Enhancing Livestock Effluents through Vermifiltration
In an aquaculture or agricultural farm, effluent management is an important environmental concern due to their potential impact on water and soil quality. Rich in nutrients (Nitrogen and Phosphorus), the valorization of these effluents often involves their spreading to amend soils. To significantly reduce their volume and accelerate the mineralization process of the nutrients they contain, innovative composting solutions are being developed, such as vermifiltration.
Suspended solids (SS) discharged in large quantities to manage
Aquaculture farming, like any living system, generates waste. These discharges, composed of SS and dissolved substances, mainly come from the feeding of the fish: some portions of the feed are not consumed, others are ingested but poorly digested, and part is digested but not fully utilized by the fish.
The amounts of waste produced mainly depend on the quality of the feed, the way it is distributed, and the health of the stock. The feeding method (manually or via automatic feeders), the timing, the frequency and duration of feedings, and even the water temperature are all factors that influence the amount of feed wasted.
Besides feed management, water flow and renewal in the system also play a crucial role in the concentration of solid and dissolved compounds. These compounds are expelled by fish as feces (solid nitrogen and phosphorus, feed residues) and through gills and kidneys as ammoniacal nitrogen and carbon dioxide.
Too high a concentration of SS can have negative effects on the farm, irritating the fish gills and promoting bacterial proliferation.[1] To avoid these problems, it is essential to filter the SS present in the water using mechanical systems such as sand filters or rotary screens.
Vermifiltration
Vermifiltration is an innovative method that uses earthworms to treat aquaculture effluents. Unlike traditional sludge storage or mineralization solutions, this process allows the direct spraying of water loaded with organic particles onto a filtering substrate populated by earthworms. These worms, true champions of mineralization, absorb up to 95% of the SS contained in the sludge, producing a vermicompost from which the water passing through the vermifilter extracts the nutrients and produces a leachate output also called "worm tea".
The vermifilter consists of a sealed container filled with an active layer of forest chips, where earthworms (Eisenia andrei or Eisenia fetida) are seeded and live. They degrade the organic matter, and the resulting percolate is then drained to be used as fertilizer either in plant loops decoupled from aquaculture circuits or in field crops.
On average, a vermifilter can digest 1.25 kg of SS per m² per day and absorb about 30% of the water from the sludge extracted from the system.
| SS removal/m²/day | % water absorbed | Field spreading |
|---|---|---|
| 1.25 kg | 30% | 8L/m²/day |
This natural solution, besides reducing waste, produces a nutrient solution and a high-quality compost, thus reinforcing the virtuous circle and possible synergies between aquaculture and agriculture. Rich in nutrients and microorganisms (bacteria, fungi, protozoa, nematodes, etc.), these fertilizers are true boosters for plant development and soil microbial balance. The "tea" thus produced can be spread in the field at a rate of 8L/m²/day or used as a fertilizing nutrient solution supplied to plants.
However, due to the potential presence of pathogenic bacteria and its high mineral concentration, the "worm tea" must not be used on plant loops coupled to aquaculture circuits to avoid disturbing the physico-chemical balance and introducing pathogens very dangerous to your stock (be careful with hand washing, tools, etc., and prevent any contact of vermicompost or worm tea with the farming system).
- ↑ LES REJETS DES STATIONS PISCICOLES ET LEURS IMPACTS ENVIRONNEMENTAUX - Guy Ouellet - 1999 http://collections.banq.qc.ca/ark:/52327/bs58581
