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The adsorption behavior of Zn2+ in four different biological sludge systems, i.e. activated sludge, denitrification sludge, short-cut nitrification sludge, and anammox granules, was investigated. The results indicated that all sludge samples possessed considerable potential for Zn2+ adsorption. Short-cut nitrification sludge possessed the highest Zn2+ maximum adsorption capacity (qm) of 36.4 mg g SS−1, which was much higher than other sludges applied (12.8-14.7 mg g SS−1). Besides, the adsorption rate for short-cut nitrification sludge was fastest among the four types of sludge after fitting with a pseudo-second-order rate equation. Comparing with the physicochemical properties of the four sludges, the soluble extracellular polymeric substances (EPS), especially soluble polysaccharide (PS), played a prior role in binding metal cations (i.e., Zn). The present study also showed that with less than 30% of Zn2+ trapped by EPS, 61.6-71.9% of Zn2+could be harvested directly by cells, indicating that the protecting capability by EPS was limited. Therefore, it is important to remove metal ions as early as possible if the activated sludge processes encountered high stress of heavy metal.ᅟ [ABSTRACT FROM AUTHOR]

BACKGROUND Copper-ammonia-containing wastewater is widely generated in various industrial sectors, such as semiconductor production, printed circuit board ( PCB) manufacturing, surface finishing, and electroplating processes. Three chemical precipitation methods, i.e. hydroxide precipitation, sulfide precipitation and struvite formation for treatment of chelated copper-ammonia wastewater have been comparatively evaluated. RESULTS The conventional hydroxide precipitation method possessed the highest copper and ammonia removal at 60.5% and 9.7%, respectively. Although sulfide precipitation decomposed the copper-ammonia complex with the high copper removal of 98.5%, the ammonia removal was just 14.0%. The struvite formation method was demonstrated to be effective for enhanced simultaneous copper and ammonia removal with efficiencies of 99.9% and 98.8%, respectively. UV-vis analysis indicated that the struvite formation method also decomposed the copper-ammonia complex ion. Using XPS and XRD spectra, struvite and cupric hydroxide were shown to be formed after the addition of magnesium and phosphate (with molar ratio n(Mg:P):n( NH3-N) ranging from 1.0-1.2:1). The larger particle size of the precipitates in the struvite forming process and the enhanced settling property indicated the binding interaction between Cu( OH)2 and struvite which enhanced the sedimentation and finally contributed to the simultaneous and highly efficient removal of copper and ammonia from the recalcitrant chelated wastewater. CONCLUSION The struvite formation method performs far better than hydroxide precipitation and sulfide precipitation methods. Binding interaction between cupric hydroxide and struvite enhanced the performance. This study provides some guidance on application of the struvite formation method for the simultaneous removal of heavy metal and ammonia from polluted water. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]