Immobilization of powdery calcium silicate hydrate via PVA covalent cross-linking process for phosphorus removal

Oyster shell powder-loaded cellulose gel beads as a high-efficiency adsorbent for phosphorus recovery: preparation, kinetics, isotherms and thermodynamic studies

Given the critical importance, resource limination and environmental toxicity of phosphorus, the study of phosphorus recovery and utilization is extremely urgent. This paper utilized unmodified oyster shell powder (OSP) and cotton fibers as raw materials to prepare OSP-loaded cellulose gel beads (OSP@Gel) through the fiber-dissolving capability of LiBr·3H2O molten salt, for phosphate recovery from water. The surface microstructure and chemical properties of OSP@Gel were characterized by using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), confirming the loading of OSP onto the gel matrix. The phosphorus adsorption capacity of a single OSP@Gel bead could reach up to 8.80 ± 0.32 mg at the optimal OSP doping amount of 1.0 g and optimal pH of 5.0. Kinetic and isotherm analyses revealed that the experimental data fit the PSO model and the Langmuir model. Thermodynamic analysis suggested that the phosphate adsorption was endothermic. Combined results from SEM and XPS analyses indicated that the adsorption of phosphate by OSP@Gel was chemical, with adsorption rate controlled by both liquid film diffusion and intraparticle diffusion. The high phosphate adsorption capacity, good mechanical stability in water, and easy degradability in plant soil provide OSP@Gel beads with great potential for phosphate recovery.

Recovering Phosphate from Complex Wastewater Using Macroporous Cryogel Composited Calcium Silicate Hydrate Nanoparticles

Since currently used natural, nonrenewable phosphorus resources are estimated to be depleted in the next 30-200 years, phosphorus recovery from any phosphorus-rich residues has attracted great interest. In this study, phosphorus recovery from complex wastewater samples was investigated using continuous adsorption on cryogel column composited calcium silicate hydrate nanoparticles (CSH columns). The results showed that 99.99% of phosphate was recovered from a synthetic water sample (50 mg L-1) using a 5 cm CSH column with a 5 mL min-1 influent flow rate for 6 h while 82.82% and 97.58% of phosphate were recovered from household laundry wastewater (1.84 mg L-1) and reverse osmosis concentrate (26.46 mg L-1), respectively. The adsorption capacity decreased with an increasing flow rate but increased with increasing initial concentration and column height, and the obtained experimental data were better fitted to the Yoon-Nelson model (R2 = 0.7723-0.9643) than to the Adams-Bohart model (R2 = 0.6320-0.8899). The adsorption performance of phosphate was decreased 3.65 times in the presence of carbonate ions at a similar concentration, whereas no effect was obtained from nitrate and sulfate. The results demonstrate the potential of continuous-flow phosphate adsorption on the CSH column for the recovery of phosphate from complex wastewater samples.

Continuous Phosphate Removal and Recovery Using a Calcium Silicate Hydrate Composite Monolithic Cryogel Column

Toward the development of a practical and green approach for removing phosphate from water, a monolithic cryogel based on starch and calcium silicate hydrate (Cry-CSH) was employed as a phosphate adsorbent in a continuous flow system for the first time. The influence of flow rate, initial phosphate concentration, and adsorbent height on the adsorption efficiency was investigated. As the rate of flow and the initial concentration of phosphate increased, the total quantity of adsorbed phosphate dropped; however, the performance of the column was greatly enhanced by an increase in adsorbent height. The experimental data fit the Adams-Bohart model better than the Thomas and Yoon-Nelson models at the beginning of the adsorption process. To evaluate its applicability, the continuous flow system based on the monolithic Cry-CSH column was applied for the removal of phosphate from the discharge effluent of the Patong Municipality Wastewater Treatment Plant (Phuket, Thailand), achieving an excellent total adsorption of 94.61%.

3D printed cylindrical capsules as a Chlorella pyrenoidosa immobilization device for removal of lead ions contamination

Immobilization is considered as a promising strategy toward the practical applications of powdered adsorbent. Herein, three dimensional (3D) printing cylindrical capsules with cross-linked PVA hydrogels membrane in encapsulate Chlorella pyrenoidosa (Cp) were utilized for removal of lead ions. The chemical compositions, hydrogels performance and morphologies of the membranes were determined by Fourier transformed infrared spectroscopy (FTIR), cross-linking degree, swelling degree, membrane flux and scanning electron microscopy (SEM). It is found that PVA cross-linking structure is successfully synthesized on the surface of capsule body and cap due to the presence of PVA in the filament. The lead ions adsorption capacity related to initial concentration of 50 mg/L in 48 h is reached 75.61%, revealing a good removal ability. The self-floating 3D printed capsules device also shows an excellent recovering property. After 7 runs of adsorption experiment, the lead ions adsorption ratio remains 78.56%, which will bring a broad prospect in wastewater treatment, chemical slow release along with sample preparation and separation.

