Polyacrylamide in hydraulic fracturing fluid causes severe membrane fouling during flowback water treatment

Deciphering polymer degradation chemistry via integrating new database construction into suspect screening analysis

Water-soluble synthetic polymers and their environmental degradation products are overlooked but important industrial pollutants in wastewater. However, the detection of degradation products is limited to bulk solution chemistry and molecular-level analysis remains unreachable. In this work, we assessed the feasibility of current suspect screening and nontarget workflow using liquid chromatography-high resolution mass spectrometry (LC-HRMS) to elucidate molecular level information about polyacrylamide (PAM) and its degraded products by free radicals. Radical chain scission of PAM (10 kDa) using heat-activated persulfate was conducted to simulate hydraulic fracturing conditions in the deep subsurface. We found that the current workflows in the commercial software generated predicted formulae with low accuracy, due to limited capability of peak picking and formula prediction for high mass and charge features. By modeling literature-reported degradation pathways, we constructed a degradation product database of over 463 000 unique formulae, which improved the accuracy of the predicted formula. For the matched features, the ratio of aldehyde/ketone terminating molecule abundance was found to increase over 24 h degradation time, suggesting increasing content of aldehydes by radical-induced oxidative chain scission of PAM. This is contradictory to previously proposed ratios of carbon-centered radical position on polymer backbone initiated by hydroxyl radicals. Using in silico fragmentation of MS1 features, we identified 11 structures with confidence levels 2b and 3 using their MS2 information. This is the first attempt to resolve complex polymer degradation chemistry using HRMS that can advance our ability to detect water-soluble polymer pollutants and their transformation products in environmental samples.

Fouling and chemically enhanced backwashing performance of low-pressure membranes during the treatment of shale gas produced water

The treatment of shale gas produced water (SGPW) for beneficial reuse is currently the most dominant and economical option. Membrane filtration is one preferred method to deal with SGPW, but membrane fouling is an unavoidable problem. In this study, two types of ultrafiltration (UF) membranes and one type of microfiltration (MF) membrane were investigated to treat SGPW from Sichuan basin. Results showed that increased total dissolved solid (31-40 g/L) and UV₂₅₄ (10-42.9 m^-1) were observed for the same shale gas plays, and the primary fluorescent organic substances were humic acid-like components. Compared to UF membranes with the flux decline by 2% to 60%, MF membranes with larger pore size were more likely to be fouled with the flux decline by 43% to 95%. Cake layer filtration was verified to be the primary membrane fouling mechanism. Statistical analysis showed that UV₂₅₄ played the most significant role in membrane fouling which had the highest correlation (0.76 to 0.93). Compared to permeate backwashing (13%), deionized water backwashing and chemically enhanced backwashing (CEB) using NaClO, H₂O₂ and citric acid improved the cleaning efficiencies (31%-95%). CEB using NaOH prepared by deionized water aggravated membrane fouling, while excellent cleaning efficiencies (39%-79%) were observed for CEB using NaOH prepared by permeate. The difference in cleaning behaviors for fouled membranes by SGPW was verified by morphology observation and element composition analysis.

Coarse-grained force-field for large scale molecular dynamics simulations of polyacrylamide and polyacrylamide-gels based on quantum mechanics

Developing a coarse-grained force field for polyacrylamide based on quantum mechanics equation of state.

Rapid removal of polyacrylamide from wastewater by plasma in the gas-liquid interface

Due to the severe restrictions imposed by legislative frameworks, the removal of polyacrylamide (PAM) rapidly and effectively from produced wastewater in offshore oilfields before discharge is becoming an urgent challenge. In this study, a novel advanced oxidation process based on plasma operated in the gas-liquid interface was used to rapidly decompose PAM, and multiple methods including viscometry, flow field-flow fractionation multi-angle light scattering, UV-visible spectroscopy, and attenuated total reflectance-Fourier transform infrared spectroscopy were used to characterize the changes of PAM. Under a discharge voltage of 25 kV and pH 7.0, the PAM concentration decreased from 100 to 0 mg/L within 20 min and the total organic carbon (TOC) decreased from 49.57 to 1.23 mg/L within 240 min, following zero-order reaction kinetics. Even in the presence of background TOC as high as 152.2 mg/L, complete removal of PAM (100 mg/L) was also achieved within 30 min. The biodegradability of PAM improved following plasma treatment for 120 min. Active species (such as O₃ and H₂O₂) were produced in the plasma. Hydroxyl radical was demonstrated to play an important role in the degradation of PAM due to the inhibitory effect observed after the addition of an ·OH scavenger, Na₂CO₃. Meanwhile, the release of ammonia and nitrate nitrogen confirmed the cleavage of the acylamino group. The results of this study demonstrated that plasma, with its high efficiency and chemical-free features, is a promising technology for the rapid removal of PAM.

