Persulfate oxidation assisted hydrochar production from Platanus Orientalis Leaves: Physiochemical and combustion characteristics

Nitrogen distribution and evolution during persulfate assisted hydrothermal carbonization of spirulina

In this study, persulfate was used during hydrothermal processing of spirulina (160℃-220℃) for enhancement of nitrogen conversion. The nitrogen distribution in aqueous phase, hydrochar and biocrude-oil was evaluated, and the elemental composition and chemical forms of hydrochar were investigated. Results suggested that the addition of persulfate during hydrothermal processing of spirulina increased the atomic N/O of hydrochar for 1.2%-2.4%, whereas the NH₄⁺-N concentration in liquid phase increased by approximately 67-155 mg/L regardless of temperature, suggesting that the persulfate could facilitate the organic nitrogen degradation and protein deamination. The N1s XPS analysis indicated that the protein-N, pyrrole-N, and inorganic-N ratio in spirulina were decreased, while more pyridine-N in hydrochar was formed, suggesting that more stable N forms were generated. In addition, the elementary composition also showed that more N was formed on the surface of hydrochar instead of the core.

Conversion of cotton textile waste to clean solid fuel via surfactant-assisted hydrothermal carbonization: Mechanisms and combustion behaviors

The cotton textile was an abundant energy resource while was otherwise treated as waste. In this work, surfactants were used as catalysts in the hydrothermal carbonization (HTC) to transform cotton textile waste (CTW) into clean solid fuel. Furthermore, the conversion mechanisms of hydrothermal products during surfactant-assisted HTC were preliminarily proposed. The results showed that Span 80 and sodium dodecylbenzenesulfonate facilitated the transformation of CTW into bio-oil, while Tween 80 was more conducive to the development of pseudo-lignin, which endowed hydrochars higher energy density and updated the fuel quality and combustion behavior. Therefore, the research presented an effective method to convert CTW to clean solid fuel through the HTC treatment combining with surfactants.

Persulfate assisted hydrothermal processing of spirulina for enhanced deoxidation carbonization

The influence of persulfate assisted hydrothermal carbonization (HTC) (160 °C-220 °C) of spirulina and hydrochar properties was assessed. The elementary composition and proximate analysis of hydrochar were investigated on the carbonization degree and basic fuel properties, and the surface functional groups and morphological characteristics of hydrochar were analyzed as well as thermal stability. Results suggested that persulfate assisted process enhanced the carbonization degree of hydrochar by oxygen reduction (1.53%-2.74%) and increase of C ratio, and HHVs increased 0.81-1.39 MJ/kg at temperature above 180 °C. The -OH and CO on hydrochar surface were significantly reduced, and C-(C, H) and C-(O, N) were weakened by persulfate addition and more C-H peaks was formed. Additionally, the persulfate addition enhanced the thermal stability of hydrochar by lowing the maximum mass loss rate. The result suggested that HTC can be conducted with persulfate at lower temperature for hydrochar biofuel production.

Fe(II) activated persulfate assisted hydrothermal conversion of sewage sludge: Focusing on nitrogen transformation mechanism and removal effectiveness

In this study, Fe(II)-activated persulfate-assisted hydrothermal treatment (Fe(II)-PS-HT) was used to improve the efficiency of removing nitrogen (N) from the sewage sludge (SS) under relatively mild conditions (i.e., at 150 °C, for 20min), and the N transformation mechanism was investigated. The total N content in the solid residue was used to evaluate the N removal efficiency. Further, the redistribution of N in the solid and liquid products was characterized and quantified to obtain a N transformation mechanism during sequential persulfate oxidation (Fe(II) and persulfate) assisted hydrothermal treatment (HT). The experimental results denote that the N removal efficiency obtained from the Fe(II)-PS-HT (persulfate/C = 0.085 and Fe(II)/persulfate = 0.5) treated SS was increased by 35.0% at a relatively mild temperature (i.e., 150 °C) when compared with that obtained by treating SS using normal HT. Elevating Fe(II)/persulfate ratio to 1.25 promoting the N removal efficiency by 59.9%-65.9%. Furthermore, the electron paramagnetic resonance (EPR) and scanning electron microscopy (SEM) results clearly denote a N removal mechanism where the sulfate radicals (SO₄^∙-) produced by Fe(II)-PS destroy the sludge structure and destructed extracellular polymers (EPS). In the absence of EPS protection, proteins were directly exposed to extreme hydrothermal circumstances, and were rapidly transformed from the SS into the liquid residue. The free radicals also provided energy for the denitrification of Heterocycle-N. Consequently, a high N removal efficiency was obtained by Fe(II)-PS-HT with persulfate/C = 0.085 and Fe(II)/persulfate = 1.25 at 150 °C for 20 min.

