Sewage Vetting: Treatment Processes & Low-Cost Technologies
Artificial Vetting of Sewage: Treatment Systems
Pretreatment
Objective: Prepare water for treatment by removing coarse solids, gravel, sand, and grease.
Processes:
- Grinding
- Sand Removal
- Degreasing
Taper: Removal of large solids using filtration screens and grates.
Desanding: Eliminates gravel and other objects. Sedimented objects are scraped and washed.
Degreasing: Removes fats and oils by reducing flow velocity, allowing them to surface.
Primary Treatment
Aims to reduce suspended solids in wastewater.
Processes:
- Elimination of Toxins
- Neutralization (pH adjustment 6.5-8.5)
- Coagulation-Flocculation
Coagulants: Substances that destabilize colloidal particles, allowing them to group.
Flocculants: Group destabilized particles into larger clusters for easier settling.
Decanting: Water stands to allow solids to settle in circular decanters with conical bottoms. Settled sludge is scraped and pumped for further treatment.
Secondary Treatment
Effluent from primary treatment is exposed to bacteria and protozoa to break down organic substances.
Biomass (activated sludge) is suspended in wastewater with oxygen and agitation. Wastewater and sludge mixture is processed for 4-8 hours before secondary decanting.
Secondary Decanting: Similar to primary decanting, reduces germs by 90% or more.
Tertiary Treatment
Further improves water quality by removing specific contaminants.
Disinfection: Pathogenic germs are removed using UV radiation.
Sludge Treatment
Residue from decanting processes with high water content and organic load.
Objectives: Reduce volume, decrease water content, increase manageability, reduce transport and disposal costs.
Processes: Concentration, thickening, flotation, centrifugation, aerobic/anaerobic digestion, conditioning (chemical reagents), dehydration, drying, filtration.
Digestion: Removes organic matter and stabilizes sludge.
Dehydration: Removes water for easier handling and disposal.
Sludge Fate: Fertilizer, direct ground application, product recovery.
Low-Cost Purification Technologies
- Impoundment (Stabilization Ponds)
- Green Filter
- Peat Beds
- Rotating Biological Contactors
Impoundment: Water stored in ponds for aerobic or anaerobic treatment. Low cost, minimal maintenance, but requires large land area.
Green Filter: Uses trees with fast growth and low-quality wood to filter pre-treated urban water.
Peat Beds: Filtered and degreased water is applied to peat.
Final Destination of Treated Water and Sludge: Cities, streets, lawns, gardens, agriculture, recreation, aquifer recharge.
Wastewater Purification in Communities
Septic tanks and Imhoff tanks are used for primary decantation and subsurface infiltration. Gases from anaerobic fermentation are vented.