ening,

Filtration resistance

s oreze,idee pe an

fermentation. The mechanism of the increase of sludge ltration resistance after pretreatment could be

ducedn andcarcitys, sludiate in

tion [8]. To date, a number of studies have investigated the ltra-tion characteristics and mechanisms of activated sludge inmembrane bioreactors for the wastewater treatment [9]. However,there is little information about sludge characteristics with highsolid concentrations during the process of anaerobic digestion,

meric substancese most impesistanceolubilized

the pretreatment process and consumed and converted induring acidogenic fermentation. Because the major compof EPS and SMP are proteins and polysaccharides, the prothese substances should be studied during the processes of pre-treatment and anaerobic fermentation.

We hypothesized that alkaline pretreatment would decreasethe dewaterability of sewage sludge, while anaerobic fermentationwould improve the dewaterability. The aims of this research wereto explore the ltration characteristics of acidogenic fermented

Corresponding authors. Tel./fax: +86 85326670.E-mail addresses: zhuyanfangjn@126.com (Y.F. Zhu), liuhongbo@jiangnan.edu.

cn (H.B. Liu), liuhe@jiangnan.edu.cn (H. Liu), huangshuai@126.com (S. Huang),834876777@qq.com (H.J. Ma), tianyue1026@126.com (Y. Tian).

Separation and Purication Technology 142 (2015) 813

Contents lists availab

Separation and Puri

.e lnumber of potential uses in various industries [6].However, the separation of VFA from the anaerobic fermented

sewage is challenging [7]. Recently, several publications reportedmembrane technology as a cost-effective method for VFA separa-

results have indicated that extracellular poly(EPS) and soluble microbial products (SMP) are thsubstances inuencing membrane ltration rOrganic matter, including EPS and SMP, will be shttp://dx.doi.org/10.1016/j.seppur.2014.11.0371383-5866/ 2015 Published by Elsevier B.V.ortant[2,11].duringto VFAonentsles offatty acids (VFA) production from sewage sludge by anaerobic fer-mentation is a promising method for recycling of the sewagesludge because it has a high organic matter (e.g. protein, carbohy-drate) content [1,2]. The VFA can be used as an alternative carbonsource to improve biological nitrogen and phosphorous removal inthe wastewater treatment process [35]. Additionally, VFA have a

sludge. Ahn [3] reported that thermal pretreatment increasedsludge dewaterability through the destruction of the sludge ocstructure. Chen et al. [10] observed that acidic pretreatmentimproved the dewaterability of sludge. However, to our bestknowledge, there is no information about how alkaline pre-treat-ment inuences the ltration characteristics of sludge. Earlier1. Introduction

The amount of sewage sludge prosignicantly because of urbanizatiotreatment capacity. Because of land sgent air pollution control regulationand incineration may not be approprattributed to the release of EPS from the microbial cells of the sludge. The degradation and conversion ofSMP into volatile fatty acids could explain the decrease in the ltration resistance after fermentation.

2015 Published by Elsevier B.V.

in China has increasedincreased wastewaterand increasingly strin-ge disposal by landllthe near future. Volatile

especially in anaerobic fermented sewage sludge for VFA produc-tion. Because the physical and chemical features of sludge inu-ence membrane ltration, it is necessary to investigate thecharacteristics of fermented sewage sludge.

To achieve a high VFA yield, sewage sludge pretreatment beforefermentation, such as thermal or/and alkaline pretreatment, is usu-ally used to improve the solubility of organic matter in solidVolatile fatty acidAnaerobic fermentation

of the sewage sludge decreased after pretreatment and fermentation. Moreover, the EPS concentration inthe sludge sharply decreased after thermal alkaline pretreatment and then increased after the followingFiltration characteristics of anaerobic fermacids production

Y.F. Zhu, H.B. Liu , H. Liu , S. Huang, H.J. Ma, Y. TiaLaboratory of Environmental Biotechnology, School of Environmental and Civil Engineer

a r t i c l e i n f o

Article history:Received 6 March 2014Accepted 29 November 2014Available online 12 December 2014

