Animal Slurry Acidification Affects Particle Size Distribution and Improves Separation Efficiency

Abstract

Solid-liquid separation is performed to improve slurry management, and acidification of the slurry is used to reduce ammonia emissions. Acidification is known to affect slurry characteristics, and we hypothesized that it may affect mechanical separation. Our objective in this study was to assess the effects of slurry acidification on particle size distribution and separation efficiency. Two types of slurry, aged pig and fresh dairy, and two different acidification additives, sulfuric acid and aluminum sulfate (alum), were studied. We found that acidification with sulfuric acid promoted phosphorus (P) solubilization for both slurries, but no change was observed with alum. More ammonium was found in the acidified dairy slurry compared with raw dairy slurry, but no difference was found in aged pig slurry. Acidification before separation increased the proportion of the solid fraction in the slurries, and the effect was significantly higher with alum. When alum was used to acidify the slurries, the proportion of particles larger than 100 μm increased significantly, as did the P concentration in this particle size range. The efficiency of P separation increased markedly in both slurries when alum was used, with the removal to the solid fraction of the dairy slurry being almost complete (90%). Because the priority in mechanical separation is to increase the P content in the solid fraction, the use of alum before centrifugation may be the most suitable option for enhancing its nutrient content. We conclude that separation efficiency and particle size distribution are significantly affected by acidification, but the extent of the effects depends on slurry type and on the type of additive used for acidification.

Reduction in Methane Emissions From Acidified Dairy Slurry Is Related to Inhibition of Methanosarcina Species

“…Thus, acidification might have little effect on growth and activities of bacterial communities involved in the anaerobic degradation of organic matter (e.g., hydrolytic, acidogenic, and acetogenic bacteria) in manure ( Lin et al, 2013 ; Kuruti et al, 2017 ). As acidification may reduce aggregation of slurry particles ( Fangueiro et al, 2015 ; Gomez-Munoz et al, 2016 ; Regueiro et al, 2016 ), substrate availability for hydrolytic and acidogenic bacteria in slurries may increase. Gradual reductions in the volatile solids contents of both acidified and untreated slurries indicated that these communities were active.…”

Nutrient Potential Leachability in a Sandy Soil Amended with Manure-Based Fertilisers

“…The addition of ammonium sulphate, an acidic mineral fertiliser, to PiS might have increased the P solubility, as commonly observed in acidified slurry [45], which could explain why a higher amount of P was lost in PiS + AS relative to PiS + U (Table 1). However, it should be highlighted that, independent of the manure used or the N source, the quantity of P leached from the MBF application was considerably lower than after the application of the corresponding raw material (even if the difference was statistically significant only for PiS + U).…”

“…For the first 10 days, the addition of phosphoric acid to PoM and CaS enhanced the potential of P leaching, more pronouncedly in the case of CaS + PA, reaching a plateau from days 17 to 24, at ~1.50 mg P kg −1 soil (Figure 2e). The addition of a liquid P source, phosphoric acid, to liquid manure, CaS, may have strengthened the P leachability when compared to its addition to PoM, also because of the acidic properties of phosphoric acid, thus increasing the solubility of P in slurry [45]. Independent of the manure used, the addition of phosphoric acid increased the cumulative P leached, four times for PoM + PA, and almost six times for CaS + PA, relative to the original manures (Table 2).…”

Acidified Animal Manure Products Combined with a Nitrification Inhibitor Can Serve as a Starter Fertilizer for Maize

“…However, the transfer of P to the solid faction varies depending on the particle size distribution of the slurry and the separation technique used. Mechanical separation by screw press forces small particles through the filter pores and a large part of the small particles ends up in the liquid fraction [28,29], which could explain the low P content in RSSF. Most of the P present in digestates is contained in the solid fraction after decanting centrifugation applied in most biogas plants, and this is likely because this separation technique is able to retain smaller particles [22] explaining the high P concentration in DSF (Table 1).…”