Development and Adoption of Solar-

Disinfection Composting Latrines in Developing

Nations

Presentation to University of Oklahoma

International WaTER Conference

October 24, 2011

Craig Adams, Joe Rendall, Mario Medina, Mary Adams, Emily Robbins,

Sarah Eberhart, Matt WilliamsUniversity of Kansas

Water Supply and Sanitation Collaborative Council (WSSCC)

Unicef Progress Report

See unicef, Progress for Children, #5 (9/06)

Open Defecation• Unfortunately, very

common• Dangerous with

respect to spread of disease

• Simply providing latrines will not change behavior

Azacilo, Bolivia:A Small Aymaran

Village in Andes above La Paz

Working with Community

Ventilated Improved Pit (VIP)

http://tilz.tearfund.orghttp://www.accessgambia.com/information/small/latrine-vip.gif

Human Composting Latrines

The Humanure Handbook

Human Composting Latrines• Advantages over pit latrines and septic systems

– Creates valuable compost– Does not promote leaching into groundwater (as can septic systems and pit

latrines)

• Disadvantages:– Must be operated properly (e.g., addition of grass and ash)– Key issue is achieving full disinfection of human parasites (e.g., ascaris)

Prep4md.blogspot.com

Composting Latrines• Options– ECOSAN Toilet

• Dehydration approach (www.ecocan.co.za)– Below grade– Double vault composting latrine

– Solar disinfection composting latrine

Our Solar Composing Latrine Design

Disinfection Requirements• Time/temp

requirements for disinfection of Ascaris eggs.

• Ultimate goal is to achieve complete disinfection:• in one time

interval• Without

internal (composting) heat being required 0.1 1 10 100 1000 10000

20

30

40

50

60

70

80EnterovirusAscaris EggsSalmonellaShiggellaEntamoeba histolytica cystsTaenia eggsVibrio choleraeHr/D,Wk/Mo/YrSeries17

Hours

Tem

pera

ture

(C )

Pathogen disinfection data fit from Cairncross and Feachem 2nd Ed.

Approach to Our Solar Composting Latrine Research

• Two primary heat sources– Composting heat

• Best to insulate and keep all heat in– Solar heat

• Best to allow as much in as possible– What is best balance, and what design achieves this?

• Constraints– Local materials, building practices– Sustainable operation and maintenance– Material handling and usage

• Goal– Achieve complete disinfection regardless of

composting heat (so that all parts of pile are known to be disinfected).• Requires achieving critical “Time x Temperature”

everywhere in pile– Improve disinfection and compost quality

• Requires significant increases in temperatures

OBJECTIVES1. Develop and optimize solar composting latrines2. Develop design criteria and options for solar

compartments for various regions3. Calibrate and validate the thermal models

APPROACH• Phase 1: Non-insulated slab

– Simulated compost (to determine worst-case temps)

– What temperatures can be achieve at various depths?

– What are the temperature profiles?• Phase 2: Insulated slab

– Simulated compost (to determine worst-case temps)

• Phase 3: Insulated and non-insulated slab– Actual compost

Laboratory Studies• The lab experiment used to test different sustainable insulation materials.

Heat Flux of Wood and Concrete Block Base Materials

Field StationNelson Environmental Study Area – KU Experimental Field Station

Field Station• 10 slabs• Data

– Outside parameters:• Ambient temperature (shade)• Ground temp (@ 4”)• Total solar radiation (at angle of lids)

– Compartments all instrumented with:• 10 Thermocouples in soil (5 readings)• 2 Thermocouples in compartment air

– Selected compartments also have• Slab temperatures• Cover interior surface temperature• Soil moisture• Additional Thermocouples

• Data collection– Agilent 34980A Logger– 60 channels collected (of 120 available) at 5 min

intervals• Meteorological station also on site

“Energy Generation in Compost” Locascio, Katinka; Wolfson, Richard

Experimental Matrix(47 permutations)

