Specific Oxygen Utilization Rate Research Articles

Pollutants removal and connections among sludge properties, metabolism potential and microbial characteristics in aerobic granular sequencing batch reactor for petrochemical wastewater treatment

Petrochemical wastewater contains inhibitory compounds such as aromatics that are toxic to microorganisms during biological treatment. The compact and layered structure and the high amount of extracellular polymeric substances (EPS) in aerobic granular sludge (AGS) can contribute to protecting microorganisms from the harsh environment. This study evaluated the changes in the granule properties, pollutants removal, microbial metabolic potential and molecular microbial characteristics of the AGS process for petrochemical wastewater treatment. Granules treating petrochemical wastewater had a higher SVI30/SVI5 value (0.94) than that treating synthetic wastewater. An increase in bioactivity and EPS secretion with higher bio-polymer composition, specifically the functional groups such as hydroxyl, alkoxy and amino in protein, was observed, which promoted biomass aggregation. The granules also had more than 2-fold higher specific oxygen utilization rate. The AGS-SBR process obtained an average COD removal of 93% during petrochemical wastewater treatment and an effluent bCOD of below 1 mg L−1. No obvious inhibition of nitrification and denitrification activity was observed in the processes attributed to the layered structure of AGS. The average effluent NH4+-N of 5.0 mg L−1 was obtained and TN removal efficiencies of over 80.0% was achieved. Molecular microbial analysis showed that abundant functional genera Stenotrophomonas and Pseudoxanthomonas contributed to the degradation of aromatics and other petroleum organic pollutants. They were enriched with the variation of group behavior while metabolisms of amino acids and carboxylic acids by the relevant functional genera (e.g., Cytophagia) were significantly inhibited. The enrichment of Flavobacterium and Thermomonas promoted nitrification and denitrification, respectively. This research revealed the rapid start-up, enhanced granule structural strength, high inhibition resistance and considerable performance of AGS-SBR for petrochemical wastewater treatment.

Effect of Cd(II) shock loading on performance, microbial enzymatic activity and microbial community in a sequencing batch reactor

The performance, microbial enzymatic activity and microbial community of a sequencing batch reactor (SBR) were explored under instantaneous Cd(II) shock loading. After a 24-h Cd(II) shock loading of 100 mg/L, the chemical oxygen demand and NH4+-N removal efficiencies decreased significantly from 92.73% and 99.56% on day 22 to 32.73% and 43% on day 24, respectively, and then recovered to the normal values gradually. The specific oxygen utilization rate (SOUR), specific ammonia oxidation rate (SAOR), specific nitrite oxidation rate (SNOR), specific nitrite reduction rate (SNIRR) and specific nitrate reduction rate (SNRR) decreased by 64.81%, 73.28%, 77.77%, 56.84% and 52.46% on day 23 in comparison with the absence of Cd(II) shock loading, respectively, and they gradually returned to the normal levels. The changing trends of their associated microbial enzymatic activities including dehydrogenase, ammonia monooxygenase, nitrite oxidoreductase, nitrite reductase and nitrate reductase were in accordance with SOUR, SAOR, SNOR, SNIRR and SNRR, respectively. Cd(II) shock loading promoted the microbial reactive oxygen species production and lactate dehydrogenase release, indicating that instantaneous shock caused oxidative stress and damaged to cell membranes of the activated sludge. The microbial richness and diversity, and the relative abundance of Nitrosomonas and Thauera obviously decreased under the stress of Cd(II) shock loading. PICRUSt prediction showed that Cd (II) shock loading significantly affected Amino acid biosynthesis, Nucleoside and nucleotide biosynthesis. The present results are conducive to take adequate precautions to reduce the adverse effect on bioreactor performance in wastewater treatment systems.

