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Article

High Loaded Bioflocculation Membrane Reactor of Novel Structure for Organic Matter Recovery from Sewage: Effect of Temperature on Bioflocculation and Membrane Fouling

by
Liguo Wan
1,2,3,*,
Ling Xiong
2,
Lijun Zhang
2 and
Wenxi Lu
1,*
1
College of New Energy and Environment, Jilin University, Changchun 130021, China
2
School of Water Conservancy & Environment Engineering, Changchun Institute of Technology, Changchun 130012, China
3
Jilin Provincial Key Laboratory of Municipal Wastewater Treatment, Changchun Institute of Technology, Changchun 130012, China
*
Authors to whom correspondence should be addressed.
Water 2020, 12(9), 2497; https://doi.org/10.3390/w12092497
Submission received: 9 August 2020 / Revised: 2 September 2020 / Accepted: 3 September 2020 / Published: 7 September 2020
(This article belongs to the Section Wastewater Treatment and Reuse)
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Abstract

:
The effect of temperature on the efficiency of high loaded bioflocculation membrane reactor (HLB-MR) flocculation and concentration of organic matter in municipal wastewater was analyzed using parallel comparative experiments. The study investigated organic matter recovery efficiency, bioflocculation effect, and membrane fouling status of the reactor at 8 °C and 15 °C. It was observed that at a low temperature of 8 °C, the organic matter recovery efficiency of HLB-MR was 80%, which was equivalent to that at 15 °C. However, the bioflocculation efficiency at 8 °C was only 65%, which was significantly lower than that of 85% achieved at 15 °C. The poor flocculation effect was related to the low yield of the extracellular polymer under low-temperature conditions and the low content of cations (sodium, calcium, and aluminum) in the sludge matrix. At the low temperature of 8 °C, the membrane fouling of the HLB-MR was more serious than that at 15 °C. Poor bioflocculation effect led to an increase in the number of fine particles (≤1 μm) in the reactor, which might be the main reason for the aggravation of membrane fouling. To overcome the adverse effects of low temperature on membrane fouling, it is recommended to adopt engineering measures, such as an appropriate increase in the solid retention time, increase in the aeration intensity, using powdered activated carbon, or enhancing the intensity of backwashing.

1. Introduction

The chemical energy of organic matter in municipal wastewater is about 1.9 kWh/m3 [1], but its traditional biological treatment process not only consumes a lot of energy for aeration but also destroys the chemical energy contained in the wastewater itself. From the perspective of sustainable development, the organic matter in wastewater should not be aerobically mineralized but should be converted into energy carriers, such as methane [2], electrical energy [3], and other valuable organic composite materials [4]. However, in general, the concentration of organic matter in municipal wastewater is relatively low. To realize its efficient recycling and utilization, the development of a pre-concentration technology becomes requisite. Considering the high proportion of suspended and colloidal organic matter in municipal wastewater, the method of separating and concentrating organic matter using membrane filtration is favored by many researchers. Direct use of membrane filtration for municipal wastewater can also achieve effective separation of organic matter using a simple process [5]; however, it causes serious membrane fouling and results in a sharp drop in membrane flux [6,7]. In order to solve this problem, coagulation has been studied as a pretreatment method. Coagulation can remove particles and colloidal substances from wastewater, thereby effectively alleviating membrane pollution [8,9,10], but adding coagulants has serious drawbacks, including high cost, secondary pollution, and possible inhibition of the anaerobic conversion of recovered organic matter. Bioflocculation can use microorganisms or extracellular polymeric substance (EPS) secreted by microorganisms to aggregate colloidal and particulate matter in wastewater [11]. Compared with coagulation, it has the advantage of lower cost and does not result in any secondary pollution, which is more in line with the requirements of the sustainable development concept. In this study, hollow fiber ultrafiltration membrane components were used to construct a high loaded bioflocculation membrane reactor (HLB-MR). By optimizing the conditions to a very short hydraulic retention time (HRT) and solid retention time (SRT), the efficient separation and recovery of organic matter from municipal wastewater could be achieved. Temperature is an important parameter that affects the efficiency of the separation and recovery of organic matter from the reactor. However, the underlying mechanism is still unclear [12,13]. In this study, the bioflocculation effect, concentrated organic matter recovery efficiency, and membrane fouling characteristics of the reactor at 8 °C and 15 °C were compared using actual municipal wastewater. These two temperatures were chosen because the long low-temperature period of the year in the northern cold region of China and the temperature of municipal wastewater during this cold period is as low as 8 °C, while 15 °C is the representative temperature of municipal wastewater in most areas of China in spring and autumn. To further explain the mechanism of bioflocculation and membrane fouling, the EPS concentration, floc particle size distribution, and related metal cation concentration of the concentrated solution in the reactor under two temperature conditions were determined. The values were compared in order to determine the effect of temperature on organic matter recovery from municipal wastewater and to determine the related mechanism. This can provide theoretical guidance for the practical application of this technology in the future.

