Construction and demolition waste as a high-efficiency advanced process for organic pollutant degradation in Fenton-like reaction to approach circular economy.

The Fenton-like reaction is a promising organic wastewater treatment reaction among advanced oxidation processes (AOP), which has emerged to replace the conventional Fenton reaction. Recycled construction and demolition waste (CDW), which is porous and rich in iron, manganese, and magnesium, can be reused as a Fenton-like catalyst. This study proposes an AOP wastewater treatment strategy using recycled porous CDW mixed with hydrogen peroxide (H2O2) to decompose methylene blue (MB) wastewater. According to the apparent first-order rate (Kapp) of 10 ppm MB adsorption, CDW-3, having the highest specific surface area, also has the highest Kapp of 0.23 min-1 g-1. The optimized conditions recommended by the Taguchi method include a 0.3 g mL-1 CDW-3 concentration, a 0.254 g mL-1 H2O2 concentration, and 10 ppm MB, resulting in an about 2.01 min-1Kapp value. In addition, MB concentration is observed as the most influential factor for Kapp, which decreases with increasing MB concentration and is about 0.62 min-1 at 1000 ppm MB. Repeating the Fenton-like reaction five times at 100 p.m. MB using the same CDW-3, the Kapp is about 0.64 min-1, which is 86% of the initial run. The synergistic effect index (ξ) is defined to quantify the level of interaction between CDW and H2O2, which produces free radicals during the Fenton-like process. The ξ of CDW-3 is about 2.16. Overall, it is demonstrated that CDW is a promising catalyst for Fenton-like reactions, and the synergistic effect index (ξ) can be used as a reference index to evaluate the catalytic generation of free radicals between the catalyst and H2O2.

Multi-objective operation optimization of spent coffee ground torrefaction for carbon-neutral biochar production.

Many energy-intensive processes are employed to enhance biomass fuel properties to overcome the difficulties in utilizing biomass as fuel. Therefore, energy conservation during these processes is crucial for realizing a circular bioeconomy. This study develops a newly devised method to evaluate SCG biochars' higher heating value (HHV) and predict moisture content from power consumption. It is found that the increasing rates of HHV immediately follow decreases in power consumption, which could be used to determine the pretreatment time for energy conservation. The non-dominated sorting genetic algorithm II (NSGA-II) maximizes SCG biochar's HHV while minimizing energy consumption. The results show that producing SCG biochar with 23.98 MJ∙kg-1 HHV requires 20.042 MJ∙kg-1, using a torrefaction temperature of 244 °C and torrefaction time of 27 min and 43 sec. Every kilogram of biochar with an energy yield of 85.93 % is estimated to cost NT$ 12.21.

Dual pretreatment of mixing H2O2 followed by torrefaction to upgrade spent coffee grounds for fuel production and upgrade level identification of H2O2 pretreatment.

Biochar is a carbon-neutral solid fuel and has emerged as a potential candidate to replace coal. Meanwhile, spent coffee grounds (SCGs) are an abundant and promising biomass waste that could be used for biochar production. This study develops a biochar valorization strategy by mixing SCGs with hydrogen peroxide (H2O2) at a weight ratio of 1:0.75 to upgrade SCG biochar. In this dual pretreatment method, the H2O2 oxidative ability at a pretreatment temperature of 105 °C contributes to an increase in the higher heating value (HHV) and carbon content of the SCG biochars. The HHV and carbon content of biochar increase by about 6.5% and 7.8%, respectively, when compared to the unpretreated one under the same conditions. Maximized biochar's HHV derived via the Taguchi method is 30.33 MJkg-1, a 46.9% increase compared to the raw SCG, and a 6.5% increase compared to the unpretreated SCG biochar. The H2O2 concentration is 18% for the maximized HHV. A quantitative identification index of intensity of difference (IOD) is adopted to evaluate the contributive level of H2O2 pretreatment in terms of the HHV and carbon content. IOD increases with increasing H2O2 pretreatment temperature. Before torrefaction, SCGs' IOD pretreated at 50 °C is 1.94%, while that pretreated at 105 °C is 8.06%. This is because, before torrefaction, H2O2 pretreatment sufficiently weakens SCGs' molecular structure, resulting in a higher IOD value. The IOD value of torrefied SCGs (TSCG) pretreated at 105 °C is 10.71%, accounting for a 4.59% increase compared to that pretreated at 50 °C. This implies that TSCG pretreated by H2O2 at 105 °C has better thermal stability. For every 1% increase in IOD of TSCG, the carbon content of the biochar increases 0.726%, and the HHV increases 0.529%. Overall, it is demonstrated that H2O2 is a green and promising pretreatment additive for upgrading SCG biochar's calorific value, and torrefied SCGs can be used as a potential solid fuel to approach carbon neutrality.