As many regions seek to supplement traditional water sources with reclaimed water, an increasing number of risk assessments are conducted for these types of applications. The most comprehensive approach is to conduct a quantitative microbial risk assessment (QMRA) combining empirical and literature data, point value estimates, and probability distribution functions (PDFs) to estimate the final risk for human health from a treatment train in quantitative terms. The variability and uncertainty of reuse systems can be more adequately assessed by probabilistic methods instead of deterministic, point value estimates. This review summarizes common assumptions in PDF selection for source water and treatment steps and dose-response models for risk assessments applied to potable and non-potable reuse scenarios. The review revealed that source water pathogen concentrations were mainly modeled using PDFs, while log reduction values (LRVs) were often derived as point estimates to describe removal efficacy of individual treatment steps. When enough point value LRVs are known, a triangular distribution is recommended to retain the stochastic characteristics of the variable being modeled. Treatment steps with the least amount of experimental data included biological activated carbonand membrane bioreactors, among others. To circumvent such lack of experimental data, an open-source, anonymized database of concentrations and LRVs could be made available for future assessments. Numerous studies mentioned that testing multiple dose-response models can help determine how the dose-response choice affects final risk. Although sensitivity analyses to determine how variables in the assessment influence final risk were performed in most studies, how PDF selection affects the final risk was not consistently evaluated. Such a discussion could help to establish more informative and comprehensive risk assessment models in future studies as the water reuse field continues to grow.@en

Quaternary ammonium compounds (QACs) are commonly used in many products, such as disinfectants, detergents and personal care products. However, their widespread use has led to their ubiquitous presence in the environment, posing a potential risk to human and environmental health. Several methods, including direct and indirect photodegradation, have been explored to remove QACs such as benzylalkyldimethyl ammonium compounds (BACs) and alkyltrimethyl ammonium compounds (ATMACs) from the environment. Hence, in this research, a systematic review of the literature was conducted using PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) method to understand the fate of these QACs during direct and indirect photodegradation in UV/H2O2, UV/PS, UV/PS/Cu2+, UV/chlorine, VUV/UV/chlorine, O3/UV and UV/O3/TiO2 systems which produce highly reactive radicals that rapidly react with the QACs, leading to their degradation. As a result of photodegradation, several transformation products (TPs) of QACs are formed, which can pose a greater risk to the environment and human health than the parent QACs. Only limited research in this area has been conducted with fewer QACs. Hence, quantum mechanical calculations such as density functional theory (DFT)-based computational calculations using Gaussian09 software package were used here to explain better the photo-resistant nature of a specific type of QACs, such as BACs C12-18 and ATMACs C12-C18, and their transformation pathways, providing insights into active sites participating in the phototransformation. Recognizing that different advanced oxidation processes (AOPs) come with pros and cons in the elimination of QACs, this review also highlighted the importance of implementing each AOP concerning the formation of toxic transformation products and electrical energy per order (EEO), especially when QACs coexist with other emerging contaminants (ECs).@en

This study evaluated the impact of precise representation of spacer geometry on numerical simulations of hydrodynamics and solute transport in feed channels of membrane processes. Three levels of increasing geometry accuracy were assessed: i) cylindrical filaments, ii) filaments with circular sections of variable diameter based on microscopic measurements, and iii) geometries obtained from X-ray computed tomography (CT scans) in three resolutions (22 µm, 11 µm, and 5.5 µm). The three-dimensional CT scans revealed quasi-elliptic, not circular, cross-sections of the filaments. Microscopic measurements fail to account for this ellipticity, resulting in overestimation of pressure drop calculated at industry-typical average velocities (0.07–0.15 m s−1) by a factor of 1.8 compared to CT-based geometries. On the other hand, the cylindrical spacer filaments representation overestimates concentration polarization at the membrane surface compared to CT-based geometries. Experimental results of pressure drop and particle deposition were in close agreement with simulations using CT scanned geometries. This work demonstrates that modeling results depend significantly on the spacer geometry accuracy. Within the investigated CT scan accuracies 20 µm was found sufficient for modeling hydrodynamics and solute transport in spacer-filled feed channels. The results may be useful for reliable investigation and development of novel spacer geometries.@en