Scholarly article on topic 'Evaluating the Removal of Organic Fraction of Commingled Chemical Industrial Wastewater by Activated Sludge Process Augmented with Powdered Activated Carbon'

Evaluating the Removal of Organic Fraction of Commingled Chemical Industrial Wastewater by Activated Sludge Process Augmented with Powdered Activated Carbon Academic research paper on "Chemical sciences"

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Abstract of research paper on Chemical sciences, author of scientific article — Dong Wang, Qing-yuan Hu, Meng Li, Can Wang, Min Ji

Abstract Three different technologies, namely, individual activated sludge (AS) biodegradation, powdered activated carbon (PAC) absorption, and a combination of absorption and biodegradation (PAC–AS), were applied to treat commingled chemical industrial wastewater from a chemical industrial park in Tianjin, China. Experimental results showed that chemical oxygen demand and total organic carbon of organic matters in the PAC–AS system were reduced by 64.4% and 68.1% respectively. These results suggested the considerable additive effects of both AS degradation and PAC adsorption. Organic matter fractionation was employed to reveal the removal characteristics of organic compounds during treatment. AS degradation preferred to remove the compounds in hydrophilic and transphilic neutral fractions, whereas PAC absorption removed the compounds in hydrophobic fractions. Further chemical identification analysis showed that hydrophobic fraction mainly contained carboxylic acids, esters, and aromatic structures. Hydrophilic and transphilic neutral fractions contained phenol compounds. Most aromatic acids-like compounds were identified in transphilic acid (TPI-A) fraction. Esters in hydrophobic neutral fraction and phenols in hydrophobic acid fraction were easily removed by biodegradation and adsorption during treatment. However, aromatic acids-like compounds, which were dominant compounds in TPI-A fraction, were difficult to biodegradation and adsorption.

Academic research paper on topic "Evaluating the Removal of Organic Fraction of Commingled Chemical Industrial Wastewater by Activated Sludge Process Augmented with Powdered Activated Carbon"

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Evaluating the Removal of Organic Fraction of Commingled Chemical Industrial Wastewater by Activated Sludge Process Augmented with Powdered Activated Carbon

Arabian Journal of Chemistry

Dong Wang, Qing-yuan Hu, Meng Li, Can Wang, Min Ji

PII: DOI:

Reference: To appear in:

S1878-5352(15)00271-3 http://dx.doi.org/10.1016/j.arabjc.2015.08.031 ARABJC 1764

Arabian Journal of Chemistry

Saudi Chemical Society & The Arab Union of Chemists

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Received Date: Accepted Date:

23 November 2014 29 August 2015

Please cite this article as: D. Wang, Q-y. Hu, M. Li, C. Wang, M. Ji, Evaluating the Removal of Organic Fraction of Commingled Chemical Industrial Wastewater by Activated Sludge Process Augmented with Powdered Activated Carbon, Arabian Journal of Chemistry (2015), doi: http://dx.doi.org/10.1016/j.arabjc.2015.08.031

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Evaluating the Removal of Organic Fraction of Commingled Chemical Industrial Wastewater by Activated Sludge

School of Environmental Science and Engineering, Tianjin University, Tianjin 300072,

Corresponding author: Can Wang

Tel.: +86-22-27406057

Dong Wang, Qing-yuan Hu, Meng Li, Can Wang *, Min Ji „V

Tianjin 300072

Fax: +86-22-27406057 E-mail address: wangcan@t

Abstract

Three different technologies, namely, individual activated sludge (AS)

biodégradation, powdered activated carbon (PAC) absorption, and a combination of

absorption and biodegradation (PAC-AS), were applied to treat commingled chemical

industrial wastewater from a chemical industrial park in Tianjin, China. Experimental

results showed that chemical oxygen demand and total organic carbon of organic

matters in the PAC-AS system were reduced by 64.4% and 68.1% respectively. These

results suggested the considerable additive effects of both AS degradation and PAC

adsorption. Organic matter fractionation was employed to reveal the removal characteristics of organic compounds during treatment. AS degradation preferred to remove the compounds in hydrophilic and transphilic neutral fractions, whereas PAC

absorption removed the compounds in hydrophobic fractions. Further chemical identification analysis showed that hydrophobic fraction mainly contained carboxylic acids, esters, and aromatic structures. Hydrophilic and transphilic neutral fractions contained phenol compounds. Most aromatic acids-like compounds were identified in transphilic acid (TPI-A) fraction. Esters in hydrophobic neutral fraction and phenols in hydrophobic acid fraction were easily removed by biodegradation and adsorption during treatment. However, aromatic acids-like compounds, which were dominant compounds in TPI-A fraction, were difficult to biodegradation and adsorption. Key words: Commingled chemical industrial wastewater; Activated sludge; Powdered activated carbon; Fractionation; Identification.

