Stratified control of chemical crystallization in a pellet fluidized bed for pH-Adjusted fluoride and phosphate reduction: An experimental study.

Chemical crystallization granulation in a fluidized bed offers an environmentally friendly technology with significant promise for fluoride removal. This study investigates the impact of stratified pH control in a crystallization granulation fluidized bed for the removal of fluoride and phosphate on a pilot scale. The results indicate that using dolomite as a seed crystal, employing sodium dihydrogen phosphate (SDP) and calcium chloride as crystallizing agents, and controlling the molar ratio n(F):n(P):n(Ca) = 1:5:10 with an upflow velocity of 7.52 m/h, effectively removes fluoride and phosphate. Stratified pH control-maintaining weakly acidic conditions (pH = 6-7) at the bottom and weakly alkaline conditions (pH = 7-8) at the top-facilitates the induction of fluoroapatite (FAP) and calcium phosphate crystallization. This approach reduces groundwater fluoride levels from 9.5 mg/L to 0.2-0.6 mg/L and phosphate levels to 0.1-0.2 mg/L. Particle size analysis, scanning electron microscopy-energy-dispersive X-ray spectroscopy, and X-ray diffraction physical characterizations reveal significant differences in crystal morphology between the top and bottom layers, with the lower layer primarily generating high-purity FAP crystals. Further analysis shows that dolomite-induced FAP crystallization offers distinct advantages. SDP not only dissolves on the dolomite surface to provide active sites for crystallization but also, under weakly acidic conditions, renders both dolomite and FAP surfaces negatively charged. This allows for the effective adsorption of PO43-, HPO42-, and F- anions onto the crystal surfaces. This study provides supporting data for the removal of fluoride from groundwater through induced FAP crystallization in a chemical crystallization pellet fluidized bed.

Induced crystallization for the simultaneous removal of hardness-iron-manganese in groundwater: An experimental study.

Hardness, iron, and manganese are common groundwater pollutants, that frequently surpass the established discharge standard concentrations. They can be effectively removed, however, through induced crystallization. This study has investigated the effectiveness of the simultaneous removal of hardness-iron-manganese and the crystallization kinetics of calcium carbonate during co-crystallization using an automatic potentiometric titrator. The impacts pH, dissolved oxygen (DO), and ion concentration on the removal efficiency of iron and manganese and their influence on calcium carbonate induced crystallization were assessed. The results suggest that pH exerts the most significant influence during the removal of hardness, iron, and manganese, followed by DO, and then the concentration of iron and manganese ions. The rate of calcium carbonate crystallization increased with pH, stabilizing at a maximum of 10-10 m/s. Iron and manganese can be reduced from an initial level of 4 mg/L to <0.3 mg/L and 0.1 mg/L, respectively. The removal rate of iron, however, was notably higher than that of manganese. The DO concentration correlates positively with the removal of iron and manganese but has minimal impact on the calcium carbonate crystallization process. During the removal of iron and manganese, competitive interactions occur with the substrate, as increases in the concentration of one ion will inhibit the removal rate of the other. Characterization of post-reaction particles and mechanistic analysis reveals that calcium is removed through the crystallization of CaCO3, while most iron is removed through precipitation as Fe2O3 and FeOOH. Manganese is removed via two mechanisms, crystallization of manganese oxide (MnO2/Mn2O3) and precipitation. Overall, this research studies the removal efficiency of coexisting ions, the crystallization rate of calcium carbonate, and the mechanism of simultaneous removal, and provides valuable data to aid in the development of new removal techniques for coexisting ions.

Pre-exposure of peracetic acid enhances its subsequent combination with ultraviolet for the inactivation of fungal spores: Efficiency, mechanisms, and implications.

