Wastewater Treatment: Primary and Secondary Stages

Primary Treatment

Primary treatment aims to reduce oils, grease, sand, and thick solids using machinery.

Removal of Solids

During mechanical treatment, the effluent is filtered through chambers with bars to remove all large objects that are deposited in the sewer system. Biological treatments are not designed to deal with these solids.

Sand Stripping

This equipment is called a sand trap. Sand and stones need to be removed in time during the process to prevent damage to pumps and other equipment in the remaining phases of treatment.

Primary Sedimentation Tank in Rural Treatment Plants

Research and Maceration

Solids are cut into small particles through the use of rotating blades mounted on a revolving cylinder. This is utilized in plants that can process these trash particles.

Sedimentation

Tanks are large enough that fecal solids can settle, and floating materials like grease and plastics can rise to the surface and be skimmed off.

Primary Stage

The general purpose is to produce a homogeneous liquid capable of being treated biologically and a sludge or slurry that can be separately treated.

Secondary Treatment

Secondary treatment is designed to substantially degrade the biological content of wastewater resulting from human waste, food, soaps, and detergents.

Roughing Filters

These are used to treat particularly strong or variable organic loads, typically industrial, allowing them to be treated by secondary treatment processes.

Activated Sludge

Activated sludge plants use a variety of mechanisms and processes to use dissolved oxygen and promote the growth of biological organisms that remove substantial organic matter.

Plates and Rotating Spirals

Establishing a biotic floc provides the required substrate.

Bioreactor

This maintains a high-density population of biomass, eliminating the cost of operating the activated sludge return line.

Aerated Biological Filters

The dual purpose of this medium is to support highly active biomass that binds to the suspended solids and acts as a biological filter.

Membrane Bioreactors

This technology ensures the removal of all suspended and some dissolved pollutants.

Secondary Sedimentation

The final step of the secondary stage of treatment is to remove biological flocs or filter material and produce treated water with low organic matter and suspended matter.