Research On Key Technology Of Online Treatment And Reuse Of Dyeing Wastewater

China has now become the largest country of textile dyeing production in the world. Textileprinting and dyeing industries are not only a significant consumer of water, dyes and chemicalauxiliaries, but also a big producer of contaminated aqueous waste streams. Textile printing anddyeing wastewater with large water volume, high content of organic pollutants and salinity, poorbiodegradability and complication of water quality is difficult to treat and reuse. Along with theincreasingly strict environmental laws and regulations as well as the rising water price, forgovernment and enterprises, advanced treatment and reuse of printing and dyeing wastewater mustbe considered. However, the available treatment and reuse technologies of printing and dyeingwastewater are time-consuming with low efficiency and high cost problems.According to the principle of separately handling light and heavy pollution of waste water, anovel online treatment and reuse technology of the printing and dyeing wastewater was proposedin this paper, which is named as OATRT (On-line Adsorption Treatment and Reuse Technology).Its technological process is as follows: the printing and dyeing wastewater is firstly treated byadsorption filtration column filled ion-exchange fiber as adsorbent, and then the yielding water isreused; the exhausted adsorbent is regenerated, and the elution and flushing effluent are subjectedto further treatment before discharge.We choosed, designed and synthesized two cellulose-based ion-exchange fiber, namelystrong base (SBIEF) and weak base type (WBIEF) ion exchange fiber, as adsorbent in OATRT.3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CHTAC) and1-chloro-2-hydroxy-3-aminopropane (CHPAC) were employed for the preparation of SBIEF and WBIEF, respectively.Static adsorption capacity of C.I. Acid Blue350was used to characterize the modified graft effectof WBIEF and SBIEF. On basis of univariate analysis, the preparation process parameters ofWBIEF and SBIEF were optimized by response surface methodology with Design Expertsoftware. The optimized preparation conditions of SBIEF were: n (NaOH): n (CHTAC)=2.02:1;drying temperature and time:58℃×2min; curing temperature and time:114℃×3min; theoptimized synthesis conditions of WBIEF were: n (NaOH): n (CHPAC)=2.56:1; drying temperature and time:63℃×2.2min; curing temperature and time:118℃×3.5min. With theabove optimized preparation process,42g/L CHTAC was applied twice to prepare SBIEF, and92g/L CHPAC was utilize for WBIEF. The degree of nitrogen substitution (DS) of SBIEF is0.022,and it is0.027for WBIEF. The point of zerocharge of WBIEF is around pH8.1. The surfaceappearance of WBIEF and SBIEF seem no significant change before and after the modification.IR spectra and CP/MAS13C-NMR spectra can confirm that WBIEF and SBIEF were successfullyobtained. Finally, at different temperatures (room temperature,60℃and90℃) and alkalisolution (room temperature,1%NaOH aqueous solution), WBIEF and SBIEF were tested for theirstability evaluation. The experiment results show that the SBIEF and WBIEF have goodadsorption and strength stability. The high temperature-resistant stability of WBIEF is better thanthat of SBIEF.Equilibrium and kinetic modeling of adsorption for soluble anionic dyes on WBIEF andSBIEF were studied in a batch system. Equilibrium data fitted very well to the Langmuir model inthe entire saturation concentration range. The maximum monolayer adsorption capacities obtainedfrom the Langmuir model are higher than those of the common adsorbents, which are243.2mg/g(SBIEF-C.I. Acid Blue350),147.1mg/g (SBIEF-C.I. Reactive Red195),113.6mg/g (WBIEF-C.I.Acid Blue350) and73.6mg/g (SBIEF-C.I. Reactive Red195). The experimental data fitted wellto the second-order kinetic model, which indicates that both adsorption behaviors belong tochemical sorption, which is dominated by the electrostatic interaction between anionic dyemolecules and the positively charged amino or quaternary amine groups on WBIEF and SBIEF.Some factors, such as initial dye concentration, temperature, initial pH, stirring speed, dyestructure, electrolyte and surfactant, will positively or negatively affect the adsorption rate andcapacity. The intraparticle diffusion models show the diffusion mass transfer of dye moleculesonto SBIEF and WBIEF can be divided into four stages: external mass transfer effect (also knownas membrane diffusion), macropore diffusion, transitional pore diffusion and micropore diffusion.The diffusion channel model was established, which can illustrate the dyes adsorption behaviorsonto WBIEF and SBIEF under different conditions. After five consecutive recycled cycles, theregeneration rates of WBIEF and SBIEF by sodium hydroxide solution were higher than84%.The characteristic shape of the breakthrough curves for C.I. Acid Red1and C.I. Reactive Red195well fit the “S-shape” curve, typical one produced in the ideal adsorption systems. WBIEF andSBIEF can provide satisfying capability of dye removal. most of the salt and nonionic organicsurfactant can successfully pass through the adsorption column filled with WBIEF and SBIEFOATRT (SBIEF) were employed for the treatment and reuses of washing wastewater fromnylon fabric dyeing by using static and dynamic experimental methods. In static experiments,SBIEF showes good adsorption ability and color removal (up to100%), and poor adsorption ability for Peregal O-25and inorganic salts. Moreover, the acidic substance in wastewater can beneutralized by SBIEF. The resulting recycled water can meet the reuse water quality standards. Itcan be reused ten times as washing water with the acceptable levels for color difference andqualities resulting saving up to90%water. In dynamic experiments, when the circulating ratioswere low and washing time was short, the color characteristics values and qualities of the sampleswere consistent with the controls. With increasing circulating ratio and washing time, the qualityof reclaimed water got better (but not completely remove the color), and the color of nylon dyedfabric became shallow resulting its washing color fastness raised half a grade. OATRT can alsomitigate negative effect of inorganic salts on dye elution from nylon dyed fabric. Withoutaffecting the quality of nylon dyed fabrics, the recycled water through OATRT can be reused atleast six times. In the recycling process, the first60℃hot water needheat only once, and thenmay be reuse as subsequent45℃and25℃washing water without further heating. In a smallpilot scale, the color characteristics values and color fastness of nylon dyed fabrics after washingby introducing SBIEF into the dyeing machine had little differences with the controls. As a result,up to75%washing water was saved.While OATRT was used in washing of cotton dyed fabrics, five times washing for cottondyed fabric can be divided into two parts. The first two washing processes were merged as onepart following OATRT (SBIEF), and the later three washing processes were combined as anotherpart with OATRT (WBIEF). This combined application can significantly enhance washing effectsof cotton dyed fabrics resulting its washing color fastness raised half a grade. Simultaneously,water and heat energy can be saved. Furthermore, OATRT (WBIEF) can replace soap flakeswithout noteworthy decrease of washing qualities. The resulting recycled water using OATRT(WBIEF) can be continuously reused six times as the next cycle washing water, as well as thosefor other color dyed fabrics.Overall, compared with the existing treatment and reuse technologies, OATRT have thefollowing advantages: Avoiding secondary pollution to the recycled water; Decreasing equipmentand operating costs; Easy to install in situ achieving fast treatment and reuse because of shortprocess; Saving or reusing water, additives and energy; Reducing wastewater discharge andwashing time while improving washing effect and productivity efficiency.