Preparation and Study of acid-base and ion-exchange properties of biochar from waste coffee grounds

Abstract

Increased consumption of coffee in the world leads to the accumulation of food waste that is not properly utilised properly, but have prospects for further processing into a targeted with added value. The aim of this study is to produce biochar from waste coffee grounds by coffee grounds by conventional pyrolysis and microwave irradiation, determination of its chemical and particle size distribution, study of acid-base and ion exchange properties, ability to bind ions and lead ions for further use as an additive in the production of biogas production. Given the high cost of conventional pyrolysis to produce the required volumes of biochar, it is promising to consider an alternative option that will be significantly cost-effective and efficient. After carbonisation, we determined the biopolymer composition, acid-base and ion exchange properties of the raw materials and biochar using various methods, such as the Kjeldahl Hogedron-Jensen, potentiometric titration and others. The results of the maximum cation exchange capacity of raw materials and biochar indicate that biochar has a less pronounced tendency to exchange cations in the range of 0.89–1.15 μeV/g than raw materials, the value of which is mainly in the range of 1–3 μeV/g, which shows less influence of biochar on the mineral balance of microorganisms during anaerobic digestion. The values of the anion exchange capacity of biochar are in the range of values 0.7–1.2 μeV/g, and the pH value of the acidic groups of biochar lie in the range of 7.1–10.7 (characterising them as weakly acidic groups), pKa is 9.6–10.7. The curves of potentiometric titration of biochar are determined by the additive contribution of all ionised groups of biochar and allow us to classify the studied products as polyfunctional ion exchangers type ion exchangers. Results of the study of biochars from waste coffee grounds show that they have ampholytic properties and act as acceptors of metal ions, as well as function as a mild pH regulator, which is important in anaerobic digestion of food waste into biogas to increase the yield of the resulting gas in accordance with the biocircular green economy model.