Water Recycling Net-zero Bathroom

As part of the the open source Earthbag Village (Pod 1), we will build and open source project-launch blueprint a rainwater recycling bathroom structure. We call this a “net-zero bathroom” because the water used for this bathroom will be supplied entirely by rainwater collection and sustainable energy infrastructure will make the energy 100% renewable too. This combined with the Earthbag construction materials makes the entire structure what we call a “net-zero” construction.

This page discusses the water recycling net-zero bathroom with the following sections:

• What is The Water-Recycling Net-Zero Bathroom
• Why Open Source a Water-Recycling Net-Zero Bathroom
• Ways to contribute
• Consultants
• Net-zero Bathroom Design Details
• Resources
• Summary
• FAQ

NOTE: THIS PAGE IS NOT CONSIDERED BY US TO BE A COMPLETE AND USABLE TUTORIAL UNTIL
WE FINISH CONSTRUCTING IT AS PART OF THE EARTHBAG VILLAGE (POD 1) AND ADD TO THIS PAGE
ALL THE VIDEOS AND EXPERIENCE FROM BUILDING AND TESTING IT
IN THE MEANTIME, WE WELCOME YOUR INPUT AND FEEDBACK

RELATED PAGES (click icons for complete pages)

WHAT IS THE WATER RECYCLING
NET-ZERO BATHROOM

The Rainwater-Recycling Net-zero Design (top-left in the image below) will be built twice in the South half of the village. It incorporates 100% water self-sufficiency through collection and use of rainwater for flushing and hand washing with traditional septic for county compliance. It will be combined with the Vermiculture Bathroom designs (right in the image below) and the Communal Eco-shower designs (bottom-left of the image below) to sustainably meet the complete bathroom needs for the entire Earthbag Village (Pod 1).

Location of Designs within the Earthbag Village – Click for the Earthbag Village Open Source Hub

WHY OPEN SOURCE A WATER RECYCLING
NET-ZERO BATHROOM

We see the water recycling net-zero bathroom as a realistic and beneficial option for eco-communities, campgrounds, developing countries/areas, and anywhere water resources are scarce and/or people are interested in sustainability. Open sourcing these designs as part of the Earthbag Village (Pod 1) is meant to demonstrate what is possible and provide everything needed for objective evaluation and replication.

Net-zero Bathroom Features Overview Image

WAYS TO CONTRIBUTE TO THE EARTHBAG VILLAGE TOILET AND SHOWER DOME DESIGNS

SUGGESTIONS     ●     CONSULTING     ●     MEMBERSHIP     ●     OTHER OPTIONS

KEY CONSULTANTS TO THE EARTHBAG VILLAGE TOILET AND SHOWER DOME DESIGNS

Alena Thompson: Mechanical Engineer
Beatriz Rocha: Mechanical Engineering Student
Diogo Rozada: Civil Engineering Student
Diwei Zhang: Mechanical Engineer
Jorge Antonio Ricardo: Mechanical Engineering Student
Jose Luis Flores: Mechanical Engineer
Matheus Manfredini: Civil Engineering Student specializing in Urban Design
Samuel Soroaster: Permaculturalist, Sustainable Builder, PhD, and founder of Green New World

NET-ZERO BATHROOM DESIGN DETAILS

The Net-zero Bathroom will be a do-it-yourself replicable structure that demonstrates zero water use beyond what can be collected and stored from rain. It will also integrate a traditional septic and traditional water source to meet county requirements and guarantee function in situations of extreme drought. This will allow others with similar local-level restrictions to duplicate this traditional and eco-option so we can all work together and further validate its effectiveness.

We discuss the design and implementation of this structure with the following sections

• Requirements, Desires, and Features
• Water Use and Collection Calculations
• Water Storage Exploration
• Water Storage Choice
• Facilities Design
  • Faucets, Toilets, and Urinals Chosen
  • Toilet Water Availability Comparison
  • Faucet Plumbing
  • Dry Urinals
  • Other Plumbing Considerations
• Final Design
  • Structure Interfaces
  • Interior Interfaces
  • Village Interface
  • Water Collection and Storage Calculations
  • Roof Design
  • Outer Structure
  • Barrels and Barrel Support Structure
  • Additional Features
• Cost Analysis
• Resources
• Summary
• FAQ

REQUIREMENTS, DESIRES, AND FEATURES

The Net-zero Bathroom was designed using the following requirements:

