可生物降解有机物在水厂净水工艺中的变化

以上海市两座不同水源的典型水厂为研究对象,分析了可生物降解有机物(BOM)和总有机物(以DOC表征)在水厂常规净水工艺中的变化规律.结果表明,水厂常规工艺对AOC、BDOC与DOC的去除能力均不高,且受水温影响明显,两水厂出水均为生物不稳定性饮用水;DOC主要在沉淀单元被去除,BDOC在沉淀、砂滤单元都有去除,AOC则主要在砂滤单元被去除;加氯可造成DOC(或BDOC)向AOC的转化,使出厂水AOC浓度增加,要确保出厂水的生物稳定性,必须同步削减水中BOM与总有机物的浓度.     

Assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC):: complementary measurements

The objective of this study was to evaluate the necessity of measuring both assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC) as indicators of bacterial regrowth potential. AOC and BDOC have often been measured separately as indicators of bacterial regrowth, or together as indicators of bacterial regrowth and disinfection by-product formation potential, respectively. However, this study proposes that both AOC and BDOC should be used as complementary measurements of bacterial regrowth potential. In monitoring of full-scale membrane filtration, it was determined that nanofiltration (NF) removed over 90% of the BDOC while allowing the majority of the AOC through. Heterotrophic plate counts (HPC) remained low during the entire period of monitoring due to high additions of disinfectant residual. In a two-year monitoring of a water treatment plant that switched its treatment process from chlorination to chlorination and ozonation, it was observed that the plant effluent AOC increased by 127% while BDOC increased by 49% after the introduction of ozone. Even though AOC is a fraction of BDOC, measuring only one of these parameters can potentially under- or over-estimate the bacterial regrowth potential of the water.     

Membrane coagulation bioreactor (MCBR) for drinking water treatment

In this paper, a novel submerged ultrafiltration (UF) membrane coagulation bioreactor (MCBR) process was evaluated for drinking water treatment at a hydraulic retention time (HRT) as short as 0.5h. The MCBR performed well not only in the elimination of particulates and microorganisms, but also in almost complete nitrification and phosphate removal. As compared to membrane bioreactor (MBR), MCBR achieved much higher removal efficiencies of organic matter in terms of total organic carbon (TOC), permanganate index (COD(Mn)), dissolved organic carbon (DOC) and UV absorbance at 254nm (UV(254)), as well as corresponding trihalomethanes formation potential (THMFP) and haloacetic acids formation potential (HAAFP), due to polyaluminium chloride (PACl) coagulation in the bioreactor. However, the reduction of biodegradable dissolved organic carbon (BDOC) and assimilable organic carbon (AOC) by MCBR was only 8.2% and 10.1% higher than that by MBR, indicating that biodegradable organic matter (BOM) was mainly removed through biodegradation. On the other hand, the trans-membrane pressure (TMP) of MCBR developed much lower than that of MBR, which implies that coagulation in the bioreactor could mitigate membrane fouling. It was also identified that the removal of organic matter was accomplished through the combination of three unit effects: rejection by UF, biodegradation by microorganism and coagulation by PACl. During filtration operation, a fouling layer was formed on the membranes surface of both MCBR and MBR, which functioned as a second membrane for further separating organic matter.     

The effect of UV/H2O2 treatment on biofilm formation potential

Greater Cincinnati Water Works (GCWW) evaluated the efficacy of ultraviolet light/hydrogen peroxide advanced oxidation (UV/H₂O₂) for reducing trace organic contaminants in natural water with varying water qualities. A year-long UV/H₂O₂ pilot study was conducted to examine a variety of seasonal and granular activated carbon (GAC) breakthrough conditions. The UV pilot-scale reactors were set to consistently achieve 80% atrazine degradation, allowing comparison of low pressure (LP) and medium pressure (MP) lamp technologies for by-product formation. Because hydroxyl radicals react non-selectively with organic compounds, unintended by-product formation occurred.Total assimilable organic carbon (AOC) concentration increased through the reactors from 14 to 33% on average, depending on water quality. Natural organic matter (NOM) contains the precursors for AOC production, so when post-GAC water (versus conventionally treated water) served as reactor influent, less AOC was produced. No appreciable difference in AOC concentration was observed between LP and MP UV reactors. The Spirillum strain NOX fraction of the AOC increased from 50 to 65% on average, depending on the quality of the water. The increase in this fraction of AOC occurred because oxidation of NOM yielded smaller more assimilable organic compounds such as organic acids that are necessary for NOX growth. The Pseudomonas fluorescens strain P17 AOC concentration increased only when conventionally treated plant water was used as pilot influent. This organism thrives in waters of differing organic energy sources, but does not thrive well in carboxylic acids alone. The CONV water had more overall TOC that could contribute to higher P17 AOC counts.Biofilm coupon studies indicated that biofilms with greater heterotrophic plate counts were observed in the granular activated carbon (GAC) effluent streams receiving UV/H₂O₂ pre-treatment. Biofilm coupon studies additionally indicated that the effluent stream of the GAC column proceeded by the MP reactor exhibited more viable biofilm than the other GAC effluent streams based on an ATP-bioluminescence method. The increased viability of the biofilm produced by the MP UV reactor is likely a result of the multiple UV wavelengths and higher energy input characteristic of this technology.     

