Phosphorus distribution with respect to particle size and microbial activity in dairy manure and implications for manure management

This work investigated the distribution of phosphorus in dairy manure as it relates to particle size and provides experimentally derived insights for improving the management of phosphorus. The data presented here illustrates some aspects of manure handling that may be optimized for controlling the distribution of phosphorus. It provides experimental data that supplements existing literature by 1) extending the limits of study regarding particle size distribution; 2) extending the limit of centrifugal forces studied; 3) demonstrating an improved pathway for phosphorus management in wastewater using a substrate mediated flocculation process; and 4) providing some experimental observations showing that the microbiota present in dairy manure can diminish stratification of suspended solids and phosphorus concentrations within separated liquid manure products. Further, based on quadratic modeling of phosphorus relative to sieve size, and the observations that accompanied progressive washing and mechanical agitation performed, a convincing argument for relating phosphorus distribution to the surface area of a substrate is made. The findings imply that much of the phosphorus present in manure is superficially bound to larger particulates, rather than an intrinsic or chemical part of the bulk material itself, and can be mediated by washing or mechanical means where the phosphorus present in coarser fractions can be shunted towards finer or liquid fractions. Approximately 80% of phosphorus was associated with particulates bound to larger substrate. Indeed, 95.5% of the phosphorus in the bulk manure was removable as particulates with cross sectional diameter less than 2mm by simple washing. Further removal of phosphorus in >2mm substrate through fermentation and leaching was also demonstrated. Some portion of this distribution in phosphorus appears to be dominated by microbes.