Multicatalytic properties of nanoparticle CaO2 synthesized by a novel, simple and economical method for wastewater treatment

Effect of thermal-calcium peroxide mediated exopolymer release on disperser pre-treatment for efficient anaerobic digestion

The present study aimed to improve the hydrolysis potential of paper mill sludge through a two-phase disintegration process. In Particular, attention was focused on removal of extracellular polymeric substance (EPS) i.e. deflocculation of sludge in order to improve the efficiency of subsequent disperser disintegration. During deflocculation, carbohydrate, protein and deoxyribonucleic acids (DNA) were used as assessment parameters. During disintegration, soluble chemical oxygen demand (SCOD) and suspended solids (SS) reduction were used as assessment index to evaluate the efficiency of disintegration. A greater EPS removal was attained while deflocculating the sludge at calcium peroxide dosage of 0.05 g/g suspended solids (SS) and at a temperature of 70 °C. When comparing the disintegrated samples, a clear variation was noted in deflocculated and disintegrated sludge (19.2%) than the disintegrated sludge alone (13.5%). This clearly shows the need for deflocculation prior to disintegration. Likewise, a higher biomethane production of 0.214 L/g COD was achieved in deflocculated and disintegrated sludge than the pretreated sludge alone. Deflocculation reduces sludge management cost from 170 USD (Disperser alone (D alone disintegration)) to 51 USD (Thermal calcium peroxide mediated-Disperser (TCaO2-D disintegration), indicating the efficiency of the proposed disintegration.

Damage mechanism of calcium peroxide on Microcystis aeruginosa PCC7806 and its potential application

Calcium peroxide (CP) is an oxidizing agent that can gradually release hydrogen peroxide (HP) to achieve selective killing of cyanobacteria in water blooms, and reduce the phosphorus content in the water column. Despite the potential of CP for use in cyanobacterial water bloom disposal, there is a lack of research on the mechanism of oxidative damage on cyanobacterial cells by calcium peroxide. Further studies are required to comprehend the underlying scientific principles and potential risks and benefits of applying this approach to cyanobacteria disposal. In this investigation, we employed varying doses of CP for the treatment of Microcystis aeruginosa (M. aeruginosa), which resulted in the following findings: (1) the HP released from CP can damage the photosystem II of M. aeruginosa, reduce cell photosynthetic pigment content, intensify the degree of membrane lipid peroxidation, and increase the extracellular protein content; (2) CP significantly increased the soluble extracellular polysaccharide (sEPS) and bound extracellular polysaccharide (bEPS) content of cells (p < 0.05), causing the cells to exist as agglomerates and effectively allowing them to flocculate and precipitate, reducing the turbidity of the water body; (3) The increased dose elevated the pH and calcium ions significantly decreased the orthophosphate content, resulting in an increase in extracellular alkaline phosphatase activity, but possibly increasing the total extracellular nitrogen content. These results suggested that CP is an effective chemical algaecide for cyanobacteria, and has the potential to be applied to dispose of cyanobacterial blooms while reducing the phosphorus content of the water column and further inhibiting the growth and proliferation of cells.

Natural and biocompatible dressing unit based on tea carbon dots modified core-shell electrospun fiber for diabetic wound disinfection and healing

Wound infection and healing in patients with diabetes is one of the complex problems in trauma treatment. Therefore, designing and preparing an advanced dressing membrane for treating the wounds of such patients is essential. In this study, a zein film with biological tea carbon dots (TCDs) and calcium peroxide (CaO₂) as the main components for promoting diabetic wound healing was prepared by an electrospinning technique, which combines the advantages of natural degradability and biosafety. CaO₂ is a biocompatible material with a microsphere structure that reacts with water to release hydrogen peroxide and calcium ions. TCDs with a small diameter were doped in the membrane to mitigate its properties while improving the antibacterial and healing effects of the membrane. TCDs/CaO₂ was mixed with ethyl cellulose-modified zein (ZE) to prepare the dressing membrane. The antibacterial properties, biocompatibility and wound-healing properties of the composite membrane were investigated by antibacterial experiment, cell experiment and a full-thickness skin defect. TCDs/CaO₂ @ZE exhibited significant anti-inflammatory and wound healing-promoting properties in diabetic rats, without any cytotoxicity. This study is meaningful in developing a natural and biocompatible dressing membrane for diabetic wound healing, which shows a promising application in wound disinfection and recovery in patients with chronic diseases.

