Chemical composition of organic matters in domestic wastewater

Desalination 262 (2010) 36–42

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Desalination j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d e s a l

Chemical composition of organic matters in domestic wastewater Man-hong Huang a,b, Yong-mei Li a,⁎, Guo-wei Gu a a b

State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai ,200092, China College of Environmental Science and Engineering, Donghua University, Shanghai, 201620, China

a r t i c l e

i n f o

Article history: Received 12 September 2009 Received in revised form 24 May 2010 Accepted 25 May 2010 Available online 26 June 2010 Keywords: Chemical composition Organic matter Domestic wastewater COD fractions Size distribution

a b s t r a c t The chemical composition of organic matters (OMs) in domestic wastewater was determined in order to investigate types and origin of OMs, which will supply a more scientific basis for COD fractions of activated sludge models (ASMs) and wastewater treatment management. Chemical hydrolysis and chromatographic analysis were used to quantify macromolecular OMs such as proteins and sugars. Results suggested that the largest group of OMs in the domestic wastewater was fibers. Proteins and sugars were the next two largest groups in the wastewater. Fibers, proteins and sugars accounted for 20.64%, 12.38% and 10.65% of TOC in the wastewater, respectively. Ten endocrine disrupting chemicals were determined in the wastewater; most of them were PAHs and phthalates. The sum of volatile fatty acids, soluble proteins and soluble sugars formed about 30% of total COD of the wastewater, and not all the soluble proteins and sugars were degradable substrates. The largest part of TOC in the wastewater was supra colloidal. Most proteins and sugars in the wastewater were larger than 0.001 μm. © 2010 Elsevier B.V. All rights reserved.

1. Introduction Organic matters (OMs) in wastewater were traditionally characterized by COD, TOC and BOD, which were often divided into particulate and dissolved fractions [1,2]. More detailed classification of OMs based on solubility and biodegradability is a current way of characterization, according to the definitions given in the activated sludge models (ASMs) [3]. However, OMs in the wastewater are highly heterogeneous, containing substances of various molecular weights, ranging from the simple compounds like acetic acid, to very complex polymers [4]. Specific OM does not always necessarily correspond exactly to the biodegradability of organic fractions. For example, proteins and sugars are different in their biodegradability, but in activated sludge mathematical models, it was assumed that they had the same biodegradation velocity. This may affect the accuracy of the modeling process. Characterization at the molecular level for the overall organic matters is of importance for expanding the knowledge about the wastewater treatment processes and activated sludge mathematical models. However, a detailed evaluation of molecular chemical composition for the purpose of wastewater characterization is time consuming and thus receives limited attention. Some studies have reported that major chemical fractions in municipal wastewater were proteins, lipids and sugars [5–8]. For instance, the fractions of proteins, sugars and lipids of the total COD in several catchment areas of Denmark were, on average, 28.18% and 31%, respectively [8]. ⁎ Corresponding author. Tel.: +86 2165982693; fax: +86 2165986313. E-mail address: [email protected] (Y. Li). 0011-9164/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2010.05.037

Narkis [6] identified soluble organics in a physical–chemical wastewater treatment plant in Israel, revealing that 30% of the total COD in the influent were proteins, and 10% of the total COD were sugars. Dignac [3] quantified proteins, sugars, lipids and polyphenolic compounds of a municipal wastewater treatment plant via chromatographic analysis after chemical hydrolysis and identified only about 50% of the total organic carbon (TOC). Some researchers have studied the particle size distribution of substances contained in municipal wastewater [8,15–17]. Four major size fractions are defined as settleable (e.g. N100 μm), supra colloidal (e.g. 1–100 μm), colloidal (e.g.0.08–1 μm) and soluble (e.g.b0.08 μm) [16]. Others focused on the trace compounds such as endocrine disrupting chemicals [9–13]. Katsoyiannis and Samara [12] investigated the persistent organic pollutants in the sewage treatment plant of Thessaloniki in northern Greece. The non-methane volatile organic compounds (NMVOCs) emissions from an urban-scale wastewater treatment plant of Turkey were estimated by Atasoy et al. [11]. Eriksson et al. [14] indicated that there were about 900 different xenobiotic organic compounds (XOCs) other than traditional nutrient pollutants in different types of grey wastewater. However, few studies aimed to simultaneously investigate the molecular composition of organic matters including major chemical fractions and trace compounds in domestic wastewater. The main objective of this work was to investigate the molecular organic composition of domestic wastewater to supply a more scientific basis for wastewater treatment processes. The major organic compounds, such as proteins, sugars, lipids, VFAs, as well as trace organic chemicals were investigated. The relationship among the molecular organic composition, the COD fractions of ASMs, size distribution of proteins, sugars and TOC were also presented.

