Investigation on removing recalcitrant toxic organic polluters in coking wastewater by forward osmosis

Investigation was made on the efficiency of two commercial membranes in removing via forward osmosis(FO)the low molecular weight organic compounds typical of coking wastewater. The membranes were supplied by Poten and HTI companies. The organics in the simulated coking water were indole and pyrridine. Under FO mode, the rejection to the organics by Poten membrane was around 50%, whereas that for HTI membrane was obviously higher, ranging from 65% to 74%. The response of the two membranes in terms of Water flux and reverse salt flux(RSF) towards changing feed/draw solution(DS) flow rates in FO mode showed similar tendency,but different degree. Generally, the flux in FO using HTI membranes was lower. For HTI membrane, FO operated with pressure retarded osmosis(PRO) mode was also performed and the overall rejection of the organics was slightly lower than that in FO mode. In the long term FO test within 15 days, both Poten and HTI membranes displayed flux reduction and rejection enhancement. But the variation with Poten membrane was much more obvious. Discussion was carried out about the reasons and the mechanisms behind the FO performance difference between two membranes and the variation in flux and rejection with operation conditions. Characterizations by SEM, FTIR, AFM, XRD and XPS were tried to support the proposed explanations.

A Combined Forward Osmosis and Membrane Distillation System for Sidestream Treatment

Separate treatment of high-nutrient sidestream is an efficient and cost effective way to decrease the loading on the main plant, resulting in lower effluent nutrient concentration. This study investigated the use of a combined forward osmosis-membrane distillation (FO-MD) system for the removal of nitrogen present in high concentration in sidestream from anaerobic digestion process. The combined system was able to achieve almost 100% rejection of solids and acetic acid, and more than 98% rejection of NH3-N from the sidestream. The high rejection of NH3-N was mainly achieved by the FO process. The solids in the feed solution contributed to fouling problem in both FO and MD, resulting in significant decline in flux. However, 76% or higher flux recovery was achieved for FO membrane by cleaning with tap water. We observed that flux recovery was due to removal of solids from the membrane surface by the cleaning process. FO membrane also demonstrated excellent performance for continuous operation when cleaned for 15 min in every 24 h interval. Overall, the combined FO-MD system was found to be an effective solution for treatment of nutrient rich sidestream.

An agent-based simulation with NetLogo platform to evaluate forward osmosis process(PRO Mode)

Forward osmosis(FO), as an emerging technology, is influenced by different factors such as operating conditions,module characteristics, and membrane properties. The general aim of this study was to develop a suitable(flexible,comprehensive, and convenient to use) computational tool which is able to simulate osmosis through an asymmetric membrane oriented in pressure retarded osmosis(PRO) mode in a wide variety of scenarios. For this purpose, an agent-based model was created in NetLogo platform, which is an easy-to-use application environment with graphical visualization abilities and well suited for modeling a complex system evolving over time. The simulation results were validated with empirical data obtained from literature and a great agreement was observed. The effect of various parameters on process performance was investigated in terms of temperature,cross-flow velocity, length of the module, pure water permeability coefficient, and structural parameter of the membrane. Results demonstrated that the increase in all parameters, except structural parameter of the membrane and the length of module led to the increase of average water flux. Moreover, nine different draw solutes were selected in order to assess the influence of net bulk osmotic pressure difference between the draw solution(DS) and feed solution(FS)(known as the driving force of FO process) on water flux. Based on the findings of this paper, the performance of FO process(PRO mode) can be efficiently evaluated using the NetL ogo platform.

Multi-functional forward osmosis draw solutes for seawater desalination

Forward osmosis(FO), as one of the emerging desalination technologies, has the potential to produce fresh water from a variety of water sources by utilizing the osmotic pressure gradient across a semi-permeable membrane.Draw solution, as an essential component of any FO process, can extract water molecules from seawater or wastewater. An ideal draw solution should meet three essential requirements, namely high osmotic pressure, low reverse flux, and facile regeneration mechanism. The selection of proper draw solutes is especially critical for an energy-efficient FO process since the energy consumption mostly arises from the separation or regeneration of the draw solution. Recently, we developed a few multi-functional FO draw solutes, mainly aiming to enhance the FO water flux and to explore facile re-concentration methods. This review summarizes these draw solutes,including Na^+_- functionalized carbon quantum dots, thermoresponsive copolymers, hydrophilic magnetic nanoparticles, and thermoresponsive magnetic nanoparticles.

