Recycling technology—Artificial lightweight aggregates synthesized from sewage sludge and its ash at lowered comelting temperature

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Currently, Taiwan's major source of gravel for construction purposes is its river systems; however, over exploitation could potentially deplete this source. To address this problem and reduce dependence on natural aggregate exploitation, this article investigates artificial lightweight aggregates (ALWAs) synthesized from industrial waste such as sewage sludge and sewage-sludge-derived ash. The ALWAs were synthesized from the sewage sludge and ash using Na2CO3. The sodium carbonate helps produce the required viscous glassy phase (needed for ALWA sintering) at a lower co-melting temperature than would otherwise be possible. Water absorption, apparent porosity, bulk density and compressive strength of the ALWAs were tested to assess resource-recycling feasibility. The required dosages of Na2CO3 were 16 and 22 wt % for conditioned sludge and ash, respectively. The dosed sludge sample required preheating at 400°C for 0.5 h, followed by sintering at 900°C for 5 min. The ash sample required sintering only at 900°C for 15 min. The sludge-derived ALWAs gave the following percentages 2.84%, 3.31%, 1.20 g/cm3, and 13.0 MPa for water absorption, apparent porosity, bulk density, and compressive strength, respectively. The corresponding values for ash-derived ALWAs were: 4.85%, 6.55%, 1.41 g/cm3, and 87.3 MPa, respectively. The characteristics of ALWAs derived in this study were then compared to those of commercially available lightweight aggregates—Lytag and Arlita F7. The characteristics mentioned above of the former were superior than those of the latter except that the value ofdensity was an interval value between Lytag and Arlita. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 740–748, 2013