此文檔是畢業(yè)設計外文翻譯成品（ 含英文原文+中文翻譯），無需調整復雜的格式！下載之后直接可用，方便快捷！本文價格不貴,也就幾十塊錢！一輩子也就一次的事！外文標題：Feasibility of applying forward osmosis to the simultaneous thickening, digestion, and direct dewatering of waste activated sludge外文作者：Hongtao Zhu , Liqiu Zhang , Xianghua Wen , Xia Huang文獻出處:Bioresource Technology , 2018 , 113 (113) :207-213(如覺得年份太老，可改為近2年，畢竟很多畢業(yè)生都這樣做)英文5098單詞， 26874字符(字符就是印刷符)，中文7485漢字。Feasibility of applying forward osmosis to the simultaneous thickening, digestion, and direct dewatering of waste activated sludgeHongtao Zhu , Liqiu Zhang , Xianghua Wen , Xia HuangAbstractThe feasibility of applying forward osmosis (FO) to the simultaneous thickening, digestion, and dewatering of waste activated sludge w as investigated. After 19 days of operation, the total reduction in efficacy of the instantaneous sludge thickening and digestion system in term of mixed liquid suspended solids (MLSS) and mixed liquid volatile suspended solids (MLVSS) was approximated at 63.7% and 80% , respectively, and the MLVSS / MLSS ratio decreased from 80.8% to 67.2%. The MLSS concentration reached 39 g / L from an initial on the day of 7 g / L, indicating a good thickening efficacy. In using FO for sludge dewatering, two major factors were verified, namely, initial sludge depth and draw solution (DS) concentration. A sludge depth of 3 m, w here a dry sludge content of approximately 35% can be achieved in approximately 60 m in, is recommended for future applications. In addition, the present study proved the feasibility of using seawater reverse osmosis concentrate as the DS.Keywords:Forward osmosis, Waste activated sludge, Sludge thickening, Sludge dewatering, Aerobic digestion 1. IntroductionLarge quantities of excess high water content are produced in wastewater treatment plants (WWTPs) everyday. To minim the costs of sludge transportation and handling, reduction in sludge volume and through water separation is the most important that needs to be addressed prior to final disposal. Sludge thickening and dewatering are usually practiced for volume and reduction. Normally, sludge thickening is performed to reduce the sludge volume and increase the sludge solid content to obtain a suitably concentrated sludge for the sludge dewatering processes. The com-only sludge thickening processes include gravity thickening, dissolved air flotation thickening, and centrifugal thickening, among others. Although these traditional thickening technologies are ready-to-use and easy to perform, some problems limit their application. For example, the gravity thickening process has the disadvantages of a large footprint, low-thickening efficacy, tendency of releasing phosphorus during long-term retention time (SRT), and emission of unpleasant odors (Wang et al., 2008a; Kim et al., 2010). On the other hand, sludge digestion treatment is a standard practice, especially for medium and large-scale WWTPs, and is used as a stabilization step after the thickening process to achieve sludge stabilization, detoxication, and minimization, among others (Wang et al., 2008a). Aside from thickening and digestion, sludge dewatering is about 70%. However, sludge dewatering currently remains the most expensive and most poorly understood wastewater treatment process (Pei et al., 2010, Yuan et al., 2011). To solve the problem s of conventional sludge thickening technologies and shorten the sludge treatment processes (i.e., to lessen the footprint and operational strength), a atsheet membrane was developed for simultaneous sludge thickening and digestion process (Wang et al., 2008a). This sludge reduction system is actually a membrane bioreactor (MBR), whose advantages include a small footprint, high pollutant removal efciency, and low cost for the retreatment of the thickened supernate, among others (Judd, 2006). Nevertheless, the relatively high energy requirement, especially from membrane fouling due to high sludge concentration, is the main obstacle for the application of membrane sludge thickening process (Wang et al., 2008b, 2009).In contrast to conventional MBR, several researchers proved that a forward osmotic MBR has better membrane fouling control performance (Cornelissen et al., 2008; Lay et al., 2011; Achilli et al., 2009b). In forward osmosis (FO), such as in the well-known reverse osmosis (RO), water is transported across a semipermeable membrane, which is impermeable to salt and is driven by the difference between the