Advanced treatment of the reverse osmosis concentrate produced during reclamation of municipal wastewater

The work investigated the treatment of the concentrate produced from the reverse osmosis treatment of an MBR effluent. Two conventional chemical processes, coagulation and activated carbon adsorption, and three advanced oxidation processes (electrochemical treatment, photocatalysis and sonolysis) were applied. Coagulation with alum gave dissolved organic carbon (DOC) removals up to 42%, while FeCl(3) achieved higher removals (52%) at lower molar doses. Adsorption with granular activated carbon showed the highest DOC removals up to 91.3% for 5 g/L. The adsorption isotherm was linear with a non-adsorbable organic fraction of around 1.2 mg/L DOC. The three oxidation methods employed, electrolytic oxidation over a boron-doped diamond electrode, UVA/TiO2 photocatalysis and sonolysis at 80 kHz, showed similar behavior: during the first few minutes of treatment there was a moderate removal of DOC followed by further oxidation at a very slow rate. Electrolytic oxidation was capable of removing up to 36% at 17.8A after 30 min of treatment, sonolysis removed up to 34% at 135W after 60 min, while photocatalysis was capable of removing up to 50% at 60 min.     

Filter pore size selection for characterizing dissolved organic carbon and trihalomethane precursors from soils

Filters with a pore size of 0.45 microm have been arbitrarily used for isolating dissolved organic carbon (DOC) in natural waters. This operationally defined DOC fraction often contains heterogeneous organic carbon compounds that may lead to inconsistent results when evaluating trihalomethane formation potential (THMFP). A finer pore size filter provides more homogeneous DOC properties and enables a better characterization of organic matter. In this study, we examined the effects of filter pore size (1.2, 0.45, 0.1 and 0.025 microm) on characterizing total organic carbon, ultra-violet absorbance at 254 nm (UV(254)) and THMFP of water extracts from a mineral and organic soil in the Sacramento-San Joaquin Delta, California. Results showed that the majority of water extractable organic carbon (WEOC) from these soils was smaller than 0.025 microm, 85% and 57% in organic and mineral soils, respectively. A high proportion of colloidal organic carbon (COC) in mineral soil extracts caused water turbidity and resulted in an abnormally high UV(254) in 1.2 and 0.45 microm filtrates. The reactivity of organic carbon fractions in forming THM was similar for the two soils, except that COC from the mineral soil was about half that of others. To obtain a more homogeneous solution for characterizing THM precursors, we recommend a 0.1 microm or smaller pore-size filter, especially for samples with high colloid concentrations.     

Fractionation of dissolved organic matter from surface waters using macroporous resins

To obtain fractions enriched with biodegradable dissolved organic carbon (BDOC) or with organic compounds responsible for the chlorine demand (CID) and for trihalomethane formation potential (THMFP), Seine river water samples were percolated on various macroporous resins (anionic, cationic and non-ionic) and compared with granulated activated carbon (GAC). In addition, measurement of UV absorbance at 254 nm and the fluorescence index (λ_excitation 320 nm) had allowed to follow up the retention of dissolved organic matter by the different adsorbants. In contrast to cationic and non-ionic resins, anionic resins confirm their excellent retention capacity of organic compounds responsible for UV 254 absorbance and fluorescence index. The relative values of BDOC/DOC ratio (mg-C/mg-C) are slightly increased in the effluents of anionic resins, indicating that they retain a little preferentially the refractory fraction instead of the biodegradable fraction. There is no significant difference between the ratio of CID/DOC (mg-Cl₂/mg-C) in influent and effluent of anionic resins. Cationic resin has a low capacity for retention of DOC, but they seem to retain significantly the organic compounds responsible for CID. The capability of anionic resins to retain THMFP is similar to that of GAC.     

