Production Of Water Purifying Agent And Its Use In Treatment Of Heavy Metal And Suspension Wastewater

Bio-treatment technology has been employed as an effective and safe method for wastewater treatment and extracellular polymeric substance (EPS) has attracted much attention as a promising bio-treatment technology. EPS are characterized by abundant specie, safety, nontoxicity and without secondary pollution, and can be a highly effective water green treatment agent. EPS is a kind of biological macromolecule including proteins, glycoproteins, polysaccharides, lipids and glycolipids and are important to life process. Its molecule is catenarian with many function groups, which is similar with chitosan. Based on the report of chitosan with biosorption and flocculation properties, EPS may be another effective biosorbent or bio-flocculant.The present study dealt with the production of EPS as wastewater purifying agent and its use in treatment of metal and suspension wastewater. A strain, Bacillus sp. F19, screened from active sludge samples, was employed as the EPS producer. Response surface methodology was used for optimization of medium for EPS yield. The properties and composition of the EPS were analyzed. Biosorption capacities and mechanism of Cu(II) and Cd(II) by EPS were investigated and the flocculation ability was also researched. The main research results are as follows:(1) Strain F19 with EPS producing capability was initially isolated from activated sludge. According to the physiological, biochemical and 16S rDNA sequence characterization, it was identified as Bacillus sp. EPS was mainly secreted to the culture medium. Experiments from growth curve indicated that this strain had stable ability of producing EPS and the EPS concentration get to 1.47 g/l at 86 hour. EPS was mainly secreted to the culture medium which was beneficial to application.(2) Single factor experiment illuminated that high inoculum density and shaking rate and alkaline cultural medium were favored by the producing of EPS. Glucose, yeast extract and K2HPO4 were identified as significant factors. When the concentration of glucose, yeast extract and K2HPO4 were 30.26 g l-1,6.41 g l-1 and 6.65 g l-1, respectively, the maximum polysaccharide concentration is get and predicated to be 2.21 g l-1, which is 3 time of un-optimized.(3) EPS, showing ivory white and porous surface, was precipitated by adding of ethanol to the culture medium. EPS had high moisture content and the density of dry EPS was low. The intrinsic viscosity of EPS was 27.57. EPS was mainly a polysaccharide with total sugar and total protein content of 66.4 % and 16.4 % (w/w), respectively. The contents of neutral sugar, uronic acid and amino sugars were 3.6 %, 37.0 % and 0.5 % and the molar ratio of mannose to glucose was approximate 1.2:1.(4) The adsorption of Cu(II) and Cd(II) from aqueous solution on EPS were investigated in the respective of pH, incubation time, concentration of initial metal ions and EPS dose. The results indicated that EPS was an effective adsorbent for Cu(II) and Cd(II). The maximum adsorption amount of Cu(II) and Cd(II) were 244 mg g-1和148 mg g-1, respectively. The adsorption capacity of Cu(II) was higher than Cd(II) at the same pH. Biosorption equilibrium was established in approximately 10 min. Biosorption of Cu(II) is highly pH dependent and the maximum uptake of Cu(II) was obtained at pH 4.8. Adsorption ability of Cd(II) increased with the increasing of pH until the maximum adsorption mount was reached at pH 6.2. The adsorption process was in accordance with both Langmuir and Freundlich isotherms. The second order model was applied to examine the kinetics of the adsorption and was found to be in harmony with the kinetic data well. EPS was able to adsorb Cu(II) to the surface with the release of K+. The presence of Cu2O and Cu on EPS after sorption showed that the Cu(II) was reduced by EPS。The complex mechanism is critical in Cd(II) adsorption process. (5) EPS was effective for flocculation of kaolin, activated carbon and fly coal suspension even without presence of cations. The flocculating activities of all the three suspensions dropped with increasing pH. The relationship between the concentration of the bioflocculant and its flocculating activity showed the typical flocculation curve of the biopolymer.