Porous Lightweight Material And Its Application In The Ecological Transformation Of Vertical Hard Revetment

River revetment is a transitional zone between water and land,which play a role of flood protection,ecological corridor and buffer,and detention.In the early days,people only focused on flood prevention and bank slopes protection,therefore,the hard concrete revetment was once widely used in many revetment works.The vertical hard revetment can cause the disturbance in river flow with the results of destroyed features,degraded biodiversity,decreasing self-purification ability and deteriorated water quality.The two kinds of lightweight materials of foam ceramics and porous concrete have low cost,simple preparation and high potential for application in the hard revetment ecological transformation.However,porous concrete and ceramic foam material are limited to apply for slope protection,soil slope rehabilitation,and ecological transformation.In fact,porous concrete and ceramic foam material have a high ability to transform hard vertical revetment to improve water purification and river ecological.Through material strength,planting and water purification experimental to achieve the best porosity and mix ratio of foam ceramics and porous concrete.The research revealed:The porous concrete block with porosity as 30%,the particle size as 10-20 mm,and the water-cement ratio as 0.3 has high compressive strength,good microorganism adhesion,and the best water purification effect.The foam ceramic block with porosity 40%,pore diameter 1-2 mm,and the pore-forming agent ratio 0.25 has higher compressive strength,good microbial adhesion effect,and the best water purification effect.With optimal porosity and mix ratio conditions,the experiment on effects of seasonal and water flow velocity changes on the biofilm structure and water quality of the material surface revealed that:Under flow velocity rate V=0.03 m/s,the biofilm formed a wavy structure and a filamentous structure.Whereby,the biofilm thickness and microorganism number were 776μm and 3.42×10⁸ CFU mL^-1,respectively;the removal of COD,NH₃-N,NO₃-N,TN and TP is 64.0%,67.7%,60.3%,65.1%and 46.9%,respectively.In the spring,due to the inhibitory effect of Cyanobacteria,the biofilm development on the surface of the material is low,the biofilm thickness and microorganism number were 242μm and 1.35×10⁸ CFU mL^-1,respectively.The removal of COD,NH₃-N,NO₃-N,TN and TP in the spring is 35.6%,-6.5%,38.7%,1.2%and 39.1%,respectively.The breeding of microorganism on the biofilm in the summer with 547μm thickness and 2.02×10⁸ CFU mL^-1 microbial number that is significant better than the spring.In autumn,the biofilm thickness and number of microorganisms on the material surface and the diversity index reached the highest value as 776μm and 3.18×10⁸ CFU mL^-1,respectively,leading to the water quality improvement effect,reached the best in the four seasons.The removal of COD,NH₃-N,NO₃-N,TN and TP in the autumn is 52.6-61.7%,60.4%,52.0%,58.3%and 56.9%,respectively.Under cold weather of the winter,the existence in the biofilm of bacteria is difficult to reproduce.The biofilm thickness and microorganism number were 974μm and 1.94×10⁸ CFU mL^-1,respectively.This research also revealed that the water quality improvement effect of the template after structural optimization has been significantly improved.The optimized structure with planting has the best water quality improvement effect.The experimental results proved that the removal of COD,NH₃-N,TN and TP by common porous concrete templates,respectively,was 40.7%,40.3%,31.4%and 43.2%while by planting common porous concrete templates,respectively,was 44.8%,42.9%,34.5%and 46.4%.The removal of COD,NH₃-N,TN and TP by advanced porous concrete templates was 62.9%,61.8%,59.7%and 64.7%,respectively.The microbial community analysis was conducted to show water quality improvement of normal and optimization of porous concrete templates.Porous concrete materials,filler and plant roots provide good conditions for the growth and attachment of microorganisms that could increase diversity and the total amount of microorganisms.The Hydrogenophaga,Pseudomonas,Nitrospira and many high ability of water purification was detected in the biofilm sapmles.The planting porous concrete was used to transform vertical hard revetment in Shedu Port,Yixing,China.The demonstration project has proved the effect of planting porous concrete in water purification and environmental restoration.The removal of COD,NH₃-N,TN and TP that were collected from experimental site of porous concrete templates was 42.1-59.1%,37.9-60.3%,41.2-63.9%and 40.2-53.7%,respectively.The laboratory experiment and demonstration project have provided technology and knowledge for the ecological transformation of the concrete hard revetment in Vietnam.