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were acidified by the addition of 0.5 mL of 6 mol/L HCl to 5 mL sample. The sample injection volume was 1 μL. The sum of measured acetic, propionic, butyric, isobutyric, valeric and isovaleric acids was regarded to be the total amount of VFA.

2. Methods 2.1. Wastewater and sludge Domestic wastewater was taken from the wastewater collection station of a large residential area in Shanghai, China. This collection station serves 12,000 population and no industrial wastewater is involved. Table 1 shows the major traditional parameters of the domestic wastewater. The sludge used for measuring nitrate utilization rate (NUR) was obtained from the aerobic reactor of a lab-scale anaerobic–anoxic–oxic (A2/O) system treating the same wastewater. All tests were operated in a temperature-controlled room at 25 °C. 2.2. Total organic carbon (TOC) and chemical oxygen demand (COD) COD was measured based on the closed reflux method [18]. TOC was measured by a total carbon analyzer (TOC-Vcpn, Shimadzu Company). When samples contained suspended substances, total and inorganic carbon concentrations were measured in freeze-dried samples to determine the concentration of organic carbon. TOC in soluble fractions was measured after acidification of samples and elimination of inorganic carbon. 2.3. Humic acids, tannic aids and linear alkylbenzene sulfonate Humic acid concentration was determined using Folin-Lowry method [19]. The sample absorbance was measured at 750 nm. Tannic aids were measured by Folin-ciocalteu method at 720 nm [5]. Linear alkylbenzene sulfonate (LAS) concentrations were determined by using HPLC [20]. The recovery for HPLC in determining LAS was about 99%. 2.4. DNA and RNA The colorimetric procedure, diphenylamine method, is used for DNA quantification [20]. Control samples were prepared using 2-deoxy-Dribose. The sample absorbance was measured at 595 nm using a 752 N spectrophotometer. RNA was measured using the Orcinol test [19]. Under acidic conditions, D-ribose was dehydrated, forming furfural, which was condensed with orcinol in the presence of ferric ion. A bluegreen color developed with maximum intensity at wavelength 665 nm, and thus the sample absorbance was measured at 665 nm using a 752 N spectrophotometer. 2.5. Volatile fatty acids Volatile fatty acids (VFAs) were measured by Hewlett-Packard 5890 Gas Chromatograph (GC) equipped with a flame ionization detector (FID) [6]. A 30 m × 0.53 nm × 1 μm INNOWAX column was used. The column and detector temperature was maintained at 110 and 220 °C, respectively. Both the inlet and outlet temperatures of the column were maintained at 200 °C. Nitrogen gas was used as the carrier gas with the flow rate of 10 cm3/min. Samples and the control

