Study On Sludge Drying Condensate Water Quality Influence By CaO&FeCl₂

With the environmental standards become increasingly stringent in China,more and more city sewage is treated,followed by a large amount of sludge.Sludge is a kind of solid waste which has high water content,large volume and is difficult to dispose,it contains large amounts of toxic and hazardous substances.These substances need proper disposal,otherwise serious secondary pollution will be caused.There are four general sludge disposal methods:landfill,land application,composting and incineration.No matter which kind of method is used,sludge drying is necessary.However,the sludge contains large amounts of volatile pollutants,condensate quality decreased with the water evaporation and condensation during sludge drying process.Condensed water of sludge drying under the high temperature belongs to high concentration organic wastewater,if it is direct emissions without processing.,serious environmental problems will be caused and human health will be threatened.In this paper,sludge was mixed with different proportions of CaO and FeCl_2,and then the mixture was dryed at 60¹20℃,the condensate was collected and measured.The results showed that:During the drying process,condensate’s pH maintained between 6 to 9.The higher temperature during drying,the more pollutants sludge drying condensate water had.The sludge was mixed with CaO and FeCl₂ before drying,this could effectively reduce the concentration of pollutants in condensate water.At 60℃,the minimum dosage of FeCl₂ in which COD and NH₄⁺-N of condensed water could reach the discharge standards was 11%.At 80℃,the minimum dosage of CaO in which COD and NH₄⁺-N of condensed water could reach the discharge standards was 14%.At 100℃,the minimum dosage of CaO in which COD and NH₄⁺-N of condensed water could reach the discharge standards was 18%.When the temperature reached 120℃,it was unable to reduce the COD and NH₄⁺-N of condensed water to the emission standard by adding CaO or FeCl₂ alone,the concentration of COD and NH₄⁺-N could be reduced to50mg/L and 38mg/L respectively by adding 14%CaO and 16%FeCl₂ to sludge.At this time,if the condensate water was mixed with raw sewage,the mixed sewage did not increase the load of sewage treatment plant basically,and it could be up to emission standards after treated by sewage treatment plant.