Sewage Sludge & Biosolids

Treating wastewater leaves a nutrient-rich sludge. Handled well, it becomes fertilizer or energy — handled badly, it pollutes.

After sewage is treated, the solid residue (sludge) is stabilised — usually by digestion — into "biosolids". That material is rich in organic matter and nutrients, so it is too useful to just dump.

Where It Goes

• Land application — as a soil conditioner on farms, under strict limits.
• Energy — digested to biogas, or burned for heat and power.
• Compost — blended with green waste for safe soil products.

Why Rules Matter

Biosolids can carry contaminants, so treatment and testing are required before spread. Good regulation keeps the nutrients working for soil without harming water or food. It connects to our biogas guide and composting guide.

Related Reading

See anaerobic digestion, composting, and the circular economy.

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