Keywords:Sewage sludge

a b s t r a c t

The ltration characteristicmented sewage sludge wetance, viscosity, particle si(SMP) were determined tocated that thermal alkalinof the sewage sludge, whil

journal homepage: wwwnted sewage sludge for fatty

Jiangnan University, 1800 Lihu Avenue, Wuxi 214122, China

f untreated sewage sludge, thermal alkaline pretreated and anaerobic fer-investigated in the process of fatty acids production. The ltration resis-extracellular polymeric substances (EPS) and soluble microbial productsntify the ltration characteristics of the sewage sludge. The results indi-retreatment signicantly increased the ltration resistance and viscosityaerobic fermentation decreased the ltration resistance. The particle size

le at ScienceDirect

cation Technology

sevier .com/locate /seppur

2 min. The injection port and detector temperatures were both

collected in a measuring cylinder within 5 min [23]. The ltrationresistance of the sludge slurry was calculated using the followingformula:

F DPl J 1

where F denotes the ltration resistance of the sludge slurry (m1);DP denotes the trans-membrane pressure (Pa); l represents thedynamic viscosity of the sludge slurry (Pa s); and J denotes theinstantaneous ltration ux, (m3/(m2 h)).

The particle size of the sludge was measured by a BT-2003 laserparticle size analyzer, which works on the principle of laserdiffraction. Viscosity was determined by a Brookeld viscometer(DVEII+pro, Brookeld Engineering Laboratories, Middleboro, MA)using the instructions provided by the manufacturer.

3. Results and discussion

3.1. VFA production

VFA production from sewage sludge with different total solid(TS) concentrations is shown in Fig. 1. The VFA concentrationsincreased as the fermentation process progressed and remainedstable after day 10. Fermentation of sewage sludge with a higherTS content produced higher VFA concentrations, as did thermalalkaline pretreatment of sewage sludge. In the thermal alkalinepre-treated sewage sludge group, the highest VFA concentration

ication Technology 142 (2015) 813 9250 C. The total VFAs concentrations were calculated as a sumof the individual VFA concentrations.

The EPS and SMP were extracted and analyzed by the phenol/sulfuric acid method [21] and Coomassie Brilliant Blue method[22].sewage sludge, and to identify how anaerobic fermentationimproves sludge ltration performance. The results can be usedto understand the mechanism of sewage sludge ltration anddevelop membrane ltration technology for VFA separation fromsewage sludge after anaerobic acidogenesis.

2. Materials and methods

2.1. Sewage sludge and seeding sludge

Sewage sludge was obtained from the dewatered stage of theTaihu Xincheng wastewater treatment plant (WWTP), Wuxi, China,and had a water content of 85 3%. Sewage sludge was diluted tototal solids (TS) values of 75 g/L and 35 g/L. Thermal alkaline pre-treatment of sludge was conducted as follows: the initial pH ofthe sludge was adjusted to 12.0 using a 20 mol/L NaOH solution,then the sludge was stirred for 2 h at 90 C. Seeding sludge inocu-lated for VFA fermentation was collected from the same site. Sew-age sludge was diluted to a TS of value of 75 g/L and heated at100 C for 2 h to kill non spore-forming methanogens [12,13].Before use, the seeding sludge was re-activated to culture the aci-dogenic microorganisms as described elsewhere [14].

2.2. Batch acidogenic fermentation

The acidogenic fermentation was conducted in 1000 mL conicalasks. A sample (500 mL) of sewage sludge (75 g/L or 35 g/L), withor without pretreatment, and 20 mL of seeding sludge (75 g/L)were added to the ask for VFA production. The initial pH of thesludge was adjusted to 10.0 using 20 mol/L NaOH solution or20 mol/L HCl solution, and the pH was maintained at 10.0 through-out the fermentation process [15]. Sodium 2-bromoethanesulpho-nate (BES, 50 mmol/L) was used to inhibit methanogen growth inthe sludge [16,17]. Before anaerobic fermentation, oxygen in theask was removed from the head space by nitrogen gas spargingfor 3 min. The asks were capped with rubber stoppers and placedin air-tight shakers with a shaking speed of 120 rpm and tempera-ture of 37 1 C. Each batch underwent VFA fermentation for15 days. Sludge samples were taken every other day for VFA deter-mination [18].