Eco-friendly recycling of silicon-rich lye: Synthesis of hierarchically structured calcium silicate hydrate and its application for phosphorus removal

Silicon-rich lye (SRL), a byproduct generated from pre-treatment of coal-based solid waste (CSW), was considered as a preponderant silicon source to prepare hierarchically nanostructured calcium silicate hydrate (C-S-H). Through the novel mild-causticization synthesis strategy, C-S-H was prepared under optimal caustic process conditions at time of 3 h, temperature of 80 °C, Ca/Si of 1.25:1, and active CaO to obtain a conversion rate of Si up to 97.33 % during the high-value utilization of SRL. The synthesized C-S-H possesses abundant mesoporous structure and massive exchangeable active sites, whose formation is advanced through an appropriate elevation regulation of caustic temperature and time. The silicate chain depolymerization occurs to C-S-H prepared in the highly alkaline system at higher caustic temperature, longer caustic period, especially at existence of massive sodium ions, but it presents higher polymerization degree at more aluminum co-existing. The adsorption capacity up to 119.27 mg/g for C-S-H presents a valid removal performance toward phosphorus in the wastewater than massive present reports. The removal mechanism of phosphorus can be identified as the surface chemisorption and formation of calcium phosphate co-precipitation. This study can provide considerable and potential guidance to the coordinated disposal between industrial solid wastes and wastewater purification.

Removal of Ni(II) Ions by Poly(Vinyl Alcohol)/Al2O3 Nanocomposite Film via Laser Ablation in Liquid

Al₂O₃-poly(vinyl alcohol) nanocomposite (Al₂O₃-PVA nanocomposite) was generated in a single step using an eco-friendly method based on the pulsed laser ablation approach immersed in PVA solution to be applicable for the removal of Ni(II) from aqueous solution, followed by making a physicochemical characterization by SEM, XRD, FT-IR, and EDX. After that, the effect of adsorption parameters, such as pH, contact time, initial concentration of Ni(II), and medium temperature, were investigated for removal Ni(II) ions. The results showed that the adsorption was increased when pH was 5.3, and the process was initially relatively quick, with maximum adsorption detected within 90 min of contact time with the endothermic sorption process. Moreover, the pseudo-second-order rate kinetics (k₂ = 9.9 × 10⁻⁴ g mg⁻¹ min⁻¹) exhibited greater agreement than that of the pseudo-first-order. For that, the Ni(II) was effectively collected by Al₂O₃-PVA nanocomposite prepared by an eco-friendly and simple method for the production of clean water to protect public health.

Microbial induced calcium precipitation based anaerobic immobilized biofilm reactor for fluoride, calcium, and nitrate removal from groundwater

In this study, the anaerobic quartz sand fixed biofilm reactor containing Cupriavidus sp. W12 was established to simultaneously remove calcium (Ca²⁺), fluoride (F^-) and nitrate (NO₃^-N) from groundwater. After 84 days of continuous operation, the optimum operating parameters and defluoridation mechanism were explored, and the microbial community structure under different pH environments were compared and analyzed. Under the optimal operation conditions (HRT of 6 h, initial Ca²⁺ concentration of 180 mg L^-1, and pH of 7.0), the removal efficiencies of Ca²⁺, F^-, and NO₃^-N were 58.97%, 91.93%, and 100%, respectively. Gas chromatography (GC) results indicate that N₂ is the main gas produced by the bioreactor. Three-dimension excitation emission matrix fluorescence spectroscopy (3D-EEM) showed that extracellular polymers (EPS) are produced during bacterial growth and metabolism. The results of Scanning electron microscopy-energy dispersive spectrometer (SEM-EDS), X-ray diffraction (XRD), and Fourier transform infrared spectrometer (FTIR) demonstrated that the defluoridation mechanism is attributed to the synergetic effects of ion exchange, co-precipitation, and chemisorption. The comparative analysis of the microbial community structure under different pH conditions show that Cupriavidus is the dominant bacteria in the bioreactor throughout the experiment, and it shows a prominent advantage at pH of 7.0. This research provides an application foundation for anaerobic microbial induced calcium precipitation (MICP) bioremediation of Ca²⁺, F^-, and NO₃^-N from groundwater.

