Waste lines for profit

Finnish chemical company Kemira is coping with new European environmental legislation by using inorganic chemistry to transform waste streams into revenue-generating raw materials, as Sarah Houlton explains.

Chemical processes make waste, and waste has to be disposed of, which costs money. Creating more efficient processes is one way that waste can be minimised and money saved. But another strategy is to use waste streams to make raw materials that can be used in-house or even sold — reducing waste disposal costs and gaining a new revenue stream at the same time.

The Finnish chemical company Kemira has been developing this strategy with promising results. Its new division, Kemwater, is pinpointing sidestream wastes that can be turned into raw materials that are useful to industry, replacing virgin raw materials.

‘It’s an attractive proposition,’ explains Hannu Luhtala, Kemwater’s vice president, industrial solutions and services.

Kemira is a big producer of titanium dioxide, which creates ferrous sulphate as waste. Rather than disposing of this, the company is now using it to make iron based coagulants. The iron(II) is oxidised to iron(III) and the resulting ferric sulphate granulated to give a product that is easily handled.

These iron coagulants are much in demand, too. Thanks to an EU directive that came into effect in January of this year, the cement industry now has to reduce its chromium(VI) residues. The iron coagulants provide a simple solution — they simply need mixing into the manufacturing process.

‘The cement industry could use as much as a couple of million tonnes a year to reduce their 6-valent chromium wastes,’ Luhtala explains. ‘This industry problem is now turning into a positive cashflow for us, solving someone else’s problem as well as ours. We had been discharging and disposing the waste outside the site, where we have a few million tonnes of the product and a big hill of it.

‘From October 2007, we won’t be able to dispose of it in this way, so we were facing a dramatic environmental investment in our TiO2 unit to meet the new demands. The timing of this drive to reduce chromium(VI) is perfect for us, as otherwise we’d have to invest in a plant to upgrade one waste to another that is not water soluble. But now we don’t have to do this — the cement industry will use up practically all of it.’ If anything, he adds, there will now be a shortage.

Recycling the iron waste into a useful product is a spin-off from Kemwater’s core business of water treatment, which offers services to third parties. Its Kemicond sludge conditioning process significantly changes the properties of sewage sludge, enabling volumes to be reduced dramatically.

Just before it is dewatered, the sludge is treated with sulphuric acid at pH4. Metal salts, such as iron phosphates and hydroxides, dissolve, breaking down the water-retaining gel structures. If a strong oxidant such as hydrogen peroxide is then added, any dissolved iron(II) is oxidised to iron(III), and the dissolved phosphate ions will be precipitated as ferriphosphate, and the organic gel structures are partly destroyed, releasing entrapped water. The sludge particles are then flocculated with polymer. The resulting sludge can be dewatered in a screw press, a centrifuge, a belt filter press or a chamber filter press.

Typically, the process leads to a 25 to 50% reduction in sludge volumes, by increasing the dry solids content and reducing the suspended solids. The sludge is also very different from traditional sludge: it has a non-sticky gravel-like structure, and hence is very much easier to handle. And the savings that can be made are dramatic.

Luhtala cites the example of a water treatment plant in Lindigö, Sweden, where savings of around a third were made by implementing the Kemicond process. Previously, while the running costs for treating 40m3 waste water were just E11 for the polymer, this created 5.6m3 of sludge, which cost E212 to dispose of.

The Kemicond process’s running costs are much higher, at E59 for 40m3 of waste water, reflecting the additional cost of sulphuric acid, oxidant and alkali on top of the polymer. But this results in just 2.2m3 of sludge, with total solids of 45% as opposed to the 18% TS of the original sludge. And because the volumes are much lower, the sludge disposal costs dropped dramatically to E84. So the total cost of treatment fell from E223 to just E143.

‘It’s not a complicated process or a heavy investment, yet it saves a third of the costs,’ Luhtala says. ‘We are in the recovery business,’ he concludes. ‘If the sidestream volumes are big enough, we always prefer to implement the investment in recycling at the customer’s site, rather than take the waste a couple of hundred kilometres away to process somewhere else. Although it’s still very early days — we’ve been operating for less than a year — we’ve had a great response and have signed 10 long-term contracts already. Now we have happy customers, we are ready to push the concept in the market. We can bring added value to waste effluent treatment, with the proportion of chemicals going to landfill being reduced, ideally to zero. We want to find new processes and ideas.’

Sarah Houlton is a freelance science and technology writer based in London