Mixed Industrial Wastewater Research Articles

Assessment of the impact of irrigating with treated wastewater on soil and crop trace metal accumulation

ABSTRACT Water scarcity is growing quickly, especially in the arid and semi-arid regions along with the growing population. So, using treated wastewater in agricultural irrigation presents a sustainable approach, enhancing soil quality, increasing organic carbon levels, and improving crop productivity are achieved through this approach, concurrently reducing the need for chemical fertilizers. Yet, escalating industrial effluent discharge raises concerns regarding trace metals in wastewater and associated health risks. Our study in the Tenth of Ramadan City focused on employing secondary treated mixed industrial and municipal wastewater for olives, mandarins, and guavas. Sampling wastewater, soil, and plant parts, we analyzed their properties and trace element concentrations, employing Visual MINTEQ for geochemical speciation. Adhering to the international guidelines, the wastewater exhibited acceptable pH and alkalinity but showed concerning trace element levels for irrigation. Differences in soil composition and trace element concentrations suggest potential contamination in soils irrigated with wastewater, raising concerns about health risks associated with elevated metal levels in plants. Variations in trace element concentrations in guavas, olives, and mandarins’ leaves and fruits were observed, with efficient translocation in olives, while mandarin and guava displayed reduced efficiency. Bioaccumulation Factor trends indicated species-specific metal uptake differences. Waste “Minimization Prioritization Tool categorized” trace element levels as of low concern. Daily Intake of Trace Metals and Health Risk Index highlighted the need for health risk assessment, especially for elevated Ni in mandarins and guavas. Regression findings emphasized soil factors influencing metal uptake in plants, highlighting the need for vigilant soil management to curb trace element contamination in agriculture, ensuring both food safety and environmental health. Therefore, water reuse adds contributes to sustainable development, which is three dimensions; Economic, Social and Environmental. It improves economics to utilize water that would be otherwise wasted, and by making water more productive. It improves the social dimension by addressing water scarcity and satisfying the increasing water demand for sustainable livelihoods. It also improves the environment by increasing wastewater treatment levels and reducing pollution.

BIOPROSES PENGURAIAN LIMBAH CAIR BUANGAN INDUSTRI PANGAN DAN NON-PANGAN BERBASIS BIOSURFAKTAN

Biosurfactants are microbial metabolites that may be utilized to replace synthetic chemical surfactant in overcoming the problem of industrial wastewater pollution. Indications of the presence of biosurfactant activity may be determined through measurement of emulsification and enzymatic activity of the tested microorganisms on their growth media, which is indicated by decreasing the BOD and COD of the tested growth media containing wastewater material as an inducer added to the microbial growth medium. This research was conducted to examine several potential microbial isolates that produce biosurfactants on growth media containing mixed waste water. The results showed that some of the microbial cultures tested showed the potential to produce biosurfactants as indicated by the emulsification and enzymatic activity of the tested microbial culture. Trial on mixed industrial wastewater showed that the tested biosurfactants were able to reduce the levels of BOD (440-1300 mg/l) and COD (1240-1760 mg/l) of the wastewater samples up to low BOD levels (82 mg/l) and COD (116 mg/l), respectively, thus that it meets the requirements of the established wastewater quality standards according to the Indonesian Standard regarding with the respective BOD (50-100 mg/l, 06-6989.9-2004 SNI) and COD (100-250 mg /l, 06-6989.2-2004 SNI).Key words : biosurfactant, emulsification, microbial enzyme, wastewater, BOD, COD.

A COMPARATIVE STUDY ON TREATMENT OF CETP WASTEWATER USING SBR AND SBR-IFAS PROCESS

The wastewater generated from industries needs to be treated before discharge but ETPs are not affordable and hence the common effluent treatment plant was provided for collectively treating wastewater from various industries. The existing treatment methods used for such wastewater are costly and hence the present study focusses on using biological method for treating pre-treated mixed industrial wastewater from CETP using a sequencing batch reactor (SBR) with suspended biomass and an SBR-IFAS, a combined suspended and attached growth process at an HRT of 10 hours. After treatment with SBR technology, the maximum COD removal efficiency obtained was 68.69% at an MLSS concentration of 2756 mg/L. Similarly, for the SBR-IFAS reactor, the COD removal efficiency reached 75.51% at an MLSS concentration of 2846 mg/L. MLVSS obtained was 1395.00 mg/L in SBR and 1433.00 mg/L in SBR-IFAS. Chromium removal reached 62.85% and 66.67% in SBR and SBR-IFAS reactors, respectively. The study revealed that the attached growth media and suspended growth media combinedly resulted in a higher reduction in industrial wastewater treatment and can ultimately help reduce the volume of the secondary treatment at CETP by increasing the footprint of the treatment plant.

