MULTIPLE-CHAMBER INSTRUMENTATION DEVELOPMENT FOR COMPARING GAS FLUXES FROM BIOLOGICAL MATERIALS

The complex and often confounding factors that influence gas emission from biological materials require a measurement procedure that is precise, accurate, repeatable, and reliable. A multiple-chamber instrumentation system was developed to rapidly and precisely measure gas emission potential from multiple sources, such as manure and biosolids, to compare gas emission reduction potential of various treatments. Up to eight steady-state flux chambers, a photoacoustic multi-gas monitor, and a hydrogen sulfide pulsed fluorescence analyzer were coupled through a multiplexer relay to measure concentrations of ammonia and hydrogen sulfide, respectively. Depending on the number of chambers used, gas concentration in the chambers was measured on 20- to 72-min intervals over a nominal 24-h period via fully-automated data collection software. Built-in quality controls allowed potential cross-contamination to be quickly identified in order to maintain the precision of the instrument. Air flow rate in each chamber was maintained at 0.5 air changes per minute using calibrated flow meters. The performance of the multiple chamber system in evaluating ammonia gas flux was tested using ammonia calibration gas (accuracy; 97.3% recovery through the system) and freestall barn-floor manure sub-samples (precision 8% for biologically heterogeneous material; standard error of 2% of mean). Using separately-collected dairy cow urine and feces the instrument system was used to evaluate impact of source depth showing an apparent slight reduction of ammonia release with increasing depth but findings were within the expected precision range of the instrument for this type of material. An example demonstrating the multiple-chamber system use in evaluating ammonia flux processes evaluated urine and feces mixed to five ratios ranging from 10:90 to 90:10. The 50:50 ratio had the highest cumulative emission over 23 h. Removing ammonia with a scrubber and moisture via condensation trap significantly improved the accuracy of hydrogen sulfide concentration measurements when analyzing dairy manure slurry. Odorous air samples were easily collected from each chamber headspace and evaluated using triangular forced-choice dynamic olfactometry and odor-quality assessments for simultaneous gas emission and odor evaluation. This instrumentation system offers repeatable, concurrent monitoring of gas and odor emission from biological sources and provides a powerful tool for gas emission research and evaluation of management practices directed at reducing gas release.