Considering that a large fraction of the global population relies on self-supplied drinking water systems, household water treatment (HWT) technologies may assist achieving the United Nations' Sustainable Development Goal 6.1, which aims at safe drinking water for all by 2030. Hydrogen peroxide disinfection has been widely known as an effective approach for microorganism inactivation, however, it has not been much explored as a standalone solution in sanitation. In this sense, this review presents systematically organized information extracted from papers on H2O2 disinfection from 2011 to 2021. Filtered data was analyzed by content and network visualization, raising a discussion on whether H2O2 could be a potential HWT intervention, and which limitations and prospects are there for its research and implementation. In short, we found a lack of consistency in operational conditions, as most of the retrieved studies address individual use of H2O2 as control to combined treatments. Additionally, oxidant demand and kinetics considering local water quality are lacking, as well as information on residual neutralization, toxicity, and up-scaling. This critical review reveals gaps that encourage further research tackling different disinfection challenges, so that this alternative can be evaluated for implementation as an HWT technology, particularly at context-specific situations.

Water treatment plant (WTP) residues, e.g. sludge and filter backwash water (FBW), may contain pathogenic microorganisms, as Giardia spp. and Cryptosporidium spp.. However, recovering protozoa from such matrices lacks a formal and precise protocol, which is imperative to improve research in their detection, removal and inactivation. The latter includes a deeper challenge as some recovery methods may compromise viability. This study applied different recovery methods for G. muris cysts and C. parvum oocysts spiked into settled sludge and FBW obtained from a bench treatment. Procedures in sludge involved direct centrifugation, alkaline and acid flocculation, including purification by immunomagnetic separation (IMS). FBW samples were tested for membrane filtration (MF) and heated Tween® scrapings followed or not by IMS. Propidium iodide (PI) inclusion was used for oocyst viability evaluation prior and after recovery. Results with purified suspensions lead to higher recovery efficiencies (RE) for C. parvum, which was assumed to relate to poor G. muris fluorescence. Analytical quality assessments were carried out with ColorSeed® for the methods that stood out for each matrix and the results indicated lower RE than when organisms from purified suspensions were recovered. Ferric sulfate flocculation and MF, both followed by IMS reached 32.25 and 11.00% RE for Giardia spp. and 19.61 and 2.00% for Cryptosporidium spp., respectively. All of the tested methods affected oocyst viability. These results encourage further research to overcome the matrices complexity explained in this paper and increase RE, taking effects in protozoa viability into consideration.

Photodynamic therapy (PDT) has been widely employed in clinical applications, healthcare, and public health (e.g. cancer research, microbiological control, vector control, etc). The photodynamic action is an advanced oxidation process based on the production of reactive oxygen species (ROS) and singlet oxygen by the excitation of a photosensitizer by specific wavelengths of light in the presence of molecular oxygen. The generation of ROS, which are highly reactive, encourages the use of PDT against recalcitrant pollutants and resistant parasites, a novel approach for PDT applications. Here, we explored recent research in PDT in water and wastewater treatment, elucidating operational conditions, main targets, potentials, and constraints, considering a collection of scientific papers curated by a well-defined research strategy. Retrieved records were filtered by subjects, and data was organized into a content network. Results showed that PDT is a timely alternative to deal with emerging chemical contaminants, resistant microorganisms, and other challenges, raising opportunities for versatile applications and sustainable solutions. Advances in environmental applications of PDT may help reach the Sustainable Development Goal 6 (SDG 6), but also positively impact other SDGs.

This study aimed to include in-situ microscopy in the analysis of floc development during coagulation-flocculation for drinking water treatment. To this end, jartest series were carried out for natural and synthetic waters using aluminum sulfate, sulfate chloride, ferric chloride, and Opuntia sp. as coagulants. Coagulation under optimized conditions was monitored by an in-situ microscope in conjunction with image analysis. Obtained results enabled some insights on the coagulation process. Images captured different stages of initial floc development, including flocs exhibiting heterogeneous, branched, and irregular surface structures. From image analysis, wide distributions of flocculated particle sizes were found for both natural (19–15834 μm) and synthetic water (19–21607 μm), suggesting the occurrence collisions by adhesion and transport between particles, thus influencing floc formation rates depending on the medium. Average size and number of flocs, as determined by the image analysis algorithm as a function of the time, showed inverse correlation of floc growth with water clarification. The microscopic images also illustrated how different coagulants in different water sources undergo breaking through fragmentation or erosion. Our findings also highlight the importance of investigating additional aspects that involve conditions of mixing, development, breaking, regrouping, and resistance of flocs. Graphical abstract