Potential use of nanofiltration like-forward osmosis membranes for copper ion removal

The discharge of industrial effluent containing heavy metal ions would cause water pollution if such effluent is not properly treated.In this work,the performance of emerging nanofiltration(NF)like-forward osmosis(FO)membrane was evaluated for its efficiency to remove copper ion from water.Conventionally,copper ion is removed from aqueous solution via adsorption and/or ion-exchange method.The engineered osmosis method as proposed in this work considered four commercial NF membranes(i.e.,NF90,DK,NDX and PFO)where their separation performances were accessed using synthetic water sample containing 100 mg·L-1 copper ion under FO and pressure retarded osmosis(PRO)orientation.The findings indicated that all membranes could achieve almost complete removal of copper regardless of membrane orientation without applying external driving force.The high removal rates were in good agreement with the outcomes of the membranes tested under pressuredriven mode at 1 MPa.The use of appropriate salts as draw solutes enabled the NF membranes to be employed in engineered osmosis process,achieving a relatively low reverse solute flux.The findings showed that the best performing membrane is PFO membrane in which it achieved N 99.4%copper rejection with very minimum reverse solute flux of<1 g·m-2·h-1.

Osmotic concentration of succinic acid by forward osmosis:Influence of feed solution pH and evaluation of seawater as draw solution

In this study, we investigated the essential role of feed solution pH so as to gain insights into the transport mechanisms of succinic acid concentration by osmotically-driven forward osmosis （FO） process. FO performances including water flux and bidirectional transport of succinate and chloride anions were systematically examined using cellulose triacetate-based FO membrane. Additionally, real seawater was explored as draw solution. Experimental results revealed that the pH-dependent speciation of succinic acid can affect the FO performances. Ionization of succinic acid at higher solution pH enhanced the osmotic pressure of feed solution, thus leading to lower water flux performance. A strong effect was pointed out on the succinate rejection for which nearly 100% rejections were achieved at pH above its pKa2 value. The rejection of succinate increased in the following order of chemical form： C2H4C2O4H2 〈 C2H4C2OH- 〈 C2H4C2O24-. With real seawater as the draw solution, low to moderate water fluxes （〈4 L. m- 2. h- 1 ） were observed. The divalent succinate anion was highly retained in the feed side despite differences in the succinic acid feed concentration at pH of approximately 6.90.

An easily recoverable thermo-sensitive polyelectrolyte as draw agent for forward osmosis process

As a potential solution to the crises of energy and resources, forward osmosis(FO) has been limited by the development of draw agents. An ideal draw agent should be able to generate high osmotic pressure and can be easily recovered. In this study, a thermo-sensitive polyelectrolyte of poly(N-isopropylacrylamide-co-acrylic acid)(PNA)is developed as an efficient draw agent, and two easy and simple methods are proposed to effectively recover the polyelectrolytes. After adjusting the pH value of polyelectrolyte solutions to around 6.0, the polyelectrolyte can generate relatively high osmotic pressure, and induce average water fluxes of 2.09 and 2.95 L·m^(-2)·h^(-1) during12 h FO processes when the polyelectrolyte concentrations are 0.20 and 0.38 g·ml^(-1) respectively. After acidifying and heating to 70 °C, the PNA-10 polyelectrolyte can aggregate together because of hydrophobic association and separate from water, so it can be easily recovered by either simple centrifugation or gravitational sedimentation. The recovery ratios of PNA-10 polyelectrolyte in both methods are as high as 89%, and the recovered polyelectrolytes can be reused with almost the same FO performance as fresh ones. The results in this study provide valuable guidance for designing efficient and easily recoverable draw agents for FO processes.