2.6. Sugars and fibers Sugars quantification was performed by GC [21]. Lyophilized wastewater samples were hydrolyzed by trifluoroacetic acid, acetylated to sugar alcohol acetates and extracted with chloroform. The extracted sugar alcohol acetates were analyzed using a gas chromatography system (Agilent 6890 A) equipped with an HP-5 column (30.0 m × 0.25 mm × 0.25 μm) and a flame ionization detector. Eight neutral sugars were analyzed with inositol as internal standard. The total sugars in the sample were calculated as the sum of measured monosaccharide. Fibers in wastewater include the crosslinked matrix of the cell wall of plants. They are measured most conveniently as neutral detergent fibers, which include cellulose, hemicellulose, and lignin as the major components. Fibers were determined by neutral detergent method according to He [19] and Van et al. [22]. 2.7. Proteins Proteins were hydrolyzed by 6 mol/L hydrochloric acid at 110 °C for 18 h in vacuum tubes. Released amino acids were separated and quantified by High Speed Amino Acid Auto-Analyzer (Hitachi 83550). Summation of all the amino acids is deemed to be the proteins. 2.8. Lipids Lipid classes were extracted with hexane and analyzed by GC/FID (Agilent 6890 N, 30.0 m × 0.25 mm × 0.25 μm, HP-5 MS column, with N2 as carrier gas) after transmethylation with BF3/MeOH and purification of lipid classes on a silica gel column. Hexanedioic acid was used as internal standard for quantification. 2.9. GC/MS analysis Volatile organic matter other than VFAs and semi-volatile organic matters were extracted with dichloromethane. 1,4-dichlorobenzened4, naphthalene-d8, acenaphthene-d10, phenanthrene-d10, chrysened12 and perylene-d12 were added as internal standards. After extracted, it was analyzed by Agilent 6890 N (30.0 m × 0.25 mm× 0.25 μm, HP-5 MS column, with N2 as carrier gas), GC temperature program was 40 °C for 0.5 min, linearly ramped to 300 °C at 8 °C/min, and held at 300 °C for 10 min. Separated fragments were identified by MS (Agilent 5973 inert MS) in the electron impact mode (EI) at 1823.5 eV. Ions in the mass range of 35 to 500 amu were detected at 1 scan/s. Recovery values for GC-MS were in the range of 72%–108% in determining volatile and semivolatile organic matters. Identification of the compounds was performed by referring to the library of mass spectrometry fragment patterns provided by the National Institute of Standards and Technologies (NIST). Quantitative estimation for the concentration of individual compound was performed by comparing the peak areas of the corresponding compound and the internal standard in the total ion chromatogram (TIC). 2.10. COD fractions in ASM1

Table 1 The traditional chemical parameters of the investigated domestic wastewater. Parameters

Concentration ranges (mg/L)

Total COD (TCOD) Soluble COD (SCOD) Total organic carbon (TOC) Dissolved organic carbon (DOC) Total nitrogen (TN)

204–440 108–372 50.3–139 22.1–56.2 50–70

A pulse dosage of wastewater to activated sludge under anoxic conditions enables to distinguish the nitrate utilization rates (NUR) on subsequent wastewater fractions and to determine the concentrations of soluble degradable substrate (Ss) and particulate degradable substrate (Xs). Before measuring NUR, the activated sludge was aerated for 12 h so that microorganisms were at the endogenous respiration status. Then the reactor was sealed and oxygen was

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Table 2 Molecular organic matters in the wastewater identified by corresponding methods other than GC/MS. Type

No. Compound name

Proteins 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Sugars 18 19 20 21 22 23 24 25 Lipids 26 27 28 29 30 31 VFA

Others

32 33 34 35 36 37 38 39 40 41

Glycine Alanine Vanine Leucine Isoleucine Aspartic Glutamic Arginine Serine Histidine Threonine Proline Cystine Tyrosine Methionine Phenylalanine Glycine Rhamnose Fucose Ribose Arabinose Xylose Mannose Galactose Glucose Myristic acid, glyceride Hexadecenoic glyceride Margaric glyceride Octadecadienoic acid, glyceride Oleic acid, glyceride Octadecanoic acid, glyceride Acetic acid Propionate acid Butyric acid iso-Butyric acid iso-Valeric acid LAS Humic acid DNA + RNA Tannic acid Fibers

Concentration TOC TOC of the compound coefficient concentration (μg/L) (μg C/L) 1700.00 2000.00 2000.00 2000.00 1500.00 3100.00 3600.00 1200.00 900.00 1700.00 1400.00 800.00 700.00 1100.00 900.00 1500.00 1700.00 4440 2660 4410 2770 8250 6020 4800 5520 40.00