2.3. Analysis

Total solids (TS) and volatile solids (VS) measurements werecarried out according to standard methods [19]. For VFA measure-ment, the sludge samples were centrifuged at 7000 rpm for 10 min.The supernatants were ltrated through 0.45 lm lter mem-branes. A gas chromatograph (GC-2010, Shimadzu Co., Kyoto,Japan) equipped with an auto injector (AOC-20i, Shimadzu Co.)was used to measure the concentrations of the VFA. The GC wasalso equipped with a ame ionization detector and a fused-silicacapillary (PEG-20M, 30 m 0.32 mm, 0.5 lm, China). 4-Methylva-leric acid was added as an internal standard and the samples wereacidied with 3 mol/L phosphoric acid [20]. The GC column wasinitially held at 80 C for 3 min, increased by 15 C/min to a naltemperature of 210 C, and then held at this temperature for

Y.F. Zhu et al. / Separation and PurThe ltration resistance of the sludge slurry was measured bypouring 50 mL of sludge slurry rapidly into a glass funnel contain-ing a folded lter paper, and measuring the volume of ltrateFig. 1. VFA proles during the anaerobic acidogenic fermentation of sewage sludge,A: 35 g/L sludge with pretreatment; B: 75 g/L sludge with pretreatment; C: 35 g/Lsludge without pretreatment; D: 75 g/L sludge without pretreatment.

with a TS of 75 g/L was 1.3 times higher (at 7.31 0.24 g/L) thanthat with a TS of 35 g/L (at 5.55 0.35 g/L). When sewage sludgewas anaerobically fermented without thermal alkaline pretreat-ment, the highest VFA concentrations at TS values of 75 g/L and35 g/L were 4.63 0.43 g/L and 3.15 0.54 g/L, respectively. Basedon the results in Fig. 1b, the VFA yields were 149.47 22.51 mg COD/g VS, 189.90 28.59 mg COD/g VS, 214.32 39.16mg COD/g VS, and 289.00 52.80 mg COD/g VS for the 75 g/Lun-pretreated, 75 g/L pretreated, 35 g/L un-pretreated, and 35 g/Lpretreated sewage sludge, respectively. With acidogenic fermenta-tion, the VFA yields for TS values of 75 g/L and 35 g/L with pretreat-ment were 27.05% and 34.86% higher, respectively, than those forsludge without pretreatment. According to the results of Liuet al. [18], total VFA yields of pretreated and un-pretreated sewagesludge were 279.6 mg COD/g VS and 213.2 mg COD/g VS, respec-tively. The VFA yields of this study are very similar to our previousresearch. Chen et al. [23] reported that pretreatment of sludge wasbenecial for VFA production, and this agrees with the results inthe present study.

3.2. Variation in the ltration resistance and viscosity

Variations in the ltration resistance and viscosity of sewagesludge during the anaerobic fermentation are presented inFig. 2a. Filtration resistance is one of the most important parame-ters for sewage sludge during the process of ltration, and it alsocan be used to indicate the characteristics of the sewage sludge.

10 Y.F. Zhu et al. / Separation and PuricaFig. 2. Changes in the ltration resistance and viscosity of sewage sludge with or

without pretreatment A: 35 g/L sludge with pretreatment; B: 75 g/L sludge withpretreatment; C: 35 g/L sludge without pretreatment; D: 75 g/L sludge withoutpretreatment.As shown in Fig. 2a, the ltration resistances were(1.04 0.22) 1011 m1 for pretreated sewage sludge and(9.06 1.02) 108 m1 for fermented sewage sludge at 75 g/L TS.The ltration resistance of sewage sludge with thermal alkalinepretreatment was 522 times higher than that of the untreated sew-age sludge. However, the ltration resistance after fermentationdecreased by almost 99% compared to the pretreated sewagesludge. Similarly, for the 35 g/L TS sewage sludge, the ltrationresistances of untreated, pretreated and fermented sewage sludgewere (3.52 0.68) 107 m1, (9.90 0.49) 108 m1 and(8.18 0.37) 108 m1, respectively. Similar trends to the 75 g/LTS sewage sludge were observed for changes in the sewage sludgeltration.

