Practical strategies for acidification of animal slurry in storage

Abstract: Animal slurry is a source of NH3 emissions which results in loss of N and decrease the nutritive value of slurry. Slurry stores in Sweden represents approximately 30% of total NH3 emissions from agricultural activities in the country. Slurry acidification is a method that effectively mitigates NH3 emissions by reducing the pH level of slurry and is done most commonly with sulphuric acid. However, slur-ry can negate pH reduction with its buffer capacity and increase pH after acidifica-tion. In this study, different acidification strategies were simulated in laboratory scale. Consumption of acid and foaming was compared between strategies to iden-tify an efficient and practical method to reduce and maintain pH of slurry at 5.5 in storage. The purpose of this study was to discover a practical procedure for farm-ers in Sweden to implement acidification of slurry in storage to control NH3 emis-sions and save N during storage. The following hypotheses were tested in this study: i) Acid consumption will be greater when addition is more frequent, ii) pH will stabilize after several re-acidifications, iii) pH will stabilize faster when addi-tion of acid is more frequent and iv) Frequent acid additions will reduce foaming and save storage capacity. Three strategies were conducted to acidify dairy and pig slurry with sulphuric acid at 20℃. In Strategy 1, daily acidification of slurry was performed in the pump pit five days per week for two weeks, then slurry was transferred to storage where pH and temperature were measured for twelve weeks. In Strategy 2, acidification of slurry was performed after the pump pit was full, just before it was transferred to storage. These steps were repeated every week for 15 weeks and during the last week, acidification was performed in storage. In Strategy 3, acidification of slurry was performed in storage and then re-acidification was performed every week if pH had elevated back to 6.0. The results of this experiment showed that Strategy 2 required least amount of acid compared to Strategy 1 and 3, except between Strat-egy 1 and 2 for dairy slurry, when two weeks had passed. However, the pH in stor-age was higher in Strategy 2. No significant difference in acid consumption oc-curred between Strategy 1 and 3 during the first two weeks, even if acid was added to slurry more frequently in Strategy 1. The pH level didn’t stabilize at 5.5 in any of the strategies. Foam production was much less in Strategy 1 compared to Strat-egy 2 and 3. The consumption of acid was not influenced by having a more frequent acid addi-tion to slurry and pH did not stabilize by several re-acidifications or frequent acid additions. However, frequent acid additions did minimize the foam production. This means that Strategy 1 was the most practical acidification method compared to Strategy 2 and 3.