2. Materials and Methods

2.1. Experimental Apparatus and Operation

The experimental apparatus is shown in Figure 1. During the experiment, the operating temperatures of the two identical HLB-MRs were controlled at 8 °C and 15 °C and were denoted as LT (8 °C) reactor and HT (15 °C) reactor, respectively. The two reactors were operated in parallel. The total volume of each reactor was 1.87 L and was equipped with a bundle of hollow fiber membrane component (Tianjin Motian Membrane Technology Co., Ltd., Tianjin, China, polyvinylidene fluoride (PVDF)). The membrane area was 0.28 m2, the membrane pore size was 0.03 μm, and the effective volume of the reactor, after deducting the volume occupied by the components, was 1.70 L. An aeration sand tray was placed at the bottom of the reactor to provide air for washing the surface of the membrane filaments and for ensuring that the concentrated solution was evenly mixed. The aeration flow rate was controlled at 70 L/min using a gas flow meter, and the dissolved oxygen concentration in the reactor was 6−8 mg/L. The peristaltic pump was used to pump water. In order to remove the reversible pollution on the membrane surface, a time relay was used to control the peristaltic pump to work for 8 min and then cease for 2 min. The peristaltic pump operated in a constant flux mode, and the HRT in both the reactors was 1 h, the inlet water flow rate was 1.7 L/h, the effluent water flow rate was 1.68 L/h, and the membrane flux was 6 L/m2/h, obtained by controlling the water flux. The trans-membrane pressure (TMP) drop was recorded by the computer using a pressure sensor. The concentrated solutions in the two reactors were discharged using a peristaltic pump, and the discharged volume was controlled to ensure that the SRT of the two reactors was 0.6 d, and the concentrated solutions discharge flow rate was 0.02 L/h. For the experiment, the raw wastewater was collected from the grit chamber effluent of a municipal wastewater treatment plant with a treatment scale of 150,000 m3/d, located in the Changchun City, Jilin Province. The wastewater collected each time was stored at 4 °C for no more than 3 days. Before each experiment, the wastewater was filtered through a 3 mm mesh screen, and the temperature was adjusted as required.

