Nanostructured fusiform hydroxyapatite particles precipitated from aquaculture wastewater

Effect of external acetate added in aquaculture wastewater on mixotrophic cultivation of microalgae, nutrient removal, and membrane contamination in a membrane photobioreactor

The mixotrophic cultivation of microalgae in wastewater has attracted extensive attention due to its many advantages. In this study, acetate, which can be prepared by hydrolysis of aquaculture waste, was used as exogenous organic matter to promote the growth of Chlorella pyrenoidosa cultured in aquaculture wastewater. Microalgae cultivation was carried out in a membrane photobioreactor (MPBR) with continuous inflow and outflow mode. The results showed that exogenous acetate greatly promoted the mixotrophic growth of C. pyrenoidosa. When the dosage of acetate reached 1.0 g L-1, the relative growth rate of microalgae in the logarithmic stage reached 0.31 d-1, which was 4.4 times that of the control. As a result, exogenous acetate also promoted the removal of nutrients from aquaculture wastewater. During the stable operation stage of the MPBR with acetate added in the influent, an average of 87.41%-93.93% nitrogen and 76.34%-88.55% phosphorus was removed from the aquaculture wastewater containing 19.41 mg L-1 total inorganic nitrogen and 1.31 mg L-1 total inorganic phosphorus. However, it was worth noting that adding exogenous acetate also led to an increase in the membrane resistance of the membrane module in the MPBR. Membrane resistance was mainly composed of internal resistance (Ri) and cake resistance (Rc), and with the increase of acetate content in the influent, their proportion in the total resistance gradually increased. Ri contributed the major membrane resistance and was most affected by acetate dosage. Ri reached 32.04 × 1012 m-1 with 1 g L-1 acetate, which accounted for 69.49% of total resistance. Moreover, with the increase of influent acetate concentration of the MPBRs, both the number of insoluble contaminants and dissolved organic contaminants in the membrane modules increased. In addition, the composition of proteins, polysaccharides, and humus in dissolved organic contaminants was close to that in extracellular polymeric substances and soluble microbial products secreted by microalgae. These results suggested that the membrane fouling of membrane modules was closely related to the algal biomass content in the MPBRs. The above results provided a theoretical basis for reducing membrane fouling of MPBR.

Evaluation of hydroxyapatite derived from flue gas desulphurization gypsum on simultaneous immobilization of lead and cadmium in contaminated soil

Flue gas desulphurization gypsum (FGD) is a major solid waste in coal-fired energy plants, and the appropriate reuse of this resources is still a major challenge. In this study, the feasibility of FGD as a calcium source to produce hydroxyapatite (FGD-HAP) for the immobilization of lead (Pb) and cadmium (Cd) in spiked soil was investigated. The effects of FGD and FGD-HAP on soil properties and redistribution, bioaccessibility and plant uptake of Pb and Cd were examined. Results showed that application of FGD and FGD-HAP could significantly improve the enzymes activities of contaminated soils, but the effectiveness was more pronounced with FGD-HAP. Addition of only 1% FGD-HAP could effectively reduce bioavailable Pb and Cd concentration in soil as measured by CaCl₂ extraction by 60.6% and 65.4%, respectively. On the other hand, plant available Pb and Cd could significantly decrease by 93.8% and 73.2% after amendment of 5% FGD-HAP. Significant changes in the micro-scale distribution of heavy metals before and after FGD-HAP treatment demonstrated that while heavy metals were predominantly associated with iron/manganese oxides in untreated soil, high correlation between heavy metals and phosphorus/sulfur was observed in FGD-HAP treated soil. In addition, results of the leaching tests showed that incorporation of FGD-HAP enhanced the retention capacity of heavy metals in soil, indicating that application of FGD-HAP could diminish the environmental risk of leachable heavy metals to groundwater. Overall, this study highlighted the potential value of FGD-HAP as a low-cost and high-efficient amendment for remediation of Pb and Cd contaminated soils.

Ion-imprinted chitosan fiber for recovery of Pd(II): Obtaining high selectivity through selective adsorption and two-step desorption

Selective separation of platinum group metals from acidic solutions is of great importance due to their cumulative supply risk and environmental concern. In this study, a Pd(II) ion-imprinted chitosan fiber (ICF) was prepared as the novel adsorbent, and a well-designed two-step desorption process was implemented for selectively recovering Pd(II) from acidic solution containing Pd(II) and interfering metals of Co(II), Ni(II), Cu(II) and Pt (IV). The ICF showed higher selectivity for Pd(II) adsorption, comparing the non-imprinted chitosan fiber (NICF) towards other metals adsorption. The first selective desorption was achieved by NaOH solution, since only Pt (IV) adsorbed on the ICF in a small amount could be eluted, without any acting on Pd(II) ions. The second desorption process was carried out using acidified thiourea solution for the exclusive Pd(II) ions desorption. Therefore, much higher selective recovery of Pd(II) was achieved through ICF with a good selective adsorption performance and a well-designed desorption process. Furthermore, the mechanisms of selective adsorption and desorption were investigated by X-ray photoelectron spectra (XPS) and X-ray diffraction (XRD) analyses. Finally, ICF-packed column system was conducted using synthetic multiple metals solution and a practical hydrometallurgy wastewater as influent, respectively, with a good adsorption capacity of 87.2 mg g^-1 and 94.2 mg g^-1, resulting quite high concentrated effluent consisted of 97.4% of Pd(II) and 99.5% of Pd(II), respectively. It was opened up a promising designed material and technique for selectively recovering Pd(II) in the further practical large-scale application.

