Compared to commercial fertilizer, the fertilizer value of digested sludge is generally:

The fertilizer value of digested sludge is generally considered to be lower than that of commercial fertilizer. This is primarily due to the differences in nutrient concentration and availability. Commercial fertilizers are specifically formulated to provide high concentrations of essential nutrients such as nitrogen, phosphorus, and potassium, making them immediately beneficial for plant growth.

In contrast, digested sludge, while it can provide some nutrient value, usually contains lower concentrations of these key nutrients. Additionally, the nutrients in digested sludge may not be as readily available to plants due to their organic content or the presence of competing substances that can inhibit nutrient uptake. The microbial biomass in the sludge may also tie up nutrients, which can further lower their availability.

Furthermore, the processing and treatment that sludge undergoes can result in various other compounds that, while possibly beneficial in the long term for soil health, do not offer the immediate nutrient kick that commercial fertilizers provide. Therefore, when comparing the two, digested sludge typically has a lower fertilizer value in terms of the immediate availability of essential plant nutrients.