Impact of UV/H(2)O(2) advanced oxidation treatment on molecular weight distribution of NOM and biostability of water

The presence of natural organic matter (NOM) poses several challenges to the commercial practice of UV/H₂O₂ process for micropollutant removal. During the commercial application of UV/H₂O₂ advanced oxidation treatment, NOM is broken down into smaller species potentially affecting biostability by increasing Assimilable Organic Carbon (AOC) and Biodegradable Organic Carbon (BDOC) of water. This work investigated the potential impact of UV/H₂O₂ treatment on the molecular weight distribution of NOM and biostability of different water sources. A recently developed flow cytometric method for enumeration of bacteria was utilized to assess biological stability of the treated water at various stages through measurement of AOC. BDOC was also assessed for comparison and to better study the biostability of water. Both AOC and BDOC increased by about 3-4 times over the course of treatment, indicating the reduction of biological stability. Initial TOC and the source of NOM were found to be influencing the biostability profile of the treated water. Using high performance size exclusion chromatography, a wide range of organic molecule weights were found responsible for AOC increase; however, low molecular weight organics seemed to contribute more. Positive and meaningful correlations were observed between BDOC and AOC of different waters that underwent different treatments.     

Reduction of dissolved organic matter and trihalomethane formation potential during laboratory-scale soil-aquifer treatment

Dissolved organic matter (DOM) in recovered groundwater from soil-aquifer treatment (SAT) has the potential to generate harmful disinfection by-products. This study investigated the reduction of mass and trihalomethane formation potential (THMFP) of DOM fractions from secondary effluent during laboratory-scale SAT. Using XAD-8 and XAD-4 resins, DOM was fractionated into three fractions: hydrophobic acid (HPO-A), transphilic acid (TPI-A) and hydrophilic fraction (HPI). HPO-A was removed by 61.1%, TPI-A by 54.9% and HPI by 75.0% as dissolved organic carbon (DOC) during the laboratory-scale SAT, respectively. The reduction of THMFP from HPO-A, TPI-A and HPI was 27.24, 26.24 and 36.08%, respectively. Specific THMFP for each DOM fraction increased across the soil columns. HPO-A was found to be the major precursor of THMs. THMFP was strongly correlated to ultraviolet light at 254 nm (UV-254) for HPO-A and HPI, while the relationship between THMFP and UV-254 for TPI-A was significantly poor.     

Combination of ferric and MIEX for the treatment of a humic rich water

Seasonal periods of high rainfall have been shown to cause elevated natural organic matter (NOM) loadings at treatment works. These high levels lead to difficulties in removing sufficient NOM to meet trihalomethane (THM) standards, and hence better alternative treatments are required. Here the removal of NOM was investigated by a new ion exchange process (MIEX) using both bulk and fractionated NOM. Initial results showed that in excess of 80% of the raw water dissolved organic carbon (DOC) and greater than 85% of the UV absorbance from the bulk raw water could be removed by the use of MIEX alone. It was also seen that the removal of the more recalcitrant isolated fractions was increased. When MIEX was combined with a significantly reduced dose of coagulant a slight improvement on the overall DOC and UV removals was observed, however a significant decrease in the amount of THM formation potential (THMFP) in the final water was seen. This combined with the reduction in coagulant would imply a more efficient process during the times when the water becomes increasingly difficult to treat.     

Membrane bioreactor for the drinking water treatment of polluted surface water supplies

A laboratory membrane bioreactor (MBR) using a submerged polyethylene hollow-fibre membrane module with a pore size of 0.4 microm and a total surface area of 0.2 m2 was used for treating a raw water supply slightly polluted by domestic sewage. The feeding influent had a total organic carbon (TOC) level of 3-5 mg/L and an ammonia nitrogen (NH(3)-N) concentration of 3-4 mg/L. The MBR ran continuously for more than 500 days, with a hydraulic retention time (HRT) as short as 1h or less. Sufficient organic degradation and complete nitrification were achieved in the MBR effluent, which normally had a TOC of less than 2 mg/L and a NH(3)-N of lower than 0.2 mg/L. The process was also highly effective for eliminating conventional water impurities, as demonstrated by decreases in turbidity from 4.50+/-1.11 to 0.08+/-0.03 NTU, in total coliforms from 10(5)/mL to less than 5/mL and in UV(254) absorbance from 0.098+/-0.019 to 0.036+/-0.007 cm(-1). With the MBR treatment, the 3-day trihalomethane formation potential (THMFP) was significantly reduced from 239.5+/-43.8 to 60.4+/-23.1 microg/L. The initial chlorine demand for disinfection decreased from 22.3+/-5.1 to 0.5+/-0. 1mg/L. The biostability of the effluent improved considerably as the assimilable organic carbon (AOC) decreased from 134.5+/-52.7 to 25.3+/-19.9 microg/L. All of these water quality parameters show the superior quality of the MBR-treated water, which was comparable to or even better than the local tap water. Molecular size distribution analysis and the hydrophobic characterisation of the MBR effluent, in comparison to the filtered liquor from the bioreactor, suggest that the MBR had an enhanced filtration mechanism. A sludge layer on the membrane surface could have functioned as an additional barrier to the passage of typical THM precursors, such as large organic molecules and hydrophobic compounds. These results indicate that the MBR with a short HRT could be developed as an effective biological water treatment process to address the urgent need of many developing countries that are plagued by the serious contamination of surface water resources.     

