Weed to Wealth: Biogas and Soil Ameliorant Production from Water Hyacinth

Water hyacinth (Eichhornia crassipes) is an aquatic weed which has one of the highest growth rates of all plants in the world. This fast-growing plant causes numerous problems in water bodies.  These problems are related to navigation, recreation, irrigation and hydropower generation. The complete elimination of water hyacinth from waterways is almost impossible due to the production of hardy seeds by the plant which remains viable for up to 20 years. Furthermore, the complete removal of water hyacinth is questionable due to its indirect ecological role in the management of polluted water bodies. Therefore, control of the plant rather than complete removal is suggested. The continuous removal of the plant will result in a sustainable organic matter supply, which makes water hyacinth attractive as a bioenergy crop. Other factors that make it ideal in terms of use as a substrate for bioenergy production include the fact that it grows naturally and does not compete with arable crop plants for nutrients, space or light. It is also easily degradable due to its relatively low lignin content. Water hyacinth can be used as feed for biogas production via anaerobic digestion (AD) which results in the reduction in the volume, mass and toxicity of the input substrate.  Furthermore, the AD process results in the production of methane-rich biogas and other value-added by-products.  Low income urban and rural communities in South Africa struggle to access affordable energy, and face high levels of unemployment and poverty.  The use of water hyacinth to generate biogas has potential to contribute towards the country’s development of alternative, affordable and sustainable energy resources. Furthermore, the proposed technology would result in job creation and environmental preservation.

Market need

The anaerobic digestion of the harvested hyacinths would result in the production of biogas, which is an environmentally friendly source of energy. The produced biogas will be bagged and commercialised for domestic cooking. The liquid by-product of the AD process will be sold as a soil ameliorant and the solid by-product will be pelleted and sold as an animal feed. The hardy hyacinth seeds will be broken down during the anaerobic digestion process to non-toxic products. Furthermore, the continuous removal of the hyacinth for biogas production will serve the additional purpose of remediating the dam of a large amount of phosphorus (P) since hyacinths remove roughly 60 t of total P from the dam water (The P taken up by the hyacinth will be removed during the harvesting process). The target group for all products include households, food-selling businesses and farms around Hartbeespoort Dam (possibly in Informal settlements in towns such as Meerhof, Ifafi, Melodie, Schoemansville and Kosmos).

Benefits

The benefits include gas production which may be utilised for cooking purposes. A soil ameliorant will also be produced for improved crop production to enhance food security in the country. A detailed feasibility study conducted at the beginning of the project will evaluate alternative options for scaling up this project and analyse the costs and benefits of the project, to determine, ex-ante the impact it will have on the targeted communities, and to estimate the potential demand for the products.

Uniqueness:

State of the art digester design with minimal water and electricity requirements; portable; feed flexibility, rapid digestion and optimized biological processes.

The idea behind the technology:

There is a dire need for a solution to the water hyacinth problem in the Hartbeespoort Dam. Water hyacinth are well-known weeds and their complete removal from water bodies has proven to be futile. One contributing factor to their persistence is seed control since seeds can remain viable for up to 20 years. Furthermore, they grow rapidly with growth rates reported at approximately 175 kg per 100 square meters per day, under favourable conditions. This results in hyacinth removal in large water bodies being an ongoing process. The elevated growth rate could be regarded as an advantageous factor if the hyacinth is to be used as a bioenergy crop.

Harvested hyacinth will be used as feed for biogas production via anaerobic digestion. Anaerobic digestion (AD) refers to the breakdown of biodegradable material by microorganisms in an oxygen-free environment.