proper filtration performance. Pilot-scale in-line filtration studies were performed to investigate the relative impacts of chitosan, alum, and FeCl₃ coagulation on the removal of Cryptosporidium parvum oocysts and oocyst-sized polystyrene microspheres by granular media filtration. Similar removals of oocysts and microspheres were achieved when optimal coagulant doses were utilized. Sub-optimal alum and FeCl₃ coagulation resulted in a deterioration filter effluent turbidity (0.2-0.3 NTU) and total particle counts (30-100 total particles ≥2 μm/mL) that were accompanied by reduced (by ∼2-3-log) median oocyst and microsphere removals by filtration. At all doses investigated, chitosan coagulation resulted in excellent turbidity and particle reductions by filtration. Nonetheless, chitosan coagulation at doses of 0.1, 0.5, and 1.0 mg/L did not result in appreciable improvements in C. parvum oocyst removal relative to complete coagulation failure (median oocyst removals were <∼1-log). As well, oocyst-sized polystyrene microspheres appear to be reasonable indicators of C. parvum oocyst removal by in-line filtration preceded by alum and FeCl₃ coagulation, but not chitosan coagulation.     

Nutrient loading on subsoils from on-site wastewater effluent, comparing septic tank and secondary treatment systems

The performance of six separate percolation areas was intensively monitored to ascertain the attenuation effects of unsaturated subsoils with respect to on-site wastewater effluent: three sites receiving septic tank effluent, the other three sites receiving secondary treated effluent. The development of a biomat across the percolation areas receiving secondary treated effluent was restricted on these sites compared to those sites receiving septic tank effluent and this created significant differences in terms of the potential nitrogen loading to groundwater. The average nitrogen loading per capita at 1.0 m depth of unsaturated subsoil equated to 3.9 g total-N/d for the sites receiving secondary treated effluent, compared to 2.1 g total-N/d for the sites receiving septic tank effluent. Relatively high nitrogen loading was, however, found on the septic tank sites discharging effluent into highly permeable subsoil that counteracted any significant denitrification. Phosphorus removal was generally very good on all of the sites although a clear relationship to the soil mineralogy was determined.     

Removal of bacterial fecal indicators, coliphages and enteric adenoviruses from waters with high fecal pollution by slow sand filtration

The aim of the present study was to estimate the performance of slow sand filtration (SSF) facilities, including the time needed for reaching stabilization (maturation), operated with surface water bearing high fecal contamination, representing realistic conditions of rivers in many emerging countries. Surface water spiked with wastewater was infiltrated at different pore water velocities (PWV) and samples were collected at different migration distances. The samples were analyzed for phages and to a lesser extent for fecal bacteria and enteric adenoviruses. At the PWV of 50 cm/d, at which somatic phages showed highest removal, their mean log₁₀ removal after 90 cm migration was 3.2. No substantial differences of removal rates were observed at PWVs between 100 and 900 cm/d (2.3 log₁₀ mean removal). The log₁₀ mean removal of somatic phages was less than the observed for fecal bacteria and tended more towards that of enteric adenoviruses This makes somatic phages a potentially better process indicator than Escherichia coli for the removal of viruses in SSF. We conclude that SSF, and by inference in larger scale river bank filtration (RBF), is an excellent option as a component in multi-barrier systems for drinking water treatment also in areas where the sources of raw water are considerably fecally polluted, as often found in many emerging countries.     

Characterisation of organic matter in IX and PACl treated wastewater in relation to the fouling of a hydrophobic polypropylene membrane

Extensive organic characterisation of a wastewater using liquid chromatography with a photodiode array and fluorescence spectroscopy (Method A), and UV₂₅₄ and organic carbon detector (Method B) was undertaken, as well as with fluorescence excitation emission spectroscopy (EEM). Characterisation was performed on the wastewater before and after ion exchange (IX) treatment and polyaluminium chlorohydrate (PACl) coagulation, and following microfiltration of the wastewater and pre-treated wastewaters. Characterisation by EEM was unable to detect biopolymers within the humic rich wastewaters and was not subsequently used to characterise the MF permeates. IX treatment preferentially removed low molecular weight (MW) organic acids and neutrals, and moderate amounts of biopolymers in contrast to a previous report of no biopolymer removal with IX. PACl preferentially removed moderate MW humic and fulvic acids, and large amounts of biopolymers. PACl showed a great preference for removal of proteins from the biopolymer component in comparison to IX. An increase in the fluorescence response of tryptophan-like compounds in the biopolymer fraction following IX treatment suggests that low MW neutrals may influence the structure and/or inhibit aggregation of organic compounds. Fouling rates for IX and PACl treated wastewaters had high initial fouling rates that reduced to lower fouling rates with time, while the untreated Eastern Treatment Plant (ETP) wastewater displayed a consistent, high rate of fouling. The results for the IX and PACl treated wastewaters were consistent with the long-term fouling rate being determined by cake filtration while both pore constriction and cake filtration contributed to the higher initial fouling rates. Higher rejection of biopolymers was observed for PACl and IX waters compared to the untreated ETP water, suggesting increased adhesion of biopolymers to the membrane or cake layer may lead to the higher rejection.     