Layer by Layer Assembly of Poly(Allylamine Hydrochloride)/Phosphate Ions and Poly(Sodium 4-Styrene Sulfonate) Membrane for Forward Osmosis Application

Based on the layer by layer(Lb L)assembly technology,the nano-scale composite membrane with excellent structure can be prepared by changing the polyelectrolyte and controlling the deposition conditions.Polyamines and phosphate ions(Pi)can be self-organized to form supramolecular systems which could be exploited to stabilize the interfacial architecture.The LbL membrane was made of the positively charged poly(allylamine hydrochloride)(PAH)self-organized with Pi and the negatively charged poly(sodium 4-styrene sulfonate)(PSS)alternatively on top of a poly(acrylonitrile)(PAN)substrate.Compared to the membrane without Pi,the membrane assembled by PAH/Pi improved forward of flux and reduced flux of salt.The concentration of PAH and PSS,deposition time,pH and number of layers showed significant influences on the performance of the membrane.In this experiment,we systematically investigated the preparation conditions and under the optimized conditions the prepared membrane exhibited high water fluxes of 13.5 L m^-2 h^-1 with corresponding salt to water flux,Js/Jv,ratio of 0.07 g L^-1 tested by forward osmosis when DI water as feed solution and 2 mol L^-1 MgCl2 as draw solution.

Potential of Magnesium Chloride for Nutrient Rejection in Forward Osmosis

Wastewater may contain high levels of the nutrients: nitrogen and phosphorus. Excessive release of nutrients to the environment can cause severe environmental problem such as eutrophication leading to algal blooms, oxygen deficiency, and fish kills. The forward osmosis (FO) could be a choice of treatment. FO process presents the results of using four kinds of variation in concentration of magnesium chloride (MgCl2) as draw solution and the two kinds of commercial membranes for nutrient rejection in the same cross flow velocity at 0.25 m/s and temperature at 25°C. Nutrients consisting of nitrogen (nitrite, nitrate, and ammonium) and phosphorus (phosphate) in feed solution were successfully rejected with an efficiency of mostly more 95%. The water flux in membrane HTI-NW achieved lower 7.55 - 9.61 L/m2·hr than in membrane HTI-ES that exceeds until 13.58 - 15.10 L/m2·hr. The reverse solute in membrane HTI-NW is seemly constant along all concentration of DS MgCl2 that the chloride diffusion is slightly higher than magnesium. In membrane HTI-ES, the reverse solute of chloride was almost three times than that of magnesium. The concentration of MgCl2 plays a significant role in rejecting nutrients by the Donnan’s potential and the diffusion constant in low and high concentration of DS, respectively.

Harvesting Microalgae Biomass Using Sulfonated Polyethersulfone(SPES)/PES Porous Membranes in Forward Osmosis Processes

This study was performed to investigate the availability of forward osmosis(FO)for microalgae harvesting using sulfonated polyethersulfone(SPES)/PES porous membranes.In FO process,porous membranes(<25.0 L m^−2 h^−1)exhibited more superior water flux than TFC FO membranes(<2.6 L m^−2 h^−1).Furthermore,the incorporation of SPES has been demonstrated to enhance membrane performance.The effects of SPES content on pore structure and separation performance were investigated.Compared with pure PES porous membranes,porous membranes with 40%SPES yielded an improved hydrophilicity and greater porosity.It exhibited two times higher water fluxes than the pure PES porous membrane.For microalgae harvesting,AL-FS mode(active layer facing the feed solution)was more favourable than AL-DS mode(active layer facing the draw solution)because less deposited microalgae on the active layer mitigate the membrane biofouling.FO operation combined with SPES/PES porous membranes is conducive to preserving microalgae cell integrity under the mild condition.In addition,FO membrane can be cleaned by a simple water rinse.Potential implications were highlighted as a sustainable method for microalgae harvesting because of no pressure input and less chemical cleaning demand.

Influence of Temperature on the Performance of Forward Osmosis Using Ammonium Bicarbonate as Draw Solute

This study investigated the influence of temperature on the performance of forward osmosis(FO) under the condition that the feed solution(FS) temperature was diff erent from draw solution(DS) temperature. An FO model considering the mass and heat transfer between FS and DS was developed, and the FO experiment with ammonium bicarbonate solution as DS and sodium chloride solution as FS was carried out. The predicted water flux and reverse draw solute flux using the developed model coincided with the experimental fluxes. Increases in the temperature of FS or DS yield corresponding increases in the water flux, reverse draw solute flux, and forward rejection of feed solute. Compared with increasing the FS temperature, increasing the DS temperature has a more significant impact on enhancing FO performance. When the temperature of DS increased from 20 to 40 ℃, the specific reverse solute flux decreased from 0.231 to 0.190 mol/L.

