Study on ammonia reduction technology by manure surface acidification in animal housing

Animal housing plays an important role in NH₃ emissions from livestock, and in situ technology for NH₃ mitigation is lacking in China. Therefore, the aim of this study was to explore an efficient, economic, and practical technology to reduce NH₃ emissions from in situ animal housing. Here, we determined the effects of sulfuric acid and silage leachate at different doses on NH₃ emissions in a simulated experiment to select the best acidification conditions that could be applied to in situ NH₃ reduction technology in animal housing. We then designed and equipped a set of NH₃ mitigation technologies (an acid spraying device) in sheep housing and applied the selected acidification conditions to explore the effect of NH₃ mitigation technology on NH₃ emissions from the perspective of NH₃ reduction efficiency and economy. The results showed that sulfuric acid and silage leachate can reduce NH₃ emissions efficiently. The NH₃ reduction rates were 39.1% (P<0.05) for sulfuric acid and 42.7% (P<0.05) for silage leachate, respectively, when the spraying dose was 0.03 g·m⁻², but it only worked within 8 h. Because sulfuric acid is difficult to obtain on the market and atomizing silage leachate is challenging, lactic acid, the main component of silage leachate, was used as an acidifier in in situ housing. When spraying lactic acid at the dose of 0.03 g·m⁻² (0.01 mol·L⁻¹) three times per day (8:00, 16:00, 0:00) by using an acid spraying device, NH₃ reduction efficiency was the highest (55.6%, P<0.01); NH₃ concentrations in the daytime were reduced by 67.0% (P<0.01) (3 m height) and 72.0% (P<0.01) (0 m height), respectively, when acid was sprayed once per day at 8:00, but there was no influence on NH₃ concentration at night. When the acidification frequency was two times per day at 8:00 and 16:00, NH₃ concentration could be reduced throughout the day, and there was a more efficient reduction in the daytime with 72.0% (P<0.01) (3 m height) and 56.5% (P<0.01) (0 m height) than that in nighttime with 32.1% (P<0.01) and 25.8% (P<0.01) at 3 m and 0 m height, respectively. As for the cost of NH₃ reduction, spraying acid twice per day was the lowest at 147 ¥·kg⁻¹(NH₃), and the cost for three- and one-time acidification was 165 ¥·kg⁻¹(NH₃) and 211 ¥·kg⁻¹(NH₃), respectively. Infrastructure was the largest cost, accounting for approximately 80% of all costs. This study provides a feasible and efficient NH₃ reduction technology for in situ animal housing, but there is a need to improve the equipment cost for the wide promotion and application of this technology.