Transport and retention of a bacteriophage and microspheres in saturated, angular porous media: effects of ionic strength and grain size

Eight saturated column experiments were conducted to examine the effects of solution chemistry and grain size on the transport of colloids through crushed silica sand. Two sizes of colloids, 0.025-μm bacteriophage (MS-2) and 1.5-μm carboxylated microspheres, were used as surrogates for the transport of pathogenic viruses and bacteria, respectively. Increasing the Ca²⁺ concentration from 1 to 4.8 mM (along with background monovalent ions) resulted in complete attenuation (>6-log decrease in C/C₀) of MS-2, but caused only a 1-log reduction (C/C₀ = 0.1) in the concentration of the microspheres. Decreasing grain size from medium sand (d₅₀ = 0.70 mm) to fine sand (d₅₀ = 0.34 mm) resulted in substantial decreases in effluent concentrations of both the MS-2 (5-log decrease) and microspheres (>2.5-log decrease). Comparison of observed colloid retention to that predicted by a recently published correlation equation for colloid filtration revealed that the model can considerably underpredict (by 4 orders of magnitude or more) colloid retention by angular sand over distances as short as 20 cm. This indicates that state-of-the-art colloid filtration models are still limited in applicability to natural systems.     

油田采出液除铁用于配注聚合物工程改造

原采出液除铁工艺采用多相流泵/锰砂过滤工艺,由于混合污水中溶解氧浓度低,氧化反应时间短,导致工艺出水Fe2+浓度未达到设计要求。改造工程采用催化曝气氧化/改性锰砂过滤新工艺,曝气氧化时间为50 min。运行结果表明,工艺出水Fe2+浓度为0.3～0.5 mg/L,注聚井口聚合物粘度>45 mPa.s,各项指标满足设计要求。     

南郊水厂超滤膜组合工艺运行情况评价

分析并评价了东营市南郊水厂(10×104m3/d)以超滤为核心的水质改善工程一年来的运行情况.生产实践表明,超滤组合工艺出水水质较工程实施前有很大提升,超滤出水浊度保持在0.02 NTU以下,组合工艺对CODMn、UV254和TOC的平均去除率分别为(44.96±3.69)%、(43.22±2.21)%和(20.10±...     

Bacterial, viral and turbidity removal by intermittent slow sand filtration for household use in developing countries: experimental investigation and modeling

A two-factor three-block experimental design was developed to permit rigorous evaluation and modeling of the main effects and interactions of sand size (d₁₀ of 0.17 and 0.52 mm) and hydraulic head (10, 20, and 30 cm) on removal of fecal coliform (FC) bacteria, MS2 bacteriophage virus, and turbidity, under two batch operating modes (‘long’ and ‘short’) in intermittent slow sand filters (ISSFs). Long operation involved an overnight pause time between feeding of two successive 20 L batches (16 h average batch residence time (RT)). Short operation involved no pause between two 20 L batch feeds (5 h average batch RT). Conditions tested were representative of those encountered in developing country field settings. Over a ten week period, the 18 experimental filters were fed river water augmented with wastewater (influent turbidity of 5.4-58.6 NTU) and maintained with the wet harrowing method. Linear mixed modeling allowed systematic estimates of the independent marginal effects of each independent variable on each performance outcome of interest while controlling for the effects of variations in a batch’s actual residence time, days since maintenance, and influent turbidity. This is the first study in which simultaneous measurement of bacteria, viruses and turbidity removal at the batch level over an extended duration has been undertaken with a large number of replicate units to permit rigorous modeling of ISSF performance variability within and across a range of likely filter design configurations and operating conditions.On average, the experimental filters removed 1.40 log fecal coliform CFU (SD 0.40 log, N = 249), 0.54 log MS2 PFU (SD 0.42 log, N = 245) and 89.0 percent turbidity (SD 6.9 percent, N = 263). Effluent turbidity averaged 1.24 NTU (SD 0.53 NTU, N = 263) and always remained below 3 NTU. Under the best performing design configuration and operating mode (fine sand, 10 cm head, long operation, initial HLR of 0.01-0.03 m/h), mean 1.82 log removal of bacteria (98.5%) and mean 0.94 log removal of MS2 viruses (88.5%) were achieved.Results point to new recommendations regarding filter design, manufacture, and operation for implementing ISSFs in local settings in developing countries. Sand size emerged as a critical design factor on performance. A single layer of river sand used in this investigation demonstrated removals comparable to those reported for 2 layers of crushed sand. Pause time and increased residence time each emerged as highly beneficial for improving removal performance on all four outcomes. A relatively large and significant negative effect of influent turbidity on MS2 viral removal in the ISSF was measured in parallel with a much smaller weaker positive effect of influent turbidity on FC bacterial removal. Disturbance of the schmutzdecke by wet harrowing showed no effect on virus removal and a modest reductive effect on the bacterial and turbidity removal as measured 7 days or more after the disturbance. For existing coarse sand ISSFs, this research indicates that a reduction in batch feed volume, effectively reducing the operating head and increasing the pore:batch volume ratio, could improve their removal performance by increasing batch residence time.     

Effects of mass retention of dissolved organic matter and membrane pore size on membrane fouling and flux decline

Ultrafiltration (UF) fouling has been attributed to concentration polarization, gel layer formation as well as outer and inner membrane pore clogging. It is believed that mass of humic materials either retained on membrane surface or associated with membrane inner pore surface is the primary cause for permeate flux decline and filtration resistance build-up in water supply industries. While biofilm/biofouling and inorganic matter could also be contributing factors for permeability decline in wastewater treatment practices. The present study relates UF fouling to mass of dissolved organic matter (DOM) retained on membrane and quantifies the effect of retained DOM mass on filtration flux decline. The results demonstrate that larger pore membranes exhibit significant flux decline in comparison with the smaller ones. During a 24-h period, dissolved organic carbon mass retained in 10 kDa membranes was about 1.0 g m⁻² and that in 100 kDa membranes was more than 3 times higher (3.6 g m⁻²). The accumulation of retained DOM mass significantly affects permeate flux. It is highly likely that some DOMs bind or aggregate together to form surface gel layer in the smaller 10 kDa UF system; those DOMs largely present in inner pore and serving as pore blockage on a loose membrane (100 kDa) are responsible for severe flux decline.