No abstract

Geopolymers can be treated as an environmentally friendly alternative for concrete and enables utilization of various wastes. This paper focuses on the possibility of application of discarded cathode ray tube (CRT) glass inside a metakaolin-based geopolymer in the form of an aggregate, providing an ecological method of recycling of this hazardous material. The main goal of this paper was to develop an optimal composition of a new geopolymer and to describe its behavior under varying curing conditions. A geopolymer made of different mixtures was subjected to flexural and compressive strength tests. The density, mass loss, temperature changes, and metals leaching were determined as well. The results demonstrated that neither the content of CRT glass nor the curing regime has a significant influence on the mechanical behavior. However, the strength of the geopolymer containing 50% CRT glass by mass increased with time in contrast to a geopolymer with a higher CRT glass content. The development of temperature inside the mixture was dependent on the amount of metakaolin. The concentration of toxic metals in an aqueous extract decreased considerably after the encapsulation of CRT glass inside the geopolymer. The presented results indicate that discarded CRT glass can be considered an aggregate for a metakaolin-based geopolymer. The new material shows high strength and makes the CRT glass safe for the environment.

Poland is facing demanding challenges to achieve a sustainable energy mix in the near future. Crucial and tough decisions must be made about the direction of the national energy economy, safety, and environmental impact. Considering the electricity and heating demand forecast, this paper proposes an optimization model based on the Grey Wolf Optimizer meta-heuristic to support the definition of ideal energy mix considering the investment and operational costs. The proposed methodology uses the present energy mix in Poland (the most recent values are from 2017) to calibrate the model implemented in the EnergyPLAN tool. Afterwards, EnergyPLAN relates to an optimization process allowing the identification of the most convenient energy mix in 2040 in Poland. The values obtained are compared with those proposed by Polish public entities showing advantage regarding the global costs of the project nevertheless respecting the same levels of CO2 and the energy import and export balance. The expected savings can achieve 1.3 billion euros a year and more than 8 million tonnes of CO2 emission reduction. Sensitivity analysis considering the decrease of the global cost of renewables-based sources is also presented.

Due to the depletion of fossil fuels and the destruction wrought by global warming caused by the combustion of fossil fuels, the search for renewable energy sources has become a major global concern. This study aimed to assess the bio-oil production from teff husk via slow pyrolysis process. The pyrolysis of teff husk took place in a batch reactor at a temperature between 400 °C and 500 °C with a 120 min retention time. At 450 °C, the pyrolysis process produced 32.96 wt.% of optimum bio-oil yield and had a HHV of 25.32 MJ/kg. TGA, FTIR, and SEM-EDX were used to analyze the produced bio-oil to investigate its thermal decomposition, functional groups, and surface morphology with its elemental composition, respectively. Alcohols, aromatic, phenols, alkanes, esters, and ethers were the primary compounds of the bio-oil produced by the slow pyrolysis of teff husk. The HHV of the biochar ranged from 21.22 to 22.85 MJ/kg. As a result, teff husk can be used to make biofuel; however, further bio-oil upgrading is needed for the produced teff husk bio-oil to be used effectively and commercially. Overall, the slow pyrolysis of teff husk offers a chance to produce biofuels with enhanced value that can be used for additional purposes.

Biochar is a way to improve the performance of the composting process and the quality of compost. This study was aimed to investigate the optimum ratio of khat straw (Catha edulis) biochar and organic municipal solid waste mixtures to improve the quality of the resulting co-composts. Khat-derived biochar during pyrolysis at 350 °C was added to organic municipal solid waste mix and four co-composting treatments were prepared with the compositions (% w/w): control compost (no biochar) and 5%, 15%, and 25% co-composted biochar in three replicates. The total organic carbon, organic matter, total nitrogen, available phosphorus, and potassium values ranged as 16.76–21.45%, 30.77–40.26%, 0.97–1.68%, 0.58–0.76%, and 12.72–15.29%, respectively. The results confirmed that 5% and 15% co-composted khat biochars had significantly reduced (p < 0.05) organic matter loss and increased the contents of cation exchange capacity, pH, phosphorous, potassium, calcium, magnesium, and zinc compared to the control compost, while some heavy metals (Fe, Cu, and Mn) and EC values in co-composted biochars are lower than the control compost. Khat-derived biochar could be added to municipal organic waste mix at 5–15% (w/w) in order to get better quality of compost, which can be used as biofertilizer.