Anion exchange membranes (AEMS) are particularly prone to fouling when employed to desalinate polymer flooding produced water (PFPW), an abundant sub-product from the oil and gas industry. The formation of fouling on an AEM will be affected by the composition of the solution, which includes various dissolved salts, partially hydrolyzed polyacrylamide (HPAM), crude oil, and surfactants. Electrodialysis experiments were performed to desalinate feed solutions with different compositions, aiming to distinguish between their individual and combined effects. The solutions contained diverse mono- and divalent ions. The analysis included data collected during the desalination and characterization of the fouled AEMs by diverse analytical techniques. HPAM produced the most severe effects in terms of visible fouling and increase of resistance. This polyelectrolyte fouls the AEM by adsorbing on its surface and by forming a viscous gel layer that hampers the replenishment of ions from the bulk solution. Ca and Mg have a large influence on the formation of thick HPAM gel layers, while the oily compounds have only a minimal influence acting mainly as a destabilizing agent. The membranes also presented scaling consisting of calcium precipitates. The effects of the gel layer were minimized by applying current reversal and foulant-free solution.

The reuse of cooling tower blowdown (CTBD) in the cooling tower itself requires CTBD deionization and a pre-treatment before deionization to remove organic compounds (OCs) that induce membrane fouling. This study assesses the potential of electrochemical oxidation (EO) with a boron-doped diamond (BDD) and a Ti/RuO2 mixed-metal oxide (MMO) anode for CTBD pre-treatment. Also, the influence of the applied current density (j), initial pH, hydrodynamic conditions, and supporting electrolyte on the process performance was evaluated. Results show that COD and TOC removal were 85 and 51%, respectively, with the BDD-anode; however, they were 50 and 12% with MMO-anode at a j-value of 8.7 mA cm-2 and neutral pH. An increased j-value increased the COD and TOC removal; however, different pHs, hydrodynamic conditions, and the addition of supporting electrolytes had a minor impact on the removal with both anodes. Liquid chromatography-organic carbon detection analysis showed that the OC in CTBD mainly consisted of humic substances (HS). EO with the BDD-anode resulted in 35% HS mineralization, while the rest of the HS were partially oxidized into low molecular weight compounds and building blocks. However, HS mineralization was limited with the MMO-anode. The mineralization and oxidation were accompanied by the formation of organic and inorganic chlorinated species. These species increased the toxicity to Vibrio fischeri 20-fold compared to the initially low-toxic CTBD. Thus, EO with a BDD-anode is a promising pre-treatment technology for the removal of OCs before CTBD deionization, but measures to minimize the chlorinated species formation are required before its application.

Cation exchange membranes (CEMs) are subject to fouling when utilized to desalinate wastewater from the oil and gas industry, hampering their performance. The kind and extent of the fouling are most likely dependent on the composition of the stream, which in practical applications can vary significantly. Fouling experiments were performed on commercial cation exchange membranes, which were used in electrodialysis runs to desalinate solutions of varying composition. The variations included ionic strength, type of ions, amount of viscosifying polyelectrolyte (partially hydrolyzed polyacrylamide), presence of crude oil, and surfactants. Performance parameters, like electric potential and pH, were monitored during the runs, after which the membranes were recovered and analyzed. Fouling was detected on most CEMs and occurred mainly in the presence of the viscosifying polyelectrolyte. Under normal pH conditions (pH ~ 8), the polyelectrolyte fouled the concentrate side of the CEMs, as expected due to electrophoresis. However, by applying a current in the opposite direction, the polyelectrolyte layer could be removed. Precipitation occurred mostly on the opposite side of the membrane, with different morphology depending on the feed composition.

This study examines the effect of mixing on the performance of anaerobic digestion of cow manure in Chinese dome digesters (CDDs) at ambient temperatures (27–32 °C) in comparison with impeller mixed digesters (STRs) and unmixed digesters (UMDs) at the laboratory scale. The CDD is a type of household digester used in rural and pre-urban areas of developing countries for cooking. They are mixed by hydraulic variation during gas production and gas use. Six digesters (two of each type) were operated at two different influent total solids (TS) concentration, at a hydraulic retention time (HRT) of 30 days for 319 days. The STRs were mixed at 55 rpm, 10 min/hour; the unmixed digesters were not mixed, and the Chinese dome digesters were mixed once a day releasing the stored biogas under pressure. The reactors exhibited different specific biogas production and treatment efficiencies at steady state conditions. The STR 1 exhibited the highest methane (CH₄) production and treatment efficiency (volatile solid (VS) reduction), followed by STR 2. The CDDs performed better (10% more methane) than the UMDs, but less (approx. 8%) compared to STRs. The mixing regime via hydraulic variation in the CDD was limited despite a higher volumetric biogas rate and therefore requires optimization.

Electrodialysis (ED) has been recently proposed to desalinate polymer-flooding produced water (PFPW), a byproduct stream from the oil and gas industry rich in charged polymers. However, process performance is limited by fouling occurring on the ion-exchange membranes, particularly on the anionic ones (AEMs). Thus, this study aimed to correlate the properties of different AEMs with their performance while desalinating PFPW, ultimately evaluating their significance when fouling is to be minimized and operation improved. Six stacks containing different homogeneous and commercially available AEMs were employed to desalinate synthetic PFPW during 8-days ED experiments operated in reversal mode. AEMs recovered from the stacks were analyzed in terms of water uptake, ion-exchange capacity, permselectivity, and area resistance, and compared with virgin AEMs. Relatively small changes were measured for most of the parameters evaluated. For most AEMs, the water uptake and resistance increased, while the ion-exchange capacity (IEC) and permselectivity decreased during operation. Ultimately, AEMs with high area resistance were linked to the fast development of limiting current conditions in the stack, so this property turned out to be the most relevant when desalinating PFPW.

Chinese dome digesters are usually operated at long hydraulic retention times (HRT) and low influent total solids (TS) concentration because of limited mixing. In this study, a newly optimised Chinese dome digester with a self-agitating mechanism was investigated at a pilot scale (digester volume = 500 L) and compared with a conventional Chinese dome digester (as blank) at 15% influent TS concentration at two retention times (30 and 40 days). The reactors were operated at ambient temperature: 27–33 °C. The average specific methane production, volatile fatty acids and percentage of volatile solids (VS) reduction are 0.16 ± 0.13 and 0.25 ± 0.05L CH₄/g VS; 1 ± 0.5 and 0.7 ± 0.3 g/L; and 51 ± 14 and 57 ± 10% at 40 days HRT (day 52–136) for the blank and optimised digester, respectively. At 30 days HRT (day 137–309) the results are 0.19 ± 0.12 and 0.23 ± 0.04 L CH₄/g VS; 1.2 ± 0.6 and 0.7 ± 0.3 g/L; and 51 ± 9 and 58 ± 11.6%. Overall, the optimised digester produced 40% more methane than the blank, despite the high loading rates applied. The optimised digester showed superior digestion treatment efficiency and was more stable in terms of VFA concentration than the blank digester, can be therefore operated at high influent TS (15%) concentration.