Evaluation of phytotoxicity of effluents from activated sludge and constructed wetland system for wastewater reuse

Phytotoxicity assessment of treated vegetable oily wastewater via environmentally coagulation/flocculation and membrane filtration technologies using lettuce (Lactuca sativa) seeds

The present investigation highlights the necessity of monitoring some basic physico-chemical water quality indicators and their phytotoxic effect using ecotoxicological bioassays such as "seed germination tests." The phytotoxicity of raw and treated vegetable oil refinery wastewater (VORW) using different treatment processes was assessed through some physiological responses (relative seed germination (RSG), seedling elongation, and germination index (GI)) using Lactuca sativa cultivar. Biotest results of different raw water samples revealed a noticeable correlation between the organic matter content and water phytotoxicity. In fact, VORW showed a very low RSG (17 ± 0.7 to -47 ± 0.58%) and high phytotoxic effects (GI < 50%). The use of coagulation/flocculation (CF) allowed a satisfactory phytotoxicity removal where RSG obtained ranged from 83 ± 1.58 to 90 ± 1.2%. However, the effluent still presents high to moderate phytotoxicity since GI remained below 80% which indicates the presence of toxic elements remaining after CF treatment. When VORW were treated using membrane processes, their phytotoxicity was gradually decreased with the decrease in the membrane pore size. The use of microfiltration membranes (MF), with pore size of 5 µm, 1.2 µm, 0.45 µm, and 0.22 µm, showed RSG values ranged from 37 ± 1.15 to 77 ± 1.68% and GI of less than 80% indicating a moderate to high phytotoxicity. However, the use of ultrafiltration (UF) membranes with molecular weight cut-off (MWCO) of 100 kDa, 30 kDa, and 10 kDa made it possible to achieve an RSG of 100% and an IG exceeding 80% showing that the VORW-treated using UF does not exhibit any phytotoxicity effect. Hence, UF appears to be the most efficient and environmentally friendly technology that could be used for safely treated VORW irrigation purposes compared to CF and MF processes.

Evaluation of the Toxicity of Cafeteria Wastewater Treated by a Coupled System (ARFB-SD)

In developing countries, achieving greater coverage in the treatment and safe reuse of graywater is a pending task. Therefore, this article presents the results obtained from cafeteria wastewater treatability tests and effluent toxicity tests. For the treatment, a serial system was applied: an aged refuse filled bioreactor (ARFB) and a solar distiller (SD). In the first stage (ARFB), two hydraulic loads (HLs) were tested (200 and 400 L/m3·day), the latter being the best of them, with an average decrease of 95.7% in chemical oxygen demand (COD). In the second stage (SD), the decrease was 62.8%, resulting in a final effluent with 67.7 mg/L COD, which corresponded to a global COD decrease of 97.4%. For the toxicity tests, radish seeds were used in the serial system effluent, obtaining a relative seed germination (RSG) rate of 93.3% compared to 80% obtained in the ARFB effluent. For the percentage germination index (PGI), it was determined that both effluents (ARFB and ARFB-SD) presented a toxicity considered low, especially the ARFB-SD effluent whose PGI value was close to zero (−0.0667). The results obtained showed not only that the ARFB-SD system is efficient in removing the high organic load that can go along with cafeteria wastewater, but also that it can provide an effluent with a very low toxicity level based on the PGI close to zero.

Current technologies and future perspectives for the treatment of complex petroleum refinery wastewater: A review

Petroleum refinery wastewater (PRW) is a complex mixture of hydrocarbons, sulphides, ammonia, oils, suspended and dissolved solids, and heavy metals. As these pollutants are toxic and recalcitrant, it is essential to address the above issue with efficient, economical, and eco-friendly technologies. In this review, initially, an overview of the characteristics of wastewater discharged from different petroleum refinery units is discussed. Further, various pre-treatment and post-treatment strategies for complex PRW are introduced. A segregated approach has been proposed to treat the crude desalting, sour, spent caustic, and oily wastewater of petroleum refineries. The combined systems (e.g., ozonation + moving bed biofilm reactor and photocatalysis + packed bed biofilm reactor) for the treatment of low biodegradability index wastewater (BOD₅/COD < 0.2) were discussed to construct a perspective map and implement the proposed system efficiently. The economic, toxicity, and biodegradability aspects are also introduced, along with research gaps and future scope.