Germination and growth of horticultural crops irrigated with reclaimed water after biological treatment and ozonation

Integration of high water-volume and nutrient-rich industrial wastewater into the existing water management plan for agriculture could be a viable option to protect freshwater resources, mitigate water scarcity problems and support the agriculture sector. Hydroponics were set-up to study the effects of treated mixed industrial and domestic wastewater on physiological traits of lettuce and silverbeet. A sustainable hybrid biological-ozonation process was employed for the wastewater treatment. The studied process showed high treatment capacity by removing 96% COD, 92% diesel and 97% methylene blue compounds. Reclaimed streams were analysed for metals using ICP-MS instrument and the concentrations of all elements tested, exception of Cu, Mn, and Mo, fall within the permissible range for crop irrigation. The crops were grown using the effluents (with/without external nutrient) and compared to a recommended nutrient culture and tap water controls. Compared to the control, plants that received external nutrient had a comparable aerial biomass and vegetative growth, higher photosynthetic pigments but exhibited some root development impairments, probably due to high activity of H+, which promoted metal toxicities on plant roots. Under pH-controlled irrigation, an improvement in root growth was observed. The biomass of plants watered with only the treated wastewater were more than 50% higher than the yield in tap water control and plants exhibited high degree of root foraging. The root concentrations of the studied metals, particularly Al, Mn, Cu and Zn were higher than the corresponding shoot concentrations. Pearson correlation analysis showed a significant positive interaction (p<0.01) between K and other elements (Mg, Ca, Cu, Mn, Zn, Fe) in plant tissues, thus indicating its role in facilitating transportation of nutrients and photo-assimilates in plant. The results suggest a high suitability of the treated wastewater for growth of crops. Thus, the reuse of treated mixed industrial and domestic wastewater for irrigation can be considered a sustainable way to cope with the growing water stress across the globe and the water shortage in agriculture. The reuse potential for irrigation of crops depends on the quality of the reclaimed water and the treatment technologies used. With the limited research data available, further studies to elucidate the long-term implications of the irrigation is highly recommended.

Mixed industrial wastewater treatment by the combination of heterogeneous electro-Fenton and electrocoagulation processes

Mixed industrial wastewater treatment efficiency of combined electro-Fenton (EF) and electrocoagulation (EC) processes was investigated in the present study. Alkali modified laterite soil was used as a heterogeneous EF catalyst and found superior performance than the raw laterite soil. Initially, the effect of catalyst dosage, initial pH, and applied voltage on the performance of EF process was carried out. A total of 54.57% COD removal was observed after 60 min of the EF treatment. Further treatment was carried out with EC process at different voltages. A total of 85.27% COD removal after 2 h treatment was observed by combining two electrochemical processes. Performance of EF followed by EC (EF + EC) process was compared with EC followed by EF (EC + EF) process. Even though efficiency is the same, EF + EC is a better strategy than EC + EF as it nullifies the neutralization requirement after EF process in addition to high mineralization efficiency, enhanced biodegradability, and lesser sludge generation.

Mixed metal oxide anodes used for the electrochemical degradation of a real mixed industrial wastewater

Mixed industrial wastewaters are often highly contaminated with heavy metals and organic pollutants. Treating these mixed wastewaters requires many stagewise unit operations. Our work investigates using an electrochemical oxidation-in-situ coagulation (ECO-IC) process as a pre-treatment step toward the efficient treatment of real mixed industrial wastewater rich with heavy metals and organic contaminants. The process degraded organic contaminants in the wastewater via anodic electrochemical oxidation. Simultaneously, heavy metals were precipitated in the solution by coagulants (iron hydroxides) formed in-situ by cathode-generated hydroxyl ions reacting with the significant amounts of dissolved iron in the wastewater. IrO2–RuO2 mixed metal oxide anodes were identified as the best electrodes for organic compound degradation demonstrating 97% degradation of methyl orange (MO) as a model compound within 15 min. These anodes were used to treat real industrial wastewater produced from the industrial cleaning of train tanker cars transporting industrial solvents. The electrochemical treatment experiments resulted in a treated solution with a lower heavy metal content, achieving 96% reduction in Fe and 30% reduction in As content. Only moderate decreases in organic content were observed up to a maximum of 13% reduction in total organic carbon after 1 h of treatment. Electrochemical treatment of the mixed industrial wastewater produced greater effective diameter of the suspended particles and distinct sediment, liquid, and suspended foam phases that could be easily separated for further treatment. ECO-IC shows promise as an efficient and chemical-free method to coagulate heavy metals in real industrial wastewaters and could be an effective pre-treatment in their separation.