Waterborne fungi pose a potential threat to water supply safety due to their high resistance to disinfectants. Peracetic acid, as a promising alternative disinfectant to chlorine, has attracted increasing attention in water treatment. In this study, the inactivation of two dominant fungal species (Aspergillus niger and Aspergillus flavus) by sequential application of peracetic acid and ultraviolet (PAA-UV/PAA) was reported for the first time. Results revealed that the pre-exposure of PAA could facilitate the subsequent process of UV/PAA combination and shorten the lag phase in fungi inactivation. After 10 min of PAA pre-exposure, PAA-UV/PAA achieved 3.03 and 2.40 log inactivation of Aspergillus niger and Aspergillus flavus, which were 2- and 4.3-fold higher than that of direct UV/PAA under the same UV and PAA doses. PAA-UV/PAA disinfection also exhibited a stronger regrowth inhibition for incompletely inactivated fungal spores than direct UV/PAA. The increase of pH (5.0-9.0) and humic acid concentration (1.0-5.0 mg L - 1) showed an inhibitory effect on PAA-UV/PAA inactivation, but PAA-UV/PAA was more adaptable in a wide pH range and the presence of humic acid compared to direct UV/PAA. The more severe cell membrane damage and higher reactive oxygen species level in PAA-UV/PAA were evidenced for the first time by flow cytometry. The increased hydroxyl radical generation and higher synergism were primarily responsible for inactivation improvement. This study enhances the further understanding of the PAA-UV/PAA process, and the findings are expected to promote the development of PAA as a promising disinfectant for effective fungi control.

Microbial-induced calcium carbonate precipitation: Influencing factors, nucleation pathways, and application in waste water remediation.

Microbial-induced calcium carbonate precipitation (MICP) is a technique that uses the metabolic action of microorganisms to produce CO32- which combines with free Ca2+ to form CaCO3 precipitation. It has gained widespread attention in water treatment, aimed with the advantages of simultaneous removal of multiple pollutants, environmental protection, and ecological sustainability. This article reviewed the mechanism of MICP at both intra- and extra-cellular levels. It summarized the parameters affecting the MICP process in terms of bacterial concentration, ambient temperature, etc. The current status of MICP application in practical engineering is discussed. Based on this, the current technical difficulties faced in the use of MICP technology were outlined, and future research directions for MICP technology were highlighted. This review helps to improve the design of existing water treatment facilities for the simultaneous removal of multiple pollutants using the MICP and provides theoretical reference and innovative thinking for related research.

Manganese redox cycling in immobilized bioreactors for simultaneous removal of nitrate and 17ß-estradiol: Performance, mechanisms and community assembly potential.

The application of bio-manganese (Mn) redox cycling for continuous removal of contaminants provides promise for addressing coexisting contaminants in groundwater, however, the feasibility of constructing Mn redox cycling system (MCS) through community assembly remains to be elucidated. In this study, Mn-reducing strain MFG10 and Mn-oxidizing strain MFQ7 synergistically removed 94.67 % of 17ß-estradiol (E2) within 12 h. Analysis of potential variations in Mn oxides suggested that MCS accelerated the production of reactive oxygen species (ROS) and Mn(III), which interacted to promote E2 removal. After continuous operation of the Mn ore-based immobilized bioreactor for 270 days, the experimental group (EG) achieved average removal efficiencies of 89.63 % and 97.57 % for NO3--N and E2, respectively. High-throughput sequencing results revealed complex symbiotic relationships in EG. Community assembly significantly enhanced the metabolic and physiological activity of the bioreactor, which promoting the expression of core functions including nitrogen metabolism, Mn cycling and organic matter resistance.

Experimental study on the effects of different factors on the crystallization rate and products of Mn-Ca co-crystallization.