Pretreatment Techniques for Produced Water with Subsequent Forward Osmosis Remediation

Unconventional oil and gas extraction is on the rise across the United States and comprises an integral component in meeting the nation’s energy needs. The primary by-product of this industrious process is produced water, which is a challenging matrix to remediate because of its complex physical and chemical composition. Forward osmosis is a viable option to treat high-salinity produced water; however, fouling has been an issue. This study aimed to treat produced water before using forward osmosis as a remediation option. Trials consisted of a series of five experiments in order to evaluate the performance of the membrane. Samples were treated by centrifugation, activated carbon, filtration, ferric chloride, as well as coagulants and a polymer. It can be concluded that forward osmosis can be used to extract water from high-salinity oil field brines and produced water, and that pretreating the produced water decreased the tendency for fouling. The pretreatment with the overall best performance was activated carbon, which also yielded the lowest total organic carbon concentrations of 1.9 mg/L. During remediation trials using produced water pretreated with activated carbon as the feed solution, there was a 14% decrease in flux over the course of the 7 h trials. The membrane performance was restored after washing.

Unraveling the water states of waste-activated sludge through transverse spin-spin relaxation time of low-field NMR

The physical states of water are crucial for the dewatering efficiency of waste-activated sludge (WAS). However, to date, there is still lack of promising methods for the distinct differentiation of water states in colloidal microbial aggregates. This study proposed that the transverse spin-spin relaxation time (T₂) distribution of low-field nuclear magnetic resonance (NMR) could be a useful tool to unravel the occurrence state of water in WAS. Due to the different interaction strengths of protons with the surrounding environment, the three water states with different T₂ ranges were identified. The water strongly trapped on the surface of solid phase through hydrogen bound could be classified as vicinal water; interstitial water refers to the water physically trapped in bio-floc by steric hindrance or adsorption; and the water that is least affected by solid compositions is categorized as moderately mobile water. The potential ways of typical conditioning approaches for shifting water states were also investigated. The removal of hydrophilic compounds in extracellular polymeric substances (EPS) and surface charge neutralization were both found to be possible ways to influence the percentage of vicinal water (Pearson correlation coefficient R_p > 0.950, p-value ≤ 0.05). The disintegration or compaction of colloidal microbial aggregates could induce the transformation of interstitial water into moderately mobile water. All the above results are believed to deepen the mechanism insights into the differentiation and interactive transformation of water states in bio-floc of WAS.

The treatment of flowback water in a sequencing batch reactor with aerobic granular sludge: Performance and microbial community structure

The extensive application of hydraulic fracturing technology has significantly promoted the large-scale development of shale gas. However, it is a great challenge for shale gas extraction to effectively manage large-volume flowback water (FW) with high salinity and complex organic substances. Here, we report an aerobic granular sludge (AGS) tolerable to high salinity, and suited to the treatment of FW. The performance of a sequencing batch reactor (SBR) with the AGS for the treatment of the synthetic FW and the microbial community structure at different salinity levels were investigated. The AGS fed with synthetic FW possessed a larger average particle size and a higher settling rate (50 m h^-1). When NaCl concentration increased to 50.0 g L^-1, the removal efficiency of total organic carbon (TOC) increased to 79 ± 1%, and the removal rate of polyacrylamide (PAM) raised up to 42.7 ± 0.7 g m^-3 d^-1. Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Sphingobacteriia dominated in the microbial community of AGS. Cellvibrionaceae, Rhodocyclaceae, Enterobacteriaceae, Moraxellaceae, Pseudomonadaceae, and Halomonadaceae belonging to Betaproteobacteria and Gammaproteobacteria played important role in degrading PAM, polycyclic aromatic hydrocarbons (PAH), and some other organics in FW at high salinity. These results suggest that an AGS-based SBR is a promising technology for the treatment of FW.