The effects of hydrogen peroxide pre-oxidation on ultrafiltration membrane biofouling alleviation in drinking water treatment

Bacterial community shifts induced by high concentration hydrogen peroxide treatment of Microcystis bloom in a mesocosm study

Hydrogen peroxide has gained popularity as an environmentally friendly treatment for cyanobacterial harmful algal blooms (cHABs) that takes advantage of oxidative stress sensitivity in cyanobacteria at controlled concentrations. Higher concentrations of hydrogen peroxide treatments may seem appealing for more severe cHABs but there is currently little understanding of the environmental impacts of this approach. Of specific concern is the associated microbial community, which may play key roles in the succession/recovery process post-treatment. To better understand impacts of a high concentration treatment on non-target microbial communities, we applied a hydrogen peroxide spray equating to a total volume concentration of 14 mM (473 mg/L, 0.04%) to 250 L mesocosms containing Microcystis bloom biomass, monitoring treatment and control mesocosms for 4 days. Cyanobacteria dominated control mesocosms throughout the experiment while treatment mesocosms experienced a 99% reduction, as determined by bacterial amplicon sequencing, and a 92% reduction in bacterial cell density within 1 day post-treatment. Only the bacterial community exhibited signs of regrowth, with a fold change of 9.2 bacterial cell density from day 1 to day 2. Recovery consisted of succession by Planctomycetota (47%) and Gammaproteobacteria (17%), which were likely resilient due to passive cell component compartmentalization and rapid upregulation of dnaK and groEL oxidative stress genes, respectively. The altered microbiome retained beneficial functionality of microcystin degradation through a currently recognized but unidentified pathway in Gammaproteobacteria, resulting in a 70% reduction coinciding with bacterial regrowth. There was also an 81% reduction of both total nitrogen and phosphorus, as compared to 91 and 93% in the control, respectively, due to high expressions of genes related to nitrogen (argH, carB, glts, glnA) and phosphorus (pntAB, phoB, pstSCB) cycling. Overall, we found a portion of the bacterial community was resilient to the high-concentration hydrogen peroxide treatment, resulting in Planctomycetota and Gammaproteobacteria dominance. This high-concentration treatment may be suitable to rapidly end cHABs which have already negatively impacted the aquatic environment rather than allow them to persist.

Existing Filtration Treatment on Drinking Water Process and Concerns Issues

Water is one of the main sources of life's survival. It is mandatory to have good-quality water, especially for drinking. Many types of available filtration treatment can produce high-quality drinking water. As a result, it is intriguing to determine which treatment is the best. This paper provides a review of available filtration technology specifically for drinking water treatment, including both conventional and advanced treatments, while focusing on membrane filtration treatment. This review covers the concerns that usually exist in membrane filtration treatment, namely membrane fouling. Here, the parameters that influence fouling are identified. This paper also discusses the different ways to handle fouling, either based on prevention, prediction, or control automation. According to the findings, the most common treatment for fouling was prevention. However, this treatment required the use of chemical agents, which will eventually affect human health. The prediction process was usually used to circumvent the process of fouling development. Based on our reviews up to now, there are a limited number of researchers who study membrane fouling control based on automation. Frequently, the treatment method and control strategy are determined individually.

Detection of morphological changes caused by chemical stress in the cyanobacterium Planktothrix agardhii using convolutional neural networks

The presence of harmful algal bloom in many reservoirs around the world, alongside the lack of sanitation law/ordinance regarding cyanotoxin monitoring (particularly in developing countries), create a scenario in which the local population could potentially chronically consume cyanotoxin-contaminated waters. Therefore, it is crucial to develop low cost tools to detect possible systems failures and consequent toxin release inferred by morphological changes of cyanobacteria in the raw water. This paper aimed to look for the best combination of convolutional neural network (CNN), optimizer and image segmentation technique to differentiate P. agardhii trichomes before and after chemical stress caused by the addition of hydrogen peroxide. This method takes a step towards accurate monitoring of cyanobacteria in the field without the need for a mobile lab. After testing three different network architectures (AlexNet, 3ConvLayer and 2ConvLayer), four different optimizers (Adam, Adagrad, RMSProp and SDG) and five different image segmentations methods (Canny Edge Detection, Morphological Filter, HP filter, GrabCut and Watershed), the combination 2ConvLayer with Adam optimizer and GrabCut segmentation, provided the highest median accuracy (93.33%) for identifying H₂O₂-induced morphological changes in P. agardhii. Our results emphasize the fact that the trichome classification problem can be adequately tackled with a limited number of learned features due to the lack of complexity in micrographs from before and after chemical stress. To the authors' knowledge, this is the first time that CNNs were applied to detect morphological changes in cyanobacteria caused by chemical stress. Thus, it is a significant step forward in developing low cost tools based on image recognition, to shield water consumers, especially in the poorest regions, against cyanotoxin-contaminated water.

Effects of microbial inactivation approaches on quantity and properties of extracellular polymeric substances in the process of wastewater treatment and reclamation: A review

Microbial extracellular polymeric substances (EPS) have a profound role in various wastewater treatment and reclamation processes, in which a variety of technologies are used for disinfection and microbial growth inhibition. These treatment processes can induce significant changes in the quantity and properties of EPS, and altered EPS could further adversely affect the wastewater treatment and reclamation system, including membrane filtration, disinfection, and water distribution. To clarify the effects of microbial inactivation approaches on EPS, these effects were classified into four categories: (1) chemical reactions, (2) cell lysis, (3) changing EPS-producing metabolic processes, and (4) altering microbial community. Across these different effects, treatments with free chlorine, methylisothiazolone, TiO₂, and UV irradiation typically enhance EPS production. Among the residual microorganisms in EPS matrices after various microbial inactivation treatments, one of the most prominent is Mycobacterium. With respect to EPS properties, proteins and humic acids in EPS are usually more susceptible to treatment processes than polysaccharides. The affected EPS properties include changes in molecular weight, hydrophobicity, and adhesion ability. All of these changes can undermine wastewater treatment and reclamation processes. Therefore, effects on EPS quantity and properties should be considered during the application of microbial inactivation and growth inhibition techniques.

