ARTICLE pubs.acs.org/IECR
Effect of Initial pH Adjustment on Hydrolysis and Acidification of Sludge by Ultrasonic Pretreatment Xiao-Rong Kang,† Guang-Ming Zhang,*,† Lin Chen,† Wen-Yi Dong,‡ and Wen-De Tian† †
School of Municipal and Environmental Engineering, and ‡Harbin Institute of Technology Shenzhen Graduate School, Harbin Institute of Technology, Harbin 150090, China ABSTRACT: Batch tests were carried out to analyze the effect of pH in the range of 712 on the hydrolysis and acidification of sludge at room temperature. Ultrasonic pretreatment was conducted to disintegrate waste activated sludge (WAS) and accelerate WAS hydrolysis. The experimental results showed that the sludge with ultrasonic pretreatment was readily degraded in the hydrolysis and acidification process, and more organic substances were released with increase of initial pH. The optimal initial pH for sludge acidification was 11, and the short chain fatty acids (SCFAs) concentration reached about 1751 mg/L after 15 days of hydrolysis and acidification. Phosphorus release was investigated during hydrolysis and acidification at any pH adjustment. The SCFAs mainly consisted of acetic and propionic, accounting for 74.684% of total SCFAs. Three microbial species, including Bacteroidetes, γ-proteobacteria, and β-proteobacteria, were involved in different pH environments of the hydrolysis and acidification process, and, simultaneously, the three species were identified as being responsible for SCFAs accumulation and protein degradation. This study indicated that the combination of ultrasonic pretreatment, alkaline adjustment for hydrolysis, and acidification of WAS was an appropriate method for SCFAs accumulation and contributed to the demand of carbon source for WWTPs.
1. INTRODUCTION The biological nutrient removal (BNR) processes, especially phosphorus removal, have become the main objectives of wastewater treatment to minimize eutrophication problems. Concentrations of readily biodegradable COD, such as short chain fatty acids (SCFAs), in wastewater strongly affect the efficiency of BNR (phosphorus and nitrogen) processes. However, these amounts of carbon source in the influent wastewater cannot meet the demands of domestic wastewater treatment process. For instance, 69 mg of SCFAs is required for biological removal of 1 mg of phosphorus,1 whereas the phosphorus removal is often limited by the available SCFAs due to the consumption of SCFAs by other organisms competing with phosphate accumulating organisms.2 Therefore, how to get and use SCFAs becomes the bottleneck of sewage treatment. An alternative strategy of increasing SCFAs concentration in the BNR facility is using an internal carbon source, that is, by acidification process of waste activated sludge (WAS) generated in wastewater treatment plants.3 As the major component of sludge is organic matter of high levels, it may become a plentiful source of inexpensive organic substrate for fermentative SCFAs production. The anaerobic digestion process usually includes three stages of hydrolysis, acidification, and methanogenesis, whereas hydrolysis is the rate-limiting step of the overall process.4 Extremely slow hydrolysis rate of anaerobic digestion for WAS, induced by the cell wall and membrane of bacteria in WAS, inhibits the release of organic substances to the outside of the cell, thus resulting in long digestion time. In an effort to accelerate the rate of sludge hydrolysis, several pretreatments can be considered, such as thermal,5,6 alkaline,7,8 Fenton, 9 ozone, 10,11 ultrasonic, 12,13 mechanical 14 treatment, and various techniques combination 15,16 treatment. The r 2011 American Chemical Society
employment of ultrasonic treatment is generally regarded as an effective way for disruption sludge flocs and is nonhazardous to the environment; concomitantly, retention time in the digester can be shortened to reduce the plant footprint. Ultrasound frequency often ranges from 20 kHz to 10 MHz.13 Particularly, at low frequency from 20 kHz to 40 kHz cavitation occurs, resulting in strong mechanical forces. Additionally, the efficiency of sludge acidification process is strongly affected by some chemical effects, such as the changes of pH. Some investigators found that alkaline pH environments (such as pH 10) could accelerate WAS hydrolysis and acidification rates without methane production.17 Noticeably, although extreme alkaline condition can improve the hydrolysis process, the hydrolytic enzyme will be