Fig. 2b shows the viscosity of the sewage sludge during theanaerobic fermentation. The viscosity of the 75 g/L sewage sludgeafter pretreatment was 5410 mPa s, which was 8.87 times higherthan that of the untreated sewage sludge (610 mPa s). The viscos-ities of the 35 g/L sewage sludge with and without pretreatmentwere 104 mPa s and 49.2 mPa s, respectively. The above resultsclearly indicate that thermal alkaline pretreatment increases theviscosity of the sewage sludge. The reason for this increase maybe that the thermal alkaline pretreatment solubilizes the solidorganic matter and releases proteins and polysaccharides intothe liquid [2,24]. Some studies of the relationship between theEPS and viscosity have demonstrated that composition and mor-phology will inuence the viscosity and ltration resistance ofthe sewage sludge [25,26]. Changes in the EPS and SMP during pre-treatment and fermentation will be discussed in detailed in Section3.4.

In addition, the viscosity of the sewage sludge deceased signif-icantly in the early stages of anaerobic fermentation. For the 75 g/Lsewage sludge, the viscosity decreased from 5410 mPa s to189.2 mPa s after pretreatment. For the 35 g/L sewage sludge, theviscosity decreased from 104 mPa s to 29.1 mPa s with pretreat-ment. Many factors will inuence the viscosity of the sewagesludge, such as the concentrations of proteins and polysaccharides,which usually cause high sludge viscosity [2]. In the present study,because the protein and polysaccharides were consumed duringVFA production by the acidogenic microorganisms, the viscositydecreased [27]. The ltration resistance and viscosity results forthe untreated, pretreated and fermented sludge veried ourhypothesis in the introduction.

3.3. The particle size distribution

The particle size distribution of sludge is an important parame-ter affecting the sludge dewaterability [28,29]. As shown in Fig. 3,the particle size decreased after fermentation for both the 35 g/Land 75 g/L sludges, regardless of whether the sludge was pre-treated or not. For the 35 g/L sludge without pretreatment, thecumulative percentage of fermented sludge with a particle sizebelow 100 lm shifted from 55.61% to 63.22%, while for the pre-treated sludge it increased from 55.84% to 80.87%. The cumulativepercentage of thermal alkaline pretreated sludge with a particlesize below 100 lm increased by 44.82% and that for un-pretreatedsludge only increased by 13.68%. A similar trend was also observedfor the 75 g/L sludge. The cumulative percentages of sludge withparticle sizes below 100 lm increased by 56.32% and 46.01% forthermal alkaline treated and un-pretreated sludge, respectively.

It should be noted that the peak of the particle size distributionof the untreated sewage sludge was 149 lm with percentages of3.25% and 3.28% for the 35 g/L and 75 g/L sludge, respectively.However, the peak of the particle size distribution for the 35 g/L

tion Technology 142 (2015) 813sludge shifted to 30.6 lm with a percentage of 2.93% without pre-treatment, and shifted to 27.9 lm with a percentage of 3.28% withpretreatment. For the 75 g/L sludge, the peak moved to 27.9 lm

(b) 7

icaFig. 3. The particle sizes of the sewage sludge (a) 35 g/L sludge with pretreatment;sludge without pretreatment d original sludge; s fermented sludge.

Y.F. Zhu et al. / Separation and Purwith a percentage of 3.37% without pretreatment, and shifted to30.6 lm with a percentage of 4.66% with pretreatment.

Liu et al. also reported that both thermo-alkaline and ultra-sonic-alkaline pretreatment could reduce the particle size. Becauseof the multi-level structure of sewage sludge oc, alkaline hydroly-sis of the extracellular biopolymer, the highly porous ocs disinte-grated into microocs or occuli and even primary particles. Thereduction in particle size was caused by cell wall damage and deg-radation. Alkaline pretreatment was more efcient at destroyingthe cell walls than many other pretreatments such as with acidor ultrasonic vibrations [30].

The particle size is very closely associated with the ltrationresistance of the sewage sludge, and the resistance is also depen-dent on the pore size of the lter membrane. When the particlesize of the sludge is bigger than or similar to the pore size of thelter membrane, the ltration resistance will increase. Therefore,our data indicate that the particle size of the sewage sludge shouldbe taken into consideration when selecting the pore size of the l-ter membrane.

