Treatment technologies for soft-drinks production

Ian Beckett, key account manager at Elga Process Water, has considered the water treatment solutions and technologies used in the production of soft drinks.

The Food Standards Agency requires that water used in the production of soft drinks must meet all the quality criteria of potable water as defined in the Water Supply (Water Quality) Regulations, which also apply to all mains-water supplies.

However, even water that meets all these requirements can still contain unacceptable levels of a variety of constituents that cause problems in soft drinks.

Consequently, most soft-drinks manufacturers will work to in-house standards (or standards imposed by licensors or customers) that are more onerous than those set out in the Regulations in order to ensure product quality.

As a result, most soft-drinks manufacturers provide some on-site treatment of both private- and mains-water supplies.

The most common of these problem constituents are alkalinity, hardness, nitrate and bacteria count so, traditionally, on-site treatment has concentrated on them.

De-alkalisation, an ion-exchange process using a weakly acidic cation-exchange resin, reduces both alkalinity and hardness by exchanging calcium ions from calcium bicarbonate with hydrogen ions.

This effectively converts the calcium bicarbonate into carbonic acid (or dissolved carbon dioxide gas) which is then removed by degassing.

The ion-exchange resin is regenerated with hydrochloric acid and, although the process is very efficient in acid utilisation, it still produces an acidic waste stream for disposal.

In addition, the treated water quality, particularly the pH, varies significantly through the ion-exchange run, and a large treated-water storage tank is needed to ensure a consistent product.

Nitrate can also be removed by ion exchange, using a strongly basic anion-exchange resin regenerated with salt.

This is much less efficient than cation exchange and produces large quantities of saline wastewater.

Treated-water quality again varies throughout the ion-exchange run, making quality control difficult.

Bacterial problems are usually dealt with by chlorination using sodium hypochlorite followed by de-chlorination to remove the chlorine taint, most commonly by activated carbon.

However, as plant operators know all too well, granular activated carbon beds provide an excellent environment for bacterial growth and often cause an increase in bacterial colony counts even after high levels of chlorine dosing.

To overcome the inherent problems of ion-exchange systems, more soft-drinks manufacturers have turned to reverse osmosis.

10 years ago, the process was expensive to operate and gave poor removal of nitrate, but improvements in membrane technology mean that the current generation of reverse-osmosis plants operate at low pressure and give greatly improved removal of dissolved salts.

This means that not only are operating costs lower, but the process now has a much lower carbon footprint.

With no regenerant chemicals it is also more sustainable than ion exchange.

Further, reverse-osmosis membranes act as a physical filter to remove particulate contaminants and bacteria.

Not only has the reverse-osmosis process itself improved, but the process engineering framework in which it is used has also changed.

Reverse osmosis has long been the process of choice for producing pharmaceutical water, and the lessons learned about microbiological control in that industry are being introduced into soft drinks water systems by Elga Process Water's engineers.

A typical modern soft-drinks water-treatment system will normally take mains water or equivalent and treat it by cartridge filtration followed by reverse osmosis, which will remove in excess of 95 per cent of the total dissolved salts including alkalinity, hardness and nitrates.

It will also remove more than 99 per cent of suspended solids and organic matter.

Reverse-osmosis membranes are susceptible to microbiological fouling, but good design and operation can minimise this.

The most important design feature is to ensure that water does not stagnate in the membrane modules when there is no demand for treated water, and this can be achieved quite easily by automatically recirculating permeate to the feed tank when the permeate storage tank is full.

Regular chemical sanitisation is also advisable and, thanks to developments in the pharmaceutical sector, there is now a range of heat-resistant membranes which, when fitted in stainless-steel modules, can be sanitised with hot water.

The permeate is chlorinated to provide disinfection and to prevent bacterial growth in the downstream storage tank.

This is followed by de-chlorination using granular activated carbon, which also removes any trace levels of organic matter.

The carbon filters are designed hygienically and manufactured from stainless steel to allow hot water or steam to be used for periodic sanitisation to avoid any microbiological problems.

Final filtration is provided by a cartridge filter with a 1um absolute membrane element, to ensure that no particulate material remains in the water.

This 1um filter serves another important function.

Some of the supermarkets are insisting that, not withstanding mains-water supplies and risk assessments, their suppliers should fit filtration to 1um absolute to ensure that cryptosporidium, which is resistant to chlorination, is removed not only from water used in production but also from water used for cleaning and sanitisation.

After the final filtration step and just prior to distribution of the treated water, an ultraviolet lamp provides final disinfection.

One of the big problems associated with upgrading an existing water-treatment plant is the need to maintain production.

Elga Process Water's Aquamove mobile plant provides an answer.

The mobile plant consists of a self-contained reverse-osmosis system in a standard 40ft trailer that can be parked outside the production facility and connected to a mains-water supply to deliver up to 25m3/h of permeate while the existing plant is being upgraded or replaced.

Back to top