Calcium and manganese are common ions that pollute drinking water and, therefore, ingestion may seriously harm human health. However, despite its importance, few studies into the synergistic removal of calcium and manganese have been reported. Calcium and manganese have similar chemical properties and, consequently, can be removed by co-crystallization, as the exact crystalline phase formed by this process and the process rate depend on the pH, the dissolved oxygen (DO) content, and the concentrations of the component ions. In this work, we experimentally studied the co-crystallization of Mn and Ca using an automatic potentiometric titrator. We found that the concentration of Mn2+ can be reduced from 3.0 to <0.1 mg/L by the co-crystallization of Mn and Ca at pH 10.5 and a DO content of 8.5 mg/L. In addition, the crystallizations of Ca and Mn are mutually inhibitory; the crystallization process of Mn is obviously divided into two stages: crystal nucleation and crystal growth. Increasing the pH, decreasing the DO content, and decreasing the Mn ion concentration increase the rate of CaCO3 crystallization, whereas the opposite changes increase the rate of Mn crystallization. Furthermore, Mn-Ca co-crystallization leads to the formation of various substances, including single crystals (CaCO3/MnCO3), mixed crystals (CaMnCO3), and Mn oxides (MnxOy/Mn(OH)O). Our findings regarding the effects, precipitation rates, and precipitation mechanisms of Mn-Ca co-crystallization serve as an important guide for the optimization and control of Mn-Ca co-crystallization processes.

Enhanced nitrate, fluoride, and phenol removal using polyurethane sponges loaded with rice husk biochar in immobilized bioreactor.

Polyurethane sponges loaded with rice husk biochar were prepared to immobilize Aquabacterium sp. CZ3 for intensified removal of nitrate, fluoride (F-), and phenol, with the maximum efficiency of 100 %, 91 %, and 99 %, respectively. The biochar load and increased carbon-to-nitrogen (C:N) ratio (below 3.0) stimulated the secretion of soluble microbial product, improved the electron transport system activity, and promoted denitrification, phenol co-metabolism, and F- and calcium crystallization. The characterization results suggested that F- was removed as fluoride-containing calcium precipitates. According to the microbial community analyses, Aquabacterium was the dominant bacterium. PICRUSt analyses showed that biochar and adequate carbon sources (C:N ratio 3.0) significantly increased the functional abundances of amino acid metabolism, carbohydrate metabolism, energy metabolism, and cell motility. The introduction of biochar reduces the demand for C:N ratio in the system, and expands the application potential of biomineralization technique in the remediation of multiple pollutants contaminated water.

Performance of hydrogel immobilized bioreactors combined with different iron ore wastes for denitrification and removal of copper and lead: Optimization and possible mechanism.

Reasonable and efficient removal of mixed pollutants (nitrate and heavy metals) in industrial wastewater under heavy metal pollution has attracted more attention in recent years. The target strain Aquabacterium sp. XL4 was immobilized with different iron ore wastes (IOW) using polyvinyl alcohol (PVA) to construct four immobilized bioreactors. The results showed that when the ratio of C/N was 1.5 and the hydraulic retention time (HRT) was 8.0h, the denitrification performance of the bioreactor was the best, and the maximum denitrification efficiency of the bioreactor with sponge iron (SI) as the iron source was 97.19% (2.42mg L-1 h-1). Furthermore, by adjusting the concentration of Cu2+ and Pb2+, the stress behavior of the bioreactor to heavy metals under the influence of each IOW was investigated. The bioreactor has stronger tolerance and removal efficiency to Pb2+ and Cu2+ in the presence of pellets ore (PO) and refined iron ore (RO), respectively. Moreover, the high-throughput data showed that Aquabacterium accounted for a high proportion in the immobilized bioreactor, and the prediction of functional genes based on the KEGG database showed that the addition of IOW was closely related to the acceleration of nitrate transformation and the inflow and outflow of iron in cells.

Synchronous removal of ammonia nitrogen, phosphate, and calcium by heterotrophic nitrifying strain Pseudomonas sp. Y1 based on microbial induced calcium precipitation.

Pseudomonas sp. Y1, a strain with superior synchronous removal ability of ammonia nitrogen (NH4+-N), phosphate (PO43--P), and calcium (Ca2+) was isolated, with the removal efficiencies of 92.04, 99.98, and 83.40 %, respectively. Meanwhile, the chemical oxygen demand (COD) was degraded by 90.33 %. Through kinetic analysis, the optimal cultivated conditions for heterotrophic nitrification-aerobic denitrification (HNAD) and biomineralization were determined. The growth curves experimental results of different nitrogen sources indicated that strain Y1 could remove NH4+-N through HNAD. The results of excitation-emission matrix (EEM) proved that the appearance of extracellular polymeric substances (EPS) promoted the precipitation of phosphate minerals. Finally, the characterization results of the bioprecipitates showed that the HNAD process produced the alkalinity required for microbial induced calcium precipitation (MICP), resulting in the removal of PO43- via adsorption and co-precipitation. This study provides a theoretical basis for the application of microorganisms to achieve synchronous nutrient removal and phosphorus recovery in wastewater.

