Removal Of Heavy Metal From Aqueous Solution And Squid Visceral Enzymatic Hydrolysate By Zygoaccharomyces Rouxii

With the rapid development of global economy, the water pollution wasbecoming more and more serious. Heavy metal pollution accounted for a largeproportion among the numerous kinds of water pollutions. Heavy metal pollution notonly caused the reduction of available water resources, but also brought great harm tomariculture and the processing and utilization of aquatic products. Biosorption was anew technology which has been developed to treat heavy metal pollution. It had broaddevelopment future and application prospect, for the advantages of rich resource, lowcost, no second pollution and so forth.Zygosaccharomyces rouxii （Z.rouxii） was an important strain in the mainfermentation period of soy sauce brewing process. It was more tolerant to salt thanSaccharomyces cerevisiae. Z.rouxii was used as the biosorbent in this paper. Theeffects of temperature, pH and adsorption time on the removal of heavy metals (Cd²⁺,Cu²⁺, Zn²⁺) from aqueous solution were studied and the biosorption mechanism wasprimarily explored. Z.rouxii was then applied to treat mixed heavy metals (Zn²⁺、Cu²⁺、Cd²⁺) aqueous solution. The feasibility of treating mixed heavy metals (Zn²⁺、Cu²⁺、Cd²⁺) aqueous solution by immobilized Z.rouxii was investigated. Finally,different forms of Z.rouxii were applied to the removal of Cd²⁺in the squid visceralenzyme solution and fish sauce. The main results were shown as follows:When freeze-dried Z.rouxii powder was used as the biosorbent, the impact oftemperature （25℃-40℃） on the removal percentage of Cd²⁺、Cu²⁺、Zn²⁺was notsignificant. However, the effect of the initial pH value on the removal percentage ofheavy metals was obvious. The removal percentages of heavy metals (Cd²⁺、Cu²⁺、Zn²⁺) increased gradually when pH increased from2.0to4.0. The removal percentageof Cd²⁺and Zn²⁺did not change significantly when pH value was larger than4.0, butthe removal percentage of Cu²⁺reduced when pH value was larger than4.0. The results showed that Z.rouxii had highest removal percentage of Cd²⁺、Cu²⁺、Zn²⁺in thepH ranging from4.0to6.0. The adsorption process of Cd²⁺、Cu²⁺、Zn²⁺was quicklyand the adsorption equilibrium could be achieved in about30min. But thephenomenon of desorption would occur with the extension of time. The removalpercentages of Zn²⁺and Cu²⁺were similar which decreased to92.3%and89.7%of themaximum removal percentage in180min, respectively. The phenomenon ofdesorption was not obvious after30min in the adsorption process of Cd²⁺. Theequilibrium removal percentages of Cd²⁺, Cu²⁺and Zn²⁺by Z.rouxii were63.58%,44.75%and49.17%respectively. The removal percentages of Cd²⁺, Cu2and Zn²⁺byZ.rouxii decreased but the adsorption capacities increased as the initial concentrationof heavy metals increased. The maximum adsorption capacities of Cd²⁺, Cu²⁺andZn²⁺by Z.rouxii were10.46mg/g,7.04mg/g and5.60mg/g, respectively. Theisotherm adsorption process of Cd²⁺, Cu²⁺and Zn²⁺by Z.rouxii could be simulated byLangmuir equation and Freundlich equation. The Langmuir equation was better forCd²⁺and Zn²⁺, and Freundlich equation was better for Cu²⁺.When Z.rouxii was used to adsorb mixed heavy metal in aqueous solutionincluding Cd²⁺, Cu²⁺and Zn²⁺, the order of the removal capacity of Z.rouxii of theheavy metals was Cu²⁺> Cd²⁺> Zn²⁺as the adsorption equilibrium was reached. Inorder to encapsulate Z. Rouxii, alginate calcium （2%, w/v） with Z.rouxii biomass （20gcell/L） was added to2%CaCl2. It was then used to adsorb mixed heavy metal cationsin aqueous water. HCl （0.1mol/L） was used as desorption reagent to wash theimmobilized Z.rouxii. When it was reused for three times, the removal percentage ofCd²⁺、Cu²⁺and Zn²⁺was24.98%,43.84%and12.14%, respectively.Finally, different forms of Z.rouxii were applied to the removal of Cd²⁺in thesquid visceral enzyme solution and fish sauce. The results showed that the removalpercentages of Cd²⁺in the squid visceral enzymatic hydrolysate by freeze-driedZ.rouxii powder and active Z.rouxii biomass were25.78%and28.36%, respectively.The removal percentage of Cd²⁺in the squid visceral enzymatic hydrolysate byimmobilization of Z.rouxii was only17.02%which was less than free Z.rouxiibiomass, but the operational feasibility increased because it was easier to separate biosorbent from the squid visceral enzymatic hydrolysate after the adsorption process.When Z.rouxii was inoculated to squid visceral enzymatic hydrolysate and fish sauce,it could grow using the nutrients and removed part of Cd²⁺in them. When the initialconcentration of Cd²⁺was about10mg/L, the removal percentage of Cd²⁺in squidvisceral enzymatic hydrolysate and fish sauce were21.5%and26.24%, respectively.