Evaluating the influence of gradient applied voltages on electro-enhanced sequence batch reactor treating aniline wastewater: System performance, microbial community and functional genes

Aniline is an important industrial raw material. Its complex structure makes it difficult to be chemically oxidized and its intense biological toxicity also increases the difficulty of biodegradation. Therefore, electro-biological system based on biological processing have become a new direction in the field of environmental governance. Comparative evaluation of the performance differences of reactors at gradient external voltages (1.5, 3.0, 4.5 and 6.0 V) was investigated to seek the optimal applied voltage in the electro-enhanced sequence batch reactor treating aniline wastewater. Results showed that all reactors degraded aniline effectively, the aniline degradation rate of five reactors was about 100%. However, the highest removal efficiency of total nitrogen was obtained at 1.5 V, up to 88.89%. Compared with control, high applied voltage (>3.0 V) deteriorated the nitrification performance and the removal efficiency of TN was descended along with the increase of applied voltages. Besides, proper applied voltage promoted the secretion of extracellular polymeric substance. The sludge activity such as specific oxygen utilization rate (SOUR), dehydrogenase (DHA) was highly increased under the applied voltage of 1.5V, so did the Ammonia monooxygenase (AMO) and nitrate reductase (NAR). Based on the high-throughput sequencing analysis, introducing applied voltages altered the microbial diversity and community structure. Particularly, several functional genera such as autotrophic nitrifying bacteria and denitrifying bacteria were enriched in the system at 1.5V. Network analysis also found that the cooperative/competitive relationship between key functional genus became simpler under the higher voltage. Additionally, the contribution of the functional flora to key metabolic pathways (benzoate and nitrogen metabolism) and the expression of various functional genes was augmented at the 1.5V applied voltage.

Synergic removal of p-chloronitrobenzene by reduced graphene oxide/BiOBr/TiO2 nanotube arrays photoelectrocatalysis coupled biodegradation: Performance and microbial response

The coupled photoelectrocatalytic and biodegradation of p-chloronitrobenzene (p-CNB) was developed with the reduced graphene oxide/BiOBr/TiO2 nanotube arrays (GB/TNAs) as the photoelectrodes. The p-CNB removal performance, microbial activity and microbial community were systematically investigated in different bioreactors. The photoelectrocatalytic degradation improved the biodegradability of p-CNB. Compared to single biodegradation, the coupled degradation process exhibited higher p-CNB removal and mineralization efficiency. The specific oxygen utilization rate and dehydrogenase activity in single biodegradation bioreactor declined by 48.63 % and 41.14 % on day 25, indicating that p-CNB inhibited the microbial metabolic activity. However, the photoelectrocatalytic degradation could effectively reduce the inhibition of p-CNB on microbial activity of bioreactors. The variations of microbial reactive oxygen species production, antioxidant enzyme activity, and lactate dehydrogenase release confirmed that photoelectrocatalytic degradation declined the biotoxicity of p-CNB to the microorganisms in the coupled degradation process. p-CNB reduced the microbial richness and diversity in the single biodegradation process, whereas they increased obviously with the increase of photoelectrocatalytic degradation time in the combined degradation process.

Understanding the effect of residual aluminum salt coagulant on activated sludge in sequencing batch reactor: Performance response, activity restoration and microbial community evolution

To investigate the effect of residual coagulant after coagulation pretreatment on activated sludge system of wastewater treatment plants (WWTPs), comparative evaluation of lab-scale sequencing batch reactors under different poly-aluminum chloride (PAC) concentrations (20 and 55 mg/L), presenting the performance differences of reactors. Results showed that the PAC concentration of 20 mg/L slightly enhanced the average removal efficiencies of chemical oxygen demand (COD) and total nitrogen (TN), up to 93.43% and 72.52%. Whereas, an inhibition effect was exerted at the PAC concentration of 55 mg/L, the average removal efficiencies decreased to 88.56% and 57.80% respectively. Similarly, the residual aluminum salts showed a concentration effect of low promotion and high inhibition on sludge activity index. The content of specific oxygen utilization rate (SOUR) and dehydrogenase (DHA) sharply decreased by 30.17% and 53.56% under the high PAC concentration of 55 mg/L. Activity recovery phase showed that the suppression of aluminum salt coagulant on biological system was reversible. High-throughput sequencing presented that the relative abundance of microbes showed obvious variations at different PAC concentrations, and certain bacteria in Chloroflexi and Bacteroidota exhibited better adaptability to the high PAC concentration environment. Nevertheless, the antagonism action between denitrifying genera and other genera as well as the downregulation of functional enzymes regarding nitrogen metabolism gave rise to the deterioration of denitrification under the high PAC concentration of 55 mg/L. This study revealed the influence mechanism of residual aluminum salt coagulant on activated sludge system, providing strategies for efficient decontamination and long-term stable operation of biological system in wastewater treatment plant under the condition of adding PAC.