significantly affected by the pH adjustment.18 Thus, how to maintain enzyme activity is a key point when the sludge anaerobic digestion environment is adjusted by alkaline. This Article presents results from hydrolysis and acidification tests, in which the ultrasonic pretreatment method has been used in combination on sludge. The effects of initial pH adjustment on sludge hydrolysis, proteins and carbohydrates solubilization, phosphorus release, and SCFAs were investigated. Of interest, the composition of SCFAs was examined, and the mechanisms of SCFAs production in this case were discussed. Microbial community throughout hydrolysis and acidification process was analyzed using polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE), and subsequent sequencing of selective DNA bands. Received: June 6, 2011 Accepted: September 27, 2011 Revised: September 21, 2011 Published: September 27, 2011 12372
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Industrial & Engineering Chemistry Research Table 1. Characteristics of Sewage Sludge Used in the Experiment item
value
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Table 2. 16S rRNA Primers Used in the Experiment primers
sequences
BSF338
50 -ACTCCTACGGGAGGCAGCAG-30
TS (mg/L)
15 000 ( 200
BSF534
50 -ATTACCGCGGCTGCTGG-30
VSS (mg/L) total COD (mgCOD/L)
10 500 ( 100 15 000 ( 200
BSF534-GC clamp 50 -ATTACCGCGGCTGCTGGCGCCCGCCGCGC
pH
6.57.0
PO43P (mg/L)
12.3
CCCGCGCCCGGCCCGCCGCCCCCGCCCC-30
Table 3. Characteristics of Ultrasonic Sludge
2. MATERIALS AND METHODS 2.1. Waste Activated Sludge Sample Characteristics. The WAS used in this study was obtained from the secondary sedimentation tank of the Luofang municipal wastewater treatment plant in Shenzhen, China. Prior to ultrasonication, the sludge was concentrated and stored at 4 °C. The detailed characteristics of the concentrated sludge are shown in Table 1, including pH, PO43P, total COD, total suspended solid (TSS), and volatile suspended solid (VSS) concentration. 2.2. Ultrasonic Pretreatment. The ultrasonic pretreatment of WAS was conducted with an ultrasonicator (JY98-IIIN, Xinzhi Inc., China) at a frequency of 20 kHz and a rated power of 1200 W. For each ultrasonic experiment, 400 mL of sludge was filled in a stainless steel beaker with the probe allocated at 2 cm below the liquid surface, and the supplied ultrasonic power was adjusted at 800 W. The ultrasonic time was operated at 30 min, and the temperature of sludge samples was controlled lower than 40 °C in the ultrasonic process. 2.3. Anaerobic Digestion Reactors. The experiments of anaerobic digestion were performed in six stirred tank reactors with a working volume of 2 L. Each anaerobic digestion reactor contained 800 mL of waste activated sludge and 800 mL of ultrasonic pretreated sludge. Initially, the pH of the mixed sludge was adjusted, respectively, at 7, 8, 9, 10, 11, and 12 by adding 5 M sodium hydroxide (NaOH) or 5 M hydrochloric (HCl). The operation of anaerobic digestion was conducted at room temperature (20 ( 2 °C) for 15 days. During the hydrolysis and acidification reaction, the pH was recorded automatically without adjustment, and the SCFAs were collected every 2 days. 2.4. Analytical Methods. The analyses of soluble COD (SCOD), PO43P, TSS, and VSS were measured according to Standard Methods.19 The carbohydrates were determined using the anthrone sulfuric method with glucose as the standard;20 and the proteins were quantified using a modified Lowry method with bovine serum albumin (BSA) as the standard.21 The composition of SCFAs was analyzed by means of gas chromatography (Agilent 6890 N) using a flame ionization detector (FID) and DB-WAXETR column (30 m 0.53 mm 1.0 μm),17 and the total SCFAs was recorded as the sum of measured acetic, propionic, n-butyric, iso-butyric, n-valeric, and iso-valeric acids. 2.5. DNA Extraction. Total DNA was extracted from each reactor biomass on the 15th day using the E.Z.N.A Soil DNA Kit (Omega Bio-Tek Inc.). Prior to extraction, samples of suspended biomass were concentrated by centrifuging at 10 000g for 5 min. Sterilized deionized water (3 mL) was used to resuspend biomass and recentrifuge for extraction. The extracted DNA was eluted in TrisHCl buffer (pH 8.0) and stored at 20 °C. 2.6. Polymerase Chain Reaction (PCR). The V3 region in the 16S rRNA of Eubacteria was amplified by PCR using the forward primer BSF338 and the reverse primer BSR534-GC clamp. The PCR primers used in the experiment are shown in Table 2.
