Improving water quality and capacity at DS Smith's Kemsley Paper Mill

The challenge: Reduced capacity due to sludge wash out from anaerobic reactors

DS Smith is a leading provider of sustainable packaging in the UK. But its wastewater treatment plant at Kemsley Paper Mill was reaching the limit of its capacity for the increasing production at the site. At the same time, it didn’t use an anaerobic stage in the treatment process which would help in treating the high organic loads in a more sustainable way.

DS Smith used a simple pre-treatment process at Kemsley to clean its wastewater, with an aeration capacity of around 2MW in a 45,000 cubic meter lagoon. Constantly operating at full capacity, this process was expensive to run and produced too much waste consuming too much energy – and couldn’t cope with unexpected load increases.

In 2015, DS Smith partnered with Royal HaskoningDHV to update the system. The expert’s team designed new anaerobic and aerobic stages as treatment, assisted DS Smith with the tender process, and developed a conversion plan to transition to the new system in stages, to avoid shutting down the mill.

Removing polystyrene was essential in the upgrade of the new treatment process. In the old system, polystyrene bypassed the pre-treatment measures and became part of the waste activated sludge, which could clog the new anaerobic reactor in the upgraded system and prevent biogas collection.

The pre-treatment was upgraded to remove floating polystyrene – but this couldn't remove other plastic particles suspended in the water. So an additional pressurised screen was installed in the feedline between the primary treatment and the reactors to remove these plastics.

The solution: An anaerobic controller optimises sludge retention

With pre-treatment now fully optimised, Royal HaskoningDHV could turn its attention to improving the efficiency of the anaerobic reactors, and ensuring DS Smith could use them to their maximum capacity and profitability. To maximise the reactor’s sludge retention, the optimization opportunities in the new system were analysed.

It was discovered that the temperature was fluctuating by up to 5°C, causing inefficiencies in the treatment process. Inconsistencies in the load were also resulting in up to 70% of the wastewater bypassing the reactor and following the old treatment route.

Royal HaskoningDHV suggested using the anaerobic controller from Aquasuite Pure, that could determine the actual capacity of the reactor 24/7 through analysis of temperature, load, and the composition of ingoing water.

This gave the company the means to control the system and prevent sludge loss, creating a cost saving on reseeding from other sites. The stability of the process improved dramatically, cutting energy costs further.