Study On The Synergistic Removal Of Heavy Metals From Residual Activated Sludge By Vermicomposting And Plant Cultivatio

With the rapid development of the city,the amount of urban domestic sewage treatment is increasing,and the output of remaining activated sludge in the city has also risen sharply.Converting sludge into organic fertilizer is now more expensive and secondary pollution in sludge treatment.For traditional processing technologies with many disadvantages,it is a harmless and resource-based method.The biggest obstacle to conversion into organic fertilizer is the extremely high heavy metal content in the sludge and its high fluidity,so removing heavy metals in the sludge and reducing its fluidity is now an urgent matter.The plant cultivation method was applied in this experiment because of its low cost,good effect of removing heavy metals,and environmental friendliness.However,because the survival rate of plants in sludge is not high and the growth is slow,so in this experiment The mud is composted with earthworms to improve its physical and chemical properties and remove some heavy metals from the sludge.After the sludge can meet the requirements of plant growth,the compost product is planted to remove heavy metals in the remaining activated sludge and reduce its fluidity through a synergistic method of earthworm composting and plant cultivation.The main results of the experiment are as follows:(1)After earthworm composting,the remaining activated sludge moisture content decreased from 71.9%to 62.5%;pH tended to be neutral;conductivity,porosity,nitrogen and phosphorus content and other indicators increased significantly,of which effective nitrogen accounted for total nitrogen The proportion increased from 49%to 57%,and the proportion of available phosphorus to total phosphorus increased from 25.3%to 39.0%.Earthworm composting significantly improves the basic physical and chemical properties of the remaining activated sludge,making it a better living environment for plants.(2)After earthworm composting,the total content of heavy metals in the remaining activated sludge decreased significantly,of which the total amount of Cu and Mn decreased by 18.8%and 13.3%;the residual state content and proportion of each heavy metal increased significantly,Among them,the proportion of residual states of Cr and Zn heavy metals both increased by more than ten percentage points.Earthworm compost removes some of the heavy metals in the remaining activated sludge and reduces its fluidity.(3)The germination rate of plants using earthworm feces as medium is above 90%,and the germination rate of plants in sludge is below 70%;the plant height and dry weight of earthworm feces are the highest;the content of nitrogen and phosphorus The peak value is also the highest;the pH,EC,TOC,total nitrogen,total nitrogen,available nitrogen,total phosphorus,and available phosphorus content of earthworm droppings in the three culture media decreased the most.Earthworm feces eliminate the inhibitory effect of sludge on plant growth and promote the absorption of nutrients by plants.(4)The total amount of heavy metals in the plant in the earthworm feces medium is the highest;the heavy metal content in the earthworm feces has the largest decrease,and the most obvious is that the Zn in the earthworm feces where the water spinach is located has dropped by 1.24 mg/g;The largest increase in the proportion of the state,the most obvious of which is that the residual state of Cu in the earthworm feces where the spinach is located has increased by 20.2%.Plant planting can better remove heavy metals in earthworm feces and reduce their mobility.Therefore,the synergistic effect of earthworm composting and plant planting can not only better remove the heavy metals of the remaining activated sludge and reduce its mobility,but also a low-cost and environmentally friendly sludge heavy metal treatment method.