Removal of hydrogen sulfide by immobilized Thiobacillus thioparus in a biotrickling filter packed with polyurethane foam

Abstract

In the work described here, a biotrickling filter with Thiobacillus thioparus (ATCC 23645) immobilized on polyurethane foam is proposed for the removal of hydrogen sulfide contained in air. The effect of surface velocity of the recirculation medium (5.9–1.2 m/h), sulfate concentration inhibition (3.0–10.7 g/L), pH (6.0–8.2), empty bed residence time (EBRT) (150–11 s) for constant loads of 11.5 and 2.9 g S/m³/h, and pressure drop of the system were investigated.

The total amount of biomass immobilized on the carrier was 8.2 ± 1.3 × 10¹⁰ cells/g. The optimal values of the operating variables were: pH between 7.0 and 7.5, surface velocity of 5.9 m/h and sulfate concentration below 5 g/L. The critical EC value was 14.9 g S/m³/h (removal efficiency of 99.8%) and the EC_max was 55.0 g S/m³/h (removal efficiency of 79.8%) for an EBRT of 150 s. For loads of 2.89 ± 0.05 and 11.5 ± 0.1 g S/m³/h, the removal efficiency was higher than 99% for an EBRT over 90 s.

Introduction

Hydrogen sulfide (H₂S) is a colourless, toxic and flammable gas that has a characteristic odour of rotten eggs.

Both natural and anthropogenic sources contribute to the total emission of hydrogen sulfide. Hydrogen sulfide occurs naturally in the gases from volcanoes, sulfur springs, undersea vents, swamps, stagnant bodies of water in crude petroleum and natural gas and as a product of the biological degradation of organic matter (Lomans et al., 2002). Considerable amounts of hydrogen sulfide are also emitted from industrial activities such as petroleum refining, pulp and paper manufacturing, wastewater treatment, food processing, livestock farming, and natural gas processing.

The concentrations of hydrogen sulfide in gas emissions are usually very dilute and traditional physical–chemical technologies such as incineration, adsorption or chemical scrubbing tend to be costly and are associated with their own pollution problems. As a result, based on the cost of the equipment and operation, biological treatment is believed to be the most economical option for the removal of hydrogen sulfide.

Many microorganisms have been used for H₂S removal, principally Acidithiobacillus and Thiobacillus. In these groups are acidophilic bacteria such as Acidithiobacillus thiooxidans (Aroca et al., 2007, Sercu et al., 2005), neutrophilic bacteria such as Thiobacillus novellus (Cha et al., 1999), Thiobacillus thioparus (Chung et al., 2000, Cox and Deshusses, 2002, Oyarzún et al., 2003) and Thiobacillus denitrificans (Ma et al., 2006). Other bacteria such as Pseudomonas putida CH11 (Chung et al., 2001), Hyphomicrobium sp. (Sercu et al., 2005) and haloalkaliphilic consortium (Gonzalez-Sanchez et al., 2008) have been used for the removal of H₂S.

The major biological reactors for the treatment of dilute gases are biofilters, biotrickling filters, and bioscrubbers. These systems differ in the presence or absence of a carrier material, the phase of the biomass (suspended or fixed), and the state of the liquid phase (flowing or stationary).

In biofilters the most commonly used carriers are compost and peat, although some authors add other materials such as perlite and/or wood chips in an effort to avoid compaction of the bed (Wani et al., 1999). Activated carbons have also been used to remove H₂S and these give very good performance (Chung et al., 2005, Ma et al., 2006). The active carbon allows the combination of adsorption and biological degradation.

The use of bioscrubbers to remove H₂S is very unusual because the solubility of H₂S in water is very low.

In biotrickling filters the most commonly used carriers are propylene rings (Jin et al., 2005), ceramics (Ruokojärvi et al., 2001) and lava rocks (Chitwood et al., 1999). However, some investigations have been carried out with polyurethane foam (Gabriel et al., 2004, Gabriel and Deshusses, 2003), but using active sludge as inoculum.

The objective of the work described here was to study the feasibility of treating air contaminated with H₂S using a biotrickling filter packed with cubes of polyurethane foam inoculated with pure culture (T. thioparus). T. thioparus was selected because this bacteria can oxidize other sulfur compounds and the optimal pH is neutral and therefore the hydrogen sulfide solubility will be greater.