Application of response surface methodology to the chemical cleaning process of ultrafiltration membrane

A numerical model was established to predict and optimise the chemical cleaning process of Polyvinylidene Fluo- ride （PVDF） Ultrafiltration （UF） membranes with the results from the experiment that applied the Response Sur- face Method （RSM） and Central Composite Design （CCD）. The factors considered in the experimental design were sodium hydroxide （NaOH） concentration, sodium bypochlorite concentration （NaCIO）, citric acid concentration and cleaning duration, The interactions between the factors were investigated with the numerical model. Humic acid （20 mg· L-1） was used as the model foulant, and chemical enhanced backflush （CEB） was employed to sim- ulate the chemical cleaning process. The concentrations of sodium hydroxide, sodium hypochlorite, citric acid and cleaning duration tested during the experiments were in the range of 0.1%-0.3% 100-300 mg· L-1 1%-3% and 0.5-1.5 h, respectively. Among the variables, the sodium hypochlorite concentration and the cleaning dura- tion showed a positive relationship involving the increased efficiency of the chemical cleaning. The chemical cleaning efficiency was hardly improved with increasing concentrations of sodium hydroxide. However, the data was sharply decreased when at a low level of sodium hydroxide concentration. In total, 54 sets of cleaning schemes with 80% to 100K cleaning efficiency were observed with the R＆M model after calibration.

Fouling behavior of poly(vinylidene fluoride)(PVDF)ultrafiltration membrane by polyvinyl alcohol(PVA)and chemical cleaning method

Severe fouling to poly(vinylidene fluoride)(PVDF)membrane is usually caused as filtrating the papermaking wastewater in the ultrafiltration(UF)process.In the paper,fouling behavior and mechanism were investigated,and the low-concentration polyvinyl alcohol(PVA)contained in the sedimentation tank wastewater was found as the main foulant.Consequently,the corresponding cleaning approach was proposed.The experiment and modeling results elaborated that the fouling mode developed from pore blockage to cake layer along with filtration time.Chemical cleaning conditions including the composition and concentration of reagents,cleaning duration and trans-membrane pressure were investigated for their effect on cleaning efficiency.Pure water flux was recovered by over 95% after cleaning the PVDF membrane using the optimal conditions 0.5 wt% NaClO(as oxidant)and 0.1 wt% sodiumdodecyl benzene sulfonate(SDBS,as surfactant)at 0.04MPa for 100 min.In the chemical cleaning method,hypochlorite(ClO−)could first chain-scissor PVA macromolecules to small molecules and SDBS could wrap the fragments in micelles,so that the foulants were removed from the pores and surface of membrane.After eight cycling tests,pure water flux recovery maintained above 95% and the reused membrane was found intact without defects.

Research and Application of New Chemical Cleaning Process for Titanium-Made Equipment

Based on the research on corrosion-resistance of titanium in various media and a great deal of tests, a newchemical cleaning process for titanium-made equipment was developed and applied to titanium-made heat exchangersof a homemade multi-stage flash distiller for sea-water desalination in Tianjin Dagang Power Plant. Scale in the tubeswas removed completely as inspected by the experts. Testing results of hydrogen content and metallographic structureof titanium tubes showed that the cleaning was successful without any damages to the equipment.[

Influence of wet chemical cleaning on quantum efficiency of GaN photocathode

GaN samples 1-3 are cleaned by a 2：2：1 solution of sulfuric acid（98%） to hydrogen peroxide（30%） to de-ionized water;hydrochloric acid（37%）;or a 4：1 solution of sulfuric acid（98%） to hydrogen peroxide（30%）.The samples are activated by Cs/O after the same annealing process.X-ray photoelectron spectroscopy after the different ways of wet chemical cleaning shows：sample 1 has the largest proportion of Ga,N,and O among the three samples,while its C content is the lowest.After activation the quantum efficiency curves show sample 1 has the best photocathode performance.We think the wet chemical cleaning method is a process which will mainly remove C contamination.

