Water Technology Comparison with Nyex™

The main disadvantage of ion exchange is the fact that you regularly and frequently need to shut down the plant to do a brine backwash to remove accumulated salts, minerals and metals. This means you either face discontinuous operations or that you need another plant as duty standby, which doubles your CapEx.

Ion exchange vessels require regular inspection and unloading and loading of new exchange resins, which are disruptive to operations and mean ongoing operational costs.

The new exchange resins must be specific to the manufacturer’s specification, making switching suppliers difficult without replacing the full system.

When you shut down an ion exchange water treatment plant, you can get microbial growth which can cause flow and treatment issues when the process is restarted. This  adds training, labour and operational cost.

GAC and PAC can cause a significant carbon footprint of which your sustainability department may not approve. This is because the effectiveness of the carbon decreases as it absorbs the pollutants. Depending on how high your COD levels are, it frequently needs to be scooped out of your treatment tank and transported offsite for regeneration or disposal, which is very environmentally unfriendly.

Operational costs can be very high in applications where chemical oxygen demand (COD) or pollutants loading is high in industrial water treatment. This is because the carbon absorbs/filters the contaminants and requires replacement once filled, which results in a regular ongoing cost.

During carbon renewal servicing, the plant is not operational so either you need to make plans to reroute the wastewater to another plant or carbon bed (double CapEx) or you need to accept discontinuous ops.

Careful maintenance of the carbon bed is required to ensure that the media is not left for too long without regeneration or replacement as this will result in the process becoming ineffective and risks COD levels or specific pollutants remaining in the effluent and causing risks of pollution and environmental fines.

An activated carbon bed provides ideal conditions for micro-organism growth which can block and inhibit treatment. However, this is not an issue when using an advanced oxidation process as hydroxyl radicals (·OH) inhibit micro-organism growth.

Activated carbon does not work on non-absorbing organics.

Ozone systems have an extremely high capital cost due to the high risk associated with ozone gases, systems must be highly automated and robust.

The operational costs of running an ozone water treatment plant is also extremely high. It typically uses 10kWh per kg of ozone. Furthermore, oxygen is expensive to buy. If you choose to make your own ozone processing oxygen from the air, you only end up with 4% of the volume as ozone, so not efficient. On top of that, ozone has a half life of 12 minutes so your plant needs to use the ozone within 5 minutes of the ozone being produced for any kind of efficiency to be achieved.

The biggest challenge for your ozone plant is how to get the ozone into the water evenly and with small enough bubbles so you maximise the treatment time period. Typically the diffusers get blocked by contaminants, which causes large areas of the treatment tank which is left untreated.

One of the main drawbacks with an ozone AOP is that it requires complex chemistry tailored to each specific contaminant.

Ozonation towers have a transfer efficiency of 50-70%, so you almost always need another water treatment plant downstream of the ozone plant.

An ozone system contains fatal concentrations of ozone, which means that detectors and careful safety procedures are essential. This takes time in monitoring the system, planning for accidents, training site staff and costs for relevant insurances. Ozone treatment also relies on the usage of liquid oxygen, which is highly flammable and must conform with facility fire safety requirements.

During treatment, ozone can produce harmful by-products such as bromate, which as a carcinogen is often more harmful than the original pollutant.

Traditional advanced oxidation processes (AOPs) such as Ozone + Hydrogen Peroxide (O3/H2O2) rely on the generation of hydroxyl radicals from the H2O2, which acts as an oxidizing agent for the process. The limitation is that the hydroxyl radicals created are nonselective – they can be used up when they ‘scavenge’ other water quality parameters such as organic matter, turbidity, alkalinity, and nitrite. This reduces system effectiveness during oxidation of contaminants and means that inlet water must be of a very specific quality for the process to be effective.

Not all contaminants or bacteria are captured by a filter process. Smaller particles pass through the membrane, requiring an additional water treatment process.

If filters in an effluent treatment plant are not sufficiently maintained, they will clog and become ineffective for the removal of suspended particles. The maintenance periods must be carefully considered dependent on the fluctuating levels of pollutants in the passing wastewater. The maintenance can sometimes be disruptive to treatment and require staff training.

The ongoing cost of water treatment chemicals to run the Fenton process is high. Moreover, as governments clamp down on wastewater treatment processes which produce by-products like sludge, the recurring cost to remove and dispose of the sludge is also increasing.

The formation of toxic sludge from the Fenton process must undergo specialist treatment by a third party, often requiring incineration or landfill. This has negative environmental implications which can damage a company’s reputation and hinder environmental strategies.

Dependent on the pollutants in need of treatment, the chemistry of the system can be complicated. This requires specialist training and ongoing maintenance which increases treatment costs.

The dosing of hydrogen peroxide can present negative impacts on later treatment steps and render the treated water unsuitable to be reused.

The effectiveness of this water treatment is a function of how well the H2O2 is mixed. It needs to be uniformly distributed into the treatment tank so that it has a chance to react with all the contaminants.

Hydrogen peroxide used to dose a UV system but this is a dangerous oxidant to store and use. It requires COSHH training and careful operations, which adds expense.

Once the contamination level has been reduced, then the random nature of the hydroxyl radicals inhibits the ability of this process to further treat the contamination. This is because as the concentration of contaminants reduces, the short-lived hydroxyl radicals may not ‘bump into’ a pollutant compound before they disappear. To achieve low levels of reduction you need more hydroxyl radicals which adds cost.

Reverse osmosis (RO) systems are high CapEx and high OpEx. They pump water at very high pressure through the filters which are made out of material similar to drum skins.

Reverse osmosis systems in general are very high maintenance. Water must be pre-treated to protect the filters from clogging. Despite attempts to protect the filters, the reality is that they do clog, and when they do, they are expensive to service or replace.

Although reverse osmosis treats water without chemical dosing, biocides are used to clean the filters and to prevent bacteria from becoming trapped in the membranes (biofouling).

The reject stream from an RO system contains twice the amount of salt as seawater which is often disposed of back to the ocean, with untold impacts on the ecosystem.

The floc forms into a sludge which then requires specialist treatment by a third party, involving incineration or landfill which are both damaging to the environment.

Coagulation and flocculation in wastewater treatment involves chemical dosing – this carries ongoing costs to buy the water treatment chemicals, training and health and safety assessments.

The process requires accurate chemical dosing and careful monitoring in order to remain effective. This may be an unsuitable wastewater treatment method if the inlet water quality fluctuates often. Factors like the type of chemical, mix amount and pH level will need to be amended and will often require a desktop ‘jar test’ to check performance.

If bacteria are not completely removed, they can remain active and re-contaminate the water after time. This means that often a second disinfection step, like dosing chlorine, is required after a physical disinfection so that bacteria do not re-grow in water as it is distributed around a water supply network.

When a chemical disinfection step is adopted, this can sometimes leave a residual taste and odour in water, causing issues for consumers.

Biological wastewater treatment is a slow process and often has a large footprint, particularly anaerobic digestion.

Aerobic treatment requires aeration which can consume high energy levels to operate.

This process also produces bio-solids/sludge which requires specialist disposal, which often involves incineration and landfill, which has negative environmental impacts.

Although biological treatment can remove a range of organic contaminants, residues of some chemicals and pharmaceuticals remain in effluent following treatment.

The inlet water to a biological process must also be carefully monitored as there are some organic contaminants which can damage biological systems, making them ineffective. This is where we can help, removing chemicals like phenol to protect bugs.