## 2 Centralized Treatment Plants
### Industrial Wastewater Remediation
#### 2.3.6 Steel Industry  
Wastewater from steel manufacturing contains an array of recalcitrant contaminants, and the review papers by [PERSON] et al. and [PERSON] et al. summarize the effectiveness of the existing treatment facilities and investigate the feasibility of emerging technologies, in particular integrated treatment techniques. A particular focus has been laid on sustainable practices and techno-economic aspects to help in decision-making for adopting the best available technology for effluent management in the steel industry, keeping in mind future scenarios. These reviews highlight that effluent treatment should not be limited to meeting discharge standards but to achieving reusable quality water. Membrane technologies, in this context, provide an adequate solution. The decisive experimental parameters which will help to overcome the limitations associated with prevailing and emerging technologies have been evaluated and summarized [103,104]. A similar paper reports a survey on the treatment of wastewater from integrated steel plants, mainly focusing on coking WW treatment, discussing the most effective integrated approaches. Biological treatment is the most-explored technology, but several techniques such as adsorption, electrochemical oxidation and AOPs can be efficient in removing organic pollutants. Innovative materials, such as carbon-based nanomaterials, nanofibers, nanometal oxides and bimetallic oxides, that were previously not explored for coking wastewater treatment are mentioned. Moreover, with the research gap existing in the biological approach, the need to isolate and test the microbes present in water, soil and wastewater near industrial locations is highlighted [105]. Producing cold-rolled steel, the resulting emulsion wastewater contains vegetable and mineral oils, emulsifier and metal ions. [PERSON] and co-workers evaluated the performance and economic aspects of a UF process in large-scale industrial applications. In two modules of a commercial tubular ceramic UF membrane ZrO\({}_{2}\)/\(\alpha\)-Al\({}_{2}\)O\({}_{3}\) with a capacity of 24 m\({}^{3}\) h\({}^{1}\), a cut-off of 20 kDa and an effective filtration area of 16.81 m\({}^{2}\), each one exhibited an average removal rate for oil and COD of 99.88% and 98.41%, respectively. The control of the feed concentration, the increase in the cross-flow velocity and proper chemical cleaning were applied, obtaining positive results in controlling membrane fouling. The service life of the ceramic membrane was extended to more than 8 years. Finally, the cooled permeate is discharged into a biochemical facility for further treatment. The total operating cost was about 3.01 USD/m\({}^{3}\), cheaper than the conventional treatments [106]. The decyanation of steel plant effluent without generation of toxic by-products has been carried out at a pilot plant consisting of a feed tank, an H\({}_{2}\)O\({}_{2}\) storage tank, a UV reactor and an air compressor for air bubbling. The CN degradation rate was faster in the first 30 min, and the CN concentration reached less than 1 mg/L in 3 h. The optimized dosing rate of H\({}_{2}\)O\({}_{2}\) and the UV lamp power were 8 L/m\({}^{3}\) and 640 W, respectively. The test revealed that the technique is highly scalable without generating any toxic sludge, and economically, the total operating cost was assessed to be 4.63 USD/m \({}^{3}\) of wastewater [107]. Steel industry effluents can also be bioremediated, and in the research work of [PERSON] et al., the tolerance capacity of _Tetradesmus obliquus, Chlorella sorokiniana_, _Chlorella vulgaris_, _Arthospira platensis_ and _Arthospira maxima_ (spirulina) to hot-rolling WW containing heavy metals and hydrocarbons have been tested. _A. maxima_ showed successful acclimation and was cultured in the presence of the WW to be remediated, scaled to semi-industrial closed systems (photobioreactors with a final volume of 100 L).