The objectives of this study were to synthesize aluminum hydroxide modified palygorskite nano-composites (Al–PG) and to investigate their suitability as adsorbents to remove phosphate from aqueous solution. The nano-composites were characterized by XRD, XRF and TEM. The characterization results showed that aluminum hydroxide gel was successfully loaded onto palygorskites (PGs) with diameters of nanometers, and the crystal composition of PG had not been changed after modification. The effects of modified mass ratios, pH, co-existing anions, and initial phosphate concentrations on phosphate removal were investigated by batch experiments. The Freundlich model provided a better description for the adsorption process than the Langmuir model. The maximum phosphate adsorption capacity was 16.86 mg g⁻¹ for Al–PG, while it was 4.08 mg g⁻¹ for natural PG. Of the adsorption isotherms and thermodynamic studies considered, the adsorption of phosphate by Al–PG was chemisorption, endothermic and spontaneous. Kinetic studies indicated that the adsorption of phosphate onto Al–PG can be fitted by a pseudo-second-order kinetic model very well. Thus, the cost-effective and high adsorption capacity of Al–PG has wide potential use in phosphate removal from aqueous solutions.

Manganese (Mn) oxide is a ubiquitous metal oxide in sub-environments. The adsorption of Cd(II) on Mn oxide as function of adsorption time, pH, ionic strength, temperature, and initial Cd(II) concentration was investigated by batch techniques. The adsorption kinetics showed that the adsorption of Cd(II) on Mn oxide can be satisfactorily simulated by pseudo-second-order kinetic model with high correlation coefficients (R² > 0.999). The adsorption of Cd(II) on Mn oxide significantly decreased with increasing ionic strength at pH < 5.0, whereas Cd(II) adsorption was independent of ionic strength at pH > 6.0, which indicated that outer-sphere and inner-sphere surface complexation dominated the adsorption of Cd(II) on Mn oxide at pH < 5.0 and pH > 6.0, respectively. The maximum adsorption capacity of Mn oxide for Cd(II) calculated from Langmuir model was 104.17 mg/g at pH 6.0 and 298 K. The thermodynamic parameters showed that the adsorption of Cd(II) on Mn oxide was an endothermic and spontaneous process. According to the results of surface complexation modeling, the adsorption of Cd(II) on Mn oxide can be satisfactorily simulated by ion exchange sites (X₂Cd) at low pH and inner-sphere surface complexation sites (SOCd⁺ and (SO)₂CdOH⁻ species) at high pH conditions. The finding presented herein plays an important role in understanding the fate and transport of heavy metals at the water–mineral interface.

This study is aimed to examine the removal of nitrogen from high strength slaughterhouse wastewater at 11°C via partial nitrification followed by denitrification (PND), using the intermittently aerated sequencing batch reactor (IASBR) technology. The slaughterhouse wastewater contained chemical oxygen demand (COD) of 6068 mg/L, total nitrogen (TN) of 571 mg/L, total phosphorus (TP) of 51 mg/L and suspended solids of 1.8 g/L, on average. The laboratory-scale IASBR reactors had a working volume of 8 L and was operated at an average organic loading rate of 0.61 g COD/(L·d). At the cycle duration of 12 h, COD was efficiently removed under three aeration rates of 0.4, 0.6 and 0.8 L air/min. Among the three aeration rates, the optimum aeration rate was 0.6 L air/min with removals of COD, TN, and TP of 98%, 98%, and 96%, respectively. The treated wastewater met the Irish emission standards. The microbial community analysis by fluorescence in situ hybridization shows 12±0.4% of ammonium oxidizing bacteria, and 7.2±0.4% of nitrite oxidizing bacteria in the general bacteria (EUB) in the activated sludge at the aeration rate of 0.6 L air/min, leading to efficient partial nitrification. PND effectively removed nitrogen from slaughterhouse wastewater at 11°C, but PND efficiency was dependent on the aeration rate applied. PND efficiencies were up to 75.8%, 70.1% and only 25.4% at the aeration rates of 0.4, 0.6, and 0.8 L air/min.