What Are the Prinmary & Secondary Stages of Wastewater Treatment?

There are three main stages of the wastewater treatment process, aptly known as primary, secondary and tertiary water treatment. In some applications, more advanced treatment is required, known as quaternary water treatment.  Arvia Technology specialise in advanced tertiary and quaternary wastewater treatment. This article seeks to give an explanation of the primary and secondary stages of wastewater treatrment

What is primary wastewater treatment?

During primary treatment, wastewater is temporarily held in a settling tank where heavier solids sink to the bottom while lighter solids float to the surface.

Once settled, these materials are held back while the remaining liquid is discharged or moved through to the more rigorous secondary phase of wastewater treatment.

These large tanks are also often equipped with mechanical scrapers that continually drive collected sludge in the base of the tank to a hopper which pumps it to sludge treatment facilities.

What is secondary wastewater treatment?

Secondary treatment of wastewater works on a deeper level than primary and is designed to substantially degrade the biological content of the waste through aerobic biological processes.

Completing secondary wastewater treatment allows for safer release into the local environment, reducing common biodegradable contaminants down to safe levels.

It is done in one of three ways:

 

1

Biofiltration

Biofiltration uses sand filters, contact filters or trickling filters to ensure that any additional sediment is removed from the wastewater.

2

Aeration

Aeration is a lengthy process which increases oxygen saturation by introducing air to wastewater. Typically, the aeration process can last for up to 30 hours, but it is very effective.

3

Oxidation ponds

Typically used in warmer climates, this method utilises natural bodies of water such as lagoons, allowing wastewater to pass through for a set period before being retained for two to three weeks.