Emerging technologies for mixed industrial wastewater treatment in developing countries: An overview

AbstractTreatment of mixed industrial wastewater is a great challenge in common effluent treatment plants due to the complex nature of wastewater from different industries. This review outlines the emerging technologies adopted for mixed industrial wastewater treatment in developing nations. The potential for integrating two or more technologies to enhance treatment efficiency is also addressed. Major issues associated with mixed industrial wastewater treatment were found to be low biodegradable nature and presence of toxic compounds in wastewater. Moreover, the composition of wastewater fluctuates and differs significantly from the composition considered during the design of common effluent treatment plants. Biological methods, constructed wetlands, membrane separation methods, electrochemical methods, and advanced oxidation processes are some of the techniques that have been applied for the treatment of mixed industrial wastewater. Advanced oxidation process–based treatment methods were found to be very efficient as the process was able to improve biodegradability and reduce toxicity levels of wastewater along with a significant reduction in organic carbon. Among the biological methods and constructed wetlands, hybrid or integrated technologies were found effective to reduce the contamination level of wastewater. Implementation, operation, and maintenance of technologies mentioned above in a real field would be the thrust areas for future research.

Chelate-modified Electro-Fenton process for mixed industrial wastewater treatment

ABSTRACT Mixed industrial wastewater (combined wastewater from small-scale industries) treatment is challenging due to the change in characteristics of the wastewater ( time and quantity). The Electro-Fenton (EF) process is one of the effective techniques for the degradation of organic pollutants from the wastewater, but it works under low pH condition, which is one of the major disadvantages of the EF process. To overcome this disadvantage, the chelate-modified EF process was used in this study. In the chelate-modified EF process, EDTA was used as the chelating agent to form complex with Fe ions and to enhance Fenton reaction at near neutral pH. Ti electrode coated with RuO2 was used as anode and graphite as cathode. The batch reactor was operated by varying initial pH, Fenton reagent dosage and chelating agent dosage. The results demonstrate that the chelate-modified EF process gives effective COD removal (67%) at near neutral pH, as comparable to that of the EF process (66%) at acidic pH. Highlights The Chelate-modified EF process for the removal of COD at near neutral pH Treatment of the mixed industrial wastewater with very low BOD/COD ratio Influence of Fenton catalyst and chelating agent dosage on COD removal. Comparable COD removal of 67% with Chelate-modified EF at near neutral pH and 66% with EF at acidic pH. Mineralization current efficiency and instantaneous current efficiency for COD removal.

Evaluation of aerobic biological process with post-ozonation for treatment of mixed industrial and domestic wastewater for potential reuse in agriculture

Suspended growth biological process (SGBP) with post-ozonation (O3) was investigated for treatment of simulated complex mixed industrial and domestic wastewater at specific conditions. The SGBP was operated under complete aeration, 30/30-min and 60/30-min on/off aeration cycles and effluent was exposed to ozone at 250 mgO3/h fixed dose and contact time 1 to 60-min. The SGBP performance was maximum under 60/30-min aeration conditions achieving 92.1, 90.6, 83.3 and 83.8% reduction in COD, BOD5, TN and PO4-P respectively. Nitrification (64.1%) was uninhibited even on transition to pulse aeration cycles. The concentrations of diesel oil and methylene blue dye were reduced by 83.6 and 93.5% respectively. Post-ozonation oxidized residual organics up to 19.9%, based on COD measurement, and increased effluent BOD5 up to 49.5%. The results including the crop growth outcomes indicate that SGBP-O3 process has great potential to improve the quality of mixed industrial and domestic wastewater considerably for various water reuse applications.

