Simultaneous removal of nanosilver and fullerene in sequencing batch reactors for biological wastewater treatment

Increasing use of engineered nanomaterials (ENMs) inevitably leads to their potential release to the sewer system. The co-removal of nano fullerenes (nC₆₀) and nanosilver as well as their impact on COD removal were studied in biological sequencing batch reactors (SBR) for a year. When dosing nC₆₀ at 0.07-2mgL^-1, the SBR removed greater than 95% of nC₆₀ except for short-term interruptions occurred (i.e., dysfunction of bioreactor by nanosilver addition) when nC₆₀ and nanosilver were dosed simultaneously. During repeated 30-d periods of adding both 2mgL^-1 nC₆₀ and 2mgL^-1 nanosilver, short-term interruption of SBRs for 4d was observed and accompanied by (1) reduced total suspended solids in the reactor, (2) poor COD removal rate as low as 22%, and (3) decreased nC₆₀ removal to 0%. After the short-term interruption, COD removal gradually returned to normal within one solids retention time. Except for during these "short-term interruptions", the silver removal rate was above 90%. A series of bottle-point batch experiments was conducted to determine the distribution coefficients of nC₆₀ between liquid and biomass phases. A linear distribution model on nC₆₀ combined with a mass balance equation simulated well its removal rate at a range of 0.07-0.76mgL^-1 in SBRs. This paper illustrates the effect of "pulse" inputs (i.e., addition for a short period of time) of ENMs into biological reactors, demonstrates long-term capability of SBRs to remove ENMs and COD, and provides an example to predict the removal of ENMs in SBRs upon batch experiments.