A Giant of China's Cleaning Industry——The Blue Star Chemical Cleaning Group Corporation

First business: to clean a tea pot. Income: RMB 0.20 (less than 10 US cents at the time). Second business: to clean a boiler. Income: RMB 1, 200. Three months later, incomereached RMB 240, 000. Ten years later, the company had 350 subsidiaries across China and four joint ventures abroad, with an annual output value of more than RMB 300 million. The data are simple but intriguing, recording the history of the Blue

Application of heat-activated peroxydisulfate process for the chemical cleaning of fouled ultrafiltration membranes

Na Cl O has been widely used to restore membrane flux in practical membrane cleaning processes,which would induce the formation of toxic halogenated byproducts.In this study,we proposed a novel heatactivated peroxydisulfate(heat/PDS)process to clean the membrane fouling derived from humic acid(HA).The results show that the combination of heat and PDS can achieve almost 100%recovery of permeate flux after soaking the HA-fouled membrane in 1 mmol/L PDS solution at 50℃ for 2 h,which is attributed to the changes of HA structure and enhanced detachment of foulants from membranes.The properties of different treated membranes are characterized by scanning electron microscopy(SEM),atomic force microscope(AFM),attenuated total reflection Fourier transform infrared spectroscopy(ATRFTIR),and X-ray photoelectron spectroscopy(XPS),demonstrating that the reversible and irreversible foulants could be effectively removed by heat/PDS cleaning.The filtration process and fouling mechanism of the cleaned membrane were close to that of the virgin membrane,illustrating the good reusability of the cleaned membrane.Additionally,heat/PDS which can avoid the generation of halogenated byproducts shows comparable performance to Na Cl O on membrane cleaning and high performance for the removal of fouling caused by sodium alginate(SA),HA-bovine serum albumin(BSA)-SA mixture and algae,further suggesting that heat/PDS would be a potential alternative for membrane cleaning in practical application.

Chemical cleaning of fouled PVC membrane during ultrafiltration of algal-rich water

Cleaning of hollow-fibre polyvinyl chloride （PVC） membrane with different chemical reagents after ultrafiltration of algal-rich water was investigated. Among the tested cleaning reagents （NaOH, HCl, EDTA, and NaClO）, 100 mg/L NaClO exhibited the best performance （88.4% ± 1.1%） in removing the irreversible fouling resistance. This might be attributed to the fact that NaClO could eliminate almost all the major foulants such as carbohydrate-like and protein-like materials on the membrane surface, as confirmed by Fourier transform infrared spectroscopy analysis. However, negligible irreversible resistance （1.5% ± 1.0%） was obtained when the membrane was cleaning by 500 mg/L NaOH for 1.0 hr, although the NaOH solution could also desorb a portion of the major foulants from the fouled PVC membrane. Scanning electronic microscopy and atomic force microscopy analyses demonstrated that 500 mg/L NaOH could change the structure of the residual foulants on the membrane, making them more tightly attached to the membrane surface. This phenomenon might be responsible for the negligible membrane permeability restoration after NaOH cleaning. On the other hand, the microscopic analyses reflected that NaClO could effectively remove the foulants accumulated on the membrane surface.

Study of Oil-Bearing Drill Cuttings Cleaning and De-Oiling Treatment Method for Shale Gas Reservoirs

Due to its extensive use in shale gas exploration and development,oil-based drilling fluids generate large amounts of oil-bearing drill cuttings during the drilling process.The large amount of oil-bearing drill cuttings generated during the drilling process can lead to serious secondary contamination.In this study,a wetting agent FSC-6 with good hydrophobic and oleophobic properties was synthesized to construct an efficient oil removal system.For the first time,the mechanism of this system was analyzed by using the theory of adhesion function,interfacial tension and wettability.At the same time,a combined acoustic-chemical treatment process was applied to the wastewater and slag generated after the cleaning of the oil-bearing drill cuttings.The experimental results show that the application of this pollution-free technology can effectively solve the environmental pollution and resource recovery problems of oil-bearing drill cuttings.It meets the standard of drilling chips with oil content less than 2%in SY/T7422-2018“Oil-based drilling fluid drilling chips treatment system for oil and gas drilling equipment”.

