Aquatic weeds and their utilization 3217.5 Harvesting, processing and uses
Harvesting aquatic weeds from the waterways and utilizing them to defray the
cost of removal is one of the most successful approaches to aquatic weed
management. It results in weed-free waterways while providing an extensive
vegetation resource. This is especially advantageous in developing countries
where forage and fertilizer are in short supply.
The removal and recycling of nutrients and other components is done by
harvesting, processing and utilizing the aquatic plants in which the nutrients are
collected. The whole process is shown by a simple schematic diagram given
below:
AQUATIC WEEDS ĺ HARVESTING ĺ PROCESSING ĺ PRODUCT ĺ USESA complete network of the possible processes used to convert aquatic weeds
to a variety of products is shown in Figure 7.6. Harvesting and chopping are
precursors to all of the other processes and all of the products. The chopped
plants can be applied directly to land, composted to stabilize and reduce mass,
digested to produce methane, pulped to produce paper, or pressed to reduce
moisture content and produce a highly reactive protein-mineral-sugar juice. The
juice can be separated to recover a high quality food-feed protein-mineral
concentrate or digested to produce methane. The pressed fibers may be ensiled
with appropriate additives or dried to produce a granular feed component.
This section deals with all uses of harvested weeds, except the use of weeds
as food and feed, which is dealt separately in section 7.6 (Food Potential of
Aquatic Weeds).
7.5.1 Harvesting
Harvesting can be accomplished manually or mechanically, depending on the
amount of weeds to be harvested and the level of available local technology.
Large floating plants such as Eichhornia crassipes and Pistia stratiotes can
be lifted from the water by hand or with a hayfork. Smaller floating plants such
asLemna or Azolla can best be removed with small mesh sieves or dip nets.
Submerged plants can be harvested by pulling rakes through the under-water
plants. Emergent and floating-leaved plants can be cut at the desired height with
knives, or in areas with loose bottom soil, pulled by hand. One man can harvest
1,500 kg or more of fresh weight of plants per day from moderately dense
stands of most species.