Removing Cadmium From Electroplating Wastewater By Biosorption

Heavy metals pollution is the one of the biggest environment pollution problems. Cadmium is the most poisonous heavy metal,the enviroment protection law stipulates that cadmium is the first kind of pollution materials.Electroplating is one of three big pollution industry,in general the Cadmium concentration of the Cadmium-containing electroplating wastewater doesn't meet domestic discharge standard before treatment,so removal of Cadmium in electroplating wastewater is very important. Removing heavy metals by biosorption has many advantages,such as,fast speed, heavy metal can be removed selectively even at its low concentration,high efficiency, a wide range of pH and temperature,less investment and running cost,in addition,some heavy metals can be recovered. Many experts domestic and abroad do a lot of work on biosorption of heavy metals for several years.Waste Saccharomyces cerevisiae,Gordona amarae,Bacillus mucilayinosus and Bacillus subtilis was used as biosorbent,Cadmium-containing electroplating wastewater of an electroplating plant was used to treat objects in studies,separation of solid and liquid was done by precipitation and flotation methods to remove cadmium from wastewater.The shape and characters of micro biology was studied and stain characters,shape appearance and structure of waste saccharomyces cerevisiae,Gordona amarae,Bacillus mucilayinosus and Bacillus subtilis were observed by biology microscope,SEM and TEM, their charge characters and the composition of cell wall and function groups were tested. The research results showed their chemistry characters had different effect on biosorption process, the physics and chemistry naturals and state of main component were studied in the paper.Influence of pH value,dosage of adsorbent,the temperature,the stiring revolution and the contact time on adsorption result were studied. The effect on precipitation result of different precipitation time of waste Saccharomyces cerevisiae before and after water-washing,flotation and removing cadmium influence of different pH value and dasoge of collectors using Gordona amarae,Bacillus mucilayinosus and Bacillus subtilis as adsorbent were studied. The adsorption mechanism to cadmium wasdiscussed by test results of Zeta potential,charge state of cells surface,infrared spectroscopy analysis of the cells, SEM,TEM and XPSThe research results show that adsorption influence of four adsorbents to cadmium in electroplating wastewater are good. The adsorption rate of cadmium in electroplating wastewater is above 96.18% by water-wsahing waste Saccharomyces cerevisiae on the normal condition,adsorption rate of cadmium are all above 92% by the other three adsorbents. Precipitation performance of waste Saccharomyces cerevisiae used in studies is good,the good index of adsorption and solid-liquid separation are got by adsorption-precipitation method by waste Saccharomyces cerevisiae,removal rate of cadmium is over 96% after adsorbing for 30 min with cadmium concentration in cadmium-containing electroplating wastewater about 26mg/L,waste Saccharomyces cerevisiae 11.4 g/L,temperature 18℃,pH 7.0 and static precipitation for 3.5 hours. The flotation method is used in solid-liquid separation when Gordona amarae,Bacillus mucilayinosus and Bacillus subtilis are used adsorbents,removal rate of cadmium was over 76% after adsorbing for 10 min with cadmium concentration in cadmium-containing electroplating wastewater about 26mg/L, Bacillus subtilis 10 g/L(wet weight),at room temperature(about 18℃),pH 6.0 and flotating by collector dibutyamine 4×10-4mol/L for 4min. The effct of removal cadmium adsorption-precipitation by waste Saccharomyces cerevisiae is better than the index of adsorption-flotation by Gordona amarae,Bacillus mucilayinosus and Bacillus subtilis obviously. Additionally, because of abundant waste Saccharomyces cerevisiae and low price,it has more obvious advantages compared with the other three biosorbents.The wide experiments are done with self-made equipment,and the good removal cadmium result is got using adsorption-precipitation by water-wsahing waste saccharomyces cerevisiae,removal rate of cadmium is over 94% after adsorbing for 30 min with cadmium concentration in cadmium-containing electroplating wastewater about 26mg/L,waste saccharomyces cerevisiae 40 g/L(wet weight),at room temperature(about 25℃),pH 7.0 and static precipitation for 4 hours. The continuing adsorption experiments are done with self-made equipment,and the adsorption rate of cadmium is 98.43%,96.46% and 86.86% repectively when the velocity of inflow of wastewater is 10.8 mL/min,40 mL/min and 167mL/min.