Chemical Characteristics and NaCl Component Behavior of Biochar Derived from the Salty Food Waste by Water Flushing

Efficient removal of Cd(II) and Pb(II) from aqueous solution using biochars derived from food waste

Massive amount of food waste has been generated annually, posing a threat to ecological sustainability and the social economy due to current disposal methods. Urgent action is needed worldwide to convert the traditional pathway for treating food waste into a sustainable bioeconomy, as this will significantly benefit food chain management. This study explores the use of pyrolysis to produce different types of food waste biochars and investigates their adsorption capabilities for removing Cd2+ and Pb2+ in aqueous solution. The results indicated that co-pyrolysis biochar from fresh food waste and rice husk (FWRB) exhibited superior adsorption performance for Cd2+ (61.84 mg·g-1) and Pb2+ (245.52 mg·g-1), respectively. Pseudo-second-order kinetics (0.74 ≤ R2 ≤ 0.98) and Langmuir isotherms (0.87 ≤ R2 ≤ 0.98) indicated that the immobilized Cd2+ and Pb2+ on biochars were mainly attributed to the chemisorption, including precipitation with minerals (e.g., carbonates, silicates, and phosphate), complexation with functional groups (-OH), cation exchange (-COO-), and coordination with π-electrons. Furthermore, FWRB demonstrated reduced EC and Na content in comparison to food waste digestate biochar (FWDB) and food waste digestate co-pyrolysis with sawdust biochar (FWSB), with levels of Cd and Pb falling below China's current guideline thresholds. These findings suggested that co-pyrolysis of fresh food waste with rice husk could be applicable to the recycling of food waste into biochar products for heavy metal stabilization in contaminated water and soils.

Responses of aquatic vegetables to biochar amended soil and water environments: a critical review

Aquatic vegetables, including lotus root, water spinach, cress, watercress and so on, have been cultivated as commercial crops for a long time. Though aquatic vegetables have great edible and medicinal values, the increasing demands for aquatic vegetables with high quality have led to higher requirements of their soil and water environments. Unfortunately, the soil and water environment often face many problems such as nutrient imbalance, excessive fertilization, and pollution. Therefore, a new cost-effective and eco-friendly solution for addressing the above issues is urgently required. Biochars, one type of pyrolysis product obtained from agricultural and forestry waste, show great potential in reducing fertilizer application, upgrading soil quality and remediating pollution. Application of biochars in aquatic vegetable cultivation would not only improve the yield and quality, but also reduce its edible risk. Biochars can improve the soil micro-environment, soil microorganism and soil enzyme activities. Furthermore, biochars can remediate the heavy metal pollution, organic pollution and nitrogen and phosphorus non-point source pollution in the water and soil environments of aquatic vegetables, which promotes the state of cultivation conditions and thereby improves the yield and quality of aquatic vegetables. However, the harmful substances such as heavy metals, PAHs, etc. derived from biochars can cause environmental risks, which should be seriously considered. In this review, the application of biochars in aquatic vegetable cultivation is briefly summarized. The changes of soil physicochemical and biological properties, the effects of biochars in remediating water and soil environmental pollution and the impacts of biochars on the yield and quality of aquatic vegetables are also discussed. This review will provide a comprehensive overview of the research progress on the effects of biochars on soil and water environments for aquatic vegetable cultivation.

Slow pyrolysis of agro-food wastes and physicochemical characterization of biofuel products

Effective management and utilization of food waste and agricultural crop residues are highly crucial to mitigate the challenges of greenhouse gas generation upon natural decomposition and waste accumulation. Conversion of biogenic wastes to biofuels and bioproducts can address the energy crisis and promote environmental remediation. This study was focused on exploring the characteristics of food waste and agricultural crop residues (e.g., canola hull and oar hull) to determine their candidacy for slow pyrolysis to produce biochar and bio-oil. Process parameters of slow pyrolysis such as temperature, reaction time and heating rate were optimized to obtain maximum biochar yields. Maximum biochar yield of 28.4 wt% was recorded at optimized temperature, heating rate and reaction time of 600 °C, 5 °C/min and 60 min, respectively. Furthermore, the physicochemical, spectroscopic and microscopic characterization of biochar, bio-oil and gases were performed. The carbon content and thermal stability of biochar were found to increase at higher temperatures. Moreover, bio-oil generated at higher temperatures showed the presence of phenolics and aromatic compounds.

Effects of Metal Oxides on Carbonation and Coking of High-Salinity Organic Wastewater

Slag is difficult to treat quantitatively due to the formation of a molten mixture in the carbonization process of high-salinity organic wastewater. Thus, aiming at solving this difficulty, the effects of metal oxide additives, additive ratio, furnace burden ratio, and carbonization temperature on the carbonization and coking of high-salinity organic wastewater are systematically analyzed. The analysis is performed using scanning electron microscopy, X-ray diffraction, and Vickers hardness tests. The results show that all five metal oxide additives can reduce the hardness of carbonized products. The relative effect of reducing the coked hardness is as follows: MgO > CaO > kaolin > Fe₂O₃ > Al₂O₃. Thus, the effect of MgO on reducing the coking hardness is stronger than that of the other four metal oxides, reducing the hardness of carbonized products by approximately 81%. Furthermore, the adding charge can reduce the hardness index by at least 60%. When the carbonization temperature is higher than 800°C, the hardness index of the carbonized product decreases by approximately 5% each 50°C of increase in temperature. This study shows that the addition of metal oxides can effectively reduce the hardness of coking during the treatment of high-salt organic wastewater by carbonization and oxidation and provide theoretical support for the subsequent treatment of high-salt organic wastewater by carbonization and oxidation.

