Capacitive Deionization (CDI) is an emerging water purification technology that removes salt and other charged contaminants using electrostatic adsorption. It works by applying a low voltage (1–2V) across two porous carbon electrodes, attracting dissolved ions from the water and storing them electrostatically. Once saturated, the electrodes discharge the ions, flushing them out.
2. Suitability for Jaffna Island Areas
Jaffna’s groundwater is slight to moderately saline (Total Dissolved Solids - TDS: 500–2000 mg/L) due to seawater intrusion. CDI is best suited for water with low to moderate salinity (TDS < 3000 mg/L), making it an ideal option for Jaffna’s conditions.
3. Key Advantages of CDI for Jaffna
Feature
CDI Benefits
Energy-Efficient
Uses ~0.5–1.5 kWh/m³, which is much lower than Reverse Osmosis (RO) (~3–6 kWh/m³).
Lower Water Wastage
Recovers up to 80–90% of input water, compared to RO, which wastes 30–50%.
Lower Maintenance
No high-pressure pumps or membranes like RO; only requires periodic electrode cleaning.
Eco-Friendly
Produces less brine waste than RO, reducing disposal issues in Jaffna’s sensitive environment.
Scalability
Can be used for household units (10–100 L/day) or community systems (1,000–50,000 L/day).
Works with Renewable Energy
Can be powered by solar panels, reducing operational costs.
4. Cost Analysis of CDI in Jaffna
Component
Household Unit (100 L/day)
Community Unit (10,000 L/day)
Initial Cost (LKR)
100,000 – 250,000
1.5M – 5M
Operating Cost (LKR/month)
1,500 – 3,000 (electricity + electrode cleaning)
15,000 – 40,000
Energy Requirement
20–100W
500–2000W (Can be solar-powered)
Filter Replacement
Every 2–3 years
Every 2–3 years
Water Recovery Rate
80–90%
80–90%
5. Challenges & Solutions
Challenge
Solution
Higher Initial Cost Than RO
Government or NGO funding for pilot projects; local manufacturing to reduce import costs.
Lower Removal Rate for High Salinity Water (>3000 mg/L TDS)
Pre-treatment with ion exchange or Nanofiltration (NF) for very saline areas.
Technology Awareness
Conduct workshops and training for local engineers and communities.
Disposal of Wastewater (10–20%)
Use for non-drinking purposes like irrigation or flushing.
6. Implementation Strategy for Jaffna
Phase 1: Pilot Project (1–2 Years)
Install small CDI units in selected villages (household & community level).
Monitor performance, cost-effectiveness, and social acceptance.
Phase 2: Scaling Up (3–5 Years)
Expand CDI systems with solar power integration to reduce electricity dependency.
Establish local manufacturing or assembly units to reduce costs.
Phase 3: Long-Term Sustainability (5+ Years)
Government & NGO involvement for subsidized CDI installations in water-stressed areas.
Public-private partnerships (PPPs) to maintain and operate CDI plants efficiently.
7. Conclusion & Recommendation
📌 CDI is a highly feasible, cost-effective, and eco-friendly water purification technology for Jaffna Island areas, especially for groundwater with low to moderate salinity (500–2000 mg/L TDS). 📌 It provides higher water recovery, lower energy use, and reduced maintenance compared to RO, making it ideal for decentralized household and community-scale applications. 📌 With proper funding and local implementation, CDI can be a game-changer for safe drinking water in Jaffna’s coastal and island communities.
Karainagar, Jaffna, faces brackish water issues due to seawater intrusion into groundwater sources. Cost-effective methods to purify slightly salted water in this region include:
1. Rainwater Harvesting (RWH)
Best for: Households, community-level water supply
Cost: Low (Rs. 50,000–150,000 for a domestic system)
Advantages: Fresh, non-saline water source, sustainable
Implementation: Install rooftop collection systems with storage tanks, first-flush diverters, and filtration (sand/charcoal filters)
2. Reverse Osmosis (RO)
Best for: Small community-scale desalination
Cost: Medium (Rs. 500,000–2 million for a small plant)
Advantages: Removes salts, impurities, and pathogens
Implementation: To reduce electricity costs, use small solar-powered RO units for remote areas.
3. Solar Desalination (Solar Stills)
Best for: Individual households, small communities
Cost: Low to medium (Rs. 30,000–100,000 per unit)
Advantages: Low maintenance, uses free solar energy
Implementation: Solar stills are used to evaporate and condense clean water, suitable for sunny climates.