2.2. Samples and Analysis

The reactor usually stabilizes after operating it for a time that is 3 times the SRT. In this study, the two reactors operated for 15 days in parallel, and on the 13th, 14th, and 15th day, the reactor influent, concentrated solution, and effluent were sampled and analyzed.
The chemical oxygen demand (COD) of the sample was classified into 4 categories—total COD (CODTO), suspended COD (CODSS), colloidal COD (CODCO), and soluble COD (CODSO). CODTO denotes the COD measured directly of the sample. CODSS denotes the difference between CODTO and the COD of the filtrate after filtering the sample using 12−25 μm filter paper. CODCO denotes the difference between the COD of the filtrate after filtering the sample using 12−25 μm filter paper and the COD of the filtrate after filtration with a 0.45 μm membrane. CODSO denotes the COD of the filtrate obtained after filtration with a 0.45 μm filter membrane [14,15]. COD and oxygen uptake rate (OUR) were determined using the standard methods [16].
EPS determination: The concentrated solution in the HLB-MR measuring 30 mL was taken in a reactor and centrifuged at 12,000× g for 5 min. The supernatant was filtered using a 0.45 μm filter membrane. The EPS measured in the obtained filtrate was free-state EPS. The remaining sludge in the centrifuge tube was diluted to its original volume with pure water. After mixing, it was placed in a water bath at 80 °C for 30 min. After the centrifuge tube cooled, another round of centrifugation at 12,000× g followed for 5 min. The supernatant was filtered using a 0.45 μm filter membrane, and the EPS measured in the obtained filtrate was the bound-state EPS. The protein and polysaccharides in free-state EPS and bound-state EPS were determined. EPS-protein was determined using the modified Lowry method [17], and EPS-polysaccharide was determined using the colorimetric method [18].
Determination of metal ions: The supernatant sample was collected after precipitation of the concentrated solution sample for 30 min. It was then filtered through a 0.45 μm filter membrane for determination. After a certain amount of precipitate was frozen and dried, a known weight of this freeze-dried solid was taken into a polytetrafluoroethylene tube, and 10 mL of 65% HNO3 was added. It was placed on a graphite digestion instrument (SCP, DigiPREP MS (Shanghai Zequan Instrument Equipment Co., Ltd., Shanghai, China)) for 45 min at 180 °C, acid was removed, and the remaining liquid volume was made to 1 mL. After the mixture cooled to room temperature, 2% HNO3 was used for rinsing, and the sample, filtered using a 0.45 μm filter, was diluted to 50 mL using distilled water for determination. The metal ions (sodium, calcium, aluminum) in samples prepared with supernatant and precipitate were measured using ICP-OES (Perkin Elmer, Optima 5300DV (Shenzhen laiaotuo Technology Co., Ltd., Shenzhen, China.
The supernatant was collected after the precipitation of the concentrated solution in the HLB-MR for 30 min, and its turbidity was measured using a turbidity meter (HACH, 2100Q). A dissolved oxygen meter (WTW, OXI 3310-SET1 (supplier, city, country)) was used to measure the dissolved oxygen concentration in the two reactors. The laser particle size analyzer (EyeTech (Ankersmid, Overijssel, Holland)) was used to measure the floc particle size of the concentrated sample, and the measurement results were recorded in the form of number particle size distribution data.

3. Results

3.1. Recovery Efficiency of Organic Matter

The COD detected from each category of influent, concentrated solution, and effluent is shown in Table 1. The mass balance analysis of CODTO based on the detection data and suspended solids (SS) concentration is shown in Figure 2. According to the figure, under a low temperature of 8 °C, the SS concentration in concentrate from HLB-MR was lower than 15 °C, the CODTO loss and the CODTO distributed to the concentrated solution were slightly lower than those at 15 °C, while the CODTO value of the membrane effluent was higher at 8 °C. This might be due to the fact that the sludge layer attached to the membrane surface has a better interception or degradation effect on the dissolved organic matter under higher temperature conditions. The related mechanism needs further study. It needs to be pointed out that the loss of CODTO in both the reactors exceeded 20%, which was not entirely caused by the mineralization of organic matter. The loss of CODTO should be the sum of the loss of CODTO from organic matter mineralization and the loss of CODTO during the membrane cleaning process. Since the operation of reactors was under extremely short SRT and HRT conditions, the nitrification in reactors could be negligible, and the mineralization loss of CODTO could be calculated using OUR. The OUR of the microorganisms in LT (8 °C) and HT (15 °C) reactors was 14.10 mg O2/L/h and 22.44 mg O2/L/h, respectively. The mineralization rates of LT (8 °C) and HT (15 °C) reactors calculated using OUR were 6% and 9%, respectively. After deducting the CODTO loss caused by mineralization, the CODTO loss caused by membrane cleaning in LT (8 °C) and HT (15 °C) reactors was 15.7% and 14.1%, respectively. The loss during the process could be further reduced by completely refluxing the membrane cleaning solution into the reactor. If the membrane cleaning loss was ignored, the organic matter recovery rate of the LT (8 °C) reactor would be 80.7%, which was slightly lower than the 81.2% of the HT (15 °C) reactor. This indicated that the HLB-MR could realize the efficient separation and recovery of organic matter from municipal wastewater under low-temperature conditions.

