Experimental Study of Fluorine Transport Rules in Unsaturated Stratified Soil

With the aid of soil column test models,the transport rules of fluorine contaminants in unsaturated stratified soils are discussed. Curves of F-concentrations at different times and sites in the unsaturated stratified soil were ob-tained under conditions of continuous injection of fluoride contaminants and water. Based on the analysis of the actual observation data,the values between computed results and observed data were compared. It is shown that the chemical properties of fluorine ions are active. The migration process of fluorine ions in soils is complex. Because of the effect of adsorption and desorption,the curve of the fluorine ion breakthrough curve is not symmetric. Its concentration peak value at each measuring point gradually decays. The tail of the breakthrough curve is long and the process of leaching and purifying using water requires considerable time. Along with the release of OHˉ in the process of fluorine absorp-tion,the pH value of the soil solution changed from neutral to alkalinity during the test process. The first part of the breakthrough curve fitted better than the second part. The main reason is that fluorine does not always exist in the form of fluorinions in groundwater. Given the long test time,fluorinions possibly react with other ions in the soil solution to form complex water-soluble fluorine compounds. Only the retardation factor and source-sink term have been considered in our numerical model,which may leads to errors of computed values. But as a whole the migration rules of fluorine ions are basically correct,which indicates that the established numerical model can be used to simulate the transport rules of fluorine contaminants in unsaturated stratified soils.

Drainage performance and capillary rise restraint effect of wicking geotextile

Wicking geotextile(WG)is considered as a possible countermeasure to reduce water content in unsaturated soil.In this research,rainfall tests were carried out to verify the drainage performance of WG.And capillary rise tests were conducted to study the effect of WG on the prevention of capillary rise.Test results indicated that WG with good drainage performance could drain gravitational and capillary water out of kaolinite soil.For kaolinite soil column with water content of 12%and compaction degree of 90%,the whole process of capillary rise in soil column with a layer of WG was a typical two-stage mode,and the maximum capillary height was about 380 mm,which provided that the WG could work as a barrier to prevent capillary rise effectively.In addition,the total vertical influential regions of WG in kaolinite soil above and below the WG layer were 400 and 100 mm,respectively.

Development of natural treatment system consisting of black soil and Kentucky bluegrass for the post-treatment of anaerobically digested strong wastewater

To develop a sound post-treatment process for anaerobically-digested strong wastewater,a novel natural treatment system comprising two units is put forward.The first unit,a trickling filter,provides for further reduction of biochemical oxygen demand and adjustable nitrification.The subsequent soil–plant unit aims at removing and recovering the nutrients nitrogen（N）,phosphorus（P）and potassium（K）.As a lab-scale feasibility study,a soil column test was conducted,in which black soil and valuable Kentucky bluegrass were integrated to treat artificial nutrient-enriched wastewater.After a long-term operation,the nitrification function was well established in the top layers,despite the need for an improved denitrification process prior to discharge.P and K were retained by the soil through distinct mechanisms.Since they either partially or totally remained in plant-available forms in the soil,indirect nutrient reuse could be achieved.As for Kentucky bluegrass,it displayed better growth status when receiving wastewater,with direct recovery of 8%,6% and 14% of input N,P and K,respectively.Furthermore,the indispensable role of Kentucky bluegrass for better treatment performance was proved,as it enhanced the cell-specific nitrification potential of the soil nitrifying microorganisms inhabiting the rhizosphere.After further upgrade,the proposed system is expected to become a new solution for strong wastewater pollution.