Hala Chaoui's current work at Penn State's Tom Richard Bioconversion Lab
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Results from a bench top experiment show that increasing the mixing frequency of a biodigester slurry decrease the volume of biogas produced. Mixing frequencies were generated using stir bars and a stirring plate. Treatments were evaluated using a pressure sensor to measure the volume of gas produced, and a gas chromatographer to measure its composition. Results will be presented at the International Conference on Progress in Biogas, organized by the International Biogas and Bioenergy Centre of Competence, September 2007, Stuttgart.
Methods used in an experiment to evaluate biofilters as a mitigation technique for gaseous emissions from stacked animal waste
- Measuring and analyzing gas fluxes through the biofilters
- 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.
- 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).
- selected data are copied and pasted as values into a compiled data set
- 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 (to evaluate interactions create input variables made of factors evaluate for interaction amongst them, multiplied by each other) > go to output, get response vs. factors for preliminary graphs > choose indicative title for the output sheet > click ok.
- 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 time saving instructions, based on macros.
- 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 BOD and 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.
The biofilter experiment was conducted over a Fall, Winter and Summer season. Results from the first season were presented at the Annual International Meeting of the Am. Soc. of Ag. and Biol. Engineers., June 2007. These results showed a significant effect of biofilters at mitigating the flux of methane, ammonia and carbon dioxide from stacked animal waste. Results also showed a correlation between biofilter moisture content and its performance.
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