Bio-Sludge Treatment
- 1. What are bio-solids?
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Bio-solids are the major by-product of the wastewater treatment process. When treated and managed appropriately,
they can be beneficially used for a number of purposes.
The bio-solids is careful to distinguish from the sewage sludge. Bio-solids can only be considered
as such once they fulfill the requirements of a set of approved bio-solids management guidelines.
- 2. What is in bio-solids?
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Bio-solids are derived from wastewater sludge, mainly a mix of water and organic materials
that are a by-product of the sewage treatment processes. Most wastewater comes from household kitchens,
laundries and bathrooms. Bio-solids may contain:
· Macronutrients, such as nitrogen, phosphorus, potassium and sulphur and
· Micronutrients, such as copper, zinc, calcium, magnesium, iron, boron, molybdenum and manganese
Bio-solids may also contain traces of synthetic organic compounds and metals, including arsenic,
cadmium, chromium, lead, mercury, nickel and selenium. These contaminants limit the extent to which bio-solids
can be used, with all applications regulated by appropriate government authorities in each State and federally.
Australia has one of the strictest regulatory regimes for bio-solids production and application in the world.
Treatment processes produce a stabilized product suitable for beneficial use. Bio-solids normally contain between 15% and 90% solids.
- 3. What are bio-solids used for?
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Bio-solids can be applied as a fertilizer to improve and maintain productive soils and stimulate plant growth.
They are also used to fertilize gardens and parks and reclaim mining sites.
Bio-solids are graded according to chemical composition and the level of pathogens remaining after production.
Not all bio-solids can be used for all applications. Lower qualities are typically used for road bases and mine site rehabilitation.
Only the highest grade of bio-solids can be used to grow crops for human consumption.
Regulators, such as State departments of Health and Environment strictly control the production, quality and application of bio-solids.
Normally, bio-solids have been used for:
· Co-generation/power production/energy recovery
· Land application in agriculture (vine, cereal, pasture, olive)
· Road base
· Land application in forestry operations
· Land rehabilitation (including landfill capping)
· Landscaping and topsoil
· Composting
· Incineration
· Landfill
· Bricks and construction material
· Vitrification (glass manufacture)
· Bio-fuel
· Fuel substitute (cement works)
- 4. How are bio-solids made?
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The main target for the bio-sludge treatment system is to reduce volume by dewatering,
drying and to disinfect. Sludge from wastewater and foodwaste represents a large volume
that needs further treatment to align with the environmental requirements
for no pollution at sea, the need for a sludge treatment process onboard is obvious.
Dewatering of sludge increases dryness up over 20% reducing the volume 90%.
To increase the dryness further, all dewatered sludge is treated in a drying process.
The process increases the dryness up to 60%, making the solids burnable.
The use of the thermal hydrolysis process in sludge treatment for WWTPs presents
some major advantages in terms of energy, public health and environmental protection.
Medium-sized plants can be converted, with the import of sludge from other nearby plants, into strategic sludge treatment centers.
Here biogas production from anaerobic digestion is maximized using existing capacity, generating a pasteurized sludge with high dry solids content.
The generation of electricity from renewable sources, produced from biogas, allows the energy costs
of the WWTP plant itself to be reduced and the WWTP may even have surplus energy production.
The use of thermal hydrolysis achieves the following:
· Generates more energy (higher biogas production).
· Reduces the final amount of sludge. It improves sludge dewatering up to 40% DS.
· Treat organic food wastes and edible fats and oils
· Ensures sludge pasteurization, i.e. a pathogen-free sludge
· Produces a stabilized an compost-like product, with 70% decrease in odour.
· Increases the speed and capacity of digestion (less digestion volume).
· Reduces carbon footprint.