• There shall be 2 Net-zero Bathroom facilities in the Earthbag Village
• The facilities shall comply with the Earthbag Village layout
• Shall be made from commercially available and tested products
• The primary source of water shall be rainfall
• Must provide facilities for 80 people
  • 20 Females and 20 Males for each facility x 2 facilities = 80 people total
• Shall comply with municipality septic system laws
• Shall meet a footprint of 28.2 feet
• The roof diameter shall not exceed 34.4 feet
• The water collection system shall be field serviceable

In addition to the above requirements, the following desires were included in the design process:

• Make the design and engineering as simple as possible
• Make the design adaptable to diverse rainfall collection situations
• Use typical construction equipment for construction and maintenance (drills, saws, etc.)
• Make maintenance periodic, not daily or weekly

The finished Net-zero Bathroom designs include the following features:

• Provides rainwater catchment and storage
• Functional even in a semi-arid environment (<1.5″ average rainfall/month)
• Water saving faucet and ultra-high efficiency toilet (UHET)
• Dry urinals with separate collection for males
• Urine-separating toilets for females
• ADA compliance
• Structure is made with Earthbags
• Water storage is provided by 55-gallon barrels in series
• Roof is designed as a reverse camber (funnel) for rain catchment
• Blackwater is collected in a traditional septic system
• Electricity is provided with PV solar

WATER USE AND COLLECTION CALCULATIONS

These Net-zero Bathroom designs are purposed to function effectively in areas of very little rainfall: <1.5″ average rainfall/month. Monthly water needs for 40 people were calculated to be 1274 gallons/month. Structure storage using twenty-two 55-gallon drums was designed to hold an equivalent amount of water: 22 x 55 = 1,210 gallons. Click this link for the open source spreadsheet containing all the calculations and the related data.

Here are the local monthly-rainfall averages we used:

We wanted a design though that would be adaptable to areas of heavier rain and areas with even less rain than ours. To achieve this, we designed the structure with a separate capture area/option and additional external storage. This allows for others to increase, decrease, or eliminate the additional capture area and size the additional storage to meet their specific needs. It also provides the added benefit of much easier roof design. If the roof of this structure by itself were sized to provide sufficient catchment for our needs, it would need to be 243% bigger (see spreadsheet cell B71) to meet these needs on an average month. Larger for low-rainfall months.

For our additional catchment area, we combined the capture from the roof of the structure, half of the nearby Tropical Atrium, and capture from the roof of the adjacent Communal Eco-shower structure. With the above-mentioned monthly rainfall statistics, the following average collection rates were calculated using these equations:

Rainfall per month (in) x Capture area (in²) = Volume of H₂O (in³)
231 in³ = 1 US gallon

• Water-collecting roof average: ≈ 522 gallons/month
• ½ the Tropical Atrium Roof (60 ft diameter): ≈ 548 gallons/month
• 1 Shower Dome roof average: ≈ 522 gallons/month

This achieved an average monthly collection total of 1,592 gallons with surplus water going to storage. Here is a chart showing the integration of rainfall for our area and the resulting collection from the additional Tropical Atrium and Communal Eco-shower roofs using the above formulas (spreadsheet):

The next graphic shows use in comparison to collection sources and the net surplus this generates. Storing the surplus is important because there is one month (June – see cells 48C and 48D) where even the combined capture areas won’t provide sufficient water. All other months provide a surplus if average rainfall patterns are maintained. The potential for drought requires the additional capture area and storage, too.

Note that the blue line shows how many gallons we would collect with only the roof. This would not provide sufficient collection from rainfall in our area but it would be sufficient in an area with an average rainfall greater than 3″ per month.

Here’s how that is calculated:

1. Area of roof catchment = 96,713 in²
2. Needed gallons of water for 40 people = 1275 gallons
3. Gallons to inches conversion is 1 US gallon = 231 in³
4. 1,275 gallons converts to 294,525 in³ of water needed
5. Volume needed (294,525 in³) divided by collection area (96,713 in²) = needed rainfall (3.05″)

Of course, rainfall like this means that the local water table would probably be sufficient such that these types of radical water-saving designs would not be necessary. Still, it is worth noting.

WATER STORAGE EXPLORATION

Water storage both inside and outside are needed for a design like this to manage periods/months of low-average rainfall or drought. Larger catchment and storage areas can also be designed so that additional water can be used for other purposes too. The main challenges with water storage are space requirements and the difficulty of do-it-yourself designs properly sealed and capable of withstanding the pressure of large volumes of water.