Characterization of Sewage Sludge and Food Waste-Based Biochar for Co-Firing in a Coal-Fired Power Plant: A Case Study in Korea

Biomass co-firing in coal-fired power plants has been widely accepted to reduce the environmental burden. In this study, food waste (FW) and sewage sludge (SS), which are the main types of municipal organic waste, were selected as solid refuse fuel (SRF). To compensate for the limitations of FW and SS, a mixture of FW and SS with varying ratios was processed using pyrolysis and desalination. The fuel properties such as the calorific value, chlorine content, alkali and alkaline earth metallic species (AAEMs) content, and heavy metal content were determined. The calorific values of all biochars were greater than 12.6 MJ/kg, which satisfies the national threshold of Bio-SRF in Korea. Chlorine and AAEMs contents exhibited clear trends for the FW ratio and pyrolysis temperature. Increasing concentrations of heavy metals were observed with increasing SS ratio and pyrolysis temperature. These results provide important insights into the practical application of municipal waste-based biochar in coal-fired plants, as well as the influence of mixing ratio and pyrolysis temperature.

Evaluation of biochar pyrolyzed from kitchen waste, corn straw, and peanut hulls on immobilization of Pb and Cd in contaminated soil

Biochar has a wide range of feedstocks, and different feedstocks often resulted in different properties, such as element distribution and heavy metal immobilization performance. In this work, batch experiments were conducted to assess the effectiveness of biochar pyrolyzed from kitchen waste (KWB), corn straw (CSB), and peanut hulls (PHB) on immobilization of Cd and Pb in contaminated soil by planting swamp cabbage (Ipomoea aquatica Forsk.) with a combination of toxicological and physiological tests. The results showed that biochar could all enhance the soil pH, and reduce extractable Pb and Cd in soil by 22.61%-71.01% (KWB), 18.54%-64.35% (CSB), and 3.28%-60.25% (PHB), respectively. The biochar led to a drop in Cd and Pb accumulation in roots, stems, and leaves by 45.43%-97.68%, 59.13%-96.64%, and 63.90%-99.28% at the dosage of 60.00 mg/kg, respectively. The root length and fresh weight of swamp cabbage were promoted, while superoxide dismutase (SOD) and peroxidase (POD) decreased after biochar treatment. The distribution of heavy metal fractions before and after biochar treatment indicated that biochar could transform Cd and Pb into a state of lower bioavailability, thus inhibiting Cd and Pb uptake by swamp cabbage. Biochar with different feedstocks could be ranked by the following order according to immobilization performance: KWB > CSB > PHB.

Recent advances on the sustainable approaches for conversion and reutilization of food wastes to valuable bioproducts

The increasing amounts of food wastage and accumulation generated per annum due to the growing human population worldwide often associated with environmental pollution issues and scarcity of natural resources. In view of this, science community has worked towards in finding sustainable approaches to replace the common practices for food waste management. The agricultural and food processing wastes rich in nutrients are often the attractive substrates for the bioconversion for valuable bioproducts such as industrial enzymes, biofuel and bioactive compounds. The sustainable approaches on the re-utilization of food wastes as the industrial substrates for production of valuable bioproducts has meet the goals of circular bioeconomy, results in the diversify applications and increasing market demands for the bioproducts. This review discusses the current practice and recent advances on reutilization of food waste for bioconversion of valuable bioproducts from agricultural and food processing wastes.

Biomass Chars: Elaboration, Characterization and Applications II

This Special Issue of Energies contains the successful invited submissions [...]

Influence of NaCl Concentration on Food-Waste Biochar Structure and Templating Effects

Food-waste-derived biochar structures obtained through pyrolysis and with different NaCl concentrations were investigated. Increased NaCl concentration in the samples inhibited cellulose and lignin decomposition, ultimately increasing the biochar yield by 2.7% for 20%-NaCl concentration. NaCl added in solution state exhibited templating effects, with maximum increases in the Brunauer–Emmett–Teller (BET) surface area and pore volume of 1.23 to 3.50 m2∙g−1 and 0.002 to 0.007 cm3∙g−1, respectively, after washing. Adding a high concentration (20%) of NaCl reduced the BET surface area. In contrast, the mean pore diameter increased owing to the increased NaCl clustering area. Increased NaCl clustering with increased added NaCl was shown to have positive effects on NaCl removal by washing. Furthermore, as the NaCl adhered to the KCl scattered in the food waste, a high NaCl concentration also had positive effects on KCl removal. This study reports on an investigation on the effects of varying NaCl concentrations injected in solution form on the structure of food-waste biochar during pyrolysis. The templating effect was considered using both added NaCl and NaCl already contained in the food waste, with implementation of a desalination process essential for food-waste treatment for recycling.