The hidden environmental costs of Activated Carbon water treatment

To get a good understanding of why this is the case, let’s briefly consider how the activated carbon absorption media is produced and subsequently renewed as well as its impact on the environment.

The carbon is created (what is referred to as ‘activated’) by pyrolysis: slowly heating the raw material like coconut shells, wood, biomass, bones or coal to around 1000°C without the presence of oxygen. (This is essentially what charcoal burners did in the woods centuries ago but on a far greater scale under highly controlled conditions.) Impurities are subsequently removed by acid washing.

The main environmental issues here are twofold:  First there’s the question of raw materials. Although coconut shells, bone and most biomass substances are by-products of recycling, coal and wood are definitely not. It could be argued that most wood used is often a by-product of another process (forestry slash, chippings and sawdust, for example.) However, the type of wood burned has a direct result upon the quality of the final GAC; almost inevitably, slow-growing oak produces a better quality than fast-growing bamboo, for example.  So on balance, the raw materials for activated carbon production may utilise precious natural resources – some of which could conceivably be used for food or fuel. And these days, that’s not a good look …

Secondly, a large amount of energy is required to turn these materials into activated carbon. In many cases, natural gas is used. Different feedstocks – even different species of plants or trees – will require different levels of energy to convert to activated carbon.

The result of the activation process is that the carbon media has an incredibly large surface area of between 1,000 – 2,000 m² per gramme, so a teaspoonful would easily cover a football field!

How GAC works is that unwanted or harmful organic compounds are absorbed by the carbon naturally, leaving far less in the water as a solution.

The massive surface area is the simplicity of GAC – yet also its drawback; because over time there won’t be enough ‘clean’ carbon left for the unwanted compounds to be absorbed and the carbon media will therefore need replacing.

In some cases, it can be returned to a reprocessing facility where it’s regenerated. This involves heating up the used carbon to over 800°C in a reactivation furnace. It vaporizes the undesirable organics and special precautions are taken to ensure emissions are safely controlled, normally by the use of an afterburner. However, doing this requires a good percentage of the energy that was used to make it in the first place! Add that to the cost of transporting it to and from the reprocessing site and the environmental impact is high.

Overall, GAC systems are reasonably predictable and may be cost-effective in some smaller systems where influent organic loading is low and media only needs changing two or three times a year.  However, carry out any kind of environmental audit on a GAC-based water treatment system and it wouldn’t score very well long-term, due to the initial energy and resource use and replenishment/disposal as well as the transportation elements involved.

Essentially a GAC-based system is an example of linear consumption with little or no recycling possibilities and a lot of energy use – the major factor in its large carbon footprint.

On the other hand, Arvia’s Nyex™ systems have little environmental impact once built and installed and are a typical example of circular economy. They carry out mainly the same tasks and score far better against activated carbon on an environmental audit basis. This is an important factor to bear in mind when considering the future; eventually, the total environmental impact (or carbon footprint) will become a major factor in any plant’s design and potentially even its permitted discharge levels.

Depending on the removal process and the particular installation, Nyex™ reactors can be scaled to any required size and configured according to the specific removal treatment. They can also be placed in various points of a wastewater treatment process, protecting existing RO (reverse osmosis) or biological systems as well as acting as a tertiary water polishing stage. It all depends upon what’s in the water and the level to which it needs to be removed.

However, the main advantage is that the Nyex™ media used in our Nyex Rosalox™ systems requires minimal replenishment – it can be as low as a couple of kilos per annum.

The unique patented process absorbs many recalcitrant compounds and as electricity passes through, chemically alters these organics, leaving very little residue.  At the same time, the unique Nyex™ media actually regenerates itself.  Depending on configuration, these systems can remove many unwanted compounds down to below measurable levels and are becoming accepted as an environmentally-responsible alternative to GAC in many industries including life sciences, specialty chemical, agrochemical, petrochemical and semiconductors. This page details all the different pollutants we can remove from water.