In our case, large-scale greywater and rainwater processing and storage were already a part of the larger/complete Earthbag Village design. So this easily solved the issue of external water storage for us. We still needed to explore the options though for internal water storage and external options best to support the Net-zero Bathroom as a more diversely applicable open source and stand-alone design.

Four different options were explored:

• Above Ground Well
• Underground Well
• Small-Capacity Water Barrels
• Large-Capacity Water Barrels

ABOVE-GROUND WELL

The above-ground well option is essentially an uncovered pond built using earth bags.

Pros:

• Can be constructed using earth bags

Cons:

• Difficult to guarantee water seal
• Ongoing loss of water due to evaporation
• Water storage walls cannot be high due to safety concerns (earthquake, improper installation, wear and tear, intense heating and cooling cycles, warping). This means this form of water storage will require larger areas
• Must drain all of stored water to clean
• Possible permitting issues
• Would require ongoing pumping if used as the only water storage source

UNDERGROUND WELL

The underground well option would consist of any underground storage container. The method shown right uses a milk crate-like filling system to prevent well walls from caving inward.

Pros:

• Simple with proper ground excavating equipment
• Many easy option to purchase
• Dependable and durable

Cons:

• May not work in all areas (depending on ground type)
• Difficult/impossible to access depending on depth
• Must utilize a pump to pump the water up to surface
• Must be drained to be cleaned
• Leakage difficult to detect
• Cost

LARGE BARRELS

Large barrels offer many of the same benefits of an underground well with the additional benefits of above-ground placement options.

Pros:

• More space efficient water storage than small barrels
• Can be used as the building’s internal storage option too
• Readily available
• Dependable and durable

Cons:

• Difficult to transport (very large and heavy)
• Difficult to replace if problems occur

SMALL BARRELS

The small barrel option consists of 55-gallon barrels connected together to meet needs.

Pros:

• Readily available & affordable
• Easy to Transport
• Leakage limited to one container
• Easily accessible for leaks and repair

Cons:

• Not the most “eco-friendly” option due to plastic
• Less storage efficiency
• More complex plumbing needed to connect all the barrels
• Would freeze in cold climates if placed above-ground for external storage

WATER STORAGE CHOICE

Small barrels were chosen for internal storage with a tie in to the large-scale greywater and rainwater processing and storage of the Earthbag Village for the external water storage. The primary reasons for choosing the small barrels for the rainwater storage within the structure were:

• Easier and less dangerous for
  non-professionals to install
• Easily replaceable, transportable, or
  repairable if something occurs
• Affordable and available almost everywhere
• Barrels are rated for human water use
• Large amounts of different installation literature already exists for particular user needs

FACILITIES DESIGN

Facilities design covers the selection of the bathroom faucets, toilets, and urinals. Our goals for bathroom fixture selection were:

1. Minimal water use
2. Dependability and effectiveness for public use
3. Durability for public use

Below are the results of our research process. Our chosen selections are discussed at the bottom and the calculations above already reflect these choices.

FAUCET OPTIONS

Standard Faucet

• 2.5 gpm
• No pump needed if water barrels are above the faucet

SLOAN OPTIMA: EAF-350 (preferred)

• .35 gpm
• Pump needed for water pressure
• Most sustainable faucet company
• Most sustainable faucet from this company

TOILET OPTIONS

Standard Toilet

Pros

• Least Expensive (~$95)
• Standard Hook-ups

Cons

• 1.6 Gallons per flush

Niagara Nano “Stealth Dual Flush” (preferred)

Pros

• Standard Toilet Fixture
• .6 gal Half Flush Option
• .8 gal Regular Flush
• Most sustainable “standard” toilet we could find

Cons:

• Cost ($220 + shipping)

EcoFlush

Pros

• Standard Toilet Fixture
• Urine diverting
• .05/.66 gal Low Flush
• http://www.ecovita.net/ekologen.html

Cons:

• Male and female operators must sit on toilet seat for Urine diverter to function correctly
• Cost ($799 + shipping)

Vacuum Toilet

Pros:

• 0.4 gal per flush
• Less likely to get clogged
• http://evac.com/solutions/vacuumcollection/evacoptima5/#building
• http://standard.jetsgroup.com/en/Products/Toilets-and-urinals.aspx

Cons:

• Must have electricity
• Must install vacuum pump (two suggested)
• Most expensive (~$1200)

