Project Name: Drain Water Harvesting at Shahdara Link Drain (Water flow is 18 MLD)
Plant capacity = 10 kL
Project Location: P6, Ranney Well Near Akshardham, Delhi
Aim to: (1) Showcase that Drain water is an ignored resource that can be utilized (2) Recharge of groundwater table (3) Cleaning of Yamuna and (4) Augmentation of Water supply
Methods used: Electrocoagulation, UV Filtration, RO Filtration & Geotextile Tube bag
In this process, the electro-dissolution of sacrificial anodes, usually made of aluminum or iron, to the wastewater leads to the formation of hydrolysis products (hydroxo- metal species) that are effective in the destabilization of pollutants. The electrochemical reduction of water in the cathode produces hydrogen bubbles that can promote a soft turbulence in the system and bond with the pollutants, decreasing their relative specific weight. In addition, the generated hydrogen can be collected and used as fuel to produce energy. This treatment has been successfully introduced in removing suspended solids, dyes, heavy metals, arsenic, hardness, phosphate, fluoride, pesticides and natural organic matter from wastewater.
For the use of electrocoagulation, there are some advantages such as requiring only simple equipment, ease of operation, less treatment time, use of less or no chemicals, and smaller amount of sludge.
The Drain water is lifted from Shahdara Link Drain, passed through electrocoagulation, then settling chambers, then passed through Sand-Carbon Filter & Multi grade filter to achieve Horticulture grade water. For achieving groundwater recharge grade water, the horticulture grade water is passed through Ultraviolet filtration. For achieving drinking water grade, the groundwater recharge grade water is passed through RO filtration. The groundwater recharge grade water is then put into a pit (preferably a rainwater harvesting pit or a normal pit) for percolation into ground.
- EC Feed Pump
The water flowing in open drain is treated as source of inlet, media to be treated for the process. This drain water is lifted through a sewage submersible pump and is pumped to EC skid.
- EC Skid
The basic EC unit typically consists of an electrolytic cell with an anode and cathode metal electrodes connected externally to a DC power source and immersed in the solution to be treated. Iron and aluminum electrodes are the most extensively used metals for EC cells since these metals are available, non-toxic and proven to be reliable. Although EC is considered to be quite similar to Chemical Coagulation/Flocculation (CC/CF) in terms of the destabilization mechanism, it still differs from CC/CF in other aspects such as the side reactions occurring simultaneously at both electrodes.
During electrocoagulation, the most important chemical reactions involve the dissolution of metal cations at the anode and formation of hydroxyl ions and hydrogen gas at the cathode Fig.1,
In this process, the electro-dissolution of sacrificial anodes, usually made of aluminum or iron, to the wastewater leads to the formation of hydrolysis products (hydroxo- metal species) that are effective in the destabilization of pollutants. The electrochemical reduction of water in the cathode produces hydrogen bubbles that can promote a soft turbulence in the system and bond with the pollutants, decreasing their relative specific weight. In addition, the generated hydrogen can be collected and used as fuel to produce energy. This treatment has been successfully introduced in removing suspended solids, dyes, heavy metals, arsenic, hardness, phosphate, fluoride, pesticides and natural organic matter from wastewater.
For the use of electrocoagulation, there are some advantages such as requiring only simple equipment, ease of operation, less treatment time, use of less or no chemicals, and smaller amount of sludge.
The Drain water is lifted from Shahdara Link Drain, passed through electrocoagulation, then settling chambers, then passed through Sand-Carbon Filter & Multi grade filter to achieve Horticulture grade water. For achieving groundwater recharge grade water, the horticulture grade water is passed through Ultraviolet filtration. For achieving drinking water grade, the groundwater recharge grade water is passed through RO filtration. The groundwater recharge grade water is then put into a pit (preferably a rainwater harvesting pit or a normal pit) for percolation into ground.
The current passes through a metal electrode, oxidizing the metal (M) to its cation (Mn+). Simultaneously, water is reduced to hydrogen gas and the hydroxyl ion (OH−). Electrocoagulation thus introduces metal cations in situ, using sacrificial anodes (typically iron or aluminum) that need to be periodically replaced. The cations (Al3+, Fe2+, etc.) destabilize colloidal particles by neutralizing charges. They also produce monomeric and polymeric hydroxide complex species as coagulants.