Treatment of mixed industrial wastewater by electrocoagulation and indirect electrochemical oxidation

Treatment of mixed industrial wastewater is a challenging task due to its high complexity. This work scrutinizes the electrochemical treatment of mixed industrial wastewater, specifically electrocoagulation and indirect electrochemical oxidation processes through COD and color removal studies. Both processes are found to be more efficient at the wastewater pH. Monopolar connection was found more effective than bipolar connection for the removal of COD and color from wastewater. The monopolar connection removed COD up to 55% and color 56% whereas bipolar connection leads to the removal of 43% and 48% respectively at wastewater pH with an applied voltage 1.5 V in the course of 1 h of electrolysis.In the case of indirect electrochemical oxidation process using graphite electrodes, the COD and color abatement efficiencies of the indirect electrochemical oxidation process were found as 55% and 99.8%, respectively within 1 h of electrolysis conducted at pH 7.7, applied voltage 4 V, and NaCl concentration 1 g L−1. This work also highlights the importance of the presence of electrolytes in the indirect electrochemical oxidation process as the external addition of sodium chloride significantly enhanced both COD and color elimination efficiency.

Removal of heavy metals from mixed domestic and industrial wastewater by activated sludge process using MWCNT

In this study, the effect of multi-walled carbon nanotube (MWCNT) on heavy metal and chemical oxygen demand (COD) removal in the continuous flow activated sludge process was investigated. In order to treat domestic and industrial wastewater together in the biological treatment unit, 50 and 100 mg.L−1 MWCNT were added to laboratory scale reactors, one of which was a control reactor (CR). It was determined that the increase of the MWCNT concentration leads to increase in the rate of removal of COD. COD removal for CR, 50 and 100 mg.L−1 MWCNT was 49.24, 64.95 and 76.46%, respectively. In the first hour Ni (II) removal was achieved in the control reactor (CR) at 65.33%. When 50 and 100 mg.L−1 MWCNT was added to reactors, Ni (II) removal was 71.14% and 79.99%, respectively. Cu (II) and Cr (VI) removal efficiencies were achieved about 99%, during the treatment. It was determined that MWCNT has a positive effect on activated sludge treatment efficiency. As a result, biokinetic coefficients show that reactor volume the size will be smaller and size of sludge handling facility will be the greater with increases in the amount of MWCNT.

Removal of heavy metals from mixed domestic and industrial wastewater by activated sludge process using MWCNT

Removal of heavy metals from mixed domestic and industrial wastewater by activated sludge process using MWCNT

Mixed industrial wastewater treatment by combined electrochemical advanced oxidation and biological processes

Nowadays, because the quality and quantity of mixed industrial wastewater keep fluctuating in recent times, the treatment of mixed industrial wastewater has gained more attention. The main target of this study is to degrade the wastewater through a combination of electrochemical advanced oxidation processes (EAOPs) and biological treatment. To enhance the biodegradability of the wastewater, Electro-Fenton process, along with external persulphate addition, was applied before the biological treatment. The effect of voltage, catalyst concentration and persulphate dosage was studied. The optimized conditions selected for the experiments were pH-3, effective area-25 cm2, electrode spacing-1 cm while voltage-10 V, persulphate dosage-200 mg L−1, and catalyst dosage-10 mg L−1 were optimized during the experiments leading towards 60% of COD removal efficiency in course of 1 h of electrolysis. Addition of tert-butyl alcohol and ethanol revealed the existence of sulphate and hydroxyl radicals as the major oxidants that help in pollutant degradation by combining EAOPs and biological treatment. Overall 94% COD removal efficiency was achieved. Therefore, for the organic pollutant degradation, combined process serves to be an efficient and effective treatment option.

Constructed wetlands for industrial wastewater treatment: Alternative media, input biodegradation ratio and unstable loading

This paper reports comparative pollutant removal performances across two parallel hybrid wetland trains, that were dosed with mixed industrial wastewater (with poor biodegradability); each train included two vertical flow (VF) wetlands arranged in series, followed by a surface flow (SF) wetland as the final treatment stage. VF wetlands of system 1 and 2 were packed with biological and construction materials, respectively. Input hydraulic load (HL) was fluctuated between 113.0–226.0 mm/d across first stage wetland units of both systems. Performance analyses indicated higher organics and nitrogen removal percentages in first stage VF wetland of system 1, due to carbon leaching from the employed organic bagasse and biochar media. On the other hand, lack of carbon supply from inorganic construction materials hindered such removals in first stage VF wetland of system 2, which was counter-balanced as the wastewater passed through second stage VF unit. Enhanced P removals were quantified in VF wetlands of system 2, which could be linked to P adsorption properties of the employed construction materials. VF wetlands of both systems were inefficient in terms of color compounds removal. Physico-chemical and microbial pathways enhanced removal in the last stage SF wetlands of both systems and improved overall removal. Organics and nitrogen removal rates (g/m2 d) in experimental wetlands were high at upper input loadings; however, load based (g/m2 d) removal percentages were high in first and third stage wetlands (of both systems) during lower loading ranges. Concentration based mean overall NH4-N, TN, P, BOD, COD and color removal percentages across both systems were: ≥ 90.0, ≥ 86.0, ≥ 91.0, ≥ 92.0, ≥ 85.0 and ≥ 87.0%, respectively. Such performances signify potential combination of VF (packed with biological and construction materials) and SF wetlands, for the treatment of hardly degradable industrial wastewater.