Adaptability and Scalability
Household-Level Use: Individuals can set up solar stills in their homes, ensuring a personal water source.
Community-Based Installations: Multiple units can be installed in schools, community centres, or local cooperatives to provide clean drinking water for a larger population.
Customizable for Different Needs: Depending on water demand, different designs (e.g., single-basin or multi-effect stills) can be used to maximise output.
Multi-Effect Solar Still (Higher Output)
Design: Uses multiple evaporation-condensation stages to improve efficiency.
Efficiency: Produces 5–10 liters per day per square meter.
Advantages:
Higher water output compared to a single-basin still
More efficient in water-scarce areas
Best for: Small community clusters (10–20 households).
Case Studies of Successful Implementations
A. Solar Still Use in Gujarat, India
Problem: Coastal villages in Gujarat faced saline groundwater issues similar to Jaffna.
Solution: Community-based solar stills were installed, producing 5–7 liters per person per day.
Outcome:
Improved water security for over 200 families.
Reduced dependence on expensive bottled water.
Easy maintenance and community-managed operation.
B. Solar Desalination in Thar Desert, Pakistan
Problem: Limited freshwater sources due to arid climate.
Solution: Villages implemented solar stills with black-coated basins to increase efficiency.
Outcome:
Clean drinking water supply for households.
Sustainable use of abundant sunlight.
C. Solar Water Purification in Rural Africa
Problem: Contaminated and saline water sources.
Solution: Solar stills were installed in schools and health centers.
Best for: Areas with slightly saline water (low TDS)
Cost: Medium (Rs. 100,000–500,000 for small plants)
Advantages: Energy-efficient compared to RO, less waste brine
Implementation: Pilot projects in Jaffna could explore its feasibility.
Real-world examples where Capacitive Deionization (CDI) has been successfully implemented for water purification, particularly in coastal and water-scarce regions similar to Jaffna:
1. India - Rajasthan (Desert Areas)
Location: Barmer & Jodhpur districts, Rajasthan
Water Challenge: High salinity in groundwater due to arid conditions
Solution: Solar-powered CDI units installed in rural villages
Outcome: Provided safe drinking water with 80-90% recovery rate, significantly reducing brine waste compared to RO.
Relevance to Jaffna: Similar water salinity issues and potential for solar integration.
2. South Korea - Island Villages
Location: Small islands off South Korea’s coast
Water Challenge: Limited freshwater sources, high cost of water transport
Solution: Decentralized CDI units installed in community centers
Outcome: Reliable, cost-effective desalination without needing large-scale RO plants.
Relevance to Jaffna: Demonstrates CDI’s effectiveness in island environments.
3. China - Coastal Towns (Shandong Province)
Location: Shandong Province, China
Water Challenge: Seawater intrusion into groundwater supplies
Solution: Government-backed CDI plants for drinking water purification
Outcome: Large-scale CDI adoption reduced reliance on bottled water and RO desalination.
Relevance to Jaffna: Highlights potential for policy-driven CDI implementation at scale.
4. Netherlands - Agricultural Water Purification
Location: Greenhouse farms in the Netherlands
Water Challenge: High salinity affecting crop irrigation
Solution: CDI-based desalination for irrigation water
Outcome: Reduced soil salinity and improved crop yield.
Relevance to Jaffna: Can be applied for agriculture and livestock water needs.
What This Means for Jaffna
CDI has been successfully tested in coastal, arid, and island regions worldwide.
The solar-powered CDI model used in Rajasthan and South Korea is especially relevant for Jaffna.
Government-backed or community-scale CDI plants like in China and the Netherlands could be replicated in Sri Lanka.
5. Constructed Wetlands & Bio-Filters
Best for: Community-level water treatment
Cost: Low to medium (Rs. 200,000–1 million depending on scale)
Implementation: Use salt-tolerant plants (e.g., mangroves, vetiver) to filter saline water. Using salt-tolerant plants like mangroves and vetiver grass for filtering saline water is a sustainable and eco-friendly approach. Here’s how they help in managing saline water:
1. Mangroves for Saline Water Filtration
Salt Excretion & Filtration: Some mangrove species (e.g., Avicennia marina) excrete salt through their leaves, reducing salinity in the surrounding water.
Sediment Trapping: Their complex root systems trap sediments and pollutants, improving water quality.
Coastal Protection: Mangroves stabilize shorelines and prevent saltwater intrusion into freshwater sources.
2. Vetiver Grass for Salinity Control
Deep Root System: Vetiver (Chrysopogon zizanioides) has a dense root system that absorbs excess water and stabilizes soil in saline-prone areas.
