To optimize the mineralization process, there are a few things to keep in mind.
The concentration of the solid waste depends on the type of solids filtration in your system. While there is no precise metric for concentration of effluent, think of Goldilocks. If the solid waste is too dilute, there isn't enough organic matter to feed a robust microbial community. If it's too thick, you can't properly aerate/mix the solids. This will create low oxygen zones, increasing the likelihood of harmful gas buildup and loss of essential nutrients. Effluent should appear slightly murky with a yellow/amber to tan "tea-like" tint, with most solids settled to the bottom after aeration is turned off. Table 1 provides a general guideline based on type of filter.
Table 1: Filter Guide
Filter Type Water Volume Discharged Solids Concentration Best Application
Cone-Bottom Clarifier Low (daily drain) High Use as-is
Radial Flow Settler Low-Medium High Use as-is
Bead Filter High (frequent backwash) Low Needs to be concentrated
Drum/Screen Filter Medium Medium-High Use as-is
Most aerobic mineralization systems are operated as batch or continuous. Batch system use multiple tanks operating in rotation. While one tank is actively mineralizing, another is being filled with fresh waste, and a third is used as the finished nutrient solution. Continuous systems are constantly being filled and then drained, without concern for complete mineralization. Many producers will opt for a continuous system, as it conserves space, requires less management, and shows comparable nutrient recovery to batch systems.
A good rule of thumb is to have your mineralization system be 5-10% of your system volume. For a 4,000-gallon system, a continuous mineralization tank will be ~250 gallons. In a batch system, you may have three 300-gallon tanks.
For mineralization, almost any tank can be utilized; however, the most important consideration is that the tank is food-grade and UV-resistant. Intermediate Bulk Containers (IBC) are a good option, as they are low cost and food safe. 5. Target a dissolved oxygen level of 4-6 mg/L
5. Target a dissolved oxygen level of 4-6 mg/L
To accomplish this, at least 1 cubic foot per minute (CFM) of aeration per 100 gallons is recommended. The air pump may need to be upsized to accommodate for the depth of the tank. Multiple air diffusers are preferred.
Mineralized fish waste can also be directly applied to soil to increase nutrient levels for soil-grown plants. Use in moderation due to potential accumulation of salts in soil.
Figure 2 (Image Source: KSU Mineralization System: Janelle Hager)
Acknowledgement: National Science Foundation No. KYX80-23-37A.
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