La Yuca rainwater catchment 2011

Background

The Humboldt State University Dominicana Program is working with the neighborhood of La Yuca in the Dominican Republic for the summer of 2011. Within Dominican Republic, tap water is not potable, and thus families must find some way to receive potable water.

Problem

The project goal is to provide a renewable alternative to other methods of receiving potable water by building a scalable and replicable rainwater catchment system.

Criteria and Constraints

The Criteria and Constraints below were developed from discussion with the Community and the necessities to build and complete a successful project.

Criteria	Weight	Constraints
Safety	8.5	Must be safe for children and others to be around
Cost	8.5	Buy Back Time within 2 years and Cost, cheap
Ability to be Reproduced	7.5	Materials Need To Be Local and Built with Community
Educational Value	7	Teach the Community About Rainwater Catchment
Potability	10	Must meet standards for water consumption
Durability	8	Must last a long time and withstand hurricanes and other natural disasters
Gravity Fed	7.5	Should not need pumps. Gravity should draw the water through the filters.

Rainfall in Santo Domingo

Month	Total Rainfall Average(in)
January	2.5
February	2.2
March	2.1
April	2.8
May	7.4
June	5.5
July	5.7
August	7.0
September	7.1
October	7.4
November	3.9
December	3.3

source: Weather Channel ^[1]

Cost & Buyback Time

This is a rough estimate. http://dl.dropbox.com/u/14930656/rainwatercalcs.xls

Research

Pre-Filtration

Pot Filters A plot filter is a simple plastic tray that, similar in shape to a planter, which is filled with gravel and covers a large basin, with an outlet on the bottom. As the water flows through debris is collected on top part of the gravel. The advantages to such a system are that is simple and extremely low maintenance. A disadvantage is that it is most effectively used on ground level.

Basket Filter Basket filters contains a large plastic filter that is housed within a plastic casing, the filter is designed to collect and trap most debris. The water flows in through the top of the filter where the debris is collected and then discharged from a side outlet, as long as the water volume is within the rated filter all the water will be filtered.

Cascade Filter Cascade filters are very similar to basket filters, the main difference is that rather than trap the debris as do the basket filters they have a second nozzle which washes it away, the cascade filter is purported to lose 5% of the water in this process, the advantage is the system needs much less maintenance than most.

Vortex Filter Vortex filters do not collect debris, they allow it to pass through in the same way a cascade filter does. The water is drawn through the side in a vortex manner,the water exits the side port allowing the debris to go through a separate drain. The system requires the least maintenance out of the system mentioned however a disadvantage is efficiency, with only 85% of the water being collected through this process. http://www.conservationtechnology.com/rainwater_prefiltration.html

Leaf Screens By far the most simple and low cost of the pre-filtering process, the leaf screen and strainer prevents any large debris from entering the system and consists of just a plain strainer. The disadvantage to the system is that the screen must constantly be cleaned to avoid blockages in the water. http://www.twdb.state.tx.us/publications/reports/rainwaterharvestingmanual_3rdedition.pdf

First-flush device /Roof Washers

• needed to prevent toxins and pollutants from roof tops to enter into the rainwater catchment system.
• first flush calculations can be found on appropedia under Basic rainwater collection calculations
• Calculation: meters squared (roof area) X pollution factor = liters to be diverted.
• Over Flow Type
• Electronic Conductivity
• constant volume container, this works by having a container that fills up with a floating ball, when the container reaches maximum capacity and is finishing the first flush, the floating ball seals off the container.
• first flush valves: optimized to meet rate of water flow, uses a ball that allows a set amount of rainwater in its core device. When it reaches a certain weight, it presses a button, and closes off the first flush, diverting the rest of the water into the catchment tank.
• Down pipe first flush water diverters: similar to a constant volume container which has a volume of pipe that will fill up and seal off before filling the storage tank

http://www.rain-barrel.net/first-flush.html : describes first flush systems

• Post/Wall stand water diverter: a larger version of the down pipe first flush, the will hold a minimum of 20 L.
• Roof Washers are placed just before the storage tank, and consist of a 30-50 gallon tank with a large filter over the exit pipe. This filter is usally smaller than human hair and must be cleaned regularly, otherwise there will be clogging and pathogen breeding.

http://www.eco-web.com/edi/index.htm : Discusses the differences in why filling a container might work better than first flush valve

Filtration

( Not all of these methods should be or will be used)

Slow Sand Filtration

• must have low turbidity
• “The process percolates untreated water slowly

through a bed of porous sand, with the influent water introduced over the surface of the filter, and then drained from the bottom.”- http://public.health.oregon.gov/HealthyEnvironments/DrinkingWater/Documents/swt/Slowsand.pdf

• reduces cloudiness, bacteria and other organic matter
• uses local materials

Distillation:

• boiling water then re-condensing the water in a separate container to remove contaminates
• removes broad range of contaminates

Pasteurization: A method of purifying water at temperature below boiling point. This method uses less water than distillation by the fact that pathogens die at lower heats than boiling temperature for water. The following table shows temperature certain pathogens die at from http://solarcooking.wikia.com/wiki/Water_pasteurization

Microbe	Killed Rapidly At
Worms, Protozoa cysts (Giardia, Cryptosporidium, Entamoeba)	55°C (131°F)
Bacteria (V. cholerae, E. coli, Shigella, Salmonella typhi), Rotavirus	60°C (140°F)
Hepatitis A virus	65°C (149°F)
(Significant inactivation of these microbes actually starts at about 5°C (9°F) below these temperatures, although it may take a couple of minutes at the lower temperature to obtain 90 percent inactivation.)

