SUPPORTING INFORMATION

Transcription

1 SUPPORTING INFORMATION Understanding mechanisms of synergy between acidification and ultrasound treatments for activated sludge dewatering: From bench to pilot scale investigation Mei Qiang Cai, Jian Qiang Hu, George Wells, Youngwoo Seo, Richard Spinney, Shih-Hsin Ho #, Dionysios D. Dionysiou, Jie Su, Ruiyang Xiao, *, and Zongsu Wei,, * School of Environmental Science and Engineering, Zhejiang Gongshang University, Hangzhou, , China Department of Civil and Environmental Engineering, Northwestern University, Evanston, Illinois, 60208, U.S.A. Department of Civil and Environmental Engineering, University of Toledo, Toledo, Ohio, 43606, U.S.A. Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio, 43210, U.S.A. # State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, , China Environmental Engineering and Science Program, University of Cincinnati, Cincinnati, Ohio, 45221, U.S.A. Institute of Environmental Engineering, School of Metallurgy and Environment, Central South University, Changsha, , China Laboratory for the Chemistry of Construction Materials (LC 2 ), Department of Civil and Environmental Engineering, University of California, Los Angeles, California, 90095, U.S.A. * To whom correspondence should be addressed. R.X. Phone: ; fax: ; address: xiao.53@csu.edu.cn; Z.W. Phone: ; fax: ; address: wzongsu@ucla.edu. Environmental Science & Technology Number of pages: 16 (including the title page) Number of figures: 6 Number of tables: 7 S1

2 Text S1: Comparison of A/US and US/A treatments in sludge dewatering performance As shown in Figure S1, both US/A and A/US treatments significantly reduced the moisture contents and CST values. Although there is no obvious difference in moisture contents for both treatments, the CST value of the US/A treatment is higher than that of A/US, indicating a poorer filterability when US was applied first. We believe that US prior to acidification treatment has broken down sludge flocs into much finer particles, thereby causing deterioration of sludge dewaterability. Although the subsequent acidification step can facilitate agglomeration of the fine sludge particles by reducing zeta potential, it cannot yield optimal dewatering performance. As compared to the US/A treatment, the process of A/US allows longer reaction time for hydrolysis reactions of organic matter. The subsequent US irradiation further facilitated the hydrolysis process by enhancing mass transfer. Finally, in the pilot scale setup, the acidification step occurred in a mix tank which acted as a reservoir for convenient control of feeding flow rates of sludges to ultrasonic systems. Based on these reasons in batch and pilot-scale tests, we believe that the A/US treatment is better than US/A for optimizing system operation and thus sludge dewatering performance. S2

3 Text S2: Organic matter and heavy metal levels in recycled filtrate Note, the filtrate containing high levels of dissolved organic matter was recycled to the biological treatment unit in the Hangzhou MWTP. The ratio of BOD (667 ± 8 mg L 1 )/COD (940 ± 10 mg L 1 ) in the supernatant of sludge samples is 0.71, indicating a good biodegradability of the recycled filtrate (a ratio of 0.5 or greater is considered to be easily treatable in the biological treatment unit). In addition, the volume of recycled filtrate (4,800 m 3 Day 1 ) is significantly smaller than the wastewater treatment capacity (600,000 m 3 Day 1 ). Thus, the recycle filtrate containing high levels of DOCs does not exhibit a detrimental effect on the operation of the wastewater treatment plant. As shown in Table S3, the level of heavy metals in the liquid phase is lower than the China sewage discharge standard. Acidification followed by US treatment slightly increased the concentration of heavy metals in the filtrate in general. However, it should be noted that the concentration of heavy metals in the municipal wastewater treatment plant is expected to be low, thus heavy metals will not be a problem in our case. S3

4 Table S1: Characteristics of the raw sewage sludge collected from a MWTP in Hangzhou, China. parameter moisture content (%) ph CST (s) VSS/TSS d 50% (μm) Zeta potential (mv) SCOD (mg L 1 ) value Note: CST: capillary suction time; VSS: volatile suspended solids; TSS: total suspended solids; d 50% : mass median diameter of sludge flocs; SCOD: soluble chemical oxygen demand. S4

5 Table S2: Purity and manufacture information for the chemicals in this study. chemical purity manufacturer H 2 SO 4 analytical reagent Huipu Chemical&Apparatus, China NaOH analytical reagent Huipu Chemical&Apparatus, China phenol analytical reagent Kelong Chemical, China glucose analytical reagent Kelong Chemical, China t butanol analytical reagent Kelong Chemical, China S5

