Renewable energy powered membrane technology: Impact of osmotic backwash on organic fouling during solar irradiance fluctuation

Tutorial review of error evaluation in experimental water research at the example of membrane filtration

Experimental water research lacks clear methodology to estimate experimental error. Especially when natural waters are involved, the characterization tools bear method-specific artifacts while the varying environmental conditions prevent regular repeats. This tutorial review identifies common mistakes, and proposes a practical procedure to determine experimental errors at the example of membrane filtration. Statistical analysis is often applied to an insufficient number of repeated measurements, while not all error sources and contributions are considered. This results in an underestimation of the experimental error. Variations in relevant experimental parameters need to be investigated systematically, and the related errors are quantified as a half of the variation between the max and min values when standard deviation is not applicable. Error of calculated parameters (e.g. flux, pollutant removal and mass loss) is estimated by applying error propagation, where weighing contributions of the experimental parameters are considered. Appropriate judgment and five-time repetition of a selected experiment under identical conditions are proposed to validate the propagated experimental error. For validation, the five repeated data points should lie within the estimated error range of the error bar. The proposed error evaluation procedure is adaptable in experimental water research and intended for researchers to identify the contributing factors of an experimental error and carry out appropriate error quantification and validation. The most important aim is to raise awareness of the necessity to question error methodology and reproducibility of experimental data, to produce and publish high quality research.

Starch-Derived Superabsorbent Polymer in Remediation of Solid Waste Sludge Based on Water–Polymer Interaction

The purpose of this study is to assess water–polymer interaction in synthesized starch-derived superabsorbent polymer (S-SAP) for the treatment of solid waste sludge. While S-SAP for solid waste sludge treatment is still rare, it offers a lower cost for the safe disposal of sludge into the environment and recycling of treated solid as crop fertilizer. For that to be possible, the water–polymer interaction on S-SAP must first be fully comprehended. In this study, the S-SAP was prepared through graft polymerization of poly (methacrylic acid-co-sodium methacrylate) on the starch backbone. By analyzing the amylose unit, it was possible to avoid the complexity of polymer networks when considering S-SAP using molecular dynamics (MD) simulations and density functional theory (DFT). Through the simulations, formation of hydrogen bonding between starch and water on the H06 of amylose was assessed for its flexibility and less steric hindrance. Meanwhile, water penetration into S-SAP was recorded by the specific radial distribution function (RDF) of atom–molecule interaction in the amylose. The experimental evaluation of S-SAP correlated with high water capacity by measuring up to 500% of distilled water within 80 min and more than 195% of the water from solid waste sludge for 7 days. In addition, the S-SAP swelling showed a notable performance of a 77 g/g swelling ratio within 160 min, while a water retention test showed that S-SAP was capable of retaining more than 50% of the absorbed water within 5 h of heating at 60 °C. The water retention of S-SAP adheres to pseudo-second-order kinetics for chemisorption reactions. Therefore, the prepared S-SAP might have potential applications as a natural superabsorbent, especially for the development of sludge water removal technology.

Removal of micropollutants through bio-based materials as a transition to circular bioeconomy: Treatment processes involved, perspectives and bottlenecks

The recent increase in micropollutant levels in water bodies is a growing concern globally. The generation of new materials and techniques for wastewater treatment often involves the release of hazardous wastes and the utilization of energy related to it. This can be resolved by the synthesis of bio-based materials through the use of already released wastes and naturally occurring components, adding their value as reusable resources. These bio-based materials find wide applications for micropollutant elimination and energy tapping due to the presence of various functional groups, large surface area, high stability, and reusability. The processes involved in micropollutant elimination through biomaterials generally include adsorption and degradation. These treatment processes are suggested to depend on various operational parameters like pH, temperature, dose, reaction time, presence of other contaminants, ions, etc. in the system, which may influence the process efficiency. Understanding the potential of bio-based materials many steps can be taken towards its large-scale application to upgrade wastewater treatment plants for micropollutant elimination. Furthermore, the recent advances of bio-based materials in energy storage and conversion have widened its scope for implementation in a circular bioeconomy. The bottlenecks towards such a transition and future recommendations are also presented and discussed.

Renewable energy powered membrane technology: Implications of adhesive interaction between membrane and organic matter on spontaneous osmotic backwash cleaning

Organic matter (OM) in surface and ground waters may cause membrane fouling that is laborious to clean once established. Spontaneous osmotic backwash (OB) induced by solar irradiance fluctuation has been demonstrated for early mineral scaling/organic fouling control in decentralised small-scale photovoltaic powered-nanofiltration/reverse osmosis (PV-NF/RO) membrane systems. However, various OM types will interact differently with membranes which in turn affects the effectiveness of OB. This work evaluates the suitability of spontaneous OB cleaning for eleven OM types (covering low-molecular-weight organics (LMWO), humic substances, polyphenolic compounds and biopolymers) regarding adhesive interactions with NF/RO membranes. The adhesive interactions were quantified by an asymmetric flow field-flow fractionation coupled with an organic carbon detector (FFFF-OCD). The underlying mechanism of OM-membrane adhesive interactions affecting OB cleaning was elucidated. The results indicate that humic acid (a typical humic substance) and tannic acid (a typical polyphenolic compound) induced stronger adhesive interaction with NF/RO membranes than biopolymers and LMWO. When the mass loss of an OM due to adhesion was below a critical range, the spontaneous OB is most effective (>85% flux recovery); and above this range, the OB becomes ineffective (<50% flux recovery). Polyphenolic compounds and humic substances resulted in lower OB cleaning efficiency, due to their higher aromatic content, enhancing hydrophobic interactions and hydrogen bonding. Calcium-facilitated adhesion of some OM types (such as humic substances, polyphenolics and biopolymers) increased irreversible organic fouling potential and weakened OB cleaning, which was verified by both FFFF-OCD and membrane filtration results. This work provides a guidance to formulate strategies to enhance spontaneous OB cleaning, such as first identifying the adhesion of OM in feedwater (surface and ground waters) using FFFF-OCD, and then removing "sticky" OM using suitable pre-treatment processes.