Study On The Mechanisms And Performances Of SAT-NPFBR In Treating Simulated Wastewater

Soil aquifer treatment （SAT）, as a kind of high-efficiency, low-energy andmanageable ecological engineering technology, is widely studied and applied innon-point source pollution treatment. However, long-term running of SAT systemleads to many problems, such as low removal efficiency of nitrogen and clogging. Inaddition, nitrifying particle fluidized biological bed （NPFBR）, based on waterbornepolyurethane embedding activated sludge with rapid oxidation of ammonia ability, isa device that can remove ammonia pollutants quickly and efficiently. While there arestill some points that we can not get the hang of in terms of the characteristics of theparticles and effect factors of nitrification performance. Hence, after studying themechanisms and performances of SAT and NPFBR separately, the author creates acombined system SAT-NPFBR by introducing NPFBR device into SAT system,aiming at investigating its effect, related effect factors and the applicability on treatingsimulated wastewater.The main conclusions of this study are as follows:（1） There are differences in pollutants concentration, according to different sitesand depths. Moreover, pollutants （organic matters, ammonia nitrogen, nitrite nitrogen,nitrate nitrogen and total nitrogen） have different degrees of variance, which arerelated to their various removal mechanisms and complex flow regime in theapparatus.（2） SAT system has good effect on the removal of COD with86.42%ofremoval rate. Specifically, the average COD effluent concentration of36mg/L ataverage and COD influent concentration of265mg/L. With the increase of runningtime, the capacity of SAT to removal NH₄⁺-N decreases. The polynomial equationfitted to the ammonia removal is:y79.150830.81807x0.00246x²,R20.93359.TN removal rate also decreases with the extension of the running time from more than80%to10%only, the main removal is contributed by NH₄⁺-N removal. SAT system has excellent removal of TP, which can maintain more than95%over the trial period.（3） The surface and inside of the embedded particle have a lot of space whichensures good mass transfer effects. A large number of rod-shaped nitrifying bacteriajust covered the surface of the particles （about85to120μm）. Activated particles’ DOpresents a symmetrical distribution where DO declines rapidly in the surface layer （0to300μm） with every100μm dropping by an average of3.62mg/L, while DO issubstantially0in the deep （600²800μm）. Dissolved uptake rate （OUR） ofnonactivated particle （4.1098±1.2607mgO₂/（L·h）） is much lower than that of theactivated particles （241.4769±11.5398mgO₂/（L·h））. When DO is over2.1mg/L,OUR is not affected; Otherwise, microorganisms will reduce the oxygen consumption,showing that activity is inhibited. Settling property of the activated particle issignificantly better than non-activated particles with average settlement rate1.19-times higher than the latter.（4） Low temperature in NPFBR is unfavorable to activate particles and reducesthe nitrification performance; Appropriate basicity is an important factor to ensurenitrification; Oxidation rates of ammonia are different at different ammoniaconcentration and do not present a linear relationship; Adding organic matters into thefluidized biological bed does not influence nitrification but increased suspended solidsconcentration in the effluent during the experimental period.（5） SAT-NPFBR has a high organic matters removal efficiency under differentreflux ratios. The removal rate increases in step with reflux ratio and reaches99.50%at the reflux ratio of1:3. The combined system shows different TN removal efficiencyunder different reflux ratio. The maximal removal rate reaches35.99%at the refluxratio of1:2. The removal of ammonia is not affected by reflux ratios during theexperimental period.（6） Water temperature has influence on organic matters removal in SAT-NPFBR,but the effect on TN removal hasn’t been determined. Performances of the combinedsystem are not affected by alkalinity under experimental conditions. Small hydraulic loading will reduce the processing quality of wastewater, on the contrary, cloggingwill occur.（7） When SAT-NPFBR is used to process synthetic wastewater at a reflux ratioof1:2, the average removal rate of CODcr, TP, NH₄⁺-N and TP are up to98.26%,99.36%,96.25%and35.99%, respectively. The removal rate of TN increased bynearly ten times compared with a single SAT system. To build a set of200L/d,4m²of land area is required, and the main costs include6,490yuan for material purchase,649yuan for installation, and1.349yuan/ton for the running.