Meta-analysis of mass balances examining chemical fate during wastewater treatment

Mass balances are an instructive means for investigating thefate of chemicals during wastewater treatment. In additionto the aqueous-phase removal efficiency (Ö), they can informon chemical partitioning, transformation, and persistence, aswell as on the chemical loading to streams and soils receiving,respectively, treated effluent and digested sewage sludge(biosolids). Release rates computed on a per-capita basis canserve to extrapolate findings to a larger scale. This reviewexamines over a dozen mass balances conducted for variousorganic wastewater contaminants, including prescriptiondrugs, estrogens, fragrances, antimicrobials, and surfactantsof differing sorption potential (hydrophobicity), here expressedas the 1-octanol-water partition coefficient ( K OW) and theorganic carbon normalized sorption coefficient ( K OC). Majorchallenges to mass balances are the collection of representativesamples and accurate quantification of chemicals in sludge.Ameta-analysis of peer-reviewed data identified sorption potentialas the principal determinant governing chemical persistencein biosolids. Occurrence data for organic wastewatercompoundsdetected in digested sludge followed a simple nonlinearmodel that required only K OW or K OC as the input and yieldeda correlation coefficient of 0.9 in both instances. The modelpredicted persistence in biosolids for the majority (>50%) of theinput load of organic wastewater compounds featuring alog10 K OW value of greater than 5.2 (log10 K OC > 4.4). In contrast,hydrophobicity had no or only limited value for estimating,respectively,Öand the overall persistence of a chemical duringconventional wastewater treatment