Characteristics of Nutrients and Heavy Metals Released by Municipal Sewage Sludge with Simulating Rainfall
Elucidating the release characteristics of nutrients and heavy metals from municipal sewage sludge(MSS)can help to predict the release amount of nutrients and heavy metals from MSS using the rainfall amount of a region during a specific period and to reasonably conduct the indirect application of MSS.By simulating rainfall on the permeable bag of MSS,the concentrations of nutrients and heavy metals in MSS leachates were analysed and the cumulative amounts were calculated.Results showed that the highly dewatered sludge from Dongguan released more N and COD than the normally dewatered sludges from Jiangmen.The release of P,K and Cu was reduced by dried Jiangmen sludge compared to the raw sludge.Dongguan sludge resulted in leachates conformed to the irrigation water standards for the pollutants of Cu,Zn,Pb,Cd.In contrast,Jiangmen sludge contained Cu exceeded the standard limit and also produced leachate with Cu concentration higher than the standard limit for irrigation water.The cumulative amount of nutrients and pollutants released from MSS was proportionally increased with the logarithm(ln)of the cumulative rainfall amount.According to the annual rainfall of Guangzhou city and N requirement of fruit tree Zizyphus mauritiana Lam.,the annual application rate of Dongguan sludge(water content 455 g/kg)was estimated to be 46.7 kg/plant or 43240 kg/ha.
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