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Supplementary Materials
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Fouling analysis of membrane bioreactor (MBR) treating antibiotic production
wastewater at different hydraulic retention times (HRTs)
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Dawei YU a, Yutao CHEN a, Yuansong WEI a, *, Jianxing WANG a, Yawei WANG a, Kun LI a
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State Key Joint Laboratory of Environmental Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of
Sciences, Beijing 100085,China.
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Corresponding author. E-mail: [email protected]; Tel: +86-10-62849690; Fax: +86-10-62849690.
Contents：
Table 1 Comparison of CAS wastewater treatment station and MBR
Fig. 1 TOC concentration (a) and removal rates (b) in long term running
Fig. 2 Effect of HRTs on COD (a) and NH4+-N (b) removals
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Table 1 Comparison of CAS wastewater treatment station and MBR
Equipment
HRT
MLSS
Effluents
Construction cost
h
g L-1
pH
COD/mg L-1
NH4+-N/mg L-1
million (300 t d-1)
CAS
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1.61~2.76
6.55±0.63
709.93±62.75
40.13±9.00
￥4.37
MBR
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3.82±0.01
6.68±0.17
280±17.32
11.29±0.85
￥3.91
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Fig. 1 TOC concentration (a) and removal rates (b) in long term running
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b
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Fig. 2 Effect of HRTs on COD (a) and NH4+-N (b) removals
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Long term performance of MBR system
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The SRT of MBR treating antibiotic wastewater was chosen over 200 d to achieve both
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accumulate sufficient sludge for refractory organic pollutants bio digestion, and avoid
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non-biodegradables substance accumulate in sludge. The prolonged SRT remained unchanged all over
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the 3 periods of 275 days, and 5 stages especially. To provide sufficient oxygen and ALK for
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bio-digestion, DO and ALK was maintained around 4 mg L-1 and 2000 mg L-1 (Table 2).
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For refractory organic wastewater, TOC is a reliable indicator of sludge and membrane removal of
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refractory organics in the long term performance. Long term TOC removal rate is presented in Fig1b,
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stabilize at 47.24%±12.35%. The TOC of influent, supernatant and permeate is 293.25±81.96mg L -1,
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215.19±65.65mg L-1 and 151.84±47.82mg L-1 in 275days. Permeate were much more stable given a
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fluctuant influent, show that membrane make TOC removal more stable than municipal
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wastewater(Kappel et al. 2014). Permeate higher than influent in 85-120 days for NF concentration
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recycling. Section removal rates are 23.40±23.89 %, 23.49±16.20 % and 47.24±12.35 % in sludge,
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membrane and total. It is lower than refractory acrylonitrile-butadiene-styrene wastewater in both
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removal rate and concentration (Chang et al. 2006). So according to organic pollutant removal, long
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term performance of MBR was steady in the study.
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Effects of HRT on COD removals
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Throughout the HRT optimization period, the pH, DO, membrane flux and gas sparging rate were
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controlled approximately constant to separate the influences of the HRT variation on system
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performance from other factors. Although the growth/decay amounts are different at different HRT,
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MLSS concentration was not correlated to HRT variations as municipal wastewater, which will be
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discussed in later sections. As sludge discharging is very limit and roughly stable, OLR was a nature
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result of HRT decrease. The influent COD concentrations are fluctuated from 800 to 2000 mg L-1. To
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prevent inhibitions of oxygen, sufficient DO is provided besides membrane wash demands (Table. 2).
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COD concentrations of the 5 stages were shown in Fig.2a. When HRT decline from 72 h to 60 h
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and 48 h, COD removal rates stable at 60 %. In later stage, COD removal rate rise to 69 % at 36 h, and
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then 73 % at 24 h respectively. Results show that HRT reductions consistent with higher COD removal
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rate except for too short HRT. This result agrees with the observation in high strength
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acrylonitrile-butadiene-styrene (ABS) wastewater (Chang et al. 2006). When HRT decreased too short
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at 24 h, the COD removal rates in the MBR suddenly fall. Meanwhile, organic loading rate (OLR)
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doubled from 0.19 kgCOD kgVSS-1 d-1 at 36 h of HRT to 0.38 kgCOD kgVSS-1d-1 at 24 h of HRT. But
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effluent COD below than 500 mg L-1 in the whole time, more stable than removal efficiency. Average
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effluent COD is 280 mg L-1 at 36 h especially, in spite of removal rate fluctuation. If we divided COD
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removal to two part of sludge and membrane removal, Fig.4b shows that COD removal by membrane
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is the lowest at 36 h, which agree with the supernatant COD and despite influent fluctuant. The
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activated sludge removal results differ with MBR treating municipal wastewater (Tay et al. 2003),
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sludge characters are the most significant difference between them in our observation, discussed in
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section 3.4. Thus, if considering COD removal rate (69%) and lowest permeate COD (280 mg L-1), 36
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h could be an optimized HRT.
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Effects of HRT on NH4+-N removals
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Ammonia is always efficient removed in municipal MBR. The major reasons regard to be that
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membrane reserve the slowly growth ammonia-oxidizing bacteria (AOB), and ammonia oxygen are
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rapid reacts. Fig.2b depicts the NH4+-N removals under different HRT. Ammonia removal rate is
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rapidly fall down at middle of 72 h. There is synchronization among NH 4+-N and COD removal rate
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fall down, TMP rise and effluent protein jump. So protein rise result in these effect at 72 h. In the next 3
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stages, HRT decreased from 60 h to 36 h. NH4+-N removal rate maintained over 95% and effluent less
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than 10 mg L-1, indicate that HRT decrease did not have bad effect on ammonia removal among the
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range. But after HRT decreased to 24 h, removal rate begins to fall and rise.
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Compared with municipal wastewater, antibiotic wastewater is much higher in antibiotic and
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salty, as ALK is sufficient. But salty does not change rapidly with HRT (Jang et al. 2013). Meanwhile,
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NH4+-N loading rate is not too high to inhibit removal at 0.094±0.02 gNH4+-N kgVSS-1 d-1. So more
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antibiotic contact and accumulate in short period, might inhibited the ammonia oxygen, leading to the
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NH4+-N removal rate wave. And as amounts of ammonia-oxidizing bacteria (AOB) could not change so
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quick in a 100 L reactor(Munz et al. 2008). So, ammonia-oxidizing bacteria (AOB) activity inhibited
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by antibiotic is a reasonable mechanism.
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