Investigating the relationship between toxicity and organic sum-parameters in kraft mill effluents

Chemical characteristics of dissolved organic matter in effluent from sludge alkaline fermentation liquid-fed sequencing batch reactors

Sludge alkaline fermentation liquid (SAFL) is a promising alternative to acetate for improving biological nitrogen removal (BNR) from wastewater. SAFL inevitably contains some refractory compounds, while the characteristics of dissolved organic matter (DOM) in effluent from SAFL-fed BNR process remain unclear. In this study, the molecular weight distribution, fluorescent composition and molecular profiles of DOM in effluent from SAFL and acetate-fed sequencing batch reactors (S-SBRs and A-SBRs, respectively) at different hydraulic retention time (12 h and 24 h) was comparatively investigated. Two carbon sources resulted in similar effluent TN, but a larger amount of DOM, which was bio-refractory or microorganisms-derived, was found in effluent of S-SBRs. Compared to acetate, SAFL increased the proportion of large molecular weight organics and humic-like substances in effluent DOM by 74.87%-101.3% and 37.52%-48.35%, respectively, suggesting their bio-refractory nature. Molecular profiles analysis revealed that effluent DOM of S-SBRs exhibited a more diverse composition and a higher proportion of lignin-like molecules. Microorganisms-derived molecules were found to be the dominant fraction (71.51%-72.70%) in effluent DOM (<800 Da) of S-SBRs. Additionally, a prolonged hydraulic retention time enriched Bacteroidota, Haliangium and unclassified_f_Comamonadaceae, which benefited the degradation of DOM in S-SBRs. The results help to develop strategies on reducing effluent DOM in SAFL-fed BNR process.

Evaluation of toxicity and estrogenicity in UASB - Treated municipal sewage

This study was undertaken to assess the capacity of the upflow anaerobic sludge blanket (UASB) reactor, one of the most commonly used systems in Brazilian sewage treatment plants, to remove municipal sewage toxicity using different Danio rerio life stages (embryo, embryo-larval, larval, adult), and estrogenicity using in vitro (yeast Saccharomyces cerevisiae) and in vivo (vitellogenin induction in D. rerio) assays. Sensitivity of chronic fish assays were compared to the chronic Ceriodaphnia dubia assay. UASB-treated sewage met Brazilian legal limits for BOD and COD removals, but did not remove toxicity, and treated sewage remained extremely toxic to D. rerio larvae and C. dubia, and highly toxic to D. rerio embryos. The 4-day embryo assay had the same sensitivity as the adult acute toxicity assay, and could safely replace it, avoiding the need to sacrifice adult fish. No significant differences were identified in vitellogenin induction among organisms exposed to sewage or control. However, the in vitro test showed that anaerobic treatment increased sample estrogenicity from 27 to 40 ng equivalents of 17-β estradiol per liter, a result corroborated by the greater induction of vitellogenin in male fish exposed to 5% (2.73 μg/g) and 20% (2.12 μg/g) treated sewage compared to the same concentrations of raw sewage (0.174 μg/g at 5% and 0.188 μg/g at 20%). Thus, UASB reactor should be followed by post-treatment to reduce risks of sewage discharge to receiving waters.

Phytotoxicity indexes and removal of color, COD, phenols and ISA from pulp and paper mill wastewater post-treated by UV/H2O2 and photo-Fenton

Pulp and paper mill wastewater (PPMWW) contains high concentrations of recalcitrant compounds that cause toxicity to organisms. Advanced oxidation processes (AOPs) have the ability to degrade these compounds and reduce overall toxicity. Physicochemical characterization and Lactuca sativa toxicity test were conducted to compare the effectiveness of two post-treatments: UV/H₂O₂ and photo-Fenton. A comparison of four phytotoxicity indexes was carried out. PPMWW from a Brazilian treatment plant was characterized by high values of phenols, color, integrated spectral area (ISA), and chemical oxygen demand (COD), and caused significant inhibition to seedling development. The use of both post-treatments allowed the removal of over 75% of phenols, color, ISA, and COD. Although UV/H₂O₂ was more effective in removing phenols and ISA, photo-Fenton better reduced phytotoxicity. The most sensitive phytotoxicity indexes were RGIC_0.8 and GIC_80%, whereas SGC₀, REC_-0.25 and REC_-0.50 better showed the effectiveness of the post-treatments. We suggest the combined use of two phytotoxicity indexes: one that evaluates the effects on seed germination and, another, on root elongation, e.g., SGC₀ and RGIC_0.8. Additionally, we recommend the use of ISA for monitoring programs of wastewater treatments because it is a cost-effective approach that allows narrowing down the search and identification of compounds present in complex mixtures.

