Novel recycling of incinerated sewage sludge ash (ISSA) and waste bentonite as ceramsite for Pb-containing wastewater treatment: Performance and mechanism.

With rapid economic growth and urbanisation, the reuse and recycling of solid wastes has become a high priority for the sustainable development of modern cities. In this study, two typical solid wastes, incinerated sewage sludge ash (ISSA) and waste bentonite, were co-valorised to produce granular adsorbents through a simple and energy-saving pelletisation/sintering process. A mixture of ISSA and bentonite at a weight ratio of 3:1 was pelletised and sintered at 700 °C. The resultant ceramsite, with good mechanical strength, could effectively remove Pb(Ⅱ) from aqueous solutions. The adsorption kinetics can be described by the pseudo-first-order (PFO) model. The results indicated that the Pb(Ⅱ) adsorption process was dominated by electrostatic attraction, precipitation, and complexation. The isothermal data exhibited a good correlation with the Freundlich model, indicating that the adsorption process was non-ideal and spontaneous. The maximum adsorption capacity was approximately 21.6 ± 0.35 mg/g at 318 K. After 5 cycles of regeneration, the adsorbent maintained good adsorption performance. Moreover, the removal rate was not greatly affected by ionic strength. These findings demonstrate that the granular adsorbent prepared with ISSA and waste bentonite can be recognised as a promising adsorbent for Pb-containing wastewater treatment.

Arsenate(V) removal from aqueous system by using modified incinerated sewage sludge ash (ISSA) as a novel adsorbent.

Adsorption methods have been widely used in wastewater treatment due to its high removal efficiency, easy operation and handling, economic efficiency and little secondary pollution to the environment. In this paper, a high-iron containing incineration sewage sludge ash (ISSA) was modified by combined acid leaching and precipitation processes to improve its adsorption capacity of As(V). The effects of pH, time, temperature and ionic strength on the adsorption of As(V) were investigated by batch adsorption experiments. The results indicated that iron (mainly present as hematite) in the ISSA was rearranged to Fe(SO4)OH. The modified ISSA showed an excellent adsorption potential for As(V) under acidic conditions and the adsorption capacity was around 9 times of the unmodified ISSA at pH 2-3. The adsorption process was fast during the first 2 h and reached an equilibrium at around 6 h. The Freundlich model could well fit the adsorption isotherm data, the presence of NO3- and Cl- had a negligible influence on the As(V) removal by the modified ISSA, while PO43- and SO42- could significantly suppress As(V) removal via competitive adsorption. After 3 cycles of regeneration, the modified ISSA still showed a satisfying adsorption capacity. As(V) was removed by the modified ISSA mainly through ligand exchange reaction with hydroxyl oxygen (OH-) to form inner-sphere complexes. Therefore, the modified ISSA can be a promising material for As(V) removal from wastewater in particular due to the waste recycling potential.