Comparison between a single unit bioreactor and an integrated bioreactor for nutrient removal from domestic wastewater

The simultaneous nitrogen and phosphorous removal efficiency of Bacillus cereus GS-5 immobilized single unit packed bed bioreactors was compared with that of integrated bioreactors. Both the single unit and integrated bioreactors were fed with domestic wastewater (NH4+-N 70 mg/L, NO3–-N 70 mg/L and PO43--P 15 mg/L) under 300–1000 mg/L carbon loading and 7.2–28.8 L/d hydraulic loading rates. The removal efficiencies of NH4+-N, NO3–-N and PO43--P in the integrated bioreactor were 94.2%, 92.3%, and 97.6%, respectively, which are slightly better than the single unit bioreactor. The specific oxygen utilization rate (SOUR) showed that the integrated bioreactor (17.06 mg-O2/g-MLSS/h) has a higher microbial activity than the single unit bioreactor (15.2 mg-O2/g-MLSS/h). Both the single unit and integrated bioreactors successfully resisted the organic as well as hydraulic shock loading conditions. This work established promising application prospects of both single unit fixed bed and integrated bioreactor for nutrient removal from domestic wastewater.

Effects of chloramphenicol on the bacterial community structure and simultaneous nitrification and denitrification performance in a sequencing biofilm batch reactor

The effects of chloramphenicol (CAP) on the performance of simultaneous nitrification and denitrification (SND), as well as on the bacterial community, were evaluated in a sequencing biofilm batch reactor (SBBR). The chemical oxygen demand (COD) removal decreased as the CAP concentration increased from 0 to 20 mg/l. But CAP had different effects on nitrification and denitrification: in contrast to continuously inhibiting nitrification, 15 mg/l CAP slightly promoted denitrification. Besides, the specific oxygen utilization rate declined with increasing CAP concentration, and the nitrifying and denitrifying rates initially displayed a trend of decreasing, and then increasing and finally decreasing, with increases in CAP concentration. In addition, the SBBR process exhibited an excellent ability to degrade CAP, especially when its concentration was 20 mg/l. The high-throughput sequencing results indicated that some obvious variations in the bacterial community at different CAP concentrations—in particular relative abundance changes in the dominant bacterial species at the phylum, class and genus levels. Overall, this study reveals that the effects of CAP on the nitrogen (N) removal performance in SBBR, provides a theoretical guide for SBBR treatment of practical wastewater.

Responses of aerobic granular sludge to fluoroquinolones: Microbial community variations, and antibiotic resistance genes

In this study, aerobic granular sludge (AGS) was operated under high levels of ammonium for removing three fluoroquinolones (FQs), i.e., ciprofloxacin (CFX), ofloxacin (OFX), and norfloxacin (NFX) at 3, 300, and 900 µg/L, respectively. Two key objectives were to investigate the differential distribution of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in sludge fractions and to evaluate correlations between ARGs and MGEs to nitrifying and denitrifying bacteria. AGS showed excellent stability under the exposure of FQs, with nitrite-oxidizing bacteria (NOB) more sensitive to FQs than ammonium-oxidizing bacteria (AOB). Specific oxygen utilization rates (SOUR) showed a reduction of 26.9% for NOB but only 4.0% of the reduced activity of AOB by 3 μg/L FQs. AGS performed better removal efficiencies for CFX and NFX than OFX, and the efficiencies increased with their elevated concentrations, except at 900 μg/L FQs. The elevated FQ concentrations led to a significant enrichment of intI1 and genus Thauera, while qnrD and qnrS showed no accumulation. Compared to nitrifiers, FQs relevant ARGs and the intI1 gene preferred to exist in denitrifiers, and the abundance of denitrifiers behaved a decreasing trend with the sludge size. Two quinoline-degrading bacteria were found in the AGS system, i.e., Alicycliphilus and Brevundimonas, possibly carrying qnrS and qnrD, respectively. Their relative abundance increased with the sludge size, which was 2.18% in sludge <0.5 mm and increased to 3.70% in sludge >2.0 mm, suggesting that the AGS may be a good choice in treating FQs-containing wastewater.

