| Eutrophication is a kind of water pollution caused by excessive nitrogen and phosphorus nutrients,which is one of the main environmental problems concerned in the field of water ecology.Phosphate is a key factor to induce water eutrophication,and when its concentration exceeds 0.02 mg/L,water eutrophication can occur.Therefore,it is of great practical significance to develop cost-effective and efficient wastewater phosphorus removal technology.For low phosphorus water bodies such as surface water,traditional biological phosphorus removal technology is unable to achieve good treatment results.In contrast,adsorption process has the advantages of high phosphorus removal efficiency and realizing phosphorus recovery,which has been widely used in the treatment of low phosphorus water bodies.The preparation of low cost and high capacity adsorbents is the key for the application of the above technology.Also,for practical application,it is of great significance to solve the problem of regeneration and recovery of powder adsorbents.To address the above issues,this work takes low phosphorus wastewater as the treatment object,and firstly investigates the feasibility of using municipal wastewater derived sludge as raw material to fabricate phosphorus adsorbent.The effectiveness of the as-prepared adsorbent for the advanced treatment of secondary effluent was evaluated.Then,the porous membrane was used as the substrate for the immobilization of phosphorus adsorbent,and the effectiveness of the new composite membrane for phosphorus removal in surface water was studied.The main conclusions of this work are as follows:(1)Phosphate adsorbents were successfully prepared by using the sludge derived from the coagulation treatment of municipal wastewater.A new iron based adsorbent for phosphate adsorption was successfully fabricated by one-step alkaline treatment of sludge under the optimal conditions of 0.5 M Na OH concentration and30 min stirring.The adsorption isotherm fitted well with the Freundlich model.The maximum adsorption capacity was 22 mg-P/g and the adsorption performance reamains stable in the p H range of 5～8.The adsorption mechanism analysis revealed that Fe O(OH)was the main adsorption site,and phosphate was primarily removed by ligand exchange mediated chemisorption.Furthermore,the continuous flow adsorption column test shows that the total phosphorus content of secondary effluent can be effectively reduced to less than 0.1 mg/L after the treatment with the as-prepared adsorbent,which can reach the environmental quality standard of China surface water class II.Finally,the biochar was obtained and used for wheat cultivation by carbonating the phosphorus-saturated adsorbent under oxygen-limiting condition.(2)The La/C nano-sized phosphorus adsorbent was successfully immobilized onto porous membrane surface via phase conversion method and used to treat low concentration phosphate surface water.Using natural tannic acid as modifier,the rod-like nano-La/C composites were synthesized.The experimental results showed that the maximum adsorption capacity of the modified material was 48.8 mg-P/g at p H=7.0,which was significantly higher than that of the un-doped La compound(37.4mg-P/g).Ligand exchange and multilayer adsorption were the main phosphorus removal mechanisms.By doping an appropriate amount of La/C into the casting solution,the composite porous membrane with dual functions of adsorption-filtration can be fabricated.The phosphorus removal efficiency of membrane was up to 90%.After the fourth cycle of use,the removal efficiency of suspended solids can be up to95%.Na OH solution cleaning strategy can effectively regenerate the membrane performance,and the phosphorus desorption efficiency of La/C composite membrane after alkaline solution cleaning can reach higher than 88%.It was found that the carbon component in La/C material was beneficial to the pore development and hydrophilicity improvement of the membrane,which results in its high filtration flux and good anti-fouling performance. |
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