0.32 0.40 0.51 0.55 0.55 0.48 0.52 0.41 0.40 0.46 0.40 0.52 0.35 0.60 0.40 0.66 0.49 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.69

544.00 808.99 1025.64 1099.24 824.43 1473.27 1878.26 496.55 364.04 789.68 564.71 417.39 242.31 656.35 362.42 987.80 838.36 1776 1064 1764 1108 3300 2408 1920 2208 27.52

30.00

0.70

21.05

120.00 270.00

0.71 0.72

84.94 193.30

770.00

0.71

548.14

120.00

0.71

84.94

13010.00 1720.00 2710.00 1250.00 399.60 2220.00 11880.00 19172.00 2500.00 64800

0.40 0.49 0.55 0.55 0.59 0.56 0.55 0.35 0.54 0.4

5204.00 836.76 1478.18 681.82 235.06 1237.63 6474.60 6691.03 1340.21 25920

purged with nitrogen gas for 20 min. When measuring NUR, nitrate was added to the grabbed samples with the initial concentration of around 15 mg/L. Samples were taken at a regular interval during the time course of denitrification, and they were filtrated immediately using a glass fiber filter (GF/F, 0.45 μm). Concentrations of nitrate and nitrite were determined according to the standard methods. The denitrification kinetics was studied according to Kujawa and Klapwijk [23]. Heterotrophic biomass (XBH )was assessed from the oxygen utilization rate of raw wastewater. Autotrophic biomass (XBA) was assessed by evaluating the respiration rate for nitrification of the autotrophs present in the wastewater and comparing it to the respiration rate determined with an available autotrophic biomass concentration. The procedure and calculation were performed by using respirometry as described by Vanrolleghem et al. [24]. 2.11. Particle size distributions of proteins and sugars by microfiltration and ultrafiltration The membranes and the testing instrument were purchased from the Membrane Institute of Nucleus Science, Academic Sciences, Shanghai, PRC. Before operation, membranes were soaked in 0.1 N NaOH solution for 30 min, and then they were soaked in distilled water for several times. At last they were rinsed by filtering distilled water in a stirred cell for 5 min. Under operation, pressure of 10 psi was applied to a stirred cell using high-purity nitrogen (purity N99.99%). 3. Results and discussions 3.1. Molecular organic composition of domestic wastewater Organic matters in domestic wastewaters may be changeable in different countries due to their different living habits. Therefore, it is necessary to determine the organic compositions in domestic wastewater in China. Proteins in the wastewater were hydrolyzed into 17 kinds of amino acids and sugars were released into 8 kinds of neutral sugars after hydrolysis. Then the hydrolysis products and lipids in the wastewater were derivatized by different methods mentioned above. Concentrations of these organic families quantified by the corresponding methods other than GC/MS are shown in Table 2. Table 2 also presents concentrations of organic matters in the wastewater such as humic acids and linear alkylbenzene sulfonate (LAS). All the organic matters were converted to TOC by using conversion factors calculated based on their individual molecular

Fig. 1. The total ion chromatogram of the domestic wastewater sample. The endocrine disrupting compounds are labelled in the figure (1. acenaphthylene, RT = 18.01 min; 2. 3-tertButyl-4-hydroxyanisole, RT = 18.45 min; 3. diethyl phthalate, RT = 20.33 min; 4. phenanthrene, RT = 22.95 min; 5. di-n-butyl phthalate, RT = 25.19 min; 6. bis(2-ethylhexyl) phthalate, RT = 31.48 min; 7. benzo(b)fluoranthene, RT = 33.72 min; 8. benzo(k)fluoranthene,RT = 33.75 min; 9. benzo(a)pyrene, RT = 34.50 min; 10. ideo(1,2,3-cd)pyrene, RT = 37.17 min).

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Table 3 Molecular organic composition in the wastewater identified by GC/MS (volatile and semi-volatile organic matters other than VFAs). Type

No.

