Effect of centrifugal microfiltration on solid-liquid separation of pig farm wastewater
摘要: 固液分离是畜禽废水处理的关键技术, 不仅可以将固体物质分离出来进一步肥料化利用, 还可减少废水中污染物浓度从而降低后续处理负荷。本文主要针对传统的固液分离设备效果差和效率低的问题, 以离心微滤机为研究对象, 通过系统监测, 科学评价猪场废水总固体浓度(1%、2%、3%、4%和5%)和离心微滤机筛网孔径(15 µm、25 µm和50 µm)对去除率的影响。结果表明, 随着总固体浓度的增高和筛网孔径的减小, 水质指标的去除率有增加趋势。随筛网孔径的增大离心微滤机单位时间内的处理量也随之增加, 50 µm时处理量为14~19 m3∙h−1, 15 µm与25 µm时处理量为2~7 m3∙h−1。综合考虑, 总固体浓度为5%和筛网孔径为50 µm为最佳处理组, 水质指标中总固体浓度、化学需氧量和总磷的去除率分别为57%、29%和43%。该离心微滤机与其他固液分离设备相比, 具有分离效果好和能耗低的优点, 因此在处理猪场废水时具有较好的应用前景。Abstract: Large amounts of livestock waste are discharged owing to the rapid development of the livestock industry, and they cause serious environmental pollution if not effectively treated. Livestock waste has high pollutant concentrations and complex compositions; hence, it requires effective pretreatment to avoid high post-treatment difficulties and low treatment effects. Solid-liquid separation has been reported to be a key technology for livestock waste treatment. This technology could produce a solid fraction that can be used as a high-nutrient fertilizer and reduce pollutants in the waste, lowering the loads for subsequent treatments. However, the effect and efficiency of the traditional solid-liquid separation process for treating livestock waste are relatively low and need to be improved. In this study, a new centrifugal microfiltration separator, used for the reduction of pollutants in livestock waste, was systematically evaluated under different conditions. This study monitored the correlation between total solid (TS) concentrations in pig farm wastewater and other related water quality parameters. The effects of different TS concentrations and mesh sizes on the rate and treatment costs of the separator were also studied. The TS was set to 1%, 2%, 3%, 4%, and 5%, and the mesh sizes were set to 15, 25, and 50 µm. The results showed that TS concentrations were negatively correlated with pH and electrical conductivity (EC), and positively correlated with chemical oxygen demand (COD), total nitrogen (TN), ammonia nitrogen (NH4 +-N) and total phosphorus (TP) in the wastewater. The correlation between TS and pH, COD, and TP was higher, with correlation coefficients (R2) of 0.57, 0.53, and 0.66, respectively. TS had no obvious correlation with turbidity, EC, TN, or NH4 +-N with R2 of 0.33, 0.02, 0.10 and 0.03, respectively. The separator effectively removed TS from pig farm wastewater with a removal rate of 17%−68%. The removal rate of turbidity, COD, TN, TP and NH4 +-N were 3%–39%, 17%–59%, 4%–43%, 18%–54%, and 2%–17%, respectively. The removal rate of pollutants from pig farm wastewater increased with an increase in TS and a decrease in mesh size. The removal rate increased with increasing mesh size. The mesh size of 15 µm had the highest removal rates of 68% for TS, 40% for turbidity, 59% for COD, 42% for TN, and 54% for TP. There was a significant difference in treatment capacity between all mesh sizes (P<0.01). The treatment capacity of 50 µm mesh size was 14‒19 m3∙h−1 and that of 15 and 25 µm mesh size was 2‒7 m3∙h−1. The operational costs of centrifugal microfiltration machine using the screen sizes of 15, 25, and 50 µm in a pig farm having stock of 10 000 pigs as an example were estimated to be 2.44, 2.06, and 1.08 ¥∙m−3, respectively. The optimal mesh size and TS for treating pig farm wastewater were 50 µm and 5%, respectively, when considering removal rate and treatment capacity. Compared with traditional solid-liquid separators, the new separator has good application prospects because of its high separation effect and low energy consumption.
图 1 离心微滤工艺流程图
1. 进料口; 2. 滤网; 3. 搅拌泵; 4. 储水桶; 5. 止水阀; 6. 螺杆泵; 7. 微滤机; 8. 固体储存池; 9. 液体储存池。1. feed inlet; 2. screen; 3. mixing pump; 4. water storage bucket; 5. water stop valve; 6. screw pump; 7. microfiltration machine; 8. solid storage pool; 9. liquid storage pool.
Figure 1. Flow chart of the centrifugal microfiltration process
图 2 离心微滤机的示意图
1. 进料口; 2. 微滤液体出口; 3. 浓缩污泥出口; 4. 流量调节器; 5.自动加油脂器; 6. 筛网; 7. 电机; 8. 支撑脚。1. feed inlet; 2. microfiltration liquid outlet; 3. concentrated sludge outlet; 4. flow regulator; 5. automatic greaser; 6. filter mesh; 7. motor; 8. support foot.
Figure 2. Schematic diagram of centrifugalmicrofiltration