Rapid cultivation of the aerobic granules for simultaneous phenol degradation and ammonium oxidation in a sequencing batch reactor

The rapid cultivation strategy of aerobic granular sludge (AGS) for simultaneous phenol degradation and ammonium oxidation was studied in a sequence batch reactor (SBR). The short-term inhibitory kinetics of phenol was studied through batch experiments. For the sodium acetate fed AGS, the phenol inhibition constants (Ki) of specific oxygen utilization rate by heterotrophic bacteria (SOURh) was 508.6 mg/L. The Ki of specific ammonium utilization rate (SAUR) was 232.3 mg/L. After 28 days’ acclimatization, the phenol and NH4+-N removal rates of the SBR reached 94.0% and 96.4% when the influent phenol and NH4+-N concentrations were 1000 and 33.5 mg/L, respectively. The phenol removal loading rate was 1.69 kg/(m3·d). For the mature phenol&ammonium degrading AGS, the polysaccharide (PS) and protein (PN) concentrations were 247.4 ± 10.3 and 68.6 ± 6.5 mg/g VSS, respectively. The functional groups analysis showed that the amount of OH, NH, CO and CC groups remained unchanged in the mature phenol&ammonium degrading AGS.

Exploring the essential factors of performance improvement in sludge membrane bioreactor technology coupled with symbiotic algae

In this study, a coupled system of algal-sludge and membrane bioreactor (AS-MBR) was established for fouling control, and meanwhile the performance of wastewater treatment was enhanced. Results indicated that the AS-MBR increased the COD, NH4+-N, TN and PO43- -P removal efficiencies from 91.7% to 95.9%, 90.8%–96.9%, 22.0% to 34.3% and 18.4%–32.6%, respectively. Further analysis suggested that in the AS-MBR, the total specific oxygen utilization rate (SOUR), the SOUR of ammonia oxidizing bacteria and the SOUR of nitrite oxidizing bacteria were 26.6%, 58.5% and 52.4% higher than the control, respectively, indicating the improvement of microbial activities in AS-MBR. Additionally, the membrane fouling rates in the AS-MBR were 52.6% and 32.2% lower than the control in the slow and rapid fouling processes, respectively. A further mechanism investigation demonstrated that the concentrations of extracellular polymeric substance (EPS) were decreased by 19.8% and 22.1% in the mixed liquid and the fouling layer, respectively, after the inoculation of algae, which was expected to have a positive effect on the higher permeability and longer operation cycle of the membrane in the AS-MBR. More regular floc morphology was observed for the fouling layer on the membrane of AS-MBR, with the polysaccharides and proteins forming large clusters and channels in the fouling layer that likely decreased the filtration resistance. Consequently, high-throughput sequencing analysis revealed that the microbial community in the AS-MBR had higher abundances of bacteria and algae related to nutrients and organic matters degradation, which was beneficial for the improvement of wastewater treatment and alleviation of membrane fouling.

Nitrogen removal enhancement and nitrous oxide emission reduction by activated sludge with pulse aeration

This paper aimed to reveal the dynamic changes of the concentrations of nitrogen transformation intermediates and the emission of the greenhouse gas nitrous oxide (N2O) of the activated sludge with pulse aeration. The results indicated that the total nitrogen (TN) removal performed better and there were no nitrite and nitrate accumulation in the pulse aerated reactor. Specific oxygen utilization rate (SOUR) and dehydrogenase activity (DHA) of the activated sludge with pulse aeration were lower than those with continuous aeration, which was in agreement with the COD removal efficiency. The specific ammonia utilization rate (SAUR) and the specific nitrite utilization rate (SNUR) decreased with time from 0.43 to 0.32mg/(g MLSS·min) and from 0.28 to 0.12mg/(g MLSS·min), respectively. Meanwhile, the nitrate reductase activity (NARA) and the nitrite reductase activity (NIRA) enhanced from 0.93 to 1.67mg/(mL·d) and from 1.19 to 1.62mg/(mL·d), respectively. The advance of NIRA in the denitrification process played a more important role in the non-accumulation of nitrite, which led to less N2O emission by pulse aeration.