item
value
soluble COD (mg/L)
5265
proteins (mg/L)
1331
carbohydrates (mg/L) PO43P (mg/L)
247 51
PCR amplification was carried out in an automated thermal cycler (Veriti, ABI). The detailed steps of the PCR reaction were according to the method in ref 22. 2.7. DGGE. DGGE was performed with the DCode Universal Mutation Detection system (Bio-Rad, U.S.). Denaturing gradient conducted in this study ranged from 40% to 60%. Electrophoresis was carried out at a constant voltage of 70 V for 8 h, and then the gel was stained.23 2.8. Cloning of 16S rRNA Fragments. For further sequencing and phylogenetic analyses, bands of interest were excised from the gel. Each gel fragment was crushed, and the DNA was resolved in 50 μL of sterile deionized water at 4 °C. PCR was performed with the primer BSF338 and BSR534 (Table 2). The PCR fragments were purified using E.Z.N.A Cycle Pure Kit (Omega Bio-Tek. Inc.) and cloned in E. coli DH5a (Takara, Dalian, China) using PMD19-T Vector (Takara, Dalian, China) according to the manufacturer’s instruction. 2.9. DNA Sequencing and Phylogenetic Tree. 16S rRNA gene fragment clones were sequenced. A search for the closest reference microorganisms in the GenBank database using the partial 16S rRNA sequences was carried out with the BLAST program (http://www.ncbi.nlm.nih.gov/blast). Neighbor-joining trees were constructed for phylogenetic analysis using MEGA 3.0 software.
3. RESULTS AND DISCUSSION 3.1. Ultrasonic Pretreatment on WAS. Previous study showed that ultrasonic pretreatment of WAS increased the solubilization and was more pronounced when power density and ultrasonic time increased. In this study, the selected power density and ultrasonic time for sludge disintegration were 2.0 W/mL and 30 min, respectively. As shown in Table 3, WAS was disintegrated and released about 5265 mg/L SCOD (accounting for 30% total COD); simultaneously, 1333 mg/L proteins and 247 mg/L carbohydrates were dissolved out. The application of additional ultrasound changed the sludge characteristics and made sludge more suitable for hydrolysis and acidification as substrate than untreated WAS. Meanwhile, it also clearly suggested that the sludge was effectively sheared by cavitation bubbles generated from the ultrasonic generator, thus shortening the hydrolysis retention time of the conventional anaerobic digestion.17 After the sludge was mixed, the initial characteristics of reactors though pH adjustment are shown in Table 4. 12373
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Table 4. Characteristics of Mixed Sludge before and after Alkaline Adjustment item
mixed sludge
pH = 7
pH = 8
pH = 9
pH = 10
pH = 11
pH = 12
soluble COD (mg/L)
1123
1293
1016
1224
1367
1830
2833
proteins (mg/L)
311
321
304
805
1098
1301
2610
carbohydrates (mg/L)
175
178
170
200
253
278
600
26
28
25
30
30
30
30
PO43P (mg/L)
Figure 1. Release of SCOD under different initial pH’s during hydrolysis and acidification period.