The Simultaneous Removal of Ammonium and Manganese from Surface Water in South China by Manganese Co-Oxide Film.

Exceeding the permitted manganese (Mn2+) and ammonium (NH4+-N) levels is a frequent seasonal occurrence in a water treatment plant in south China. An iron Fe-Mn complex oxide film was found capable of removing more than 95% of Mn2+ and NH4+-N at a water temperature of 20 °C and an alkalinity level of 30 mg/L. It could remove up to 5.5 mg/L of Mn2+ and up to 3.5 mg/L of NH4+-N in a stable manner. Alkalinity is a crucial factor in the removal process. The morphology, elemental composition, and micro-structure of the oxide film were investigated using a scanning electron microscope, an energy-dispersive spectrometer, a Brunauer-Emmett-Teller specific surface-area analyzer, an X-ray diffractometer, and a Fourier-transform infrared spectrometer. The capacity of the Fe-Mn complex oxide film on the surface of the filter medium increased appreciably as its content and specific surface area increased. This research, which provides a theoretical basis for simultaneous manganese and NH4+-N removal by catalytic oxidation, demonstrates an engineering reference value.

Application of Chemical Crystallization Circulating Pellet Fluidized Beds for Softening and Saving Circulating Water in Thermal Power Plants.

The circulating pellet fluidized bed (CPFB) softening method is a highly efficient and environmentally friendly softening technology that can be used to reduce water hardness during the pretreatment process of circulating water in thermal power plants. The performance of chemical crystallization CPFB reactors was tested for increasing the concentration ratio and softening the circulating water in a thermal power plant in Dingzhou, Hebei. The results show that usage of CPFB reactors removed water hardness and Ca2+ ions with efficiencies exceeding 60% and 90%, respectively. The size of the particles discharged from the reactors was approximately 1-3 mm, and the content of CaO in these particles was found to be greater than 50%. All the discharged particles were reused in the desulfurization system in the power plant. The operational cost of the CPFB system is US$0.074 per cubic meter of water. After adopting the proposed CPFB softening method in the Dingzhou Power Plant, the concentration ratio of the circulation cooling water was increased from 4.5 to more than 9. In addition, the amount of replenished water and sewage discharge were both reduced by 150 m3/h, and the amount of scale inhibitor used in the system was reduced by more than 30%. These improvements contribute to approximately US$200,000 in annual savings in the power plant. In summary, the CPFB softening method demonstrated a high hardness removal rate, strong economic benefits, and remarkable environmental and social benefits. Therefore, this method seems ideal for softening replenished circulating cooling water, increasing the concentration ratio of the water and achieving zero liquid discharge (ZLD) in thermal power plants.

Full-Scale Experimental Study of Groundwater Softening in a Circulating Pellet Fluidized Reactor.

The softening effect of a new type of circulating pellet fluidized bed (CPFB) reactor on groundwater was studied through a full-scale experiment. The operation of the CPFB reactor in the second water plant in Chang'an District in Xi'an China was monitored for one year, and the results were compared with those for the Amsterdam reactor in The Netherlands. The removal efficiency of Ca2+ in the CPFB reactor reached 90%; the removal rate of total hardness was higher than 60%; effluent pH was 9.5⁻9.8; the turbidity of the effluent and the turbidity after boiling were lower than 1.0 NTU; the unit cost was less than €0.064 per m³; and the softened effluent was stable. The pellets in the CPFB reactor were circulated, providing higher crystallization efficiency. The diameter of the discharged pellets reached between 3⁻5 mm, and the fluidized area height of the CPFB reactor was 4 m. The performance parameters of the CFPB reactor were optimized.