High Molecular Weight Organics Research Articles

Moderate pre-photocatalysis-enhanced coagulation alleviates ultrafiltration membrane fouling of algae-laden water

Moderate chemical pre-oxidation of coagulation to remove algae without breakage of the algae cells and release of algal organic matter has been well reported, while little was known about moderate pre-photocatalysis followed by coagulation on the ultrafiltration performance and membrane fouling control during algae-laden water treatment. Herein, three pretreatment methods (photocatalysis, coagulation and moderate pre-photocatalysis-enhanced coagulation (PC)) were investigated to reduce membrane fouling during ultrafiltration of algae-laden water. Moderate photocatalysis by a composite of Bi2O3-TiO2/PAC (Bi-doped TiO2 nano-composites supported by powdered activated carbon) not only avoided algae cell breakage and controlled the release of intracellular organic matter, but also halved the aluminum sulphate (AS) coagulant dosage, since Bi2O3-TiO2/PAC acted as both a photocatalyst and flocculation core. Under optimal conditions (1.2 g/L Bi2O3-TiO2/PAC irradiated under visible light for 20 min and 0.1 mM AS), the removal of OD680, DOC and UV254 were 83.8 %, 60.3 % and 77.3 % respectively. Moderate photocatalysis degraded medium and high molecular weight organics (biopolymers, humic substances and building blocks) to low MW acidic and neutral organics, resulting in effective removals of humic substances and microbial metabolites typically present in algal-derived pollutant. Following PC pre-treatment with ultrafiltration, 87.5 % increase in the final specific flux, 96.1 % reduction in irreversible resistance, and a change in the fouling mechanism from cake layer blockage to intermediate blockage. In addition, the zeta potential was reduced and the interaction force between pollutant-pollutant/membrane became a repulsive force. This work demonstrates the potential benefits of moderate pre-photocatalysis-enhanced coagulation to remove algal contaminants and mitigate ultrafiltration membrane fouling.

Alleviating Ultrafiltration Membrane Fouling Caused by Effluent Organic Matter Using Pre-Ozonation: A Perspective of EEM and Molecular Weight Distribution.

Wastewater reclamation has gradually become an important way to cope with the global water crisis. Ultrafiltration plays an imperative part as a safeguard for the aim but is often limited by membrane fouling. Effluent organic matter (EfOM) has been known to be a major foulant during ultrafiltration. Hence, the primary aim of this study was to investigate the effects of pre-ozonation on the membrane fouling caused by EfOM in secondary wastewater effluents. In addition, the physicochemical property changes of EfOM during pre-ozonation and the subsequent influence on membrane fouling were systemically investigated. The combined fouling model and the morphology of fouled membrane were adopted to scrutinize the fouling alleviation mechanism by pre-ozonation. It was found that membrane fouling by EfOM was dominated by hydraulically reversible fouling. In addition, an obvious fouling reduction was achieved by pre-ozonation with 1.0 mg O3/mg DOC. The resistance results showed that the normalized hydraulically reversible resistance was reduced by ~60%. The water quality analysis indicated that ozone degraded high molecular weight organics such as microbial metabolites and aromatic protein and medium molecular weight organics (humic acid-like) into smaller fractions and formed a looser fouling layer on the membrane surface. Furthermore, pre-ozonation made the cake layer foul towards pore blocking, thereby reducing fouling. In addition, there was a little degradation in the pollutant removal performance with pre-ozonation. The DOC removal rate decreased by more than 18%, while UV254 decreased by more than 20%.

Cobalt oxide decorated activated carbon/peroxymonosulfate pretreatment for ultrafiltration membrane fouling control in secondary effluent treatment: Insights into interfacial interaction and fouling model transformation