Pilot study on treatment of low turbidity and low temperature water by coagulation-immersed membrane process

The objective of this paper was to investigate the practicability of coagulation-immersed membrane process during low-temperature period through the study of steady operation,chemical cleaning methods,water quality and agent consumption.Experimental results showed that:membrane performance decreases with the reduction of temperature,but low temperature has little effect on stable operation of immersed membrane when coagulation as pretreatment.EFM with 1200 mg/L sodium hypochlorite after every 48 filtration cycles was made for reducing membrane fouling efficiently,and the method,with 1.5% sodium hydroxide and 3500 mg/L sodium hypochlorite for 10 h and then 2% hydrochloric acid for 4 h,is an appropriate cleaning method under low temperature.Compared with convention treatment process,immersed membrane process not only has same agent consumption,but also permeated water quality is more superior such as fine removal effect on turbidity with average 0.10 NTU.Therefore,coagulation-immersed membrane process is more appropriate for increasing water quality demand and the treatment of low turbidity and low temperature water.

Formation of disinfection by-products during sodium hypochlorite cleaning of fouled membranes from membrane bioreactors

Periodic chemical cleaning with sodium hypochlorite(NaClO)is essential to restore the membrane permeability in a membrane bioreactor(MBR).However,the chlorination of membrane foulants results in the formation of disinfection by-products(DBPs),which will cause the deterioration of the MBR effluent and increase the antibiotic resistance in bacteria in the MBR tank.In this study,the formation of 14 DBPs during chemical cleaning offouled MBR membrane modules was investigated.Together with the effects of biofilm extracellular polymeric substances(EPS),influences of reaction time,NaClO dosage,initial pH,and cleaning temperature on the DBP formation were investigated.Haloacetic acids(HAAs)and trichloromethane(TCM),composed over 90%of the DBPs,were increasingly accumulated as the NaClO cleaning time extended.By increasing the chlorine dosage,temperature,and pH,the yield of TCM and dichloroacetic acid(DCAA)was increased by up to a factor of 1–14,whereas the yields of haloacetonitriles(HANs)and haloketones(HKs)were decreased.Either decreasing in the chlorine dosage and cleaning temperature or adjusting the pH of cleaning reagents toward acidic or alkaline could effectively reduce the toxic risks caused by DBPs.After the EPS extraction pretreatment,the formation of DBPs was accelerated in the first 12 h due to the damage of biofilm structure.Confocal laser scanning microscopy(CLSM)images showed that EPS,particularly polysaccharides,were highly resistant to chlorine and might be able to protect the cells exposed to chlorination.

Probing particle removal in brush scrubber cleaning with fluorescence technique

Brush scrubber cleaning is widely used for post chemical mechanical polishing(CMP)cleaning in semiconductor manufacturing.In this study,an experimental system based on fluorescence technique and particle-tracking velocimetry(PTV)technique was employed to characterize the particle removal displacement and velocity in the interface between a transparent copper film and a porous polyvinyl alcohol(PVA)brush during the cleaning process.Several different cleaning conditions including rotation speeds,loading pressure and cleaning agent were examined and the particle removal rate was compared.Elastic and friction removal,hydrodynamic removal and mixed-type removal are the three types of particle removal.Particles with an arc trace and uniform velocity curves were removed by friction and elastic force which were related to the brush load.Particles with a random trace and fluctuant velocity curves were removed by hydrodynamic force which was determined by the brush rotation speed.The increase of particle removal rate(PRR)with brush rotation speed is a logistic function.It is easier to improve PRR by increasing the brush load or by adding surfactant than by increasing the brush rotation speed.