PAC/PS预处理对水中镉的去除及UF膜污染控制

采用粉末活性炭耦合过硫酸盐(PAC/PS)作为超滤的预处理工艺,考察其对原水中镉和天然有机物的去除效果,以及对超滤膜污染控制的影响。结果表明,对于镉超标6倍的原水水样,当PAC和PS投加量分别为30 mg/L和300μmol/L、接触时间为60 min时,UV₂₅₄、DOC和镉的去除率分别可达到91.7%、68.2%和92.7%,镉浓度可降至《生活饮用水卫生标准》(GB 5749—2006)规定的限值(5μg/L)以下;与直接超滤相比,设置PAC/PS预处理工艺后超滤膜比通量提升了50.5%,XDLVO预测模型中胶体污染物-超滤膜相互作用的总界面能降低了75.38%,超滤膜污染减轻。     

HPLC-fluorescence detection and adsorption of bisphenol A, 17beta-estradiol,and 17alpha-ethynyl estradiol on powdered activated carbon

The adsorption of three estrogenic compounds (bisphenol A (BPA), 17beta-estradiol (E2), and 17alpha-ethynyl estradiol (EE2)) on several powdered activated carbons (PAC) was investigated. Without preconcentration, method detection limits (MDL) using high-performance liquid chromatography (HPLC) with fluorescence detection at an excitation wavelength of 280 nm and an emission wavelength of 310 nm were 0.88, 1.15, and 0.96 nM for BPA, E2, and EE2, respectively. Compound recoveries were >90% in raw drinking water matrices. PAC screening studies (six PAC brands) indicated all three compounds were removed by PAC, but the percentage removal ranged from 31% to >99% based upon PAC type/dosage and presence/absence of natural organic matter. The order of removal (E2>EE2>BPA) corresponded with logK(ow) values for the compounds (3.1-4.0, 3.7-3.9, 3.3, respectively). Kinetic and PAC dose-response experiments were conducted with the two best performing PACs. Increasing contact time and PAC dose improved compound removal. Freundlich isotherm parameters were fit to the experimental data. This study confirms that PAC treatment is feasible for >99% removal of three estrogenic compounds from raw drinking waters that may be at risk for containing such compounds, at least at initial concentration of 500 ng/l and higher.     

Chemical coupling of photocatalysis with flocculation and adsorption in the removal of organic matter

An experimental investigation was made to study the effects of chemical coupling of flocculation and adsorption with photocatalysis in treating persistent organic pollutants in wastewater. The photocatalysis alone showed initial reverse reaction when titanium oxide (TiO(2)) was used in catalysis. The effect of the pretreatment of adsorption with powdered activated carbon (PAC) on photocatalysis was studied. The results showed that PAC adsorption followed by photocatalysis was not effective in alleviating reverse reaction. On the other hand, when PAC and TiO(2) were added simultaneously, the reverse reaction was eliminated. Further, the organic removal was also improved by simultaneous PAC and TiO(2) additions. When flocculation with ferric chloride (FeCl(3)) was used as pretreatment, the organic removal efficiency was superior. The initial reverse reaction was also eliminated/minimized. However, inadequate doses of FeCl(3) (less than 30 mgl(-1)) resulted in initial reverse reaction and inferior DOC removal.     

