Passive solid-liquid separation of anaerobically digested dairy manure using two-stage filtration

Solid-liquid separation makes further treatment and disposal of dairy manure easier. High concentrations of solids and long times-to-filter of anaerobically digested dairy manure present a challenge to cost-effective solid-liquid separation. This study operated a two-stage filtration system by batch modes to develop passive solid-liquid separation of anaerobically digested dairy manure. In the 1st-stage, pebble filters attained solid-liquid separation through surface filtration and evaporation. Filtration was completed after 7-33 d into each cycle of batch operation. Evaporation became the predominant mechanism for manure dewatering 2-3 weeks after each batch loading. Filtration was faster at higher temperatures, higher initial solids concentrations, and shorter times-to-filter. Two weeks after batch loadings, the pebble filters had removed 81.4-97.7% of total solids and 87.1-98.8% of total volatile solids from the filtrate and the manure retained on the pebble beds was thickened to 6.3-24.6% solids. Dewatering on the pebble beds was faster at a lower loading rate and more efficient at a higher loading rate (0.20 versus 0.16 and 0.12 m(3) m(-2)). In the 2nd-stage, the sand filters removed suspended solids via depth filtration. (C) 2012 IAgrE. Published by Elsevier Ltd. All rights reserved.