Efficient removal of Hg2+, Cd2+ and Pb2+ from aqueous solution and mixed industrial wastewater using a designed chelating ligand, 2-pyridyl-N-(2'-methylthiophenyl) methyleneimine (PMTPM).

The present study is focused on the removal of Hg2+, Cd2+ and Pb2+ ions from aqueous solution using a tridentate chelating agent, 2-pyridyl-N-(2'-methylthiophenyl) methyleneimine (PMTPM); and applicability of such removal from industrial wastewater using PMTPM is also investigated. The results showed that the metal ions removal efficiency using PMTPM was in the order of Hg2+(99.46%) > Cd2+(95.42%) > Pb2+(94.54%) under optimum reaction conditions (L:M2+ = 3:1, pH = 9, time = 24 h, temp. = 30 °C). Formed chelated complexes such as [Hg(PMTPM)Cl2] (1), [Cd(PMTPM)Cl2] (2) and [Pb(PMTPM)Cl2] (3) were characterized by numerous spectroscopic tools and X-ray structure determination of a representative complex of Hg2+. In the X-ray structure of [Hg(PMTPM)Cl2], 1, the Hg2+ adopted a distorted tetrahedral coordination geometry surrounding two N donors of PMTPM and two chloride ions. A similar coordination geometry surrounding the respective metal centres in 2 and 3 was established. The thermogravimetric analysis (TGA) revealed a stability order of [Cd(PMTPM)Cl2] > [Hg(PMTPM)Cl2] > [Pb(PMTPM)Cl2]. Further the comparative metal leaching behaviour of these chelate complexes exhibited higher stability in alkaline solution than in acidic. Moreover, PMTPM was applied in real mixed industrial wastewater with alkaline pH, and adequate removals of toxic metals were achieved.

Investigating metal removal potential of aquatic macrophytes at different harvest regimes to maximize remediation of metal contaminated wastewater in constructed wetland

In present study, the metal accumulation potential and growth dynamics of two aquatic macrophytes viz. Sagittaria sagittifolia and Colocasia esculenta were investigated at varying harvest time and frequency for maximum metal removal from mixed industrial wastewater employing horizontal flow constructed wetland (CW) technology. Both plant species were harvested five times i.e. 0, 30, 60, 90 and 120 days during experiment. S. sagittifolia attained maximum biomass (216.2 g dw m−1) and growth rate (1.25 g plant−1 day−1) at H3, whilst that of C. esculenta (204.3 g dw m−1 and 1.01 g plant−1 day−1 respectively) at H4. The plant species also differed in their metal uptake capability. With exception of Cr, other heavy metals viz. Zn, Cu and Cd accumulated more in S. sagittifolia than C. esculenta. In general, the metal uptake efficiency of S. sagittifolia was higher than that of C. esculenta, which increased up to H3 in former, whilst up to H4 in latter. The maximum Zn, Cu and Cd removal (115.55, 53.78 and 4.26 g/wetland respectively) was observed by S. sagittifolia in CW1, whilst Cr removal (12.79 g/wetland) by C.esculenta was recorded in CW2. Both plants showed metal tolerance ability in terms of reduced and oxidized glutathione content in their leaves. As such, the optimum harvesting regimes (time and frequency) in sequential manner accumulating maximum metals could enhance the metal removal efficiency of aquatic macrophytes.