3.4. Variations of EPS and SMP

To investigate the mechanism causing changes in the ltrationcharacteristics of the sewage sludge with pretreatment and anaer-obic fermentation, the EPS and SMP concentrations were deter-mined. The EPS declined sharply after pretreatment but increasedafter fermentation for both the 35 g/L and 75 g/L sludges(Fig. 4a). For the 35 g/L sludge, the EPS was 9.66 0.51 mg EPS/g VSS for the untreated sludge, 1.49 0.67 mg EPS/g VSS for thepretreated sludge and 6.32 0.55 mg EPS/g VSS for the fermentedsludge. For the 75 g/L sludge, the EPS concentrations of theuntreated, pretreated and fermented sludge were15.61 0.78 mg EPS/g VSS, 3.31 0.84 mg EPS/g VSS, and5 g/L sludge with pretreatment; (c) 35 g/L sludge without pretreatment; (d) 75 g/L

tion Technology 142 (2015) 813 118.13 0.35 mg EPS/g VSS, respectively. EPS represents the organicmatter, usually proteins and polysaccharides, on the surface ofthe suspended microbial cells in the sludge solid. Therefore, wecan conclude that the pretreatment results in solubilization andrelease of organic matter from the sludge ocs into the liquid. Itshould be noted that there was a 34.6% EPS decrease (fromuntreated to fermented sludge) for the 35 g/L sludge and a 47.9%decrease for the 75 g/L sludge with pretreatment. However, therewere only 20.7% and 37.8% EPS decreases for the 35 g/L and 75 g/Lsludges, respectively, without pretreatment. The results clearlydemonstrate that pretreatment greatly improves EPS solubilizationand release from the sludge into the fermentation liquid.

Fig. 4b shows changes in the SMP in the liquid from sewagesludge fermentation. For the 35 g/L sludge, the concentrations ofSMP for the untreated, pretreated and fermented sludge were140.47 15.26 mg/L, 2102.21 211.74 mg/L and 1416.88 220.60 mg/L, respectively. While for the 75 g/L sludge, the valueswere 209.21 11.29 mg/L, 4180.45 309.99 mg/L and 2745.24 362.83 mg/L for the untreated, pretreated and fermented sludge,respectively. It can be seen that the SMP increased considerablyduring pretreatment and fermentation, which is concomitant withthe EPS decrease. However, the SMP concentration decreased by46.96 mg/L (from the untreated to fermented sludge) for the35 g/L sludge and by 50.30 mg/L for the 75 g/L sludge. This was adifferent trend to that observed with the pretreated sludge. Thereason for this is that pretreatment improves the release of theEPS from the surface of the microbial cells into the liquid andresults in a large increase in SMP. Without pretreatment, theSMP in the liquid was degraded and converted into VFA, resultingin the decrease observed after fermentation.

The changes in EPS and SMP for the three kinds of sludgeexplain the variations observed in the sludge ltrationcharacteristics, namely why ltration performance was worse after

ica12 Y.F. Zhu et al. / Separation and Purpretreatment and better after fermentation. This demonstratesthat the EPS and SMP inuence the ltration characteristics ofthe sludge [31].

The total amount of released EPS were 285.6 mg/L for the 35 g/Lsludge and 922.5 mg/L for 75 g/L sludge after pretreatment and fer-mentation. However, the determined SMP in the liquid were1961.74 mg/L and 3971.24 mg/L for the 35 g/L and 75 g/L sludge,respectively. The results indicate that the SMP is much higher thanthe released EPS from the sludge ocs. This is because the SMP notonly comes from the EPS, but also from intracellular biopolymerssuch as proteins and polysaccharides in the microbial cells.