Preparation of novel magnetic nanoparticles as draw solutes in forward osmosis desalination

Novel magnetic nanoparticles(MNPs),Fe_(3)O_(4)@SiO_(2) and Fe_(3)O_(4)@SiO_(2)@PEG-(COOH)_(2),were prepared by loading different amounts of SiO_(2) or/and PEG-(COOH)_(2) onto Fe_(3)O_(4) nanoparticles,and their feasibility to be used as forward osmosis(FO)draw solutes was investigated.The characterization of the materials showed that,compared to normal Fe_(3)O_(4) nanoparticles,the modified MNPs exhibited enhanced dispersity and high osmotic pressure in aqueous solution.The FO experiment indicated that the synthesized draw solutes could obtain a water flux as high as 10 L·m^(-2)·h^(-1) with an aquaporin FO membrane.The optimal concentration of the added tetraethyl orthosilicate was 30%during the synthesis.The novel MNPs could be easily recovered from draw solutions by magnetic field,and the recovery rate of Fe_(3)O_(4)@SiO_(2) and Fe_(3)O_(4)@SiO_(2)@PEG-(COOH)_(2) was 83.95%and 63.37%,respectively.Moreover,after 5 recycles of reuse,the water flux of Fe_(3)O_(4)@SiO_(2) and Fe_(3)O_(4)@SiO_(2)@PEG-(COOH)_(2) as draw solutes still remained 64.36%and 85.26%,respectively.The experimental results demonstrated that the synthesized core–shell magnetic nanoparticles are promising draw solutes,and the Fe_(3)O_(4)@SiO_(2)@PEG-(COOH)_(2) was more suitable to be used as draw solute in FO process.

不同粒径UiO-66混掺改性TFN-FO膜的构建及性能评价

以锆基金属-有机骨架材料(MOFs)UiO-66作为研究对象,制备了三种不同粒径的UiO-66纳米颗粒,并将其混掺到薄层复合膜(TFC)的聚酰胺(PA)层内,研究了UiO-66纳米颗粒的粒径对薄层复合纳米正渗透(TFN-FO)膜性能的影响。通过扫描电子显微镜(SEM)、原子力显微镜(AFM)、水接触角(WCA)测量仪、X射线光电子能谱仪(XPS)等表征手段,探究了TFN-FO膜的性质变化。结果表明,减小UiO-66的粒径不会影响TFN-FO膜的高亲水性,并且随着UiO-66粒径的减小,TFN-FO膜的粗糙度降低、交联度升高。通过以去离子水和2 mol/L氯化钠溶液作为进料液和汲取液的实验室自制的正渗透系统对膜性能进行评价,发现混掺小粒径(50 nm)UiO-66的TFNFO膜可以在保持较低反向盐通量的同时实现35%的水通量提升。有机污染实验表明,TFN-FO膜具有良好的抗污染性能。

Ultralong hydroxyapatite-based forward osmosis membrane for freshwater generation

Increasing global water shortages are accelerating the pace of membrane manufacturing,which generates many environmentally harmful solvents.Such challenges need a radical rethink of developing innovative membranes that can address freshwater production without generating environmentally harmful solvents.This work utilized the synthesized ultra-long hydroxyapatite(UHA)by the solvothermal method using the green solvent oleic acid in preparing UHA-based forward osmosis membranes.The membranes were developed using different loading ratios of graphene oxide(GO)by vacuum-assisted filtration technique.The prepared GO/UHA membranes were identified using X-ray diffraction,scanning electron microscope,Fourier-transform infrared spectroscopy,and X-ray photoelectron spectroscopy.Water contact angle and pore size distribution were determined for the obtained GO/UHA membranes.The obtained hierarchical porous structure in the prepared membranes with interconnected channels results in a stable water flux with reverse salt flux.The best water flux rate of 42±2 L·m^(–2)·h^(–1)was achieved using the 50 mg GO/UHA membrane,which is 3.3 times higher than the pristine membrane,and a reverse salt flux of 67 g·m^(-2)·h^(–1).The obtained results showed a promising capability of a new generation of sustainable inorganic-based membranes that can be utilized in freshwater generation by energy-efficient techniques such as forward osmosis.

