Biosorption Characteristics Of Heavy Metal Ions In Solution By Activated Sludge

In this paper, batch experiments were adopted to study the adsorption propertiesof activated sludge on the heavy metal ions in water, including a single heavy metalion adsorption system, two heavy metal ions competitive adsorption system, and threeheavy metal ions competitive adsorption system. The following research:（1）A single heavy metal ion adsorption system: five factors such as adsorptionequilibrium time, pH value, the sludge concentration, temperature and metal ionstrength were used to study the impact of a single heavy metal ion adsorption onactivated sludge. Cu²⁺, Cd²⁺, Ni²⁺, Cr⁶⁺, Pb²⁺and Zn²⁺, six kinds of environmentalhazards to humans and animals and plants large heavy metal ions, were selected asactivated sludge adsorption object. The experimental results showed that the activatedsludge had high adsorption capacity of Cu²⁺, Cd²⁺, Pb²⁺and Zn²⁺, but Ni²⁺and Cr⁶⁺adsorption capacity was weak. With the initial concentration of Cu²⁺, Cd²⁺, Pb²⁺andZn²⁺was40mg/L and Ni²⁺and Cr⁶⁺, respectively,10mg/L and5mg/L, thebiosorption of Cu²⁺, Pb²⁺, Cd²⁺, Zn²⁺and Ni²⁺needed1h to reach adsorptionequilibrium, while Cr⁶⁺needed2h to balance. The best adsorption pH of Cu²⁺andPb²⁺was4, while the best adsorption pH of Cd²⁺, Ni²⁺, Zn²⁺, Cr⁶⁺was6. Insubsequent experiments, the adsorption experimental pH of Zn²⁺did not choose6,taking into account the high metal concentrations caused Zn²⁺precipitation when pH=6. The overall trend showed that the adsorption capacity decreased with increasingof sludge concentration. Taking into account the matter of the amount of sludgerequired, the experimental concentration of sludge was set at1g/L in subsequentexperiments. Temperature had obvious impact on the heavy metal ions adsorption onactivated sludge. The overall trend was, with increasing temperature, the adsorptioncapacity of sludge increased. At40℃, the sludge adsorption capacity of Pb²⁺, Cr⁶⁺and Ni²⁺fell slightly. Two isothermal adsorption models, Langmuir adsorption curveand Freundlich adsorption curve, were fitted to the single adsorption of six heavymetal ions. Zn²⁺and Cr⁶⁺single heavy metal ion adsorption could be described better by Freundlich adsorption curve, the other four heavy metals fitted Langmuiradsorption curve better. Thus it could be speculated that the adsorption of Zn²⁺andCr²⁺were monolayer adsorption, while the other four heavy metals were theadsorption of multilayer. The sequence of adsorption amount of single heavy metalion was Pb²⁺> Zn²⁺> Cr⁶⁺> Cu²⁺> Cd²⁺> Ni²⁺, the adsorption affinity sequence wasCu²⁺> Cd²⁺> Pb²⁺> Zn²⁺> Ni²⁺> Cr⁶⁺.（2） Two kinds of heavy metal ions competitive adsorption system: In view of theactivated sludge having a higher adsorption capacity of Cu²⁺,Cd²⁺, Pb²⁺and Zn²⁺, thecompetitive adsorption experiments of the adsorption of Pb²⁺was conducted with theexistence of Cu²⁺,Cd²⁺and Zn²⁺, respectively. The results showed that the existenceof Cu²⁺had a strong inhibition effect of biosorption of Pb²⁺. Different Cu²⁺concentrations inhibited on the biosorption of Pb²⁺by activated sludge in ascendingorder was10mg/L>50mg/L>30mg/L. When c (Pb²⁺)=c (Cu²⁺), the inhibition effectwas the largest. The existence of10mg/L Cd²⁺in the binary competitive system hadno impact on the biosorption of Pb²⁺by activated sludge, while30mg/L and50mg/LCd²⁺showed up a role in promoting the biosorption of Pb²⁺. So it could be concludedthat low concentrations of Cd²⁺could promote the adsorption of Pb²⁺by activatedsludge. But very high concentrations of Cd²⁺also inhibit the Pb²⁺biosorption. In spiteof the presence of low or high concentration of Zn²⁺did not influence the adsorptionof Pb²⁺, even when c (Pb²⁺)=c (Zn²⁺), the highest inhibitory rate was only17.27%.Through the preference adsorption experiments under the conditions of two heavymetal ions co-exist, the activated sludge had a better adsorption of Pb²⁺, leavinganother coexistence heavy metal ion desorped more. The adsorption inhibitioncomparative experiments showed that the order of inhibition rates of coexistenceheavy metal ion with increasing concentrations on Pb²⁺biosorption was Cu²⁺> Cd²⁺>Zn²⁺.（3） Three heavy metal ions competitive adsorption system: Experiments wereconducted to study the effects of a fixed concentration of the other two combinationof heavy metal ions （both at a concentration of30mg/L） on activated sludgeadsorption of Pb²⁺in the coexistence of three types of heavy metal ions competitive adsorption system. The results showed that Zn²⁺and Cu²⁺coexistence in the systeminhibited the adsorption of Pb²⁺by activated sludge, while Zn²⁺and Cd²⁺coexistenceor Cd²⁺and Cu²⁺conexistence promoted the activated sludge adsorption of Pb²⁺.