Hydrothermal carbonization improves the quality of biochar derived from livestock manure by removing inorganic matter

Microwave-assisted hydrothermal carbonization of rabbit manure

Hydrothermal carbonization (HTC) is an efficient process capable of treating organic waste without the need for a pre-drying step. Animal manure is among the waste that can be treated using HTC. Manure is a nutrient-rich waste produced in large quantities and contains pathogens; therefore, proper management is required. The use of microwave irradiation in HTC process is considered as a fast and efficient method to treat manure. Rabbit manure (RM) represents the main waste stream generated by rabbit farming activities. In this study microwave-assisted HTC of RM was performed and the effect of operating conditions on the characteristic of the products was evaluated. Hydrochars are produced by varying temperature (180 °C and 230 °C), residence time (30, 60 and 120 min) and solid-to-liquid (S/L) ratio (1/10 and 1/20). Moreover, the potential application in agriculture was evaluated. Results indicate that varying operation conditions have different effect on process products. Specifically, increasing treatment temperature from 180 °C to 230 °C leads to hydrochar yield reduction, while increasing severity of the treatment increases fixed carbon and total phosphorus content in the hydrochar. Thus, by applying the microwave-assisted HTC process in RM at 230 °C for 120 min and with an S/L ratio of 1/10, a hydrochar with an increased content of fixed carbon (17.5 %) and phosphorus (16.4 g/kg) was obtained. Subsequently, germination assays performed using the abovementioned hydrochar confirm a phytostimulatory effect at low application rates (5 %), while applying the HTC process water induces phytotoxicity, at all concentrations examined.

Synergetic construction of color and multifunction for sustainable lyocell fabric by Coptis chinensis and BTCA

In the context of escalating standards of living, the demand for healthy and multifunctional textiles is increasing. As a kind of cellulose macromolecular-based material, lyocell fiber has low carbon, is environmentally friendly, and demonstrates superb performance. The utilization of some Chinese herb dyes solves the pollution problem in the color and functionality construction of lyocell fabric by synthetic dyes and finishing agents. However, problems such as low dye utilization rate, light apparent color, and weak functionality of dyed fabrics remain, thus limiting the further application of the powerful combination of lyocell fabric and Chinese herb dyes. Here, a color and multifunction construction method of lyocell fabric with Coptis chinensis and 1,2,3,4-butanetetracarboxylic acid was proposed. Under the optimal color construction condition, the color depth increased remarkably, and the dye exhaustion rate of the modified fabric enhanced by 332.3 % compared with the unmodified one. The multifunction construction imparted outstanding fuzz and pilling inhibition, fibrillation resistance, and antiwrinkle performance for lyocell fabrics. Moreover, the dyed lyocell fabric exhibited considerable UV protective activity and antibacterial property against Staphylococcus aureus. This work provided an efficient color and multifunction construction technology for lyocell fabric with high value added.

Comprehensive assessment of cow manure hydrothermal treatment products for land application and energy recovery

In this study, cow manure was hydrothermally treated in a 2-litre reactor for 1 h at temperatures between 100 °C and 260 °C. Both the raw manure and the solid and liquid products of the hydrothermal treatment were characterized to understand the fate of the inorganic elements and to assess the suitability of the products for land applications and energy recovery. Satisfactory elemental balances were obtained for the organic and most inorganic elements and indicated that most inorganic elements were incorporated into the solids with lower solubility, with the exception of potassium and sodium, which were mostly solubilized in the process water; calcium and chlorine were also solubilized to a lesser extent in the process water. Elemental composition and surface functional groups showed that hydrochar produced within the hydrothermal carbonization range (180-260 °C) seemed better suited for utilization as a soil amendment than raw cow manure. The potential for energy recovery lies in the anaerobic digestion of the process water, from which higher methane yields can be obtained than from raw cow manure. Lower temperatures in hydrothermal carbonization are considered a compromise for the safe land applications of cow manure, energy recovery from the process water, and enhanced dewaterability. These findings can help to eliminate bottlenecks in the upscaling of cow manure hydrothermal treatment and promote the circular bio-economy.