osmotic pressures across the membrane (Cath et al., 2006). Even though osmosis has been recognized and utilized for decades, FO remains a unique and emerging technology (Chung et al., 2010). For the last couple of years, increasing efforts on FO have been exerted due to the availability of more efcient FO membranes (Cornelissen et al., 2008). Present-day FO applications extend from water treatment and food processing to power generation and novel methods of controlling drug release (Wallace et al., 2008; Garcia-Castello and McCutcheon, 2011; Achilli et al., 2009a Sotthivirat et al., 2007). However, in the past 30 years, no studies on the direct use of FO in sludge thickening, digestion, and dewatering were conducted. The only related creative study was performed by Pugsley and Cheng (1981) m ore than 30 years ago. Their study primarily proved the feasibility of applying FO to sludge dewatering. Nevertheless, because of limitations such as the lack of efcient FO membranes, m any issues, including the exploration and optimization of the factors affecting FO performance, need further systematic investigation.In FO, the reconcentration of the draw solution (DS), usually com posed of dissolved salts, is a major part of the energy consumption. The current study proposes the utilization of RO concentrates in seawater desalination as the DS. In RO, typical seawater recoveries are between 30% and 50% (Ji et al., 2010; McCutcheon et al., 2005). Discharge of the concentrated brine back into the sea is proven to affect marine fauna and ora (Latorre, 2005) and dam ages benthic organism s due to the coagulants present in the brine (Lattemann and Hpner, 2008). This phenomenon is a critical environmental drawback to seawater desalination RO, which has been set up worldwide. If the concentrated brine from RO is used as the DS for FO sludge dewatering, the diluted brine could be directly discharged into the sea without causing any dam age. For the FO sludge dewatering process without DS reconcentration, the energy requirements would be reduced to near zero.In the current study, FO was innovatively applied to simultaneous thickening, digestion, and direct dewatering of raw waste activated sludge from WWTPs. The DS was synthesized to simulate the concentrated brine of seawater desalination RO (Ji et al., 2010) and was not reconcentrated to minimize the energy demand. The current work aims to conduct a preliminary study on the characteristics (including the digestion efciency, the reversed salt transport, and the effects of DS concentration on the FO ux) of the simultaneous thickening and digestion system and on the sludge depth and DS concentration on FO dewatering performances. Other issues, such as the process modeling and membrane fouling mechanism s, will be discussed in subsequent studies.2.Methods2.1. Experimental setup and the FO membraneThe bench-scale FO experimental setups for simultaneous sludge thickening, digestion, and dewatering are shown in Fig. 1. In the sludge thickening and digestion system , the single FO membrane module unit consisted of two plexiglass cells that clipped the FO membrane sheet. The effective membrane surface area of a single unit was approximately 0.0133 m 2. Depending on the ux requirements, one to three membrane modules can be used for one reactor. The reactor had a cylindrical conguration and a total volume of 1.8 L. Air was supplied through a ne bubble diffuser to supply oxygen to the microorganism s. Two peristaltic pumps, produced by LanGe Company (China), were used for the circulation of the DS and the sludge. The weight change rates over time of the DS and the diluted DS tanks were recorded via a computer. Based on these data, the ow rates of the DS (i.e., the solution that went into the membrane module) and the diluted DS (i.e., the solution that went out of the membrane module) were calculated. The real-time membrane ux for a certain DS was calculated from the difference between the two measured ow rates.The membrane module used in the sludge dewatering system was similar to a sandwich. The circulation pump pushed the DS through the airtight channel, the bottom layer of the sandwich. The middle layer was the FO membrane, and the top layer was a sludge container. Both the DS and the sludge were in direct contact with the FO membrane. The effective membrane area of this module was approximately 0.0035 m 2,and the sludge container had a length of 7 