Study On Resource Utilization By Anaerobic Digestion And Soil Restoration In Rare Earth Mining Areas

Ganzhou was largest mining area for ionic rare earth elements?REEs?in China,while bringing great financial profit,the ecological environment of the wasteland had also caused widespread concerns in society.This paper applied the model of?Resource utilization plus Ecological restoration for soil?,with Dicranopteris dichotoma?DD?,Phytolacca americana L?PAL?and later planted Pennisetum sinese Roxb?PSR?,Pennisetum americanum×P.purpureum?PAP?to produce biogas by anaerobic digestion?AD?.Secondly,the wasteland was irrigated with biogas residues and effect of ecological restoration for soil was explored.The main conclusions were as follows:1.To investigate the performance of gas production with DD and PAL under pretreatments of acid,alkali and liquid hot water,and explored the effect of REEs on performance of AD by adding La³⁺.The removal rate of lignin varied with different pretreatments at order:alkali>acid>liquid hot water,50.02%and 48.62%lignin were removed with alkali pretreatment from DD and PAL respectively,yield of methane was also highest,which was 165.06 mL/g VS and 260.40 mL/g VS respectively,82.51%and 79.38%higher than untreated.In addition,acid and liquid hot water had better effect on methane production with DD,which was 43.80%and 57.73%higher than untreated,however,there was no obvious effect on methane production with PAL.External adding with 0.01 mg/L and 0.05 mg/L La³⁺had no effect with AD;Adding with 0.50 mg/L La³⁺had obvious effect with an increase of 14.08%and adding with5.00 mg/L La³⁺inhibitted performance of AD significantly.2.The performance of methane production by multiple raw materials of PSR,PAP and pig manure were studied with VS raito of 4:0:0,0:4:0,0:0:4,2:2:0,3:0:1,0:3:1and 1.5:1.5:1.The maximum methane yield was 297.51 mL/g VS with VS ratio of1.5:1.5:1,which was 12.30%,45.38%and 63.64%higher than mono-digestion of PSR,PAP,and pig manure respectively,the average concentration of methane was also highest with 52.51%and synergistic effect index?SEI?was 26.86%in this condition.In addition,SEI was 9.05%and 15.75%with VS ratio of 3:0:1 and 0:3:1,respectively,however,the SEI was-2.03%with VS ratio of 2:2:0;The analysis of modified Gompertz equation indicated that the model had feasibility to describe the dynamic process of AD,the R² values of the fitting curves was between 0.997⁰.999;Group of PAP+pig manure had longest lag phase???with 5.75d,and T₈₀ was 19d;The shortest?was achieved by mono-digestion of pig manure with 2.01d,and T₈₀ was 13d only.3.The effects on physicochemical properties of wastelands by irrigation with biogas residues were studied.The organic matter in three wastelands were increased by64.97%,49.60%and 13.10%,respectively.Total amounts of REEs?La,Ce,Pr,Nd,Sm,Y?in wasteland 1 and 2 were reduced by 15.30%and 40.51%,respectively,and increased slightly in wasteland 3;The content of heavy metals?Cd,Hg,Cr,Cu,Ni,As,Pb,Zn?by irrigation with biogas residues varying degrees of increase,but it was still in margin of safety;Coefficient of variation?CV?of pH,NH₄⁺and SO₄^2-was in the order of NH₄⁺>SO₄^2->pH,both NH₄⁺and SO₄^2-belong to medium variability with their CV was higher than 50%,while pH was relatively weak with CV being 4.27%.Particle of clay and silt in wasteland 1 increased by 4.27%and 2.39%,respectively,and soil desertification had been alleviated,however,there was no effect with wasteland 2 and soil desertification was aggravated with wasteland 3.Correlational analysis of physicochemical properties of wastelands showed that there was a very significant positive correlation between organic matter with total nitrogen,total phosphorus and available phosphorus,the related coefficient was 0.901,0.819 and0.858,respectively.In addition,threre was a significant correlation between organic matter and available potassium with related coefficient of 0.709,what's more,a very significant positive correlation between two of total nitrogen,total phosphorus,available phosphorus and available potassium was found,while there was little relationship between pH and soil nutrients.