3.2. Effects of Initial pH on SCOD Production. Sludge hydrolysis can be expressed by the changes of SCOD concentrations.24,25 Simultaneously, the changes of SCOD at various initial pH and anaerobic digestion time are shown in Figure 1. It was obvious that SCOD concentration increased with the increase of initial pH value. Additionally, the SCOD concentration in the reactor fist rapidly increased with the extension of hydrolysis and acidification time, but gradually leveled off after 3 days of hydrolysis and acidification, except at pH 7. For instance, at pH 12, SCOD concentration increased from 2833 to 6613 mg/L within 3 days, and then remained steady. On the basis of SCOD analysis, initial pH 10, pH 11, pH 12 adjustments were more beneficial for hydrolysis of ultrasonic sludge than initial pH 7, pH 8, and pH 9. Because of the same characteristics of the ultrasonic sludge and inoculated sludge, the different dissolution rates of sludge were mainly attributed to the different pH adjustments. During the process of the ultrasonication, sludge floc was disintegrated extensively and solublized by the action of cavitations. The alkaline dosing adjusted the pH value of anaerobic digestion environment as well as strengthened the role of ultrasonic sludge. 3.3. Effects of pH on Soluble Proteins and Carbohydrates. The sludge proteins and carbohydrates were respectively converted to soluble proteins and carbohydrates in hydrolysis and acidification process of sludge. The effects of pH and reaction time on the production of soluble proteins and carbohydrates are shown in Figure 2. It was obvious that concentrations of these two products at different pH’s had a trend similar to the changes of reaction time. At the beginning, the higher were the initial pH’s, the more proteins and carbohydrates were released. For example, the proteins concentration increased from 321 to 2610 mg/L as the initial pH increased from 7 to 12, and the corresponding concentration of carbohydrates increased from 178 to 600 mg/L. As is also seen in Figure 2, during the 5 days of
hydrolysis and acidification, the concentration of soluble proteins and carbohydrates gradually reduced, and the declining concentration of soluble proteins was larger than that of carbohydrates. For instance, at pH 11, proteins and carbohydrates were reduced by 331 and 103 mg/L, respectively. After 5 days, the concentrations of proteins and carbohydrates fluctuated and remained relatively constant concentration in most cases, except at pH 12. At pH 12, the proteins and carbohydrates concentration were continuous decreased. The detailed reasons for occurrence of this phenomenon would be explained as follows. Initially, the sludge hydrolysis process was accelerated due to the ultrasonic pretreatment and alkaline regulation. It is well know that both proteins and carbohydrates are the main composition of extracellular polymeric substances (EPS). The alkaline pH resulted in the dissociation of acidic groups in EPS and repulsion between the negatively charged EPS. Thus, higher concentrations of proteins and carbohydrates were observed at higher initial pH’s. The reduction of the concentration of soluble proteins and carbohydrates during the first 5 days can be explained from two aspects. One reason for the reduction was the fact that soluble proteins and carbohydrates were consumed as substrates to produce short chain fatty acids, especially the proteins.26 Another reason for the reduction was that a part of soluble proteins was reflocculated when the environmental pH value was near the isoelectric point of proteins. The environmental pH value had a great influence on the proteins charge magnitude and charge distribution. Flocculation happened when the pH value was close to the isoelectric point of proteins; otherwise, repulsion occurred as the pH value was far away from the isoelectric point. Thus, as the acidification reaction continued, the reduction of proteins and carbohydrates was observed. In the following hydrolysis and acidification process at pH 711, particulate substrates were hydrolyzed to release proteins and carbohydrates due to the biological hydrolysis; concomitantly, the acidification process also occurred in that soluble proteins and carbohydrates were degraded. When the rate of release was close to the degradation, the proteins and carbohydrates concentration maintained a dynamic balance on the basis of hydrolysis and acidification environment. If the degradation rate was less or more than the release, the proteins concentration would be higher or lower than the balance. However, in the case of pH 12, the degradation rate was not corresponding to the concentration of the release despite that plenty of biodegradable soluble proteins and carbohydrates were obtained. This might be attributed to the reason that sludge degradable capacity was greatly affected by high alkaline concentration. Hence, the high alkaline environment of pH 12 value damaged the biological enzyme activity and reduced the acidification activity. 3.4. Effects of pH on the SCFAs Production and Composition. The effects of initial pH adjustment and hydrolysis and acidification time on SCFAs concentration are shown in Figure 3a. The SCFAs concentration increased with the extension 12374
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Figure 2. Effects of initial pH on (a) soluble proteins concentration and (b) soluble carbohydrates concentration during hydrolysis and acidification period.
