Development of waterfowl manure pretreatment device based on low speed centrifugal separation technology

Resource utilization of animal manure can be used to reduce environmental pollution in the recycling of nutrients from the manure. Solid-liquid separation can serve as one of the pretreatment to improve the utilization efficiency for cost saving. However, existing treatments cannot fully meet the large-scale production in recent years, such as the high energy consumption, and low separation efficiency for sewage with a high viscosity and small solid particles, such as waterfowl feces and biogas slurry. Single-factor experiments were carried out to determine the effects of the centrifugal separation time, mesh number, and centrifugal separation speed on the separation effect of waterfowl feces. The quadratic general rotary unitized design was used to implement an optimization test. The optimal combination of parameters was obtained after the analysis of the data and consideration of the actual operating conditions. The data were analyzed by Excel 2016, Origin 2021, and Design Expert 12. The results showed that the treatment was achieved in better solid removal with the shorter hydraulic retention time of subsequent biochemical treatment. The content of pollutants in the waterfowl feces showed a trend of gradual decrease with the increase of screen mesh. The reason was that the aperture size decreased, as the number of sieve meshes increased. The larger solid particles were passed through to be trapped in the filter bag. The better performance of solid-liquid separation of waterfowl feces was achieved with the increase in centrifugal separation speed, due to the retention effect of the screen and stronger centrifugal action. The solids removal effect cannot be significantly enhanced under the action of low-speed centrifugation when the centrifugal separation speed continued to increase. The separation effect of free water was mainly achieved, where the adsorbed water was not strong enough to detach from the inter-particle adsorption. The thickness of the filter cake in the filter bag gradually increased, as the separation time increased. The solid particles were retained, whereas, the liquid also had sufficient time to separate through the filter cake. But the excessive separation time led to the clogging of the screen pores, where the liquid was difficult to pass through the filter cake. After the centrifuge separation optimization test and verification, the optimal separation effect was obtained, when the centrifuge separation time, mesh number, and centrifugal separation speed were set as 3 min, 120 mesh (aperture size 0.13 mm), and 700 r/min, respectively. At the same time, the removal rates of total solid (TS), volatile solids (VS), chemical oxygen demand (COD), NH₄⁺-N, and total phosphorus (TP) were 50.20%, 57.59%, 5.39%, 4.39%, and 5.76%, respectively. The separation effects (removal rates of TS and VS were 53.21% and 58.61%) were comparable to the separation effect of a high-speed centrifuge after the field operation of the prototype. The treatment cost was reduced by nearly 22% for one ton of sewage, indicating the feasible low-speed differential centrifugal separation. This finding can provide a promising scheme for the removal of suspended solids from the waterfowl feces in engineering popularization.