Compound name

Concentration of the compound (μg/L)

TOC coefficient

TOC concentration (μg C/L)

RT (min)

Alkyl and aromaticity hydrocarbon

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72

Dodecane, 2-methyl-8-propylCyclotetradecane, 1,7,11-trimethyl-4-(1-methylethyl)Pentadecane Hexadecane, 2,6,10,14-tetramethylCyclohexadecane Cyclohexadecane, 1,2-diethylHeptadecane Octadecane Nonadecane, 1-chloroEicosane Cyclopentasiloxane, decamethylCinnoline, 3-phenylNaphthalene 2-Methylnaphthalene Phenanthrene Fluoranthene Benzo(b)fluoranthene Benzo(k)fluoranthene Ideo(1,2,3-cd)pyrene Dibenzo(a,h)anthracene Benzo(ghi)perylene Toluene Benzo(a)pyrene 7-Hexadecene, (Z)1-Octadecene Cyclohexene, 1-methyl-3-(1-methylethenyl)-, (.+/-.)8-Heptadecene 2,6,10,14,18,22-Tetracosahexaene, 2,6,10,15,19,23-Hexamethyl-, (all-E)9-Nonadecene 17-Pentatriacontene Acenaphthylene 1-Nonadecene 1-Hexanol, 2-ethyl7-Octen-2-ol, 2,6-dimethyl1,6-Octadien-3-ol, 3,7-dimethylPhenylethyl alcohol Isoborneol Cyclohexanol, 5-methyl-2-(1-methylethyl)-, (1alpha,2beta,5alpha)-(+/−)3-Cyclohexene-1-methanol, .alpha.,.alpha.4-trimethyl- . .α. 6-Octen-1-ol, 3,7-dimethyl-, (R)5-Cholestene-3-ol, 24-methylFarnesol isomer a Beta-sitosterol Benzyl alcohol Cholestanol Cholesterol Hexanoic acid, 2-methylHexanoic acid, 2-ethyl6-Octadecenoic acid, (Z)Octadec-9-enoic acid Octadecanoic acid Heptadecanoic acid n-Hexadecanoic acid Dodecanoic acid Oleic acid Benzenepropanoic acid Tetradecanoic acid Cyclohexanone Bicyclo[2.2.1]heptan-2-one, 1,7,7-trimethyl-, (1R)9,10-Anthracenedione Androstan-17-one, 3-hydroxy-, (3.alpha.,5.beta.)Cholest-4-en-3-one Phenol Chloroxylenol 4-Methylphenol 4-Chloro-3-methyl phenol 5H-1-pyrindine Quinoline, 2-methylPyridine, 3-(1-methyl-2-pyrrolidinyl)-, (S)Azobenzene Caffeine Pyridine-3-carboxamide, oxime, N-(2-trifluoromethylphenyl)-

1.99 2.42 6.19 2.91 7.01 1.85 3.31 0.57 1.25 3.10 0.45 1.75 0.16 0.07 0.06 0.02 0.18 0.13 0.74 0.52 1.12 0.75 0.27 1.21 8.60 2.85 11.25 22.90 1.87 1.59 0.14 0.90 6.30 1.63 1.07 1.98 1.37 7.45 9.67 1.16 6.46 1.11 11.01 0.92 35.37 59.32 7.90 1.42 40.59 3.02 45.26 2.05 103.27 7.32 1.00 0.61 11.45 0.92 2.21 5.06 1.05 1.18 8.43 8.93 1.44 0.14 2.84 1.68 2.22 0.09 13.66 1.55

0.85 0.86 0.85 0.85 0.86 0.86 0.85 0.94 0.75 0.85 0.59 0.87 0.94 0.93 0.94 0.95 0.95 0.95 0.92 0.95 0.96 0.92 0.95 0.86 0.87 0.86 0.86 0.88 0.86 0.86 0.95 0.86 0.74 0.77 0.76 0.79 0.78 0.76 0.77 0.74 0.84 0.81 0.78 0.68 0.82 0.84 0.65 0.67 0.77 0.77 0.76 0.76 0.75 0.72 0.77 0.72 0.74 0.73 0.79 0.65 0.79 0.84 0.77 0.61 0.78 0.58 0.76 0.84 0.74 0.79 0.49 0.59

