Abstract: Systems and methods for separating manure into a solid fraction and a liquid fraction, and optionally further separating the liquid fraction to capture a sand-rich second solid fraction and a second liquid fraction. Some separators have an adjustable inclination, forcing the manure passage to be slightly up hill, with an overflow box capturing and re-feeding excess manure inflow. One system includes an internally fed rotary screen separator having a perforated outer tube, the perforations being holes less than about 3/16 inch diameter. The outer tube can include spiral inner flights which may be interrupted near the discharge end to allow free fluid to flow back into the separator. The manure can be fed into an inlet conduit having an adjustable angle discharge slot. Some outer tubes have non-perforated end regions serving as the foundation for drive tracks. The solid fraction discharge can be further dewatered in a roller press.