Martín Ramírez

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

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/m(3)/h, and pressure drop of the system were investigated. The total amount of biomass immobilized on the carrier was 8.2+/-1.3x10(10) 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/m(3)/h (removal efficiency of 99.8%) and the EC(max) was 55.0 g S/m(3)/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/m(3)/h, the removal efficiency was higher than 99% for an EBRT over 90 s.

Biofiltration of reduced sulphur compounds and community analysis of sulphur-oxidizing bacteria

The present work aims to use a two-stage biotrickling filters for simultaneous treatment of hydrogen sulphide (H(2)S), methyl mercaptan (MM), dimethyl sulphide (DMS) and dimethyl disulphide (DMDS). The first biofilter was inoculated with Acidithiobacillus thiooxidans (BAT) and the second one with Thiobacillus thioparus (BTT). For separate feeds of reduced sulphur compounds (RSC), the elimination capacity (EC) order was DMDS>DMS>MM. The EC values were 9.8 g(MM-S)/m(3)/h (BTT; 78% removal efficiency (RE); empty bed residence time (EBRT) 58 s), 36 g(DMDS-S)/m(3)/h (BTT; 94.4% RE; EBRT 76 s) and 57.5 g(H2S-S)/m(3)/h (BAT; 92% RE; EBRT 59 s). For the simultaneous removal of RSC in BTT, an increase in the H(2)S concentration from 23 to 293 ppmv (EBRT of 59 s) inhibited the RE of DMS (97-84% RE), DMDS (86-76% RE) and MM (83-67% RE). In the two-stage biofiltration, the RE did not decrease on increasing the H(2)S concentration from 75 to 432 ppmv.

Biogas biodesulfurization in an anoxic biotrickling filter packed with open-pore polyurethane foam.

Biogas biodesulfurization by an anoxic biotrickling filter packed with open pore polyurethane foam at the laboratory scale (packed volume 2.4L) has been studied. The biotrickling system was operated for 620 days with biogas supplied continuously and two nitrate feeding regimes were tested (manual and programmed). Biomass immobilization was carried out under the manual nitrate feeding regime and a study was then carried out on the effects on removal efficiency of the following parameters: nitrate source, H2S inlet load, nitrate concentration, sulfate accumulation, temperature, pH and trickling liquid velocity. The effect of increased H2S inlet load was studied under the programmed nitrate feeding regime. The results show that a removal efficiency of 99% can be obtained when working under the following conditions: inlet loads below 130gSm(-3)h(-1), a programmed nitrate feeding system, temperature of 30°C, sulfate concentration below 33gL(-1), a pH between 7.3 and 7.5, and a trickling liquid velocity higher than 4.6mh(-1).

Removal of ammonia by immobilized Nitrosomonas europaea in a biotrickling filter packed with polyurethane foam.

A biotrickling filter with Nitrosomonas europaea immobilized on polyurethane foam is proposed for treating ammonia contaminated air. The effect of the surface velocity of the recirculation medium, nitrite concentration, pH, empty bed residence time (EBRT) and ammonia inlet load on the NH(3) removal process was investigated. The total amount of biomass immobilized on the carrier was 3.29+/-0.52 x 10(10) cells g(-1) dry carrier. The maximum elimination capacity of the biotrickling filter was 270 g Nm(-3)h(-1) at pH 7.5, an EBRT of 11s, and nitrite concentrations below 100mM. These results show that system studied can be considered as a viable alternative for the treatment of gaseous emissions containing high concentrations of ammonia.

Dimethyl sulphide degradation using immobilized Thiobacillus thioparus in a biotrickling filter.