Stability of aerobic granular sludge in a pilot scale sequencing batch reactor enhanced by granular particle size control

Aerobic granulation was successfully achieved in a pilot scale sequencing batch reactor within 40 days. Then, stability of different particle size granules was explored according to their activity and resistance to ultrasonic crushing. Different particle size granules (0.3–0.6 mm, 0.6–1 mm, 1–1.43 mm, 1.43–2 mm, 2–3 mm and 3–4 mm) were exposed under different ultrasonic power separately. It was found that the granules with 2–3 mm always had the maximum granulation rates after ultrasonic crushing. Meanwhile, activity data showed that the 2–3 mm granules had the lowest specific oxygen utilization rates, which indicated that they were easier to maintain stability as the increase of their particle sizes was the slowest. So, 500 mL mixed liquid of the reactor were taken out and sieved to obtain the 2–3 mm granules, which were subsequently returned to the reactor to increase their proportion. Through the manual regulation, the proportion of 2–3 mm granules kept increasing which gradually became dominant in the reactor. Under the strategy of 86 days of operation, the aerobic granules were regular and compact, which had good removal effects of the real wastewater. The results indicated that the stability of the system could be greatly enhanced by the method, which provided a new strategy to maintain the granular stability.

Difference of respiration-based approaches for quantifying heterotrophic biomass in activated sludge of biological wastewater treatment plants

Estimation of heterotrophic biomass concentration in activated sludge is essential to the design, operation and management of activated sludge process for wastewater treatment plants (WWTPs), and many methods have been developed for such a purpose. In this study, three respiration-based methods: the Exponential-growth-rate-based method (Exp-M), the Maximum-respiration-rate-based method (Max-M) and the Endogenous-respiration-rate-based method (End-M), which are frequently used for determining kinetic parameters in activated sludge models, were comparatively examined using experimental results from both full-scale municipal WWTPs and laboratory-scale reactors. Our study revealed the pros and cons of each method, which is valuable for method selection in different applications. The End-M can estimate all the fraction of biomass. However, the proper control of measuring condition is of great challenge. The Exp-M can only determine the exponential growth part of biomass as conditions employed during measuring may make a considerable part of biomass in a nongrowth status, resulting underestimation or even failure of calculation. The Max-M can determine the viable biomass including the nongrowth part, and it is recommended for rapid assessment of biomass. The Max-M was modified after the introduction of a coefficient SOURSRT=0 (the specific oxygen utilization rate when the sludge retention time was assumed zero) and was validated by using the experimental results reported in previous studies. Because of its simplicity and much improved accuracy, the modified Max-M method is able to provide more useful information about activated sludge compositions and has a promising application potential in wastewater treatment plants.

Storage of aerobic granular sludge embedded in agar and its reactivation by real wastewater.

Aerobic granular sludge (AGS) was preserved using an agar embedding method to maintain its stability. No obvious damage was imposed on the granular appearance during 30 days of cold and dry storage, but the granular microstructure had an uneven surface with a large number of holes. The results were consistent with the extinction of microbial communities and the monitored consumption of extracellular polymeric substances, in which granular specific oxygen utilization rate and mixed liquor volatile suspended solids/mixed liquor suspended solids ratio, respectively, decreased by 72.4% and 62.5% during storage. A mass conversation calculation indicated that the loss of granular mass was 1.6393 g. An offensive odour was smelled during storage, and the results indicated that a material transformation and mitigation were involved between AGS and the gas phase. Although the granular structure was destroyed to a certain extent, no obvious damage was imposed on the granular skeleton during storage. After it was aerated again after a feeding with real wastewater, the residual skeleton served as a carrier for the rapid proliferation of microorganisms, and good granular properties were obtained after 11 days of reactivation.