4. Conclusions

Filtration characteristics were investigated for untreated, ther-mal alkaline pretreated and anaerobic acidogenic fermented sew-age sludge. The hypothesis of this study was well veried by thedetermination and analysis of the ltration resistance, viscosity,particle size, and ow properties of the three kinds of sludge. Themost important conclusions were as follows: (1) fermentation ofsewage sludge with a high TS value gave a high VFA concentration,and thermal alkaline pretreated sewage sludge also gave a highVFA concentration; (2) thermal alkaline pretreatment led to a highltration resistance, but the ltration resistance after fermentationdecreased by almost 99% of the pretreated sewage sludge; (3) bothpretreatment and fermentation decreased the sludge particle size;(4) the increase in the ltration resistance was attributed to therelease of EPS from the microbial cells of the sludge; and (5) deg-radation and conversion of the SMP into VFA explained thedecrease in the ltration resistance of the fermented sludge.

oc matrix, Appl. Microbiol. Biotechnol. 43 (1995) 755761.[22] M.M. Bradford, A rapid and sensitive method for the quantitation of

Fig. 4. The concentration of EPS (a) and SMP (b) during the anaerobic fermentation.A: 35 g/L sludge with pretreatment; B: 75 g/L sludge with pretreatment; C: 35 g/Lsludge without pretreatment; D: 75 g/L sludge without pretreatment.microgram quantities of protein utilizing the principle of protein-dyebinding, Anal. Biochem. 72 (1976) 248254.

[23] Y. Chen, S. Jiang, H. Yuan, Q. Zhou, G. Gu, Hydrolysis and acidication of wasteactivated sludge at different pHs, Water Res. 41 (2007) 683689.

[24] M.T. Agler, B.A. Wrenn, S.H. Zinder, L.T. Angenent, Waste to bioproductconversion with undened mixed cultures: the carboxylate platform, TrendsBiotechnol. 29 (2011) 7078.

[25] H.P. Yuan, X.B. Cheng, S.P. Chen, N.W. Zhu, Z.W. Zhou, New sludgepretreatment method to improve dewaterability of waste activated sludge,Bioresour. Technol. 102 (2011) 56595664.Acknowledgements

We gratefully acknowledge support from the National NaturalScience Foundation of China (Grant No. 51208231), Natural ScienceFoundation of Jiangsu Province of China (Grant No. BK2012121),and the Environmental Protection Department of Jiangsu Province(Grant No. 2012035).

References

[1] F.Y. Garcia Becerra, E.J. Acosta, D.G. Allen, Alkaline extraction of wastewateractivated sludge biosolids, Bioresour. Technol. 101 (2010) 69836991.

[2] E. Neyens, J. Baeyens, A review of thermal sludge pre-treatment processes toimprove dewaterability, J. Hazard. Mater. 98 (2003) 5167.

[3] Y.H. Ahn, R.E. Speece, Elutriated acid fermentation of municipal primarysludge, Water Res. 40 (2006) 22102220.

[4] A.S. Ucisik, M. Henze, Biological hydrolysis and acidication of sludge underanaerobic conditions: the effect of sludge type and origin on the productionand composition of volatile fatty acids, Water Res. 42 (2008) 37293738.

[5] Y. Chen, A.A. Randall, T. McCue, The efciency of enhanced biologicalphosphorus removal from real wastewater affected by different ratios ofacetic to propionic acid, Water Res. 38 (2004) 2736.

[6] M.F. Colmenarejo, E. Snchez, A. Bustos, G. Garca, R. Borja, A pilot-scale studyof total volatile fatty acids production by anaerobic fermentation of sewage inxed-bed and suspended biomass reactors, Process Biochem. 39 (2004) 12571267.

[7] P. Gluszcz, T. Jamroz, B. Sencio, S. Ledakowicz, Equilibrium and dynamicinvestigations of organic acids adsorption onto ion-exchange resins,Bioprocess Biosyst. Eng. 26 (2004) 185190.

[8] B. Yordanov, L. Boyadzhiev, Pertraction of citric acid by means of emulsionliquid membranes, J. Membr. Sci. 238 (2004) 191197.

[9] G. Skouteris, D. Hermosilla, P. Lpez, C. Negro, . Blanco, Anaerobic membranebioreactors for wastewater treatment: a review, Chem. Eng. J. 198199 (2012)138148.

[10] Y. Chen, H. Yang, G. Gu, Effect of acid and surfactant treatment on activatedsludge dewatering and settling, Water Res. 35 (2001) 26152620.