3.2. Bioflocculation Effect

The percentage of COD in the influent and concentrated solution of LT (8 °C) and HT (15 °C) reactors, as well as the flocculation efficiency, calculated based on the proportion of CODCO in the influent and concentrated solution, is shown in Figure 3. The CODSS and CODCO percentage in the influent was 72.9% and 12.6%, respectively, and their proportions in the concentrated solution of LT (8 °C) and HT (15 °C) reactors were 89.9% and 6.3%, 94.6% and 2.6%, respectively. The flocculation efficiencies of the LT (8 °C) reactor and HT (15 °C) reactor, calculated based on the mass load of CODCO in the influent and concentrated solution, were 65% and 85%, respectively. It was observed that in both the reactors, a large amount of CODCO was converted into CODSS. Compared with the HT (15 °C) reactor, the LT (8 °C) reactor had a lower degree of bioflocculation and thus poor flocculation effect. The turbidity of the supernatant after precipitation of the concentrated solution in the LT (8 °C) and HT (15 °C) reactors was 76 NTU and 35 NTU, respectively. The higher turbidity value in the supernatant of the LT (8 °C) reactor also confirmed that the bioflocculation effect in this reactor was poor.
Interval statistics were performed on the particle size of the concentrated solution in the LT (8 °C) and HT (15 °C) reactors, and the results are shown in Figure 4. It was observed that the particle size was mainly distributed within 1−10 μm, with a proportion of about 61%. The proportion of particles within ≤1 μm range was 22.61% in the LT (8 °C) reactor, which was significantly higher than that of 17.15% in the HT (15 °C) reactor. However, the proportion of particles within the 10−30 μm range was 15.02% in LT (8 °C), which was significantly lower than that of 19.53% in the HT (15 °C) reactor. This indicated that low temperature was not conducive to the aggregation of fine particles into larger particles in the HLB-MR, further confirming the inhibitory effect of low temperature on bioflocculation.

3.3. EPS and Metal Cation Concentration

The concentration of EPS in LT (8 °C) and HT (15 °C) reactors is shown in Figure 5. The concentrations of bound-state and free-state EPS in the HT (15 °C) reactor were 15.67 mg/g volatile suspended solids (VSS) and 8.71 mg/L, respectively. These values were significantly higher than the corresponding concentrations in LT (8 °C) reactor—9.55 mg/g VSS and 4.41 mg/L, respectively. This indicated that low temperature inhibited the production of EPS in the HLB-MR. Besides, there was only EPS-polysaccharide, and no EPS-protein, observed in free-state EPS in both LT (8 °C) and HT (15 °C) reactors, while the EPS-protein concentration in the bound-state EPS in the two reactors was 25.5% and 27.1%, respectively. This concluded that the content of EPS-protein was lower than that of EPS-polysaccharide, and it mainly existed in the sludge matrix. EPS-polysaccharide, however, was the main existing form of EPS and was easily diffused from the sludge to the supernatant.
Metal cations had a greater impact on bioflocculation. From Table 2, the concentration of sodium, calcium, and aluminum ions in the solid bound-state and in the supernatant of the concentrated solution could be observed. In the solid bound-state, the concentration of calcium was the highest, followed by aluminum and sodium. For these three cations, the solid bound-state concentrations in the HT (15 °C) reactor were all higher than those in the LT (8 °C) reactor. Whereas, in the supernatant, except for aluminum, the concentrations of sodium and calcium were both lower than those in the LT (8 °C) reactor. This data showed that compared with the HT (15 °C) reactor, fewer cations were distributed in the precipitation of the concentrated solution in the LT (8 °C) reactor. This data was in line with the observation of lower concentration bound-state EPS in the LT (8 °C) reactor. This might be because the low temperature inhibits the bridging effect between the metal cations and the EPS, leading to their lower content embedded in the concentrated solution sludge matrix through precipitation.