Unraveling the Long-Term Effects of Cr(VI) on the Performance and Microbial Community of Nitrifying Activated Sludge System

The long-term effects of different influent Cr(VI) concentrations (0–0.5 mg L−1) on the nitrification activities and microbial community structures of nitrifying activated sludge system were investigated in this study. Results showed that the performance of ammonia oxidation was significantly inhibited, and the effluent concentration of ammonia nitrogen (NH4+-N) increased markedly when the influent Cr(VI) loading was equal or greater than 0.2 mg L−1. The specific oxygen utilization rate (SOUR), specific ammonium oxidation rate (SAOR), and specific nitrite oxidation rate (SNOR) of the system decreased from 53.24, 6.31, and 7.33 mg N g−1 VSS h−1 to 18.17, 1.68, and 2.88 mg N g−1 VSS h−1, respectively, with an increase of Cr(VI) concentration from 0 to 0.5 mg L−1. The protein/polysaccharide (PN/PS) ratio increased with the increasing Cr(VI) concentration, indicating that excessive PN secreted by microorganisms was conducive to resisting the toxicity of Cr(VI). High-throughput sequencing revealed that the relative abundance of ammonia-oxidizing bacteria (Nitrospira) and nitrite-oxidizing bacteria (Nitrosomonas and Nitrosospira) all decreased with the increasing Cr(VI) concentration, and ammonia-oxidizing bacteria were more sensitive to heavy metal toxicity than nitrite-oxidizing bacteria. The activities of nitrifying activated sludge system could not be completely recovered after a 30-d recovery process.

Achieving enhanced denitrification via hydrocyclone treatment on mixed liquor recirculation in the anoxic/aerobic process

This work presents the novel application of hydrocyclones for mixed liquor recirculation (MLR) treatment in the anoxic/aerobic (A/O) process to enhance the denitrification process. An exhaustive investigation on treated activated sludge and A/O effluents was conducted in batch and continuous operation tests. The median diameter of the sludge flocs was decreased from 78.82 μm to 15.77–23.31 μm, and the extracellular polymeric substances (EPS) desorption was observed, thus leading to the release of the soluble chemical oxygen demand (SCOD). A marked increase in the BOD5/TN ratio was consequently achieved, which supplied the carbon source and improved the biodegradability of the MLR. The hydrocyclone treatment also enabled a 7.17% ± 0.93% specific oxygen utilization rate (SOUR) increase at the optimal hydrocyclone intensity of 0.13 MPa, owing to the desorption of positioned microbial secretion from the microorganism cells. The nitrate reductase and nitrite reductase were also improved by 15.13% ± 1.16% and 17.61% ± 1.55%, respectively. The nitrate removal efficiency was enhanced by 13.6%, and the nitrogen oxide gases varied slightly; this behavior was consistent with the variations in the key enzymes involved in denitrification. The A/O process operated in the mode of hydrocyclone-treated MLR, compared with in the conventional mode, resulted in a 15.56% higher TN removal, and the other effluent parameters remained stable. Hydrocyclone disruption is thus a convenient and energy-efficient process with broad implications in denitrification development.

Effect of florfenicol on performance and microbial community of a sequencing batch biofilm reactor treating mariculture wastewater

ABSTRACTThe effects of florfenicol (FF) on the performance, microbial activity and microbial community of a sequencing batch biofilm reactor (SBBR) were evaluated in treating mariculture wastewater. The chemical oxygen demand (COD) and nitrogen removal were inhibited at high FF concentrations. The specific oxygen utilization rate (SOUR), specific ammonium oxidation rate (SAOR), specific nitrite oxidation rate (SNOR) and specific nitrate reduction rate (SNRR) were decreased with an increase in the FF concentration from 0 to 35 mg/L. The chemical compositions of loosely bound extracellular polymeric substances (LB-EPS) and tightly bound EPS (TB-EPS) could be affected with an increase in the FF concentration. The high-throughput sequencing indicated some obvious variations in the microbial community at different FF concentrations. The relative abundance of Nitrosomonas and Nitrospira showed a decreasing tendency with an increase in the FF concentration, suggesting that FF could affect the nitrification process of SBBR. Some genera capable of reducing nitrate to nitrogen gas could be inhibited by the addition of FF in the influent, such as Azospirillum and Hyphomicrobium.