To control the ultrafiltration (UF) membrane fouling caused by the secondary effluent, cobalt oxide loaded activated carbon (CoOx-PAC) activating peroxymonosulfate (PMS) was applied as a pretreatment. The degradation of natural organic matter (NOM) and membrane fouling mitigation performance for the CoOx-PAC/PMS pretreatment were comprehensively investigated. The dissolved organic carbon (DOC), fluorescent organics, and phenol in the secondary effluent system were utilized to evaluate the removal effect of the CoOx-PAC/PMS process on the organic matter. Results showed that 100 mg/L 0.5 %CoOx-PAC combined with 2 mM PMS (0.5 %CoOx-PAC/PMS) had an excellent degradation on NOM, removing 84.92 % of DOC, and above 97 % of fluorescent organics within 120 min. The catalytic activity of phenol in this process was even superior to that of homogeneous catalysis (Co2+/PMS). Moreover, the normalized specific flux and membrane fouling resistance were employed to verify the influences of the CoOx-PAC/PMS on membrane fouling. The 0.5 %CoOx-PAC/PMS system significantly improved the specific flux, with a 94.26 % decline in reversible membrane fouling resistance and a 53.05 % reduction in irreversible fouling resistance. O2•− and 1O2 were involved in the reaction as crucial reactive oxide species according to electron paramagnetic resonance and quenching tests. They changed the physicochemical properties of NOM, which decomposed the high molecular weight organics into low molecular weight hydrophilic fractions, thereby delaying the formation of cake layers and alleviating membrane fouling. The Extended Derjaguin-Landau-Verwey-Overbeek theory was used to assess the interaction between the foulants and the UF membranes. The transformation of fouling models was analyzed and found that the intricate membrane fouling filtration mechanisms were transformed into a single standard blocking mode after 0.5 %CoOx-PAC/PMS pretreatment.

Interaction of operating HRT and temperature on fouling of tertiary membranes treating municipal wastewater

This paper presents the first study to quantify and demonstrate the interactions between SBR operating conditions (hydraulic retention time (HRT) and temperature) and soluble microbial product (SMP) generation, as well as the impact of SBR operating conditions and filtration temperature on fouling of membranes used in tertiary treatment. Reducing SBR operating HRT from 20 to 10 h resulted in an increase in SMP concentrations, however, the extent of the increase in high and low molecular weight (MW) organics was different for the effluents from SBRs operated at 8 and 20 °C. Results of SMP modelling demonstrated that a reduction in SBR operating HRT induced decreased utilization associated product (UAP) yields and the influence was greater at the SBR operating temperature of 8 °C. In contrast, biomass associated product (BAP) yields were relatively stable with SBR operating HRT but greater at lower SBR operating temperature. The effects of SBR operating HRT and temperature on fouling indices were also interactive. Reducing SBR operating HRT led to a lower increase in hydraulically reversible resistances and a greater increase in hydraulically irreversible resistances for the effluent from the SBR operated at 8 °C. Reducing the filtration temperature resulted in additional increase in membrane resistances, and the increase was greater at lower SBR operating HRT. The contribution of filtration temperature was observed to have the greatest impact on membrane resistances, followed in importance by SBR operating HRT and temperature. The comprehensive analysis undertaken in the present study provides insights into the interaction between secondary and tertiary operations on fouling development. The results can be employed to understand the limits of fouling control for tertiary treatment under challenging conditions.

Degradation performance of high-concentration coking wastewater by manganese oxide ore acidic oxidation.

The degradation of coking wastewater using a manganese oxide ore acidic oxidation was investigated. This work was performed in three stages. Firstly, the advantageous degradation conditions were measured by the degradation tests, and under the optimal conditions percentage degradation was obtained of 91.6% chemical oxygen demand measured by potassium dichromate oxidation (CODcr), 94.7% total nitrogen (TN), 98.3% phenols, 98.2% fatty acid, 89.5% tar, and 98.9% sulphide for the oxidized effluent, simultaneously cogenerating a Mn2+concentration of 46.2 g/L for Mn-electrolytic stock solution. Secondly, the transformation analysis of the special chemical group of coking wastewater contaminants illustrated that the employment of manganese oxide ore generated the degradation of low and high molecular weight organics, especially causing polymers to break down into oligomers. Thirdly, the electrochemical characteristics of the interface between wastewater and ore revealed that the contaminant degradation of coking wastewater greatly depended on the oxidation capacity of the surface oxide species, involving a simple answer to the MnO2 oxidation for small-molecule organic materials and a strengthening response to the MnO·OH oxidation for high-weight molecule organic substances. The treatment of coking wastewater using the Mn-oxide ore acidic oxidation process is an effective and value-added method, which is particularly applicable to high-concentration coking wastewater.

