Floating plant (Macrophyte) pond

Applicable to the following sanitary systems Single pit system Blackwater treatment system with infiltration Blackwater treatment system with sewerage (Semi-) Centralized treatment system Sewerage system with urine diversion

Inputs Effluent

Application Level Management Level Household: o Household: o Neighbourhood: x Shared: x City: xx Public: xx xx - suitable, x - less suitable, o - not suitable

Description

A floating plant pond is a modified maturation pond with floating (macrophyte) plants. Plants such as water hyacinths or duckweed float on the surface while the roots hang down into the water to uptake
nutrients and filter the water that flows by.

Water hyacinths are perennial, freshwater, aquatic macrophytes that grow especially fast in wastewater. The plants can grow large: between 0.5 to 1.2m from top to bottom. The long roots provide a fixed medium for bacteria which in turn degrade the organics in the water passing by.

Duckweed is a fast growing, high protein plant that can be used fresh or dried as a food for fish or poultry. It is also tolerant of a variety of conditions and can remove significant quantities of nutrients from wastewater.

To provide extra oxygen to a floating plant technology, the water can be mechanically aerated but at the cost of increased power and machinery. Aerated ponds can withstand higher loads and can be built with smaller footprints. Non-aerated ponds should not be too deep otherwise there will be insufficient contact between the bacteria-harbouring roots and the wastewater.

Adequacy

The technology can achieve high removal rates of both BOD and suspended solids, although pathogen removal is not substantial.

Harvested hyacinths can be used as a source of fibre for rope, textiles, baskets, etc. Depending on the income generated, the technology can be cost neutral. Duckweed can be used as the sole food source to some herbivorous fish.

This technology is only appropriate for warm or tropical climates with no freezing temperatures, and preferably with high rainfall and minimal evaporation. Different, locally appropriate plants can be selected depending on availability and the wastewater type.

Trained staff is required for the constant operation and maintenance of the pond.

Health Aspects/Acceptance

Water hyacinth has attractive, lavender flowers. A well designed and maintained system can add value and interest to otherwise
barren land.

Adequate signage and fencing should be used to prevent people and animals from coming in contact with the water.

Maintenance

Floating plants require constant harvesting. The harvested biomass can be used for small artisanal businesses, or it can be composted. Mosquito problems can develop when the plants are not harvested regularly. Depending on the amount of solids entering,
the pond must be desludged periodically. ^[1]

Pros & Cons

How to build

Costs

References

1. ↑ Tilley, Elizabeth et al, 2008. Compendium of Sanitation Systems and Technologies. Swiss Federal Institute of Aquatic Science and Technology (Eawag). Dübendorf, Switzerland., pp.143-144 ISBN 978-3-906484-44-0