It has been reported that about 100–200 L of water is required to process 1 kg of the textile product, depending on the type of process [6]. First, various stages of the textile treatment operation and wastewater characteristics are discussed to identify. The dye molecules have difficulty diffusing into the yarn or fabric due to the presence of the glue compounds.
Most of the by-products of the dyeing process, including metals, salts and dyes, can be found in wastewater from the textile industry. Dirt such as oil and grease that floats to the top of the sedimentation tank is removed by the skimmer. The process generates a significant amount of sludge, and sludge disposal is one of the biggest challenges.
A rotary biological contactor (RBC) is a type of aerobic reactor often used in textile wastewater treatment. The riser operates in circulation mode (sufficient fluid velocity to entrain particles), and the downcomer operates in conventional mode (low fluid velocity unable to entrain particles). So the downward flow of particles increases in the lower part due to their increased density.
The riser operates in the circulation regime (high enough fluid velocity to entrain particles), and the downer operates in the conventional regime (low fluid velocity unable to entrain particles). Thus, the downward flow of particles is enhanced in the lower part due to their increased density. Another reason for the popularity of the oxidation process is the production of more stable and less amount of sludge [139].
As part of H2O2 is used to oxidize alkali and forms dioxygen and H2O, H2O2 available for OH. the formation of radicals decreases, decreasing the decolorization efficiency [146]. Since some of the OH produced reacts with H2O2, the formation of OH is not proportional to the concentration of H2O2. So, which way the reaction will take place depends on the pH of the medium and the dose of ozone [152].
Usually ozone is used in accordance with UV or H2O2 for higher efficiency. The results of wastewater treatment by photocatalysis can be studied using a UV-Vis double beam spectrophotometer. The usefulness of microfiltration in the treatment of textile wastewater is limited due to the fact that it is analogous to more conventional coarse filtration methods [177].
When treating textile wastewater, ultrafiltration (UF) does not work satisfactorily for direct use.
Road towards ZLD: Resource Recovery from Wastewater
In this context, in the following sections of this article we study the state of the art for the recovery of two resources commonly used in the textile industry, namely salts and caustic solutions. Salts are used in the dyeing process to help fix colors to the fabric. As a result, significant amounts of total dissolved solids (TDS) and chlorides are produced in the wastewater, both of which are resistant to biodegradation.
In the event that it is not adequately treated before being released into the sewage network, it has the potential to inactivate the microorganisms used in the biological treatment procedures [200]. It is recommended that mercerization water be reused due to the enormous volume and high alkalinity of the water produced by the mercerization process. In circumstances such as these, treatment by thermal vaporization has been shown to be the only viable option.
Streams with certain concentrations can be recycled and condensation water is reused in the process. The influence of NaCl on the solubility behavior of Na2SO4 at different temperatures was studied by Bharmoria et al., along with the temperature dependence of the solubility transition of Na2SO4. According to their findings, when the amount of NaCl in the solution was increased to 15 wt%, the solubility of Na2SO4 increased.
Mercerizing is a type of alkaline treatment used in the textile industry during the preparation of fabrics to achieve a permanent shine, to increase the luster, hand and other attributes of the fabric. Therefore, the recovery of NaOH, which can be used in the causticization process, from the highly alkaline effluent from the main caustic bath discharges may be an attractive opportunity in the textile sector. The recovery and reuse of highly alkaline caustic in the textile sector have not been well covered in the literature, despite the fact that many researchers have examined the removal of dyes from textile wastewater [201].
The following section details a number of caustic treatments in textile wastewater research that have been reported in the literature. After concentration, the resulting caustic stream recovered about 98–100% NaOH in the feed and had a concentration of 30–40 g/L, making it suitable for recycling. Several caustic and dye/salt recovery techniques described above have shown encouraging results.
Conclusions
Performance evaluation of textile wastewater treatment techniques using sustainability index: An integrated fuzzy approach to assessment.J. Lema, J.M.; Martinez, S.S. Innovative Wastewater Treatment and Resource Recovery Technologies: Impact on Energy, Economy and Environment; IWA Publishing: London, UK, 2017. Wastewater Treatment and Reuse: A Review of Its Applications and Health Implications. Water Air Soil Pollut.
Performance evaluation of an aerobic fluidized bed bioreactor coupled to a tubular settler for hospital wastewater treatment.J. Baseline Assessment Study for a Wastewater Treatment Plant for Al Gozayyera Village, West Kantara City, Ismailia Province, Egypt. In the Network of Demonstration Activities for Sustainable Integrated Wastewater Treatment and Reuse in the Mediterranean; SWIM Sustain Water MED: Cairo, Egypt, 2013.
Performance evaluation of column SBR in paper and pulp wastewater treatment: Optimization and biokinetics.Desalting. After wastewater treatment: Photoassisted electrochemical degradation of 2-nitrophenol and orange II dye at a tungsten trioxide-exfoliated graphite composite electrode.Chem. In Electrochemical Water and Wastewater Treatment; Martínez-Huitle, C.A., Rodrigo, M.A., Scialdone, O., Eds.; Butterworth-Heinemann: Oxford, UK, 2018; pp.
Bioassays as a tool for evaluating advanced oxidation processes in water and wastewater treatment.Water Res. Advanced oxidation processes for in-situ hydrogen peroxide/hydroxyl radical production for textile wastewater treatment: a review.J. Continuous photocatalytic, electrocatalytic and photoelectrocatalytic degradation of a reactive textile dye for wastewater treatment processes: batch, microreactor and scaled-up operation.J.
Performance of a new ceramic microfiltration membrane based on kaolin in textile industry wastewater treatment.Chem.
![Figure 3. Schematic diagram of two types of Circulating Fluidized Bed Bioreactor containing a) two fluidization regimes, b) one fluidization regime [81]](https://thumb-ap.123doks.com/thumbv2/filepdfnet/10908762.0/9.892.261.828.710.1043/figure-schematic-circulating-fluidized-bioreactor-containing-fluidization-fluidization.webp)
![Figure 4. Schematic diagram of different components and zones of a UASB reactor [90].](https://thumb-ap.123doks.com/thumbv2/filepdfnet/10908762.0/11.892.261.783.153.435/figure-schematic-diagram-different-components-zones-uasb-reactor.webp)
