## 2 Centralized Treatment Plants
### Industrial Wastewater Remediation
#### 2.3.3 Textile Industry  
The textile industry WW, 20% of total wastewater produced by all industries, contains non-degradable organic materials, toxic substances, surfactants, organic halogens, heavy metals, salt, dissolved solids and, most of all, dyes which are resistant to biotransformation and photodegradation. Conventional physicochemical processes are usually indicated and eventually combined with biological treatment for textile WW reclamation. Their limitations are low color removal and formation of residual sludge. Adsorption techniques have occupied a prominent place in recent times owing to their low cost, flexibility, ease of operation and lower energy consumption and have been the subject of a recent review [89].  
On the other hand, advanced treatment technologies based on membrane processes obtained satisfactory results in the treatment of textile WW. The pilot- and full-scale applications of membrane technologies have been recently reviewed by [PERSON] et al., highlighting the particular efficiency of hybrid systems and the need to obtain more data from the full-scale application of these treatments [90].  
A less expensive but still efficient treatment train was implemented at pilot scale by adopting two bio-based, combined processes: an AMC (Anaerobic Microorganism Carrier)-UASB (Upflow Anaerobic Sludge Blanket) and a PBG (Porous Bio-Gel)-MBBR (moving bed biofilm reactor), which operated for 118 days. UASB and MBBR reactors were established and inoculated with municipal anaerobic sludge and municipal aerobic sludge, respectively, and connected in series to enhance the treatment efficiency. This strategy allowed for both highly efficient nutrient removal and sludge reduction, representing the best choice for upgrading the traditional process of the sewage treatment plant. The co-metabolism among dominant species achieved the effective removal of color (84%), organic matter and ammonia nitrogen. The dual-carrier bioprocess has the advantage of easy operation, free of membrane fouling, at low cost [91].  
The combination of moving bed biofilm and membrane technologies in textile WW remediation was tested and compared to the conventional activated sludge (CAS) treatment. A hybrid MBBR-MBR pilot plant was designed and built to evaluate its economic and environmental feasibility at industrial scale. The overall operation lasted 222 days, and removal values were COD (93%), color (85%) and TSS (99%), with 1-day hydraulic retention time (HRT). The possibility to reduce HRT by 50% with the application of industrial scale is very attractive. Reclaimed water was employed in new dyeing processes, and 100% achieved new dyeing, replacing 70% of the textile industry's water consumption. The values of Capital Expenditure (CAPEX) calculated for the hybrid MBBR-MBR system are profitable because of the reduction in effluent discharge tax and the decolorizing agent saved. The results of the Net Present Value (NPV) and the Internal Rate of Return (IRR) of 18% suggested that MBBR-MBR is financially applicable for implantation into the industrial scale. The treatment showed lower environmental impacts in the life cycle assessment (LCA) study, especially in the category of climate change, thanks to the avoidance of using extra decolorizing agents [92].  
A modified design of a pilot-scale micro-pre-treatment unit using a solar-triggered AOP reactor demonstrates complete remediation of textile effluent with effective reuse of the discharge for different industrial purposes. After a controlled coagulation-flocculation process, the effluent is passed through chemically modified sand filters acting as an adsorbent for the removal of color. This stage is followed by a batch photocatalysis reactor for remediation by solar irradiation through a ZnO/ZnO-GO NanoMat-based AOP. The remaining color and other organic compounds were removed by polyacrylamide fiber and activated carbon filtration steps. The installed pilot treatment plant remediates textile effluent, resulting in a zero liquid discharge (ZLD) system [93].