Adsorption of methylene blue and Cd(II) onto maleylated modified hydrochar from water

A new carboxylate-functionalized hydrochar (CFHC) was successfully prepared by reaction of hydrochar with maleic anhydride under solvent-free conditions and followed by deprotonating carboxyl group of hydrochar with NaHCO₃ solution. CFHC was characterized using X-ray photoelectron spectroscopy (XPS), elemental analysis (EA), zeta potential, Brunauer-Emmett-Teller surface area (BET) and Fourier-transform infrared spectroscopy (FTIR), and its adsorption properties and mechanisms to methylene blue (MB) and Cd(II) were investigated using the batch method. The isotherm adsorption data were accorded with Langmuir model and the maximum uptakes were 1155.57 and 90.99 mg/g for MB and Cd(II) at the temperature of 303 K, respectively. The joint analysis of batch experiments and characterizations of hydrochar confirmed the π-π interaction was accompanied by electrostatic interaction and hydrogen bond for MB adsorption, while the surface complexation and ion exchange were predominant mechanisms for Cd(II) adsorption. Therefore, a highly effective adsorbent CFHC prepared by a simple and environmentally friendly solid-phase synthesis is a promising candidate for wastewater treatment.

Degradation of 4-nonylphenol in marine sediments by persulfate over magnetically modified biochars

In this study, an environmentally friendly and economically viable bamboo biochar (BB) was modified by Fe₃O₄ and was applied for the treatment of real river sediments containing the endocrine disruptor chemical (EDC) 4-nonylphenol (4-NP). The microporosity of Fe₃O₄-BB was clearly observed from the N₂ adsorption isotherms. The catalytic performance of Fe₃O₄-BB is highly dependent on pH and the catalyst dosage. The degradation efficiency of 4-NP (85%) was achieved at pH 3.0 using an initial dosage of 3.33 g L^-1 Fe₃O₄-BB and 2.3 × 10^-5 M persulfate (PS) in a biochar-sediment system. The kinetic behavior of 4-NP degradation with catalysis can be accounted by using the Langmuir-Hinshelwood type kinetic model. The MTT assay results indicated that Fe₃O₄-BB has a low potent cytotoxic effect and is therefore suitable for application in remediation of contaminated sediment.

ANN-Kriging hybrid model for predicting carbon and inorganic phosphorus recovery in hydrothermal carbonization

Modeling of hydrothermal carbonization (HTC) of poultry litter to high-value materials was conducted in order to understand the process and predict the influence of process parameters on product properties. Reaction temperature and time were considered as inputs, whereas carbon and inorganic phosphorous recovery were considered as responses in the model. Artificial neural network (ANN) model was used in order to correlate the process parameters to the outputs. The model was trained and validated using the data collected from HTC experiments carried out at temperatures between 150 ≤ T ≤ 300 °C, and residence time between 30 ≤ t ≤ 480 min. In order to improve the predictability of ANN, more theoretical data points were generated using Kriging approach based on the available measured data. Kriging interpolation improved the ANN model dramatically in training and validation phases, where the carbon recovery model fitting was improved by 0.94% and 9.2% in training and validation respectively, and the inorganic phosphorous (IP) recovery model fitting was improved by a staggering 16.4% and 19.6% in training and validation respectively. This improvement is also reflecting on the derived profiles of carbon and IP recovery in terms of the process parameters. The validated model was then used to understand the effect of process parameters on the response. It was revealed that temperature has more significant effect on the carbon and phosphorous recovery, while the effect of reaction time is more important at low reaction temperatures. The derived profiles shows a monotonic increase in IP recovery and a monotonic decrease in Carbon recovery at higher temperatures and time, this is due to multiple mechanism occurring simultaneously in the HTC reactor at various temperatures and times.