Industrial wastewater treatment in constructed wetlands packed with construction materials and agricultural by-products

Abstract This paper reports pollutant removal performances from mixed industrial wastewater employing subsurface flow constructed wetland systems in Bangladesh. Two parallel hybrid wetland trains were established; each train included a vertical flow (VF) followed by a horizontal flow (HF) wetland. One hybrid system was packed with construction materials (i.e. recycled bricks), whereas the other system included agricultural by-products (i.e. sugarcane bagasse). All wetland units were planted with Canna indica. The hybrid trains were operated under non recirculation and recirculation phases; input hydraulic loading across each VF system ranged between 219.3 and 438.0 mm/d. Mean nitrogen, organics, solids, phosphorus and color removals across the hybrid systems were 67.5–80.0, 74.0–85.0, 55.0–95.0, 64.0–89.0 and 46.0–83.0% respectively. Lower input biodegradation ratio influenced organics removal routes in wetland systems that employed recycled bricks. In contrast, organic contents of sugarcane bagasse material supported microbial routes in the other system. VF wetland with organic media achieved higher TN removal rates (1.82 g/m2 d), due to internal carbon (C) generation. Higher phosphorus removals (89.0%) were observed in hybrid system packed with recycled brick media, due to adsorption process. HF wetland packed with recycled brick was efficient in removing color compounds, whereas the other HF system (with organic media) showed high sulfate removals. Nitrogen and BOD removal improvement was observed in VF wetland (packed with recycled brick media) during recirculation period; in contrast, effluent recirculation reduced removal rates of such pollutants in VF system that employed organic media. In general, this study shows potential application of particular materials as the main media of wetland systems, to achieve pollutant removals from industrial wastewaters in Bangladesh.

Spatial distribution and contamination assessment of heavy metals in marine sediments of the southern coast of Sfax, Gabes Gulf, Tunisia

In order to investigate the current distribution of metal concentrations in surface marine sediments of the southern coast of Sfax (Tunisia), thirty-nine samples were collected in the vicinity of a mixed industrial and domestic wastewater effluent discharge. In comparison with the threshold effect level and probable effect level, the majority of metals had high ecological and biological risks. Enrichment factor and geoaccumulation Index showed that the majority of sediments are unpolluted by As, Ni and Pb, moderately polluted by Cr and Cu and moderately to strongly polluted by P, Y, Zn. Besides, all sites are extremely polluted by Cd. Principal component analysis indicates that As, Cu and Ni were mainly from lithogenic sources, whereas Cd, Cr, F, P, Pb, Y and Zn were mainly derived from anthropogenic source. Findings of this research can be used as suitable reference for future studies and environmental management plans in the region.

Demonstration of a full-scale plant using an UASB followed by a ceramic MBR for the reclamation of industrial wastewater

This study comprehensively evaluated the performance of a full-scale plant (4550m3d−1) using a UASB reactor followed by a ceramic MBR for the reclamation and reuse of mixed industrial wastewater containing many inorganics, chemical, oil and greases. This plant was demonstrated as the first full-scale system to reclaim the mixed industrial wastewater in the world. During 395days of operation, influent chemical oxygen demand (COD) fluctuated widely, but this system achieved COD removal rate of 91% and the ceramic MBR have operated flux of 21–25LMH stably. This means that this system adsorbed the feed water fluctuation and properly treated the water. Energy consumption of this plant was achieved 0.76kWhmm−3 and this value is same range of domestic sewage MBR system. The combination of an UASB reactor and ceramic MBR is the most economical and feasible solution for water reclamation of mixed industrial wastewater.

Water quality of urban streams: the Allium cepa seeds/seedlings test as a tool for surface water monitoring.

The present study investigates the genotoxic, mutagenic, and cytotoxic potential of surface waters in urban streams using Allium cepa and analyzes the applicability of this assay for environmental monitoring. Water samples were collected from three streams located in the urban area of a municipality in the south of Brazil. For each stream, two samples were collected, one upstream and one downstream of the pollution discharge site. Physicochemical evaluation indicated that all samples had various degrees of environmental impact, but substantial impact was seen for the downstream samples of the Preto and Pedras streams. All samples increased the frequency of chromosome aberrations (P < 0.05). The sample from Pedras downstream site also caused a decrease in mitotic index (P < 0.08) and increase in micronuclei (P < 0.08) frequency, indicating potential cytotoxicity and mutagenicity. The Pedras stream receives mixed industrial and urban wastewater, while the Lajeado and Preto streams receive wastewater predominantly domestic in nature, which may partially explain the difference in toxicity among the samples. Moreover, the Allium cepa seeds/seedlings were shown to be extremely sensitive in detecting the genotoxicity of environmental water samples and can be applied as the first tool for environmental health hazard identification and prediction.