 anaerobic digestion, biogas composition. Part 1, sample setup. Weigh out 30 to 35 grams of the seed solution for each trial you will be doing. Place each sample into its corresponding vial. Then add varying amounts of the waste substrate. Seal the vial with the pressure-resistant cap. You will select a certain concentration of the waste substrate, but to each bottle you will add varying volumes of the waste substrate. Make sure the volumes you select do not exceed half the bottle. You will place all of your bottles inside an oven set to 35 to 38 degrees C. The bottles will rest inside the oven for 7 days. Part 2, CO2 trap setup and CO2 capture. To each vial, pipette 5 milliliters of .5 molar NaO8 solution. Then seal the vials with injectable caps. Collect your sample bottles from the oven, your CO2 trap vials, and your 60 milliliters syringe. Inject the needle into the cap of the sample bottle. With the gas withdrawn into the syringe, inject the gas into the CO2 trap vials and record the volume injected. Swirl the CO2 trap vials to ensure the hydroxide solution has absorbed all of the CO2 in the gas. Part 3, CO2 determination by titration. Set up your titration apparatus as shown in the picture. To each CO2 trap vial, remove the cap and add 2 to 3 drops of phenol-failing indicator. Then begin titrating with .1 molar HCl solution until the first endpoint is met. You should see the solution go from pink to colorless. Record the volume of HCl solution used inside the burette. Now that the first endpoint has been reached, add 2 to 3 drops of methyl-orange indicator to each CO2 trap vial. Continue your titration with .1 molar HCl solution until the second endpoint is reached. Record the volume again in the burette.