This research was conducted for dewatered sludge cake of industrial wastewater treatment, i.e., as the object of inorganic sludge discharged especially in iron & steel manufacturing shop which used Air drying system to reduce water content. That drying system's single-type cyclone separator was confirmed to have significantly lower separation efficiency on the conditions 20μm and below of particular size through computational fluid dynamics(CFD) analysis. However, we found out the primarily advanced value of separation efficiency on dual-type directly connected. Regarding separation efficiency on size of 10μm, the efficiency of a single-type was presented at 51.91%. On the other side, the efficiency of the dual-type was 97.88%. This advanced effect of the dual cyclone separator was checked at a demo facility of air drying equipment designed by 340m3/min of airflow on site.

The performance of the new aerobic digestion system combined with inorganic sludge separation unit and sludge solubilization unit, CaviTec II, is evaluated. Anaerobic digester effluent sludge is used for feed sludge of CaviTec II system. By addition of CaviTec II, the amount of cake generated is reduced by 27%, and the soluble nitrogen is reduced by 92%.

The performance of inorganic sludge separation system is evaluated. Anaerobic digester effluent sludge is used for feed sludge of this system and hydrocyclone is used for inorganic sludge separation. For phosphorus removal and recovery MgCl2 is pumped into MAP growth tank, a component of inorganic sludge separation system. Using this system inorganic sludge which contained less than 40 % of organic matter can be discharged stably and the maximum amount of separated inorganic sludge is 13.4 % of influent sludge based on dry solid. The amount of phosphorus recovered as MAP(as P) is 16.7 % to influent T-P.

Magnetite and inorganic sludge were mainly composed of Fe2O4 and Fe2O3, respectively. Initial specific surface areas of magnetite and inorganic sludge were 130 m2/g and 31.7 m2/g. CO2 decomposition rate for inorganic sludge was increased with temperature. Maximum CO2 decomposition rates were shown 89% for magnetite at 350℃ and 84% for inorganic sludge at 500℃. Specific surface area for magnetite was not varied significantly after CO2 decomposition. However, specific surface area for inorganic sludge was greatly decreased from initial 130 m2/g to approximately 50~60 m2/g after reaction. Therefore, it was estimated that magnetite could be used for CO2decomposition for a long time and inorganic sludge should be wasted after CO2 decomposition reaction.

According to the revised version of Waste Control Act to enter into force in 2017, Wastes could only be recycled assuming that the use of recycled wastes is safe for the environment and human health by environmental safety assessment. Even before this revision of the law, inorganic sludges could have been recycled as alternative materials for filler and cover materials by mixing with soil. However, in case of inorganic sludge from car-washing facilities, the revised law provides that the waste has to be landfilled. To assess the possibility of recycling this waste, we investigate the characteristics of the generation and concentration level of hazardous substances and evaluate the safety of recycling this material to assess whether this process meets the environmental standards. We obtained a total of eight sludge samples from car-wash shops, such as those in gas stations, car-repair shops and car-wash facilities. According to the results of leaching tests, most of the samples(8) fell under the detection limit and thus could be legally treated as general waste. However, in the results of contents some heavy metals, such as hexavalent chromium, lead, copper and zinc, exceeded the standards for soil contamination. We can conclude that the recycling of inorganic sludge from car-wash facilities could cause pollution in soil media when recycled and should not be recycled for filler and cover materials.