Abstract: The textile industry, a prominent water polluter, faces increasing pressure due to evolving environmental regulations. Recognising the urgent need for sustainable practices, we, SAVANNA WATER TECHNOLOGIES Pvt. Ltd presents insights into Zero Liquid Discharge (ZLD) Effluent Treatment Plants (ETP). The industry’s extensive water consumption, particularly in dyeing and finishing processes, contributes significantly to water pollution. Our study reveals that the Indian textile industry consumes 200-250 litres of water per kilogram of cotton cloth, surpassing global benchmarks. Through water conservation efforts, we aim to mitigate the environmental impact by recycling water within processes and achieving ZLD.
Part 1 of this article focuses on inlet effluent characteristics and the general treatment flow chart for ZLD. Textile processes, especially dyeing, contribute 15-20% of total wastewater flow, containing residues of dyes and chemicals. The proposed ZLD module addresses these challenges, emphasising the importance of sustainable water management practices.
As environmental stewards, we aim to provide essential knowledge to enable the textile industry to adapt, sustainably meet environmental requirements, and ensure our global existence. The selected wastewater treatment process for the textile industry involves a systematic approach, integrating anaerobic and aerobic treatments with advanced filtration techniques to achieve comprehensive water purification.
- Initial Effluent Handling:
- Effluent from dyeing and washing undergoes screening in a Bar Screen to remove fibrous materials and solid particles.
- Directed to an Equalization Tank for homogenisation and cooling, maintaining a temperature below 38°C.
- Anaerobic Treatment:
- Effluent undergoes mixing, homogenisation, and pH neutralisation before entering an Anaerobic Digester with a 48-hour retention time.
- Expected reductions: COD & BOD (60-70%), colour (70-80%).
- Hybrid Anaerobic Digester and Coagulation:
- Subjected to coagulation using polymer-based decolourant (CRP), PAC, and polyelectrolyte.
- Coagulated matter settles in a primary clarifier, with the settled sludge directed to sludge drying beds/filter press for dewatering.
- Aerobic Biological Treatment:
- Effluent, treated in the Anaerobic Digester, undergoes further biological treatment in an Aeration Tank.
- Optimise oxygen transfer efficiency by using an energy-efficient diffused aeration system with a non-buoyant Diffuser grid.
- Secondary Clarification:
- Treated effluent and activated sludge move to a secondary clarifier, where biomass settles.
- Recirculation of settled biomass maintains optimal MLSS levels for the activated sludge process.
- Tertiary Clarification and Chemical Addition:
- Overflow from the secondary clarifier, containing residual colour, is treated with CRP and PAC.
- The effluent enters a Tertiary Clarifier with a low-speed racked arm for sludge removal.
- Advanced Filtration and Water Recovery:
- Overflow from the tertiary clarifier undergoes Sand and Carbon filtration, followed by a 4-stage RO Plant for water recovery.
- RO reject is sent to an NF Plant for Brine Solution Recovery, and NF reject is processed in an MEE Evaporator for condensate recovery.
- The mother liquor from MEE is directed to ATFD, and the recovered mixed salt is stored in a closed shed.
- Proposed Upgrade:
- To maximise water recovery, A pre-treatment stage is proposed, including an MF (Microfiltration) Plant and a 4-stage RO Plant.
This integrated approach showcases the industry’s commitment to sustainable water management, reducing COD, BOD, and colour. The proposed upgrade with pre-treatment and advanced filtration technologies aligns with the evolving need for enhanced water recovery and environmental responsibility in the textile industry. The comprehensive treatment system efficiently minimises environmental impact while maximising water reuse.