Mn+ –
(aq) + nOH (aq) → M(OH)n(s)
These coagulants form amorphous metal hydroxide precipitates. Their high adsorption properties impart strong affinity for dispersed particles and dissolved pollutants. Thus the pollutants can be separated from aqueous phase by coagulation.
The hydrogen bubbles at cathode promote turbulence in the system and bond with the pollutants, decreasing their relative specific weight. Consequently, they enhance the separation process by flotation.
- Poly Dosing System, Flash Mixture &Tube Settler
After treatment of wastewater in Electrocoagulation tank, wastewater flows to Tube settler clarifier via a Flash mixing tank, The polymer is stored in poly dosing tank which is dosed to flash mixture continuously through a dosing pump. The polymer is used to flocculate the sludge particles
Tube settler use multiple tubular channel sloped at an angle of 60° and adjacent to each other, which combine to form an increased effective settling area. This provides for a particle settling depth that is significantly less than the settling depth of a conventional clarifier, reducing settling times. Tube settlers capture the settle able fine flock that escapes the clarification zone beneath the tube settlers and allows the larger flock to travel to the tank bottom in a more settle-able form. The tube settler’s channel collects solids into a compact mass which promotes the solids to slide down the tube channel
- Filter Feed Tank
Overflow of Tube settler clarifier flows to filter feed tank via gravity,…..
- Filter Feed Pump
The water stored in filter feed tank is pumped to dual media filter through filter feed pump
- Multi Grade Filter (MGF)
Multigrade filter is a depth filter that makes use of coarse and fine media mixed together in a fixed proportion. This arrangement produces a filter bed with adequate pore dimensions for retaining both large and small suspended particles. This filter performs at a substantially higher specific flow rate than conventional filters. Specific flow rates of 0.82 – 1.64 ft/min have been successfully obtained for treating waters containing 25 – 50 ppm suspended solids respectively to produce filtrate with less than 5 ppm.
Features
- Activated Carbon Filter (ACF)
Carbon filtering is a method of filtering that uses a bed of activated carbon to remove contaminants and impurities, using chemical absorption. Activated carbon works via a process called adsorption, whereby pollutant molecules in the fluid to be treated are trapped inside the pore structure of the carbon substrate. Carbon filtering is commonly used for water purification. Typical particle sizes that can be removed by carbon filters range from 0.5 to 50 micrometres. The particle size will be used as part of the filter description. The efficacy of a carbon filter is also based upon the flow rate regulation. When the water is allowed to flow through the filter at a slower rate, the contaminants are exposed to the filter media for a longer amount of time. These so-called active, or activated, charcoals are widely used to adsorb odorous or colored substances from gases or liquids. The word adsorb is important here. When a material adsorbs something, it attaches to it by chemical attraction. The huge surface area of activated charcoal gives it countless bonding sites. When certain chemicals pass next to the carbon surface, they attach to the surface and are trapped.
- Geo Tube
Media after treatment from EC skid is pumped into the Geotube bag. Environmentally-safe polymers are added to the sludge, which makes the solids bind together and water separate. The Geotube bag’s unique fabric confines the fine grains of the material.
Clear effluent water simply drains from the Geotube bag through the small pores in the specially engineered textile. This results in effective dewatering and efficient volume reduction of the contained materials. The volume reduction allows for repeated filling of the Geotube bag. Over 90-95% of solids are captured, and clear filtrate can be collected and recirculated through the system. The decanted water is often of a quality that can be reused/returned for processing or returned to native waterways without additional treatment. After the final cycle of filling and dewatering, the solids remain in the bag and continue to densify due to desiccation as residual water vapor escapes through the fabric. Volume reduction can be as high as 90 percent. When full, the Geotube bag and contents can be deposited at a landfill, remain on-site, or the solids can be removed and land-applied when appropriate.
- Reverse Osmosis (RO)
Reverse Osmosis works by using a high pressure pump to increase the pressure on the salt side of the RO and force the water across the semi-permeable RO membrane, leaving almost all (around 95% to 99%) of dissolved salts behind in the reject stream. The amount of pressure required depends on the salt concentration of the feed water. The more concentrated the feed water, the more pressure is required to overcome the osmotic pressure.
