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Methods used in a Biofilter experiment

• Measuring and analyzing gas fluxes through the biofilters

1. biofilters are set up on the surface of a stack of anaerobically stored animal waste, then gaseous emission data is collected using a static flux chamber and a photoacoustic sensor.
2. an Excel program created to extract relevant data (from the continuous data collected by the photoacoustic sensor every minute) is used. The same program also calculates the flux of selected gases from the tested surface, using Pedersen's equation (2001).
3. selected data are copied and pasted as values into a compiled data set
4. a regression analysis is performed to evaluate the effect of time, biofilter treatment, and other input variables on the flux level of each analyzed gas: ammonia, methane, carbon dioxide, nitrous oxide and water vapor. The Sagata Regression Pro software (ltd) is used: go to regression > pick inputs > pick outputs > chose data types (categorical or continuous) > chose regression model (if you want interactiuons, ,ultiply the factors) > go to output, get response vs. factors for preliminary graphs > choose indicative title for the output sheet > click ok.
5. the statistical analysis output is interpreted: the first Anova table shows possible treatment effect. The "term significance" table shows effect of individual factors (or interactions).

• Temperature data: temperature data is collected by temperature probes placed at a 5-, 20-, and 40-cm depth in the animal waste stack and stored in a data logger. Data processing and analysis is conducted according to the following instructions.
• Biofilter respiration (Biological Oxygen Demand, BOD), Moisture and Volatile Solids (organic matter) content data: biofilter samples are periodically collected and analyzed in the lab according to the following instructions for Moisture and VS analysis.

Once processed into an compatible format, temperature, BOD, and moisture content data is included in the statistical analysis as both an input affect gaseous flux and and output affected by time and biofilter treatments.

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