3.4. Trans-Membrane Pressure (TMP)

The TMP of LT (8 °C) and HT (15 °C) reactors at the end of each membrane suction was analyzed, as shown in Figure 6. In the first 3 h, the TMP of the two reactors increased rapidly, with values close to 15 kPa. However, the TMP of the HT (15 °C) reactor remained almost at this level till 100th h, while the TMP of the LT (8 °C) reactor maintained a continuously increasing trend, rising to about 30 kPa at the 48th h. It was thus concluded that the simple suction and ceasing could not remove membrane surface fouling. Instead, the membrane components had to be removed from the reactor, rinsed with clean effluent, and replaced back into the reactor. It was observed that the TMP had recovered well. In the following 50 h, its value was maintained at about 10 kPa, but the highest value did not exceed 14 kPa. The membrane fouling of the two reactors was reflected macroscopically (Figure 6). It can be observed from the figure that the membrane fouling of the LT (8 °C) reactor was more serious than that of the HT (15 °C) reactor. This might be due to the poor flocculation effect and the larger proportion of fine particles (0−1μm) in the HLB-MR under low-temperature conditions.

4. Discussion

4.1. The Effect of EPS and Metal Cations on Bioflocculation

The bioflocculation of particles in sludge is mainly caused by the EPS secreted by microorganisms. Due to the viscosity of EPS, an interconnected matrix between the particles is formed [19]. The literature shows that EPS is mainly composed of protein, carbohydrate, fat, nucleic acid, humic acid, and uronic acid [20,21]. However, since there is no standard method to characterize EPS, it is generally described using the concentration of EPS-protein and EPS-polysaccharide. In this study, the concentration of the EPS-protein and EPS-polysaccharide in the sediment and supernatant of the concentrated solution in LT (8 °C) and HT (15 °C) reactors was determined. The EPS-polysaccharides in the two reactors were found to be the main component that constituted the total EPS. Its proportion in the sediment of the concentrated solution exceeded 70%, while in the supernatant, it was as high as 100%. However, some research works have reported that EPS-protein is the main component of the total EPS in sludge and biofilm [22,23]. This might be due to the different wastewater quality used for the experiment and the different extraction methods of EPS. The EPS-protein and EPS-polysaccharide in the HT (15 °C) reactor were both higher than those in the LT (8 °C) reactor and had better bioflocculation effects. It could be inferred that both EPS-protein and EPS-polysaccharide were effective in promoting bioflocculation. EPS-protein was not detected in the supernatant of the concentrated solution, indicating that it had stronger bioflocculation ability than EPS-polysaccharide and was distributed in the sludge matrix. EPS-polysaccharide was more susceptible to shearing and got easily separated from the sludge matrix.
Microorganisms and particulate matter in wastewater usually have negative charges [24,25], and the introduction of metal cations can promote flocculation. Electric double-layer interaction theory, ion bridging theory, and alginate theory are commonly used to explain this flocculation mechanism [26,27]. In this study, compared with the HT (15 °C) reactor, the LT (8 °C) reactor showed a poor bioflocculation effect, which was related with lower concentration of total EPS secreted by the concentrated solution and fewer metal cations (Na, Ca, and Al) uptake from the sludge. Regarding the influence of Na+ on bioflocculation, there is a controversy in the previous research literature. Some researchers have believed that the high concentration of Na+ would hinder the bioflocculation process or result in de-flocculation [28,29]. On the other hand, some researchers have found that in ocean systems with very high Na+ concentration, biological flocs and biofilm could be produced through bioflocculation [30]. The promoting effect of polyvalent metal ions on bioflocculation has been widely proved by researchers. The increase in Al3+ concentration can improve the flocculation effect of activated sludge [31,32]. The important effect of Ca2+ on flocculation has also been reported; Bruus et al. found that the discharge of Ca2+ led to the dispersion of activated sludge flocs [33].

4.2. The Influence of Temperature on Bioflocculation

The COD flocculation effects of the two reactors at different temperatures (Figure 3) showed that under low temperature (8 °C), the bioflocculation effect of the HLB-MR was poor. This was further proved by the higher turbidity and higher amount of fine particles (0−1μm) in the supernatant of the concentrated solution (Figure 4). The study by Brink et al. concluded that when the temperature dropped from 15 °C to 7 °C, the size of particles in the membrane bioreactor became smaller, and the sub-micron particles were released from the sludge flocs [34]. Some literature works have also reported that lowering the temperature can enhance the de-flocculation effect of activated sludge and weaken the re-flocculation effect of particulate matters [35,36]. The poor bioflocculation effect under low temperature might be related to the increase in liquid viscosity or the decrease in the diffusion velocity of sub-micron particles caused by Brownian motion.