Effects of biogas slurry on hydrothermal carbonization of digestate: Synergistic valorization of hydrochars and aqueous phase

In this study, livestock manure digestate (LMD) was used as feedstock for hydrothermal carbonization (HTC) at different temperature (180-260 °C) and residence time (0-4 h). Nutrient flow and distribution during the HTC process were evaluated by comparing the effects of livestock manure biogas slurry (LBS) and ultrapure water (UW) to determine the optimal reaction conditions for the synergistic production and application of hydrochars (HC) and aqueous phases (AP). Compared with UW, the HC yields derived from LBS as solvent were increased by 27.05-38.24% under the same conditions. The C content, high heating value (HHV), and energy densification of HC obtained from LMD and UW were higher than those obtained from LMD and LBS, and the ash content was lower. While, LBS circumstance improved the porosity, N content and some trace elements e.g. Ca, Fe and Mg in HC that showed excellent fertility potential. In addition, the recovery rate of K, TOC, NH4+-N, and TN concentrations in AP were significantly higher in the LBS circumstance than in UW. The results show that the addition of UW is more favorable for fuel generation, and the HC obtained from LMD and UW at 220 °C has the potential to be used as a fuel. Whereas, the addition of LBS enhanced the potential of HC and AP for agricultural applications simultaneously. It is recommended to use HC and AP obtained from LMD and LBS at 240 °C for using as fertilizer.

A novel method for production of nitrogen fertilizer with low energy consumption by efficiently adsorbing and separating waste ammonia

Recovering waste NH3 to be used as a source of nitrogen fertilizer or liquid fuel has recently attracted much attention. Current methods mainly utilize activated carbon or metal-organic frameworks to capture NH3, but are limited due to low NH3 adsorption capacity and high cost, respectively. In this study, novel porous materials that are low cost and easy to synthesize were prepared as NH3 adsorbents by precipitation polymerization with acid optimization. The results showed that adsorption sites (‒COOH, -OH, and lactone) which form chemical adsorption or hydrogen bonds with NH3 were successfully regulated by response surface methods. Correspondingly, the dynamic NH3 adsorption capacity increased from 5.45 mg g-1 to 129 mg g-1, which is higher than most known activated carbon and metal-organic frameworks. Separation performance tests showed that NH3 could also be separated from CO2 and CH4. The findings in this study will advance the industrialization of NH3 polymer adsorbents and provide technical support for the recycling of waste NH3.

Persistent free radicals generated from a range of biochars and their physiological effects on wheat seedlings

Biochar is a promising soil conditioner and environmental remediation material. However, the amount, type, and environmental effect and risk of persistent free radicals (PFRs) associated with biochar need to be better understood. Thus, this study characterized PFRs in a range of biochar types and their effects on the growth and oxidative stress of wheat seedlings. Among the biochars prepared by pyrolysis of different types of biomass at 500 °C, the concentrations of PFRs in cow dung and egg shell biochar were the highest and the lowest, respectively. They both increased with artificial weathering treatment but decreased with aging. The dominant types of biochar PFRs were transformed from carbon-centered to oxygen and carbon/oxygen-centered free radicals with weathering. The amount and type of biochar PFRs in mixtures of biochar and soil varied with soil type and biochar dose. After 30 d incubation in different soil-biochar mixtures, measures of wheat plant germination and growth and antioxidant enzyme activity showed increases at lower biochar doses but decreases at higher doses. Catalase activity was 38.1 % greater at 20 g·kg-1 biochar dosage and 25.2 % less at 80 g·kg-1 dosage, on average. In contrast, leaf malondialdehyde content and staining by Evans Blue, both indicators of plant cell membrane damage, generally increased with increasing biochar dosages. Finally, soil hydrolase enzyme activity also displayed an inverted U-shaped dose response. The toxicity indicators showed an increasing trend with higher PFR concentrations in the soil-biochar combinations. While these findings provide evidence for significant potential agricultural and ecological risks associated with the application of biochar due to PFRs damage, it also points to ways that these risks could be mediated such as through biochar dosage restrictions and pre-aging. This study provides new insights into the potential toxicological mechanism and ecological risks associated with the application of biochar in agricultural and environmental settings.