• Baseline– Mounded compost pile (covered with Black & Translucent

6 mil plastic sheet)• Sides:

– Single and Double Wood, – Concrete, – Single and Double ¼” PC

• Covers– Single and Double 1/16” PC (corrugated)– Single and Double ¼” PC (flat)– Unpainted and Black Metal (corrugated)– 6 mil Translucent plastic sheet– White fiberglass (corrugated)

• Insulation– None vs. Hay

• Moisture– Dry (10%) vs. 30-50%

• Internal Heat– None vs. 100 W/compartment (~ 200 W/m2)*

• Interior Walls– Uncovered vs. Al-foil covered

Thermally Inert Soil Assumption• Typical composting heat generation: 200 W/m2 (Cornell Univ.)

0 6 12 18 0 6 12 18 00

5

10

15

20

25

30

35

40

700 ml of Baked Soil in a Mason Jar 700 ml of Unbaked Soil in a Mason Jar

Time of Day

Tem

p (C

)

Reproducibility in Designs

0 6 12 18 0 6 12 18 020

25

30

35

40

45

Compartment 1Compartment 2Compartment 5Compartment 6Compartment 4Compartment 7Compartment 8Compartment 9

Time of Day

Tem

p (C

)

• Comp. 1 & 2: Straw Insulated Concrete• Comp. 5 & 6: Straw Insulated Double Wood• Comp. 4 & 7: Uninsulated Double Wood• Comp. 8 & 9: Single Sided Wood

Temp. Profile of Uninsulated Concrete w/ Dbl 1/16” PC Cover~28°C DAY

0 2 4 6 8 10 12 14 16 18 20 22 005

1015202530354045505560657075808590

0

400

800

1200

1600

2000

2400

2800

3200

3600T-Internal AirT-4" MidT-4" NE CornerT-6" MidT-8" MidT-8" SW CornerT-Top of Slab (ave)T-External AirSolar Radiation (W/m2)

HOUR

Tem

pera

ture

(C )

Sola

r Rad

iatio

n (W

/m2)

0.1 1 10 100 100020

30

40

50

60

70

80

90EnterovirusesAscaris EggsSalmonellaShigellaEntamoeba histolytica cystsTaenia eggsVibrio cholerae0" (>Air)4"6"8"

Hours of Sustained Temperature

Com

post

Tem

pera

ture

(C )

at D

epth

P18: Uninsulated Double Wood -Single 1/16” Clear PC

Date: 8/25/2011Max Solar Radiation: 8.01 kWhr-m2

Max ambient T: 28.2 °C (82 °F)

Uninsulated Wood – Single 1/16” PC (DRY)

Infiltration issues

Discussion• Building materials

– Insulated wood and concrete both effective. Infiltration should be prevented.• Cover Materials

Double Clr PC > 6mil Plastic sheet ~ Single Clr PC > White Fiberglass > Black Metal > Metal

• Moisture– Moisture required for composting– Moisture decreased temperatures by ~5C (evaporation)

• Reflective interior (foil)– Increased soil temps ~3C

• Clear sides– Increased solar heating– Increased solar heating may be offset by increased heat losses– May be impractical

Discussion• Internal heat generation

highly beneficial• Infiltration and exfiltration

potentially significant heat loss mechanism

• Turning piles – Lower parts of pile cycled

up to top of pile to be disinfected

– Can not assure that parts of pile aren’t left on bottom

– Requires increased handling – health implications

Acknowledgements• Funding – DOD ARO, Constant DP funds• Matthew Maksimowicz, Jay Bernard, Jim Weaver• Aurelien Jean • KU Exp. Field Station / NESA: Dean Kettle, Bruce Johanning• Many EWB-KU students who have contributed to building

latrines working with Azacilo, Bolvia• EWB-USA• Sumaj Husai and Engineers-In-Action• People of Azacilo, Bolivia

• Questions/Comments/Discussion?