Simultaneous Separation of Phosphorus Sludge and Manure Solids with Polymers

Abstract

In this article, we describe improvement of a manure treatment system without a lagoon through implementation of a concept of simultaneous separation of solids. The original system consisted of three basic processes in series: solid-liquid separation of raw swine manure (SM) using cationic polyacrylamide (PAM), subsequent treatment of liquid through nitrification-denitrification, and a soluble P removal unit. The P removal unit used hydrated lime to precipitate P and anionic PAM to enhance dewatering of the P-rich sludge (PS). Our objectives were to evaluate if it is technically feasible to flocculate and dewater both the PS and SM in a simultaneous operation, using the same dewatering equipment and producing only one stream of solids. The simultaneous separation concept was tested in a laboratory prototype using PS and SM materials from a first-generation version of the system without a lagoon installed in a swine farm in North Carolina. Compared with SM, the PS material had a higher pH (10.1 vs. 7.5), about 5 times more total suspended solids (TSS) (29.5 vs. 5.7 g L-1), and 9 times the total P (2.7 vs. 0.3 g L-1). We found that the PS remained as a solid when mixed with SM, and all the solids were efficiently separated (>90%) using a single polymer application (cationic PAM). The simultaneous separation process did not increase the amount of PAM that would normally be used to effectively treat SM alone. The same dosage of PAM (60 mg L-1) was effective even when the mixture contained 43% more TSS and 94% more TP as a result of PS addition (up to 150 mL L-1). PAM effectiveness in terms of TSS or TP increased with the simultaneous separation process, from 108 to 160 g TSS g-1 PAM, and from 4.7 to 11.4 g TP g-1 PAM. Mass removal efficiencies at the higher PS rate were 96.8% for TSS and 94.7% for TP. The quality of the treated liquid in terms of TSS, COD, and TP concentrations was also improved, and the P content of the separated solids was significantly increased (from 9.5% to 16.9% P2O5). Our results indicate that simultaneous separation of two contrasting sludges with PAM is technically feasible, and that the combined separation process is more efficient in terms of polymer use and equipment needs compared with a situation in which two dewatering units are used to separate the same amount of solids. Thus, its implementation can reduce installation and operational cost of the overall treatment system.