Toilet Options Overview

FAUCETS, TOILETS, AND URINALS CHOSEN

• A combination of the Zeroflush Waterless Urinal and Niagara Nano “Stealth Dual Flush” Toilet were selected due to the simplicity of use, installation and lower water usage.
• With water limitations, standard, lower cost toilets were not feasible.
• Notes: Composting or incinerating toilets do not currently meet many municipal standards in the United States, so we didn’t choose those

TOILET WATER AVAILABILITY COMPARISON

FAUCET PLUMBING

• Due to bird or other animals’ feces possibly being in the rain water system from roof, hands will be cleaned from external source (or a bacteria killing filter needs to be involved)
• Water provided is in series with shower facility in village
• Pressure required is 30-60 psi

DRY URINALS

The Zeroflush Waterless Urinal was the best and most sustainable urinal we could find. Benefits include:

• Odor-barrier liquid made from 100% natural and biodegradable oils
• 100% natural and biodegradable sealant
• Saves around 40,000 gallons of water per urinal per year
• No complex installation is required, just a drainage outlet
• Easy web access to all the product specs, installation, CAD drawings, etc.
• It is a reasonably priced urinal
• Sleek and modern design

OTHER PLUMBING CONSIDERATIONS

• All sewage plumbing must be at a 2% grade
• Sewage plumbing systems must interconnect
• No “T”s suggested in system (only “Y”s)
• Rain barrels must be interconnected for equal distribution

FINAL DESIGN

• Sloped Roof for maximum water capture
• Approx. 8.9 meter diameter roof
• A 22 Barrel interconnected system
• Dry Urinal and Toilets drain to a central septic system
• Faucets receive plumbing from shower facility
• Toilets receive water from barrels
• Facilities similar to common bathrooms

STRUCTURE INTERFACES

1. Exterior Structure
   1. 8 Entrances
   2. Uses Earthbags 24x12x6
   3. ~738 Individual bags if continuous bag not used
      1. (Calculated Using Bag Calculations Spreadsheet)
2. Bathroom Furnishings
   1. 8 unisex bathrooms
      1. 1 Dry Urinal, 1 Toilet and 1 Faucet
3. Storage Room Access
   1. 22-Barrel Storage
   2. Access via Bathroom
4. Ladder/Hatch Access
   1. Hatch Access to Roof
5. Overflow Pipe Vertical
   1. Gutter to outside
   2. Prevents excessive water on roof

INTERIOR INTERFACES

1. Storage Room
   1. 22-Barrel Rainwater Storage System
2. Inner Roof
   1. Funnels water to central barrel
3. Barrel Structure
   1. Use Load Calculations to determine type of wood and dimensions
   2. May be a floating shelf or a supported shelf
4. Central Pipe Connection
   1. Filters and circulates rainwater into storage system.
5. Equilibrium Pipe Connection
   1. Common pipe connection to distribute water to barrels equally.
6. Pipe Drainage Connection
   1. All barrels have a spigot and end-cap to drain
7. Funnel Filtration System (needs to be researched)
   1. Mesh screen to prevent large debris build up
   2. Sediment system to prevent small debris
8. Pressure Gauge
   1. Determines the amount of water available in the storage system
9. Drain overflow out
   1. Overflows excess water in the water storage system
10. Drain on Floor
    1. Floor in storage room sloped 2 degrees
    2. Drains any spilled water to the outside

Click to Enlarge

VILLAGE INTERFACE

1. Sewage (Dry Urinals/Wet Urinals)
   1. Dry urinal and toilet sewage combined to central sewage location
2. Faucet Water
   1. Procured in series with shower facilities
   2. Water excess evaporates

MAINTENANCE CONSIDERATIONS

• System Maintenance
• Cleaning/Removing Barrel
• Cleaning Filter
• Cleaning Roof
• Checking Water Levels

SYSTEM MAINTENANCE

• Roof is accessible by internal ladder to clear roof debris
• Toilets can be unclogged and cleaned with conventional means
• Rain barrels are accessible and able to be replaced if necessary or interchanged
• Septic tank will need normal draining and maintenance

CLEANING / REMOVING BARRELS

• Shut off Valve
• Connect hose to spigot or use drainage bucket
• Turn spigot on until the barrel runs dry
• Undo secondary cap over bucket until
  runs dry (optional)
• Disconnect from overflow (if applicable)
• Remove Barrel

Options (use flexible hose for more maneuverability)