6 Table S3: Heavy metal contents in aqueous phase before and after the A/US treatments. Metal Filtrate of raw sludge, Filtrate of A/US treated Discharge Standard, mg L 1 sludge, mg L 1 mg L 1 Pb Cr Cu Hg < < Ni Cd < < Zn S6

7 Table S4: Influence of ph on EEM of S EPS, LB EPS and TB EPS. ph aromatic protein I (Region I) aromatic protein II (Region II) fulvic acid-like (Region III) S EPS SMP (Region IV) humic acid-like (Region V) raw LB EPS raw TB EPS raw Note: S EPS, LB EPS and TB EPS samples were diluted by 50 times. S7

8 Table S5: Influence of US power density (PD, W ml 1 ) on EEM for S EPS, LB EPS and TB EPS fraction. PD aromatic protein I (Region I) aromatic protein II (Region II) fulvic acid-like (Region III) S EPS SMP (Region IV) humic acid-like (Region V) LB EPS TB EPS Note: S EPS, LB EPS and TB EPS samples was diluted by 50 times. S8

9 Table S6: Operational conditions and dewatering results of pilot scale A/US treatments. run ph H 2 SO 4 dosage (kg d 1 ) NaOH dosage (kg d 1 ) energy input (kj L 1 ) water content (%) dry solids per liter (g) # # # # S9

10 Table S7: Cost estimation for A/US treatment per ton of dry solids (DS). item value water content of sludge cakes (%) 58.9 CST value (s) 18.0 energy demand per ton DS (kwh) 211 For 180 kg DS = [3 unit 3 kw 2 h (for US system) + 1kW 2 h (for pump system) + 6 kw energy cost 2 h (for feeding pressure in the filtration system) + 3 kw 2 h (for keeping pressure in the filtration system)] 0.12 USD (electricity fee) = 4.56 USD For 1 ton DS = 4.56 USD 180 kg DS 1000 DS = 25.3 USD For 180 kg DS = 0.17 USD (cost of 0.54 L H 2 SO 4 ) USD (cost of 0.8 kg NaOH) = 0.72 chemicals cost USD For 1 ton DS = 0.72 USD 180 kg DS 1000 DS = 4.00 USD total cost per ton of DS 29.3 USD S10

11 cake moisture (%) water in sludge cake total solid content cake moisture CST CST (s) weight (g) raw sludge A/US US/A 20 0 Figure S1: Comparison of A/US and US/A treatments in sludge dewatering performance. S11

12 80 cake moisture CST cake moisture (%) CST (s) 0 raw sludge with t-butanol 0 Figure S2: Influence of t-butanol on cake moisture and CST. S12

13 EX (nm) S-EPS LB-EPS TB-EPS 0 W ml 1 0 W ml 1 0 W ml W ml W ml W ml W ml W ml W ml W ml W ml W ml W m W m W m W ml W ml W ml W ml 1 10 W ml 1 10 W ml EM (nm) Figure S3: Influence of US power density on EEM profile of EPS under conditions of ph = 3 and 2 min sonication. S13

14 (a) (b) (c) (d) Figure S4: Optical microscopic images for raw sludge (a), acidified sludge (b), US treated sludge (c), and A/US treated sludge (d) under conditions of PD = 2.5 W ml 1 and 2 min sonication. Note, ph = 6.7 for (a) and (c), ph = 3 for (b) and (d). S14

15 raw sludge US acidification A/US concentration (mg L -1 ) PS PN 0 S-EPS LB-EPS TB-EPS S-EPS LB-EPS TB-EPS S-EPS LB-EPS TB-EPS S-EPS LB-EPS TB-EPS Figure S5: The effect of different treatments on proteins (PN) and polysaccharides (PS) concentrations under conditions of PD = 2.5 W ml 1 and 2 min sonication. Note, ph = 6.7 for raw sludge and US treatment, ph = 3 for acidification and A/US treatments. S15

16 UV 254 (cm -1 ) cake moisture (%) cake moisture UV 254 CST A B C D US w/temp ctrl US w/radical scavenger (t-butanol) US w/o Temp ctrl Acidification and heat 20 CST(s) Figure S6: Thermal effect, radical oxidation and shear forces of ultrasound on CST, cake moisture and UV 254 under different conditions: A is US with temperature control, B is US without temperature control, C is US with t butanol, and D is acidification and heat. Noted, these experiments were performed under conditions of ph = 3, PD = 2.5 W ml 1, and 2 min sonication. S16