Eco-restoration Techniques For Contaminated Groundwater And Sludge At An Agricultural Site

There has been considerable progress in groundwater restoration techniques in contaminated sites,but environmental friendly,cost-effective ecological and bioremediation technologies still need to be innovated.This study follows the roadmap of "pollution site investigation and characterisation of pollutants ? objective pollutant degradable bacteria separation and identification ? laboratory based study of the obtained strains for polycyclic aromatic hydrocarbons(PAHs)degradation performance ? site-based AS(Air Sparging)remediation techniques and mechanism? R&D of the constructed wetland eco-restoration" as a systematic study.Findings are as follows:(1)On the basis of field investigation,collection and analysis of water samples were carried out to determine the types and sources of groundwater pollution in the demonstration site,so as to determine the repair technology of site pollution.The concentration of PAHs in groundwater in the region was between 1.2~2.25 ?g/L,and the concentration increased gradually from east to west.The concentration of arsenic in groundwater was increasing from southeast to northwest,and the average concentration was up to 18 ?g/L.The total iron content increased gradually from east to west,while the concentration of mn increased gradually from the north to the south.The average content of PAHs in sludge was 6.4 mg/kg.To solve the problem of PAHs contamination as common pollutants,it remains difficult to clean up the PAHs contaminated groundwater at site scale.(2)Isolated from contaminated field soil samples,an efficient degradation of PAHs,the function of pyrene,morphology of the bacteria and the use of molecular biology techniques were measured 16 s rDNA sequences in GenBank Blast than judgment for bacillus.The strain was first identified as B4 in the agricultural contaminated sites.Under the condition of same examined strains B4 for several typical containing aromatic hydrocarbons degradation effect,more experimental results strains B4 on phenanthrene,naphthalene,fluoranthene,and fluorene removalefficiencies were 91%,96%,79%,96%,show that the bio-degradation of PAHs,which has good broad spectrum performance.In addition,we also test the different pH,temperature,dissolved oxygen,and the intensity of the electrolyte effect on the activity of microbial growth,B4 strain is most suitable for growth of the pH value of 7.0,temperature is 29 ?C,dissolved oxygen was 2.5 mg/L,electrolyte strength was 1%.(3)The strain B4 was identified as a culture for pyrene degradation as a unique substrate biodegradation,the low concentration of pyrene activity has certain stimulative effect to the strain B4 growth,increase the strain of biological activity,in the best rate is as high as 91.2%.During the incubation period of 30 d,the enzyme-assisted strain B4 reached 84.3% and stabilized after 20 d.The plants in artificial wetland play a significant role in the ecological restoration of pyrene,which is more than 90% efficient.By enzyme aided B4 strains,higher biological B4 and B4 to other PAHs biodegradation performance study,can get higher biological auxiliary B4 strains of PAHs degradation effect in short time,high efficiency,because of higher organisms in the process of growth,its root system itself to produce enzymes,by adding enzyme after the effect is more ideal.(4)In view of the agricultural setting of the groundwater pollution,in-situ air sparging(AS)was put forward for remediation engineering,on the basis of the original groundwater monitoring Wells,8 from layout borehole,one place for gas injection(AS well),the other 7 Wells for monitoring Wells(M1~M7).Demonstration project running results show that:(a)The subsurface porous media have porosity and permeability,monitoring borehole water level rose sharply after the remedial system running of 30 min,water levels in most wells were falling and keep relatively stable after 120 min.This phenomenon shows that the higher the groundwater level was,the higher the increase amplitude,and the water-gas response time is also short.(b)The range of effective response of the dissolved oxygen DO in groundwater during AS process,which is basically consistent with the response range of the water level,covering the area between the gas injection point and the monitoring hole.(c)The concentration of arsenic in pollutants rose to a peak in a moment between 1~6 h,then the concentration of arsenic will gradually decrease with the increase of aeration time.The peak is due to the effect of aeration on the groundwater,which causes the release of arsenic and other pollutants in the sediment.Taking M6 as an example,the concentration of arsenic decreased from the highest 19.6 ?g/L to 2.5 ?g/L,and the analysis suggested that this was due to the co-precipitation of arsenic iron.(5)The constructed wetland technology proposed that B4 microbial synergistic plant is the driving force of ecological restoration,which has the advantages of low energy consumption and good effect.The results show that:(a)The plant grows better than the wild reed because of the nutritive effect of the sludge.The plant biomass per unit area is about 66% higher.From the perspective of resource utilization,the resource transfer is realized while the sludge is stabilized.(b)Through the determination of wetland treatment indicators,the anaerobic reed wetland has the best effect on total phosphorus removal.Aerobic reed for total nitrogen and total carbon and pahs removal effect is good,after which successively invested B4 strains and enzyme,wetland of PAHs,treatment effect is remarkable,through on-site validation than traditional wetland significantly shorten the time.(c)When the moisture content of sludge was reduced from 97.55% to 66.77%,the volume decreased from 200 L to14.75 L,which was good to achieve the target of residual sludge reduction treatment.