ionation; I

1. Introduction

ingled

industrial effluents to treat and reuse. This kind of wastewater contains complex

Commingled chemical industrial wastewater is one of the most challenging

chemical composition and shows remarkable inhibitory and toxic effects to microorganisms in traditional biological treatment processes (Lei et al., 2010). Certain chemical and physical technologies were recently developed to improve the performance of biological processes (Jiang et al., 2011).

Activated carbon adsorption is an effective chemical-physical treatment

technology widely used in the treatment of industrial wastewater and potable water (Foo and Hameed, 2010; Nguyen et al., 2012; Reungoat et al., 2012). Most organic components inside water can be strongly adsorbed into activated carbon because of a well-suited surface and micro pores (Yapsakli and Cecen, 2010). Some researchers have applied powdered activated carbon (PAC) into the activated sludge (AS) process to improve the performance of biological treatment. Aziz et al. (2011) investigated the performance of a PAC-AS system in a sequencing batch reactor to treat landfill leachate. The system displayed superior performance in the removal efficiencies of chemical oxygen demand (COD), color, ammonia nitrogen, and total dissolved salts compared with the control biological technology. Jaafarzadeh et al. (2010) also employed the conventional AS process with and without the addition of PAC to treat pharmaceutical wastewater. Results showed that the addition of PAC could help remove antibiotic compounds and subsequently enhance removal efficiencies compared with the situation without PAC addition. Orozco et al. (2011) analyzed Cr (VI) removal by combining AS and PAC, and found that Cr (VI) removal using the PAC-AS system was higher than that using only AS or PAC. Additional PAC could also protect microorganisms from toxicants in wastewater, such as heavy metals and inhibition compounds (Kuai et al., 1998; Mochidzuki and Takeuchi, 1999).

The organic matter in commingled chemical industrial wastewater is a heterogeneous mixture of hydrocarbons, aromatic compounds, carboxylic acids, phenol, alcohols, esters, aldehyde, ether, and ketone (Augulyte et al., 2009; Zhang et al., 2012). However, limited information exists about the removal characteristics of

different types of contaminants inside the PAC-AS system. In commingled chemical industrial wastewater, some organic pollutants are hydrophilic while others are hydrophobic. Hydrophobic organics can be further divided into several fractions,

trea proc

including hydrophobic acid (HPO-A) and hydrophobic neutral (HPO-N) (Bu et al., 2010). Various fractions of organics present different adhesion characteristics to PAC

and biodegradability to AS.

To reveal the removal characteristics of contaminants inside the PAC-AS system, GC-MS or other spectroscopic approaches is one of commonly applied methods of organic matter identification (Schulten and Gleixner, 1999). However, the identified compounds by chromatographic analysis are usually limited to less than 50% of total organic matter in wastewater (Leenheer, 2009). Hence, ultraviolet-visible (UV-vis) spectrometry, fourier transform infrared (FT-IR) spectroscopy, and fluorescence excitation-emission matrix spectroscopy have been employed to determine the molecular structures of the compounds (Kim et al., 2006).

The objective of this study was to reveal and compare the removal characteristics of organic matters in commingled chemical industrial wastewater by using different atment technologies (i.e., standalone AS degradation process, PAC adsorption cess, and combined PAC-AS process). The fractions of organic matters were analyzed during different treatment. Various instrumental analysis methods were adopted to identify organic matters in the commingled chemical industrial wastewater. The removal characteristics of various organic pollutants were also qualitatively and quantitatively established. Especially, the chemicals removed by the PAC-AS system

were indentified in the comparison with the other two standalone treatments, which will help in proposing effective processes to treat the complex wastewater produced in the chemical industry.