Sunlight-mediated CaO2 inactivation of pathogen indicator organisms in surface water system: Roles of reactive species, characterization of pathogen inactivation

In the era of the current epidemic, it is urgent to control pathogens in sewage, eliminate the source of infection, and optimize the technology for killing pathogens. Combining calcium peroxide (CaO₂) with sunlight is considered a potentially efficient, economical, and eco-friendly method for pathogen-contaminated water remediation. This paper evaluated the solar activating properties of CaO₂ for inactivating pathogenic indicators and explored the roles of reactive species contributing to pathogen inactivation. Moreover, these reactive species' average steady-state concentrations and second-order reaction rate were tentatively explored, and mechanistic model for photoinactivation were establishment. Pathogen's inactivation was mainly attributed to direct photoinactivation (13∼50%) and exogenous indirect mechanisms with corresponding contributions of reactive species, i.e., OH^- (14∼23%), ¹O₂ (12∼28%), •OH (20∼32%), O₂^•- (12∼16%), and H₂O₂ (6∼11%). Furthermore, cell membrane rupture and DNA damage were observed by transmission electron microscopy (TEM) and agarose gel electrophoresis (AGE) experiments. Among experiments on common aqueous constituents influencing photoinactivation, copper and iron ions were found to promote a pathogen-inactivating ability of the system, while fulvic acids (FA) and humic acid (HA) had the opposite effect. This study revealed the potential of CaO₂/sunlight to inactivate pathogens and laid a foundation for its application in inactivating pathogens in surface water.

A Self-Reinforcing Nanoplatform for Highly Effective Synergistic Targeted Combinatary Calcium-Overload and Photodynamic Therapy of Cancer

While calcium-overload-mediated therapy (COMT) is a promising but largely untapped therapeutic strategy, combinatory therapy greatly boosts treatment outcomes with integrated merits of different therapies. Herein, a BPQD@CaO₂ -PEG-GPC3Ab nanoplatform is formulated by integrating calcium peroxide (CaO₂ ) and black phosphorus quantum dot (BPQD, photosensitizer) with active-targeting glypican-3 antibody (GPC3Ab), for combinatory photodynamic therapy (PDT) and COMT in response to acidic pH and near-infrared (NIR) light, wherein CaO₂ serves as the reservoir of calcium ions (Ca²⁺ ) and hydrogen peroxide (H₂ O₂ ). Navigated by GPC3Ab to tumor cells at acidic pH, the nanoparticle disassembles to CaO₂ and BPQD; CaO₂ produces COMT Ca²⁺ and H₂ O₂ , while H₂ O₂ makes oxygen (O₂ ) to promote PDT; under NIR irradiation BPQD facilitates not only the conversion of O₂ to singlet oxygen (¹ O₂ ) for PDT, but also moderate hyperthermia to accelerate NP dissociation to CaO₂ and BPQD, and conversions of CaO₂ to Ca²⁺ and H₂ O₂ , and H₂ O₂ to O₂ , to enhance both COMT and PDT. After supplementary ionomycin treatment to induce intracellular Ca²⁺ bursts, the multimodal therapeutics strikingly induce hepatocellular carcinoma apoptosis, likely through the activation of the calpains and caspases 12, 9, and 3, up-regulation of Bax and down-regulation of Bcl-2 proteins. This nanoplatform enables a mutually-amplifying and self-reinforcing synergistic therapy.

Enhanced biohydrogen generation through calcium peroxide engendered efficient ultrasonic disintegration of waste activated sludge in low temperature environment

Waste activated sludge is a renewable source for biohydrogen production, whereas the presence of complex biopolymers limits the hydrolysis step during this process, and thus pretreatment is required to disintegrate the sludge biomass. In this study, the feasibility of utilizing waste activated sludge to produce biohydrogen by improving the solubilization by means of thermo CaO₂ engendered sonication disintegration (TCP-US) was studied. The optimized condition for extracellular polymeric substance (EPS) dissociation was obtained at the CaO₂ dosage of 0.05 g/g SS at 70 °C. The maximum disintegration after EPS removal was achieved at the sonic specific energy input of 1612.8 kJ/kg TS with the maximum solubilization and SS reduction of 23.7% and 18.14%, respectively, which was higher than the US alone pretreatment. Thus, this solubilization yields higher biohydrogen production of 114.3 mLH₂/gCOD in TCP-US sample.

