Jerónimo Hernández

Development and application of a hybrid inert/organic packing material for the biofiltration of composting off-gases mimics

The performance of three biofilters (BF1-BF3) packed with a new hybrid (inert/organic) packing material that consists of spherical argyle pellets covered with compost was examined in different operational scenarios and compared with a biofilter packed with pine bark (BF4). BF1, BF2 and BF4 were inoculated with an enriched microbial population, while BF3 was inoculated with sludge from a wastewater treatment plant. A gas mixture containing ammonia and six VOCs was fed to the reactors with N-NH(3) loads ranging from 0 to 10 g N/m(3)h and a VOCs load of around 10 g C/m(3)h. A profound analysis of the fate of nitrogen was performed in all four reactors. Results show that the biofilters packed with the hybrid packing material and inoculated with the microbial pre-adapted population (BF1 and BF2) achieved the highest nitrification rates and VOCs removal efficiencies. In BF3, nitratation was inhibited during most of the study, while only slight evidence of nitrification could be observed in BF4. All four reactors were able to treat the VOCs mixture with efficiencies greater than 80% during the entire experimental period, regardless of the inlet ammonia load.

Startup and long-term performance of biotrickling filters packed with polyurethane foam and poplar wood chips treating a mixture of ethylmercaptan, H2S, and NH3

Treatment of a mixture of NH3, H2S, and ethylmercaptan (EM) was investigated for more than 15 months in two biotrickling filters packed with poplar wood chips and polyurethane foam. Inlet loads ranging from 5 to 10 g N-NH3 m−3 hr−1, from 5 to 16 g S-H2S m−3 hr−1, and from 0 to 5 g EM m−3 hr−1 were applied. During startup, the biotrickling filter packed with polyurethane foam was re-inoculated due to reduced biomass retention as well as a stronger effect of nitrogen compounds inhibition compared with the biotrickling filter packed with poplar wood. Accurate pH control between 7 and 7.5 favored pollutants abatement. In the long run, complete NH3 removal in the gas phase was achieved in both reactors, while H2S removal efficiencies exceeded 90%. EM abatement was significantly different in both reactors. A systematically lower elimination capacity was found in the polyurethane foam bioreactor. N fractions in the liquid phase proved that high nitrification rates were reached throughout steady-state operation in both bioreactors. CO2 production showed the extent of the organic packing material degradation, which allowed estimating its service lifetime in around 2 years. In the long run, the bioreactor packed with the organic packing material had a lower stability. However, an economic analysis indicated that poplar wood chips are a competitive alternative to inorganic packing materials in biotrickling filters. Implications: We provide new insights in the use of organic packing materials in biotrickling filters for the treatment of H2S, NH3, and mercaptans and compare them with polyurethane foam, a packing commonly used in biotrickling filters. We found interesting features related with the startup of the reactors and parameterized both the performance under steady-state conditions and the influence of the gas contact time. We provide relevant conclusions in the profitability of organic packing materials under a biotrickling filter configuration, which is infrequent but proven reliable from our research results. The report is useful to designers and users of this technology.

Environmental assessment of different biofilters for the treatment of gaseous streams

Biological techniques have been considered as an interesting alternative to treat gaseous streams from industrial processes. In this work, the performance of biofilters was evaluated from an environmental point of view by using Life Cycle Assessment methodology. More specifically, the potential impacts of four biofilters packed with different organic materials: spherical clay pellets covered with compost, a mixture of coconut fibre and sludge based carbon, peat and heather and pine bark have been quantified. The impact categories considered in this work were: eutrophication, acidification, global warming, photochemical oxidation, malodorous air, human toxicity and marine, terrestrial and freshwater ecotoxicity. From an environmental point of view, the reactor packed with coconut fibre and sludge based carbon appears to be the most suitable alternative since it presented the lowest values in almost all the impact categories assessed. On the other hand, the biofilter packed with clay pellets covered with compost seems to be the most penalized bioreactor providing the highest impacts for six of the nine impact categories evaluated, mainly due to the significant pressure drop achieved in the reactor which led to a considerable increase of energy demand. The reactor packed with coconut fibre and sludge based carbon is also the most beneficial alternative after performing the normalization step. In this case, the alternatives of peat and heather and pine bark are the less favourable ones in terms of photochemical oxidation, which was attributed to the lowest efficiency of methyl isobutyl ketone removal efficiency observed in both configurations. On the other hand, the option of treating off-gases is, in general, more positive and advisable than the direct discharge to the atmosphere.

Identifying the limitations of conventional biofiltration of diffuse methane emissions at long-term operation.

ABSTRACT There is growing international concern about the increasing levels of greenhouse gases in the atmosphere, particularly CO2 and methane. The emissions of methane derived from human activities are associated with large flows and very low concentrations, such as those emitted from landfills and wastewater treatment plants, among others. The present work was focused on the biological methane degradation at diffuse concentrations (0.2% vv−1) in a conventional biofilter using a mixture of compost, perlite and bark chips as carrier. An extensive characterization of the process was carried out at long-term operation (250 days) in a fully monitored pilot plant, achieving stable conditions during the entire period. Operational parameters such as waterings, nitrogen addition and inlet loads and contact time influences were evaluated. Obtained results indicate that empty bed residence times within 4–8 min are crucial to maximize elimination rates. Waterings and the type of nitrogen supplied in the nutrient solution (ammonia or nitrate) have a strong impact on the biofilter performance. The better results compatible with a stable operation were achieved using nitrate, with elimination capacities up to 7.6 ± 1.1 g CH4 m−3 h−1. The operation at low inlet concentrations (IC) implied that removal rates obtained were quite limited (ranging 3–8 g CH4 m−3 h−1); however, these results could be significantly increased (up to 20.6 g CH4 m−3 h−1) at higher IC, which indicates that the mass transfer from the gas to the liquid layer surrounding the biofilm is a key limitation of the process.

Characterization and biological abatement of diffuse methane emissions and odour in an innovative wastewater treatment plant.

An innovative and patented process for medium-high strength sewage which comprises an anaerobic step followed by a hybrid anoxic–aerobic chamber and a final ultrafiltration stage was characterized in terms of methane fugitive emissions as well as odours. The operation at ambient temperature implies higher methane content in the liquid anaerobic effluent, which finally causes concentrations around 0.01–2.4% in the off-gas released in the anoxic–aerobic chamber (1.25% average). Mass balances indicate that these emissions account for up to 30–35% of the total methane generated in the anaerobic reactor. A conventional biofilter (BF) operated at an empty bed residence time of 4 min was used to treat these emissions for 70 d. In spite of the fluctuations in the methane inlet concentrations derived from the operation of the wastewater treatment plant (WWTP), it was possible to operate at pseudo-steady-state conditions, achieving average removal efficiencies of 76.5% and maximum elimination capacities of 30.1 g m−3 h−1. Odour removal was quantified as 99.1%. Fluorescence in situ hybridization probes as well as metabolic activity assays demonstrated the suitability of the biomass developed in the WWTP as inoculum to start up the BF due to the presence of methanotrophic bacteria.