2. Materials and methods

2.1. Wastewater characteristics

t of a full-sc anjin, Chi luding pharm

Raw wastewater was obtained from the influent of a full-scale wastewater treatment plant in a chemical industrial park in Tianjin, China. More than 50 types of industrial plants are located in the area, including pharmaceutical, manufacturing, petroleum chemical, electronics, chemical reagent, household, and personal care product plants. The wastewater contains the following components: chemical oxygen demand (COD), 982 mg/L to 1,602 mg/L; 5-day biochemical oxygen demand (BOD5), 208 mg/L to 824 mg/L; total nitrogen, 24.5 mg/L to 30.8 mg/L; ammonia nitrogen, 17.9 mg/L to 20.6 mg/L; total phosphorus, 2.3 mg/L to 2.4 mg/L, and total dissolved solids, 4,532 mg/L to 9,670 mg/L.

2.2. Wastewater treatment process

Three sequencing batch reactors (SBR) were employed for PAC-AS process (1#) individual AS process (2#), and PAC process (3#) (Fig. 1). Each reactor had a working volume of 2 L and was operated one cycle per day at room temperature with the following sequence: filling (0.09 h), anoxic reaction with stirring (6 h), aerobic

reaction (14 h), settling (1.5 h), decanting (0.5 h), and idleness (1.91 h). The inoculated sludge in reactors was obtained from a local municipal wastewater treatment plant and acclimated for 30 d. The approximate mixed liquor suspended

solids of AS in reactors were kept at 3.6 g/L to 4.2 g/L. The sludge was removed every day and the sludge retention time was kept at 30d.

The PAC, which was added to the reactors, was produced by the company of Zhejiang Rong Xing Activated Carbon and the product number was 785. The characteristics of PAC are depicted in Appendix A. Approximately 2g/L of PAC was added to the first system initially and the system was replenished with 0.25g /L of PAC per 4 days to maintain the removal performance of the system (PAC-AS system). The amount and the adding method of PAC were determined according to the optimization of the PAC adding dosage test. The second system was operated without PAC addition (AS system). In the third system, the same amount of PAC was added and replenished, but the AS was inactivated by 120 °C autoclave to prevent biodegradation (PAC system). And the PAC system was also aerated, because aeration could blow off a part of organic matters, especially the volatile organic matters. Maintaining PAC system aerated could eliminate the effect to make it as a control group to the other two groups.

2.3. Fractionation of wastewater organic matter

Organic matters in the wastewater were divided based on polarity into hydrophobic fractions (hydrophobic acid HPO-A and hydrophobic neutral HPO-N), transphilic

fractions (transphilic acid TPI-A and transphilic neutral TPI-N), and hydrophilic fraction (HPI). According to the previous study (Bu et al., 2010), the transphilic fractions refer to the materials whose solubility is between hydrophobic fractions and hydrophilic fractions. Fractionation was conducted using the method of Bu et al.

(2010). Wastewater was fractionated by two serial columns filled with Amberlite

XAD-8 and XAD-4 resins. The resins were cleaned with methanol and acetonitrile by Soxhlet extraction method for 12 h before addition into the columns. The wastewater samples were first filtered through a 0.45 ^m glass fiber filter to remove suspended solids. The filtrate was then acidified to a pH of 2 with 6M HCl and passed through the XAD-8 and XAD-4 resin columns in series. Materials retained on XAD-8 were hydrophobic fractions, whereas materials retained on XAD-4 were transphilic fractions. The materials not retained on either resin comprised the HPI fraction. HPO-A and TPI-A were eluted by backwashing with 0.1M NaOH from the XAD-8 and XAD-4 columns respectively. The resins were washed with distilled water and extracted with a solution of 75% acetonitrile and 25% ultrapure water (Millipore Milli-Q). Extracts from the XAD-8 and XAD-4 columns were condensed by rotary evaporator and then freeze-dried. Next, the extracts were separately redissolved in Milli-Q water with pH 7, which comprised the HPO-N for XAD-8 columns and TPI-N for XAD-4 columns.

2.4. Molecular weight and polydispersity

The apparent molecular weight (MW) distribution of organic matter was

characterized by a dead-end batch ultrafiltration apparatus. The experimental procedure was conducted by Zhao et al. (2012). Wastewater samples were first filtered through a 0.45 |im cellulose acetate fiber filter to remove suspended solids. Then, about 240 ml of wastewater sample was pressed through the membrane disc (63.5 mm) driven by pressure (120 kPa) from an N2 tank. The MW cut-offs of membrane discs used in the present study were 0.5, 1, 10, and 100 kDa. Wastewater samples were collected in glass bottles and stored at 4 °C for further analysis.

