Desulphurization of medium sulphur Waterberg steam coal in a batch operated scale : microbial solution

Abstract

The current study evaluates pre-combustion microbial desulphurization of medium – sulphur type coal containing total sulphur (1.45 wt.%) and pyritic sulphur (≥ 0.51 wt. %) in a laboratory scale. Coal samples used in the current study were supplied by one of South African Power Utility, Eskom power station as received from the nearby Waterberg coalfield in Limpopo in South Africa. Coal samples were size fractioned using 13.2, 9.5, 8.0, 6.3, 5.6, 4.7, 2.36, 2.00, 1.00, 0.85 mm and below using automatic screens shaker. Coal sample containing particle size in the range of − 0.85 mm was used in the experiments with bacteria isolated from the native coal mine site. After a stipulated hydraulic retention time (HRT), the coal samples were filtered, washed, dried and used for total sulphur and calorific value analysis. The calorific value of the coal significantly improved from 20.42 MJ/Kg to 24.16 MJ/Kg on the 5th day.The process removed up to 41% of the total sulphur content in the coal samples at a HRT of 8 days. This study provides a novel breakthrough of an alternative microbial desulphurization process of Waterberg steam coal as a further pre-treatment technique in order to meet stringent environmental emissions standards for SO2.