STUDY OF THERMAL TREATMENT RETENTION TIME EFFECT ON PHENOL CONTENT AND PH OF SPENT COFFEE GROUND

Abstrak

Indonesia, as a tropical country that is ideal for growing coffee beans, produced 760.2 thousand metric tons of coffee beans in 2023. With such huge production, the sustainability of its waste, such as spent coffee grounds, becomes a concern that needs to be addressed. Thermal Treatment, a partial oxidation combustion process, becomes one of the keys to the sustainability of this byproduct. Thermal Treatment turns spent coffee grounds into more useful products, such as liquid smoke. Bio-oil, the product produced by the Thermal Treatment process, often called Liquid Smoke, is a multifunctional liquid, contains phenolic compounds with antimicrobial properties. By integrating Thermal Treatment technology into waste management, sustainable and circular bio-economy models can be promoted. This research aims to investigate and study one of the Thermal Treatment parameters, the effect of retention time. Does retention time affect the products produced in Thermal Treatment, like the phenol content and pH in liquid smoke. The Research method involves an experiment on two different retention times of 60 and 90 minutes, where spent coffee grounds are subjected to thermal treatment at different retention times to produce smoke liquid. At first, spent coffee was gathered, for pre-treatment, spent coffee grounds were baked in an oven at 100°C for 1 hour, then the spent coffee ground was divided into 500g with two samples each, as the samples would go through two different Retention times of 60 minutes and 90 minutes at a temperature of 150℃. Then, these samples would be put in the Thermal Treatment chamber for them to go through the Thermal Treatment process once at a time. A study with two sets of different retention times was conducted. The resulting Liquid Smokes is then analyzed for its chemical composition, the pH and phenol content. The result in phenol content is 375.7 mg/L, 364.8 mg/L, for a retention time of 60 minutes, and 412.3 mg/L, 401.6 mg/L for a retention time of 90 minutes, which shows there is a significant difference. Liquid Smoke shows 20.7% higher yield at 90 mins (198.5 mL vs. 164.5 mL), while on the other hand, biochar shows no significant difference with an average of around 70 grams across both 60 and 90 minute retention times, and pH became less acidic with longer retention from 6.85 to 7.75. In conclusion, the research on Thermal Treatment’s retention time reveals that retention time durations do affect the outcomes. The result shows 90 minute retention time is more ideal since the result shows it produces higher Liquid Smoke volume (198.5 mL vs. 164.5 mL) at 60 mins, 9.8% more phenols content (412.3 mg/L vs. 375.7 mg/L).