Tuning the adsorptive properties of drinking water treatment residue via oxygen-limited heat treatment for environmental recycle

• Oxygen-limited heat treatment significantly increased SSA and TPV of DWTR.
• The treatment increased the amorphous Al/Fe contents in DWTR at 200–400 °C.
• The treatment induced organic matter in DWTR with higher aromaticity.
• The lability of heavy metals in DWTR tended to decrease after treatment.
• The Hg adsorption capability of DWTR treated at 200–400 °C significantly enhanced.

As a by-product generated increasingly during potable water production, drinking water treatment residue (DWTR) recycling for environmental remediation can lead to a win–win situation. In this study, oxygen-limited heat treatment was applied to DWTR, attempting to tune the properties of DWTR for better recycling. The results showed that after the treatment, N2 sorption capacity of DWTR was enhanced significantly: the specific surface area (SSA) and total pore volume (TPV) increased from 72.7 to 148–184 m2 g−1 and from 0.0746 to 0.189–0.201 cm3 g−1, respectively. The treatment also relatively increased the amorphous Al/Fe contents in DWTR although Al/Fe aging and transformation from hydroxides to oxides with high stability were observed. The retained organic matter (OM) was dominant in humin, with higher aromaticity and lower aliphaticity as the treatment temperature increased. Further analysis suggested that aromaticity increase induced higher SSA, the combined effect of OM aromaticity increase, OM loss (e.g. C in COO−), and metal oxides formation resulted in larger TPV, OM inhibited Al/Fe aging, while Al/Fe oxides formation in turn enhanced OM aromaticity. Additionally, the maximum Hg adsorption capacity of DWTR treated at 200–400 °C (estimated by Langmuir model) increased from 53.5 to 69.9–147 mg g−1, and the lability of heavy metals (e.g. Cu) in DWTR tended to decrease after treatment. The overall results demonstrated that oxygen-limited heat treatment sequestrated C, making DWTR be a more reliable adsorbent.