The use of airlifts to provide circulation, aeration, and carbon dioxide stripping not only saves energy, but also provide s a degree of disease isolation and a relatively stable head environment facilitating implementation of pneumatic sludge discharge. Pneumatic sludge discharge utilizes head differentials generated in the cyclic backwashing of a PolyGeyser® bioclarifier to drive sludge removal eliminating the need for manual or pumped intervention for this crucial task.
Use of a RAS specific (localized) sludge basin provides for nearly 100% return of the immediate water loss associated with the sludge removal process . These discharged waters are encouraged to drop (settle) solids before being returned to the bioclarifier as pressure conditions change. Captured sludge is then dramatically reduced in mass by digestion before being finally removed after many backwash cycles .
The sludge digestor can be operated aerobically , anaerobically, or sequentially. For aquaponic applications sludge residence times of 5-10 days appear sufficient to achieve a high degree of nutrient release as the sludge volume is reduced by nearly 50% under aerobic conditions . Use of a hypolimnetic aerator (HLA) configuration maximizes clarification potential. Splitting return waters post airlift facilitates “solids free” dosing to hydroponic systems with nutrient enriched waters. Isolation of the hydroponic component from the fish component allows for optimization of water quality for plant growth while avoiding long term salt accumulation.
After considering digestion modeling analysis, a sizing recommendation of 83 liters/kg feed-day ( 10 gallons/lb feed-day) is being made for aquaponic applications. W hen pairing the digestor with a fl oating bead bioclarifier , a guideline of 1.3 liters-digestor/liter -beads (10 gallons/ft3-beads) can be used when current aquaponic filter loading criteria 62 liters/ kg feed-day (1 ft3/lb feed-day) are considered.