2.5. Molecular spectrum analyses

Ultraviolet (UV) absorbance was measured with a Cary 100 UV-vis spectrometer at

200 nm to 500nm using a quartz cell with 1 cm path length. All samples were adjusted to pH 7 with HCl prior to measurement. Milli-Q water was used as a blank.

For FT-IR analysis, the wastewater samples were freeze-dried under -75 °C and 3 kPa pressure. A3 mg sample was thoroughly mixed with about 100 mg of KBr desiccated under infrared radiation. The mixture was pressed into a tablet, and infrared spectrum was recorded on a Nicolet 6700 FT-IR spectrometer. The FT-IR spectra of solid samples were obtained in a wavenumber range of 4000 cm-1 to 400 cm-1 and baseline-corrected for analysis. The absorbance bands at 3400 cm-1 and 1640 cm-1 were the

absorbance of H2O, which could not be avoided in KBr tablets.

2.6. GC-MS analysis

Samples were collected from the influents and effluents in the three reactors. Aqueous samples were filtered with 0.45 | m glass filters and stored at 4 °C. Based on the contents of organic compounds, 200 ml of raw wastewater and treated effluents

were extracted with CH2Cl2 under acidic, neutral, and alkaline conditions using the extraction procedure proposed by Lai et al. (2008). The compositions of organic compounds in the wastewater were analyzed via GC-MS. Then, 1 ^L pretreated extracted samples were injected into the GC-MS system (Agilent, USA). The carrier gas was pure helium at a flow rate of 1 ml/min. A 30 m-long HP-5MS capillary

S capillar system. Th

column with an inner diameter of 0.25 mm was used in the separation system. The temperature control program was implemented as follows. The initial temperature of 40 °C was maintained for 4 min. Afterwards, the oven temperature was increased to 250 °C at a rate of 5 °C/min, to 300 °C at a rate of 10 °C/min, and then maintained for 10 min. Organic compound analysis was conducted according to the National Institute of Standards and Technology 05 mass spectral library database.

2.7. Methods for analyzing wastewater quality

The parameters of COD, BOD5, pH, ammonium nitrogen (NH4+ - N), total nitrogen (TN), total phosphorus (TP), and total dissolved solids (TDS) were measured according to standard methods (EPA of China, 2002). Total organic carbon (TOC) was determined by a fully automated TOC-Vcph analyzer.

3. R esults and discussion

3.1. Comparison of organic matter removal by different technologies

Figure 2 shows the performance of organic matter removal in terms of COD and TOC by the three systems. The standalone AS system removed 40% of COD and 45%

ved by PAC

of TOC from the wastewater. The standalone PAC system removed 37% of COD and 38% of TOC. Results also suggested that about 40% to 45% of organic matter in the wastewater could be biodegradable, whereas residual organic matter could be hard-biodegradable. However, only 37% to 38% of organic matters were adsorbed by PAC, which indicated that some organic matters were not easily removed adsorption because of molecular characteristics.

In the combined PAC-AS system, higher removal efficiencies of COD (64%) and TOC (68%) were obtained, which took advantages of both AS biodegradation and PAC adsorption. Some non-biodegradable organic matters were removed by adsorption. The removal of organic matter by the PAC-AS system involved complex processes. Hence, multiplicate analytical methods such as UV-visible, FT-IR spectroscopy, and GC-MS, were combined to characterize organics in wastewater. Insights into the removal characteristics of organic matters during treatment were thus provided.

3.2. Molecular weight distribution of raw wastewater and treated effluents

ar weig

Fig. 3 shows the MW distribution of organic matters in raw wastewater and treated effluents. In raw wastewater, the organic matter with MW less than 500 Da accounted for 69% of TOC. Low-MW organic compounds were the main components in the commingled chemical industrial wastewater. The low-MW fraction (<500 Da) was effectively removed in all the treatment systems, whereas the other MW fraction (>500 Da) presented low removal efficiencies. Results suggested that both AS biodegradation and PAC adsorption demonstrated good removal performance on the low-MW fraction

(<500 Da). The low-MW organics were easier to move into the microbial cell and micropores inside the activated carbon (Antony et al., 2012; Newcombe, 2002). The fraction with MW of 1 to 0.5 kDa was reduced from 51 mg/L-TOC to 23 mg/L-TOC by the AS system. However, TOC values with the same MW fraction decreased to 38 mg/L in the PAC system. Organic matter in the fraction of 1 k to 0.5 kDa was more

significantly biodegraded compared with PAC adsorption. Organic matter with MW

a was mo er with MW

more than 1k Da was removed insignificantly in the PAC system. The lack of capacity to high MW organics removal of PAC was revealed, which was related to the pore structure of PAC (Ho et al., 2013).