Evaluation of the impact of SBR operating temperature and filtration temperature on fouling of membranes used for tertiary treatment

Ultrafiltration (UF) is a cost-effective technology for water reclamation, however, its use in tertiary filtration in cold climates is impacted by changes in secondary effluent characteristics and membrane properties under low temperatures. In the present study, a series of filtration tests with the effluents from sequencing batch reactors (SBR) were conducted to evaluate the impact of SBR operating temperature and UF filtration temperature on fouling of membranes used for tertiary treatment. The results demonstrated increased total membrane resistances of 27%, 45% and 82% over multiple filtration cycles when the SBR operating temperature was 20, 14 and 8 ℃, respectively. The greater total membrane resistance at low SBR operating temperatures was attributed to increased hydraulically reversible and irreversible resistances. Moreover, a reduction in filtration temperature induced 55% and 122% increases in total membrane resistance when compared to a filtration temperature of 20 ℃, with the effluents from the SBRs operated at 14 and 8 ℃, respectively. The greater total membrane resistance at low filtration temperature was attributed to increased intrinsic resistance and the greater retention of hydraulically reversible and irreversible foulants. Pearson correlation revealed that the fouling of membranes used for tertiary treatment was governed by both high and low molecular weight organics, which were generated to a greater extent at low SBR operating temperatures. In addition, the generation of biomass associated products (BAP) was greatly affected by SBR operating temperature resulting in higher fouling potential at lower temperatures. The outcomes of the present study provide insights into the effects of operating temperature on biological and filtration processes that influence the fouling behavior of membranes used for tertiary treatment and can be employed to assist with the design of fouling mitigation measures in cold climates.

Regulated-biofilms enhance the permeate flux and quality of gravity-driven membrane (GDM) by in situ coagulation combined with activated alumina filtration

It is a critical challenge for drinking water production when treating algae-contaminated surface water. In this study, the impact of in situ coagulation (C), activated alumina filtration (AA) and their combination (CAA) on the performance of gravity-driven membrane (GDM) was systematically assessed during 105-day operation. The results indicated that pretreatments in particular CAA could effectively enhance GDM flux, and the stable fluxes were increased to 3.1, 4.9 and 8.3 L/(m2·h) (LMH) for CGDM, AA/GDM and CAA/GDM, respectively when compared to the control GDM (2.0 LMH). Coagulation was beneficial to formation of thick but loose biofouling layer, while AA filtration was effective to retain foulants including extracellular polymeric substances (EPS), organics, total nitrogen and total phosphorus. The CAA/GDM could mostly remove these foulants, and facilitate the proliferation of bacterial genera that could consume EPS, further alleviating membrane fouling. The difference in loosely bound EPS and tightly bound EPS of biofouling layer attributed to the difference of reversible fouling and irreversible fouling, respectively. Morphological observations, variation in functional groups or elements further confirmed the difference in biological layers in different GDM systems. The occurrence of specific bacterial genera involving the potential to degrade protein, chitin and other high molecular weight organics was responsible for contaminant removals.

Self-forming dynamic membrane filtration for drinking water treatment

Abstract Lab-scale continuous operation of self-forming microfiltration (MF) or ultrafiltration (UF) dynamic membranes were investigated simultaneously by applying iron oxide as an alternative treatment option in those waters having natural organic matter (NOM), iron and manganese. Both dynamic membranes gave high removal rates and effluent concentrations of pollutants were below the limit values in synthetic water. 60 and 62% (of DOC) and 75 and 78% (of UV254) were removed in low dissolved organic carbon (DOC) synthetic (LS) water by MF and UF dynamic membranes, respectively. Although only 42 and 49% (of DOC) and 48 and 53% (of UV254) could be removed by MF and UF dynamic membranes, respectively, a remarkable effect on fouling alleviation was observed in high DOC synthetic (HS) water. Iron oxide did not enhance the removal of organic matter in low DOC natural (LN) water as much as it did in synthetic water. Iron oxide led to the removal of high molecular weight organics, thus reversible fouling was reduced almost 2 orders of magnitude through both types of dynamic membranes in high DOC natural (HN) water. Reversible and irreversible resistances were reduced by iron oxide to some extent in LN water. Nevertheless the effect of iron oxide on fouling alleviation was much higher in HN rather than in LN water.

