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...

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Microbial activity is the cause of a variety of problems in water injection systems, e.g., microbial corrosion, plugging, and biofouling. Efficient monitoring of Saudi Aramco's vast water injection system requires the development of online and automated technologies for monitoring microbial activities in the system. A previous system review and technology screening has identified five single-analyte strategies [1], which were evaluated in this study with a laboratory-scale setup to determine their applicability for automated determination of microbial activity in the injection water system. Four of the five single-analyte measuring principles tested in the laboratory setup were deemed less suitable for automation and/or reliable for use in the detection of microbial activity in the company injection water system. These four principles were: luminescence assay for adenosine-5'-triphosphate (ATP), detection and electrochemical measurements of H2S, determination of pH by electrochemical sensor, and measurement of oxidation-reduction potential (ORP). The strategy of staining cells with fluorescent DNA dyes, followed by quantification of fluorescence signals, was identified to hold, with proper optimization of DNA staining and fluorescence detection, a very promising potential for integration in automated, online sensors for microbial activity in the injection water system.

Microbial activity in the water injection system in oil and gas industry leads to an array of challenges, including biofouling, injectivity loss, reservoir plugging, and microbiologically influenced corrosion (MIC). An effective mitigation strategy requires online and real-time monitoring of microbial activity and growth in the system so that the operators can apply and adjust countermeasures quickly and properly. The previous study [1] identified DNA staining technology-with PicoGreen and SYBR Green dyes-as a very promising method for automated, online determination of microbial cell abundance in the vast Saudi Aramco injection seawater systems. This study evaluated DNA staining technology on detection limit, automation potential, and temperature stability for the construction of automated sensor prototype. DNA staining with SYBR Green dye was determined to be better suited for online and real-time monitoring of microbial activity in the Saudi Aramco seawater systems. SYBR Green staining does not require sample pre-treatment, and the fluorescence signal intensity is more stable at elevated temperatures up to 30˚C. The lower detection limit of 2 × 10 3 /ml was achieved under the optimized conditions, which is sufficient to detect microbial numbers in Saudi Aramco injection seawater. Finally, the requirements for design and construction of SYBR-based automated sensor prototype were determined.

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