In PAC-AS SBR system effluent, organic compounds in all size fractions, especially in the <500 Da size fraction, were significantly removed according to the TOC value in Fig. 3. The organic matter removal efficiency in <500 Da size fraction was 86%. An additive effect was shown because of the combination of AS transformation and PAC adsorption.

which wa

3.3. Removal characteristics of various organic matter fractions

Fig. 4 shows the removal characteristics of various organic matter fractions by different technologies. In raw wastewater, the organic matters in hydrophobic fractions (including HPO-A and HPO-N) were dominant, accounting for more than 48% of TOC. The compounds in transphilic fractions accounted for 29% and 22% for HPI of the TOC. The results revealed that the predominance of hydrophobic organic compounds over the transphilic and hydrophilic compounds in the raw commingled

chemical industrial wastewater (Greenwood et al., 2012). These hydrophobic organic compounds may have high persistence properties in aquatic ecosystem (Waller et al., 1996).

In the standalone AS system, the organic matters in TPI-N and HPI fractions showed the highest removal efficiencies of 73% and 60% respectively. However, the

owever, th ; PAC systei

removal efficiencies of TPI-N and HPI fractions were 44% and 21% in the PAC system respectively. The PAC system preferred to remove organic matters in HPO-A and HPO-N fractions with removal efficiencies of 70% and 63% respectively, while the AS system removed 47% of organic matters in HPO-A fraction and 53% of compounds in HPO-N fraction. Organic matters in TPI-A fraction were removed inefficiently in the AS and PAC systems, which indicated organic matters in TPI-A fraction were refractory to biodegradation and PAC adsorption.

Biological technologies prefer to remove hydrophilic fractions and transphilic neutral fractions in wastewater, whereas activated carbon prefers to remove hydrophobic fractions (including HPO-A and HPO-N). Previous research reported that hydrophobic organics are apt to be adsorbed and have their final destination on the surface of porous material, such as activated carbon or soil, because of their strong hydrophobicity (Cui et al., 2013). On the contrary, hydrophilic organics can be utilized easier by microorganisms. A similar conclusion was also represented by Wang et al. (Wang et al., 2004), who showed that activated carbon can adsorb hydrophobic compounds, whereas microorganisms probably remove hydrophilic biodegradable matters.

In the PAC-AS system, the removal performance of organic matter in various fractions was superior to these in the individual AS and PAC system. The hydrophobic compounds could be biodegraded by AS and adsorbed by PAC (Imai et al., 2001). The organic matters in TPI-N and HPI fractions were mainly transformed by AS, whereas the TPI-A fraction, refractory to biodegradation, was partially adsorbed by PAC. Hence, the PAC-AS system can enhance overall removal performance owing to the additive effects of biodegradation and PAC adsorption.

efflue

3.4. UV absorbance analysis of raw wastewater and treated effluents

UV absorbance analysis can reveal preliminary information on organic matter molecule structures and achieve quantitative analysis. Fig. 5 shows the UV scanning spectra of various organic matter fractions in both raw wastewater and treated effluents. The wavelength for UV scanning ranged from 200 to 350 nm, since there is no absorption in the UV region of 350 to 500 nm. For all the samples (including overall organic matter and various fractions), the treated effluents presented similar but lower absorbance curve compared with the raw wastewater. The organic matters decreased after the three treatment systems. Absorbance curves of the PAC-AS system also decreased significantly compared with that of the individual AS and PAC systems,

which were consistent with the results in Figs. 2 and 4.

