It is undeniable that removal efficiency is the main factor in coagulation-flocculation (C-F) process for wastewater treatment. However, as far as environmental safety is concerned, the ecotoxicological aspect of the C-F process needs to be examined further. In this study, a systematic review was performed based on publications related to the toxicity research in C-F technology for wastewater treatment. Through a series of screening steps, available toxicity studies were categorized into four themes, namely acute toxicity, phytotoxicity, cytotoxicity, and genotoxicity, which comprised 48 articles. A compilation of the methodologies executed for each theme was also outlined. The findings show that conventional metallic coagulants (e.g., alum, iron chloride, and iron sulfate) were less toxic when tested on test species such as Daphnia magna (water flea), Lattuca sativa (lettuce), and animal cells compared to synthetic polymers. Natural coagulants such as chitosan or Moringa oleifera were less toxic compared to metallic coagulants; however, inconsistent results were observed. Moreover, an advanced C-F (electrocoagulation) as well as integration between C-F and Fenton, adsorption, and photocatalytic does not significantly change the toxicological profile of the system. It was found that diverse coagulants and flocculants, species sensitivity, complexity in toxicity testing, and dynamic environmental conditions were some key challenges faced in this field. Finally, it was expected that advances in technology, interdisciplinary collaboration, and a growing awareness of environmental sustainability will drive efforts to develop more effective and eco-friendly coagulants and flocculants, improve toxicity testing methodologies, and enhance the overall efficiency and safety of water and wastewater treatment processes.
The aquatic ecotoxicity of chemicals involved in the manufacturing process of thin film transistor liquid crystal displays was assessed with a battery of four selected acute toxicity bioassays. We focused on tetramethylammonium hydroxide (TMAH, CAS No. 75-59-2), a widely utilized etchant. The toxicity of TMAH was low when tested in the 72 h-algal growth inhibition test (Pseudokirchneriellia subcapitata, EC50=360 mg L(-1)) and the Microtox® test (Vibrio fischeri, IC50=6.4 g L(-1)). In contrast, the 24h-microcrustacean immobilization and the 96 h-fish mortality tests showed relatively higher toxicity (Daphnia magna, EC50=32 mg L(-1) and Oryzias latipes, LC50=154 mg L(-1)). Isobologram and mixture toxicity index analyses revealed apparent synergism of the mixture of TMAH and potassium iodide when examined with the D. magna immobilization test. The synergistic action was unique to iodide over other halide salts i.e. fluoride, chloride and bromide. Quaternary ammonium ions with longer alkyl chains such as tetraethylammonium and tetrabutylammonium were more toxic than TMAH in the D. magna immobilization test.
A new mathematical model has been developed that expresses the toxicities (EC₅₀ values) of a wide variety of ionic liquids (ILs) towards the freshwater flea Daphnia magna by means of a quantitative structure-activity relationship (QSAR). The data were analyzed using summed contributions from the cations, their alkyl substituents and anions. The model employed multiple linear regression analysis with polynomial model using the MATLAB software. The model predicted IL toxicities with R²=0.974 and standard error of estimate of 0.028. This model affords a practical, cost-effective and convenient alternative to experimental ecotoxicological assessment of many ILs.