Wastewater Purification Methods

Wastewater Treatment

Wastewater treatment is a widely used plant purification method. Separating gray water from black water (sewage) can reduce costs, as can removing detergents and oils. Purifying water involves a series of physical and chemical processes, which vary depending on the order in which they are applied.

Wastewater Treatment Plant Classification

• Primary Treatment: Primarily removes inorganic solids, often with the aid of adjuvants.
• Secondary Treatment: Removes organic matter using microorganisms.
• Tertiary Treatment: Eliminates specific components or purifies microorganisms.

Primary Treatment Processes

Sand Chamber

Mineral residue is removed.

Sedimentation

After removing mineral waste, water passes through a sedimentation tank where organic materials are deposited for disposal.

Flotation

Water is saturated with air upon inlet, then moved to an open tank. Air bubbles rise and carry suspended solids to the surface, where they are removed.

Digestion

This microbiological process converts sludge into methane. Reactions occur in a closed, anaerobic tank (without O₂).

Drying (Desiccation)

Digested sludge is laid on sand beds to air dry, which requires a warm, dry climate. The dried sludge can be used as fertilizer.

Secondary Treatment

Secondary treatment reduces organic matter in water. Normally, microbial processes remove organic matter aerobically. In the presence of O₂, aerobic bacteria convert organic matter into stable forms. Remaining organic matter should be removed before discharging water into the receiving channel.

Secondary Treatment Processes

• Trickle Filter: Wastewater flows through a porous bed coated with a film of microorganisms that convert organic matter into CO₂ and water.
• Activated Sludge: Gelatinous sludge particles containing millions of aerobic bacteria are suspended in an aerated tank, absorbing and converting organic matter.
• Treatment Ponds (Lagoons): These ponds have an anaerobic zone near the bottom for solid decomposition and an aerobic zone near the surface for oxidizing organic and colloidal matter.

Tertiary and Advanced Treatment

Tertiary treatment is often used to remove phosphorus, while advanced treatment includes additional steps to improve water quality by removing recalcitrant pollutants. Processes exist that can eliminate 99% of dissolved solids. Suspended solids are removed by reverse osmosis and electrodialysis. Removing ammonia, nitrates, and phosphates can significantly reduce nutrient content.