Treatment of petroleum wastewater contaminated with hydrocarbons and inorganics by anoxic-aerobic sequential moving bed reactors

The present study deals with the biotransformation of virulent petroleum refinery concoction with phenol (750 mg/L), emulsified crude oil (300 mg/L), S2− (750 mg/L), NH4+-N (350 mg/L) and NO3−-N (1000 mg/L) in anoxic (A1) - aerobic (A2) moving bed reactors operated in series. The efficacy of the system was analysed through measurement of pollutant concentrations, GC-MS and FTIR peaks of the influent and effluent, and biomass activity studies. The system was able to eliminate the organics and inorganics with more than 99% efficiency at 80 h HRT and 64 h cycle time. GC-MS results revealed breakage of high molecular weight organics to smaller compounds after anoxic treatment. Further treatment of anoxic effluent by aerobic biomass reduced the number of peaks in the final effluent significantly. FTIR results were in accord with the GC-MS results. Heterotrophic activity (HA) of the aerobic biomass was higher than anoxic biomass due to its higher free energy change. Anoxic biomass showed chemolithotrophic activity (CA), suggesting survival in the absence of organics. Gas generated from anoxic reactor consisted of 91% nitrogen, 1% CO2, 1% H2S and rest was unaccounted.

Sequential treatment for stabilized landfill leachate by ozonation–adsorption and adsorption–ozonation methods

This paper investigates the potential use of sequential treatment using ozonation–adsorption and adsorption–ozonation processes for stabilized landfill leachate treatment. Zeolite was used as adsorbent due to its novel composition of naturally hydrated aluminosilicate minerals. Preliminary tests were conducted to determine the optimum conditions of ozone and zeolite. Results demonstrated that the usage of ozonation as a post-treatment for adsorption could effectively remove 92%, 82%, and 75% of colour, COD, and NH4–N, respectively. In addition, the application of ozonation as a pre-treatment showed a good removal for colour, COD, and NH4–N with a removal efficiency of 93%, 80%, and 71%, respectively. Also, an improvement in biodegradability of the leachate was achieved after ozonation/adsorption and adsorption/ozonation which increases the BOD5/COD ratio from 0.016 to 0.195 and 0.194, respectively, where the maximum BOD5/COD in the raw leachate was 0.02. This is attributed to the oxidation of high molecular weight organics in the sample. A combined treatment leads to a removal of inorganic and small non-biodegradable organic molecules, which decreases the COD and further improve the BOD5/COD ratio. This study demonstrates that the application of ozonation as a pre- and post-treatment with zeolite is an effective treatment method that can improve the treatment of stabilized landfill leachate .

Innovative Treatment of Organic Contaminants in Reverse Osmosis Concentrate from Water Reuse: a Mini Review

Reverse osmosis concentrate (ROC) from wastewater reclamation in water reuse retains concentrated toxic bio-refractory organics, and developing technologies for their removal is essential. This paper reviews innovative treatment technologies for organic contaminants in the ROC, and treatment options for applications are proposed. To adequately manage ROC, volume reduction and quality improvement are important. Forward osmosis (FO) can reduce the ROC volume. Advanced oxidation processes (AOPs) result in degrading organic contaminants and producing biodegradable organics, but the reduction of energy consumption is required. Coagulation is an effective option as a pre-treatment of AOPs and can improve the biodegradability of ROC. Partial use of short-time AOPs can transform high molecular weight organics into relatively biodegradable organics. Among AOPs, a rotating advanced oxidation contactor (RAOC) can be an energy-saving technique for removing bio-refractory organics from ROC using solar light irradiation. Post-biological treatment can significantly save energy and efficiently eliminate biodegradable organics that are produced by AOPs. Microalgae cultivation is also an effective option for resource recovery from ROC. Considering the techniques, an integrated process comprising FO, pre-coagulation, short-time and/or solar-driven AOPs (e.g., RAOC), and post-biological treatment is proposed as an energy-saving and cost-effective technology for ROC treatment.

