The effects of electrocoagulation on phosphorus removal and particle settling capability in swine manure

Swine manure is conventionally used as a fertilizer because it contains necessary nutrients for plant growth. When the application rate is formulated based on plant nitrogen requirement, phosphorus will accumulate in the soil over the years and may cause eutrophication in surrounding water bodies. Phosphorus separation from liquid manure before the land application can contribute to better nutrient management, but an appreciable amount of phosphorus exists in the form of fine particles smaller than 45 µm and is therefore difficult to separate by natural sedimentation or other mechanical solid-liquid separation systems. This work evaluated low carbon steel-based electrocoagulation (EC) for phosphorus separation in liquid swine manure sampled from two swine barns, and assessed the mechanisms for improved particle and phosphorus settling ability after EC treatment. The results show that EC pretreatment followed by one-day natural precipitation removed 72.6–86.3% of phosphorus from liquid swine manure. Phosphorus removal kept increased until it reached a plateau (60 min and 140 min for the two types of swine manure). The settling property of EC treated swine manure improved and about 90% of particles was removed. Further analyses indicated that the particle density of the majority part of manure solids (particles with sizes between 25 µm and 45 µm) increased from 1.29 g/mL to 1.36 g/mL after EC, and that the background viscosity of liquid manure decreased from 1.99 g/m∗s to 1.64 g/m∗s. All of those manure property changes expedited particle and phosphorus settling. Overall, the EC method developed in this study successfully achieved the goal of improving phosphorus recovery and solid-liquid separation from swine manure, and has a potential to achieve better separation and to consume less energy after process optimization.