CLEANING FILTER

• Filter needs to be further designed and looked into

CLEANING ROOF

• Use ladder to access roof hatch
  • Note: Recommend not cleaning during inclement weather
• Remove leaves and debris from inner roof

CHECK WATER LEVELS

• Inspect water pressure gauge
• Refer to included chart to determine water level based off of water pressure reading

WATER COLLECTION AND STORAGE CALCULATIONS

9/15/20 NOTE: UPDATES COMING FOR THIS SECTION

Water usage was based on:

• Village of 80 adults (40 males and 40 females)
• Bathroom usage
  • 5 times per day – 0.05 gallons liquid waste
  • 1 time per day – 0.66 gallons solid waste
• Males use dry urinal when urinating
• Annual rainfall statistics for semi-arid climate
• Roof diameter of bathrooms was initially assumed to be 29.3 ft (x2 structures)
• Faucet uses 0.035 gallons/min
  • It takes an average of 25 seconds to wash hands
• Given:
  • Water collection diameter of Atrium – 60 ft
  • Water collection diameter of shower facilities – 29.3 ft (x2 structures)

WATER USAGE CALCULATIONS

9/15/20 NOTE: UPDATES COMING FOR THIS SECTION

• Assumed 500 gallons of water were available to start
• Chose 2,400 gallons as desired tank capacity

36.4 Gallons Flushing per day
1128.4 Gallons Flushing per month (31 days)
4.7 Gallons sink/day
145.7 Gallons sink/month

• Adding all of the collection areas together
  • Atrium: pi*(60ft/2)^2
  • Shower: pi*(29.3ft/2)^2 * 2 structures
  • Bathroom: pi*(29.3ft/2)^2 * 2 structures
• Total Area = 5,525 ft^2 or 795,522 in^2
• Month Rain Captured = Total Area * inches-of-rain in calendar month
• Monthly Net Gallons = Water in Storage/Previous Month Net + Month Rain Captured – toilet use-sink use

BARREL SIZING

The barrel sizing was based on:

• Standard small barrels can store 55 gallons
• Maximum volume of water that needs to be stored is 1,275 gallons
• 22 barrels = 1,210 gallons of storage
• 2-Tiered barrel configuration was chosen to save space

INNER STRUCTURE

The inner structure was sized based on:

• Diameter of barrels/size of barrel stands
• Minimum maintenance access
• Number of barrels needed (22) and configuration of barrels

Additional Design Considerations:

• Doorway entrance
• Funneling central structure

• Ladder and hatch access

Resulting Diameter: 156”

ROOF DESIGN

The roof design was based on:

• Water collection area
• Strength of Earthbag structure
• Retainment of water after capture
  • Water should run to the center and not to the outside edge
  • Trade study was done with gutters and it was found that they are less efficient than a central funnel
• Manufacturability
• Maintenance & Accessibility

Final Design:

• 8 identical steel polygon panels assembled in an inverted roof for exterior
• 6 identical steel polygon panels assembled in an inverted roof for interior with hatch access
  

  

OUTER STRUCTURE

The exterior structure was designed to:

• Accommodate Roof Size
• Adequately support panels for water capture and maintenance
• Interior water storage needs
• Handicap access doorways and toilets
• Number of bathrooms with toilet fixtures
• Earthbag strength properties

BARREL SUPPORT STRUCTURE

• Needs to support 55Ga*8.2 lbs/Ga + 25 lbs (barrel)
• Deflect only 1/400 (Max Deflection Ratio) of the woods total length
• Equation for Max Deflection for Simply Supported Beam
  • Deflection=Load*Length^3/(48*E*I)
  • Deflection/Length=Load*Length^2/(48*E*I)=Max Deflection Ratio
  • Load=((48*E*I)/Length^2)*Max Deflection Ratio
  • Where I is second moment of inertia for a rectangular beam, E is the Modulus of Elasticity for structural wood, Length is the long length of the beam, and Load is the weight of the barrel
• Has four 1×4 primary horizontal wooden beams to support each barrel

• Vertical 4 x 4 beams tie to the ground
• Same structure for central structure

WATER BARREL FEATURES

Each Barrel is required to include:

• Top hole vents to prevent suction
• A connection to an overflow barrel
  • Does not need to be included in every barrel if barrels are interconnected
• A spigot to drain
• A bottom tap to drain and clean
• Shut off valve to system

WATER BARREL INTEGRATION

• All top-tier barrels are directly connected to the barrel immediately beneath them
  • There is a shutoff valve between the top and bottom tier
• All bottom tier barrels are connected to the adjacent barrel (except at the ends)
  • Each barrel has a shut off prior to adjacent union
• Between every other barrel union, there is a connection to the central barrel
• Top barrels and bottom barrels can be removed from the system between shut off valves
  • Example: 3 Barrels are removed in the system but all barrels remain tied without leakage. Barrels can additionally be moved and re-positioned.