A comparison study of sand filtration and ultrafiltration in drinking water treatment: Removal of organic foulants and disinfection by-product formation.

A detailed comparison of sand filtration (SF) and ultrafiltration (UF) was conducted in this study with the aim to provide systematic support for alternative UF and SF technologies. The results of natural organic matter (NOM) removal indicated that SF conferred a slightly higher removal rate for UV-absorbing compounds, humic-like substances and protein-like substances than UF, with removal efficiencies of 21.9%, 19.8% and 26.1%, respectively. In addition, SF and UF exhibited different removal performances for organic fractions: UF better removed high molecular-weight (MW) organics, while SF exhibited higher removal of medium-MW organics. Furthermore, chlorine and chlorine dioxide were used as disinfectants to compare the different influences of SF and UF on disinfection by-product (DBP) formation. Unexpectedly, SF exhibited a better capacity for reducing the formation of chlorite than the UF process, with concentrations of 0.57 mg/L and 0.69 mg/L, respectively. Importantly, for the emergency scenario, e.g. seasonal algae pollution, the UF process achieved significantly higher removal of algae cells (98.7%) than SF due to size exclusion, indicating substantial resistance to algae load shocks. Therefore, these findings are beneficial for making practical decisions to adopt SF or UF technology in drinking water treatment plants.

Effect of Permanganate Preoxidation to Natural Organic Matter and Disinfection by-Products Formation Potential Removal

Laboratory scale experiments was conducted to examine effect of permanganate (KMnO4) peroxidation in characterizing and to remove natural organic matter (NOM) in source water. The experimental results shows that increasing permanganate dosage could decreased aromatic matter, as indicated by decreasing UV254 and SUVA value about 23% and 28%, respectively. It seems that permanganate preoxidation caused the breakdown of high molecular weight (MW) organics into low MW ones, as represented by increasing NPDOC about 10%. Further, disinfection by-products formation potential (DBPFP) in terms of trihalomethanes formation potential (THMFP) and haloacetic acid formation potential (HAAP) decreased about 15% and 23%, respectively. HAAFP removal is higher than THMFP removal and that DPBFP removal is consistent with UV254 and NPDOC removal.

Comparison between HPSEC-OCD and F-EEMs for assessing DBPs formation in water

ABSTRACTIn this study, natural organic matter (NOM) in source water, as well as the treated water after coagulation with or without potassium permanganate (KMnO4) preoxidation, was characterized by using high performance size exclusion chromatography with organic carbon detector (HPSEC-OCD) and fluorescence excitation emission matrices (F-EEMs) with parallel factor (PARAFAC) analysis. Bulk parameters, such as dissolved organic carbon (DOC) and ultraviolet light absorbance at 254 nm (UV254), were also analyzed. The results show that KMnO4 preoxidation caused the breakdown of high molecular weight (MW) organics into low MW organics. All organics, whether those that existed in the source water or those generated by KMnO4 preoxidation, could be partly removed by coagulation. Combining the derived organic fractions obtained from HPSEC-OCD with peak-fitting and from F-EEMs with PARAFAC on the same sample, humic substances have been specified as the main organic composition. Further, the predictive models for trihalomethanes formation potential (THMFP) and haloacetic acids formation potential (HAAFP) based on organic fractions from HPSEC-OCD have higher accuracy than those based on the components from PARAFAC modeling. These models provide useful tools to specify the organic fractions from HPSEC-OCD and F-EEMs that constitute active precursors towards trihalomethanes (THMs) or haloacetic acids (HAAs) formation in water. Further, by knowing the major organic precursors, it would facilitate choosing the appropriate water treatment process for disinfection by-products (DBPs) control.