In the absorbance curves, the absorption bands were observed in the UV region of 220 nm to 240 nm and 250 nm to 300 nm, which indicated conjugated C=C or C=O structure and aromatic rings respectively according to Appendix B. The fractions of

HPO-A, HPO-N, TPI-A, and HPI might contain carboxylic acids, esters, phenol, and unsaturated hydrocarbons. HPO-N fractions also contained aromatic ring compounds.

For UV absorbance analysis of treated effluents, the organic matter in various fractions showed similar degrees of removal during the individual AS and PAC system treatments. However, the absorbance of organic matter in HPO-N fraction significantly decreased in the PAC-AS system. The organic matter removal in HPO-N and HPI fractions also showed an additive effect of AS biodegradation and PAC adsorption, which might contain conjugated C=C or C=O structure and aromatic rings. The organic matters of HPO-A, TPI-A, TPI-N, and HPI fractions during the PAC-AS system treatment also showed similar degrees of removal as the AS and PAC system treatment effluents.

3.5. Function group investigation of raw wastewater and treated effluent by FT-IR

FT-IR analysis can provide insights into the information of organic compounds molecule structures, which are difficult to find using qualitative and quantitative analysis. FT-IR analysis can also reveal the removal characteristics of organic matter during treatment. Fig. 6 shows the FT-IR spectra of various fractions in the raw tewater and treated effluents.

In the HPO-A fraction of raw wastewater, the main absorbance bands of organic matter were at 2923, 1625, 1374, 1240 to 1015, 750, and 650 cm-1, which were indicative of the aliphatic group (-CH3/-CH2-), carboxylic acid group (-COO-), C-O in carboxylic acid, -(CH2)n -(n>4) and -OH group respectively. The results suggested

that the fraction organic matter might contain fatty carboxylic acids, fatty hydrocarbon, and phenol among others. Similar function group bands, except the acid group (-COO-), were found in the HPO-N fraction because the pH was adjusted to neutral.

However, distinct function groups, including C=C and the substituent group out of plane aromatic band, were detected in the TPI-A fraction, which indicated a great difference of the organic composition to other fractions. In both TPI-N and HPI

fractions, the function groups of aromatic structure, C-O-C, substituent group out of plane aromatic band and -OH were observed.

substituer

For the FT-IR analysis of treated effluent, -OH structure in HPO-A fraction and C-O-C in HPO-N fraction were reduced significantly during treatment. The compounds contained in both structures were easily removed by both AS and PAC systems. However, C-O-C structures in hydrophilic and transphilic fractions were reduced insignificantly. It indicated that esters in hydrophobic fractions were easily removed by AS degradation and PAC adsorption, whereas these compounds in hydrophilic and transphilic fractions were difficultly removed. Other fraction groups might be partially removed because the FT-IR spectroscopic analysis was difficult to conduct to achieve the quantitative analysis by KBr tablet samples.

3.6. Organic matter identification

The organic matters of various fractions in the raw wastewater sample were further identified using the GC-MS technique, as shown in Table 1. The identified compounds confirmed the function group detected by the previous FT-IR analysis. The organic

matters in HPO-A fraction mainly contained hexadecanoic acid, dichlorobenzoic acid, and hydroxybenzal dehyde, which were consistent with the function groups of the aromatic structure and fatty acid group in Fig. 6. In TPI-A fraction, the compound of

benzoic acid was identified, which also contained the function group of aromatic

structure and acid group. Experimental results also indicated that the hydrophobic fraction (HPO-A and HPO-N) mainly contained bicyclic aromatic compounds and heterocyclic ring structures, which were difficult to biodegrade. Most aromatic acid-like compounds were identified in TPI-A fraction.

According to the results of spectrum analysis (Fig. 5 and 6), esters in HPO-N, including phthalate esters, were easily removed by biodegradation and adsorption (Huang et al., 2008; Huang et al., 2010). Phenols in neutral fractions preferred to be utilized by microorganisms (Baird et al., 1974; Dignac et al., 2000). On the contrary, the aromatic compounds and carboxylic acid in hydrophobic and transphilic fractions showed refractory characteristics during treatment.

3.7. Influence mechanism of PAC on activated sludge system

The w;

ater used in the experiment was refractory comprehensive industrial iewater, which had the characteristic of poor biodegradability. Results showed that the removal efficiencies of COD and TOC in PAC-AS process were higher than those in AS and PAC system, which was mainly because of the additive effects of biodegradation and PAC adsorption.