4.3. Influence of Temperature on Membrane Fouling

The changes in the TMP of the two reactors at different temperatures (Figure 6) showed that the HLB-MR had more serious membrane fouling when the temperature was 8 °C. This corresponded to the fact that LT (8 °C) reactor has a poor bioflocculation effect than HT (15 °C) reactor. This further proved that the good bioflocculation effect could effectively alleviate the membrane fouling in the membrane separation process [37]. The reasons for more serious membrane fouling of the HLB-MR under low-temperature condition might be: (1) The viscosity of the concentrated solution in the reactor increases, the shear force generated by the bubbles washing the surface of the membrane is reduced, and the particulate pollutants are more likely to settle on the membrane surface, resulting in more serious membrane fouling [38]; (2) The low temperature strengthens the de-flocculation of sludge and increases the number of sub-micron particles in the concentrated solution, which blocks the membrane pores or make them smaller, leading to serious membrane fouling [39]; (3) The activity of microorganisms is reduced under low-temperature condition, and the degradation of COD is reduced, resulting in a higher concentration of soluble COD and colloidal COD in the concentrated solution, thereby causing more serious membrane fouling [40].

4.4. Practical Significance

This study showed that low-temperature conditions had a negative impact on the recovery of organic matter, bioflocculation of particulate matter, and caused membrane fouling of the HLB-MR. Therefore, temperature parameters should be taken into consideration when designing the process in cold regions. Since the activity of microorganisms and the degree of aerobic mineralization of organic matter in the reactor are both low under low-temperature conditions, the SRT could be appropriately increased. This would enrich more microorganisms in the reactor, thereby increasing the content of EPS to promote bioflocculation and reduce membrane fouling. Thus, the SRT needs to be optimized, and the contradiction between minimizing organic matter mineralization and maximizing recovery rate needs to be solved. On the other hand, increasing aeration intensity can also be considered. This can overcome the disadvantage of low temperature in weakening the shear force of the air bubbles and can appropriately increase the dissolved oxygen concentration in the reactor. This promotes the production of EPS and enhances the bioflocculation effect, thereby reducing membrane fouling. This measure requires an optimization of the aeration parameters so as to balance the benefits of reduced membrane pollution and the expenditures caused by increased aeration energy consumption, under the premise of an ideal organic recovery rate. In this study, a submerged HLB-MR constructed by hollow fiber membranes with a large filling amount per unit volume was used. In practical application, a small amount of powdered activated carbon could be added into the reactor to prevent the sludge de-flocculation at a low temperature, thereby increasing the recovery of organic matter and reducing membrane fouling [41,42]. To overcome the serious problem of membrane fouling under low-temperature conditions, enhanced backwashing can also be adopted. This method has achieved good results in both the traditional membrane filtration process and membrane bioreactor process [43,44].

5. Conclusions

In this study, the effect of temperature on bioflocculation, concentrated characteristics of organic matter, and membrane fouling in the HLB-MR was analyzed. Conclusions were as follows:
  • The HLB-MR can achieve a highly efficient recovery of organic matter in municipal wastewater at a low temperature of 8 °C. If the loss of organic matter due to the membrane cleaning process is ignored, the recovery rate could reach more than 80% at 8 °C and 15 °C.
  • The bioflocculation efficiency of the HLB-MR under a low temperature of 8 °C is 65%, which is significantly lower than the flocculation efficiency of 85% at 15 °C. A large number of fine particles and high turbidity in the supernatant of the concentrated solution in the 8 °C reactor further confirms the inhibitory effect of low temperature on bioflocculation. Under a low temperature of 8 °C, the EPS concentration and the cations (sodium, calcium, and aluminum) are lower than that at 15 °C. With the increase of the EPS concentration secreted by microorganisms in the HLB-MR, the bioflocculation is enhanced, so that the uptake of the cations (sodium, calcium, and aluminum) from the sludge matrix increases.
  • Compared with 15 °C, the poor bioflocculation in HLB-MR at 8 °C leads to more serious membrane fouling. It is recommended to appropriately increase SRT, increase aeration intensity, add powdered activated carbon, or enhance the backwashing intensity during the cold season to overcome the problem of serious membrane fouling during the operation of the HLB-MR.