Jamil SNA, Li F, Mat Azmi ID, Chiang PC, Choong TSY. Synthesis of Controlled-Release Calcium Peroxide Nanoparticles Coated with Dextran for Removal of Doxycycline from Aqueous System

Nanoscale calcium peroxide (nCP) has turned out to be one of the effective and environmentally friendly approaches for wastewater remediation purposes. The rapid hydrolysis of nCPs and burst oxygen release caused by the high surface-to-volume ratio of nCPs could surpass the appropriate demand for oxygenation and pollutant degradation in the aqueous system. Thus, coated oxidants (COs) have been prepared using polymeric materials to ensure long-term efficacy and slow-release capability. Therefore, the nCPs were first prepared using dextran as a stabilizer to prevent irreversible agglomeration by the chemical precipitation method and had an average mean size of 2.33 ± 0.81 nm. The synthesized nCPs were then coated with dextran to produce dextran-coated nCPs. Their characteristics and effectiveness in doxycycline (DOX) degradation were assessed. The characterization of nCPs and dextran-coated nCPs was performed using X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), fourier transform infrared spectroscopy (FTIR), Brunauer, Emmett and Teller analysis (BET), dynamic light scattering (DLS) and thermogravimetric analysis (TGA) techniques. This work suggests that dextran-coated nCPs are beneficial in wastewater treatment practice in terms of the long-term efficacy of DOX degradation potential.

Calcium peroxide pre-treatment improved the anaerobic digestion of primary sludge and its co-digestion with waste activated sludge

Primary sludge (PS) and Waste activated sludge (WAS) as two main sludge streams in wastewater treatment plants are commonly anaerobically co-digested, which though may be differently affected by pretreatment. Previous work has found that calcium peroxide (CaO₂) pretreatment effectively enhanced anaerobic digestion of WAS. However, the feasibilities of this strategy on PS anaerobic digestion and co-digestion of WAS and PS are still unclear. Herein, this work provided new insights into these systems. Biomethane potential test demonstrated that CaO₂ pretreatment at 0.02-0.26 g/g-volatile suspended solids (VSS) promoted anaerobic digestion of PS. Then the feasibility of CaO₂ pretreatment for improving anaerobic co-digestion of PS and WAS mixture was confirmed, with the highest improvement in methane production, VSS destruction and sludge reduction being approximately 37.4%, 38.9% and 19.9%, achieved at 0.14 g/g-VSS of CaO₂. Process modelling analysis revealed that CaO₂ pretreatment increased both degradable faction and actually degraded fraction in sludge mixture. The changes of sludge characteristics via pretreatment and key enzyme activity in sludge anaerobic co-digestion system demonstrated that increased CaO₂ concentration resulted in increased soluble organics release from sludge mixture in the pretreatment stage and inhibited activity of coenzyme F₄₂₀ responsible for methanogenesis. Further mechanism investigation disclosed that OH^-, O₂^- and OH were main contribution factors, and the order of their contributions were OH^- >O₂^- >OH. This work laid the theoretical foundation and provided guidance for the practical application of CaO₂ pre-treatment technology.

Enhancing the decomposition of extracellular polymeric substances and the recovery of short-chain fatty acids from waste activated sludge: Analysis of the performance and mechanism of co-treatment by free nitrous acid and calcium peroxide

At present, the bioproduction of short-chain fatty acids (SCFAs) from waste activated sludge (WAS) has attracted worldwide attention due to the demand of carbon neutrality during waste treatment. Calcium peroxide (CaO₂) has been reported to be an effective method for the solubilization of WAS and the accumulation of SCFAs, but the high reagent cost limits its industrial application. Therefore, free nitrous acid (FNA) was introduced into the WAS pretreatment system to assist with CaO₂ for enhancing the disruption of extracellular polymeric substances (EPS) and the subsequent acidogenesis process. The results showed that FNA and CaO₂ synergistically enhanced EPS decomposition and the release of biodegradable organic compounds during pretreatment. The highest soluble chemical oxygen demand (3.1- and 2.6-fold higher compared to individual pretreatments at the same concentrations) after pretreatment and the highest SCFAs accumulation (2.0- and 6.4-fold compared to individual pretreatments at the same concentrations) after a 2-day fermentation period was observed in the FNA + CaO₂ (0.15 g/g VSS) co-treated group. Therefore, the FNA + CaO₂ (0.15 g/g VSS) co-treatment was determined to be the optimal strategy for ensuring the disintegration of the EPS matrix and enhancing the accumulation of SCFAs in pretreated sludge during anaerobic digestion.