cm , a width of 5 cm , and a maxim um depth of 1 cm . The calculated maxim um sludge volume of the container was 35 m L, whereas the DS was norm ally m ore than 1000 m L. Therefore, the volume increment of the DS during the dewatering course was omitted (i.e., the DS concentration used for sludge dewatering was considered as constant).The FO membrane used in the study was supplied by Hydration Technology (HTI, Albany, Oregon, US) and classied as cartridge type. The 50 l m -thick FO membrane was made of cellulose triacetate embedded in a polyester screen mesh (Cath et al., 2006). The HTI membranes, which have been used in a number of studies, are currently viewed as the best available membranes for FO applications (Achilli et al., 2009b; Lay et al., 2011;Holloway et al., 2007; Cornelissen et al.,2008; Xiao et al.,2011). The membrane orientation has a signicant effect on the FO ux due to concentration polarization (CP) or membrane fouling. Com pared with the rejection layer facing the DS, the conguration of the rejection layer facing the feed water showed a remarkable ux stability against both bulk DS dilution and membrane fouling, although its ux was relatively lower (Tang et al., 2010). In the current study, the conguration of the rejection layer facing the feed water was adopted to prevent a significant ux decline.2.2. DS and activated sludgeAs previously stated, synthetic DS # 1 was prepared to simulate the concentrated brine from RO (30%recovery rate) by dissolving(7996 m g/L), NaHCO3 (274 m g/L), and Na2SO4 (4526 m g/L) in ultrapure water. For future applications, the RO concentrate can be discharged into the sea after dilution, similar to natural seawater. Synthetic DS # 5 was also used in the tests and was prepared to simulate natural seawater by dissolving reagent grade NaCl 25,053 m g/L), CaCl2 2H2O (1608 m g/L), MgCl2 (5597 m g/L), NaH- CO3 (192 m g/L), and Na2SO4 (3168 m g/L) in ultrapure water. Synthetic DSs # 2, # 3, and # 4 were also prepared using the same salts but at proportional concentrations between those of solutions # 1 and # 5. The detailed information is shown in Table 1.The activated sludge was obtained daily from a 60,000 m 3/d MBR facility in a WWTP located in the northern part of Beijing. The sludge samples had a MLSS of 7.3 g/L, a MLVSS of 5.9 g/L, a soluble COD in supernatant of 103 m g/L, and a conductivity of 310 l S/cm .2.3. Analytical methodsAnalyses of the mixed liquor suspended solids (MLSS), mixed liquor volatile suspended solids (MLVSS), chemical oxygen demand (COD), ammonia nitrogen, and total phosphate were perform ed based on the standard methods proposed by the State Environ- mental Protection Administration of China. The soluble COD (SCOD) samples were prepared using lter papers with a nominal pore size of 0.45 l m . The dissolved oxygen (DO) concentration was determined using a DO meter (Model YSI 58, YSI Research Incorporated, Ohio, US). The mixed liquor viscosity value was obtained using a viscometer (Brookeld, US). The specic oxygen uptake rate was determined based on the standard procedure provided by Zhang (1988). The conductivity of the sludge was monitored using a conductivity probe (Fisher Scientic, Ham pton, NH, US) to calculate the reversed salt transport and the total accumulation of salt in the bioreactor. The equivalent salt (NaCl) concentration was calculated from the conductivity values using a calibration curve. The digestion efciency was calculated as described in previous studies (Wang et al., 2008a,b, 2009) and is given by where Ect is the cumulate digestion efficiency at day t (%), Qt is the influent sludge flow at day t (m3/d), Xit is the influent sludge concentration at day t (g/L), V is the effective volume of the reactor (m3), and Xt is the sludge concentration in the reactor at the end of day t (g/L).3. Results and discussion 3.1. Variations in the sludge concentration and digestion efficiencyThe DO in the reactor was maintained at around 2.0 mg/L and the hydraulic retention time was about 1 day. During the experi-ments, the fluctuation in the room temperature during daytime was 2229 LC. The feed sludge volume for each day depended on the average FO membrane flux of that day. The concentration of the feed sludge also varied, depending on the operation of the MBR facility. No sludge was withdrawn during the experiments.The variations in MLSS and MLVSS and, consequently, the MLSS/ MLVSS ratio with the operation