Figure 3. Effects of initial pH on (a) the SCFAs production and (b) the SCFA composition.
of anaerobic digestion time in most cases except at pH 7, similar to the results observed with SCOD. The initial total SCFAs concentration in the reactor was about 1.2 mg/L. After 15 days, the SCFAs concentration increased significantly under alkaline conditions, which followed the order: pH 11 (1753 mg/L) > pH 10 (1621 mg/L) > pH 12 (1357 mg/L) > pH 9 (1110 mg/L) > pH 8 (903 mg/L) > pH 7 (554 mg/L). During the hydrolysis and acidification process, the environment pH value gradually converted from initial alkaline to acid, which might be correlated with two points. On one hand, the production of SCFAs during hydrolysis and acidification neutralized the previous dosage alkaline. On the other hand, the acidification process was initiated due to the lack of continuous alkaline regulation. In the transition of the acidity, methanogenesis was expected to occur due to plenty of SCFAs and the appropriate neutral environment, reflected in a decreased rate of SCFAs production. The environmental pH value then gradually switched to the acidic range due to the increased production of SCFAs, in which methanogenesis was inhibited and SCFAs were accumulated again. Thus, it seemed that SCFAs were accumulated and the production of methane was inhibited under the alkaline or acidic environment. Besides, it can be seen from Figure 3a that the concentration of SCFAs at initial pH 12 is extremely lower than that at pH 10 and pH 11. The result showed that the overdose of alkaline was harmful for the microbial
environment and acidification activity, which was responsible for degradation of the proteins and carbohydrates. Increasing evidence suggests that the performance of enhanced biological phosphate removal relies not only on the total amount but also on the composition of SCFAs. As shown in Figure 3b, the distribution and percentage of SCFAs are compared under different initial pH’s. The order of individual SCFAs content was as follows: acetic > propionic > n-butyric > iso-butyric > iso-valeric > n-valeric, and the acetic and propionic were the main products at all initial pH’s. The sum of the acetic and propionic accounted for 74.684.0% of total SCFAs at pH 712, respectively. These results clearly revealed that the suitable pH could be controlled at 11 for its enhanced SCFAs yield. 3.5. Effects of pH on Phosphorus Release. The effects of initial pH adjustment on the phosphorus release are presented in Figure 4. During 15 days of hydrolysis and acidification period, the released phosphorus concentration had the same trend at different initial pH’s and increased in fluctuation. At the end of 15 days of hydrolysis and acidification, the phosphorus concentration was in a range of 131.7143.6 mg/L for all initial pH’s; simultaneously, the released ratios (phosphorus/VSS) were in a range of 9.6910.8 mg PO43P/gVSS. Lipid in the hydrolysis and acidification process was degraded into long chain fatty acids with phosphorus release;26 thus the concentration of soluble phosphorus reflected the extent of organic phosphorus 12375
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Figure 4. Effects on release of phosphorus at different initial pH’s.
Figure 5. Denaturing gradient gel electrophoresis (DGGE) profiles of the V3 region of the 16S rRNA gene amplified with primers 338F-GC and 534R from DNA samples.