Enhanced nitrogen removal upon the addition of volatile fatty acids from activated sludge by combining calcium peroxide and low-thermal pretreatments

This study investigated a combined low-thermal and CaO₂ pretreatment to enhance the volatile fatty acid (VFA) production from waste activated sludge (WAS). The fermentative product was added to a sequencing batch reactor (SBR) as an external carbon source to enhance nitrogen removal. The results showed that the combined pretreatment improved WAS solubilization, releasing more biodegradable substrates, such as proteins and polysaccharides, from TB-EPS to LB-EPS and S-EPS. The maximum VFA production of 3529 ± 188 mg COD/L was obtained in the combined pretreatment (0.2 g CaO₂/g VS + 70 °C for 60 min), which was 2.1 and 1.4-fold of that obtained from the sole low-thermal pretreatment and the control test, respectively. Consequently, when the fermentative liquid was added as an external denitrification carbon source, the effluent total nitrogen decreased to Class A of the discharge standard for pollutants in rural wastewater treatment plants in most areas of China.

Degradation of diclofenac sodium using Fenton-like technology based on nano-calcium peroxide

A nano-calcium peroxide (nCaO₂) powder with a purity of 89.1% was prepared using an improved traditional method. Then, the as-prepared nCaO₂ was used as the source of hydrogen peroxide (H₂O₂) for the Fenton-like degradation of diclofenac sodium (DCF). The results showed that nCaO₂ performed better for DCF removal when compared to nCaO₂ prepared by a conventional method and commercial calcium peroxide (CaO₂). Further experimental results indicated that 97.5% of DCF could be removed in 180 min at a nCaO₂/Fe²⁺-EDTA/DCF molar ratio of 16/8-8/1, which was more efficient than in the H₂O₂/EDTA-Fe²⁺/DCF and nCaO₂/Fe²⁺/DCF systems. The best removal rate of DCF was at pH 6.0, unlike previous claims that stated that the lower the pH in the buffer system, the better the degradation of DCF. In addition, the influence of water quality parameters, such as Cl^-, NO₃^-, SO₄^2-, HCO₃^-, and humic acid (HA), on DCF removal were evaluated. A free radical masking experiment revealed the existence of hydroxyl radical (OH), superoxide radical (O₂^-) and singlet oxygen (¹O₂), and indicated that the degradation of DCF was mainly due to oxidation caused by OH. Electron paramagnetic resonance (EPR) studies for different systems and different active oxygen species were carried out, and it was further confirmed that OH radicals have high intensity in the Fenton-like system based on nCaO₂. EPR results also showed that the addition of EDTA can promote the production of OH. According to the identification of the dominant reactive species and GC-MS, the possible theoretical DCF degradation pathways were proposed.

The underlying mechanism of calcium peroxide pretreatment enhancing methane production from anaerobic digestion of waste activated sludge

Recent investigations verified that calcium peroxide (CaO₂) could be used to pretreat waste activated sludge to promote methane yield from anaerobic digestion. However, the underlying mechanism of how CaO₂ pretreatment promotes methane production is unclear. This work therefore aims to provide insights into such systems. Experimental results showed that with an increase of CaO₂ dosage from 0 to 0.14 g/g VSS (volatile suspended solids) the methane yield increased linearly from 146.3 to 215.9 mL/g VSS. Further increases of CaO₂ resulted in decreases in methane yield. CaO₂ pretreatment promoted the disintegration of sludge and the degradation of sludge recalcitrant organics (especially humus and lignocellulose), thereby providing more substrates for subsequent methane production. Ultraviolet absorption spectroscopy indicated that CaO₂ enhanced the cleavage of unsaturated conjugated bonds and reduced the aromaticity of humus and lignocellulose. Fourier transform infrared spectroscopy showed that CaO₂ changed the structures and functional groups of humus and lignocellulose, making them transform to be biodegradable. GC/MS analyses exhibited that the degradation products of humus and lignocellulose included several types of small molecular organics such as ester-like, acid-like, and alcohol-like substances. Further investigation demonstrated that substantial methane could be produced from these degradation products. It was also found that the presence of recalcitrant organics was detrimental to anaerobes relevant to anaerobic digestion, and the degradation of such recalcitrant organics mitigated their inhibitions to the anaerobes. Model-based analysis suggested that CaO₂ pretreatment increased the maximum methane yield and methane production rate, which were consistent with the analysis above.

