ENHANCED PHOSPHORUS REMOVAL FROM SWINE-NURSERY MANURE IN AERATED BATCH REACTORS

Phosphorus–based land application of swine manure slurry results in under–application of nitrogen (N), while nitrogen–based application leads to over–application of phosphorus (P). Significant amounts of P must be removed from swine manure to reduce P over–application, and at the same time, safely apply targeted amounts of N. This study compared three schemes of soluble orthophosphate (ortho–P) reduction from liquid swine nursery manure during batch aeration: (1) solids–liquid separation before aeration (pre–aeration solids–liquid, or PASL, separation), (2) solids–liquid separation in the middle of aeration (mid–aeration solids–liquid, or MASL, separation) and (3) no solids–liquid separation (control). Significantly more ortho–P was converted to non–soluble species with MASL separation (92%) than with either PASL separation (87%) or the control (84%). MASL separation also significantly improved the removal of total phosphorus (TP) in the sludge from the liquid after an overnight sedimentation process: 80%, 70%, and 66% for MASL separation, PASL separation, and control, respectively. Solids–liquid separation enhanced the maintenance of higher oxidation potentials (depicted by higher values of ORP in the separated manures than in the control) in the manure during the latter days of aeration, implying that substantial energy saving is possible for prolonged aeration of separated liquid manure. This is an important element in the post–aeration treatment for ensuring that P removed from the solution stays in the sludge and is not released back into solution, if removal of the sludge does not immediately follow scheduled aeration treatment.