Solid/Liquid Separation of Pig Manure by Biological Flotation: Pilot-Scale Study

Many problems are associated with pig manure production like high biochemical oxygen demand, chemical oxygen demand, nitrogen, and phosphorus contents. Manure produces may be used in land spreading for agricultural purposes. Over application of liquid manure or runoff caused by precipitation contribute notably to surface or overland flow of phosphorus. In this study, the LISOX process is proposed for use in medium size farms, namely a 2,000-head swine farm. The LISOX process uses biological passive flotation, without any gas addition, to enable the flocs to rise to the surface. Results show that this technology is able to considerably reduce the solids content in the final effluent to $1.1\pm 0.3\%$ and reached solids content of $17.9\pm 2.6\%$ in the combined solid manure obtained at the end of the LISOX process. Total phosphorus $\left(P_t\right)$ concentrations have been reduced from $1,234\pm 428\text{mg}/\text{L}$ to $146\pm 46\text{mg}/\text{L}$ in the final effluent, while a value of $P_t$ of $20.6\pm 7.9\text{g}/\text{kg}$ has been obtained in the final solid fraction of the treated manure. The initial ammonium ion/total phosphorus ratio of $2.3\pm 1.0$ has been increased to respectively $16.4\pm 4.6$ and $17.6\pm 5.4$ after the primary and the secondary flotation, which is clearly much higher than the target value $\left({\text{NH}}_4/P_t>7\right)$ .