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.

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.

Laundry greywater is considered as an alternative source of non-potable water, as it is discharged in approximately 70% of homes. Because this water contains compounds such as biodegradable and recalcitrant organic matter, surfactants, and microbiological compounds, it must be treated prior to reuse. Therefore, the objective of this study was to assess the behavior of organic matter and antibiotic-resistant bacteria (ARB) in greywater treated by a constructed wetland (CW). The results show that the organic matter removal efficiencies were 67.19%, 50.15%, and 63.57% for biological oxygen demand (BOD₅), chemical oxygen demand (COD) and total organic carbon (TOC), respectively; these efficiencies were not significant (p > 0.05). In addition, the CW allows the distribution of TOC and ionic compounds in the fractions below 1000 Da to increase by 5.03% and 13.05%, respectively. Meanwhile, the treatment of microbiological compounds generated non-significant removals (p > 0.05), along with increases in bacteria resistant to the antibiotics ciprofloxacin (CIP) and ceftriaxone (CTX) of 36.34%, and 40.79%, respectively. In addition, a strong association between ARB to CIP, CTX, cationic and non-ionic surfactants was determined, indicating the role of surfactants in ARB selection. It is suggested that disinfection systems should be employed prior to the reuse of the treated water.

The kraft pulp process generates liquors with different physicochemical characteristics at each treatment stage. These liquors can accidentally spill into the biological treatment, hindering it and harming ecosystems where the effluents are discharged. Due to the lack of studies on the effects these liquors can have on the aerobic biomass of activated sludges and ecosystems, this investigation aims to assess the toxicity of each liquor spill to the aerobic biomass of an activated sludge, using Selenastrum capricornutum as a bioindicator of water quality. This evaluation used a laboratory-scale activated sludge, which was fed with an effluent with pH 6.62–6.67 and chemical organic demand (COD) of 611–638.5 mg/L. The liquors used had the following parameters: pH = 13 and COD = 1911 mg/L (white); pH = 13 and COD = 141,350 mg/L (black); pH = 13 and 2755 mg/L (green); and pH = 7.5 and COD = 358 mg/L (condensate). White liquor produced the greatest toxicity (EC₂₀ of 17.8 mgCOD/L) and lowest oxygen uptake rate (8.42 mgO₂/L·h with 287.7 mgCOD/L) in the aerobic biomass compared to the other liquors. White liquor presented the greatest inhibition of Selenastrum capricornutum, with 81.7% (48 h) and 98.0% (96 h). Meanwhile, black liquor presented an inhibition of 94.7% (48 h), but a 13% increase in microalga growth at 96 h of culture. The information from this study makes it possible to calculate how much liquor can be fed to an activated sludge system, keeping it optimized to eliminate liquor discharges generated within the kraft mill’s processing units.

Acid mine drainage (AMD) is one of the main environmental problems in mining operations. The objective of this study was to assess AMD obtained from a copper mine via toxicity identification evaluation (TIE) using Daphnia magna and Chlorella vulgaris as indicator organisms. AMD was fractionated via filtration and aeration at pH 3 and 11, activated carbon, cation resin, anion resin, and ethylenediaminetetraacetic acid (EDTA). The results showed that unfractionated AMD has a low organic matter content (total chemical organic demand, COD_T-183.05 mg/L), low pH (3.9), and high sulfates concentrations (2900 mg/L) and metal ions in solution (0.2–418.9 mg/L), producing high toxicity to Daphnia magna (0.00016% v/v) and no observable acute toxicity to Chlorella vulgaris (72 h-RFU 64.9%). For Daphnia magna, TIE fractionations with the greatest reduction in acute toxicity (LC₅₀) were filtration/pH11 (non-toxic) and anion resin (LC₅₀ = 0.43% v/v), with toxicity reduction percentages of 100% and 99%, respectively. Because of this, Cu was determined to be the main cause of acute toxicity to Daphnia magna. For Chlorella vulgaris, the activated carbon fraction stands out, increasing the % relative fluorescence units by 4% from 48 h to 72 h, demonstrating tolerance to AMD. The TIE technique is presented as an effective strategy to identify toxic compounds in complex samples and evaluate their effect on environmentally relevant organisms. Therefore, this study allows the analysis of the ecological risk in aquatic environments affected by mining activities, which supports environmental decision-making and the design of efficient treatment strategies.