Research On The Bypass Purification Technology Of River Water

River pollution has become one of the global issues, among which river andwetland ecosystems are most threatened. River pollution has become more serious andinduced great public concerns, and many river pollution control projects have beencarried out in China. In recent years, the strategies of river pollution controls have beenfurnished and the new theory and techniques for recovering damaged river ecosystemare explored. In some regions renovations of ecological environment has beenembarked. River basins as a whole should be taken into consideration in the ecologicalremediation. Measures such as buffer remediation, construction of wetlands,construction of shoals and deep pools, and abolishment of the concrete lining should betaken in order to recover the natural state of river.Land treatment as an ecological sewage treatment method has been widely useddue to its benefits. Therefore, considering the low C/N ratio and low phosphorusconcentration in river, new land treatment method to river cleaning should be explored.The improved artificial wetland system and aeration circulation flow systems wereboth equipped with the selected high-phosphorus removal filler and analyzed in detailsfor their purification performance for river water. The removal efficiencies of organics,nitrogen and phosphorus were investigated for both systems, and the appropriatetreatment method were determined. This research could provide some theoreticalbackground and data support to the design and operation of the pilot system.The main research contents and results are shown as follows:(1) In river water treatment, deficient of carbon source in biological denitrificationprocess is often the key issue. In this experiment, eight kinds of common natural organic matters, including eight kinds of natural organic matters were selected ascarbon sources for denitrifying bacteria to study their degradation ability to NO3--N.The results showed that phragmites australis and rice straw had strong adsorptioncapability of nitrate-N however, large amount of ammonium-N was released impactingthe overall denitrification efficiency. In comparison, corncob and sawdust exhibitedbetter denitrification performances with over95%denitrification efficiencies, as wellas minute nutrient released. Therefore, according to the nitrogen removal rate,nutrient release potential and nitrate adsorption capability, corncob and sawdust areconsidered as the best denitrification carbon sources in river water treatment.（2）The phosphorous removal abilities of four test fillers, oyster shells, zeolite,red bricks, and cement bricks, were studied systematically and their performances werecompared. Through the dynamic test screening and a series batch adsorption studies,including adsorption thermodynamics, isotherm and kinetics, on cement bricks, itshowed that the surface of the cement brick is conducive to the growth of biofilm, andphosphorous adsorption capability of the filler mainly determined by the chemicalcomposition of cement bricks while cement blocks also showed high phosphorusremoval potential. Both Langmuir and Freundlich equations can well fit the adsorptionisotherms of low concentration phosphorus on cement bricks. The Langmuir maximumadsorption capacity of cement bricks is0.644mg/g. Both pseudo-first-order kineticequation and double constant rate equation could well describe the adsorption kineticsof cement bricks in the low phosphorous water with pseudo-first-order kinetics modelgives a better fit. Phosphorus adsorption on cement bricks is a spontaneous process.Elevated temperature is not conducive for the adsorption of phosphorus on cementbricks as the adsorption process is an exothermic process. Considering thecharacteristics of cement bricks, it could be an ideal filler for system construction..（3）The purification capability of river water by improved artificial wetlandsystem was studied. Results showed that the removal rate of NH4-N and TN couldreach90%when the hydraulic load was12cm/d. Moderate phosphorous removalefficiency was observed when treating low concentration phosphorus water. Carbonsource filled in the system did not deteriorate the quality of water. The purificationcapability of river water by aeration circulation flow system was studied. Results showed that, when the hydraulic load was12cm/d, DO become the main factoraffecting the nitrogen removal in system. The nitrogen removal efficiency was bestwhen the aeration rate was57.6m3/d, while the removal of TN could reach50%-80%in aeration stage. Moderate phosphorous removal efficiency was observed whentreating low concentration phosphorus water. Carbon source filled in the system wouldnot deteriorate the quality of water.