Removal and recovery of phosphate using a novel calcium silicate hydrate composite starch cryogel

Phosphate is a major pollutant that deteriorates water quality and causes eutrophication, a novel calcium silicate hydrate composite cryogel (Cry-CSH) was thus successfully prepared for phosphate removal and recovery in this work. Calcium silicate hydrate (C-S-H) was mixed with the gel precursor (7.5% w/w) prepared from native starch and limewater (saturated calcium hydroxide solution as the cross-linker). The mixture was frozen and thawed for 3 cycles giving an interconnected macroporous composite. This had C-S-H nanoparticles (75 mg) immobilized on a monolithic floatable cryogel network (2.5 cm diameter × 1.0 cm height) enabling an easier recovery and without the losses that occur when using C-S-H nanoparticles. The phosphate adsorption reaches equilibrium at 120 min with adsorption capacity of 2.50 mgPO₄^3-/g_Cry-CSH (65.42 mgPO₄^3-/g_C-S-H) under optimum conditions. Adsorption equilibrium data were well fit by the Freundlich isotherm model, while kinetic results were well fit by the pseudo second-order model. The calculated activation energy (E_a) of 43.9 kJ/mol indicates chemical adsorption, while a positive change in enthalpy (ΔH⁰, 19.3 kJ/mol) indicates the endothermic nature of phosphate adsorption. Cry-CSH can remove phosphate from wastewater and effluent samples with excellent removal efficiency (>98%). It can float on water surface for at least 105 days without damage, while its phosphate adsorbed form can be biodegraded within 10 days under soil buried conditions. Thus, this work demonstrated the significant potential of Cry-CSH for practical and environmentally friendly phosphate removal and recovery.

Engineering Calcium-bearing Mineral/Hydrogel Composites for Effective Phosphate Recovery

Effectively recovering phosphate from wastewater streams and reutilizing it as a nutrient will critically support sustainability. Here, to capture aqueous phosphate, we developed novel mineral-hydrogel composites composed of calcium alginate, calcium phosphate (CaP), and calcium silicate (CSH) (CaP + CSH/Ca-Alg). The CaP + CSH/Ca-Alg composites were synthesized by dripping a sodium alginate (Na-Alg) solution with ionic precursors into a calcium chloride bath. To change the mineral seed's properties, we varied the calcium bath concentrations and the ionic precursor (sodium dibasic phosphate (NaH₂PO₄) and/or sodium silicate (Na₂SiO₃)) amounts and their ratios. The added CSH in the mineral-hydrogel composites resulted in the release of calcium and silicate ions in phosphate-rich solutions, increasing the saturation ratio with respect to calcium phosphate within the mineral-hydrogel composites. The CSH addition to the mineral-hydrogel composites doubled the phosphate removal rate while requiring lesser initial amounts of Ca and P materials for synthesis. By incorporating both CSH and CaP mineral seeds in composites, we achieved a final concentration of 0.25 mg-P/L from an initial 6.20 mg-P/L. Moreover, the mineral-hydrogel composites can remove phosphate even under CaP undersaturated conditions. This suggests their potential to be a widely applicable and environmentally-sustainable treatment and recovery method for nutrient-rich wastewater.

Phosphorus and sulphates removal from wastewater using copper smelter slag washed with acid

Abstract

In this study, we present the performance of acid washed copper smelter slag for the adsorption of phosphates and sulphates from wastewater. The aim of the study was to investigate the removal of phosphates and sulphates from wastewater using acid washed copper smelter slag at batch scale by exploring influences of different variables. The leachate concentrations of copper, iron, manganese and lead released from the adsorbent were 1.8, 128.2, 0.32 and 0.20 mg L−1, respectively at pH 2. The point of zero charge was at pH 6.04, Pseudo-Second Order kinetic model described the adsorption process better with an R2 value of 0.99. The experimental maximum adsorption capacities for phosphates and sulphates were 0.51 and 0.24 mg g−1 media, respectively, and 0.96 mg P g−1 media at pH 12 and 0.39 mg g−1 media for sulphates at pH 2, respectively. The process was endothermic with temperature having insignificant impact during adsorption. The maximum adsorption capacities for thermodynamic study were 0.103 ± 0.09 and 0.046 ± 0.004 mg g−1 media respectively, for PO43− P and SO42− at 60 °C. This study showed that acid washed copper smelter slag has an improved adsorption capacity for phosphate and sulphate ions but further investigations should be conducted to find ways of further improving the adsorbent performance.