Phytoremediation: It absorbs heavy metals and excess nutrients, improving water quality.
Soil Reclamation: Vetiver helps reclaim saline-affected soils, making them suitable for agriculture.
Application in Irrigation & Wastewater Management
Constructed Wetlands: These plants can be used in wetlands to treat saline wastewater from agriculture, aquaculture, and industry.
Desalination Support: Pre-treatment with vegetation can reduce the load on desalination plants by removing sediments and organic matter.
Biosaline Agriculture: These plants help in reclaiming saline lands, making them productive for other crops.
Implementation Strategies for Using Salt-Tolerant Plants in Saline Water Filtration
The selection and application of mangroves, vetiver, and other salt-tolerant plants depend on the site conditions, salinity levels, and project goals. Below are tailored strategies for different applications:
1. Coastal and Estuarine Areas – Mangrove-Based Filtration
Best for: Protecting shorelines, filtering brackish/saline water, and preventing saltwater intrusion.
Implementation Steps:
✅ Site Selection:
Identify intertidal zones where mangroves naturally thrive (salinity range: 10-35 ppt).
Avoid highly eroded areas unless supported by sediment trapping measures.
✅ Species Selection:
High Salinity:Avicennia marina (Grey mangrove) – salt-excreting species.
Use nursery-grown seedlings or direct planting methods.
Maintain buffer zones to allow natural regeneration.
Monitor for growth, survival rates, and pollution removal efficiency (e.g., heavy metals, nutrients).
✅ Expected Outcomes: ✔ Reduces salinity intrusion into groundwater. ✔ Enhances coastal water quality by filtering pollutants. ✔ Provides habitat for biodiversity and supports fisheries.
2. Inland & Agricultural Lands – Vetiver Grass for Saline Water Filtration
Best for: Treating saline wastewater, rehabilitating salt-affected soils, and stabilizing embankments.
Implementation Steps:
✅ Site Selection:
Choose areas with moderate to high salinity (EC: 4-15 dS/m).
Ideal for agricultural drainage canals, irrigation channels, and salt-affected farmlands.
✅ Planting Method:
Spacing: 10-15 cm apart in hedgerows along drainage lines or bunds.
Depth: Plant 15 cm deep to ensure strong root anchoring.
Water initially for establishment, then rely on natural moisture.
✅ Maintenance:
Trim leaves periodically (used for fodder or mulch).
Monitor soil EC levels and adjust planting density if needed.
✅ Expected Outcomes: ✔ Absorbs excess nutrients (N, P) and heavy metals. ✔ Reduces soil erosion and salinity accumulation. ✔ Enhances wastewater quality before reuse in agriculture.
3. Constructed Wetlands for Saline Wastewater Treatment
Best for: Municipal and industrial wastewater treatment with moderate salinity levels.
Implementation Steps:
✅ Design Considerations:
Use a hybrid system with mangroves, vetiver, and other halophytes (e.g., Salicornia).
Combine surface flow wetlands (mangroves) with subsurface flow (vetiver) for better filtration.
✅ Water Quality Parameters:
Target salinity: <15 ppt for optimal plant function.
Monitor for: Nitrogen, phosphorus, heavy metals, and suspended solids.
✅ Expected Outcomes: ✔ Reduces salinity, organic pollutants, and toxins in wastewater. ✔ Produces biomass for biofuel or fodder. ✔ Supports sustainable water reuse in irrigation.
Key Considerations Before Implementation
🔹 Water Salinity Testing – Determine site-specific salt tolerance levels. 🔹 Hydraulic Load & Retention Time – Optimize water flow rates in treatment systems. 🔹 Regulatory Compliance – Check environmental laws for wetland restoration or wastewater discharge. 🔹 Community Engagement – Involve local communities in mangrove conservation and wetland maintenance.
Case Study & Project Design Framework for Using Salt-Tolerant Plants in Saline Water Filtration
To develop an effective mangrove- or vetiver-based saline water filtration system, let’s look at a case study followed by a custom project design framework.
📌 Case Study: Mangrove & Vetiver-Based Filtration in Saline Water Management
🔹 Location: Coastal Bangladesh
Problem: Agricultural fields and freshwater ponds were affected by saltwater intrusion due to rising sea levels and tidal surges.
Solution: A combination of mangrove buffer zones and vetiver hedgerows was implemented.
Results: ✅ 25-30% reduction in salinity levels in groundwater after 2 years. ✅ Improved water retention and soil fertility, enabling the growth of salt-resistant crops. ✅ Increased fish productivity due to better water quality in aquaculture ponds.