New and effective cassava bagasse-modified biochar to adsorb Food Red 17 and Acid Blue 9 dyes in a binary mixture

A promissory technic for reducing environmental contaminants is the production of biochar from waste reuse and its application for water treatment. This study developed biochar (CWb) and NH4Cl-modified biochar (MCWb) using cassava residues as precursors. CWb and MCWb were characterized and evaluated in removing dyes (Acid Blue 9 and Food Red 17) in a binary system. The adsorbent demonstrated high adsorption capacity at all pH levels studied, showing its versatility regarding this process parameter. The equilibrium of all adsorption experiments was reached in 30 min. The adsorption process conformed to pseudo-first-order kinetics and extended Langmuir isotherm model. The thermodynamic adsorption experiments demonstrated that the adsorption process is physisorption, exhibiting exothermic and spontaneous characteristics. MCWb exhibited highly efficient and selective adsorption behavior towards the anionic dyes, indicating maximum adsorption capacity of 131 and 150 mg g-1 for Food Red 17 and Acid Blue 9, respectively. Besides, MCWb could be reused nine times, maintaining its original adsorption capacity. This study demonstrated an excellent adsorption capability of biochars in removing dyes. In addition, it indicated the recycling of wastes as a precursor of bio composts, a strategy for utilization in water treatment with binary systems. It showed the feasibility of the reuse capacity that indicated that the adsorbent may have many potential applications.

Hydrothermal carbonization of coking sludge: Formation mechanism and fuel characteristic of hydrochar

In this study, the chemical structures, fuel characteristic, and formation mechanism of hydrochar during hydrothermal carbonization (HTC) at 150-270 °C for 0-120 min were investigated using coking sludge (CS) as the feedstock. The results showed that the yield decreased from 96.86 to 60.98%, whereas the carbonization rate increased from 6.74 to 93.41% at 270 °C. More stable structures with aromatic and N-heterocycles rings were formed through hydrolysis and polymerization. The H/C and O/C ratio decreased from 1.75 to 0.60 to 1.04 and 0.09, and the combustion stability index (Hf) decreased from 0.86 to 0.60 °C.103, and the flammability index (S) increased from 24.16 to 26.42 %/(min2 °C3) 10-8, indicating an improvement of fuel performance. A kinetic model to describe the conversion of organic components of CS was developed to elucidate the formation mechanism of hydrochar combined with the change of water-soluble intermediates (SM). The solid-solid conversion reaction of protein and humus components was the predominant hydrochar formation pathway, with an activation energy (Ea) of 26.06 kJ/mol. The polymerization of aromatic compounds slightly participated in the hydrochar formation, with an Ea of 86.12 kJ/mol. The water-soluble intermediates mostly transformed into inorganic substances (IS) through decarboxylation, deamination, or decomposition reaction, with an Ea of 5.73 kJ/mol. This study provided insights for understanding the formation of hydrochar from CS through HTC, which is vital for controlling the polymerization of intermediates and solid-solid conversion to enhance the carbonization efficiency.

Emerging applications of biochar: A review on techno-environmental-economic aspects

Biomass fast pyrolysis produces bio-oil and biochar achieving circular economy. This review explored the emerging applications of biochar. Biochar possesses the unique properties for removing emerging contaminants and for mine remediation, owing to its negative charge surface, high specific surface area, large pore size distribution and surface functional groups. Additionally, biochar could adsorb impurities such as CO2, moisture, and H2S to upgrade the biogas. Customizing pyrolysis treatments, optimizing the feedstock and pyrolysis operating conditions enhance biochar production and improve its surface properties for the emerging applications. Life cycle assessment and techno-economic assessment indicated the benefits of replacing conventional activated carbon with biochar.

Multivariate and multi-interface insights into carbon and energy recovery and conversion characteristics of hydrothermal carbonization of biomass waste from duck farm