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degradation in the hydrolysis and acidification process. With disintegration of sludge after ultrasonic pretreatment, organic phosphorus was released at the same time. In the subsequent hydrolysis and acidification process, released organic phosphorus was degraded to phosphorus at different initial pH’s. As seen in Figure 4, the reason for the release of phosphorus concentration was mainly related to ultrasonic pretreatment, influenced slightly by the initial pH’s. 3.6. DGGE Analysis: Community Structure of Anaerobic Digestion. The specific PCR amplification was followed by DGGE, cloning, and sequencing of 16S rRNA genes to reveal the microbial structure of the anaerobic digestion reactors. The sample sequences were extracted from the hydrolysis and acidification sludge in the six reactors. As is shown in Figure 5, the DGGE fingerprints of the six samples are generally similar. Almost all predominant bands were present in the samples from different bioreactors, except band 3 and band 4 were clearly present in the pH 12 sample. During the sludge anaerobic digestion, the populations and numbers of hydrolytic bacteria and acidogenic bacteria were closely related to the production of SCFAs. DGGE banding patterns do provide a means for measuring the apparent diversity of anaerobic digestion microbial community under initial alkaline adjustment. The results of DGGE fingerprints demonstrated that initial alkaline adjustment did not have a significant effect on the anaerobic digestion community. Together with the analysis of SCFAs production efficiency, the initial alkaline dosage, which raised the pH value of the initial anaerobic digestion environment less than 12, did not undermine the microbial community structure. Ten predominantly different bands (110) were carefully excised from the DGGE gel, reamplified, cloned, and sequenced. The nucleotide sequences were then compared to similar bacteria available in the GenBank database using BLASTN. All sequences were found to be 94100% homologous with previously identified 16S rRNA gene sequences. A comprehensive phylogenetic 16S rRNA tree reflected the relationships of nucleotide sequences and similar sequences available on NCBI. As shown in Figure 6, the phylogenetic 16S rRNA tree shows that
Figure 6. Phylogenetic tree of 16S rRNA sequences from DGGE profiles represented the relationship of the anaerobic digestion sludge population. The scale bar represents two substitutions per 100 nucleotide positions. 12376
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Industrial & Engineering Chemistry Research the anaerobic anaerobic digestion sequences are grouped within the genera of Bacteroidetes, γ-proteobacteria, and β-proteobacteria. Of all of the bands, bands 8, 9, 7, 10 belonged to β-proteobacteria, bands 6, 2, 3 belonged to γ-proteobacteria, and bands 4, 1, 5 belonged to Bacteroidetes. Microbial structure is related to the environment and substrates; only few bacteria phyla survived in the high alkaline environment. Because of ultrasonic pretreatment, plenty of proteins and carbohydrates were biodegraded, and SCFAs were produced in the reactors. Thus, the three bacteria phyla contributed to the proteins biodegration. Bacteroidetes are well represented by the available sequences, and the corresponding microorganisms are probably important participants in the anaerobic digestion process.27 In research about proteins degradation investigated by Yueqin Tan,28 Bacteroidetes proved to be predominant bacteria for proteins biodegradation. γ-Proteobacteria are significant components of the microbial communities during the anaerobic decomposition of olive mill solid wastes.29 Some of the γ-proteobacteria played the role of acidogenesis and contributed to SCFAs production.30 In this study, bands 3 and 4 were involved in the pH 12 environment and survived in the initial high alkaline condition. Some of the Acinetobacter and Dysgonomonas similar to bands 3 and 4 could tolerate the initial pH 12 environment; simultaneously, they were adapted to acidic conditions after 15 days of hydrolysis and acidification process. β-Proteobacteria were studied by Tan;31 β-proteobacteria were part of microbial communities in excess sludge after heat-alkaline treatment and acclimation and contributed to excess sludge reduction. Thus, the three main populations in this experiment played an important role in the hydrolysis and acidification process and tolerated pH values in the range of 712.
4. CONCLUSIONS The experiments demonstrated that ultrasonic pretreatment had an important effect on accelerating sludge hydrolysis, and, simultaneously, the efficiency of hydrolysis and acidification was enhanced by initial alkaline regulation. Hydrolysis and acidification effluent, rich in SCFAs and hydrolyzate, could be used to promote BNR process. The concluding remarks of this study are outlined as follows: • WAS was hydrolyzed and acidified under the coeffect of ultrasonic pretreatment and initial alkaline adjustment; simultaneously SCOD concentration was positive as related to the initial pH value. Soluble proteins and carbohydrates were consumed largely during the acidification process. • The efficiency of the total SCFAs concentration was improved with the increase in initial pH from 7 to 11. Simultaneously, extremely high initial pH adjustment (pH = 12) was harmful for bacteria activity. Acetic and propionic acids were the major components of SCFAs at any pH value. • The release of phosphorus was mainly related to ultrasonic pretreatment in the hydrolysis and acidification process. • Bacteroidetes, γ-proteobacteria, and β-proteobacteria involved in the hydrolysis and acidification process contributed to proteins and carbohydrates biodegradation and SCFAs production; simultaneously, some of the three bacteria could survive in the initial alkaline environment and subsequent acid conditions.
