ABSTRACT
An integrated technique consisting of oxidation and coagulation-flocculation processes was investigated in order to provide an effective method for the treatment of biologically pre-treated leachate and to reduce pollutants to values under the limit required for discharging to the receiving waters. Leachate containing 985 mg L(-1) chemical oxygen demand (COD) was treated by using oxidation with NaClO, coagulation/flocculation with aluminium sulfate (alum) or poly-ferric sulfate (PFS) as well as combined pre-oxidation followed by coagulation/flocculation. Oxidation resulted in the removal of COD and colour up to 78.9 and 88.4%, respectively, however residual COD values were over 200 mg L(-1) even under intensive experimental conditions (high dosage of NaClO and prolonged oxidation time). Coagulation with PFS was found to be more efficient in comparison with alum, and it yielded a residual COD of 184 mg L(-1) the optimum coagulation conditions (polyacrylamide (PAM) 5 mg L(-1), PFS 30 mg L(-1), pH 6, reaction time 20 min). The combined process involving oxidation followed by coagulation/flocculation with PFS resulted in residual COD values lower than 100 mg L(-1) the following conditions: 40-60 min pre-oxidation with 30 mg L(-1) NaClO followed by coagulation with 200-250 mg L(-1). Hence, pre-oxidation with NaClO followed by coagulation with PFS was recommended for removal of biologically-treated substances from the biologically-treated or stabilized leachate.
Subject(s)
Waste Disposal, Fluid/methods , Alum Compounds , Biological Oxygen Demand Analysis , Color , Ferric Compounds/chemistry , Flocculation , Hydrogen-Ion Concentration , Oxidation-Reduction , Water Pollutants, Chemical/chemistryABSTRACT
In this study, municipal solid waste incineration (MSWI) fly ash was used as a blending in making ceramic brick based on its characterization and an orthogonal test was performed to determine the optimal mixture ratio of the materials. Besides, the fired bricks made in accordance with the optimal mixture ratio were characterized for performance, phase transformation, microstructure, leaching toxicity of the heavy metals in accordance with GB/T 2542-92 (Detection methods for bricks analysis, China) and by means of XRD, SEM and leaching toxicity analysis. It was found that the optimal mixture ratio of materials (MSWI fly ash:red ceramic clay:feldspar:gang sand) was 20:60:10:10 by mass, and the optimal sintering temperature was 950°C. Leaching results of heavy metals from sintered bricks were reduced considerably in comparison with those from green bricks prior to sintering process. The results as a whole suggested that utilization of MSWI fly ash in ceramic brick constituted a potential means of adding value.
Subject(s)
Carbon/chemistry , Ceramics/chemical synthesis , Construction Materials/analysis , Incineration , Particulate Matter/chemistry , Refuse Disposal , Aluminum Silicates , Ceramics/analysis , Ceramics/toxicity , Clay , Coal Ash , Compressive Strength , Construction Materials/toxicity , Metals, Heavy/analysis , Microscopy, Electron, Scanning , Salts/chemistry , Silicon Dioxide , X-Ray DiffractionABSTRACT
In this work, MSWI (municipal solid waste incineration) fly ash is used as a blending in production of ceramic tile by taking advantage of its high contents of SiO(2), Al(2)O(3) and CaO. Besides, macro-performance and microstructure of the product as well as its leaching toxicity in practical application were studied by means of XRD, IR and SEM analysis, and leaching toxicity and sequential chemical extraction analysis of the product. It is found that when 20% fly ash is added, the product registers a high compressive strength of 18.6MPa/cm(2) and a low water absorption of 7.4% after being sintered at 960 degrees C. It is found that the glazed tile shows excellent resistance against leaching, in accordance with HVEP stand, of heavy metals with Cd<0.0002ppm, Pb<0.0113ppm and Zn<0.0749ppm, and Hg below the low detection limit. These results show that heavy metals are cemented among the solid lattice in the product and can hardly be extracted. Leaching toxicity of heavy metals in the product, especially Hg, Pb, Zn and Cd, is substantially reduced to less than one-tenth of that in fly ash. In addition, specifications of Hg, Pb, Zn and Cd are largely changed and only a small portion of these heavy metals exists in soluble phases. These results as a whole suggest that the use of MSWI fly ash in ceramic tile constitutes a potential means of adding value.
