Biosorption of rare earth metal ion on aerobic granules

Cultivation of autotrophic nitrifying granular sludge for simultaneous removal of ammonia nitrogen and Tl(I)

Autotrophic nitrifying granular sludge (ANGS) was cultivated for the simultaneous removal of ammonia nitrogen and Tl(I) from inorganic wastewater. The chemical oxygen demand (COD) in the influent gradually decreased to approximately zero in four parallel sequencing batch reactors (B1: blank controller, B2: 10 mL of added nitrifying bacteria concentrate in each cycle, B3: 1 mg/L Tl(I) added in each cycle and B4: 10 mL of added nitrifying bacteria concentrate and 1 mg/L Tl(I) in each cycle) within 15 days. The main properties, such as the granulation rate and specific oxygen uptake rate (SOUR) of the ANGS in B1, B2, B3 and B4 tended to be stable within 40, 33, 30 and 33 days, the removal efficiencies of Tl(I) were 59.5%-82.9% and 57.1%-88.6% in B3 and B4 after Day 30, the removal efficiencies of ammonia nitrogen in B1, B2, B3 and B4 were usually above 90% after Day 33, and the total inorganic nitrogen (TIN) in the effluent of B1, B2, B3 and B4 gradually stabilized after Day 36, 32, 32 and 36, indicating that mature ANGS was successfully cultivated in B1, B2, B3 and B4 within 40, 33, 33 and 36 days. The nitrogen degradation kinetic parameters of ANGS indicated that B3 had the strongest ability to remove ammonia and nitrite, suggesting that Tl(I) stress was beneficial to ammonia nitrogen removal and nitrite oxidation. The adsorption of Tl(I) can be described by the Freundlich equation, and the addition of external nitrifying bacteria improved the adsorption ability of ANGS.

Adsorption of RE3+ from aqueous solutions by bayberry tannin immobilized on chitosan

Bayberry tannin immobilized on chitosan (CS-BT) was successfully prepared, and its adsorption performance was studied for aqueous solutions of rare earth ions. The as-prepared absorbents were characterized by Fourier transform infrared spectrometry and scanning electron microscopy. The equilibrium adsorption capacity was achieved in approximately 30 min. The adsorption process of CS-BT for Nd³⁺ was well fitted with a Freundlich model and the kinetics followed the pseudo-second-order rate equation. The maximum adsorption capacity for Nd³⁺ was 133.72 mg/g and dynamic adsorption characteristics of single ion (La³⁺, Ce³⁺, Nd³⁺) were investigated. The solution concentration was less than 30 mg/L when effluent volume was approximately 800 mL. Subsequently, the adsorbent column was desorbed by HNO₃ solution. There was no significant loss of adsorption capacity after three cycles of regeneration, showing a satisfactory recyclability. Furthermore, CS-BT exhibited excellent dynamic adsorption performance of two mixed ions (La³⁺/Ce³⁺, La³⁺/Nd³⁺, Ce³⁺/Nd³⁺) and three mixed ions (La³⁺/Ce³⁺/Nd³⁺). The competitive adsorption capacity was La³⁺ < Ce³⁺ < Nd³⁺. The results indicate that the adsorption selectivity of column adsorption could provide a theoretical basis for the adsorption and separation of light rare earth ions. Therefore, this efficient adsorbent shows promising potential for the treatment of industrial wastewater.

The characteristics of heat-driven ammonium adsorption in aerobic granular sludge

Adsorption is an important step during the migration of ammonium from the aqueous phase to biomass in biological nitrogen removal processes. A deeper understanding of the adsorption mechanisms is encouraged in constructing nitrogen conversion models. In this study, the ammonium adsorption in aerobic granular sludge was investigated at different conditions. Analysis of kinetic data indicated that ammonium adsorption was a fast process and followed pseudo-second-order kinetics (adsorption rate constant k₂ was between 0.031 and 0.065 g/(mg · min)). The maximum adsorption capacity and half saturation constant K_L in the Langmuir isotherm model were 4.95 mgNH₄ ⁺-N/g total suspended solids and 0.0126 L/mg, respectively. Effects of environmental conditions such as temperature, pH and competitive cations were also estimated. The optimum pH was 7 and the effects of competitive cations were in the order Ca²⁺ > Mg²⁺ > K⁺ > Na⁺. Values of thermodynamic parameters (ΔH^Ɵ = -14.697 kJ/mol, ΔS^Ɵ = -6.65 J/(mol · K)) indicated that the adsorption process was spontaneous and exothermic. Desorption tests showed that the process was reversible and low temperature had a negative effect on ammonium desorption. These findings could be useful for completing the mathematical model of the nitrogen removal process in bioreactors.

