Controlled chlorination of polyamide reverse osmosis membranes at real scale for enhanced desalination performance

Unveiling challenges of aluminium electrode fouling and passivation in electrocoagulation treatment system for sustainable water management of coastal Borneo peatlands: A focused review

The treatment of brackish peat water presents a formidable challenge due to its elevated levels of natural organic matter and salinity which not only hinder conventional water treatment systems but also necessitate an innovative approach to effectively manage these complex water characteristics. In response to these challenges, electrocoagulation has emerged as a promising alternative by utilizing electrochemical processes to efficiently destabilize and eliminate contaminants in brackish peat water sources. As such, this review aims to unveil challenges of aluminium electrodes fouling and passivation in electrocoagulation treatment system for sustainable water management of coastal Borneo peatlands. Several studies in the literature highlight that key operating parameters, especially electric current and voltage which play a pivotal role in influencing the overall effectiveness of these electrocoagulation systems. Although aluminium electrodes demonstrate high contaminants removal efficiencies, it remains susceptible to fouling and passivation due to contaminant buildup and oxide layer formation which increase electrical resistance and decrease electroactivity of redox reactions. The novelty of this review lies in its focused synthesis of fouling and passivation dynamics through the integration of Tafel plot analyses and advanced characterization techniques, particularly Energy Dispersive X-Ray (EDX) spectroscopy. Furthermore, a thorough understanding of the adsorption mechanisms, particularly through the interaction between aluminium hydroxides and contaminants is essential for enhancing system efficiency and mitigating fouling. Additionally, optimizing the electrocoagulation treatment system and conducting a detailed analysis of adsorption mechanisms, particularly through Tafel plot analysis are pivotal for enhancing the system efficiency. Advanced analytical methods such as Energy Dispersive X-Ray (EDX) spectroscopy provide deeper insights into floc composition that essential for improving contaminants removal strategies. Overall, this review offers a focused assessment on the interplay between brackish peat water and electrocoagulation in order to provide a foundation for future research aimed at developing sustainable treatment systems for coastal Borneo peatlands.

Degradation of polyamide nanofiltration membranes by free chlorine and halide ions: Kinetics, mechanisms, and implications

The kinetics of polyamide membrane degradation by free chlorine and halide ions (Br- and Cl-) were innovatively evaluated based on physicochemical properties and filtration performance, using water/solute permeability coefficient in addition to bromide incorporation as important indicators. The reaction rate constants for the reduced water and H3BO3 permeability coefficient were 1-2 orders of magnitude higher at 0-1 h than 1-10 h. N-bromination and bromination-promoted hydrolysis are dominant degradation mechanisms at 0-1 h (reflected by the breakage of hydrogen bond, the increased Ca binding content, and the increased charge density), and ring-bromination further occurs at 1-10 h (reflected by the disappearance or weakening of aromatic amide band and the nearly constant hydrogen bond). The more reactive but less abundant brominating agents (Br2O, BrOCl, BrCl, and Br2) played significant roles in membrane degradation, contradicting the conventional belief that HOBr is the only reactive species. BrCl at pH 4.0 and BrOCl and Br2O at pH 7.0 made significantly higher contributions to membrane degradation than HOBr (>76 % vs. <13 %). The increased contribution of BrCl and Br2 with the increased [Cl-] and [Br-]ex (the excess bromide, defined as [Br-]o - [HOCl]o when [Br-]o > [HOCl]o), respectively, was responsible for the greater reduction of water permeability coefficient. The innovative and simple approach developed in this study provides important insights to evaluate and predict membrane degradation.

Modification Mechanism of Polyamide Reverse Osmosis Membrane by Persulfate: Roles of Hydroxyl and Sulfate Radicals

Oxidative modification is a facile method to improve the desalination performance of thin-film composite membranes. In this study, we comparatively investigated the modification mechanisms induced by sulfate radical (SO₄^• -) and hydroxyl radical (HO^•) for polyamide reverse osmosis (RO) membrane. The SO₄^• -- and HO^•-based membrane modifications were manipulated by simply adjusting the pH of the thermal-activated persulfate solution. Although both of them improved the water permeability of the RO membrane under certain conditions, the SO₄^• --modified membrane notably prevailed over the HO^•-modified one due to higher permeability, more consistent salt rejection rates over wide pH and salinity ranges, and better stability when exposed to high doses of chlorine. The differences of the membranes modified by the two radical species probably can be related to their distinct surface properties in terms of morphology, hydrophilicity, surface charge, and chemical composition. Further identification of the transformation products of a model polyamide monomer using high-resolution mass spectrometry demonstrated that SO₄^• - initiated polymerization reactions and produced hydroquinone/benzoquinone and polyaromatic structures; whereas the amide group of the monomer was degraded by HO^•, generating hydroxyl, carboxyl, and nitro groups. The results will enlighten effective ways for practical modification of polyamide RO membranes to improve desalination performances and the development of sustainable oxidation-combined membrane processes.

Treatment of reverse osmosis membrane by sodium hypochlorite and alcohols for enhanced performance using the swelling-fastening effect

Chemicals soaking is generally acknowledged as a convenient and efficient method to improve the performance of reverse osmosis (RO) membranes. The conventional soaking of RO membranes in alkaline sodium hypochlorite (NaClO) usually promotes extensive hydrolysis and cleavage amide bonds, resulting in improved water flux but declined salt rejection. Here, alcohols were added into the NaClO solution to regulate the chlorination processes using their "swelling-fastening" effect. The alcohols could interact with polyamide chains, and thus swell the polyamide network. Due to this interaction, the NaClO has less probability of attacking the polyamide chains. Hence, the chlorine-promoted hydrolysis was partly eased, which could weaken the decrease of salt rejection. Besides, after removing alcohols as well as the dissolved small oligomers and fragments of polyamide, the network was compacted and the loosened sites were healed, which is also beneficial to increase the difficulty of salt penetration. The treatment of RO membrane by the NaClO and alcohols could produce a hydrophilic surface with increased water flux and high salt rejection. The membrane chloridized at 2000 ppm NaClO exhibited a water flux improvement of 20.28% and a salt rejection declination of 0.95%. When treated with 2000 ppm NaClO associated with 5% methanol, the water flux improved 20.13% with little declination in salt rejection.