The desalinated water that is demineralized or deionized, is called permeate (or product) water. The water stream that carries the concentrated contaminants that did not pass through the RO membrane is called the reject (or concentrate) stream.
As the feed water enters the RO membrane under pressure (enough pressure to overcome osmotic pressure) the water molecules pass through the semi-permeable membrane and the salts and other contaminants are not allowed to pass and are discharged through the reject stream (also known as the concentrate or brine stream), which goes to drain or can be fed back into the feed water supply in some circumstances to be recycled through the RO system to save water. The water that makes it through the RO membrane is called permeate or product water and usually has around 95% to 99% of the dissolved salts removed from it.
It is important to understand that an RO system employs cross filtration rather than standard filtration where the contaminants are collected within the filter media. With cross filtration, the solution passes through the filter, or crosses the filter, with two outlets: the filtered water goes one way and the contaminated water goes another way. To avoid build up of contaminants, cross flow filtration allows water to sweep away contaminant build up and also allow enough turbulence to keep the membrane surface clean.
Potential: Initial estimates indicates that the pilot plant can augment around 4 million gallons per day water supply for East Delhi. The whole process also reduces the pollutant load in the drain which in turn affects the helps in reducing the pollution in Yamuna River. Overall Drain Water Harvesting potential in Delhi is 700 million gallons per day.
Sustainability: Solar Power can be deployed to bring down the operation expenditure.
Logic behind Drain Water Harvesting: Drain Water Harvesting can be done 365 days a year while Rain Water Harvesting can only be done for 15-20 days in a year given on an average Delhi receives only 700-800 mm rainfall for only 15-20 days.
Pros & Cons: Need less space (This plant takes only 9 sq mtr), can treat extremely poor quality water, can treat heavy metal, phosphate and other pollutants but per kL cost is expensive than the natural system.
| Sample Test Result by DJB ( Horticulture Grade Purification) |
| S.No |
Particulars |
Unit |
Drain/STP Inlet |
STP Outlet |
| 1 |
Temperature |
.C |
14.43 |
14.43 |
| 2 |
pH-Value |
– |
7.3 |
7.5 |
| 3 |
E.Conductivity |
|
990 |
758 |
| 4 |
T. Alkalinity |
Mg/l |
347 |
337 |
| 5 |
Chlorides |
Mg/l |
104 |
63 |
| 6 |
Oxy. Abs |
Mg/l |
43.84 |
4.84 |
| 7 |
T.S |
Mg/l |
804 |
509 |
| 8 |
T.S.S |
Mg/l |
168 |
16 |
| 9 |
T.D.S |
Mg/l |
639 |
493 |
| 10 |
B.O.D |
Mg/l |
|
|
| 11 |
Ammonia |
Mg/l |
45.70 |
23.39 |
| 12 |
Phosphate |
Mg/l |
4.5 |
0.1 |
| 13 |
C.O.D |
Mg/l |
194 |
38 |
| 14 |
O.G |
Mg/l |
14.8 |
1.46 |
| Sample Test Result by DJB ( Drinking Water Grade Purification) |
| S.No |
Particulars |
Unit |
Drain/STP Inlet |
RO Outlet |
| 1 |
Temperature |
.C |
14.43 |
14.43 |
| 2 |
pH-Value |
– |
7.3 |
7.7 |
| 3 |
E.Conductivity |
|
990 |
177 |
| 4 |
T. Alkalinity |
Mg/l |
347 |
47 |
| 5 |
Chlorides |
Mg/l |
104 |
11.4 |
| 6 |
Oxy. Abs |
Mg/l |
43.84 |
2.52 |
| 7 |
T.S |
Mg/l |
804 |
118 |
| 8 |
T.S.S |
Mg/l |
168 |
03 |
| 9 |
T.D.S |
Mg/l |
639 |
115 |
|
10 |
B.O.D |
Mg/l |
|
|
| 11 |
Ammonia |
Mg/l |
45.70 |
0.79 |
| 12 |
Phosphate |
Mg/l |
4.5 |
0.08 |
| 13 |
C.O.D |
Mg/l |
194 |
6.4 |
| 14 |
O.G |
Mg/l |
14.8 |
<1.0 |
From Right to Left: Drain Water, EC Outlet Water, Horticulture grade & drinking grade water
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