time are shown in Fig. 2(a). Both the MLSS and MLVSS concentrations showed increasing trends be-cause of the FO thickening process and the absence of sludge dis-charge. The quantity of pure water extracted from the FO thickening process was calculated and will be discussed in the next section. In the 19 days of operation, the MLSS and MLVSS concentrations quickly increased during the first 7 days and gradually slo-wed down thereafter. At the end of the tests, the MLSS and MLVSS concentrations reached approximately 39 and 27 g/L, respectively. Fig. 2(a) shows the evolution of the MLVSS/MLSS ratio, which continuously decreased from 80.8% to 67.2% throughout the 19 days of operation, indicating a continuous sludge reduction via aerobic digestion in the reactor.The total reduction efficiency values of MLSS and MLVSS were approximately 63.7% and 80%, respectively Fig. 2(b). The MLSS reduction efficiency is comparable to the results of Kim et al. (2010), where they achieved an MLSS destruction efficiency rate of 60% using a submerged MBR. However, the obtained MLSS reduction efficiency was lower than that of another submerged MBR sludge thickening system used by Wang et al. (2008a), where the latter achieved an MLSS digestion efficiency of about 80% in 15 days. A possible reason for the difference is that, in their studies, part of the fixed suspended solids permeated through the microfil-tration membrane as colloids, whereas almost no colloid passed through the FO membrane used in the current study. On the other hand, the MLVSS reduction efficiency obtained in the present study is higher than those reported by other researchers using MBR or conventional aerobic digestion process. These results included the following: 73% for a submerged MBR during 15 days (Wang et al., 2008a), 5364% under a 35-day SRT at an ambient tempera-ture of approximately 20 LC (Bernard and Gray, 2000), 63% under a 16-day SRT with microwave-alkali pretreatment (Chang et al., 2011), 39.59% under a 17.5-day SRT (Song et al., 2010), and 50% un-der a 50-day SRT (Novak et al., 2003). The MLSS and MLVSS reduc-tion efficiencies in an aerobic digestion can be enhanced by the addition of digested sludge into undigested sludge, which can serve as the source of the viable cell mass needed for the degrada-tion of organic solids. This is the theory behind the high digestion efficiency achieved in the application of FO to the simultaneous sludge thickening and digestion process, as proposed by Khalili et al. (2000) and supported by Wang et al. (2008b). In the current study, the digested sludge was retained in the reactor and blended with the daily influent (i.e., undigested sludge), resulting in a higher digestion efficiency compared with that of a conventional aerobic digestion process.3.2. Membrane flux decline and reversed salt transport during sludge thickeningThe aerobic digestion and sludge thickening simultaneously occurred. Based on the MLSS concentration of 39 g/L and total MLSS digestion rate of 63.7% on the 19th day, the final calculated MLSS without sludge digestion was approximately 107 g/L. Thus, through the FO sludge thickening system, the activated sludge can be thickened from a water content of 99.3% to approximately 90%, higher than that of most conventional sludge thickening processes.The water ux under different DS concentrations as a function of operating time is shown in Fig. 3(a). The ux evolution curves of DSs # 1, # 2, and # 3 share similar trends, with a rapid decrease at the beginning followed by a smooth development. This phenomenon shows that CP as well as a possible membrane fouling, rapidly occurred within the rst several days. Based on the variations in the relative ux over time Fig. 3(b), the ux reduction range of each test Fig. 3(a) decreased from DS # 1 to DS # 5, which is in accordance with the conclusion that higher DS concentrations result in severe CP (Tang et al., 2010). In other words, DS with low salt concentration exhibited a stable ux even though the resulting ux was relatively low. The initial water ux decreased from DS # 1 to DS # 5, indicating a positive correlation between the water ux and salt concentration (i.e., osmotic pressure). As the experiment progressed, the water ux under all ve conditions was reduced with time, indicating the occurrence of CP, accumulation of reversely transported salt, and/or the development of membrane fouling. A com m on effect of CP and