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The textile wastewaters have a diverse composition depending both on the used raw materials and applied manufacturing technologies. These wastewaters may contain various pollutants such as organic compounds (e.g. residual dyes), suspended solids, metal ions etc. Most of dyes are synthetic compounds with aromatic molecular structures and non-biodegradable. The oxidative destruction via homogenous oxidation processes with hydrogen peroxide (simple chemical oxidation with H 2 O 2 or advanced oxidation processes (AOPs) as Fenton oxidation, ozonation, photo-oxidation and photo-Fenton oxidation etc.) are attractive alternatives to conventional treatments, easy to be applied and not so expensive. The use of H 2 O 2 in AOPs has the advantage that the decomposition products of organic pollutants are common harmless compounds. Moreover, H 2 O 2 decomposes itself in water and oxygen. This paper is a review of authors' researches regarding homogenous oxidation with hydrogen peroxide applied for different types of textile dyes in order to perform high textile dye removals considering some relevant factors: pH, agitation regime, temperature, H 2 O 2 concentration, textile dye concentration, oxidation time, ferrous or metallic ions concentration, etc.

The environmental issues associated with residual colour in treated textile effluents are always a concern for each textile operator that directly discharges, both sewage treatment works and commercial textile operations, in terms of respecting the colour requirements. This paper aims to help a textile operator to decide on options available to plan forward strategy that will ensure compliance with the environmental regulators' requirements on a progressive basis. To achieve this objective the paper is structured in order to present various options and solutions that are explained and developed mainly based on different physico-chemical treatment steps (i.e. adsorption using different unconventional adsorptive materials as 'low cost' adsorbents of coal ashes, sawdust wastes, peat and comparisons with a classic commercial 'activated carbon'; catalysed chemical oxidation with hydrogen peroxide; coagulation-flocculation with iron salts and organic polyelectrolyte) integrated into a specific order in the wastewater technological treatment process for decolorization or large-scale colour removal processes of textile effluents produced into a private Northern Romanian textile plant. The influence of different operating parameters (i.e. pH, material or chemical reagent concentration, temperature, operational time, agitation and operational working regime) is discussed together with the textile effluent treatment efficiency obtained for each studied influencing parameters (the best solutions for each parameters are in view and discussed). These technical and operational treatment solutions are both threats and opportunities for the textile operator, and the best colour removal option is obtained from combination of technologies or proposed treatment steps rather than from one single-stage process.

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Sorption is one of the several methods that have been successfully utilized for dyes removal. A large number of materials have been used as suitable sorbents for decolourization of industrial effluents: activated carbon (the most common but expensive adsorbent), polymeric resins, various low-cost adsorbents (agricultural and industrial by-products, peat, chitin, silica, bentonite, other clays, fly ash). Our paper is a review about our researches regarding different types of industrial and agricultural waste materials with sorptive properties (ashes, textile fibres, sawdust, lignin, sun flower shells, corn cob, etc.) that were utilized into textile wastewater treatment. Batch sorption experiments were carried out in order to establish the favourable conditions to uptake of dyes. The studied operating variables were: pH, sorbent dose, dyes concentration, temperature and sorption time. The sorption systems were described using Freundlich, Langmuir and Dubinin-Radushkevich isotherm models.

The experimental results performed after the application of one single-stage treatment by sorption onto coal fly ash are evaluated in order to decolorize a real textile effluent of a private company specializing in manufacturing of cotton fabrics (i.e., sorption performance applied for a real textile effluent collected after the fabric dyeing, rinsing, and final finishing steps). The experiments are focused on studying the effect of initial textile effluent pH, adsorbent dose, temperature and adsorption time, considered as operating parameters of sorption process for high pollutant removals (e.g., organic pollutants as dyes, phenols, polymeric, and degradation compounds), and decoloration. The results indicate high values of decoloration degree (55.42-83.00%) and COD removal (44.44-61.11%) when it is worked at pH ≤2 with coal ash dose of 12-40 g/L, temperature higher than 20-25 °C, and continuous static operating regime (with an initial agitation step of 3-5 min). The treated textile effluent fulfills the quality demand, and is recyclable, inside reused or discharged after a stage of neutralization (standard pH of 6.5-8.5 for all textile effluent discharges). Also, the final effluent is able to follow the common path to the central biological treatment plant (i.e., a centralized treatment plant for all companies acting in the industrial site area with mechanical-biological steps for wastewater treatment) or may be directly discharged in the nearly watercourse.

Natural polymers can themselves be efficient as materials with biosorptive properties but can also be used to transform microbial biomass into an easy-to-handle form, respectively, into biosorbents, through immobilization. The article aims to study biosorbents based on residual microbial biomass (Saccharomyces pastorianus yeast, separated after the brewing process by centrifugation and dried at 80 °C) immobilized in sodium alginate. The biosorptive properties of this type of biosorbent (spherical particles 2 and 4 mm in diameter) were studied for removal of reactive dye Brilliant Red HE-3B (with concentration in range of 16.88–174.08 mg/L) from aqueous media. The paper aims at three aspects: (i) the physico-chemical characterization of the biosorbent (Scanning Electron Microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX) and Fourier Transform Infrared (FTIR) spectra); (ii) the modeling of biosorption data in order to calculate the quantitative characteristic parameters using three equilibrium isotherms (Langmuir, Freundlich, and Dubinin–Radushkevich—DR); and (iii) the evaluation of thermal effect and the possible mechanism of action. The results of the study showed that biosorption capacity evaluated by Langmuir (I) model is 222.22 mg/g (ϕ = 2 mm) and 151.51 mg/g (ϕ = 4 mm) at 30 °C, and the free energy of biosorption (E) is in the range of 8.45–13.608 KJ/mol (from the DR equation). The values of thermodynamic parameters suggested an exothermic process due the negative value of free Gibbs energy (ΔG0 = −9.031 kJ/mol till −3.776 kJ/mol) and enthalpy (about ΔH0 = −87.795 KJ/mol). The obtained results underline our finding that the immobilization in sodium alginate of the residual microbial biomass of Saccharomyces pastorianus led to an efficient biosorbent useful in static operating system in the case of effluents with moderate concentrations of organic dyes.