| The pollution of phosphorus is increasingly serious, and the phosphorusresources which are available are becoming more and more shortage. So how toeconomically and effectively recover phosphorus from the polluted water was puton the agenda all over the world. Massive phosphorus can be found in the sludge ofwater treatment plant. If the phosphorus can be recovered and utilized with highrecovery rate, the shortage above and waste utilization can be solved together.In this paper, the phosphorus recovery using the sludge of water treatmentplant was studied. Different plants have different flocculating agent, causingdifferent kinds of sludge. The conditions of phosphorus recovery from them aredifferent. The effects of the operation parameters (pH, amount of sludge, adsorptiontime, stirring intensity etc.) on the recovery of phosphorus were studied. Theresults indicated that adsorption conditions of Poly Aluminum Ferric Chloride(PAFC) sludge and Polymeric Ferric Sulfate (SPFS) sludge were roughly the same:adsorption process of phosphorus was stable when pH at the range of4-4.5, therecovery rate and unit adsorption quantity increase gradually with time. Recoveryrate of phosphorus in polluted water increased as the amount of sludge increased,but reduced as the initial concentration of phosphorus increased. Compared to nostirring, recovery rate of phosphorus increased by5%with stirring. In a suitablescope of stirring, recovery rate of phosphorus was mainly consistent withadsorption quantity of sludge. The recovery rate and adsorption quantity of PAFCsludge can respectively reach95%and3.0mg/g in the condition of pH=4.5, amountof sludge (1.6g), concentration of phosphorus (50mg/L), stirring rate (50rpm),adsorption time (3h, the sample was stable). While the recovery rate andadsorption quantity of SPFS sludge can respectively reach93%and3.23mg/g,under the condition of pH=4.0, amount of sludge (7.2g), concentration ofphosphorus (50mg/L), stirring rate (50rpm), adsorption time (3h,the sample wasstable). Comparing Langmuir adsorption isotherm with Freundlich isothermbetween PAFC sludge and SPFS sludge, it is found that adsorption capacity of PAFC sludge is stronger than that of SPFS sludge.Sludge has a strong adsorption capacity to phosphorus in polluted water, butmany adsorption points on the face of sludge have already been occupied by othergroups. So it is required to increase adsorption capacity of sludge by modification.The adsorption experiments before and after acid operation for SPFS were abservedand it is found that the optimal pH is6for acid-modified SPFS sludge. Therecovery rate and adsorption quantity of acid-modified SPFS sludge respectivelyreach98%and3.83mg/g in the condition of pH=6, amount of sludge (6.2g),concentration of phosphorus (50mg/L), stirring rate (50rpm), adsorption time(3h,the sample was stable). Comparing Langmuir adsorption isotherm andFreundlich isotherm of SPFS sludge before and after modification, it is found thatadsorption capacity of acid-modificated SPFS sludge is better than that notmodificated. All the results showed that acid-modification of sludge is feasible. |
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