Alleviation of membrane fouling in a submerged membrane bioreactor with electrochemical oxidation mediated by in-situ free chlorine generation

The control of membrane fouling is still the biggest challenge that membrane bioreactor (MBR) for wastewater treatment faces with. In this report, we evince that an in-situ electrochemical free chlorine generation is effective for membrane fouling mitigation. An electrochemical oxidation (EO) apparatus with perforated Ti/IrO2 anodes and Ti/Pt cathodes was integrated into a conventional MBR with microfiltration module (EO-MBR). The membrane fouling characteristics of EO-MBR fed with synthetic wastewater were monitored for about 2 months in comparison to control MBRs. In the EO-MBR at a direct current density of 0.4 mA/cm2, the frequency of membrane fouling when the trans-membrane pressure (TMP) reached 30 kPa was effectively reduced by 40% under a physical membrane cleaning regime. The evolution patterns of TMP together with hydraulic resistance analysis based on resistance-in-series model indicated that the electrochemically generated active chlorine alleviated the physically irremovable membrane fouling. Further analysis on extracellular polymeric substances (EPS) of sludge cake layer (SCL) revealed significant reductions of protein contents in soluble EPS and fluorescence emission intensities from humic acids and other fluorophores in bound EPS, which in-turn would decrease the hydrophobic accumulation of organic foulants on membrane pores. The chlorine dosage from the EO apparatus was estimated to be 4.7 mg Cl2/g MLVSS/day and the overall physicochemical properties (bio-solids concentration, floc diameter, zeta-potential) as well as the microbial activity in terms of specific oxygen utilization rate and removal efficiency of dissolved organic carbon (>97%) were not affected significantly. A T-RFLP (terminal restriction fragment length polymorphism) analysis suggested noticeable shifts in microbial community both in mixed liquor and sludge cake layer. Consequently, our electrochemical chlorination would be an efficient fouling control strategy in membrane-based water treatment processes where additional electricity consumption and cathodic scale deposition are not of serious concerns.

Performance comparison of biofilm and suspended sludge from a sequencing batch biofilm reactor treating mariculture wastewater under oxytetracycline stress

ABSTRACTThe performance, extracellular polymeric substances (EPS) and microbial community of a sequencing batch biofilm reactor (SBBR) were investigated in treating mariculture wastewater under oxytetracycline stress. The chemical oxygen demand and –N removal efficiencies of the SBBR decreased with the increase of oxytetracycline concentration, and no obvious –N and –N accumulation in the effluent appeared at less than 10 mg L−1 oxytetracycline. The specific oxygen utilization rate of the suspended sludge was more than that of the biofilm at different oxytetracycline concentrations. The specific ammonium oxidation rate (SAOR) of the biofilm was more easily affected by oxytetracycline than that of the suspended sludge, whereas the effect of oxytetracycline on the specific nitrite oxidation rate (SNOR) of the biofilm was less than that of the suspended sludge. The specific nitrate reduction rate of both the biofilm and suspended sludge was higher than the sum of the SAOR and SNOR at different oxytetracycline concentrations. The protein and polysaccharide contents in the EPS of the biofilm and suspended sludge increased with the increase of oxytetracycline concentration. The appearance of oxytetracycline in the influent could affect the chemical composition of the loosely bound EPS and tightly bound EPS. The amino, carboxyl and hydroxyl groups might be involved with interaction between EPS and oxytetracycline. The denaturing gradient gel electrophoresis profiles indicated that the variation of oxytetracycline concentration in the influent could affect the microbial communities of both the biofilm and suspended sludge.

New insight into fouling behavior and foulants accumulation property of cake sludge in a full-scale membrane bioreactor

Cake sludge attached on membrane surfaces was collected and characterized in a full scale membrane bioreactor (MBR) compared with bulk sludge. The morphological, chemical and microbial properties were examined through microscopic observations, particle size distribution (PSD) analysis, chemical analysis, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and energy-diffusive X-ray (EDX) analysis, specific oxygen utilization rate (SOUR) measurements and Biolog assay. The results showed that fiber-like substances might have served as the skeleton of larger size aggregates in cake sludge. Moreover, much more polysaccharides and inorganic elements such as multivalent cations were accumulated in cake sludge than proteins and humics. Cake sludge showed lower microbial activity for aerobic degradation than bulk sludge, but higher metabolic activity for the degradation of refractory substances (aromatic proteins and humics) other than polysaccharides. Based on batch filtration experiments, it was found that cake sludge had much higher cake layer fouling potential but lower membrane pore blocking resistance, probably due to the heterogeneous structure of cake sludge resulting from accumulation and interaction of various inorganic and organic foulants. This investigation could assist in obtaining a better understanding of the fouling behavior and foulants accumulation properties of cake sludge in the full-scale MBRs.