Clearing dense aquatic vegetation through mechanical harvesting can restore and improve waterbody function while reducing nutrient loads. It also increases recreational use. Mechanical dewatering separates sludge into liquid and solid components for waste minimization. This is achieved through a physical process in filter presses or a chemical process using conditioning polymers.

Removing Nutrients

Invasive plants interfere with a lake’s natural beauty and ecosystem, restrict fish growth rates, cause water quality issues, block recreational use, and negatively impact property values. The District is constantly evaluating and monitoring nuisance aquatic vegetation and the best ways to control it. This can include lowering water levels (drawdowns) and mechanical, biological, and chemical methods, including herbicides, harvesters, and triploid grass carp, a weed-eating fish. Mechanical dewatering separates a solid product from its liquid part using mechanical force like belt filter presses, centrifuges, or sludge drying beds. The result is less material that is easier to transport, compost, or incinerate and easier to dispose of in a landfill.

Increasing Recreational Use

For many pond owners, aquatic vegetation management is one of their most complex problems. Vegetation can interfere with swimming, fishing, and other recreational activities, detract from the beauty of a lake or pond, and create fish habitat problems. Licensed professional applicators can use draglines, cutters, rakes, booms, and mechanical harvesters to remove unwanted plants from ponds and lakes. These control methods don’t require introducing chemicals into the water body and can reduce the frequency of chemical treatments.

Identifying your specific nuisance plant is the first step in proper vegetative management. Some plants cannot be treated with a herbicide; others may not be controlled by grass carp, and some species benefit your pond. It is also essential to recognize that a weed-free aquatic system is not necessarily biologically healthy. This is particularly true when a ‘good’ plant species goes rogue in a pond where it cannot compete with other plants.

Increasing Water Flow

Mechanical dewatering separates sludge (residual sludge from wastewater treatment plants or fecal sludge from on-site sanitation such as septic tanks or pit latrines) into a liquid and solid component that is easier to transport, easier and more cost-effective to process for composting or incineration, or disposal. It does not treat sludge or sewage sludge; the solid and liquid components still contain pathogens and pollutants.

The most common methods for dewatering sludge are belt filter presses and centrifuges. These devices are sophisticated and expensive to operate. They also require a high amount of conditioning polymer to function effectively. Drying beds are another option for dewatering, but they require large areas of land or tanker trucks to transport sludge for the drying process. 

Reducing Nutrient Loads

While mechanical concentration does not eliminate the wastewater’s nutrient load, it significantly reduces it. The nutrient-rich reject water from conventional mechanical concentration systems contains from 10% to 20% of the nitrogen and phosphorus that entered the treatment plant in the first place. This rejected water can be pumped out of the process, sent to a drying pond, or transported in tanker trucks. However, these options require the presence of large areas of land within pumping distance and proper permitting.

By contrast, chemical separation and dewatering processes use less land because the liquid and solid components remain separated. Moreover, the higher calorific value of drier biomasses decreases the need for auxiliary fuels and cuts production plants operating costs.