Design of an automatic fecal-cleaning system with solid-liquid separation in tethered cattle shed

Manual cleaning of feces still remains in many cattle sheds at present. The architectural structure and breeding form cannot fully meet the large-scale production in recent years. Various pathogenic bacteria in feces can also be easy to contaminate the shed and body surface of cattle, leading to lameness and air pollutants. Besides, the independent solid-liquid separation has been a huge hindrance to promoting manure treatment in modern dairy farming. In this study, an automatic fecal-cleaning system was designed with the solid-liquid separation in tethered cattle shed. The new system was installed in the waste ditch, at the end of which a septic tank was built in this case. Specifically, the excrement fell on the conveyer belt, where the liquid flew out through the filter hole on the belt. The electric machine was installed to avoid corrosion at the beginning of the ditch. The solid matter on the belt was moved and fell into the septic tank, as the conveyer belt was driven by the electric machine through the chains and rollers. Belt tensioner and carrier rollers were assembled to prevent skidding and deflection, and further to ensure the smooth running of the system. A trial test was also carried out to obtain the related parameters of the system at an experimental dairy farm in Yangzhou, Jiangsu Province, China in June 2022. A tethered cow shed and all healthy cows were selected as the research objects. The body measurements were performed on the 30 heads of replacement cows and 69 heads of lactating cows. The results indicate that the body length was more outstanding to reflect the individual differences than the body height at the late stage of cows' growth. The lactating cows shared 75.4% of the total body length in the size of 1.60-1.75 m. The body length showed a significant positive correlation with the feces drop point of cows (P<0.01). If the width of the waste ditch was 40 cm, 79.4% of cows were within the scale excreting completely into the waste ditch. Once the body length of cattle was too long or short, the neck lever lifting or lowering was valid to regulate the excretion position (P<0.01). Thus the efficiency of fecal cleaning was promoted during this time. A simulation experiment of cow's excretion was conducted to test the moisture content of solid matter, the turbidity of filtrate dilution, and the precipitation volume, in order to compare the filtration effect with different hole diameters. Nevertheless, the filter holes were congested by the feces, as the water fell straight on the solid matter if the hole diameter was shorter than 8 mm. Therefore, the belts were introduced to the different degrees of standing water. The filtration effect of the 8 mm group was not as good as 9, and 10 mm, because of the surface tension of the filtrate. More importantly, the 10 mm group was significantly higher than the 9 mm one, in terms of the precipitation volume in the filtrate. Therefore, 9 mm was proven to be the most suitable diameter for the filter hole. The intensity was calculated as 0.57 MPa far within the tensile strength of the polyvinyl chloride belt, when a hoof stepped on the belt, according to the weight of a cow and the area of a cow's hoof. Furthermore, the finite element analysis was carried out to calculate the loading density of the system. The maximum deformation was 1.138 cm for the belt with the carrier rollers. The frequency and running speed of the system were also adjusted in practical application, according to the specific situation of cattle's excretion. The automatic fecal-cleaning system can be expected to realize the solid-liquid separation in cattle sheds. A suitable design of the waste ditch and the cow bed can be greatly conducive to improving the efficiency of cleaning. This finding can provide data support and technical reference to optimize effective waste treatment.