Article highlights

System optimization of an embedding protocol to immobilize cells from Candida bombicola to improve the efficiency of sophorolipids production

This study introduces the implication of immobilization technology in the fermentation process of sophorolipids (SLs) production by Candida bombicola. Firstly, an evaluation system was established for the performance of embedding immobilization and subsequently applied to guide the optimization of operating conditions for sodium alginate immobilization. Correspondingly, the SLs titer increased from 11.4 g/L to 14.6 g/L. Secondly, polyvinyl alcohol was introduced for composite embedding to improve the stability of immobilized beads. Then exogenous addition of 1.5% diatomite further enhanced the fermentation performance of immobilized cells, thereby increasing the SLs titer to 35.9 g/L, which was 2.1 times higher than the original immobilized cells method. Finally, the immobilized cells were tested for three repeated batches of SLs fermentation. Compared to the free cells fermentation, the SLs productivity and substrate conversion rate were increased by 35.5% and 9.1%, respectively. The obtained results showed high potential for application on an industrial scale.

Fe(III) loaded chitosan-biochar composite fibers for the removal of phosphate from water

Excess phosphorous (P) in aquatic systems causes adverse environmental impacts including eutrophication. This study fabricated Fe(III) loaded chitosan-biochar composite fibers (FBC-N and FBC-C) from paper mill sludge biochar produced under N₂ (BC-N) and CO₂ (BC-C) conditions at 600 °C for adsorptive removal of phosphate from water. Investigations using SEM/EDX, XPS, Raman spectroscopy, and specific surface area measurement revealed the morphological and physico-chemical characteristics of the adsorbent. The Freundlich isotherm model well described the phosphate adsorption on BC-N, while the Redlich-Peterson model best fitted the data of three other adsorbents. The maximum adsorption capacities were 9.63, 8.56, 16.43, and 19.24 mg P g^-1 for BC-N, BC-C, FBC-N, and FBC-C, respectively, indicating better adsorption by Fe(III) loaded chitosan-biochar composite fibers (FBCs) than pristine biochars. The pseudo-first-order kinetic model suitably explained the phosphate adsorption on BC-C and BC-N, while data of FBC-N and FBC-C followed the pseudo-second-order and Elovich model, respectively. Molecular level observations of the P K-edge XANES spectra confirmed that phosphate associated with iron (Fe) minerals (Fe-P) were the primary species in all the adsorbents. This study suggests that FBCs hold high potential as inexpensive and green adsorbents for remediating phosphate in contaminated water, and encourage resource recovery via bio-based management of hazardous waste.

Investigation of water treatment sludge from drinking water treated with Zetafloc 553I coagulant for phosphorus removal from wastewater

Water treatment sludge have shown promising results as adsorbent for phosphorus and sulphate removal from real wastewater. The study was conducted through batch kinetics and equilibrium isotherm modes. The chemical composition reveal that aluminium compounds were dominant in the fresh sludge and aluminium phosphates were also observed in the used sludge. The results reveal that Manganese was leached from the material at all pH values investigated with the highest level observed at pH 2 and all concentrations higher than the national standard of discharge into the relevant environment. The point of zero charge of the adsorbent was pH 8.04 and high adsorption capacities for both sulphate and phosphate ions were observed at pH values lower than this point. Batch kinetic results revealed 96.0 ± 3.0% sulphates removal in the first 30 min whereas the highest phosphates removal was 88.0 ± 4.0% attained at 300 min of the experiment. Pseudo - second order reaction fitted the data better than Pseudo-first order reaction. The percentage removal of sulphates was observed decreasing with increasing adsorbent dose after 2.4 g dose but removal increased with increasing media dosage for phosphorus. The equilibrium data was better described by Freundlich isotherm with constants relating to adsorption capacities being 6.76 and 6.2 L g^-1 respectively, for sulphates and phosphates adsorption. The adsorption capacity of phosphates was observed decreasing with increasing temperature, but the results were not conclusive in the case of sulphates. The results reveal that copper, nickel, and zinc have affinity for sulphates. The water treatment sludge can be used for phosphate and sulphate removal from wastewater though the leachability of manganese is a concern. Further investigations through fixed bed columns will need to be investigated before field trials. In conclusion, the sludge can be used as adsorbent for phosphorus and sulphates removal from wastewater through filtration and onsite treatment methods such as vertical or horizontal flow wetland systems. The success of the adsorbent will reduce the costs associated with its disposal which can also lead to leachability of metals into the environment with time.