Characterization of natural organic matter in conventional water treatment processes for selection of treatment processes focused on DBPs control

Natural organic matter (NOM) from raw and process waters at a conventional water treatment plant was isolated into hydrophobic and hydrophilic fractions by physicochemical fractionation methods to investigate its characteristics. Formation potential of trihalomethanes (THMs) was highly influenced by the hydrophobic fraction, whereas haloacetic acids formation potential (HAAFP) depended more on the hydrophilic fraction. However the hydrophobic fraction was removed more than the hydrophilic fraction through conventional water treatment. Therefore residual hydrophilic NOM after conventional treatment needs to be removed to reduce HAAFP. Feasible additional processes are required to be evaluated by comparing preferential removal efficiency of hydrophilic NOM through pilot tests. The structural and chemical characteristics of hydrophobic NOM (i.e., humic substances (HS)) were further investigated to know how they are influenced by conventional treatment. The phenolic fraction in the hydrophobic NOM was mainly removed compared to the carboxylic fraction through water treatment, and a higher formation potential of THMs resulted from NOM with a higher phenolic content. The Fourier-transform infrared (FT-IR) and proton nuclear magnetic resonance ((1)H-NMR) employed for characterization of NOM through water treatment were insightful revealing that their results were quite close to each other. Decreases of ratio of UV absorbance at 253 and 203 nm, respectively (A(253)/A(203) ratio) and trihalomethane formation potential/dissolved organic carbon (THMFP/DOC) showed consistent trends; therefore, the A(253)/A(203) ratio may be a good indicator of tendency for the formation potential of disinfection by-products (DBPs).     

Trihalomethane formation by chlorination of ammonium- and bromide-containing groundwater in water supplies of Hanoi, Vietnam

The occurrence and the fate of trihalomethanes (THMs) in the water supply system of Hanoi City, Vietnam was investigated from 1998 to 2001. The chlorination efficiency, THM speciation, and, THM formation potential (THMFP) was determined in the water works and in tap water. With regard to THM formation, three types of groundwater resources were identified: (I) high bromide, (II) low bromide, and (III) high bromide combined with high ammonia and high dissolved organic carbon (DOC) concentrations. Under typical treatment conditions (total chlorine residual 0.5-0.8 mg/L), the total THM formation was always below WHO, EU, and USEPA drinking water standards and decreased in the order type I > type II > type III, although the THMFP was > 400 micrograms/L for type III water. The speciation showed > 80% of bromo-THMs in type I water due to the noticeable high bromide level (< or = 140 micrograms/L). In type II water, the bromo-THMs still accounted for some 40% although the bromide concentration is significantly lower (< or = 30 micrograms/L). In contrast, only traces of bromo-THMs were formed (approximately 5%) in type III water, despite bromide levels were high (< or = 240 micrograms/L). This observation could be explained by competition kinetics of chlorine reacting with ammonia and bromide. Based on chlorine exposure (CT) estimations, it was concluded that the current chlorination practice for type I and II waters is sufficient for > or = 2-log inactivation of Giardia lamblia cysts. However, in type III water the applied chlorine is masked as chloramine with a much lower disinfection efficiency. In addition to high levels of ammonia, type III groundwater is also contaminated by arsenic that is not satisfactory removed during treatment. N-nitrosodimethylamine, a potential carcinogen suspected to be formed during chloramination processes, was below the detection limit of 0.02 microgram/L in type III water.     

Hybrid photocatalysis/membrane treatment for surface waters containing low concentrations of natural organic matters

Since the mid-1990s, numerous studies on the treatment of drinking water by photocatalysis have been reported. Once optimised, the photocatalytic process can completely degrade numerous natural and artificial organic compounds. In this study, a hybrid photocatalysis/membrane process was used as a polishing treatment of surface water containing a small concentration of natural organic matters (i.e. total organic carbon (TOC) concentration of around 3mg/L) which may be difficult to remove using conventional filtration or coagulation. An optimum pH of 4.5 and a TiO(2) concentration of 0.1g/L were found to lead to the highest removal efficiencies. The relative effect of the individual processes featuring in the hybrid system (UV radiation, TiO(2) adsorption and membrane filtration) was also assessed for different pH values. The membrane separation process was accounted to remove around 18% of the initial TOC concentration, while TiO(2) adsorption alone was generally responsible for less than 5% of TOC removal during the 120 min of the experiments. However, when the natural water was only radiated by UV light, up to 70% of TOC was removed. A synergetic effect was observed when the three processes (TiO(2), UV and membrane) were used together. Comparison of removal efficiencies obtained during real and model (International Humic Substance Society) waters treatment by photocatalysis is also presented, revealing the importance of the nature of the feed in this type of treatment.     