Recent Advances in Precombustion Coal Cleaning Processes

The mineral matter in coal constitutes a major impediment to the direct use of coal in power plants.A concerted effort has been mounted to reduce the ash/sulfur contents in product coal to meet theever mcre stringent environmental regulations. In recent years, significant advances have taken placein fine coal cleaning technologies. A review of recent developments in advanced physical, chemical andbiological processes for deep-cleaning of fine coal is presented.

Using loose nanofiltration membrane for lake water treatment:A pilot study

Nanofiltration(NF)using loose membranes has a high application potential for advanced treatment of drinking water by selectively removing contaminants from the water,while membrane fouling remains one of the biggest problems of the process.This paper reported a seven-month pilot study of using a loose NF membrane to treat a sand filtration effluent which had a relatively high turbidity(∼0.4 NTU)and high concentrations of organic matter(up to 5 mg/L as TOC),hardness and sulfate.Results showed that the membrane demonstrated a high rejection of TOC(by<90%)and a moderately high rejection of two pesticides(54%–82%)while a moderate rejection of both calcium and magnesium(∼45%)and a low rejection of total dissolved solids(∼27%).The membrane elements suffered from severe membrane fouling,with the membrane permeance decreased by 70%after 85 days operation.The membrane fouling was dominated by organic fouling,while biological fouling was moderate.Inorganic fouling was mainly caused by deposition of aluminum-bearing substances.Though inorganic foulants were minor contents on membrane,their contribution to overall membrane fouling was substantial.Membrane fouling was not uniform on membrane.While contents of organic and inorganic foulants were the highest at the inlet and outlet region,respectively,the severity of membrane fouling increased from the inlet to the outlet region of membrane element with a difference higher than 30%.While alkaline cleaning was not effective in removing the membrane foulants,the use of ethylenediamine tetraacetate(EDTA)at alkaline conditions could effectively restore the membrane permeance.

Performance of landfill leachate treatment system with disc-tube reverse osmosis units

Reverse osmosis system with the disc-tube mod-ule(DT-RO)was applied to treat landfill leachate on full scale at the Changshengqiao Sanitary Landfill,Chongqing City,China.In the first six-mouth operation phase,the treatment performance of DT-RO system had been excel-lent and stable.The removal rate of chemical oxygen demand(COD),total organic carbon(TOC),electrical con-ductivity(EC),and ammonia nitrogen(NH 3-N)reached 99.2–99.7%,99.2%,99.6%,and over 98%,respectively.The rejection of Ca^(2+),Ba^(2+),and Mg^(2+)was over 99.9%,respectively.Suspended solid(SS)was not detectedin prod-uct water.Effective methods had been adopted to control membrane fouling,of which chemical cleaning is of utmost importance to guarantee the long smooth operation of the DT-ROsystem.The DT-ROsystemiscleanedinturnswith Cleaner A and Cleaner C.At present,the 1st stage cleaning cycle by Cleaner A and Cleaner C is conducted every 100 and500 h,respectively,dependingonrawthewaterquality.

Green production of sugar by membrane technology:How far is it from industrialization?

Application of membrane filtration in sugar production is attractive because it can reduce the usage of chemicals,produce high-quality clarified juice,and obtain various high value-added products.However,some technical problems,such as insufficient membrane performance,high sucrose loss in membrane retentate,severe membrane fouling,and incomplete cleaning protocols,limit its industrial applications.In order to facilitate the development of membrane technology for sugar production,this review summarizes recent progress on the applications of membrane filtration in different stages of sugar production as well as the integrated membrane processes for various purposes.Moreover,some important issues including membrane fouling,membrane cleaning,economic feasibility and engineering problems of the membrane-based sugar production process are discussed.Finally,the existing challenges and future research prospects for the industrialization of this green technique are pointed out.