Impact of ozonation, anion exchange resin and UV/H2O2 pre-treatments to control fouling of ultrafiltration membrane for drinking water treatment

ABSTRACTThe effects of ozonation, anion exchange resin (AER) and UV/H2O2 were investigated as a pre-treatment to control organic fouling (OF) of ultrafiltration membrane in the treatment of drinking water. It was found that high molecular weight (MW) organics such as protein and polysaccharide substances were majorly responsible for reversible fouling which contributed to 90% of total fouling. The decline rate increased with successive filtration cycles due to deposition of protein content over time. All pre-treatment could reduce the foulants of a Ultrafiltration membrane which contributed to the improvement in flux, and there was a greater improvement of flux by UV/H2O2 (61%) than ozonation (43%) which in turn was greater than AER (23%) treatment. This was likely due to the effective removal/breakdown of high MW organic content. AER gave greater removal of biofouling potential components (such as biodegradable dissolved organic carbon and assimilable organic carbon contents) compared to UV/H2O2 and ozonation treatment. Overall, this study demonstrated the potential of pre-treatments for reducing OF of ultrafiltration for the treatment of drinking water.

Removal of humic substances from reverse osmosis (RO) and nanofiltration (NF) concentrated leachate using continuously ozone generation-reaction treatment equipment

Concentrated leachate from membrane treatment process, which contains large amount of difficult-to-degrade humic substances, can induce potential hazards to ecological environment. In this study, the concentrated leachates from reverse osmosis (RO) and nanofiltration (NF) were treated by continuous ozone generating-reaction integrated equipment, and the removal characteristics of humic substances were analyzed using gel filtration chromatography (GFC), excitation-emission matrix fluorescence spectroscopy (EEM), XAD-8 resin fractionation, and Fourier transform infrared spectroscopy (FTIR). The results of XRD-8 fractionation and SUVA254 showed that the humic substances including humic acid (HA) and fulvic acid (FA), were effectively removed along with the breakdown of aromatic hydrocarbons and decrease in the degree of humification during the ozonation process. After 110min of reaction, HA in both concentrated leachates was completely removed. GFC analysis indicated that both concentrated leachates had much broader distribution after the degradation. The high molecular weight (MW) organic matter was transformed into low molecular weight of <10kDa. The majority of high MW organics in NF concentrate were converted to low MW molecules of 10kDa–1kDa, while those in RO concentrate were decomposed to small MW molecules of <1kDa. The results of EEM analysis implied that the degradation of HA and FA led to a significant decrease in the fluorescence intensity. Though the effluent of two concentrated leachate did not meet the maximum allowable criterion for leachate direct or indirect discharge standard in China, the composition and properties of organic matters in concentrated leachate were changed significantly after entire ozonation reaction, which would be conducive to the further biological treatment or other advanced treatment.

Effect of biological and coagulation pre-treatments to control organic and biofouling potential components of ultrafiltration membrane in the treatment of lake water

ABSTRACTBiological aerated filter (BAF), sand filtration (SF), alum and Moringa oleifera coagulation were investigated as a pre-treatment for reducing the organic and biofouling potential component of an ultrafiltration (UF) membrane in the treatment of lake water. The carbohydrate content was mainly responsible for reversible fouling of the UF membrane compared to protein or dissolved organic carbon (DOC) content. All pre-treatment could effectively reduce these contents and led to improve the UF filterability. Both BAF and SF markedly led to improvement in flux than coagulation processes, and alum gave greater flux than M. oleifera. This was attributed to the effective removal and/or breakdown of high molecular weight (MW) organics by biofilters. BAF led to greater improvement in flux than SF, due to greater breakdown of high MW organics, and this was also confirmed by the attenuated total reflection-Fourier transform infrared spectroscopy analysis. Coagulation processes were ineffective in removing biofouling potential components, whereas both biofilters were very effective as shown by the reduction of low MW organics, biodegradable dissolved organic carbon and assimilable organic carbon contents. This study demonstrated the potential of biological pre-treatments for reducing organic and biofouling potential component and thus improving flux for the UF of lake water treatment.