Photocatalytic thin film composite forward osmosis membrane for mitigating organic fouling in active layer facing draw solution mode

As a high-flux operation mode of thin film composite-forward osmosis(TFC-FO)membrane,active layer facing draw solution(AL-DS)mode suffers from the severe membrane fouling tendency,which is not addressed well.Here,we introduced a photocatalyst(Anatase titanium dioxide,A-TiO_(2))onto the support layer of TFC-FO membrane via the bonding of polydopamine(PDA)and polytetrafluoroethylene(PTFE),and prepared two photocatalytic membranes,A-TiO_(2)/PDA@TFC and A-TiO_(2)/PTFE@TFC.Compared with the pristine TFC-FO membrane,both A-Ti O_(2)/PDA@TFC and A-TiO_(2)/PTFE@TFC had an improved water permeability(10.5 L m^(-2)h^(-1)and 9.5 L m^(-2)h^(-1),respectively)and reduced reverse Na Cl flux salt(0.8 g m^(-2)h^(-1)and 0.7 g m^(-2)h^(-1),respectively)in the AL-DS mode using 1 mol/L Na Cl as draw solution and pure water as feed solution.Moreover,in the 16 h fouling experiment using 200 ppm bovine serum albumin(BSA)solution as a representative pollutant,the flux decline rate of both photocatalytic membranes was dramatically alleviated from 39.7%and 21.7%in the darkness to 8.5%and 9.7%under UV irradiation,respectively,indicating a significant anti-fouling capacity of photocatalytic effect.In all,the presence of A-TiO_(2)endowed membrane with high permeability,high rejection efficiency and excellent anti-fouling capacity under UV spotlight.As bonding agent,PTFE provided the modified membrane with a high photocatalytic effect and high self-cleaning capacity,while PDA increased the membrane permeability and protected membrane against photocatalytic damage.This work provides a simple and feasible method to improve the anti-fouling capacity of TFC-FO membrane in AL-DS mode.

Fabrication of novel thin-film composite membrane based on ultrathin metal-organic framework interlayer for enhancing forward osmosis performance

To improve operation efficiency,an interlayered thin-film composite forward osmosis(iTFC-FO)membrane was designed by introducing an ultrathin and porous interlayer based on aluminum tetra-(4-carboxyphenyl)porphyrin(a stable metal-organic framework nanosheet,Al-MOF).Surface characterization results revealed that Al-MoF spread evenly in the macro-porous substrate,and provided a flat and smooth reaction interface with moderate hydrophilicity and uniform small aperture.The resultant polyamide(PA)layer had a thin base(without intrusion into substrate)and crumpled surface(with abundant leaves).The leaves size and cross-linking degree of PA layer firstly increased and then decreased with the Al-MOF loading.Compared to the original membrane,the iTFC-FO showed an enhanced water permeability and a reduced reverse sodium flux in both modes of active layer facing feed solution(ALFS)and active layer facing draw solution(AL-DS).To be specific,the specific reverse sodium flux(reverse sodium flux/pure water flux)decreased from 0.27 g/L to 0.04 g/L in the AL-FS mode,while from 1.36 g/L to 0.23 g/L in the AL-DS mode with 2 mol/L NaCl as DS.Moreover,the iTFC-FO maintained high stability and high permeability under high-salinity and contaminated environment.This study offers a new possibility for the rational fabrication of high-performance TFC-FO membranes.

Enhanced permeability and biofouling mitigation of forward osmosis membranes via grafting graphene quantum dots

In this paper,graphene oxide quantum dots with amino groups(NH_(2)-GOQDs)were tailored to the surface of a thin-film composite(TFC)membrane surface for optimizing forward osmosis(FO)membrane performance using the amide coupling reaction.The results jointly demonstrated hydrophilicity and surface roughness of the membrane enhanced after grafting NH_(2)-GOQDs,leading to the optimized affinity and the contact area between the membrane and water molecules.Therefore,grafting of the membrane with a concentration of 100 ppm(TFC-100)exhibited excellent permeability performance(58.32 L·m^(–2)·h^(–1))compared with TFC membrane(16.94 L·m^(–2)·h^(–1)).In the evaluation of static antibacterial properties of membranes,TFC-100 membrane destroyed the cell morphology of Escherichia coli(E.coli)and reduced the degree of bacterial adsorption.In the dynamic biofouling experiment,TFC-100 membrane showed a lower flux decline than TFC membrane.After the physical cleaning,the flux of TFC-100 membrane could recover to 96%of the initial flux,which was notably better than that of TFC membrane(63%).Additionally,the extended Derjaguin–Landau–Verwey–Overbeek analysis of the affinity between pollutants and membrane surface verified that NH_(2)-GOQDs alleviates E.coli contamination of membrane.This work highlights the potential applications of NH_(2)-GOQDs for optimizing permeability and biofouling mitigation of FO membranes.