1.69 2.07 5.26 2.47 6.01 1.59 2.81 0.53 0.94 2.64 0.27 1.52 0.15 0.07 0.06 0.02 0.17 0.12 0.68 0.49 1.07 0.69 0.26 1.03 7.49 2.46 9.64 20.11 1.60 1.36 0.13 0.77 4.65 1.26 0.81 1.56 1.07 5.66 7.49 0.86 5.43 0.90 8.58 0.63 29.08 49.79 5.10 0.94 31.09 2.31 34.43 1.55 77.45 5.27 0.77 0.44 8.44 0.68 1.75 3.30 0.83 0.99 6.46 5.48 1.12 0.08 2.15 1.40 1.65 0.07 6.76 0.91

21.82 35.05 23.07 23.20 24.14 28.84 21.73 29.97 28.94 24.35 12.97 26.83 13.45 15.55 22.95 25.48 33.72 33.75 37.17 37.25 37.77 3.75 34.50 31.01 26.59 13.79 24.94 34.02 35.17 38.06 18.01 30.92 10.38 11.29 11.86 12.21 13.19 13.32 13.66 14.37 37.50 33.75 38.40 10.60 36.22 35.56 10.94 12.44 27.26 27.31 27.54 26.34 25.27 19.89 33.46 16.41 22.64 7.07 12.75 25.42 31.18 37.72 9.45 17.16 11.52 15.57 15.59 15.81 16.48 20.86 23.85 40.97

Alkene

Alcohols

Organic acids

Ketone

Phenolic

Nitrogenous compounds

(continued on next page)

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Table 3 (continued) Type

No.

Compound name

Ether

73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90

3-tert-Butyl-4-hydroxyanisole Triethylene glycol monododecyl ether Bis(2-chloroisopropyl)ether 2H-Indazol-3-amine, 2-methylBenzenesulfonamide, N-ethyl-2-methylAniline N-nitroso-di-n-propylamine Cyclopentaneacetic acid, 3-oxo-2-pentyl-, methyl ester 1,2-Benzenedicarboxylic acid, bis(2-methylpropyl) ester 1,2-Benzenedicarboxylic acid, diisooctyl ester 7-Trimethylsilyloxy-7-methyloctanoic acid, trimethylsilyl ester Dimethyl phthalate Diethyl phthalate di-n-Butyl phthalate di-n-Octyl phthalate bis(2-Ethylhexyl)phthalate Kitazin P Cyclic octaatomic sulfur

Amine

Ester

Others

Concentration of the compound (μg/L)

composition. For example, the molecular composition of glycine is C2H5NO2, so its TOC coefficient was calculated as follows: TOC coefficient of glycine =

2×C 2×C+5×H+N+2×O

ð1Þ

= 2 × 12 = ð2 × 12 + 5 + 14 + 16 × 2Þ = 0:32 With the molecular analysis performed directly and after hydrolysis, the characterization of OMs in the wastewater samples was not completed. TOC of the tested wastewater sample was about 126 mg/L. The total TOC of the OMs listed in Table 2 added up to 63.7% of the wastewater TOC. Therefore, a complementary analysis by GC/MS was conducted to qualitatively investigate the composition of the uncharacterized fractions. TIC of the domestic wastewater sample is shown in Fig. 1 and the organic compounds identified by GC/MS are shown in Table 3. From a total of 90 compounds identified by GC/MS, only 18 compounds (Nos. 13, 15–23, 31, 63, 75, and 84–88 in Table 3) are classified as priority pollutants regulated by the U.S. EPA [25]. Among these 18 compounds, 10 compounds (Nos. 15, 17–19, 23, 31, 73, 85, 86, and 88 in Table 3) are endocrine disrupting chemicals [26] (as labelled in Fig. 1). They are phenanthrene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a) pyrene, ideo(1,2,3-cd)pyrene, acenaphthylene, 3-tert-Butyl-4-hydroxyanisole, diethyl phthalate, di-n-butyl phthalate and bis(2-ethylhexyl) phthalate. Total TOC of the compounds listed in Table 3 only takes 0.35% of the wastewater TOC. Apart from the chemicals listed in Table 3, a large number of small peaks in the TIC remain unidentified. 3.2. Origin of OMs in the wastewater In terms of the TOC concentrations of the major OM families (fibers, proteins and sugars in Table 2) and the total TOC of the Table 4 COD fractions in the wastewater sample based on ASM1. Organic component Definition

