Most macrophytes have an extremely high reproduction rate, and could double the area they cover in a few days.
Macrophytes are best used as fertilizer, although they could also be used for animal feed. Their greatest value is to return nutrients to the soil for agriculture in the garden.
Most conventional experts think of water hyacinth when they hear about water based plants. These are the most commonly seen macrophytes in polluted rivers and lakes. However, water hyacinth is eliminated from this system due to harvesting difficulties. More commonly used plants are: Lemna, Azolla, Pistia stratioides & Salvinia auriculata.
This means that macrophytes must be harvested regularly. If the plants are not harvested, they begin to discharge nutrients back into the system. Therefore, an efficient harvesting method is needed. Macrophytes are 90-95 percent water, so they are heavy to harvest. The most efficient harvesting method found after much experimentation was the simplest:
Construct a metal or wood frame with a screen about one meter in diameter, attached to a long pole then use this process:
- Drag the screen along the macrophyte pond. When the screen is full it is tilted at a 90 degree angle and the macrophytes fall beside the pond and excess water filters through the screen. At a one ha. site this process requires about ten minutes daily.
- The macrophytes are left to decompose on the pond dykes and act as fertilize. This eliminates long hours of transport. Over months and years this remarkably improves soil quality, especially when combined with passive irrigation by wastewater.
- If required, some of the decomposed macrophytes are deposited in a composting box next to the macrophyte ponds to avoid long transport. The resulting compost is then fed to worms to produce protein.
Check with local agriculture authorities to determine the best mix. However certain general points are:
- The richest soil areas are the dykes between ponds, as they receive constant passive irrigation plus fertilizer from macrophytes. It is necessary to carefully determine the soil elevation of these dykes. Too high and they miss the irrigation. Too low and they flood. An agricultural expert is required to help set the elevation.
- It is preferable to grow several layers of products: at ground level, just above ground level and a tree level. The rich soil is able to support this multiple use. Above ground level it is preferable to grow fruit trees such as bananas or citrus. Closer to ground level, crops such as tomatoes. At ground level, root crops which are only used for cooking to avoid the possibility of contamination.
- Garden areas on dykes appear dry on top, but are moist underneath.
- Integrated cropping and crop rotation are practiced to avoid soil exhaustion, parasite problems, plus increase productivity.
Photo: Food grown on site for human consumption is tested periodically, but in every case is either peeled or cooked prior to consumption. Products such as bananas, squash, sweet potatoes from the site are sold in local community store in Petropolis, Brazil.
Crops from gardens are for operator own use, sale on the market or use by the community, and feeding animals on site. The decision on use is entirely a local one. However it is good practice to feed livestock on site with food grown on site. This eliminates feed costs which constitute 70-80 percent of the cost of raising livestock. All food grown on site is tested periodically for parasites before being sold for human consumption. However crops such as fruits from trees are completely free from pathogens related to wastewater. The fruit never touches wastewater during growth.
For this reason it is necessary to avoid overhead, aspiration-based irrigation in wastewater facilities. Root systems of trees do not take up human pathogens into the fruit. The only pathogen risk to fruit occurs during harvesting. During harvesting, avoid doing other wastewater-related maintenance, to prevent contamination. In any case, it is common practice to wash fruits in potable water prior to delivery to market.