Effect of solid-liquid separation on bod and VFA in swine manure

Fresh swine manure was sieved into seven different particle size categories , i.e., <0.075 mm, <0.15 mm, <0.25 mm, <0.5 mm, <1.0 mm, <1.4 mm, and <2.0 mm. Manure was stored in seven PVC columns and sampled every 5 days up to 3 0 days. Manure samples were analyzed for total volatile fatty acids (VFAs), 5-day biochemical oxygen demand (BOD5), total solids (TS), total suspended solids (TSS), and total volatile solids (TVS). Two parameters (VFAs and BO D5) were used to determine the odor generation potential of the test manure . The results showed that total VFAs correlated well with BOD5 (R-2=0.8297) . The levels of TSS only explained 40% of BOD5 and 46% of VFAs, both of whi ch increased with storage time, regardless of solid particle sizes. Also, t he data inferred that most of the odorous compounds (measured by VFA and BO D levels) were contained in manure solid particles less than 0.075 mm. Thes e cannot be removed by commercial mechanical separators with screen size ra nging from 0.5 to 3.0 mm. With an average separation efficiency of 25% for most commercially available mechanical separators, the removal efficiencies of BOD5 and VFAs were as low as 10% and 12%, respectively. These findings cannot justify the use of solid-liquid separation to control odor. Data als o showed that for swine manure, it is critical to run separation treatment within the first ten days after the manure is excreted to potentially impro ve the separation efficiency. After ten days, the degradation of TSS was ac celerated due to the increased biological activities, which may greatly red uce the separation efficiency.