Concentration Unit

TCOD SCOD Ss XS SI XI XBA XBH

249 111 58.22 103.33 50 8.89 bL.D.a 28.56

a

Total COD Soluble COD Soluble degradable substrate Particulate degradable substrate Soluble inert substrate Particulate inert substrate Nitrifiers Heterotrophs

Lower than the limit of detection.

mg COD/L mg COD/L mg COD/L mg COD/L mg COD/L mg COD/L mg COD/L mg COD/L

4.35 2.13 0.35 3.39 4.23 0.10 0.21 4.16 17.30 9.60 4.45 0.09 2.75 2.45 0.03 2.32 1.16 4.61

TOC coefficient

TOC concentration (μg C/L)

RT (min)

0.73 0.59 0.42 0.68 0.50 0.35 0.55 0.69 0.69 0.74 0.70 0.62 0.65 0.69 0.74 0.74 0.54 0.27

3.19 1.27 0.15 2.30 2.11 0.04 0.12 2.87 11.95 7.09 3.09 0.06 1.78 1.69 0.02 1.71 0.63 1.23

18.45 28.67 10.94 18.84 21.25 9.27 11.29 21.17 24.03 31.47 37.14 18.22 20.33 25.19 33.20 31.48 23.74 26.17

wastewater, the percentages of these major OMs can be calculated. Fibers were found to be the largest group of OM in the wastewater, which accounted for 20.64% of the total TOC of the wastewater. Proteins and sugars accounted for 12.38% and 10.65% of the total TOC in the wastewater, respectively. Apparently, the food related substances discharged to sewers were the main sources of these major OMs in the domestic wastewater. Aromatic hydrocarbons (Nos. 11–23 in Table 3) found in the wastewater were mainly priority pollutants [25]. Polycyclic aromatic hydrocarbons (PAHs) are generally regarded as a class of carcinogenic compounds [27], which occur whenever fossil fuels (petroleum,coal, etc.) are burned [9]. Alcohols, ketones (Nos. 23–46 in Table 3) and ethers (Nos. 58–62 in Table 3) were mainly used in degreasing, cleaning, lacquering and coating applications [14]. LAS (No 37 in Table 2) was related to washing and cleaning of clothes and vegetables. Although the toxicity of LAS to mammals has not been reported, some surfactants could be very toxic to aquatic organisms [28,29]. Long-chain fatty acids and their methyl and ethyl esters (Nos. 47– 57 in Table 3) originated from human excreta, soaps and food oils and fats [14]. Caffeine (No. 71 in Table 3) was from drinks like coffee and tea [9]. A group of phthalates esters and hydroxybenzoic acid esters (Nos. 80–88 in Table 3) were found in the wastewater for the household application containing plasticizers made up of phthalates esters and food additives containing hydroxybenzoic acid [14]. 3.3. Comparison with COD fractions in ASMs With regards to the activated sludge models (ASM Nos. 1, 2 and 3), the total COD of wastewater is separated into different fractions, depending on the complexity of treatment processes. There is close relationship between wastewater molecular characterization and Table 5 Concentration of the major organic matters in the wastewater sample. Organic component

Definition

Concentration

Unit

CVFA CTSUG CSSUG CTPRO CSPRO CHA CLAS CLIP CNU CTA CLIG

Volatile fatty acids Total sugars Soluble sugars Total proteins Soluble proteins Humic acids LAS Lipids DNA and RNA Tannic acids Fibers

