Insights into the foulants characteristics in a walnut shell biofilm-membrane bioreactor during treatment of hypersaline oilfield produced water

The characteristics and behavior of membrane fouling in oilfield produced water treatment systems are highly affected by the complex nature of this stream. The present study is dedicated to the characterization of the membrane foulants in a hybrid moving bed and membrane bioreactor (MBBR-MBR) system using walnut shell as a bio-carrier, for treatment of real produced water at total dissolved solids (TDS) concentrations of 35,000, 90,000 and 200,000 mg/L. The impact of using walnut shell on fouling was also investigated. Various analytical methods including attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), gas chromatography- mass spectrometry (GC–MS) were used to identify the organic compounds and inductively coupled plasma- optical emission spectrometry (ICP- OES), X-ray fluorescence (XRF), energy-dispersive X-ray spectroscopy (EDS) and X-ray powder diffraction (XRD) were applied in order to investigate the inorganic constituents present in the foulants. Additionally, field emission scanning electron microscopes (FE-SEM), atomic force microscopy (AFM) and particle size distribution (PSD) analysis were used as auxiliary tools to investigate the morphology and particle size distribution of the cake layer. The results indicated that the most important organic compounds identified included microorganisms, microbial products, and hydrocarbons. Also, the most important inorganic elements included Na, Cl, K, Ca, S, and P which probably originated from NaCl, CaCO3, and Ca-P precipitates. Walnut shell was effective in reducing membrane fouling due to the scouring effect, as well as altering the properties of sludge, and adsorption of oil compounds.