| Sludge generated from wastewater treatment plants represent a potentially harmful solid waste threatens to human health and environment. The amount of sludge is continuously increasing with due to the growth of urbanization in China. Sludge is characterized with high moisture content, huge volume, poor mechanic properties is therefore difficult to be stored and transported. Moreover, combined with a substantial amount of toxic component contains; the sludge poses a threat as a secondary pollution if not handled properly.Nowadays, mature sludge-management method generally contains sanitary landfill, land utilization, drying and combustion. But flows inherently exists limited its application and therefore, it is necessary to deal with through innovative treatment methods. In this article, we assessed the potential of ceramsite produce in sludge mixing with different proportions of clay and coal ashbase while analyzing the fundamental nature of sludge, combine with clay ceramsite sintering process. This method revealed the opportunity of producing light ceramsite under some certain conditions. At last, we established a new municipal sludge treatment characterized with ceramsite sintering after low temperature drying and building material production.Comparing the inorganic components in sludge, clay and coal ash, we concluded that the sludge is qualified as a feed material to produce ceramsite. And we also found that a low eutectic point will likely occurs at 1100℃-1200℃for sludge and clay, as well as for sludge and coal ash mixtures according to thermodynamics balance system of SiO2-Al2O3-MgO.In our laboratorial test, we simulated commercial ceramsite produced from using a self-design columnar stamping granulator to produce sludge ceramsite blank. Some fundamental natures of material, such as volume, ignition loss, bulk density and apparent density were determined to assess the sintering and expanding property. And we also estimated the specific surface area, cylinder compres strength, compressive strength and 24h water absorption to evaluate the potential of ceramsite for building. All the ceramisre used were sintered with modifying ratios of feed mixture and sintering temperature, and all the properties were determined after cooling of ceramsite. The optimum temperature range for sludge ceramsite ranging 1150℃-1175℃, ceramsite produced among this temperature is eligible for building material qualification. The physical characteristics of ceramsite varied with mixture proportion and the ceramsite could be an excellent light aggregate if the mixtures are fired with clay content set at 10-20% of total mixture and temperature set at 1175℃, with cylinder compressive strength large than 4MPa and specific surface area reaching 2m2/g. However, properties of sludge ceramsite produced with coal ash failed to reach the national standard thus it is essential to change the experimental design.Combined two-stage drying process and laboratorial results, we designed a sludge re-using process integrated with the sludge dewatering, ceramsite sintering and block manufacturing. According to our design, the moisture content of sludge was primarily reduced to 30% using flue waste heat from ceramsite production and then mix with auxiliary material. Secondly, the mixture is subject to rotary kiln and burned to produce ceramsite. And the ceramsite is further process into light aggregate block. This process is characterized with the full usage of mineral and heat value of sludge, reducing the influence of atmospheric thermal pollution and also a desirable utilizing of waste heat from flue. At present, the production line with a daily municipal sludge disposal capacity is of 20t and an annually ceramsite production is of 0.18 million m3 and it already began in trial operation. It is estimated that this project will be economically feasible and commercially applicable.
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