Using axial vibration membrane process to mitigate membrane fouling and reject extracellular organic matter in microalgae harvesting

Membrane fouling caused by algae cells and extracellular organic matter (EOM) is a major challenge in microalgae harvesting. In the present study, the axial vibration membrane (AVM) process can effectively reduce membrane fouling by increasing vibration frequency. An equation was obtained to explain why the vibration frequency has a more important impact on critical flux than the amplitude. During the continuous filtration, the flux decline rate was only 3.6% at the frequency of 10Hz and amplitude of 1cm. While at the frequency of 5 and 0Hz the decline rates were 34% and 64.2%, respectively. At high frequency, AVM can not only prevent the deposition of algae cells on membrane, but also reduce the adsorption of EOM on membrane. Scanning electron microscope and fourier transform infrared spectroscopy analysis showed that AVM can effectively reduce EOM adsorbing on membrane at 10Hz. AVM had better rejections of protein (28–39%) and polysaccharide (about 35%) at 10Hz, compared with 0 and 5Hz. Membranes had obvious rejection of low molecular weight EOM, regardless of at high or low frequency; however, compared to low frequency at high frequency AVM could reject more high molecular weight organics.

Single-particle characterization of biomass burning organic aerosol (BBOA): evidence for non-uniform mixing of high molecular weight organics and potassium

Abstract. Biomass burning organic aerosol (BBOA) can be emitted from natural forest fires and human activities such as agricultural burning and domestic energy generation. BBOA is strongly associated with atmospheric brown carbon (BrC) that absorbs near-ultraviolet and visible light, resulting in significant impacts on regional visibility degradation and radiative forcing. The mixing state of BBOA can play a critical role in the prediction of aerosol optical properties. In this work, single-particle measurements from a Soot-Particle Aerosol Mass Spectrometer coupled with a light scattering module (LS-SP-AMS) were performed to examine the mixing state of BBOA, refractory black carbon (rBC), and potassium (K, a tracer for biomass burning aerosol) in an air mass influenced by wildfire emissions transported from northern Québec to Toronto, representing aged biomass burning plumes. Cluster analysis of single-particle measurements identified five BBOA-related particle types. rBC accounted for 3–14 wt % of these particle types on average. Only one particle type exhibited a strong ion signal for K+, with mass spectra characterized by low molecular weight organic species. The remaining four particle types were classified based on the apparent molecular weight of the BBOA constituents. Two particle types were associated with low potassium content and significant amounts of high molecular weight (HMW) organic compounds. Our observations indicate non-uniform mixing of particles within a biomass burning plume in terms of molecular weight and illustrate that HMW BBOA can be a key contributor to low-volatility BrC observed in BBOA particles. The average mass absorption efficiency of low-volatility BBOA is about 0.8–1.1 m2 g−1 based on a theoretical closure calculation. Our estimates indicate that low-volatility BBOA contributes ∼ 33–44 % of thermo-processed particle absorption at 405 nm; and almost all of the BBOA absorption was associated with low-volatility organics.

Effect of NaCl concentration on the performance of sequential anaerobic and aerobic membrane bioreactors treating textile wastewater

This study aims at evaluating the performance of sequential anaerobic (AnMBR) and aerobic MBRs (AeMBR) treating synthetic textile wastewater containing varying concentrations (0–1000mg/L) of NaCl. High COD (up to 90%) and dye (⩾99%) removals were achieved in the AnMBR and increasing salinity did not significantly affect the process performance, although biomass concentrations decreased appreciably in both MBRs. In the AeMBR, although COD remaining in the effluent of the AnMBR was further degraded, dye concentration increased due to autooxidation of aromatic amines. A significant portion of the aromatic amines generated in the AnMBR was also degraded in the AeMBR. Gel permeation chromatography (GPC) analyses illustrated that high molecular weight organics generated in the AnMBR may be entrapped in the gel/cake layer developed on the membrane surface and salinity affected the molecular weight distribution of the organics. Relatively large organic molecules were detected in the external membrane foulants, which may originate from loosely bound EPS. Denaturing gradient gel electrophoresis (DGGE) analysis of 16S rDNA genes showed quite stable community structure in both MBRs. When AnMBR and AeMBR were operated at 4.2 LMH and 8.1 LMH, respectively, MBRs could be operated at low TMPs without any chemical cleaning for long durations. The biogas sparging rate significantly affected cake formation and TMP in the AnMBR. In both MBRs, chemical cleaning almost completely removed irreversible fouling.