Detection and characterization of refractory organic and inorganic pollutants discharged in biomethanated distillery effluent and their phytotoxicity, cytotoxicity, and genotoxicity assessment using Phaseolus aureus L. and Allium cepa L

The color effluent discharged by alcohol distilleries comprises very high pollution loads due to the plethora of refractory chemicals even after anaerobic treatment and causing adverse effects to the environment. The present study aimed to examine the phytotoxic, cytotoxic, and genotoxic potential of the identified refractory organic and inorganic pollutants discharged in bio-methanated distillery effluent (BMDE). Physico-chemical analyses revealed that BMDE retains high BOD, COD, TDS along with heavy metals like Fe (572.64 mg L^-1), Mn (4.269 mg L^-1), Cd (1.631 mg L^-1), Zn (2.547 mg L^-1), Pb (1.262 mg L^-1), (Cr 1.257 mg L^-1), and Ni (0.781 mg L^-1) beyond the permissible limits for effluent discharge. GC-MS analysis revelaed the presence of hexadecanoic acid, TMS ester; octadecanoic acid, TMS ester; 2,3 bis[(TMS)oxy]propyl ester; stigmasterol TMS ether; β-sitosterol TMS ester; hexacosanoic acid; and tetradecanoic acid, TMS ester as major refractory organic pollutants, which are listed as potential endocrine disruptor chemicals (EDCs) as per USEPA. Furthermore, phytotoxicity assessment with Phaseolus aureus L. showed the toxic nature of BMDE as it inhibited various seedling growth parameters, seed germination, and suppression of α-amylase activity in seed germination experiment. Moreover, genotoxicity and cytotoxicity evaluation of the discharged BMDE evidenced in root-tip meristematic cells of Allium cepa L. where chromosomal aberration such as disturbed metaphase, c-mitosis, laggard chromosomes, sticky chromosomes, prolonged prophase, polyploid cells, and apoptotic bodies etc. were observed. Thus, this study's results suggested that BMDE discharged without adequate treatment poses potential risk to environment and may cause a variety of serious health threats in living beings upon exposure.

Biomonitoring of urban wastewaters treated by an integrated system combining microalgae and constructed wetlands

The objectives of the present study were to apply different, toxicological assays for monitoring the toxicity of treated and untreated urban effluents produced at a university campus. The research was conducted at the wastewater treatment plant of the University of Santa Cruz do Sul, (UNISC), from october 2018 to april 2019. An integrated system with, anaerobic reactor (AR), microalgae (MA) and constructed wetlands (CWs) was, proposed for detoxification of the wastewaters produced at the university campus with a hydraulic detention time of 17 days. Daphnia, magna (ecotoxicity) and Allium cepa (phytotoxicity, cytotoxicity, and, genotoxicity) were used as tools to monitor the efficiency of the integrated system. Obtained results showed that the integrated system (MA, + CWs) presented good COD and BOD5 reductions, besides removal rates of, almost 98% for N-NH3, being much more efficient than the UNISC wastewater, treatment plant (UWTTP). The results of ecotoxicity presented the raw wastewaters (RW) as slightly toxic and an absence of ecotoxicity in all the treatments steps. Regarding phytotoxicity, the results showed no significant differences between the treatments. The cytogenetic assays indicated a significant increase in mitotic index (MI) (p < 0.001) after treatment by CWs compared to the final treatment UWTTP while the results, regarding binucleated cells (BNC) did not present significant differences, among the treatments. Micronucleus (MN) indexes were significantly different between the UWWPT and the integrated system (p < 0.01). In relation to chromosome aberrations (CA) the results indicate a significant difference between the CWs and UWWTP treatments (p < 0.01) and, RW and CWs (p < 0.001), confirming the detoxifying potential of the integrated system when compared to UWWPT. Thus, the results of the present research highlight the relevance in the proposition of the integrated system as an alternative of cleaner technology to the detriment of conventional technologies applied in wastewater treatment.

Disinfection behavior of a UV-treated wastewater system using constructed wetlands and the rate of reactivation of pathogenic microorganisms

The use of constructed wetlands as a wastewater treatment system is a feasible solution for rural areas. However, these systems do not efficiently eliminate pathogenic microorganisms. Therefore, it is necessary to implement disinfection systems such as ultraviolet (UV) disinfection systems in constructed wetlands. To evaluate the behavior of a UV system, a pilot system of artificial wetlands connected to one such disinfection system was operated. The results show that when the total suspended solids (TSS) of the influent (already treated by the system of constructed wetlands) reached values of 26.7 mg/L, a reduction of 2.03 uLog in fecal coliforms was obtained. However, when the TSS increased to 34.7 mg/L, the reduction was only 0.33 uLog. In addition to the influence of the TSS on the fecal coliform reduction efficiency, there is a direct relationship between the transmittance and the sizes of the particles present in the influent. After UV treatment, the microorganisms showed a peak in photoreactivation of 27.8% at 4 h after irradiation with visible radiation, while under conditions of darkness, no reactivation was observed.