Electrophoretic deposition of collagen-reinforced HA/CTS biocomposite coatings

In this study, the biomimetic approach described as reverse engineering by trying to copy the excellent concepts of nature and taking nature as a model has been used. In order to mimic the structure of natural bone, hydroxyapatite (HA), chitosan (CTS) and collagen have been combined as a novel type of biocomposite coating. HA/CTS/collagen biocomposite coatings have been successfully electrophoretically deposited on Ti6Al4V biomedical implants. A novel type of a polyelectrolyte consisting of ethanol, water and isopropyl alcohol has been used for the electrophoretic deposition process. The effect of collagen concentration on the structural and corrosion protection performance of the biocomposite coatings has been investigated by X-ray diffraction, field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, potentiodynamic polarization (Tafel extrapolation) and electrochemical impedance spectroscopy techniques. The electrophoretically deposited HA/CTS/collagen biocomposite coatings have exhibited corrosion protection against simulated physiological body fluid up to five times better than that of bare Ti6Al4V alloy.

Influence of draw solution type and properties on the performance of forward osmosis process: Energy consumption and sustainable water reuse

Single and multi-component fertilizers were used as a draw solution (DS) in forward osmosis (FO) to produce high-quality water from synthetic and seawater solution, eliminating the need for DS regeneration and reducing the operational energy. The effect of DS type, concentration, circulation flow rates on the FO water flux (WF), specific water flux (SWF), percentage water recovery (%W_recovery), reverse salt flux (RSF) and percentage salt rejection (%R) were studied. The results showed that single fertilizer draw solution (SFDSs) produced higher WF (4.43 L/m².h), %W_recovery (30%) and RSF (60%) in comparison with multi-component draw solution (MCDS) with WF, %W_recovery and RSF of 2.57 L/m².h, 17% and 46%, respectively. DS with higher concentration produced the highest SWF and %W_recovery and consumed less energy. MCDS with concentration of 200 g/L showed SWF in the range of 14.0 to 10.4 L/m²h and energy consumption of 0.312 kW/h m³ in comparison with 10 to 7.8 L/m²h and 0.23 kW/h m³ for MCDS with concentration of 100  g/L. Increasing the recirculation flow rate showed minimum effect on WF and up to 35% energy saving. Pure water extracted using liquid fertilizers utilizing the unique FO mass transport properties balanced nutrient requirement and the water quality parameters, thereby sustaining the aquaponics industry.

Nanosorbent of hydroxyapatite for atrazine: A new approach for combating agricultural runoffs

The attention of current work was on the fabrication of effective nanoadsorbent of hydroxyapatite (HAp) for the controlled release of atrazine (ATZ) formulation. The ATZ-HAp complex (ATZ@HAp) was able to inhibit the growth of Brassica sp. under in situ conditions. This developed methodology aspires to cease the agricultural runoffs of ATZ applied with the HAp adjuvant and ensure their effective functioning. The efficacy of the protocol was mainly accomplished by adsorbing ATZ over the surface of HAp NPs that restricted its premature runoff and promoted the prolonged herbicidal efficiency. The influence of fundamental parameters i.e., HAp dose, ATZ dose and initial pH on the adsorption process was investigated systematically. The suitability of ATZ@HAp complex for real world application was adjudged after proofing its toxicological behaviour and its role in Zea mays plantations. The complex was found to be non-toxic and nurturing due to its phosphate rich nature. Further investigations of ATZ@HAp complex and its effect on the non-target species will help in establishing an effective framework for their commercial use in agricultural practices.

The preparation of hydroxyapatite from unrefined calcite residues and its application for lead removal from aqueous solutions

Calcite originating from waste treatment technologies was utilised for the chemical precipitation of hydroxyapatite (HAP). The physicochemical properties of the as-synthesised-HAP was fully characterised using FT-IR, BET, SEM and TEM, confirming its crystal structure and formation of high purity HAP by XRD. The product was employed for removal of lead from aqueous media at pH 5.0, achieving almost 80% of the adsorption in the first 5 min and a maximum adsorption capacity for Pb²⁺ of 224.4 mg g⁻¹. A contact time of 40 min was required to achieve equilibrium with Pb²⁺ uptake of 98%. The kinetics of the cation exchange of HAP from calcite were predicted using integrated rate laws, revealing a pseudo-second order cation exchange process with a rate constant of 6.84 × 10⁻⁴ g (mg min)⁻¹. All obtained results are benchmarked against a control HAP sample simultaneously derived from eggshells, which were demonstrated to offer slower kinetics of cation exchange (4.82 × 10⁻⁴ g (mg min)⁻¹) and almost half the maximum adsorption capacity (129.1 mg g⁻¹). The results showed that hydroxyapatite synthesised from calcite waste represents a low-cost material for the adsorption of hazardous Pb²⁺ in contaminated waters and a promising alternative for heavy metals remediation in aquatic environments.

HAP is synthesized directly from waste calcite and is demonstrated to sequester lead at a quicker rate than comparable materials.