ADDITIONAL FEATURES

Pressure Gauge

• Measuring the water level can be done with a pressure gauge
• With a known PSI, the water height can be estimated
• A pressure switch can activate an external pump whenever water is low
  • System will draw water from external sources anytime water levels reach ¼ filled

Drainage Pump

• A small pump either manual or electric can be used to siphon water from the spigot of a defective barrel to another barrel

WATER BOOSTER (IF APPLICABLE)

For water that is stored above toilets:

• The water storage system will serve as the a universal water storage tank for all toilets
• Water is simply gravity fed to toilets

For water that is stored below toilets:

• Water pressure booster/pump is required to pump water up to toilets

COST ANALYSIS

Notes

¹Storm Rated Exterior Wood

²With finished walls and floor

³Sewage Output certified by professional

Communal-use rainwater recycling bathrooms will be within a short walk for all residents of the South, East and West parts of the village (see the Pod 1 layout). These bathrooms will integrate traditional septic for all toilets. The rainwater collection cistern in the center will capture and store enough water to meet all of the hand-washing and toilet-flushing.

The One Community Earthbag Village Communal Shower and Net-Zero Bathroom | Concept Render – View Looking Northeast – Click to enlarge

The One Community Earthbag Village Communal Shower and Net-Zero Bathroom | Concept Render – View Looking Northeast – Click to enlarge

The One Community Earthbag Village Communal Shower and Net-Zero Bathroom | Concept Render – View Looking South – Click to enlarge

The One Community Earthbag Village Communal Shower and Net-Zero Bathroom | Concept Render – Cutaway View

This study by Samuel Soroaster (Permaculturalist, Sustainable Builder, PhD, and founder of Green New World) assesses the feasibility of designing a shared restroom to serve 40 uses per day with self-sufficiency of water and energy for all its demands.

DESIGN GOALS

• Zero water use beyond what can be collected and stored from rain. Integration of a traditional water source to meet county requirements and guarantee function in situations of extreme drought
• Allow us to meet county requirements with the traditional septic while we explore more sustainable models with the vermiculture and other eco-options we are open source project-launch blueprinting
• Allow others with similar local-level restrictions to duplicate this traditional and “experimental” eco-option so we can all work together and further validate the effectiveness of these more sustainable models
• Allow us to keep the cost of the earthbag village (Pod 1) as low as possible so it is more easily replicated

Rainwater Recycling Bathroom Design

FEATURES

1. Rainwater catchment and storage.
2. Reuse of greywater from sinks to flush toilets
3. Water saving faucet and ultra-high efficiency toilet (UHET)
4. Dry urinals with separate collection for males
5. ADA compliancy
6. Structure is made with Earthbags; foundation and water tank are made with ferrocement
7. Roof is designed as a reverse camber (funnel) for rain catchment
8. Blackwater is collected in a septic system that produces biogas for energy needs
9. Hot water is heated by solar and biogas, backup is heated with natural gas
10. Electricity is provided with PV solar
11. Septic system is heated with biogas and natural gas for backup (still exploring this)

1. RAINWATER CATCHMENT DESIGN

Fifteen inches (38cm) of average rainfall a year would be sufficient to meet the water needs of this shared bathroom design. Here are the calculations for our specific location:

• The location receives an annual estimated 15 inches (38cm) of rain. The annual distribution of rainfall is roughly 1 inch (2.5cm) per month +/- .5 (1.25cm)
• For 40 persons per day, an estimate of 50 gallons (190 liters) is needed to wash hands totaling in an annual need of 18,250 gallons (69.3m3)
• With a roof of 200 sq. meters and annual rainfall of 38 cm p.a. a total of 76m3 water can be collected

Here are the catchment design specifics:

• A first rain diverter is installed to clean roof of debris and potential pathogens of 0.5mm equating to 100liters per rainfall. Assuming 24 rainfalls per year mounting to 2m3 p.a. of water
• Pre-filtration: The roof contains a circular flat section of 2m diameter to slow water flow to trap sediment and debris in pebbles. A fine mesh 450micron is placed to exclude debris and animals from entering the cistern. The intake is 1.5 inches (4cm) above the roof to facilitate the sedimentation process
• All pipes to the cistern will be made of HDPE (High-density polyethylene).
• After the water enters the 4 inch (10cm) intake it meets the first diverter. When the first diverter is full water is automatically redirected to the water tank
• A hyperbolic nozzle maximizes oxygenation and implosion of water prior to entering the cistern
• The cistern has a capacity of 50m3 – with a cylindrical shape of 4 x 4 m
• Water within the cistern is recirculated for the continuous addition of oxygen though a hyperbolic nozzle
• There shall be included a clean out valve 4 in (10cm); a 2 in (5cm) overflow valve
• Collection of the water for use is done at 2ft (60cm) below the water surface to collect the best quality water. A buoy maintains the outflow at a consistent depth.
• The water tank shall be built with a super-adobe wall 12in (30cm) of 200PSI. The interior of the cistern shall be made with ferro-cement 1000PSI of 3 in (7.5cm) with a 1/4in (0.6cm) welded steel lattice. (Needs engineer verification to meet code)
• Since rain has a tendency to be acidic, pH of water tank will be checked on a monthly basis and adjusted with dolomite lime to a pH of 7.6 – 8.0

Plumbing Design Described Above with Additional Details Below

2. PRIMARY PLUMBING

Here are the plumbing details:

• All pipes from between the cistern to the pressure tank shall be ¾ inch galvanized steel
• All pipes after the pressure tank to toilet faucets will be ¼ inch copper TYPE L
• Filtration/Disinfection: Water from the cistern is filtered through a 3-stage filter consisting of a 200 micron pre-filter, a 0.5 micron fine filter and a GAC filter. Disinfection is performed with an inline ozonator. Alternatively, code permitting, ionization with silver and copper is performed
• After filtration a ½ HP pump will pressurize a 50 Gallon pressure tank to 20 PSI
• Plumbing is separated at the pressure tank to run one line to the hot water system while the other line runs to the sinks of the toilets
• Sinks are equipped with 1 GPM faucets that have motion sensors.
• Toilets are of UHET norm with a dual flush feature of 0.5 and 0.8 gallons (1.9 and 3.4 liters) per flush

3. HOT WATER SYSTEM

The hot water system will also be built with self-contained sustainability in mind:

• Hot water lines runs from the pressure tank to the roof where a radiant solar panel will heat the water.
• Secondary hot water with NG/biogas on demand water heater.
• The distance to the most remote sink is 8 m @ 1/4in pipe has a water retention of 0.6 Gallons (2.5 liters).

4. GREYWATER RECYCLING FOR UHET FLUSH TOILETS

Greywater will be used to flush the ultra-high-efficiency toilets:

• A 5 gallon chamber underneath the sink will store the greywater from the sink
• The chamber is equipped with a micro-ozonator or UV light to disinfect the greywater
• The chamber has 3 lines connected: overflow, secondary inlet, outlet to toilet chamber
• Secondary inlet is connected to float valve when water level drops below one gallon a gallon of potable water is added
• Microfloat switch in toilet tank is activated when toilet is flushed to fill toilet tank
• Small 1/16 HP 1 GPM pump will be used to fill toilet tank
• Alternative to an overflow a second float switch can activate the pump if water is too full in the greywater chamber

5. DRY URINALS FOR MALES

• Dry urinals will be placed in all toilets except the ADA toilet
• 1.5inch plumbing will serve to run all urinals to a collection chamber that will be used for fertilizer production (to be determined)

6. SEWAGE SYSTEM / BIODIGESTER

Here are the sewage system design details:

• Assumption for UHET daily usage: 40 uses for fecal matter per day with 0.9 gallon per flush, 80 uses for urinal with 0.5 gallons for females. Total flush volume 36 gallons and 40 gallons
• All sewage lines shall be of the HDPE 4 inch type
• A dual chamber septic tanks shall be installed connected to a leachfield
• Sewage lines shall be vented and equipped with a p-trap prior to the septic tank
• The hydraulic retention (HRT) shall be at least 30 days for the septic tank.

