Organic Waste Recycling

322 Organic waste recycling: technology and management

Figure 7.6 Different end products of harvested aquatic weeds (from Bagnell 1979;

reproduced from the permission of the American Society of Agricultural (Engineers)

Large-scale harvesting is done with the help of various mechanical devices

mounted on boats or barges. Harvesting can be carried out from a site at the

water's edge or with a self-propelled, floating harvester. Shoreside harvesting

requires that the plants float to the harvester. Rooted species must be uprooted

or mowed and then moved to the harvester by boat or by wind and current.

Plants can then be lifted from the water by hand, crane, mechanical conveyor, or

pump. On the other hand, mobile harvesters sever, lift, and carry plants to the

shore. Consisting of a large barge on which a belt conveyor and a suitable

cutting mechanism are mounted, these harvesters are mostly intended for

harvesting submerged plants. Nowadays, some harvesters have also been

designed to harvest floating plants or the mowed tops of submerged plants.

Harvesting frequency has to be chosen depending on the initial area of

coverage of the plants (or stocking density) and the area doubling time. For

example, if a plant is stocked to cover half of the pond area harvesting may be

done to remove half of the plants at every interval of doubling time. Plants such

as duckweeds which are easily piled up due to wind or could not compete with

Pulp

Wilt

Pellet

Mix

Harvest Chop Press Fiber Dry

Digest Separate Dry

Paper

Compost Ensile

Silage Dry feed

Soil amendment

Aquatic
weeds

Chemicals

Grain

Juice

Methane Feed-food

Mix