Heavy metals at concentration higher than the limited defined by standards, may create problems for environment. Due to the wide usage of metals in industries and their degradation at environment, the accumulation of heavy metals in the environment is beyond that amount removed through natural processes. In comparison with other methods of metal removal, biological uptake is more effective, economical and environmentally friendly. Fungi and especially zygomycetes have good adsorption capability, because of presence of chitin and chitosan in their cell wall. In this study, zygomycete fungus Rhizomucor pusillus biomass and Mucor indicus were used for nickel removal. Untreated dried biomass of Rhizomucor pusillus showed 64.6% Ni(II) removal. Enzymatic and chemical approaches were successfully employed to improve nickel biosorption capacity of Rhizomucor pusillus biomass. Increasing concentration of sodium hydroxide (from 0.002 to 17.5 g/l) was accompanied with enhancement of Ni removal (from 93.2 to 100.0%). Moreover, at higher concentrations (5-17.5 g/l), the pretreated biomass removed nearly all Ni (II) ions from solutions. Analysis of pretreated biomass composition showed that the increasing in concentration of NaOH, decreased protein content of cell wall and also increased glucosamine and N-acetyl glucosamine which are indicators for chitosan and chitin. SEM analysis indicated that alkali treatment using 0.002 g/l NaOH, created a more swollen structure. Higher concentration (10 mg/l) however, considerably changed the morphology of biomass and formed a sheet structure. Pretreatment of biomass, with just 0.1 µl neutrase/g biomass, improved Nickel removal to 91.8%. SEM analysis indicated that enzymatic enhanced the porosity of biomass. Protein analysis showed both pretreatments removed a major part of fungal biomass proteins and exposure more available binding sites for metal biosorption. In this study also chitosan extracted from Mucor indicus cell wall (grown on medium containing palm sap as a main source of food) and shrimp chitosan used for nickel removal. Equilibrium study showed resulting isotherms for both chitosan were fitted using Langmuir model. Simplified models such as pseudo-first-order, pseudo-second-order and intra-particle diffusion equations were used to determine the rate controlling step. The analysis of kinetic models showed that pseudo-second-order is predominant, and the overall rate of the metal ion adsorption process is therefore controlled by adsorption reactions. Key Words Adsorption, Alkali Pretreatment, Biomass, Chitosan, Enzymatic Pretreatment, Mucor Indicus , Rhizomucor Pusillus .