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’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
’ ACKNOWLEDGMENT This work was financially supported by a Special Project of the National Water Pollution Control and Management of China (Grant no. 2008ZX07317-02). Special thanks to those people at the Harbin Institute of Technology Shenzhen Graduate School who provided help with this manuscript. ’ REFERENCES (1) Pitmam, A.; Ltter, L.; Alexander, W.; Deacon, S. Fermentation of raw sludge and elutriation of resultant fatty acids to promote excess biological phosphorus removal. Water Sci. Technol. 1992, 25, 185–194. (2) Yuan, H.; Chen, Y.; Zhang, H.; Jiang, S.; Zhou, Q.; Gu, G. Improved bioproduction of short-chain fatty acids (SCFAs) from excess sludge under alkaline conditions. Environ. Sci. Technol. 2006, 40, 2025– 2029. (3) Elefsiniotis, P.; Wareham, D.; Smith, M. Use of volatile fatty acids from an acid-phase digester for denitrification. J. Biotechnol. 2004, 114, 289–297. (4) Bougrier, C.; Carrere, H.; Delgenes, J. Solubilisation of wasteactivated sludge by ultrasonic treatment. Chem. Eng. J. 2005, 106, 163–169. (5) Gavala, H. N.; Yenal, U.; Skiadas, I. V.; Westermann, P.; Ahring, B. K. Mesophilic and thermophilic anaerobic digestion of primary and secondary sludge. Effect of pre-treatment at elevated temperature. Water Res. 2003, 37, 4561–4572. (6) Bougrier, C.; Albasi, C.; Delgenes, J. P.; Carrere, H. Effect of ultrasonic, thermal and ozone pre-treatments on waste activated sludge solubilisation and anaerobic biodegradability. Chem. Eng. Process. 2006, 45, 711–718. (7) Lin, J. G.; Ma, Y. S.; Huang, C. C. Alkaline hydrolysis of the sludge generated from a high-strength, nitrogenous-wastewater biological-treatment process. Bioresour. Technol. 1998, 65, 35–42. (8) Kim, T.-H.; Nam, Y.-K.; Park, C.; Lee, M. Carbon source recovery from waste activated sludge by alkaline hydrolysis and gammaray irradiation for biological denitrification. Bioresour. Technol. 2009, 100, 5694–5699. (9) Tokumura, M.; Sekine, M.; Yoshinari, M.; Znad, H. T.; Kawase, Y. Photo-Fenton process for excess sludge disintegration. Process Biochem. 2007, 42, 627–633. (10) Chu, L. B.; Yan, S. T.; Xing, X. H.; Yu, A. F.; Sun, X. L.; Jurcik, B. Enhanced sludge solubilization by microbubble ozonation. Chemosphere 2008, 72, 205–212. (11) Chu, L.; Yan, S.; Xing, X. H.; Sun, X.; Jurcik, B. Progress and perspectives of sludge ozonation as a powerful pretreatment method for minimization of excess sludge production. Water Res. 2009, 43, 1811–1822. (12) Tiehm, A.; Nickel, K.; Zellhorn, M.; Neis, U. Ultrasonic waste activated sludge disintegration for improving anaerobic stabilization. Water Res. 2001, 35, 2003–2009. (13) Pilli, S.; Bhunia, P.; Yan, S.; LeBlanc, R.; Tyagi, R.; Surampalli, R. Ultrasonic pretreatment of sludge: A review. Ultrason. Sonochem. 2011, 18, 1–18. (14) Nah, I. W.; Kang, Y. W.; Hwang, K. Y.; Song, W. K. Mechanical pretreatment of waste activated sludge for anaerobic digestion process. Water Res. 2000, 34, 2362–2368. (15) Kim, D.-H.; Jeong, E.; Oh, S.-E.; Shin, H.-S. Combined (alkaline + ultrasonic) pretreatment effect on sewage sludge disintegration. Water Res. 2010, 44, 3093–3100. (16) Vlyssides, A.; Karlis, P. Thermal-alkaline solubilization of waste activated sludge as a pre-treatment stage for anaerobic digestion. Bioresour. Technol. 2004, 91, 201–206. 12377
