Green process for supercritical water oxidation of sewage sludge with red mud as CO2 absorbent. Issue 3 (September 2016)

• Record Type: Journal Article
• Authors: Chen, Hongzhen; Wang, Guangwei; Xu, Yuanjian; Chen, Zhong; Yin, Fengjun
• Is Part Of: Journal of environmental chemical engineering. Volume 4:Issue 3(2016:Sep.)
• Page Start: 3065
• Page End: 3074
• Publication Date: 2016-09
• Subjects: Sewage sludge -- SCWO -- Red mud -- CO2 mineralization; Chemical engineering -- Environmental aspects -- Periodicals; Environmental engineering -- Periodicals; Chemical engineering -- Environmental aspects; Environmental engineering; Periodicals; 660.0286
• DOI: 10.1016/j.jece.2016.06.013
• Languages: English
• ISSNs: 2213-2929

Abstract

Highlights: A green SCWO system involving the treatment of sewage sludge with red mud as CO2 absorbent was developed. The primary CO2 mineralization occurred inside the SCWO reaction vessels to improve the corrosion resistance of set-up. The second CO2 mineralization was achieved in the exhaust cleaning reaction vessel by red mud slurry at certain pressures. CO2 levels in the exhausts were cut to below 800 ppm (mg/L); SO2 and nitrogen oxides (NO, NO2 ) diminished to below 15 ppm and 12 ppm, respectively. Abstract: To mineralize CO2 produced in situ and other acidic substances originating from organic components in sewage sludge, we developed a green SCWO system involving the treatment of sewage sludge with red mud as an alkaline absorbent. In this new system, two steps of mineralization were covered. Primary mineralization occurred inside the SCWO reaction vessels with part of CO2 produced in situ. By this primary treatment, total inorganic carbon of the solid residue increased rapidly, predominantly in the form of calcite. Moreover, the S and P content increased by more than ten times compared with that of pure sludge. The pH of the drained water increased from 5.16 to about 7.7 with the addition of 2% red mud. The second mineralization step involved the exhausts cleaning reaction using red mud slurry. With 2.5 h of cleaning reactions at pressures of 0.1, 1, 3, and 5 MPa, approximately 4.49, 5.30, 6.06, and 7.52 g, respectively, of CO2 per 100 g of red mud were bound in calcite. The high CO2 absorption capacity was ascribed to the high pressure cleaning reaction, which was conveniently achieved in this SCWO system just by a simple adjustment of the back-pressure valve. With this green SCWO disposal, CO2 level in the exhausts were cut to below 800 ppm (mg/L); SO2 and nitrogen oxides (NO, NO2 ) diminished to below 15 ppm and 12 ppm, respectively. Due to the comparative stability of the solid residues obtained, they can easily be handled using conventional methods or recycled for a range of industrial applications including building materials, water treatment materials, special ceramics, or silicate cements.