The pyrolysis of food waste has high economic potential and produces several value-added products, such as gas, bio-oil, and biochar. In South Korea, biochar production from food waste is prohibited, because dioxins are generated during combustion caused by the chloride ions arising from the high salt content. This study is the first to examine the water quality and the applicability of food waste-based biochar as solid refuse fuel (SRF) based on a demineralization process. The calorific value increased after demineralization due to the removal of ionic substances and the high carbon content. The chloride ion removal rate after demineralization increased with the increasing pyrolysis temperature. A proximate analysis of biochar indicated that the volatile matter decreased, while ash and fixed carbon increased, with increasing pyrolysis temperature. At 300 °C pyrolysis temperature, all domestic bio-SRF standards were met. The organic matter concentration in water decreased with increasing carbonization temperature, and the concentrations of soluble harmful substances, such as volatile organic compounds (VOCs), were within the standards or non-detectable. These results suggest that biochar can be efficiently generated from food waste while meeting the emission standards for chloride ions, dissolved VOCs, ash, and carbon.

This study used biogas from a wastewater treatment plant and bacterial community where methanotrophs, Methylophilus, and ammonia-oxidizing bacteria clusters coexisted to propose an effective method for biological carbon fixation and nitrogen removal in wastewater treatment for carbon capture, utilization, and storage (CCUS). Biogas from wastewater treatment plant was provided, instead of purified CH₄, to provide operation and maintenance conditions of bio-catalyst reaction for efficient biological carbon fixation by bacterial community using methane and CO₂. This study assessed the conditions to induce type X methanotrophs that can use CO₂ as a carbon source, as dominant species in the bacterial community and continuously and effectively supply reducing equivalents required for the conversion of CO₂ to methanol within the system. Herein, the results of inducing efficient co-existence of methanotrophs, Methylophilus, and ammonia-oxidizing bacteria cluster in the bacterial community were shown.

Biochars prepared from macro-algae have a lower C/N ratio compared to lignocellulosic biochar, which is advantageous for direct nutrition. In particular, Sargassum, a marine macro-algae, has a high Mg content; hence, it can be expected to adsorb P and N simultaneously. In this study, Sargassum horneri biochar (SB), pyrolyzed at 400, 500, and 600 °C, was doped with innate Mg through water leaching, and nutrient recovery from the wastewater-mimicking solution was confirmed. The biochar pyrolyzed at 600 °C showed maximum Mg adsorption during water leaching, and the efficiency of K and Na removal was also high, at 92.7% and 91.9%, respectively. The addition of MgCl₂ during pyrolysis and high ion exchange did not show distinct advantages for surface modification and nutrient adsorption. X-ray photoelectron spectroscopy analysis confirmed the participation of biochar in the surface adsorption of Mg and PO₄ recovery. The PO₄ sorption capacity of biochar reached >120 mg·g⁻¹, while the sorption capacity for NH₄ was low, at 22.8–28.2 mg·g⁻¹, suggesting that Mg-surface-doped SB presented excellent phosphorus recovery. Hence, upgrading an adsorbent as a wastewater-treatment material and soil ameliorant that recovers nutrients using innate Mg from Sargassum is possible through appropriate surface modification.

The efficiency of methane production by anaerobic digestion (AD), during which energy is generated from organic waste, can be increased in various ways. Recent research developments have increased the volume of gas production during AD using biochar. Previous studies have used food waste itself in AD, or, added wood-biochar or sewage sludge charcoal as an accelerant of the AD process. The application of food-waste biochar in AD using activated sludge has not yet been studied and is considered a potential method of utilizing food waste. Therefore, this study investigated the use of biochar prepared by the thermal decomposition of food waste as an additive to AD tanks to increase methane production. The addition of food-waste biochar at 1% of the digestion tank volume increased the production of digestion gas by approximately 10% and methane by 4%. We found that food-waste biochar served as a medium with trace elements that promoted the proliferation of microorganisms and increased the efficiency of AD.

Using reclaimed water has been increasing to manage water shortages arising due to climate change. Research has been conducted on reclaimed water production, but few studies have investigated the pipe network and supply of reclaimed water. Reclaimed water contains greater amounts of organic matter, nutrients, and ionic substances compared to tap water. Therefore, it is highly likely to cause problems, such as water pollution due to microbial propagation in pipes, and leakage due to pipe corrosion, which interfere with water supply system operations. This study investigated the residual chlorine decay characteristics of chlorine disinfectants applied to a control biofilm in reclaimed water pipe networks. The bulk decay coefficient was compared between reclaimed water and a humic acid solution, and the origin of organic matter was analyzed using fluorescence excitation-emission matrices. The experimental results show that residual chlorine was consumed because protein and amino acid-based organic matter reacted more rapidly with chlorine than natural organic matter, such as humic acid. Moreover, chlorine bulk decay occurred rapidly in reclaimed water when total organic carbon was 3 mg/L or higher. These results confirm that removing organic matter during reclaimed water treatment may affect the management of the pipe network system.

Ash-related issues from a considerable amount of alkali and alkaline earth metal species in biochar are major obstacles to the widespread application of biomass in thermoelectric plants. In this study, food wastes were converted into biochar through pyrolysis at 450 °C or 500 °C and four different demineralization approaches, using deionized water, citric acid, nitric acid, and CO₂ saturated water. The chemical properties of the resulting biochars were investigated, including proximate analysis, concentrations of inorganic species in biochar and ash, and the crystalline structure. All demineralization treatments produced food waste biochar with sufficient calorific value (>4000 kcal/kg) and a chlorine concentration <0.5%. Among the inorganic species in biochar, Na and K exhibited a significantly higher removal rate through demineralization, which ranged from 54.1%–85.6% and 53.6%–89.9%, respectively; the removal rates of Ca and Mg were lower than 50.0%. The demineralization method was more critical than the pyrolysis temperature in the removal of alkali and alkaline earth metals. Especially, the lower slagging and fouling tendency was expected for the biochar demineralized with citric acid. Our results suggested that food waste biochar pyrolyzed at 500 °C and demineralized with citric acid is a promising co-firing material for electric power generation in thermoelectric power plants.