The Use Of Aquatic Macrophytes Fermented Broth As A Carbon Source For Sulfate-reducing Bacteria To Treat Wastewater Containg Heavy Metals

Aquatic macrophytes are widely used to degrade,assimilate,metabolize or detoxify contaminants in the eutrophic water.The resource utilization issues of aquatic macrophyte have caused wide concern.The most common treatments for heavy metal pollution are lime precipitation,absorption and electrolytic and so on.The anaerobic sulfate-reducing treatment is a promising alternative method,which could use an inexpensice carbon source for reducing equivalents.In this paper,we explored the utilization on aquatic macrophytes by anaerobic fermentation to produce volatile fatted acids(VFAs).The aquatic fermented broth was used as carbon source for sulfate-reducing bacteria and the removal efficiency of heavy metals was evaluated.Further more,the aquatic fermented broth was added into biological filter in order to strength the heavy metal removal effect.The goal of this study was to provide both laboratory and field information on the use of aquatic macrophyte fermented borth for revitalizing the acitivity of sulfate-reducing bacteria.The main results of this thesis are as follows:(1)In this paper,the aquatic macrophytes collected from constructed wetland were used as raw mateirals for anaerobic fermentation to produce VEAs,including Hydrocotyle verticillate,Phragmites australis and Thalia dealbata.Compared with Phragmites australis and Thalia dealbata,Hydrocotyle verticillate is more suitable for produce VFAs.The total amount of the volatile fatted acids in the fermented broth of Hydrocotyle verticillate was 5.1 and 8.5 times of the Phragmites australis and Thalia dealbata.Different aquatic macrophytes types had little effect on the distribution of volatile fatted acids,and the acetic acid was the main fermentation product.Crushing and high temperature can effectively improve the anaerobic fermentation rate and shorten the fermentation cycle time.Under alkaline conditions,the total amount of the volatile fatted acids was 1.74 and 1.56 times of acid and neutral condition.The nitrogen release rates of Hydrocotyle verticillate,Phragmites australis and Thalia dealbata were 68%,79%and 43%,respectively.Under alkaline conditions,phosphate forms calcium phosphate with calcium ions,which can be used as a way of phosphorus recovery.The optimum conditions of anaerobic fermentation were as follows:the crushed Hydrocotyle verticillate was fermented at 37 under alkaline condition.(2)Hydrocotyle verticillata fermentation broth can be used as carbon source of sulfate-reducing bacteria to treat wastewater containing heavy metals,and this may have significant implication for resource utilization of aquatic macrophytes.Sulfate-reducing bacteria could utilize the organic matter in the fermentation broth,and the sulfate reduction rates were 26%,43.6%and 60%when the ratios of COD to SO42-were 1.2,5 and 7,respectively.(3)In the batch experiment,the sulfate reducing bacteria could utilize the Hydrocotyle verticillata fermented broth and remove the Cd2+,Cue+,Pb2+ and Ni2+ effectively.When the concentrations of Cd2+,Cu2+,Pb2+ and Ni2+ were 10 mg/L,the removal rates of these heavy metals were more than 90%,and the activity of sulfate-reducing bacteria were not inhibited.(4)In order to strengthen the removal capacity of heavy metals in biological filter,the Hydrocotyle verticillata fermented broth was added as an external carbon source to activate the sulfate reducing bacteria.The removal rates of Ni2+,Pb2+,Cd2+ and Cu2+ were 90%,75%,92%and 87%,respectively.If the initial COD was 300 mg/L its removal rate was 84%-98%.The volatile fatty acids such as acetic acid,propanoic acid and butyric acid were utilized completely.The sulfate reduction rates were 18.8%and 42.8%when the ratios of COD to SO42-were 3 and 7,respectively.