13.46 89.2 36.39 39.47 26.62 14.21 4.49 2.90 14.20 2.61 38.56

mg mg mg mg mg mg mg mg mg mg mg

COD/L COD/L COD/L COD/L COD/L COD/L COD/L COD/L COD/L COD/L COD/L

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Fig. 2. TOC, protein and sugar concentrations of different particle size ranges in the wastewater (concentrations of sugars and proteins were converted to TOC by using conversion factors calculated by Eq. (1)).

organic components in the models. The COD fractions in ASM1 and organic matters in the domestic wastewater were determined respectively, and the results are shown in Tables 4 and 5. It was concluded from Table 4 that Ss was about 23.4% of the total COD in the wastewater. This is in accordance with the data reported by Raunkjer et al. [1]. Table 5 gives concentrations of the main organic matters in the wastewater sample. Concentrations of soluble proteins (CSPRO) and soluble sugars (CSSUG) were 26.62 mg/L and 36.39 mg/L, respectively. CSPRO, CSSUG and volatile fatty acids (CVFA) are the main constituents of SS. The sum of these three OMs accounted for 30% of the total COD, which was in agreement with the report of Henze et al. [4]. Because not all of the soluble proteins and sugars are readily biodegradable substrates, the sum of CVFA, CSPRO, and CSSUG (76.47 mg/l) is greater than SS.

3.4. Comparison of molecular fraction by particle size distribution Knowledge of particle size distribution is essential for choosing the potential treatment process [16], and it is more helpful to get information between molecular composition and particle size distribution of the wastewater. Size distributions of proteins, sugars and TOC in the sewage wastewater are shown in Fig. 2. It indicated that the particle sizes of most proteins and sugars in the wastewater were larger than 0.001 μm. For the particles smaller than 0.1 μm, 62% of the TOC was attributed to proteins and sugars. While the particles were smaller than 0.001 μm, only 12% and 3% of the TOC were attributed to sugars and proteins, respectively. Fig. 3 shows the

percentages of different sizes of proteins, sugars and TOC. The significant part of TOC distributed between the particle sizes of 1 μm and 100 μm, which are defined as supra colloidal. This is because most of the fibers exist in the size range of 1–100 μm. 4. Conclusions The largest group of OMs in the domestic wastewater was fibers. Proteins and sugars were the next two largest groups in the wastewater. Fibers, proteins and sugars accounted for 20.64%, 12.38% and 10.65% of the TOC in the domestic wastewater, respectively. The food related substances discharged to sewers were the main sources of these OMs. The sum of volatile fatty acids, soluble proteins and soluble sugars forms about 30% of the total COD of the wastewater. Comparison with the soluble degradable substrate (Ss) of ASM 1 indicated that not all of the soluble proteins and sugars were readily biodegradable substrates. Particle size distribution of TOC, proteins and sugars indicated that the largest part of TOC in the wastewater was supra colloidal. While 62% of the TOC was attributed to proteins and sugars for the particles smaller than 0.1 μm, only 15% of the TOC was attributed to proteins and sugars for the particles smaller than 0.001 μm. GC/MS analysis detected 90 kinds of organic matters. Among them, 10 endocrine disrupting chemicals were identified; most of them were PAHs and phthalates. Acknowledgements The authors would like to thank National Science Foundation Project Grants of China (50878165), Program for New Century Excellent Talents in University (NCET-08-0403), Foundation of The State Key Laboratory of Pollution Control and Resource Reuse, China (PCRRY08009), Research Fund for the Doctoral Program of Higher Education of China (20090075120007), Shanghai Committee of Science and Technology, China (09230500200), the Fundamental Research Funds for the Central Universities of China (10D11308), Shanghai Leading Academic Discipline Project (B604) and Young Teacher Foundation of Donghua University (113-10-0044018) for financial support. References

Fig. 3. Percentages of different size of proteins, sugars and TOC.

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