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(17) Chen, Y.; Jiang, S.; Yuan, H.; Zhou, Q.; Gu, G. Hydrolysis and acidification of waste activated sludge at different pHs. Water Res. 2007, 41, 683–689. (18) Batstone, D.; Keller, J.; Angelidaki, I.; Kalyuzhnyi, S.; Pavlostathis, S.; Rozzi, A.; Sanders, W.; Siegrist, H.; Vavilin, V. Anaerobic Digestion Model No. 1 (ADM1), IWA scientific and technical report no. 13; IWA Publishing: London, UK, 2002. (19) Apha, A. WEF Standard Methods for the Examination of Water and Wastewater; American Public Health Association: Washington, DC, 1998. (20) Morris, D. L. Quantitative determination of carbohydrates with Dreywood’s anthrone reagent. Science 1948, 107, 254–255. (21) Frolund, B.; Griebe, T.; Nielsen, P. H. Enzymatic activity in the activated-sludge floc matrix. Appl. Microbiol. Biotechnol. 1995, 43, 755–761. (22) Shin, S. G.; Han, G.; Lim, J.; Lee, C.; Hwang, S. A comprehensive microbial insight into two-stage anaerobic digestion of food wasterecycling wastewater. Water Res. 2010, 44, 4838–4849. (23) Kim, J.; Shin, S. G.; Han, G.; O’Flaherty, V.; Lee, C.; Hwang, S. Common key acidogen populations in anaerobic reactors treating different wastewaters: Molecular identification and quantitative monitoring. Water Res. 2011, 45, 2539–2549. (24) Andreasen, K.; Petersen, G.; Thomsen, H.; Strube, R. Reduction of nutrient emission by sludge hydrolysis. Water Sci. Technol. 1997, 35, 79–85. (25) Hatziconstantinou, G.; Yannakopoulos, P.; Andreadakis, A. Primary sludge hydrolysis for biological nutrient removal. Water Sci. Technol. 1996, 34, 417–423. (26) Miron, Y.; Zeeman, G.; Van Lier, J. B.; Lettinga, G. The role of sludge retention time in the hydrolysis and acidification of lipids, carbohydrates and proteins during digestion of primary sludge in CSTR systems. Water Res. 2000, 34, 1705–1713. (27) Nelson, M. C.; Morrison, M.; Yu, Z. A meta-analysis of the microbial diversity observed in anaerobic digesters. Bioresour. Technol. 2011, 102, 3730–3739. (28) Tang, Y.; Shigematsu, T.; Morimura, S.; Kida, K. Microbial community analysis of mesophilic anaerobic protein degradation process using bovine serum albumin (BSA)-fed continuous cultivation. J. Biosci. Bioeng. 2005, 99, 150–164. (29) Rincon, B.; Raposo, F.; Borja, R.; Gonzalez, J. M.; Portillo, M. C.; Saiz-Jimenez, C. Performance and microbial communities of a continuous stirred tank anaerobic reactor treating two-phases olive mill solid wastes at low organic loading rates. J. Biotechnol. 2006, 121, 534–543. (30) Supaphol, S.; Jenkins, S. N.; Intomo, P.; Waite, I. S.; O’Donnell, A. G. Microbial community dynamics in mesophilic anaerobic codigestion of mixed waste. Bioresour. Technol. 2011, 102, 4021–4027. (31) Tan, R.; Miyanaga, K.; Toyama, K.; Uy, D.; Tanji, Y. Changes in composition and microbial communities in excess sludge after heatalkaline treatment and acclimation. Biochem. Eng. J. 2010, 52, 151–159.
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