Minimizing environmental impacts of water purification

amanda.cove

With ever-increasing discussions on the impacts that we are having on the environment, how do suppliers ensure that the products that they produce don’t add to the problem?

Guest blogger Dr Paul Whitehead will be posing this very question while discussing how the choice of technologies used within these very systems can help to move towards safeguarding our future.

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Given that we live in a world where the scope to use resources is limited by climate change, it is important for us to minimize the effects of water purification on the environment. Some of these effects have recently been discussed in a number of events and webinars; however, these have failed to include an overview and to tackle a number of important aspects of the issue.

Potential environmental impacts arise in all areas of pure water delivery: the production, testing and transport of a new purification system and the entire life-cycle of its use and disposal, including servicing and consumables. Water purification system design and the choice of technologies and components play key roles in limiting the environmental impact of a system.

The key and largest impacts on the environment are placed by total energy consumption, expressed as carbon footprint, water usage and component composition and disposal/reuse. However, reductions of environmental impacts can be affected by the corporate ethos of the system manufacturer.

Environmental Innovation

 Veolia is an organisation linked closely with resolving environmental issues and it works to increase employee awareness and involvement. For example, a recent employee-orientated campaign “Together, committed to the environment” has been launched. In practical terms, such initiatives can lead to significant environmental and, in the mid-to-long term, financial savings.

Examples include the use of spin-welding and ultrasonic welding rather than hot-plate welding to seal together the sections of water purification cartridges and the recycling of water used in testing new units. The former has led to significantly lower energy usage and also saved time and increased reliability, making further energy savings, while the latter has saved considerable volumes of water without any loss in effectiveness of testing.

Carbon Footprint Calculator

As a holistic approach to ‘environmental impact’, an online calculator has been set up to estimate the carbon footprint for each product (and a combination of products) for their full lifetime. It takes into account the estimated water usage, consumables, accessories, product delivery, number of services required as well as an assessment of the transport mode.  This approach allows for the comparison of different products and identifies the steps which produce most carbon so that alternative solutions can be considered.

Production and Distribution of Water Purification Systems

In manufacturing and production, the choice and types of component used and their suppliers, and the use of energy-efficient and/or water-efficient techniques all lead to reduced environmental impact directly, and to reduced service call-outs through increased product reliability. In addition, the following factors are also taken into consideration: localized distribution centres, lower carbon sea rather than air transport and reduced product packaging.

Operational Aspects

The purification technologies selected will have a major impact on water and power usage throughout the life of a product. Each consumable will have a carbon footprint and there will also be a footprint for any service visits. Overall the objective is to maximise the lifetime of components and the reliability of the system, hence to minimize service visits. Other operational aspects include the reduction of power usage by 5% per product and reducing the product waste water by 12% per unit.

Purification Technologies

Reverse Osmosis versus Distillation

The choice of technology to remove the great majority of impurities in the feed water lies between distillation and reverse osmosis (RO). In environmental (and economic) terms, distillation requires far more energy. For example, producing 1 litre of distilled water typically requires 1.65kW of power and about 9 litres of cooling water; in comparison, producing 1 litre of RO permeate requires less than 0.1 kW and less than 5 litres of water. The waste water from RO is cold and similar to the feed water and could be used in various grey water roles. ELGA uses only reverse osmosis in its water systems due to the energy costs of distillation and its limited purification capabilities.

Optimization of RO

Optimum operation of RO systems minimizes the frequency of changing subsequent purification consumables, notably the purification packs. For this reason, simply minimizing water rejection in RO can be counter-productive environmentally in the long term.

Dissolved Carbon Dioxide

Dissolved carbon dioxide is a common contaminant of hard feed waters that is not removed by RO. Its presence will seriously reduce purification pack lifetimes. It is effectively reduced to low levels by degassing the RO permeate, with significant benefits environmentally. Degassing also reduces the load on water purifiers using electro-deionization (EDI) systems and enables them to be used effectively with a much wider range of feed-waters. EDI deionizers have a relatively high carbon footprint to manufacture but reduce subsequent cartridge change frequency significantly.

Optimization of ion-exchange

Good design ensures that, as far as possible, each purification step is run optimally to minimize, for example, the change out of filters and UV lamps. With ion exchange, a twin-bed approach with intermediate resistivity monitoring maximises the use of active media.

Other considerations

Seemingly minor enhancements all accumulate to reduce environment impacts e.g. the use of high purity quartz in the UV chambers prolongs life and increases robustness. Bacterial build-up can seriously reduce component life and system performance. System sanitization must be available but only needs to be done as required to maintain specifications and to minimize filter changes; a rigid regime can be wasteful.

Recirculation of the purified water through the purification technologies is vital but power usage and water warming can be minimized by intermittent recirculation. Overall, after the RO stage there need be no water wastage. Point-of-use filters will need a brief flush to rinse them but point-of-use cartridges containing media are particularly environmentally poor as they are not part of a recirculation system and require extensive flushing with highly purified water before use.

Recycling of components, especially consumables and purification media would be environmentally desirable, but is difficult to achieve in practice due to costs (both environmental and financial) of transport and processing.  This is an area which will develop with other more general recycling.

Overview

There are significant environmental impacts from the manufacture and use of water purification systems. The possible effects on the environment need to be built into corporate thinking to be really effectively tackled. Establishing carbon footprints is an important step.  Water purification system design and the choice of technologies and components to use clearly play key roles in limiting the environmental impact of a system in manufacture and routine running costs and servicing. Enhancements, such as intermediate resistivity monitoring and degassing, which optimise the lifetimes of components will minimize the environmental impact of both the production and transport of consumables and service visits. Of specific techniques, RO offers significant energy savings over distillation.  Practical difficulties limit the value of recycling at this time.