Digester Step 1 - BOM

1” PVC valve

+ amazon

1” uniseal

Slightly bent-up 1” PVC pipe

Can tee in here to mix second digester tank

2” NPT to PVC

​

2” pipe

​

Gravity Overflow 3”

Tee to prevent siphon

Vent To Outside

To Drain

3”

1” check valve recirculation

1” check valve from sink/toilet

2” gas out

• Initial Operation - kitchen waste only
• Recirculation is added later
• Connection to second tank is added later
• Gravity overflow is added later
• Initial install requires venting of gas

Order of install:

1. Kitchen inlet - 1” PVC ball valve
2. Heating coils inlet (⅜” uniseals)
3. 2” gas out pipe - venting needs to be immediate; connect to gas bag later

$1.34

Requirements and Design Rationale - 30 bit depth

Components

1. Loading
2. Circulation
3. Effluent
4. Drain
5. Venting
6. Heating
7. Stacking
8. Enclosure
9. Automation
10. Gas System

Gas System

1. Gas pressure buildup is determined by column of water at effluent pipe
2. Condenser/dryer traps condensed water vapor from gas line
3. Sulfur and CO2 scrubber for gas delivery to home
4. Pressure relief and pressure gauge at gas bag
5. Gravity-based gas pressure (weight on bag)
6. System produces sufficient pressure (1 foot of water = .4 psi) - 15 cm water = .2 psi
7. Gas delivery to gas bag does not suffer from trapped water

Operation

1. Modular system allows loading of one tote at a time. 2 totes for resilient design.
1. Gas is contributed by both totes only when full, otherwise gas is vented
2. Agitation pump is external to allow easy maintenance
3. Completely automatic operation - outside of person switching between tanks every 30 days or as needed.
• Effluent escapes by gravity every time fill action occurs
• Gas collection is continuous; limited by water column height of effl. pipe
• Heating is automatic by temperature sensor. Hydronics in winter and hillbilly in summer
• Circulation occurs via timer on pump

​

Loading

• Input from toilet and sink via direct macerator pumping into the digester
• System allows an unmodified toilet to separate urine and feces
• Does not inject large amounts of air into system upon loading

Circulation

1. Macerator pump stirring function circulates and chews so system never clogs
2. Circulation allows good feedstock distribution and pre-digestion
3. Circulation breaks surface scum so gas can escape

Effluent

• Effluent goes to the drain via continuous overflow

Venting

• Venting system vents the drain system to outside

Draining

1. Gravity drain allows passive draining. Tee at exit prevents siphon

Enclosure

1. Insulated cabinet for retaining heat
2. Enclosure has all exits on one side to facilitate a door
3. Electronic display on Arduino shows temperature

Heating

• Allows for heating with pumped hydronics
• Holes for hydronic tubes are liquid tight
• Automated heating system based on temperature, uses hot water circulator pump

Stacking

1. Selectability between one or other tote
2. Valves are as close to pathway forks as to minimize unused plumbing

Automation

1. Agitation is via timer
2. Temperature feedback is via sensor. Arduino has a temperature display.
3. One sensor measures biodigester temp, second sensor measures heater temp
1. If biodigester <100 (optimal) and heater>= 103, then turn heat on

​

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Digester Flows

1” PVC valve

1” uniseal

Slightly bent-up 1” PVC pipe

1” hose

¾”

1”

Can tee in here to mix second digester tank

​

2” pipe

​

2” NPT to PVC

​

3” pipe

​

​

2”

​

p

I

pe

​

Gravity Overflow 3”

Tee to prevent siphon

Vent To Outside

To Drain

3”

2” to 3”

2”

1” check valve recirculation

1” check valve from sink/toilet

2”

To gravity drain

2” gas out

Feed into top cistern first

Flex Coupler so top can be disconncted.

1

2

3

4

5

6

7

8

9

10

T Sensor

11

12

12

13

14

Cleaning and Troubleshooting Requirements

Stuckage

• Cleanouts are used in strategic locations
• Flex couplers and coupling is done whenever possible to facilitate disconnection
• Pipes can be slid out of uniseals for adjustment and repair

Troubleshooting

1. Openable enclosure door, all plumbing on one side for easy access

Backup

• Worst case scenario is shutting down one tote and operating the other.

