Study On The Annual Dissolution Of Pig Farm Biogas Slurry By Hydroponic Watercress And Water Spinach

In this study,the growth and quality indexes of watercress and water spinach in floating beds with different concentrations of pig manure digested slurry for hydroponic system were investigated and the purification effect of watercress and water spinach on different dilution times of digested slurry were studied in order to solve the problem of post-treatment of digested slurry and reduce the cost of nutrient solution in soilless culture conditions.Results were as follows:1.Hydroponic watercress experiments in winter and spring showed the inhibitory effects of high concentration digested slurry on the root growth and plant height growth of watercress.Different concentration gradients were set up(from high to low:The ammonia nitrogen contents in D1,D2,D3 and D4 are 130 mg/L,100 mg/L,70 mg/L,40 mg/L,respectively.).Compared with CK,the root lengths of D1 and D2 were smaller;D3 grew well,and its fresh weight reached 4.11kg/m2 at harvest,which was the highest but not significantly different from D2.The soluble protein content in watercress increased under hydroponic with digested slurry.D3 gained the highest soluble protein content at 3.97mg/g,which was outstandingly higher than CK1.The concentration of digested slurry showed the negative correlation with the soluble sugar content,and the soluble sugar content of D4 was the highest,reaching 9.64 mg/g;the VC content in D2,reaching 256.49 mg/kg,not significantly different from CK2,was notably higher than those under other treatments.The contents of chlorophyll a and chlorophyll b in D3 were significantly higher than those under other treatments,and its average contents were 0.427 mg/g and 0.103 mg/g,respectively.The highest average contents of TN,TP and TK in watercress were detected in the samples from the treatments of D2,D1 and D1,reaching 104.09 mg/g,3.47 mg/g and 1.371 mg/g,respectively.Watercress with treatments of D4,D4,D4,D3 and D4 led to the highest removal rates of TN,ammonia nitrogen,TP,TK and COD in the biogas slurry,respectively.After 21 days,the contents of ammonia nitrogen,TP and COD in D2 digested slurry decreased to 79.51 mg/L,1.85 mg/L and 213.25 mg/L,respectively,which achieved the best purification benefit,meeting the national standards for the discharge of water pollutants from intensive livestock and poultry farming.2.Different concentration gradients were set up(from high to low:The ammonia nitrogen contents in K1,K2,K3 and K4 are 130 mg/L,100 mg/L,70 mg/L,40 mg/L,respectively.).Experiments of hydroponic water spinaches in summer and autumn presented that the average root length of K1 was the shortest,but K1 maintained the highest growth rate during the whole growth period with the highest average plant height and fresh weight of 29.66 cm and 2.60 kg/m2,respectively.High concentrations of digested slurry inhibited the production of soluble protein in water spinach,and the content of soluble protein in K3 was certified the highest,reaching 4.22 mg/g,significantly higher than those in K1 and K2.The contents of soluble sugar and VC in K4 were 8.23 mg/g and 924.48 mg/kg,respectively,which were remarkably higher in comparison with those under other treatments.The contents of chlorophyll a and chlorophyll b in K3 were the highest,reaching 1.093 mg/g and 0.261 mg/g,respectively.The highest average contents of TN,TP and TK in the whole planting cycle of the water spinach were detected in the treatments with K1,K2 and K3,which were 51.59 mg/g,3.03 mg/g and 0.418 mg/g,respectively.Water spinaches with treatments of K2,K1,K4,K4 and K1 led to the highest removal rates of TN,ammonia nitrogen,TP,TK and COD in digested slurry,respectively.After 7 days,the contents of ammonia nitrogen,TP and COD in K1 digested slurry decreased to 74.56 mg/L,6.44 mg/L and 139.71.Mg/L,which achieved the best purification benefit,meeting the national standards for the discharge of water pollutants from intensive livestock and poultry farming.3.The nitrate and nitrite contents in watercress and water spinach under the hydroponic culture in digested slurry were below the national limited standard after,and the contents of Cu,Zn,Pb,Cr and Cd were also below the national limited standard.