Trimethylamine (TMA) is the main responsible for the odor often associated with rotting fish and is one of the major sources of annoying odors generated in many industrial activities, like composting facilities, fish-meal manufacturing plants, wastewater treatment plants, landfills and livestock farms. Traditionally amines can be removed by acid scrubbers that require the continuous supply of acid and generates large amounts of wastewater. Biofiltration has been proved to be an effective and sustainable technology treating many odorous compounds but the efficient removal of TMA using biofilters has not been completely shown. There are different microorganisms with the ability to use TMA as nutrient for their growth and presents different rates of TMA bio-degradation and biomass yields. Between those Hyphomicrobium vulgare and Aminobacter aminovorans are two bacteria known for their capability to use TMA as carbon and energy source.
In order to select one of these bacteria as inoculum for biofilters, TMA bio-degradation capacity of both bacteria was determinated in batch cultures. Each bacterium was cultivated at 30°C and 200 rpm in 125 ml shake flasks with a minimum mineral medium and TMA as source of carbon. To determine the effect of H2S on the biodegradation of TMA, H2S was added in the headspace of the flasks, the experiments were performed using 0, 20 and 70 ppm of H2S as initial concentration in headspace.
The maximum biomass concentration obtained during the cultures was 1.17 g L-1 for Hyphomicrobium and0.44 g L-1 for A. aminovorans, it growth at a maximum specific growth rate of 0.15 h-1, higher than the obtained for Hyphomicrobium; 0.09 h-1. The biomass yield for TMA was 0.35 (g g-1) for Hyphomicrobium and 0.10 (g g-1) for A. aminovorans. The specific consumption rate was 0.47 h-1 in the culture of A. aminovorans and 0.12 h-1 in the culture of Hyphomicrobium. Although A. aminovorans shows higher TMA specific consumption rate than Hyphomicrobium, its biomass yield value (0.1 g g-1) indicates that in the case of A. aminovorans the carbon from TMA was metabolized to other products like carbon dioxide, formaldehyde or formate in detrimentof biomass production. The biodegradation of TMA by A. aminovorans is negatively affected by H2S, meanwhile in the case of Hyphomicrobium sp. the specific rate of biodegradation of TMA is positively influenced by the presence of H2S, making it even higher than the one obtained for A aminovorans without the presence of H2S. In conclusion, due to its specific growth rate and TMA specific consume rate Aminobacter aminovorans is a suitable candidate to be used as inoculum for biofilters designed for removing gas emissions containing TMA when there is not H2S in the mixture. However, if H2S is present, Hyphomicrobium vulgare would be the best choice for the inoculum or being part of the inoculum of the biofilter.