Strategies for pH control in a biofilter packed with sugarcane bagasse for hydrogen sulfide removal

The biological removal of hydrogen sulfide at low concentration (<120 ppmv) was studied in a laboratory-scale biofilter packed with sugarcane bagasse and inoculated with a sulfur-oxidizing bacterial consortium isolated from activated sludge from a wastewater treatment plant (WWTP). Inlet loads from 1.31 to 20.2 g Sm-3 h(-1) were supplied to the biofilter, and empty bed residence times (EBRTs) of 30, 20 and 10 s were tested. In all cases, the removal efficiency was greater than 99%. Two methods for the pH control were tested: increasing the phosphate buffer capacity of the mineral medium (method I), and a new method, which involves the addition of solid CaCO3 to the bagasse at the upper inlet of the biofilter (method II). For method I, pH increased gradually along the bed (from the bottom to the top), from a constant value of 3.0 to 7.0. For method II, pH was constant (2.4 +/- 0.8) along the bed, and then a steep increase of pH was observed at the top to 7.1. We suggest the use of CaCO3 instead of phosphate buffer because the former is less expensive, it is a simple method and the results obtained with the two methods are similar.