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 Biosolids
are the nutrient-rich organic by- product of municipal wastewater
treatment. When treated and processed, wastewater solids become biosolids
which can be safely recycled and applied as fertilizer. Only biosolids
that meet the most stringent federal and state standards are approved
for use as a fertilizer. Standards limit the amount of heavy metals
and potential pathogens that are allowed in biosolids. Biosolids recycling
has been a smart conservation and environmental practice for decades
and is on the increase in the United States. More than 25% of all
municipal biosolids generated in this country are applied to farmland.
Today, compositing is the recycling technique of choice for biosolids at the
Portland Water District. Composting uses high heat for extended periods of time
to kill disease-causing organisms and produces the cleanest biosolids.
- returning resources back into nature's cycle
- utilizing waste as a resource rather than landfilling or incineration
- adding nutrients to the soil that may not be added by commercial fertilizers
- improving soil structure and overall soil fertility
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Treated biosolids contain the three primary crop nutrients: nitrogen,
phosphorus and potassium. They also contain several nutrients that crops need in
smaller amounts: sulfur, magnesium, manganese, iron, calcium, copper and zinc.
These nutrients are not found in most commonly used commercial fertilizers.
Organic matter in biosolids releases nitrogen and other nutrients over
several growing seasons, while chemical fertilizers are much more quickly
removed from the root zone by water trickling through the soil. Organic matter
also improves soil structure, increasing its ability to absorb and hold
moisture.
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