Treatment Of Slightly-polluted River Water By Alum Sludge-based Ecological Floating Bed

The pollution of water environment has become a critical problem to the construction of ecological civilization in China,and eutrophication of river or lake not only affects the ecological environment,but also harms people’s physical and mental health.As a new kind of in-situ water restoration technology,ecological floating-bed has many advantages in comparison with other water pollution purification processes.It can simultaneously purify water body and beautify environment.In accord with China’s sustainable development strategy,ecological floating bed was considered as a promising alternative approach of ecological civilization construction to some polluted rivers and lakes.Alum sludge,a by-product of waterworks,is formed by adding the aluminous coagulants to raw water.Because of the large production and the special physicochemical characteristics,there is a great challenge for most waterworks to dispose alum sludge.However,it has been reported that alum sludge was a good wetland filler with the ability of phosphorus adsorption.As such,this study aims to focus on ecological floating bed to strengthen the traditional ecological floating bed by introducing dewatered alum sludge as bed substrate.Thus,the integrated ecological floating bed system was developed,allowing to treating polluted water.In this system,dewatered alum sludge of the waterworks was used as the filler while the aquatic vegetation was planted on the top.The effects of static and dynamic conditions and the effects of the size of the alum sludge filler on treating the slightly polluted water under the eco-floating bed were explored in great detail.The following main conclusions may be obtained:The results of the dynamic test showed that the removal of the pollutants can be affected by the water flow strategy of the floating bed.The way of bottom-in & upper-out of the floating bed is better than the way of upper-in & upper-out of the floating bed.The average removal rate of COD,TN and TP was 54.6%,31.2%,32%,respectively.In addition,the average removal efficiency of COD,TN and TP increased to 75%,53% and 63%,respectively,after introducing the artificial intermittent aeration on the basis of bottom-in scheme.The results showed that the increase of aeration can improve the quantity and bioactivity of microorganisms and can also enhance the function of microbial nitrification and denitrification in water.A better contact between sewage and alum sludge filler can be occurred by the disturbance of water when aeration,which proved the feasibility of applying the alum sludge to the ecological floating bed as filler.Static test was conducted for the comparison purpose.There were three devices to make comparison including the integrated ecological floating bed(alum sludge &plant),traditional ecological floating bed(only plant),and a blank control(only water without any substrate).During the 30-day test,COD had decreased from 80 mg/L to 12 mg/L,while TP from 1.4 mg/L to 0.18 mg/L,and the COD,TP of traditional ecological floating bed had decreased to 18 mg/L,0.75 mg/L,respectively.The integrated ecological floating bed showed higher treatment performance than the traditional ecological floating bed,especially the removal of TP.The results not only related to the structure and composition of alum sludge,microbes are fixed on the alum sludge also played an important role.Different sizes of 1.6 cm,0.8 cm and 0.2 cm ~2.0 cm of the alum sludge balls were used to fill in the integrated ecological floating bed.The results showed that the alum sludge ball filler with size of 0.8 cm had a better effect on COD removal.The average removal rate of COD was 64.7%.Because the smaller particle size of fillers,the more microbes attached.The alum sludge ball filler with the diameter of 0.2 cm ~2.0 cm had the best removal effect on TN and TP,with average removal rate of 27.9% and 30.2%,respectively.Because the smaller space between filler will be of great benefit to denitrification.And the smaller particle size,the bigger specific surface area,the more favorable for the adsorption of phosphorus.Overall,the smaller of the alum sludge ball,the better of the removal effect on the pollutants.The results showed that the integrated ecological floating bed using alum sludge as filler is effective in removing pollutants from slightly-polluted water body and has great application potential in the field of river water restoration.