Experimental Study Of Zn²⁺ Removal By Algal Biofilm From Wastewater

Nowadays, the problem of environmental pollution by heavy metal has become oneof the most serious cosmopolitan problems. The exploration and research of effective andpractical methods for heavy metal removal are paid much attention by environmentalscholars. Algal biofilm is a new method in this field. It has been used to treat nitrogen andphosphor wastewater and gets the nice result. But the reports about the treatment of heavymetal wastewater by algal biofilm are rarely. This study will use the algal biofilm as aspecial kind of adsorbing material and put it into the treatment of heavy metal wastewater.The result and mechanism of heavy metal removal by algal biofilm will be researched.That will provide a new technology for the treatment of heavy metal removal. The studyhas three aspects in the following and gets the relevant conclusion:（1） The effects of Zn²⁺on algal biofilm growth and physiological property.1) There are some effects on the algal biofilm growth under different concentrationsof Zn²⁺. When concentration of Zn²⁺is5mg/L, the content of chlorophyll has obviousfacilitation by Zn²⁺. But when concentration reaches20mg/L, the content of chlorophyllhas obvious inhibitory action by Zn²⁺. The cells of algae start to die, the photosynthesisbecomes weaker and the content of chlorophyll reduces quickly.2) There are different effects on algal enzyme under different concentrations of Zn²⁺.The content of SOD in Oedogonium sp. receives obvious inhibitory along with the risingconcentration of Zn²⁺. But when concentration of Zn²⁺is below10mg/L, the content ofnitrate reductase has obvious facilitation.3) There are some effects on the algal protein under different concentrations of Zn²⁺.In the initial stage, the content of protein in Oedogonium sp. is increased in each group.But it is decreased in the following. In the first two days, the content of EPS hasfacilitation in each group. In especially when the concentration of Zn²⁺is20mg/L, the facilitation is most obvious.（2） The analysis of reaction kinetics and influencing factor on Zn²⁺removal byalgal biofilm.1) Through the result, it can be summarized that there are three stages （adaptivephase, quickly absorbing phase, absorptive balance phase） in the absorbing process ofZn²⁺by algal biofilm. And in the quickly absorbing phase, the absorbing process meetswith Langmuir and gets the first-order kinetics equation:lnC=-0.097t+3.0139ï¼›R²=0.9864.2) Effects on removing different initial concentration of Zn²⁺using algae biofilm aredifferent. When the concentration of Zn²⁺is3.0mg/L and10mg/L, the removalefficiencies reach90.34%and90.01%. But when the concentration of Zn²⁺is40mg/L, theremoval efficiency reaches54.80%.3) Effects on removing different initial pH using algae biofilm are different. Whenthe initial pH is7.0, the removal efficiency reaches89.89%.（3） The analysis for removal result and mechanism about Zn²⁺by algal biofilm.1) In the dynamic analog experiment, the removal efficiency of Zn²⁺by algal biofilmis very good. When the inflow concentration of Zn²⁺is10mg/L, the average effluentconcentration of Zn²⁺is0.2471mg/L and the average removal efficiency is97.70%. Theeffluent concentration of Zn²⁺reaches GB25466-2010.2) In the algal biofilm reaction system, algae keeps constantly update, the content ofchlorophyll keeps increasing, the content of SOD and nitrate reductase keeps constantlychanging. Through the synthesis of protein and EPS by algae, the algal biofilm canpreferably adapt to the wastewater environment with Zn²⁺.3) Through the analysis of SEM and FT-TR, the algal biofilm can secrete abundantEPS under the stimulation by heavy metal. The functional group in algal cell and heavymetal can also take place binding reaction. In the last, the heavy metals are removed fromthe wastewater.