| Municipal and industrial wastewaters often have high concentrations of phosphorous containingcompounds. It is important to remove Phosphorus from wastewater as too high concentrationleads to eutrophication effect and rapid deterioration of water quality.The standard discharge limit for total phosphorus effluent to receiving bodies varies according tothe region. In China, according to the GB18918–2002B standards, the phosphorus dischargeeffluent limit should be less than1mg/L. In recent years, research of water treatment technologyhas strengthened. At present, the domestic water treatment technology is relatively fastflocculation method, with less investment, quick and low cost.In this study, red mud, bauxite and fly ash are raw materials used to prepare four different typesof coagulants whose material compositions were Red Mud: Al2O3, Fe2O3, SiO2, Na2O; mainphase of quartz (SiO2), hematite (Fe2O3), goethite (α-FeOOH), calcite (CaCO3), illite (KAl2(Si,Al)4O10(OH)2) and was presented by Si-O-Si, Fe-OH, H-OH groups.Bauxite:Al2O3, Fe2O3,SiO2; with its main mineral composition being; gibbsite (Al(OH)3), aluminum oxide (Al2O33H2O), zeolite, hematite and Fly Ash: Al2O3, SiO2, and the main phases being mullite(Al2O3-2SiO2), quartz (SiO2), silica oblique (SiO2), and sillimanite (Al2SiO5). By changing theconcentration of hydrochloric acid, the solid-liquid ratio, the ratio of raw materials as well asreaction time, four groups of inorganic composite coagulants were preparedThe physical properties of the four coagulants were measured and compared to the“polyaluminum chloride industrial national standard”(GB/T22627-2008). The results showedthat coagulant#1,#3and#4pH were in line with the PAC national standard of water treatment3.5–5.0. In terms of alumina content, only coagulant#3was in line with the nationalstandard≥29%though coagulant#4of26.83%was close to the national standard. For basicity,all the four coagulants were able to meet the national standard.The prepared four coagulants were than tested with simulated waste water for their optimum pH,dosage and hydraulic conditions. Results showed that for coagulant#1the optimum pH was6-8,optimum dosage0.6g/L and optimum hydraulic conditions of fast speed300r/min, time60s;slow speed20r/min, time10min. For coagulant#2the optimum pH was6-8; optimum dosage 0.6g/L; optimum hydraulic conditions of fast speed300r/min, time30s; slow speed of20r/min, time15min. For coagulant#3the optimum pH was7-8; optimum dosage0.1g/L;optimum hydraulic conditions of fast speed200r/min, time60s; slow speed20r/min, time10min and for coagulant#4, the optimum pH was7-8; optimum dosage0.4g/L; optimumhydraulic conditions of fast speed300r/min, time30s; slow speed20r/min, time was10min.Based on phosphorus removal percentage and economic principles, coagulant#3and#4wereselected in this study for experimental treatment of sewage waste water.For treatment of sewage waste water with coagulant#3and#4, results of phosphorus removaland other waste water indicators such as COD, TN, NH3-N and Turbidity showed that forcoagulant#3, the phosphorus removal rate was96.7%with effluent phosphorus content of0.076mg/L while for coagulant#4, the phosphorus removal rate was99.58%with effluentphosphorus content of0.012mg/L. Both results were far less than the "urban sewage treatmentdischarge standards" of1mg/L for phosphorus. For COD removal rate, results showed that forcoagulant#3that percentage was65.38%while for coagulant#4the percentage was33.69%.Turbidity removal rate was92.72%for coagulant#3while coagulant#4the removal percentagewas83.14%. TN removal rate was27.5%and8.07%for coagulant#3and#4respectively whileNH3-N removal rate was21.22%for coagulant#3and24.35%for coagulant#4. As a whole,the removal of other waste water indicators by coagulant#3showed better results thancoagulant#4. Other than NH3-N whose effluent concentration of17.83mg/L, higher than8mg/L for urban sewage discharge standards, all other waste water indicators where within thestandard for coagulant#3. For coagulant#4, COD, TN, NH3-N removal was quiet low hence itcan be recommended for more appropriate measures to taken to enhance COD, TN and NH3-Nremoval.Analysis of the homemade inorganic composite coagulant#3and#4was done using X-rayfluorescence spectroscopy, infrared spectroscopy; X-ray diffraction and scanning electronmicroscopy while the main coagulant mechanism analysis were accomplished by double layercompression (charge neutralization mechanism) and adsorption of coagulant onto the particlesurface (bridging mechanism). |
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