Tertiary Wastewater Treatment

Tertiary Treatment Modules Guide | Alternatives | Comparison

In this week’s blog post we cover the topic of tertiary treatment modules and compare popular units such as cocofilters, peat filter modules and filterpods. We will discuss what they are, what they do and why they might be specified in a site characterisation report by a site suitability assessor.

tertiary treatment module

What is a tertiary treatment module?

A tertiary treatment module is a wastewater treatment unit that cleans effluent to higher levels after secondary treatment. Secondary treated effluent from a sewage system either flows by gravity or is pumped to the treatment module. Inside, it filters through a medium before it discharges to ground for disposal.

There are many modules on the market but the type of medium and the size and structure of the unit will differ. The medium can consist of organic material such as peat or coconut shells. Alternatively, it can be made up of inorganic material.

How does a tertiary treatment unit work?

The basic principle of the tertiary treatment unit is biofiltration and adsorption which occurs throughout the media inside the module. The porous nature of the media adsorps pollutants in the wastewater. At the same time, microorganisms colonise the high surface area of the media and breakdown the remaining waste components. This results in a high level of treatment before the final effluent is discharged to ground.

What options are available for tertiary treatment modules?

Coco filters, peat filter modules and filterpods are some examples of tertiary treatment modules that are available on the market today.

cocofilter

Coco Filter Media

What is a cocofilter?

As the name suggests, a coco filter uses derivatives of coconut shell as the filtration media. This is an organic material with a high capacity to adsorb (retain) pollutants.

Eventually, this type of media will become saturated with pollutants and need complete replacement. The length of time this takes depends on the manufacturer’s specifications. Generally speaking, every 5-10 years is the average.

Advantages: Medium cost. Easy to install.

Disadvantages: Moderate to high operation and maintenance costs due to complete replacement media. Risk of clogging.

What is a peat filter?

Peat filter modules contain pre-compacted peat or peat fiber as media. This is a special form of peat with a very specific moisture content and degree of decomposition. It provides an ideal environment for supporting the microorganisms’ biological treatment of the sewage. Like coconut, peat will settle and decompose over time. Replenishing or topping up the peat on yearly basis can help combat problems with odor. Eventually the peat media will need complete replacement, usually every 8-12 years.

Advantages: Low to medium cost. Easy to install.

Disadvantages: Moderate to high operation and maintenance costs due to complete replacement media. Risk of clogging.

RDX media

RDX Media

What is a filterpod?

A filterpod is a tertiary treatment module which uses a synthetic medium in the form of RDX filter media. This has been specifically engineered for the purpose of wastewater treatment. The matrix of the RDX filter promotes the growth of aerobic bacteria and provides rapid adsorption of wastewater. Air can also circulate freely through the media. The top layer of the filter media needs annual replacement, but the cost is generally 25-30% less than replacing media of other forms.

According to the EPA Code of PracticeWastewater Treatment and Disposal Systems Serving Single Houses (p.e < 10), any tertiary treatment system selected for treating secondary effluent must conform to prEN 12566-7, this is easily checked with the supplier/manufacturer.

Advantages: Low cost. Easy to install. Can be used to replace percolation area.

Disadvantages: Top layer of media needs to be replaced intermittently.

Advantages of tertiary treatment units

By comparison to alternative forms of advanced treatment such as sand polishing filters, tertiary treatment modules are very straightforward to install. They do not have to be constructed on site as the unit is already fully equipped by the supplier. Additionally, they have a smaller footprint and are suitable for installation above or below ground. This means that installation is quicker, easier and less costly than other forms of tertiary treatment.

Why do I need a tertiary treatment module?

An engineer or site assessor specifies a tertiary treatment system based on a number of factors including the site conditions, the level of secondary treatment and the requirements of the receiving waters. The sensitivity of the receiving waters and the permeability of the soil depend largely on the site location. The loading rates will dictate the level of tertiary treatment required.

If you do need a tertiary treatment module, bear in mind that it does not have to be the exact model specified in the report. You may choose a suitable alternative that meets the treatment standards set out in the report. The treatment efficacy of any unit on the market today is easily checked with the supplier/manufacturer.

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