Till this day coffee is the most consumed beverage worldwide. As a result, plenty of waste is being generated during the coffee brewing process. It was estimated that from 1 ton of green coffee beans, 650 kg of spent coffee grounds (SCG) are generated, making the SCG a major threat to the environment [1]. This type of biomass is rarely used somewhere else, therefore most of the time SCG end up in landfills. Due to their decomposition, spent coffee grounds emit environmentally harmful carbon dioxide and methane gases, which contribute to the faster global warming [2]. Moreover, SCG are rich in various chemical compounds, which can be extracted to make higher value products. For example, the oil content in SCG makes around 15-20 % and later can be used for biodiesel production [3]. Unfortunately, the information about what happens with SCG after oil extraction and where they can be further utilized, instead of ending up in the landfills again, is rather scarce.
The aim of the present study was to determine the impact of solvent treated spent coffee grounds on the building gypsum properties. In this research Arabica spent coffee grounds were treated with isopropanol for 0.5 and 2 hours. Gypsum and SCG were characterized using STA, XRF, XRD and FTIR analysis methods. Various properties, such as water/gypsum ratio (W/G), setting time, compressive strength, density, water absorption and open porosity of gypsum samples with 5 wt.% spent coffee grounds were determined.
When treated SCG were used it was found that the W/G ratio of gypsum paste decreased, setting time shortened, compressive strength of the samples increased, open porosity and water absorption values decreased compared to the samples with untreated SCG. However, the treatment duration of SCG, whether it was 0.5 or 2 hours, had just a minor difference on the obtained results. Additionally, the FTIR spectrum showed, that the lipids content in SCG decreased after the treatment.
All things considered, there is not a big difference in SCG treatment time between 0.5 and 2 hours. However, research results showed that by using isopropanol treated SCG, gypsum samples had good properties. And this kind of SCG application could be one of the solutions on how to reduce the large amount of spent coffee grounds in the landfills.