PAM汲取液制备及FO浓缩模拟城市污水可行性

通过共沉淀法制备了超顺磁性纳米颗粒,并利用聚丙烯酰胺对其改性,制备了新型正渗透汲取液Fe_(3)O_(4)@PAM,探究其正渗透浓缩模拟城市污水的可行性。通过SEM、FTIR、XRD和VSM等技术对改性前后的磁性纳米颗粒形貌结构进行表征,表明PAM可很好地负载在Fe_(3)O_(4)表面。PAM、MNPs和Fe_(3)O_(4)@PAM汲取液在相同FO运行条件下,Fe_(3)O_(4)@PAM汲取液的水通量最大,为5.1 L/(m^(2)·h);AM(PAM的前聚体)/MNPs在质量比分别为3、2.5、2、1.5时制备改性磁纳米颗粒,质量比为3制备的20 g/L的Fe_(3)O_(4)@PAM水通量最大,为7.7 L/(m^(2)·h);当Fe_(3)O_(4)@PAM(3∶1)的浓度从10 g/L增加至70 g/L时,水通量从4.3 L/(m^(2)·h)增至12.7 L/(m^(2)·h),呈稳定上升趋势;50 g/L的Fe_(3)O_(4)@PAM汲取液正渗透浓缩模拟城市污水,水通量最大可达10.5 L/(m^(2)·h),汲取液的3次重复利用后的平均回收率达到了84.3%,表明其有一定的城市污水浓缩可行性。

H2O2氧化/CaO沉淀预处理化学镀镍废槽液及其FO浓缩减量效果研究

为了降低高浓度化学镀镍废槽液处理成本,采用氧化-沉淀预处理-正渗透(FO)组合工艺对废槽液进行常温浓缩减量.FO膜为水通道蛋白膜(AQP),汲取液为4 mol·L^(-1)NaCl溶液,FO过程采用活性层朝向原料液(AL-FS)的模式.当采用H2O2加CaO进行预处理时,废液电导率、TP、TOC和Ni的去除率远高于其他预处理方案.当CaO添加量为5%时,系统水通量可达到5.89 L·(m^(2)·h)^(-1);浓缩后污染物TP、Ni和TOC的截留率分别达到73.97%、92.90%和84.65%.三维荧光图谱(EEM)结果显示,有机物类腐殖酸组分比酪氨酸或色氨酸蛋白类物质更容易透过半透膜从原料液进入到汲取液中.适量的CaO预处理不仅可以有效的降低污染物的浓度和渗透压,有利于后续FO工艺浓缩减量,而且节约了经济成本.

太阳能真空膜蒸馏和肥料汲取液正渗透处理反渗透浓水的节能性和经济性分析

针对太阳能真空膜蒸馏(Solar vacuum membrane distillation,SVMD)和肥料汲取液正渗透(Fertilizer draw forward osmosis,FDFO)系统处理反渗透(Reverse osmosis,RO)浓水的试验研究较多,而对其能耗和经济性分析的较少.通过对试验规模和工业规模条件下2种系统的膜通量、能耗和成本进行对比分析,结果表明,在试验规模条件下,将RO浓水浓缩4倍,无辅助热源SVMD系统的膜通量为2.46 kg/(m^(2)·h),比能耗为110.6 kWh/m^(3),单位水生产成本为96.6元/m^(3);有辅助热源SVMD系统的膜通量为3.75 kg/(m^(2)·h),比能耗为230.7 kWh/m^(3),单位产水成本为13.4元/m^(3);FDFO系统的膜通量为3.62 kg/(m^(2)·h),比能耗为20.44 kWh/m^(3),单位产水成本为26.8元/m^(3).在工业化规模条件下,设计产水量均为240 m^(3)/d时,SVMD系统比能耗为12.8 kWh/m^(3),单位产水成本为10.8元/m^(3);FDFO系统比能耗为12 kWh/m^(3),单位产水成本为9.38元/m^(3).可见生产规模越大,不同系统的产水成本越小,差别也越小.