Author Contributions

Conceptualization, L.W. and W.L.; methodology, writing—review and editing, L.W.; writing—original draft preparation, L.X.; investigation, data curation, L.Z; supervision, project administration, funding acquisition, W.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Natural Science Foundation of Jilin Province, grant number 20180101317JC, Jilin Provincial Special Fund project for Industrial Innovation, grant number 2019C055, and Science and Technology Fund Project of Changchun Institute of Technology, grant number 320200031.

Conflicts of Interest

The authors declare no conflict of interest.

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Water 12 02497 g001 550
Figure 1. Schematic of the experimental setup.
Figure 1. Schematic of the experimental setup.
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Figure 2. CODTO mass balance at different temperatures and SS concentrations.
Figure 2. CODTO mass balance at different temperatures and SS concentrations.
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Figure 3. Flocculation efficiency for COD at different temperatures.
Figure 3. Flocculation efficiency for COD at different temperatures.
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Figure 4. The proportion of particles in different particle size intervals in the concentrate at different temperatures.
Figure 4. The proportion of particles in different particle size intervals in the concentrate at different temperatures.
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Figure 5. Bound EPS (extracellular polymeric substance), free EPS, EPS-protein, and EPS-polysaccharide concentrations in the concentrate and the supernatant at different temperatures.
Figure 5. Bound EPS (extracellular polymeric substance), free EPS, EPS-protein, and EPS-polysaccharide concentrations in the concentrate and the supernatant at different temperatures.
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Figure 6. Development of the trans-membrane pressure (TMP) of high loaded bioflocculation membrane reactors (HLB-MRs) at different temperatures.
Figure 6. Development of the trans-membrane pressure (TMP) of high loaded bioflocculation membrane reactors (HLB-MRs) at different temperatures.
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Table
Table 1. Classified COD concentration of influent, concentrate, and effluent. Unit: mg/L.
Table 1. Classified COD concentration of influent, concentrate, and effluent. Unit: mg/L.
InfluentCODssCODCOCODSOCODTO
1803136247 ± 21
LT(8 °C)concentrate2223 ± 227155 ± 1296 ± 82474 ± 316
effluent 35 ± 5
HT(15 °C)concentrate2413 ± 23567 ± 672 ± 82552 ± 306
effluent 26 ± 3
Table
Table 2. Na, Ca, and Al concentration in the supernatant and concentrate of the HLB-MRs.
Table 2. Na, Ca, and Al concentration in the supernatant and concentrate of the HLB-MRs.
Supernatant Concentration (mg/L)Sediments Concentration (mg/gTSS)
NaCaAlNaCaAl
LT(8 °C)43.859.3429.243.4115.6313.25
HT(15 °C)40.048.2336.443.7118.2016.06

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Wan, L.; Xiong, L.; Zhang, L.; Lu, W. High Loaded Bioflocculation Membrane Reactor of Novel Structure for Organic Matter Recovery from Sewage: Effect of Temperature on Bioflocculation and Membrane Fouling. Water 2020, 12, 2497. https://doi.org/10.3390/w12092497

AMA Style

Wan L, Xiong L, Zhang L, Lu W. High Loaded Bioflocculation Membrane Reactor of Novel Structure for Organic Matter Recovery from Sewage: Effect of Temperature on Bioflocculation and Membrane Fouling. Water. 2020; 12(9):2497. https://doi.org/10.3390/w12092497

Chicago/Turabian Style

Wan, Liguo, Ling Xiong, Lijun Zhang, and Wenxi Lu. 2020. "High Loaded Bioflocculation Membrane Reactor of Novel Structure for Organic Matter Recovery from Sewage: Effect of Temperature on Bioflocculation and Membrane Fouling" Water 12, no. 9: 2497. https://doi.org/10.3390/w12092497

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