[11] G.P. Sheng, H.Q. Yu, X.Y. Li, Extracellular polymeric substances (EPS) ofmicrobial aggregates in biological wastewater treatment systems: a review,Biotechnol. Adv. 28 (2010) 882894.

[12] S.-E. Oh, S. Van Ginkel, B.E. Logan, The relative effectiveness of pH control andheat treatment for enhancing biohydrogen gas production, Environ. Sci.Technol. 37 (2003) 51865190.

[13] W. Park, S.H. Hyun, S.-E. Oh, B.E. Logan, I.S. Kim, Removal of headspace CO2increases biological hydrogen production, Environ. Sci. Technol. 39 (2005)44164420.

[14] Y. Nie, H. Liu, G. Du, J. Chen, Enhancement of acetate production by a novelcoupled syntrophic acetogenesis with homoacetogenesis process, ProcessBiochem. 42 (2007) 599605.

[15] H. Yuan, Y. Chen, H. Zhang, S. Jiang, Q. Zhou, G. Gu, Improved bioproduction ofshort-chain fatty acids (SCFAs) from excess sludge under alkaline conditions,Environ. Sci. Technol. 40 (2006) 20252029.

[16] J. Wang, H. Liu, B. Fu, K. Xu, J. Chen, Trophic link between syntrophic acetogensand homoacetogens during the anaerobic acidogenic fermentation of sewagesludge, Biochem. Eng. J. 70 (2013) 18.

[17] K. Xu, H. Liu, J. Chen, Effect of classic methanogenic inhibitors on the quantityand diversity of archaeal community and the reductive homoacetogenicactivity during the process of anaerobic sludge digestion, Bioresour. Technol.101 (2010) 26002607.

[18] X.L. Liu, H. Liu, J. Chen, The Condition Optimization of Sewage Sludge forProducing Volatile Fatty Acids and the Investigation of Acidogenic Mechanism,Jiangnan University, Wuxi, 2008.

[19] A. Apha, WEF, Standard Methods for the Examination of Water andWastewater 20th Edition-4500-NO3-D Nitrate Electrode Method, AmericanPublic Health Association, Washington, DC, 1998.

[20] W.N. Chan, Thermophilic Anaerobic Fermentation of Waste Biomass forProducing Acetic Acid, Texas A & M University, 2002.

[21] B. Fr/olund, T. Griebe, P.H. Nielsen, Enzymatic activity in the activated-sludge

tion Technology 142 (2015) 813[26] A. Sweity, W. Ying, M.S. Ali-Shtayeh, F. Yang, A. Bick, G. Oron, M. Herzberg,Relation between EPS adherence, viscoelastic properties, and MBR operation:biofouling study with QCM-D, Water Res. 45 (2011) 64306440.

[27] A.S. Eissa, Newtonian viscosity behavior of dilute solutions of polymerizedwhey proteins. Would viscosity measurements reveal more detailed molecularproperties?, Food Hydrocolloids 30 (2013) 200205

[28] P.R. Karr, T.M. Keinath, Inuence of particle size on sludge dewaterability, J.Water Pollut. Control Fed. (1978) 19111930.

[29] J.H. Kang, D. Kim, T.J. Lee, Hydrogen production and microbial diversity insewage sludge fermentation preceded by heat and alkaline treatment,Bioresour. Technol. 109 (2012) 239243.

[30] X. Liu, H. Liu, J. Chen, G. Du, J. Chen, Enhancement of solubilization andacidication of waste activated sludge by pretreatment, Waste Manage. 28(2008) 26142622.

[31] G.P. Sheng, H.Q. Yu, X.Y. Li, Extracellular polymeric substances (EPS) ofmicrobial aggregates in biological wastewater treatment systems: a review,Biotechnol. Adv. 28 (2010) 882894.

Y.F. Zhu et al. / Separation and Purication Technology 142 (2015) 813 13

Filtration characteristics of anaerobic fermented sewage sludge for fatty acids production1 Introduction2 Materials and methods2.1 Sewage sludge and seeding sludge2.2 Batch acidogenic fermentation2.3 Analysis

3 Results and discussion3.1 VFA production3.2 Variation in the filtration resistance and viscosity3.3 The particle size distribution3.4 Variations of EPS and SMP

4 ConclusionsAcknowledgementsReferences