Ion Exchange:

• water is funneled through a basin with resin beads in side. These beads are made of chemicals that will react with the water and remove nitrates, phosphates and other chemicals. Ions are exchanged hence the name ion exchange resin
• one of the few ways to remove nitrates from water, as nitrates are almost always soluble.
• does not remove particles
• used in Brita filters

Activated Carbon:

• channels water through activated carbon
• removes chemicals, gasses, some micro-organisms by attracting the particles to stick to the surface of the activated carbon
• used in Brita filters
• different types:
  • Powdered activated carbon-smaller particle size
  • Granulated activated carbon-larger particle size

Reverse Osmosis:

• forces water through a semipermeable membrane that will only allow water molecules or molecules of certain diameter through.
• works well for removing

Settling Basin: Large basin that collects water, and allows time for suspended solids to settle out, and fall to the bottom of the basin through gravity

Grit Chamber/Primary Screening:

• removes large objects that will clog later stations of filtration
• necessary to remove leaves and other large objects

Pleated Sediment Filter (Used in Mexico City rainwater catchment for potable water with Isla Urbana): Removes sediments , allow small increase in flow rate, easily reparable as the pleats and filters slide in and can easily be changes

Cartridge Filters

• must be replaced regularly
• able to place different sized and type filters in one chamber

UV Lights

• uses ultraviolet light to kill pathogens
• rated in gallons per minutes
• must be replaced after 10,000 hours

What to Look for in Filtration for Rainwater (Isla Urbana):

• flow rate on filter
• ending effect on head
• what suspended solids will be removed
• sequence or how to combined filters
• cost

http://www.freedrinkingwater.com/water-education/quality-water-filtration-method.htm Goes through different types of filtration and how the filtration works and its effectiveness

Roof Design and Types

Types

• Metal:
• Clay/Concrete/Tile: works well for potable situations, but may contribute to a 10% loss in rainwater captured due to inefficient flow, texture and evaporation. Roof type is safer when painted to prevent bacterial growth on porous materials
• Composite/Asphalt Shingle:leach toxins, not appropriate for potable systems
• Wood Shingle, Tar and Gravel:not appropriate for potable systems
• Slate:smooth surface with no toxic sealants make it ideal for potable systems

Design

• Gutters: Installed to capture rainwater running off buildings. For potable systems, lead gutters can not be used. Most common materials are half pipe p.v.c., vinyl, seamless aluminum, and galvanized steel. Gutters should be installed with a slope toward the downspout. Rain Gutter Design
  • Downspout pipe: pipe that leads the water to the storage tank from the gutters.
  • Leaf Screens:Screens (usually mesh) that catches leaves and other debris before entering the downspout. This will require routine cleanings. built up leaves can lead to leaf decay and bateria
  • Leaf Guards:mesh that fits attop the gutter to prevent leaves from entering the gutter by falling. This is only needed where a tree overhang is above the gutter.

Storage

Several different items can be used for the storage tank or sistern. The following are some common items used.

• Barrels-50-75 gallon drum
• Tanks:
  • metal tanks(expecially galvanized steel)
  • fiberglass tanks- make sure to have USDA food grade fiberglass for potable water, easily repaired, expensive if storage needed is under 1,000 gallons
  • Polypropylene tanks
  • wood lined with food grade plastic
  • ferrocement-low cost steel and mortar composite material. easy to repair small cracks and leaks
• Gardens (this will not work for this situation)
• Buckets
• earthenware sisterns
• stone and mortar sisterns
• Dominican Republic already currently use rodoplast for water storage

In order to determine what material will work best, the size of the sister or storage tank must be determined. This dependes on the following factors.

• rainwater supply
• demand
• amount of time with out water
• catchment area
• budget

Requirements of storage tanks or sisterns

• must be opaque
• must never been used to store toxic materials if going to be used for potable water
• must be covered and vent screen to prevent mosquitos
• must be able to be cleaned^[2]

Mosquito Proofing Tank

• must have mosquto proof screens on all opening and outlets (this should be 1mm mesh)
• all fittings and inlets must be fitted tightly to not allow mosquitos inside
• check screens and water tank regularly to insure no wear and tear or mosquites inside. ^[3]

Examples with Contact Information

Isla Urban-Rainwater Catchment in Mexico City http://www.appropedia.org/Rainwater_catchment_at_Isla_Urbana

http://www.arcsa-usa.org/content.asp?pl=45&contentid=45 American Rainwater Catchment Systems Association-page has several photos of projects completed within the united states

Gov. of Karnataka http://www.rainwaterclub.org/docs/MANUAL%20ON%20ROOFTOP%20RAINWATER%20HARVESTING%20SYSTEM%20FOR%20SCHOOLS.pdf

http://www.harvesth2o.com/RainwaterHarvestingManual_3rdedition.pdf The Texas Rainwater Harvesting Manual

Meeting on 6/14/2011

After meeting with el bario de la yuca, the following were some of the most important points covered, and what la yuca said they wanted.

• Criteria:
  • potable
  • used for cleaning
  • used for bathing
• location
  • one system on the school
  • one system for the community
  • possible house for the community location
• Resources/who will want to help build this
• People to help protect materials

Next Steps

• Thursday- go to pastors house and check out site
• Begin Designing potable system
• find out what materials are local and can be used for filters
• need to look at painting the roof or what is on the roof

• Ana Elesa- looking for university class that can come test the system periodically

need to be understanding "can't garentee potable-need testing

Footnotes