Examination of purified single-walled carbon nanotubes on activated sludge process using batch reactors

This paper evaluated the impact of over 90% purified single-walled carbon nanotubes (SWCNTs) on the activated sludge wastewater treatment process through a batch-scale study. We found that SWCNTs adsorbed 16.9% of the soluble COD (sCOD, soluble chemical oxygen demand) without activated sludge present. Statistical analysis of the experimental data demonstrated that only four experimental parameters, i.e., surface charge, sCOD, mixed liquor suspended solids, and sludge volume index were significantly impacted by the addition of SWCNTs; other parameters such as pH, dissolved oxygen, specific resistance to filtration, and relative hydrophobicity were not significantly impacted. Further examination of the four affected parameters illustrated that SWCNTs improved sludge settleability and made the surface of the activated sludge flocs less negatively charged. The addition of SWCNTs appeared to improve sCOD removal due mostly to absorption. This research also found that the impacts observed were from the SWCNTs, not the impurities within the SWCNTs tested.