Distribution and Rate of Microbial Processes in an Ammonia-Loaded Air Filter Biofilm

Abstract

The in situ activity and distribution of heterotrophic and nitrifying bacteria and their potential interactions were investigated in a full-scale, two-section, trickling filter designed for biological degradation of volatile organics and NH 3 in ventilation air from pig farms. The filter biofilm was investigated by microsensor analysis, fluorescence in situ hybridization, quantitative PCR, and batch incubation activity measurements. In situ aerobic activity showed a significant decrease through the filter, while the distribution of ammonia-oxidizing bacteria (AOB) was highly skewed toward the filter outlet. Nitrite oxidation was not detected during most of the experimental period, and the AOB activity therefore resulted in NO 2 ؊ , accumulation, with concentrations often exceeding 100 mM at the filter inlet. The restriction of AOB to the outlet section of the filter was explained by both competition with heterotrophic bacteria for O 2 and inhibition by the protonated form of NO 2 ؊ , HNO 2 . Product inhibition of AOB growth could explain why this type of filter tends to emit air with a rather constant NH 3 concentration irrespective of variations in inlet concentration and airflow.Emissions of NH 3 , odorous organic gasses, and dust from pig facilities cause significant problems for neighbors and the surrounding natural environment. In Denmark, swine production accounts for 34% of the total atmospheric NH 3 emission, of which 50% originates from pig house emissions (19). Furthermore, multiple volatile and very odorous organic compounds are emitted with animal house exhaust air and constitute a severe nuisance in residential areas (16,31). While biofilters based on wood chips, compost, and peat have proven efficient in removing complex mixtures of volatile organic compounds (VOC) from piggery exhaust air, biotrickling filters have been shown to be efficient in both odor and NH 3 removal (30). In these filters, airborne VOC and NH 3 are taken up by an irrigated biofilm and oxidized by organoheterotrophic and nitrifying bacteria, respectively, resulting in the production of CO 2 , NO 2 Ϫ or NO 3 Ϫ , and microbial biomass (43). The nitrification process, which comprises the two-step oxidation of NH 3 via NO 2 Ϫ to NO 3 Ϫ , is catalyzed by ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea and by nitriteoxidizing bacteria (NOB), respectively (22, 23). However, in many biotrickling filters, NOB activity seems to be absent, resulting in NO 2 Ϫ being the end product of nitrification (29). Waste products often accumulate in biotrickling filters, as the water is recycled many times to minimize wastewater discharge. In particular, NO 2 Ϫ may accumulate to concentrations above 100 mM (29), resulting in high levels of free nitrous acid (FNA, or HNO 2 ), which is inhibitory to many microorganisms (2, 40, 50). As a result of an overall countercurrent air-water flow, FNA, VOC, and NH 3 concentrations are expected to decrease from the filter air inlet toward the outlet, potentially promoting a gradient of microbial p...

Ecotoxicological assessment of antibiotics: A call for improved consideration of microorganisms

“…Environmental quality regulation Sewage and waste treatment (Bitton, 2010;Minz et al, 2010) Nitrifiers, denitrifiers, P accumulators, flocs formers, aerobic organic matter degraders, anaerobic fermenters, methanogens Specific microbial activities OECD 209, OECD 224, ISO 15522, ISO 9509 Biofilters (Juhler et al, 2009;Zearley and Summers, 2012) Nitrifiers, contaminant degraders etc. (depend on specific filter function) Specific microbial activities Specific tests to be standardized Natural attenuation of contaminants (Wackett and Hershberger, 2001) Specific fungal and bacterial degrader strains belonging to various genera Specific microbial activities Specific tests to be standardized Human health risk regulation Pathogen mitigation (Chee-Sanford et al, 2009) Competitive exclusion of pathogenic bacteria of human or animal origin Pathogen abundance Specific tests to be standardized Antibiotic resistance (AR) mitigation (CheeSanford et al, 2009) Competitive exclusion of antibiotic-resistant bacteria of human or animal origin Community tolerance and antibiotic resistance Specific tests to be standardized Cultural services Negligible c Supporting services Primary productivity (photosynthesis) (Paerl, 2002) Cyanobacteria and eukaryotic microalgae Growth of primary producers OECD 201, ISO 10253 Secondary productivity (heterotrophic growth) (ChinLeo, 2002) Heterotrophic bacteria, archaea and fungi Growth (biomass production) of secondary producers ISO 10712, ISO 15522…”

Enhanced long-term ammonium removal and its ranked contribution of microbial genes associated with nitrogen cycling in a lab-scale multimedia biofilter

“…NH 4 + -N = 150.391amoA/archaea + 950.531(nirS + nirK)/anammox + 2.659anammox/(narG + napA) À 619.955(amoA + napA + narG)/ (nxrA + anammox + nirS + nirK) + 30.562 À -N = 3.565(narG + napA)/(narG + napA + nirS + nirK + qnorB + nosZ) À 107.550anammox/bacteria À 8.746nosZ/ (narG + napA + nirS + nirK + qnorB + nosZ) + 0.330 amoA + napA + narG)/(nxrA + anammox + nirS + nirK) had a direct negative contribution on the NH 4 + -N transformation rate (À21.6%), suggesting that NO 2 À -N accumulation in the biofilter was not conducive to the removal of NH 4 + -N(Juhler et al, 2009). …”

Butyric Acid- and Dimethyl Disulfide-Assimilating Microorganisms in a Biofilter Treating Air Emissions from a Livestock Facility

“…Various types of Gammaproteobacteria have been proposed to be important degraders of butyric acid in a biofilter by means of cultivation, but Sheridan et al (45) also noted that Gammaproteobacteria are fast growing in cultures, possibly overgrowing important microorganisms. Major parts of the biofilm in the SKOV-type biofilter are oxic (20), which reflects the aerobic microbial community taking up butyric acid identified in the present study with the exception of Propionibacterium.…”

“…Finally, ammonia was completely eliminated by the primary filter. Ammonia was likely oxidized by nitrifying bacteria, which have been detected in a similar biofilter (20), causing the accumulated concentrations of nitrate and nitrite. Thus, various VOCs with different properties and ammonia emitted from the pig facility were removed by the SKOV-type biofilter.…”

“…Few molecular studies have provided descriptions of the microbial communities associated with biofilters treating air emissions (14,15,20,52). Compre-hensive characterization and understanding of air biofilter metabolism requires knowledge about in situ metabolic function and activity.…”