📌 Project Design Framework for Saline Water Filtration
This framework outlines a step-by-step plan for implementing salt-tolerant plant-based filtration in your region.
🌿 Step 1: Site Selection & Assessment
✅ Identify areas affected by salinity intrusion (coastal, estuarine, or inland). ✅ Measure:
Soil Salinity (EC in dS/m) – Test at multiple points.
Water Salinity (ppt or TDS mg/L) – Assess seasonal variations.
Water Flow & Drainage – Determine suitable planting locations.
🔹 Example:
If EC > 10 dS/m, prioritize mangroves in tidal areas.
If EC between 4-10 dS/m, use vetiver in agricultural drainage zones.
Ensure natural tidal flushing for effective salt removal.
Avoid water stagnation by maintaining tidal creek flow.
🔹 Vetiver Wetlands:
Use a subsurface flow system to maximize water retention.
Introduce baffle structures to enhance pollutant removal.
✅ Regular Monitoring:
Monthly water salinity testing (ppt or EC values).
Soil quality assessment every 6 months.
Vegetation health & biomass measurements.
📊 Step 4: Expected Outcomes & Benefits
1️⃣ Reduction in Water Salinity (15-40%)
Improves irrigation water quality for agriculture.
2️⃣ Soil Salinity Improvement (10-30%)
Enhances land productivity for biosaline agriculture.
3️⃣ Wastewater Treatment (Nutrient & Metal Removal)
Vetiver removes nitrogen (N) by 50-70% and phosphorus (P) by 40-60%.
Mangroves capture heavy metals (Pb, Cd) in sediments.
4️⃣ Sustainable Land & Water Use
Supports aquaculture and agroforestry.
Promotes biodiversity conservation.
⚙️ Step 5: Scaling Up & Integration
✅ Pilot Project (1-2 years): Start with a 10-20 ha area to test effectiveness. ✅ Community Engagement: Train local farmers in vetiver planting and mangrove conservation. ✅ Integration with Irrigation Systems: Link with constructed wetlands for water reuse. ✅ Funding Sources: Explore government subsidies, foreign aid (e.g., ADB, World Bank), or CSR funding for environmental restoration.
6. Nanofiltration (NF)
Best for: Water with low-to-moderate salinity
Cost: Medium (Rs. 400,000–1.5 million)
Advantages: More efficient than RO for slightly saline water, requires less energy.
Implementation: NF units for household/community level.
Community-Level NF Plants (Medium Scale)
Capacity: 1,000–10,000 liters per day.
Best For: Schools, small villages, hospitals, or places with brackish groundwater.
Advantages: Provides clean water for 100+ people per day, lower operational cost than RO.
Why NF is a Game-Changer for Karainagar ✔ Energy-efficient & cost-effective solution for reducing salinity in well water. ✔ More sustainable than high-energy RO plants. ✔ Can be implemented at household, community, and municipal levels. ✔ Ensures long-term drinking water security for Karainagar’s residents. The cost of the NF unit itself varies based on capacity and manufacturer. For instance, a 100-gallon-per-minute (GPM) commercial-quality NF system can cost around $250,000.
A basic 5 to 10 gallons per minute (GPM) NF system might cost less than $60,000.
Here’s a cost-benefit comparison table for the different water purification methods suitable for slightly salted water in Karainagar, Jaffna:
Method
Initial Cost (LKR)
Operating Cost
Efficiency
Energy Requirement
Advantages
Challenges
Rainwater Harvesting (RWH)
50,000 – 150,000
Low (Only tank cleaning & minor repairs)
High (Freshwater)
None
Sustainable, low-maintenance, free water source
Seasonal dependence requires storage tanks
Reverse Osmosis (RO)
500,000 – 2 million
High (Electricity, filter replacement)
Very High (Removes 99% salts & contaminants)
High
Effective desalination, widely used
High waste brine, high energy use
Solar Desalination (Solar Stills)
30,000 – 100,000
Very Low
Medium (Removes ~98% of salts)
Low (Solar energy)
No electricity needed, low maintenance
Slow water production requires sunny conditions
Capacitive Deionization (CDI)
100,000 – 500,000
Medium (Electrode replacement, low power use)
Medium-High (Removes 60-90% salts)
Low
Energy-efficient produces less waste than RO
Still developing technology, limited availability
Constructed Wetlands & Bio-Filters
200,000 – 1 million
Low
Medium (Removes salts gradually, improves groundwater quality)
