Effects of acidification during storage on emissions of methane, ammonia, and hydrogen sulfide from digested pig slurry

The effects of acidification reduction on methane (CH4), ammonia (NH3) and hydrogen sulphide (H2S) emissions from digested pig slurry during storage were investigated. Pilot-scale experiments designed with three different pH levels including one control and two acidified treatments were conducted. Digested pig slurry was stored and tested in nine mechanically ventilated reactors. An online and continuous monitoring system was used to acquire gas emissions data during the whole storage period. Temperatures and pH in digested slurry were continuously measured with sensors. Off-gas from the reactors and air from room environment were sampled alternately then supplied to gas analysers for CH4 and H2S determination. Headspace NH3 from the 9 reactors were regularly sampled by an air sampling instrument and then determined for concentration by spectrophotometer. The study found that digested pig slurry characteristics still didnʹt satisfy the national standards after 95 days treatments. Both temperature and pH were crucial factors to influence CH4 and NH3 emissions from digested pig slurry. In the control group (Gn) CH4 and H2S emissions mainly occurred in the first 20 days and 12 days, respectively; while no predictable NH3 emission patterns were found in the experiment. Comparing with Gn, adjustment of initial pH to 5.5 significantly reduced CH4 emissions by 80.8% and NH3 emissions by 40.2%, but increased H2S emissions by 11,324% (average increasing emission flux was 4.1 μg m−2 min−1). Acidification with pH adjusted to 6.5 reduced CH4 emissions by 31.2%, but did not affect NH3 and H2S emissions significantly.