Removal of organics from shale gas fracturing flowback fluid using expanded granular sludge bed and moving bed biofilm reactor

ABSTRACT

Shale gas fracturing flowback fluid contains various degradation difficulty organic compounds after hydraulic fracturing. A hybrid treatment method was developed for treating flowback and produced water (FPW) using pre-treatment (NaClO) followed by the expanded granular sludge bed (EGSB) and moving bed biofilm reactor (MBBR). Gas chromatography–mass spectrometry (GC-MS) was employed to detect organic composition in the FPW, the pre-treated FPW, EGSB and MBBR effluent. FPW had high chemical oxygen demand (COD) (3278 mg/L) and the majority of organic compounds in the FPW composed of alkanes and heteroatomic compounds with polymers and polarity. 20% COD removal was achieved after adding 5 g/L of NaClO in FPW (pH = 7, stirring for 20 mins) as pre-treatment and > C₃₀ alkanes in FPW were decomposed a lot in the pre-treatment process. The pre-treated FPW was diluted (volumetric ratio of 20%/50%) with synthetic wastewater/pure water. In the final stage of operation, Cl⁻ and COD concentration of influent to EGSB-MBBR system was around 7000 ± 100 mg/L and 3000 mg/L. EGSB-MBBR system achieved 93.84% COD removal rate, in which EGSB dominated COD removal (>80%). According to the GC-MS results, EGSB had an increase of C₁₁-C₃₀ compounds and a decrease of less C₁-C₁₀ content due to the consumption of  > C₃₀ compounds and low molecular weight (LWM) compounds. Meanwhile, aerobic microorganisms in MBBR metabolized LWM organics which contributed a lot to the COD removal (25.06∼68. 22%). The results indicated that the pre-treatment and biological EGSB-MBBR system could be an efficient option used for FPW treating.

GRAPHICAL ABSTRACT

KEYWORDS:

• Flowback and produced water
• organic compounds
• expanded granular sludge bed
• moving bed biofilm reactor

Acknowledgements

This work was supported by Sichuan Province Science and Technology Support Program (Project No. 2015SZ0009) ‘Development and Demonstration of Integrated Treatment and Recycling Technology for Fracturing and Returning Fluid in Shale Gas Production’.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Sichuan Province Science and Technology Support Program [Project No. 2015SZ0009] ‘Development and Demonstration of Integrated Treatment and Recycling Technology for Fracturing and Returning Fluid in Shale Gas Production’.