A ZnO@ABS/TPU/CaSiO3 3D skeleton and its adsorption/photocatalysis properties for dye contaminant removal

Both adsorption and photocatalysis are considered to be effective methods for removing organic contaminants from dye wastewater. In this study, the construction of 3D skeletons based on the nanoparticles ZnO and ABS/TPU/calcium silicate (CaSiO3) (shortened as ATC) were fabricated via fused deposition molding (FDM) technology. Characterization by scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) depicted that ZnO nanospheres had been successfully grown on the 3D skeleton surface with an enlarged specific surface area. As the results of the RhB adsorption and photocatalytic degradation experiments showed, the removal ratio of RhB onto the ZnO-ATC skeleton was as high as 97.94% and the synergistic effect of adsorption and photocatalysis greatly shortened the RhB degradation time under ultraviolet light irradiation. The nanocomposites synthesized in this study showed a significant removal ability for organic pollutants, and could effectively overcome the limitation of the secondary removal of photocatalysts.

Field Research on Mixing Aeration in a Drinking Water Reservoir: Performance and Microbial Community Structure

Field research on the performance of pollutant removal and the structure of the microbial community was carried out on a drinking water reservoir. After one month of operation of a water-lifting aeration system, the water temperature difference between the bottom and the surface decreased from 9.9 to 3.1 °C, and the concentration of the dissolved oxygen (DO) in the bottom layer increased from 0 to 4.2 mg/L. The existing stratification in the reservoir was successfully eliminated. Total nitrogen (TN), total phosphorus (TP), and total organic carbon (TOC) concentrations were reduced by 47.8%, 66.7%, and 22.9%, respectively. High-throughput sequencing showed that Proteobacteria, Bacteroides, and Actinomycetes accounted for 67.52% to 78.74% of the total bacterial population. Differences in the bacterial changes were observed between the enhanced area and the control area. With the operation of the water-lifting aeration system, the populations of bacteria of the main genera varied temporally and spatially. Principal component analysis pointed out a clear evolution in the vertical distribution of the microbial structure controlled by the operation of the aeration system. Permutational analysis of variance showed a significant difference in the microbial community (p < 0.01). Redundancy analysis showed that physical (water temperature, DO) and chemical environmental factors (Chl-a, TOC, TN) were the key factors affecting the changes in the microbial communities in the reservoir water. In addition, a hierarchical partitioning analysis indicated that T, Chl-a, ORP, TOC, pH, and DO accounted for 24.1%, 8.7%, 6.7%, 6.2%, 5.8%, and 5.1% of such changes, respectively. These results are consistent with the ABT (aggregated boosted tree) analysis for the variations in the functional bacterial community, and provide a theoretical basis for the development and application of biotechnology.

Immobilization of Lactobacillus rhamnosus in polyvinyl alcohol/calcium alginate matrix for production of lactic acid

Immobilization of Lactobacillus rhamnosus ATCC7469 in poly(vinyl alcohol)/calcium alginate (PVA/Ca-alginate) matrix using "freezing-thawing" technique for application in lactic acid (LA) fermentation was studied in this paper. PVA/Ca-alginate beads were made from sterile and non-sterile PVA and sodium alginate solutions. According to mechanical properties, the PVA/Ca-alginate beads expressed a strong elastic character. Obtained PVA/Ca-alginate beads were further applied in batch and repeated batch LA fermentations. Regarding cell viability, L. rhamnosus cells survived well rather sharp immobilization procedure and significant cell proliferation was observed in further fermentation studies achieving high cell viability (up to 10.7 log CFU g^-1) in sterile beads. In batch LA fermentation, the immobilized biocatalyst was superior to free cell fermentation system (by 37.1%), while the highest LA yield and volumetric productivity of 97.6% and 0.8 g L^-1 h^-1, respectively, were attained in repeated batch fermentation. During seven consecutive batch fermentations, the biocatalyst showed high mechanical and operational stability reaching an overall productivity of 0.78 g L^-1 h^-1. This study suggested that the "freezing-thawing" technique can be successfully used for immobilization of L. rhamnosus in PVA/Ca-alginate matrix without loss of either viability or LA fermentation capability.