Identifying bioaccessible suspect toxicants in sediment using adverse outcome pathway directed analysis

Chemical mixtures are a common occurrence in contaminated sediment and determining causal relationship between sediment contamination and adverse outcomes is challenging. The bioavailability and choice of bioassay endpoints played important roles in elucidating causality. As such, bioaccessibility-based XAD extraction and adverse outcome pathway (AOP) guided bioassays were incorporated into an effect-directed analysis to more effectively determine sediment causality. XAD extracts of sediments from urban waterways in Guangzhou, China were examined using cell viability bioassays with four human tumor cells from lung, liver, breast, and bone marrow. Pronounced effects to SH-SY5Y cells were noted, thus neurotoxicity was subsequently focused in the AOP-guided bioassays. Intracellular calcium influx, mitochondrial membrane potential inhibition, reactive oxygen species generation, and cell viability were utilized as evidence for neurotoxicity AOP-guided analysis. Suspect toxicants were identified in active fractions using GC-MS. Toxicity confirmation was performed by evaluating toxicity contributions of the candidates to the pathway. Cypermethrin, bisphenol A, galaxolide, tonalide, and versalide were found as the major stressors across key events of the studied pathway. Moreover, good correlations among key events validated the feasibility of method to predict in vivo response, suggesting that considering bioavailability and AOP improved environmental relevance for toxicant identification in a complex mixture.

Algal toxicity induced by effluents from textile-dyeing wastewater treatment plants

This research aimed to evaluate the alga Scenedesmus obliquus toxicity induced by textile-dyeing effluents (TDE). The toxicity indicator of TDE in alga at the physiological (algal growth), biochemical (chlorophyll-a (Chl-a) synthesis and superoxide dismutase (SOD) activity) and structural (cell membrane integrity) level were investigated. Then we further study the relationship among toxicity indicators at physiological and biochemical level, and supplemented by research on algal biomacromolecules. According to the analysis of various endpoints of the alga, the general sensitivity sequence of toxicity endpoints of Scenedesmus obliquus was: SOD activity > Chl-a synthesis > algal growth. The stimulation rate of SOD activity increased from day 3 (57.25%~83.02%) to day 6 (57.25%~103.81%), and then decreased on day 15 (-4.23%~-32.96%), which indicated that the antioxidant balance system of the algal cells was destroyed. The rate of Chl-a synthesis inhibition increased gradually, reaching 19.70%~79.39% on day 15, while the rate of growth inhibition increased from day 3 (-12.90%~10.16%) to day 15 (-21.27%~72.46%). Moreover, the algal growth inhibition rate was positively correlated with the inhibition rate of SOD activity or Chl-a synthesis, with the correlation coefficients were 0.6713 and 0.5217, respectively. Algal cells would be stimulating to produce excessive reactive oxygen species, which would cause peroxidation in the cells, thereby destroying chloroplasts, inhibiting chlorophyll synthesis and reducing photosynthesis. With increasing exposure time, irreversible damage to algae can lead to death. This study is expected to enhance our understanding of the ecological risks through algal tests caused by TDE.

