Lanthanum-doped activated carbon derived from municipal sludge for enhanced defluoridation: characteristics and mechanism

Abstract

The sewage sludge production has been increasing along with the ever-growing populations and wastewater treatment rate. Lanthanum-doped activated carbon (AC-La) was derived from municipal sludge via chemical activation and utilized for fluoride removal. Batch experiments were conducted to discuss the effect of lanthanum dosage, time and pH on the adsorption process. The results showed that 4 g/L AC-La exhibited a fluoride removal rate of 80.9% with 10 mg/L initial fluoride concentration, and the optimal pH range for adsorption was 3–10. X-ray fluorescence, scanning electron microscopy with energy-dispersive X-ray spectroscopy, Brunauer-Emmett-Teller, X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses were conducted to analyze the microstructure and chemical properties of sludge, unmodified activated carbon (AC) and AC-La. The results showed that with initial lanthanum dosage of 15 wt%, the final loading amount of La in AC-La was 13.8 wt%. After modification, the specific surface area of AC-La increased from 1.8 m2/g (sludge) to 133.0 m2/g. The removal mechanism of fluoride onto AC-La was mainly the inner-sphere complexation between lanthanum and fluoride, facilitated by exchange interaction with hydroxyls. A stability study showed that AC-La maintained a quite small dissolution and was safe in waters (La dissolution rate < 0.2‰).

Photocatalytic performance of biochar-modified TiO2(C/TiO2) for ammonia–nitrogen removal

“…Dehydrated sewage sludge from a local municipal wastewater treatment plant (WWTP) was collected as the raw material to prepare the biochar, as described in our previous work, for further utilization. 23,24…”

“…The product was washed by deionized water several times and dried to obtain the final compound, named as C/TiO 2 , with a TiO 2 and biochar composition. 23 …”

“…Dehydrated sewage sludge from a local municipal wastewater treatment plant (WWTP) was collected as the raw material to prepare the biochar, as described in our previous work, for further utilization. 23,24 First, 20 mL ethanol and 7.2 mL butyl titanate were mixed in a container and shaken for 0.5 h (450 rpm). Hydrochloric acid was then added into the solution and stirred together for 0.5 h in order to maintain an acidic condition.…”

Efficient removal of humic acid in water using a novel TiO2 composite with biochar doping

“…8d, the characteristic peaks at 20.9, 26.6, 36.6, 39.5, 45.8, 50.2, and 60.0°were ascribed to the (100), ( 011), ( 110), ( 102), (021), (112), and (211) crystal planes of SiO 2 (JCPDS card #79-1906) respectively on biochar. 25 Fig. 8b shows that the composed Ti-C prepared by the sol-gel method had obvious mentioned characteristic peaks of both SiO 2 and TiO 2 , indicating a typical anatase structure.…”

“…The details of biochar production were in accordance with our previous research. 25 First, 7.2 mL butyl titanate mixed with 20 mL ethanol was shaken at 450 rpm for 0.5 h. Then, hydrochloric acid was carefully added to adjust the solution pH to about 3.0 during the whole operation and oscillated for 0.5 h. Aer that, 0.2 g biochar powder was added into the solution and stirred for another 0.5 h (450 rpm) to get thorough mixing. Subsequently, 10 mL of 44% ethanol was added to this solution and stirred continuously until gel formation occurs.…”