Gravity Solid-Liquid Separation with Continuous Solids Removal System
Need:
The integrated swine manure treatment approach depends on reliable, inexpensive liquid-solid separation to produce a solids stream that will go on to one of the value-added processes being studied. There are two extremes in the liquid-solid separation equipment realm: (1) the mechanical separator, with substantial capital and maintenance costs, and (2) the gravity settling tank, which is simple in design, has no moving parts and requires little maintenance. Many studies show that the gravity process is more efficient than a mechanical separator in removing fine solids from swine manure. However, a gravity settling tank requires periodic solids removal from its bottom, using a vacuum tank or chopper pump/slurry tank combination. Furthermore, results have indicated that long-term storage of solids within the tank allows biological activity within the solids to bulk up the solids, causing particulate material to be re-suspended in the liquid. The solids removal efficiency thus goes down with time. There is a need to combine the efficiency and simplicity of the gravity settling process with a very simple, very reliable continuous solids removal system.Objectives:
Develop a gravity liquid-solid separation basin with a low maintenance, low cost continuous solids removing system. The separated solids can be further processed or land applied, and the liquid will go to a storage structure or an existing lagoon.Approach:
The proposed liquid-solid separation system will consist of a sloping-bottomed settling tank with a horizontal trough at the v-bottom and a slow-turning non-metallic auger. Influent from the swine barn will be discharged periodically into the settling basin, which will be designed for the retention time and average flow velocity recommended for most efficient solids settling. Solids settling to the bottom will make their way to the trough where they will be slowly augered to one end of the tank, then up the inclined side within an auger tube, and finally out of the tank above the liquid level (Figure). The lifting auger will have a low power requirement and will turn very slowly and continuously. The solid and liquid separated streams will be frequently analyzed for total nitrogen, ammonium nitrogen, phosphorus, potassium, total solids, suspended solids, and volatile solids. The sample results will be compared with the high-cost mechanical separator system being evaluated by another related project.
Expected outcome:
An evaluation of the system combining gravity settling with continuous solids removal will (1) prove the validity of the concept, (2) if it is successful, provide a high-solids-content manure product for further value-added processing research, and (3) establish design parameters for a farm-constructed settling tank system.Related Papers
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