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Membrane Technology: Unique Solution for Waste Water Treatment & Reuse for Industrial Water
Hyflux Ltd has recognized vital drivers to present its membrane based technology for waste water treatment and reuse in the Indian market, oscillating from treating sewage up to industrial grade water, to the model of integrated membrane solutions for Zero Liquid Discharge (ZLD). The article discusses about treatment schemes, case studies along with latent applications, innovative membrane technologies for cooling tower blow down and ZLD in power plants.
A ZLD system encompasses treatment to the waste generated from the water treatment process & produces the good quality of water to recycle it back to the main process. Discharge from the ZLD plant is only in solids form which can be disposed easily. There are wide ranges of advanced wastewater treatment technologies to recycle, recovery and reuse of the 'treated' wastewater and thereby ensure there is no discharge of wastewater to the environment.

In power plants, fresh water consumption is very high in terms of steam generation, cooling tower make up. Over a period of time cooling water gets saturated with minerals & needs to be bleed off/ blow down from the cooling tower. This waste cooling tower blow down water we can recycle back to the Cooling Tower by giving membrane based treatment & waste generated from the CTBD treatment can be reused in the different processes of Power plant.

The article deliberates about the prevailing Hyflux installations on subsequent applications of industrial waste water:
  • Cooling tower blow down water - Power Plant
  • Secondary treated waste water to Boiler feed water - Chemical & fertilizer Plant
  • Waste water treatment through membrane system for ZLD plant - Textile effluent
Case Study 1: National Thermal Power Corporation (NTPC) Jhajjar ZLD

NTPC used a conventional Clarification, multi-grade filtration pre-treatment system for the Ultra Filtration & reverse osmosis (RO) process at a Cooling Tower Make Up plant. The plant recycles Cooling Tower Blow Down into high-grade industrial water for cooling Tower makeup & high grade of boiler feed water.

Treatment Process
Cooling water used in the power plant primarily for condensation of steam and auxiliary heat transfer needs & it is recycled back to the cooling tower. Over a period of time high mineral concentration at cooling water will be bleed off / blow down. Simultaneously it will get replaced with cooling tower make up water. This cooling tower blow down (CTBD) water needs to be treated & recycled back to cooling tower as cooling tower make up and for production of boiler feed water.


Hyflux Ultrafiltration Installation on Cooling Tower Blow Down Recycle


Treatment Scheme


Cooling Tower Make Up Analysis

CTBD treatment plant has a membrane system (UF/RO) system installed to produce high quality of water which can be reused as a cooling tower make up & also as boiler feed water. A conventional high rate clarification followed by multigrade filtration pre-treatment system is used before the UF & RO process to remove suspended solids, organics & microorganisms, and salts. Clarified water from pre-treatment is fed to the UF system to achieve SDI less than 3, to make it suitable for RO process. UF system is operating at 95% recovery.

UF permeate water is feeding to RO system to reduce TDS from 2080 ppm to cooling water make up quality (TDS – less than 100 ppm). RO system is operating at 85% recovery. High concentrated RO reject (13500 ppm) is recycled back to Coal Handling plant for Ash suppression. As a result there is no waste disposed to environment in a liquid from.

Case Study 2: Rashtriya Chemicals and Fertilizers (RCF), Mumbai
RCF, a government-owned company and one of the leading fertiliser producers in India, uses ultra-filtration membrane technology followed by the reverse osmosis (RO) process at a sewage recycling plant. The plant recycles municipal sewage into high-grade industrial water for chemical and fertiliser production processes.

Treatment Process
Municipal sewage is collected from the city and treated into high-grade industrial water for chemical and fertiliser production processes. Pretreatment scheme correct the pH and homogenize to remove floating particles and scheme of aeration. Biological treatment to reduce the BOD and COD value and pass into the scheme of clarifier. Adding chemicals for flocculation and coagulation and settled the sludge TSS particle in the secondary clarifier and high rate clarifier.

Treatment Scheme

Rapid gravity filter, Pressure sand filter and cartridge filter has been replaced by the Ultrafiltration system. Ultra filtration removes the suspended and turbidity particle and RO remove all dissolved particles and colors.

By treating domestic/municipal sewage we are producing good quality water which can be reused in process as boiler feed water (TDS less than 100 ppm). In this way we are reducing the wastage of water upto 80% by treating and reusing domestic sewage in Industrial applications.

Case Study 3: Jay Jay Mills, Tiruppur, Tamil Nadu
Textile Company Jay Jay Mills was established in 1971 in Tirupur in the South Indian state of Tamil Nadu as a manufacturer of Cotton Knitwear. Jay Jay mills were keen to improve the quality of the waste water discharge from one of its factories while lowering water consumption.

Treatment Process
To reclaim the waste water, a combined UF and RO waste water treatment was required. The entire treatment process involved a number of steps to remove lint, chemicals and large suspended solids before the waste water was feed into the UF-RO system.

Waste water from the textile industry is generated from chemical processing and dyeing process of textiles.


Treatment Scheme

In the pretreatment, correct the pH and homogenization is done to remove floating particles. Textile effluent is treated biologically further to reduce the BOD and COD in the water followed by electro chlorination. Chemicals like coagulant & flocculants are dosed in pretreatment for coagulation and flocculation. Flocculated particles are settled in the clarifier. Clarified water is fed to Pressure sand filter to reduce the suspended particle and to ACF to remove the chlorine, turbid particle and colour if any.

Treated water recycles back to textile process and final reject is evaporated in 4 stage Multiple effect evaporator. Final reject from the RO plant having 45000 ppm concentration which is concentrating upto 350000 ppm. Condensate from the evaporation plant is having 100 ppm TDS which we is blended with the RO permeate water. Slurry from evaporator of 35% concentration is fed to the centrifuge for further recovery of water. Output of the centrifuge is sodium chloride salts & filtrate is recycled back to the feed water tank.


Water Quality at Different Stages

Conclusion
Membrane based treatment process is the utmost dire & significant process to accomplish Zero Liquid Discharge through a ZLD process plant. ZLD plants are advantageous in realizing various advantages to the industries and environment when compared to other conservative methods.
  • Reclaim a scarce water resource.
  • ZLD technology is beneficial for the plant's water management; encouraging close monitoring of water usage, avoiding wastage and promotes recycling
  • Possibility of use of sewage for recovery of water, for Industrial and municipal use, using ZLD technologies.
  • Reduce wastewater discharge by as much as 70-80%.
  • A more sustainable growth of the industry while meeting most stringent regulatory norms
  • Reuse of consistent, high-quality water source for lower cost than the cost of purchased water.
  • Increase operating profit by reusing an existing resource
  • Reduction in water demand from the Industry frees up water for Agriculture and Domestic demands.