Ecofriendly laccases treatment to challenge micropollutants issue in municipal wastewaters

In this study, a multidisciplinary approach investigated the enzymatic degradation of micropollutants in real, not modified, municipal wastewaters of a plant located in Italy. Stir Bar Sorptive Extraction combined to Gas Chromatography-Mass Spectrometric detection (SBSE-GC-MS) was applied to profile targeted pollutants in wastewaters collected after the primary sedimentation (W1) and the final effluent (W2). Fifteen compounds were detected at ng/L - μg/L, including pesticides, personal care products (PCPs) and drugs. The most abundant micropollutants were bis(2-ethylhexyl) phthalate, diethyl phthalate and ketoprofen. Laccases of Trametes pubescens MUT 2400 were very active against all the target micropollutants: except few cases, their concentration was reduced more than 60%. Chemical analysis and environmental risk do not always come together. To verify whether the treated wastewaters can represent a stressor for the aquatic ecosystem, toxicity was also evaluated. Raphidocelis subcapitata and Lepidium sativum tests showed a clear ecotoxicity reduction, even though they did not evenly respond. Two in vitro tests (E-screen test and MELN assay) were used to evaluate the estrogenic activity. Treatments already operating in the plant (e.g. activated sludge) partially reduced the estradiol equivalent concentration, and it was almost negligible after the laccases treatment. The results of this study suggest that laccases of T. pubescens are promising biocatalysts for the micropollutants transformation in wastewaters and surface waters.

Toxicity evaluation of textile dyeing effluent and its possible relationship with chemical oxygen demand

Textile dyeing wastewater was the focus of much research because of its adverse effect on aquatic biota. In the present research, textile dyeing influent and effluent samples were collected from four textile dyeing wastewater treatment plants (TDPs) in Guangdong province, China, and their conventional indicators and toxicity were examined to reveal relationships. The relationship between toxicity and chemical oxygen demand (COD) was clearly established at individual TDPs. Results indicated the highest removal efficiencies of 94.4%, 90.6%, 91.9%, 94.6%, 92.8% and 97.5% for TOC, mixed-liquor volatile suspended solids (MLVSS), COD, ammonia nitrogen (NH₃-N), total phosphorus (TP) and colour, respectively. The primary clarifier used in TDP3 and TDP4 was beneficial for removing macromolecular organic substances, and membrane filtration and sedimentation basin employed at TDP1 and TDP2, respectively, helped to remove toxic substances. Toxicity to V. fischeri or D. subspicatus was found to be related to certain conventional indicators such as TOC, COD, TP, colour, and MLVSS, and was positively correlated with COD in different textile dyeing effluents (R² > 0.84). It was recommended that the relationship between toxicity and COD in wastewater should be established individually at each plant. Therefore, this study could be useful in providing suggestions for guiding effluent management when no toxicity experiments were conducted.

Reduction in toxicity of wastewater from three wastewater treatment plants to alga (Scenedesmus obliquus) in northeast China

The toxicity of municipal wastewater to the receiving water bodies is still unknown, due to the lack of regulated toxicity based index for wastewater discharge in China. Our study aims at gaining insight into the acute toxic effects of local municipal wastewater on alga, Scenedesmus obliquus. Four endpoints, i.e. cell density, chlorophyll-A concentration, superoxide dismutase (SOD) activity and cell membrane integrity, of alga were analyzed to characterize the acute toxicity effects of wastewater from municipal wastewater treatment plants (WWTPs) with different treatment techniques: sequencing batch reactor (SBR), Linpor and conventional activated sludge. Influent and effluent from each treatment stage in these three WWTPs were sampled and evaluated for their acute toxicity. Our results showed that all three techniques can completely affect the algal chlorophyll-A synthesis stimulation effects of influent; the algal cell growth stimulation effect was only completely removed by the secondary treatment process in conventional activated sludge technique; toxic effects on cell membrane integrity of two influents from WWTPs with SBR and conventional activated sludge techniques were completely removed; the acute toxicity on SOD activity was partially reduced in SBR and conventional activated sludge techniques while not significantly reduced by Linpor system. As to the disinfection unit, NaClO disinfection enhanced wastewater toxicity dramatically while UV radiation had no remarkable influence on wastewater toxicity. Our results illustrated that SOD activity and chlorophyll-A synthesis were relatively sensitive to municipal wastewater toxicity. Our results would aid to understand the acute toxicity of municipal wastewater, as well as the toxicity removal by currently utilized treatment techniques in China.