UV disinfection is cost-effective and easy to maintain for decentralized areas. However, to ensure its effectiveness, some parameters need to be considered. In this study, a general search of Web of Science articles was performed to determine the possible influence of these parameters on the reactivation of microorganisms in UV systems; in addition, different search strings were used focusing exclusively on wastewater treatment, UV systems and Advanced Oxidation Processes (AOPs). It was found that in order to maintain low transmittance, it is essential to remove suspended solids and reduce water hardness. It is recommended to control the zeta potential in the range of 0–5 mV to avoid the aggregation of particles and bacteria. Determining the appropriate UV dose is essential to mitigate the reactivation of microorganisms. A minimum dose of 40 mJ/cm² can contribute to effective disinfection and reduce the likelihood of reactivation. In addition, maintaining a residual chlorine level of at least 0.5 mg/L provides an additional barrier to reactivation. It is also important to optimize the design flow rate of the UV system as recommended for each individual unit. These measures, together with the combination of UV disinfection and chemical or AOP_S, can effectively reduce the reactivation.

The main objective of this review is to evaluate the performance of constructed wetlands (CWs) used to reduce antibiotic-resistant genes (ARGs) during sewage treatment. To accomplish this objective, statistical and correlation analyses were performed using published data to determine the influence of operational and design parameters on ARG reduction in CWs. The effects of design and operational parameters, such as different CW configurations, seasonality, monoculture and polyculture, support medium, and hydraulic retention time (HRT), on ARG removals, were analyzed. A comparison of ARG reduction under different CW configurations showed that the hybrid configuration of surface flow (SF)–vertical subsurface flow (VSSF) achieved the highest reductions, with values of 1.55 ulog. In this case, aeration is considered an important factor to reduce ARGs in CWs, and it should be considered in future studies. However, statistical analyses showed that the ARG reductions under different CW configurations were not significant (p > 0.05). The same behavior was observed when the effects of operational factors on ARG reductions were analyzed (p > 0.05). The results of this study show that CWs are not optimal technologies to reduce ARGs in sewage. The combination of CWs with advanced wastewater technologies can be a solution for enhancing ARG reduction and reducing the spread of antibiotic resistance.

Kraft mill effluents are characterized by their content of suspended solids, organic matter and color due to the presence of lignin, lignin derivatives and tannins. Additionally, Kraft mill effluents contain adsorbable organic halogens and wood extractive compounds (resin acids, fatty acids, phytosterol) and show high conductivity due to the chemical compounds used in the digestion process of pulp. Currently, Kraft mills are operating under the concept of a linear economy and, therefore, their effluents are generating serious toxicity effects, detected in daphnia, fish and biosensors. These effluents are treated by activated sludge and moving bed biofilm systems that are unable to remove recalcitrant organic matter, color and biological activity (toxicity) from effluents. Moreover, under climate change, these environmental effects are being exacerbated and some mills have had to stop their operation when the flows of aquatic ecosystems are lower. The aim of this review is to discuss the treatment of Kraft pulp mill effluents and their impact regarding the current practices and future perspectives towards sustainability under climate change. Kraft pulp mill sustainability involves the closure of water circuits in order to recirculate water and reduce the environmental impact, as well as the implementation of advanced technology for these purposes.

The vermifilter (VF) is regarded as a sustainable solution for treating rural sewage. However, few studies have investigated the performance of a full-scale vermifilter. The objective of this study is to evaluate the performance of a full-scale vermifilter in reducing organic matter, nutrients, and antibiotic-resistant bacteria contained in sewage. Influent and effluents were obtained from a rural sewage treatment plant using a VF and UV disinfection system. The results show a significant removal (p < 0.05) of chemical organic demand (COD) (77%), biochemical oxygen demand (BOD₅) (84%), total nitrogen (TN) (53%), and total phosphorus (36%). Seasonality is an influential variable for COD, BOD₅, and TN removal. In addition, the molecular weight distribution shows that the VF does not generate a considerable change in the distribution of organic matter (COD and total organic carbon (TOC)) and NH₄⁺-N. The UV disinfection system eliminated 99% of coliform bacteria; however, they are not eliminated to safe concentrations. Therefore, it is possible to detect bacteria resistant to the antibiotics ciprofloxacin, amoxicillin, and ceftriaxone at 63.5%, 87.3%, and 63.5%, respectively, which were detected in the effluents. This study shows the potential of a system for the removal of pollution and the need to optimize the VF to be a safe treatment.

The main objective of this study is to evaluate the water quality of different rainwater harvesting (RWH) systems and the social acceptance of their reuse in young users as an exploratory approach. Three RWH systems were implemented, and the quality of harvested rainwater was evaluated focusing on physicochemical and in situ parameters. Social acceptance was studied in one of the RWH systems using an adapted technology acceptance model. An informative talk about the operation of RWH was given to the users, who were students from a rural primary school. Surveys were conducted before and after the talk to evaluate the impact of providing information to users. The social acceptance was studied in one of the RWH systems. The results indicated that the harvested rainwater from RWH systems was suitable for reuse in agriculture despite the increase in turbidity and chloride concentrations in the outlet tap. The concentration of turbidity, phosphate as phosphorus, chloride and nitrate ranged between 0.8 and 1.9 NTU, 0.01–0.2 mg/L, 2.8–5.0 mg/L and 0.3–0.9 mg/L, respectively. In the acceptance study, the survey results and correlation analyses showed that providing information to users is crucial for increasing the acceptance of RWH systems. Moreover, this study demonstrated that RWH systems are a viable alternative technology for reusing and supplying water in arid and semiarid areas.

The objective of this study is to evaluate the stability of activated sludge (AS) in the treatment of kraft pulp mill effluent exposed to black liquor shock, as well as the effect of its exposure on the morphology of Daphnia magna and DNA damage through mutagenicity and genotoxicity response in Salmonella typhimurium. To this end, we applied doses of 2-, 4-, 10-, and 30-mL black liquor/L influent—shock 1 (S1), shock 2 (S2), shock 3 (S3), and shock 4 (S4), respectively—to kraft pulp mill effluent. The system stability was checked by analyzing heterotrophic biomass activity and discharge quality, evaluated using Ames test and Daphnia magna. The results show that the chemical oxygen demand (COD) removal efficiency for normal conditions was 64.84%, falling to 61.68%, and 61.31% for S1 and S2, respectively, and values of 52.11% for S3 and 20.34% for S4. The biomass activity decreased after each shock was applied, but then recovered. There was no evidence of lethal toxicity (LC₅₀) to Daphnia magna at any of the concentrations. Therefore, it is feasible to apply doses S1 and S2 to an AS system that treats kraft pulp mill effluent.