Struvite Reactor Tank

Target SDGs

Market Suggested Retail Price

$367.00

Target Users (Target Impact Group)

Household, Community

Distributors / Implementing Organizations

Eawag has implemented various projects in both Nepal (STUN) and South Africa (VUNA).

Countries

Nepal, South Africa

Manufacturing/Building Method

The Construction Manual provides guidance to interested individuals and households to build a tank using plastic containers or galvanized steel sheets.

The Operation Manual for a larger system includes further instructions for operation and maintenance based on experiences from earlier implementations.

Intellectural Property Type

Open-source

User Provision Model

This product is not for sale. Open source information packs available online (e.g. Construction Manual and Operation Manual).

Distributions to Date Status

Unknown

Design Specifications

The tank is made of metal such as galvanized sheet metal or stainless steel. The stirring mechanism is also made of metal. The nylon filter bag allows liquid to pass through but keeps the struvite inside the bag. There is also a plastic switch between the tank and bag so that flow can be regulated. The dimensions of the tank can be adjusted according to the users' preferences.

Source-separated urine and magnesium is added to the tank and mixed manually for 10 min with a crank connected to stirring blades in the tank. A valve connecting the tank to a nylon filtering bag is then opened. The mixture enters the filtering bag so that struvite stays in the bag while liquid runs through. The bag is then removed from the tank and dried for 1-2 days. The struvite in the bag can then be applied as fertilizer.

Technical Support

As an open-source technology, users can refer to online manuals to carry out maintenance works.

Replacement Components

The product is generally repairable using available materials. The components and exact materials of the product can vary while still maintaining the same function. Online manuals are available for reference.

Lifecycle

The lifecycle of the tank is long but some components may need to be replaced continuously such as the nylon bag. The product is mainly constructed by recyclable materials such as metal and plastic. The nylon bag is the most challenging to recycle correctly, especially in the global south.

Manufacturer Specified Performance Parameters

The amount of struvite depends on the size of the tank and the efficiency of the process. When filled and mixed with added magnesium, results should be achieved after 10 min of stirring following by air drying for 1-2 days.

The goal of the product is to increase crop production sustainably and while potentially creating another source of income for people selling the struvite. The tank is stated by Eawag as low-cost and easy-to-use. Furthemore, the ease of transportability of struvite and application of struvite powder than urine directly, are also desireable characteristics.

Vetted Performance Status

Field experiments have shown that the reactor can recover over 90% of the phosphorus in the urine.

Safety

The tank is driven manually, so there are no hazards regarding electricity. However, there are potential health risks regarding unsafe contact with the urine when filling the tank.

Complementary Technical Systems

Users and organisations can automate stirring and add a rotating biological contractor (RBC) to reduce nitrogen content in the effluent. Schematics to inform this option is found in the Operation Manual.

Academic Research and References

Compliance with regulations

Application of urine as fertilizer is legal but if the struvite product is going to be patented and sold on the market as fertilizer, permission may be required. An example of this is Aurin fertilisers.

Evaluation methods

The reactor has been developed and tested in regards to percentage of nutrient recovery, production cost and demands of operation. There is also an academic article written about the social and economical feasibility using the product in communities in Nepal.

Other Information

• The Construction Manual can be found here.
• The Operation Manual can be found here.
• Device schematics illustrating the basic steps of struvite production in the precipitation reactor.
• Factsheet - Struvite
• EAWAG - Projects: Aurin – Fertilisers from urine, Struvite from Urine in Nepal (STUN) and Nutrient Recovery from Urine (VUNA)