Ultrafiltration of up-flow biological activated carbon effluent: Extracellular polymer biofouling mechanism and mitigation using pre-ozonation with H2O2 backwashing

Biofouling is a key problem in membrane filtration, and extracellular polymer substances (EPS) play a key role in biofouling. Biofouling contributes to membrane fouling during ultrafiltration of up-flow biological activated carbon filter (UBACF) effluent. EPS are released when pollutants get attached with membrane surface and when pollutants are in solution phase from cell lysis and by cell secretions. In our study of EPS + humic acid (HA) prepared as the effluent pollutants for ultrafiltration, we found that EPS increased the interfacial forces between the pollutants and the membrane, resulting in membrane fouling. In the early stages of filtration, the main contribution of EPS to membrane fouling was to bond with organic colloids, which led to an increase in the pollutant particle size and zeta potential. This increased the short-range Lewis acid-base (AB) forces from -4.89 nN to -12.59 nN and accelerated the formation of a cake layer. In the late stage of filtration, the EPS increased both the AB and London-van der Waals (LW) forces, thus accelerating membrane fouling. In order to mitigate biofouling, we developed a method of pretreating the effluent with 0.4 mg/L ozone prior to ultrafiltration and backwashing with 8 mg/L H₂O₂ to sterilize bacteria attached to the membrane surface. This method not only changed the characteristics of the EPS, but also inactivated bacteria by disinfection with H₂O₂, thereby reducing the amount of EPS. The proposed method provided a long-term stable operation guarantee for ultrafiltration of UBACF effluent.

Untouchability of natural spa waters: Perspectives for treatments within a personalized water safety plan

Natural SPA waters and their environments were known since ancient times and used for health or recreational purposes in different societies, worldwide. The composition and uses of these spring waters may not allow standard disinfection in pools, representing a challenge for hygiene management. Several safety and quality procedures were proposed, but a systematic approach is still needed. Here, we focus on alternative strategies to provide hints for developing a sustainable Water Safety Plan, based on intrinsic water properties and photocatalytic materials. The antimicrobial activity of four different SPA waters with high mineral content and one drinkable spring water with a low mineral content, was assessed and then tested for the additional bactericidal activity of Titanium Dioxide (TiO₂) nanomaterials and/or light exposure at different wavelengths (200-635 nm). A native antibacterial activity was observed in all high mineral content waters, with a CFU reduction of 75-80%. The bactericidal action of TiO₂ showed an additional incremental effect, with a reduction of over 99% within 2-5 h. Interestingly, the antibacterial photocatalytic effect was detected also in the visible light range, with a possible pick around 450-455 nm, blue-light. Based on observed results, we propose a model for developing a water safety plan, considering water properties and bather exposure. This candidate approach is personalized on water composition and pool use, trying to avoid chemical disinfectants. Photocatalytic nanotechnologies represent one of the promising alternative treatments and can provide novel perspectives for a sustainable managing of natural SPA water hygiene.

Effect of pre-oxidation on low pressure membrane (LPM) for water and wastewater treatment: A review

Low pressure membrane (LPM) filtration is a promising technology for drinking water production, wastewater reclamation as well as pretreatment for seawater desalination. However, wider implementation of LPM is restricted by their inherent drawbacks, i.e., membrane fouling and insufficient rejection for dissolved contaminants. Pretreatment of feed water is a major method to improve the performance of LPM, and pre-oxidation has gained extensive attention because it can significantly alter compositions and properties of feed water through chemical reactions. This paper attempts to systematically review efficiency and mechanisms of pre-oxidation in membrane fouling control and permeate water quality improvement. On the basis of briefly discussing major foulants and fouling mechanisms of LPM, advantages and disadvantages of pre-oxidation in mitigating organic fouling, inorganic fouling and biofouling are discussed in detail. Impacts of pre-oxidation on removal of micropollutants, bulk organic matter and inorganic pollutants are summarized, and potential by-products of different oxidants are presented. As a prerequisite for the integration of chemical oxidation with LPM filtration, compatibility of membrane with oxidants at low concentration and long exposure time are highlighted. Finally, the existing challenges and future research needs in practical application of chemical oxidation to improve performance of LPM are also discussed.

Recreational Use of Spa Thermal Waters: Criticisms and Perspectives for Innovative Treatments

Natural spa springs are diffused all over the world and their use in pools is known since ancient times. This review underlines the cultural and social spa context focusing on hygiene issues, public health guidelines and emerging concerns regarding water management in wellness or recreational settings. The question of the "untouchability" of therapeutic natural waters and their incompatibility with traditional disinfection processes is addressed considering the demand for effective treatments that would respect the natural properties. Available strategies and innovative treatments are reviewed, highlighting potentials and limits for a sustainable management. Alternative approaches comprise nanotechnologies, photocatalysis systems, advanced filtration. State of the art and promising perspectives are reported considering the chemical-physical component and the biological natural complexity of the spa water microbiota.