Removal of humic substances (HS) from water by electro-microfiltration (EMF)

Humic substances (HS) represent the common agents contributing to flux decline during membrane filtration of natural water. In order to minimize the fouling during microfiltration (MF) of HS, modifying the operation of MF presents a promising alternative. A laboratory-scale electro-microfiltration (EMF) module was used to separate Aldrich HS from water by applying a voltage across the membrane. The presence of an electric field significantly reduced the flux decline. A flux comparable to that of ion-free water was attained when the voltage was near the critical electric field strength (Ecritical), i.e., the electrical field gradient that balances the advective and electrophoretic velocities of solute. At an applied voltage of 100 V (approximately 110 V/cm), it was able to reduce UV absorbance at 254 nm (UV254), total organic carbon (TOC) and trihalomethane formation potential (THMFP) by over 50% in the permeate. Results from 1H nuclear magnetic resonance (1H NMR) analysis suggest that the aromatic and functionalized aliphatic fractions decreased significantly in the permeate. The charged HS have large molecule weight compared with those passing through membrane. Results clearly indicate that a combination of electric force with MF can increase HS rejection and decrease flux decline. Electrophoretic attraction was the major mechanism for the improvement of flux and rejection over time.     

Characterisation and removal of recalcitrants in reverse osmosis concentrates from water reclamation plants

Water reclamation plants frequently utilise reverse osmosis (RO), generating a concentrated reject stream as a by-product. The concentrate stream contains salts, and dissolved organic compounds, which are recalcitrant to biological treatment, and may have an environmental impact due to colour and embedded nitrogen. In this study, we characterise organic compounds in RO concentrates (ROC) and treated ROC (by coagulation, adsorption, and advanced oxidation) from two full-scale plants, assessing the diversity and treatability of colour and organic compounds containing nitrogen. One of the plants was from a coastal catchment, while the other was inland. Stirred cell membrane fractionation was applied to fractionate the treated ROC, and untreated ROC along with chemical analysis (DOC, DON, COD), colour, and fluorescence excitation-emission matrix (EEM) scans to characterise changes within each fraction. In both streams, the largest fraction contained <1 kDa molecules which were small humic substances, fulvic acids and soluble microbial products (SMPs), as indicated by EEM. Under optimal treatment conditions, alum preferentially removed >10 kDa molecules, with 17-34% of organic compounds as COD. Iron coagulation affected a wider size range, with better removal of organics (41-49% as COD) at the same molar dosage. As with iron, adsorption reduced organics of a broader size range, including organic nitrogen (26-47%). Advanced oxidation (UV/H₂O₂) was superior for complete decolourisation and provided superior organics removal (50-55% as COD).     

Spectrometric characterization of effluent organic matter of a sequencing batch reactor operated at three sludge retention times

Effluent organic matter (EfOM) from activated sludge systems is composed primarily of influent refractory compounds, residual degradable substrate, intermediate products and soluble microbial products (SMPs). Depending on operational conditions (hydraulic and sludge retention time (SRT)), the quantity and quality of EfOM significantly changes. The main objective of this research was to quantify and characterize the EfOM of a lab-scale activated sludge sequencing batch reactor (SBR), which was operated at three SRTs and fed glucose, an easily biodegradable substrate. EfOM was followed with two direct-quantification methods (chemical oxygen demand (COD) and dissolved organic carbon (DOC)), three spectrometric methods (ultraviolet absorbance at 254 nm (UVA₂₅₄), excitation-emission matrix (EEM) fluorescence and parallel factor analysis (PARAFAC)) and three organic matter (OM) indices (specific UVA₂₅₄ (SUVA), SUVA-COD, COD/DOC ratio). The significant increment of UVA₂₅₄ and OM indices after treatment indicated an accumulation of refractory high-molecular-weight humic-like compounds in the EfOM, which demonstrated that EfOM was composed mainly by SMPs and not glucose. On the other hand, as the SRT increased, the amount of EfOM decreased, but SUVA, SUVA-COD and fluorescence intensity increased; these trends indicated the accumulation of SMPs of increased molecular weight and aromaticity. Increasing SRT in the SBRs reduced the amount of EfOM, but increased its aromaticity and reactivity. Visual analysis of EfOM EEMs showed two protein- and one humic-like peak, which were attributed to SMPs generated within the SBRs. PARAFAC determined that a two-component model best represented EfOM EEMs. The two-components from PARAFAC were mathematically correlated to the visually identified protein- and humic-like SMPs peaks.