Gaseous dimethyl sulphide (DMS) was eliminated in a biotrickling filter with Thiobacillus thioparus grown in polyurethane foam cubes as carrier material. The temperature, pH and empty bed residence time of the gas were maintained at 30 °C, 7.0 and 40 s, respectively. In the first 45 days, DMS loads of around 2.0 gDMS m−3 h−1 were fed to the BTF to adapt T. thioparus to DMS consumption, attaining close to 100% removal efficiency (RE) on day 46, and the maximum elimination capacity (EC) was 4.0 gDMS m−3 h−1 with a RE of 77%. The overall performance was enhanced by adding a nitrogen‐enriched (9×) medium but was negatively affected by high superficial liquid velocity (8.18 m h−1) and high pH (>7.5). Sulphate concentrations (up to 10 g L−1) showed no effect. The system supported shock loads up to 58 gDMS m−3 h−1 with increased elimination. With nitrogen‐enriched medium and a pH of 7.0 it was possible to increase the EC of DMS up to a maximum of around 23 gDMS m−3 h−1 with 65% RE.

Hydrogen sulfide removal from air by Acidithiobacillus thiooxidans in a trickle bed reactor

A strain of Acidithiobacillus thiooxidans immobilized in polyurethane foam was utilized for H2S removal in a bench-scale trickle-bed reactor, testing the limits of acidity and SO42− accumulation. The use of this acidophilic strain resulted in remarkable stability in the performance of the system. The reactor maintained a >98–99 % H2S removal efficiency for c of up to 66 ppmv and empty bed residence time ≤12–15 s. Removal of >98 % H2S was achieved under steady-state conditions, over the pH range of 0.44–7.30. Despite the accumulation of acidity and SO42− (up to 97 g/L), the system operated without inhibition.

Immobilization of Cells on Polyurethane Foam

In this chapter, protocols and details for the immobilization of a model cell onto polyurethane foam carriers are provided in order to facilitate the use of such systems in laboratory or industrial reactors. Polyurethane foam has recently acquired great relevance as a carrier for its good mechanical properties, high porosity, and large adsorption surface. In addition, it has a very low commercial cost. Two different immobilization protocols have been described, differing in the flow regime or the possibilities for the reactor: immobilization in a stirred tank reactor working in a discontinuous regime (by cycles) and immobilization in a packed column working in continuous operation mode. Protocols for carrier sterilization, analytical methodology, and immobilization are described.

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.

Removal of hydrogen sulfide and ammonia from gas mixtures by co-immobilized cells using a new configuration of two biotrickling filters

The simultaneous removal of H(2)S and NH(3) was investigated using two biotrickling filters packed with polyurethane foam cubes. One biotrickling filter was inoculated with Thiobacillus thioparus ATCC 23645 for the removal of H(2)S (BTT) and the other filter with Nitrosomonas europaea ATCC 19718 for the removal of NH(3) (BNE). Three different configurations were studied by modification of the gas line and recirculation medium line. The best results were obtained with the BNE biotrickling filter after the co-immobilization of the two bacteria. A removal efficiency of 100% for 230 ppmv of NH(3) and 129 ppmv of H(2)S was reached at an EBRT of 60 seconds. The results obtained show that it is possible to co-immobilize both microorganisms using the same recirculation medium and remove successfully H(2)S and NH(3) from a gas mixture.

2.22 – Biofilters

Current environmental legislation is focused in removal and/or reducing emissions of pollutants. Biological treatments of wastes are considered as an alternative opposite traditional physicochemical methods. In recent decades, the use of biofilters to removal of contaminants from wastewater and waste gases is being developed. Biofilters use microorganisms, which are capable of degrading many compounds, fixed to an inorganic/organic medium (carrier) to break down pollutants present in a fluid stream. In this article, basic aspects about biofilter configuration, filter media, microorganisms involved, and properties that affect the biofilter performance are presented. Once these aspects are clarified, work deals with the biofilter design. Efforts are focused to summarize the terminology, operational features, and design equations that are essential for this kind of bioreactors. In the design, treatments of liquid and gaseous waste streams, due to the singular differentiating characteristics of these equipments, are distinguished.