Pyrolysis is an environmental friendly alternative method compared with incineration, and the least time-consuming and smallest infrastructure footprint method compared with bio-chemical and thermo-chemical conversion. Baseline data for the pyrolysis of food waste was obtained in a kinetic study of the thermal decompositions by thermogravimetric analysis. To simulate the difference in the types of food waste, the study was done using model compounds, such as cereals, meat, vegetable, and mixed food waste; the pyrolysis commenced at 150 °C for most food waste and the process terminated at 450 °C to 500 °C. Between one and three peaks were observed on a differential thermogravimetry (DTG) graph, depending on the type of waste being pyrolyzed, reflecting the difference in the time required for pyrolysis of different components of food waste to take place. Depending on the composition of each food, one or four peaks were found, and the pyrolysis patterns of carbohydrate, protein, fat, and cellulose were found. Activation energies and frequency factors were calculated from the rates of conversion, using differential equation analyses. The activation energy increased from 10 kJ/mol to 50 kJ/mol as conversions increased from the 10% to 90%, regardless of the food waste type. The activation energy was measured as 50 kJ/mol, with a slight variation among the type of the food waste. Due to the activation energy being low, food waste consists of carbohydrates and other substances rather than cellulose, hemicellulose, and lignin.

Biochar is the product of the pyrolysis of organic materials in a reduced state. In recent years, biochar has received attention due to its applicability to organic waste management, thereby leading to active research on biochar. However, there have been few studies using food waste. In particular, the most significant difference between food waste and other organic waste is the high salinity of food waste. Therefore, in this paper, we compare the chemical characteristics of biochar produced using food waste containing low- and high-concentration salt and biochar flushed with water to remove the concentrated salt. In addition, we clarify the salt component behavior of biochar. Peak analysis of XRD confirms that it is difficult to find salt crystals in flushed char since salt remains in the form of crystals when salty food waste is pyrolyzed washed away after water flushing. In addition, the Cl content significantly decreased to 1–2% after flushing, similar to that of Cl content in the standard, non-salted food waste char. On the other hand, a significant amount of Na was found in pyrolyzed char even after flushing resulting from a phenomenon in which salt is dissolved in water while flushing and Na ions are adsorbed. FT-IR analysis showed that salt in waste affects the binding of aromatic carbons to compounds in the pyrolysis process. The NMR spectroscopy demonstrated that the aromatic carbon content, which indicates the stability of biochar, is not influenced by the salt content and increases with increasing pyrolysis temperature.

This study investigated the possibility of applying pyrolysis as an alternative method to recycle powdered activated carbon-containing water treatment residuals (PAC-WTRs) discharged from the Cheongju water treatment plant as a multifunctional adsorbent. WTRs pyrolyzed for 1 h at 200-700 °C were compared with raw material. The carbon content of the PAC-WTR reaches 19.27%, with about 25% Al and 17% Si. Changes in PAC through pyrolysis imparted new adsorbent properties to WTR. As the pyrolysis temperature increased, the purity of PAC increased, and pores were regenerated to recover the Brunauer-Emmett-Teller (BET) from 6.5 m2 g-1 to 131.8 m2 g-1. In addition, the basicity increased as the carboxylic and phenolic groups on the carbon surface were decomposed, which increased the cation (methylene blue) adsorption capacity and reduced heavy metal leaching. As the coagulant regenerated with increasing pyrolysis temperature, the amount of aluminum leached and phosphate removal efficiency were increased. In the case of simultaneous removal of cations (MB+) and anions (PO43-), the removal efficiency was higher than that for single adsorption without competition through multi-layer adsorption by Al complex and PAC complex. Therefore, the pyrolyzed PAC-WTR is capable of adsorbing and removing anions and cations simultaneously without the peril of substance leaching. The regenerated WTRs containing PAC is expected to be utilized as a multi-functional remediation material for wastewater containing various pollutants.

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.

We developed a lab-scale aerobic–methane oxidation bioreactor (MOB)–anoxic system, combining a MOB and the aerobic–anoxic denitrification process, and evaluated its potential for advanced nitrogen treatment in wastewater treatment plants (WWTPs). The MOB used biogas generated from a WWTP and secondary-treated wastewater to support mixed methanotroph cultures, which mediated the simultaneous direct denitrification by methanotrophs and methanol production necessary for denitrifying bacteria in the anoxic chamber for denitrification. Compared to the aerobic–anoxic process, the aerobic–MOB–anoxic system with an influent concentration of 4.8 L·day⁻¹ showed a marked increase in the reduction efficiency for total nitrogen (41.9% vs. 85.9%) and PO₄⁻³-P (41.1% vs. 69.5%). However, the integrated actions of high nitrogen and phosphorus consumption are required for methanotroph growth, as well as the production and supply of methanol as a carbon source for denitrification and methane monooxygenase-mediated oxidation of NH₃ into N₂O by methanotrophs. After three months of continuous operation using actual wastewater, the total nitrogen removal rate was 76.3%, equivalent to the rate observed in a tertiary-advanced WWTP, while the total phosphorus removal rate reached 83.7%.