Further analysis found that the addition of PAC in AS system (PAC-AS system)

could not only improve the removal of organic matter in low-MW fraction (<500 Da), but also removed the organic matter with MW more than 500 Da. Moreover, PAC had a strong adsorption capacity for hydrophobic substances and absorbed TPI-A fraction

partially. The removal of hydrophobic refractory organic compounds and TPI-A fraction was enhanced after the addition of PAC to the AS system.

In addition to the above reasons, the addition of PAC might enhanced the biomass and the biological stability, because PAC had large surface area, acting as a supporting medium and supplying bacteria with suitable living micro-environment (Ma et al., 2013; Ma et al., 2012). More biomass could adhere to the surface of PAC and degraded the components adsorbed to the PAC as them being released slowly. The addition of PAC in AS system might also improve the metabolic activity (Hu et al., 20,5)ofm,e_S a„dtese,Peab,lltype_0fAS ^ et a, 201,

system, P

biodegradation except to the adsorption effect.

Therefore, in the PAC-AS systei m, PAC also plays a role in the reinforcement of

4. Conclu

rganic matter fractions and removal characteristics of chemical industrial tewater by different treatment technologies (AS process, PAC process, and PAC-AS process) were investigated in this study. The following conclusions were obtained.

(1) COD and TOC removal efficiencies of 64.4% and 68.1% in the PAC-AS system showed superior performances than the AS and PAC system respectively. Based on

the organic matter fraction analysis, the AS biodegradation preferred the removals of hydrophilic and transphilic neutral fractions in wastewater, whereas the activated carbon absorption removed hydrophobic fractions. The PAC-AS system can

enhance overall removal performance owing to the additive effects of biodegradation and PAC adsorption.

(2) The MW distribution showed that organic matter in low-MW fraction (<500 Da) was effectively removed in AS system and PAC system, but other MW fractions (>500 Da) presented low removal efficiencies. In PAC-AS system, organic compounds in all size fractions, especially in the <500 Da size fraction, were significantly removed. An additive effect was shown because of the combination of AS transformation and PAC adsorption.

(3) Results of UV absorbance, FT-IR spectra and GC-MS showed that the aromatic compounds, carboxylic acids, alkane, and esters were the main organic compounds in the raw wastewater. Esters in hydrophobic neutral fraction and phenols in hydrophobic acid fraction were easily removed by biodegradation and adsorption. However, aromatic acids-like compounds, which were dominant compounds in TPI-A fraction, were difficult to biodegradation and adsorption.

This work was supported by the Science and Technology Support Project of Tianjin, China (12ZCZDSF01800).

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46,383

7-3848.

Table captions

Table 1. Organic matter identification of various fractions in raw wastewater sample using

GC-MS technique.

Table 1 Organic matter identification of various fractions in raw wastewater sample using GC-MS

technique.

Fraction

Molecular formula Molecular structure

HPO- A

n-Hexadecanoic acid 2, 4-dichloro-Benzoic acid

3,5-di-tert-butyl-4-hydroxybenzal dehyde

C16H32O2 C7H4O2Cl2

C15H22O2

Dibutyl phthalate Dimethyl phthalate

Diisobutyl phthalate

Neneicosane Naphthalene Methylnaphthalene Acenaphthene

C16H22O4

C10H10O4

C16H22O4

C20H42 C1oHS C11H10

Benzenecarboxylic acid C7H6O2

2-methyl-Benzoic acid CsHsO2

2, 4-dichloro -Benzoic acid C7H4O2Cl2

4-tert-butyl-2,6-disopropyphenol C16H26O

2,6-dibutyl-nitrophonel

C14H21O3N

2,4-di-tert-butyl-phenol C14H22O

2,6-di-tert-butyl-4-methylphenol C15H24O

Diethyltouamide C12H17NO

Quinline C9H7N

2,4,6-tribromophenol C6H3OBr3

Appendix A Characteristics of powdered activated carbon (PAC)

Parameter Unit Value

Particle size u m 60 - 120

Bet surface area Sq. m/g 882

Langmuir surface area

Sq. m/g 1104

Micropare area Sq. m/g 416

Micropore volume cc/g 0.19

Average pore diameter (4 v/a by Langmuir) A 17.4

Appendix B List of band assignment for FT - IR and UV - Vis spectra (Mecozzi et al., 2009).