Recent advances on biosorption by aerobic granular sludge

Aerobic granular sludge is a form of microbial auto-aggregation, and a promising biotechnology for wastewater treatment. This review aims at providing the first comprehensive, systematic, and in-depth overview on the application of aerobic granules as biosorbents. The target pollutants encompass heavy metals (both cationic and oxyanionic), nuclides, dyes, and inorganic non-metal substances. Different granule types are discussed, i.e. intact and fragmented, compact and fluffy, original and modified, and the effects of granule surface modification are introduced. A detailed comparison is conducted on the characteristics of granular biomass, the conditions of the adsorption tests, and the resultant performance towards various sorbates. Analytical and mathematical tools typically employed are presented, and possible interactions between the pollutants and granules are theorized, leading to an analysis on the mechanisms of the adsorption processes. Original granules appear highly effective towards cationic metals, while surface modification by organic and inorganic agents can expand their applicability to other pollutants. Combined with their advantages of high mechanical strength, density, and settling speed, aerobic granules possess exceptional potential in real wastewater treatment as biosorbents. Possible future research, both fundamental and practical, is suggested to gain more insights into the mechanism of their function, and to advance their industrial application.

Aerobic Granular Sludge

Aerobic Granular Sludge (AGS) has been successfully applied for carbon, nitrogen and phosphorous removal from wastewaters, in a single tank, reducing the space and energy requirements. This is especially beneficial for, often space restricted, industrial facilities. Moreover, AGS holds a promise for the toxic pollutants removal, due to its layered and compact structure and the bacteria embedding in a protective extracellular polymeric matrix. These outstanding features contribute to AGS tolerance to toxicity and stability. Strategies available to deal with toxic compounds, namely granulation with effluents containing toxics and bioaugmentation, are addressed here. Different applications for the toxics/micropollutants removal through biosorption and/or biodegradation are presented, illustrating the technology versatility. The anthropogenic substances effects on system performance and bacterial populations established within AGS are also addressed. Combination of contaminants removal to allow water discharge, and simultaneous valuable products recovery are presented as final remark.

Biosorption: a mechanistic approach

The ability of microbial cells to sequester solutes selectively from aquatic solutions, via nonmetabolically mediated pathways, has been termed biosorption. The mechanism of biosorption has been shown not to be simple and often specific to the biomass-solute pair. The understanding of the mechanism at play, in each biosorption system, is a prerequisite for the understanding of the stoichiometry, the equilibrium, the kinetics, the selectivity, and the engineering process application potential. Biosorption has been studied mostly for inorganic ionic solutes, but there is also reported work on the biosorption of organic molecules. Reference is also made to the biosorption engineering application issues.

Microbial extracellular polymeric substances: central elements in heavy metal bioremediation

Extracellular polymeric substances (EPS) of microbial origin are a complex mixture of biopolymers comprising polysaccharides, proteins, nucleic acids, uronic acids, humic substances, lipids, etc. Bacterial secretions, shedding of cell surface materials, cell lysates and adsorption of organic constituents from the environment result in EPS formation in a wide variety of free-living bacteria as well as microbial aggregates like biofilms, bioflocs and biogranules. Irrespective of origin, EPS may be loosely attached to the cell surface or bacteria may be embedded in EPS. Compositional variation exists amongst EPS extracted from pure bacterial cultures and heterogeneous microbial communities which are regulated by the organic and inorganic constituents of the microenvironment. Functionally, EPS aid in cell-to-cell aggregation, adhesion to substratum, formation of flocs, protection from dessication and resistance to harmful exogenous materials. In addition, exopolymers serve as biosorbing agents by accumulating nutrients from the surrounding environment and also play a crucial role in biosorption of heavy metals. Being polyanionic in nature, EPS forms complexes with metal cations resulting in metal immobilization within the exopolymeric matrix. These complexes generally result from electrostatic interactions between the metal ligands and negatively charged components of biopolymers. Moreover, enzymatic activities in EPS also assist detoxification of heavy metals by transformation and subsequent precipitation in the polymeric mass. Although the core mechanism for metal binding and / or transformation using microbial exopolymer remains identical, the existence and complexity of EPS from pure bacterial cultures, biofilms, biogranules and activated sludge systems differ significantly, which in turn affects the EPS-metal interactions. This paper presents the features of EPS from various sources with a view to establish their role as central elements in bioremediation of heavy metals.