Treatment by coagulation–adsorption

The application of chemical coagulants and powdered activated carbon was investigated to reduce turbidity, dissolved organic carbon, total petroleum hydrocarbons, and poly(ethylene glycol)s in four hydraulic fracturing waste waters [112]. Jar tests were performed to evaluate both the powdered activated carbon and coagulants. Treatment goals were operationally defined targeting 90% reduction of turbidity, poly(ethylene glycol)s, and total petroleum hydrocarbons.

Coagulation is a chemical process that involves neutralization of charge, whereas flocculation is a physical process and does not involve neutralization of charge [113]. The dose of the coagulant to be used can be determined via the jar test [114,115]. The jar test involves exposing same-volume samples of the water to be treated to different doses of the coagulant and then simultaneously mixing the samples at a constant short mixing time.

Powdered activated carbon was found to be effective for removing both poly(ethylene glycol)s and total petroleum hydrocarbons from the waste waters, but would not settle without the addition of a coagulant. Ferric chloride achieved a 90% reduction in turbidity at a lower dose than aluminum chlorohydrate, in the presence and absence of powdered activated carbon.

The optimized coagulant dose by itself had little to no effect upon concentrations of dissolved organic carbon and poly(ethylene glycol)s, while greater than 80% removal of total petroleum hydrocarbons, a minor component of dissolved organic carbon, was observed in three of the waters.

Powdered activated carbon at 1000 mgl−1 achieved greater than 80% reductions of the total ion chromatogram, while dissolved organic carbon removals ranged from 9.5% to 48.3%. These results suggested that coagulation with ferric chloride at doses as low as 5 mgl−1 is an effective process for turbidity and total petroleum hydrocarbon reduction in hydraulic fracturing waste waters. When coupled with powdered activated carbon the method can also remove dissolved organic carbon and targeted organic contaminants such as poly(ethylene glycol)s [112].