FT - IR UV - Vis

Wavenu mber(cm-1) Functional group Wavelength (nm) Functional group

3400 - 3200 3250 3060 3015 2950 - 2850 2500 - 2000 2260 1740 1700 - 1715 1650 - 1550 and 1440 - 1350

1620 - 1450

1650 1540

1460 - 1440

1420 - 1390

1300 - 1000

1240 - 1150

1160 - 1120 1120 - 1000

850 - 650

OH carbohydrate

NH2 aminoaciddic group

CH aromatic group

CH alkene group

CH3 and CH2 aliphatic group

C^C or C=N

C=C aromatic group

C=O ester fatty acid group

C=O fatty acid group

- COO- fatty acid salt group

Aromatic C=C double bonds that are conjugated with C=O of COO-C=O Amide □ band C-N Amide^band Carboxylic acid inplane C-O bending Aliphatic C-H deformation OH vibration of carboxylic group; C - H deformation abutted upon C=O

C - O - C esters

C - O in carboxylic acid, alcohols, esters and ethers C - O - C polysaccharide C - O carbohydrate

H or C-X (X=F, Cl, Br and I) out of plane aromatic band

275 255 - 260 220 - 230 190 - 200

C=C aromatic group C=C aromatic group C=C conjugated C=O or - OH

Fig. 1.

Fig. 2. Fig. 3. Fig. 4.

Fig. 5. Fig. 6.

Figure captions

Schematic layout of the reactor system: 1 - SBR reactor; 2 - magnetic stirrer; 3 -air vent; 4 - sampling port; 5 - air pump; 6 - timer controller; 7 - water bath; 8 -mass flow controller.

COD and TOC concentrations of the raw wastewater and the effluent sampl (values are given as average value with n=3). Molecular weight distribution of organic matters in the raw wastewater and treated effluents (values are given as average value with n=3).

TOC of the raw wastewater and the effluents from various systems (upper); TOC removal efficiencies of various organic matter fractions by various treatment systems (middle); Polarity fraction distribution of various samples (lower) (values are given as average value with n=3).

UV absorption spectra of overall organ latters and various fractions in the raw wastewater and treated efflue

FT-IR spectra of organic n er fractions in the raw wastewater and treated effluents.

- —~1— " —-1— —-1-

1# (AS+PAC) 2# (AS) 3# (PAC)

Fig. 1. Schematic layout of the reactor system: 1 -SBR reactor; 2 - magnetic stirrer; 3 - air vent; 4 -sampling port; 5 - air pump; 6 - timer controller; 7 - water bath; 8 - mass flow controller.

Fig. 2. COD and TOC concentrations of the raw wastewater and the efflu (values are given as average value with n=3)

Fig. 3. Molecular weight distribution of organic matters in the raw wastewater and treated effluents (values are given as average value with n=3)

□ HPO-A SHPO-N BTPI-A HTPI-N □ HPI

Fig. 4. TOC removal efficiencies of various organic (upper); Polarity fraction distribution of various

ous samples (

ions by various treatment systems (values are given as average value with

Fig. 5. UV absorpti

rption spectra o „

200. 0 250. 0 300. 0 330. 0 200. 0 250. 0 300. 0 350. 0 3.000 t- 3.000

200. 0 2o0. 0 300. 0 3o0. 0 200. 0 250. 0 300. 0 350. 0

Wavelength (rim)

f overall organic matters and various fractions in the raw wastewater and treated effluents

HPO-A Raw wastewater PAC-AS effluent AS effluent PAC effluent

HPO-N Raw wastewater PAC-AS effluent AS effluent

-CH2-/-CH3

-COO- C-O

TPI-A Raw wastewater PAC-AS effluent

4000 3500 3000 2500 2000 1500 1000 500 Wavelength (cm-1)

TPI-N W. -CH2-/-CH3 Aromatic structure C-O-C CH -OH

Raw wastewater

PAC-AS effluent AS effluent PAC effluent

4000 3500 3000 2500 2000 1500 1000 500

Wavelength (cm-1)

Raw wastewater PAC-AS effluent AS effluent PAC effluent

Aromatic structure C-O-C -OH^

4000 3SOO 3000 2500 2000 1500 IOOO 500 Wavelength (cm-1)

Fig. 6. FT-IR spectra of organic matter fractions in the raw wastewater and treated effluents.