Azolla and Duckweed Calculations

Introduction

Consistent with OSE's integrated design approach, we are developing an integrated house and Greenhouse where a separating toilet reclaimed urine to produce duckweed andazola. This duckweed in a Solo may be fed to fish in an aquaponics system thereby combining wastewater treatment and food production.

To this end it is important to produce and document design calculations which correlate average human waste production with a required duckweed and azolla system size.

Further, this must consider pond design and existing nitrogen loading from fish if one is to produce an integrated system.

Calculations

Nitrogen-Based First Principle Calculations

• Percentage of protein (nitrogen) in azolla - 25-35% - [1]
• Growth rate of duckweed per square meter of surface area - 5 grams dry weight - [2]
• Growth rate of azolla for the same -
• Average grams ammonia produced per person per day - a person needs 2/grams nitrogen, so assume that a person eliminates approximately the same per day.
• Square meters of azolla required to treat an average person's nitrogen loading - 2 square meters roughly.
• Duckweed area required for the same -
• Existing greenhouse - has 224 square feet of trays for growing on the walls - about 20 sq meters.
• say 2 people weigh 300 lb and fish mass is 300 lb - assuming they produce similar amounts of protein - we would need 8 sq meters of azolla to handle the nitrogen loading.