Calculations for septic anaerobic digestion system:

• 40 daily stool deposits at 400g average per visit resulting in a daily amount of 16kg of feces.
  • Human Feces: Total solids (TS) of 25% and volatile solids (VS) 85% of TS with an average N of 5% and C:N ratio of 8.
  • Every gram of VS provides 0.9 liters of biogas

Objective to maximize biogas production:

• C:N 30:1
• 10 % final w/v Total Solids
• Total Solids of 2.5g per liter per day
• Hydraulic retention of 40 days

Volume and density septic tank calculations

• 40 flushes x 3.4 l H20 per flush + 0.4 l feces = 152 l per day of slurry = 40 G
• 0.4kg feces / (3.4 liters + 0.4 liters) = 0.105 = 10.5% (w/v) slurry
• 400g x 40 /2.5g TS per liter per day = 6,400 liters volume needed = 1680 G
• 1680 slurry volume x 1.1 gas space = 1848 Gallon Septic Tank Volume
• 6,400 liters / 152 liters = 42 days HRT

Nutrient balance calculations

• 400g x 0.25 TS x 40 = 4000 g = 4 kg of TS per day
• 4000 x 0.05 N = 200 g of N per day
• 200g x 8 C:N = 1600 g of C provided
• 200g x 30 C:N = 6000 g of C required per day
• 6000 g – 1400 g = 4600 g of additional C needed per day

As recycled or unbleached toilet paper is mostly cellulose it can be assumed that every toilet user will utilize 15 g of toilet paper which is 100% C x 40 persons results in 600 g of C per day.

Compensation can be achieved with sawdust: C:N 400 with N 0.1%

• 1000 g x 0.001 N x 400 C:N = every kg of sawdust provides 400 g of C
• 4600 g C need – 600g Toilet paper = 4000g needed of C per day
• 4000 g / 400 g = 10 kg of sawdust added every day will optimize the C : N ratio – in other words, 287 g of sawdust added per person providing feces

Energy calculations:

For Human feces:

• 40 persons x 400 g x 0.25 x 0.85= 3400 g of Volatile Solids per day
• 3400 g x 0.9 l biogas/g VS = 3060 liters biogas = 3.06 m3 = 110 FT3 Biogas produced per day
• Assuming the biogas will be 70% CH4 with CH4 @ 1060 BTU/ FT3
• 110FT3 x 1060 BTU/FT3 x 0.7 = 81,620 BTU per day from feces of 40 people

For Sawdust:

• Calculations coming

7. ENERGY CONSUMPTION

Here are the energy consumption calculations for each of these bathroom domes:

• Conversion of gas to electricity is 3,412 BTU per 1 kWh with engine efficiency of 35%
• 16 light LED light bulbs 3 watts each running 6 hrs = 0.3kWh
• Greywater pumps 0.05 kWh running 2 hrs = 0.1kWh
• Pressure pump 20PSI, 80 Gallons, 0.5kWh running 2hr = 1kWh CHECK
• Electric total is 0.3 + 0.1 + 1 = 1.4 kWh
• Electricity generation is 1.4 kWh / 0.35 efficiency x 3412 BTU/kWh = 13,648 BTU per day
• On demand water heater 45,000 BTU per hr = 45,000 BTU per day
• 81,620 BTU generated – 45,000 BTU – 13,648 BTU = 22,972 BTU remaining to heat digester.
• Heating demands to maintain digester at 90F needs to be determined

LAYOUT DETAILS

The total area of the bathroom below is 58 m². Each bathroom has the area of approximately 4.6m². The water storage is located on the center of the structure and has an area of 12.5 m² and a volume of 44 m³. The rainwater collected on the storage will be used for flushing the toilets and washing hands. The idea is to wash hands with filtered rainwater and recycle the water to flush toilets.

To check the rules for the ADA compliant bathroom this guide was used. The dimensions are shown below.

The dimensions of the toilet, sink and door are illustrated in centimeters here:

To simplify the visualization of the bathroom, the software Revit (version 2014) was utilized to create the 3D drawings. Some views are shown below.

Figure 7 – Top View bathroom, Revit

Figure 8 – Section Box, Revit

Figure 10 – Section 1, Revit

Figure 11 – Section 2 and components dimensions, Revit

Figure 12 – Section 3, Revit

Figure 13 – Elevation East, Revit

RESOURCES

• Use this page (click here) if you have a resource you’d like to suggest be added here

SUMMARY

A rainwater recycling communal bathroom structure has the potential for broad application in communities, campgrounds, developing countries/areas, and anywhere else water resources are scarce and/or people are interested in sustainability. Housing and sustainable showers and solid waste processing can be added to these designs with the Earthbag Village (Pod 1) and its Vermiculture Bathroom designs and Communal Eco-shower designs.

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