High lipid, high nitrogen duck manure (DM) with high lipid, high lignocellulosic litter materials (LM) are the main wet biomass wastes from duck farms and both are naturally abundant carbon resources. The synthesis of duck farming biomass waste into carbon-rich materials for high value utilization by hydrothermal carbonization (HTC), which can directly treat wet biomass, has not been investigated. In this study, the physicochemical properties of hydrochar derived from co-HTC of DM and LM and its carbon and energy recovery patterns were systematically investigated under multivariate conditions of raw materials ratios, solids contents, temperatures and residence times. The application of synchrotron-based near-edge X-ray adsorption fine structure technique (C K-edge NEXAFS) combined with gas chromatography-mass spectrometry (GC-MS) to the hydrochar and hydrothermal liquid, respectively. At multiple interfaces provided an in-depth analysis of the important material transformations of the co-HTC process and the structure of the hydrochar. Extending residence time (180 min) and increasing LM ratio (M@4%) in co-HTC reaction of DM and LM is beneficial to achieve hydrochar containing higher carbon content (44.84%) at lower reaction temperatures (180 °C). The heating value (HHV) of the hydrochar ranges between 17.12 and 25.05 MJ/kg. The carbon recovery rate of the co-HTC of DM and LM all exceeded 55% and was more closely related to the carbon content of the hydrochar than to its yield. Additionally, the model ERR=0.97±0.01CRR+2.40±0.71 (R2 = 0.99, P < 0.01) was developed to predict energy recovery rate (ERR) based on carbon recovery rate (CRR). Esters were an important intermediate during co-HTC of DM and LM, and the derived hydrochar consisted of a wide range of polycyclic aromatic hydrocarbons, alkanes and N-aromatic heterocycles as well as polyfuran, pyrrole and pyridine structures.

"One-can" strategy for the synthesis of hydrothermal biochar modified with phosphate groups and efficient removal of uranium(VI)

Significant selectivity, reasonable surface modification and increased structural porosity were three key factors to improve the competitiveness of biochar in the adsorption field. In this study, a hydrothermal bamboo-derived biochar modified with phosphate groups (HPBC) was synthesized using "one-can" strategy. BET showed that this method could effectively increase the specific surface area (137.32 m2 g-1) and simulation of wastewater experiments indicated HPBC had an excellent selectivity for U(VI) (70.35%), which was conducive to removal of U(VI) in real and complex environments. The accurate matchings of pseudo-second-order kinetic model, thermodynamic model and Langmuir isotherm showed that at 298 K, pH = 4.0, the adsorption process dominated by chemical complexation and monolayer adsorption was spontaneous, endothermic and disordered. Saturated adsorption capacity of HPBC could reach 781.02 mg g-1 within 2 h. The introduction of phosphoric acid and citric acid by "one-can" method not only provided abundant -PO4 to assist adsorption, but also activated oxygen-containing groups on the surface of the bamboo matrix. Results showed that adsorption mechanism of U(VI) by HPBC included electrostatic action and chemical complexation involving P-O, PO and ample oxygen-containing functional groups. Therefore, HPBC with high phosphorus content, outstanding adsorption performance, excellent regeneration, remarkable selectivity and green value provided a novel solution for the field of radioactive wastewater treatment.

Hydrothermal carbonization of cow dung with human urine as a solvent for hydrochar: An experimental and kinetic study

Hydrothermal carbonization (HTC) is the most cost-effective, environmentally friendly, and efficient physicochemical and biochemical process for converting biomass to products with added value. The objective and novelty of this work is to produce and investigate the qualities of hydrochar fuel (as a solid fuel) from cow manure using human urine as a solvent in order to find a suitable replacement for conventional fuel (i.e., coal). HTC based studies were conducted in batch, at three different reaction temperatures (180 °C, 200 °C, and 220 °C) and two different reaction periods (2 and 4 h). For kinetic analysis and reaction mechanism of the combustion behavior of the produced hydrochar, the model free kinetic methods and the z-master plot were used. From the model free kinetics methods, it was observed that the resultant optimum average activation energy and pre-exponential factor for the produced hydrochar at 180 °C and 2 h reaction period (HTC_180_2) were ∼120 kJ/mol and ∼5.59 × 10²⁵ sec^-1, respectively. In addition, the little variation between ΔE_α and ΔH_α (∼10 kJ/mol) suggests that the combustion of produced hydrochar (HTC_180_2) occurred with minimal energy use. Furthermore, the hydrochar exhibited its highest heating value at 200 °C for 4 h (HTC_200_4) which was 1.44 times higher than the raw dung (13.4 MJ/kg) due to the HTC process. The produced hydrochar demonstrated a significant improvement compared to the conventional solvent, i.e. water.