​

Separating Toilet with Unmodified Toilet

Principle

1. Toilet is not modified - helps adoption
2. Big flush:
1. Activates the macerator (pipe in front of macerator is ½ filled with water)
2. Starts a gravity flush sends a slug to the macerator pump
3. Activates water jet at the same time
4. Purge has a dual purpose - both to unclog pee weep hole and to prevent macerator from running dry
5. Complete logic needs to be tested.
3. Little flush simply drains down the drain
• Macerator is simply not run, so overflow goes into Drain
• 1 gallon flush - requires all of 3’ of 3” pipe length. So only half the flush may flush - and rest may go down slowly.

Toilet

Pedestal

Big Flush to Digester

Little Flush to Drain

Toilet

WaterJet

To Drain

Macerator Pump to Digester

Pee drain mid-way up the pipe to allow ½ fill of pipe leading to macerator

Valve

Curves downstream to prevent clogging

Curves upstream to water jet to allow better flushing

½” check valve

Pressure Considerations

• Gas bubbles from bottom of tote create 4 feet of pressure, or about 1.7 PSI
• But, this pressure is limited to 15 cm of the effluent pipe above the tote.
• Gas bubbles float to top of tote
• Water column of 15 cm is the max pressure - as water is free to escape to drainage from this pipe
• Weight on gas bag produces pressure
• 7.5 to 15 cm water column is desired (0.1 to 0.2 PSI)
• To get 0.2 PSI, use 20 lb on a 100 square inch plate

​

Digester

Gas bubbles

Gas Out

Gas Bag

4 feet

Effluent pipe

To Drain

Setting this to water column to 15 cm limits pressure to an equivalent 0.2 psi

Fill

Vent

15 cm

bag

20 lb

8”x 12” plate

Make sure that surface scum does not block gas pipe

Pressure Considerations 2

Initial state: digester fills up

​

Digester

Gas bubbles

Gas Bag

To Drain

Fill

Vent

15 cm

Mid state: digester is full

​

Digester

Gas bubbles

Gas Bag

To Drain

Vent

15 cm

Overflow line

Digester full to overflow line

Fill

End state:

digester is pressurized to 15 cm water column

​

Digester

Gas bubbles

Gas Bag

To Drain

Vent

15 cm

Overflow line

Fill

The 15 cm elevation is good to fill the entire tote with water for more reactor area. If we avoid the 15 cm height raise, we will push down the water level by 15 cm for 0.2 psi.

​

Modular Digester Design

Consensation trap on West wall. All gas pipes go through it. Emptied at comfortable height. Just clear ½” PVC tubing with valve at end.

Inlet from

top

⅜” uniseal - .675 ID

½” PEX =.629 OD

Uniseal size chart.

PVC pipe slightly bent up to break up scum, inserted from outside.

Gas Out

⅜” uniseal. PEX inserted through outisde and inside (needs to reach in tank

Daily mixing

5 minutes per cistern

Gravity Overflow

Gravity Overflow with suction from mid tank

or

or

Black holes mark uniseal locations

Geometrical Digester Body Design

Inlet from

Kitchen and Toilet

Gas Out

Daily mixing

5 minutes per cistern

Gravity Overflow

or

Tee to prevent siphon

Tee

50’ of ½” PEX

Vent To Outside

Phase 1:

1. Start. No H2S scrubber
2. No Lime Water Scrubber
3. Vent to outside.
4. Automate pump, 12V. 30A power supply.
5. Tee in the supply line
6. Fill the bottom tank first.

To Drain

12V 16A

Macerating Pump

(PDF manual)

Depth allows for sufficient gas pressure buildup

Tote Detail

3” Overflow

⅜” uniseal - .675 ID

½” PEX =.629 OD

2”

3”

1”

Mix Suction

Mix Pressure Line agitates at top so overflow doesn’t get clogged

Overflow

• Fill 1 tote for 30 days or until full (10 gallons/day fill)
• Move on to the next one
• Agitate one tote per day - shifting through the 4
• Turn on one suction line only per day to do mixing, 5 minutes daily to break up films

Sampling exit tee