Highly pure MgO2 nanoparticles as robust solid oxidant for enhanced Fenton-like degradation of organic contaminants

In typical Fenton/Fenton-like reactions, H₂O₂ was usually used as an oxidant to degrade organic contaminants. However, liquid H₂O₂ is unstable, easy to decompose and has high biological toxicity especially at high concentration. Herein, highly pure magnesium peroxide (MgO₂) nanoparticles were first synthesized and used instead of H₂O₂ to degrade organic dyes. The structure and morphology of as-prepared products were confirmed by XRD, SEM, TEM and FTIR techniques. The active oxygen content of MgO₂ nanoparticles reached up to 26.93 wt%, suggesting a high purity of the as-prepared sample. The degradation performance of MgO₂ nanoparticles towards organic contaminants was systematically investigated in the terms of the molar ratio of Fe³⁺ to MgO₂, the dosage of MgO₂, initial solution pH and different organic dyes. The results indicated the as-prepared MgO₂ exhibited excellent degradation ability to various types of organic dyes. 10 mg of MgO₂ nanoparticles could almost completely degrade 200 mL of 20 mg/L methylene blue (MB) in 30 min with a TOC removal rate of 70.2%. The efficient degradation performance was ascribed to the generation of hydroxyl radicals in the MgO₂/Fe³⁺ system. The pathways of MB degradation were also proposed based on the determination of the reaction intermediates.

Synthesis and characterization of stabilized oxygen-releasing CaO2 nanoparticles for bioremediation

Bioremediation is one of the general methods to treat pollutants in soil, sediment, and groundwater. However, the low concentration and restricted dispersion of dissolved oxygen (DO) in these areas have limited the efficiency of remediation especially for microorganisms that require oxygen to grow. Calcium peroxide (CaO₂) is one of the oxygen-releasing compounds and has been applied to magnify the remediation efficacy of polluting areas. In this study, CaO₂ nanoparticles (NPs) were synthesized and evaluated by wet chemistry methods as well as dry and wet grinding processes. The characteristics of CaO₂ particles and NPs were analyzed and compared by dynamic light scattering, transmission electron microscopy, scanning electron microscopy, and X-ray powder diffraction. Our results showed that wet-grinded CaO₂ NPs had an average particle size of around 110 nm and were more stable compared to other particles from aggregation and sedimentation tests. In addition, we also observed that CaO₂ NPs had better DO characteristics and patterns; these NPs generated higher DO levels than their non-grinded form. Accordingly, our results suggested that wet-grinding CaO₂ particles to nanoscale could benefit their usage in bioremediation.

Controlled chemical synthesis of CaO2 particles coated with polyethylene glycol: characterization of crystallite size and oxygen release kinetics

The oxygen release pattern of CaO₂ nanoparticles was biphasic: an initial burst phase for the first 24 hours followed by a descending release rate for three days. The oxygen release rate in the second phase mainly depended on the shrinking-core model for CaO₂ hydrolysis.

Application of calcium peroxide in water and soil treatment: A review

Calcium peroxide (CP) has been progressively applied in terms of environmental protection due to its certain physical and chemical properties. This review focuses on the latest progresses in the applications of CP in water and soil treatment, including wastewater treatment, surface water restoration and groundwater and soil remediation. The stability of CP makes it an effective solid phase to supply H₂O₂ and O₂ for aerobic biodegradation and chemical degradation of contaminants in water and soil. CP has exerted great performance in the removal of dyes, chlorinated hydrocarbons, petroleum hydrocarbons, pesticides, heavy metals and various other contaminants. The research progress in the encapsulation technologies of CP with other materials and the preparation of CP nanoparticles were also presented in this review. Based on the summarized research progresses, the perspective of CP application in the future was proposed.