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Managing water responsibly

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Managing water responsibly
Total water withdrawal by source (m3/adt)

Comment:
Globally, the trend for total water withdrawal was stable. It decreased in SEU, while in SNA total surface water withdrawal decreased at Cloquet Mill and was stable at Somerset Mill. Withdrawal in SSA was stable.

Specific water returned to extracted (m3/adt)

Comment:
Globally, consumption was stable. There was an increase in water consumption in SEU, due mainly to the rebuild of PM9, PM8 and PM6 at Gratkorn, Lanaken and Maastricht Mills respectively. Water consumption was higher year-on-year at Stockstadt Mill because of 15% higher pulp production. The decrease in specific water consumption in SNA was due to increased production at Cloquet and Somerset Mills, combined with decreased total use. Decreased water consumption in SSA was due to initiatives at all mills:

  • Saiccor Mill: Reduced specific consumption due to an increase in production and a number of water-savings initiatives including repairing leaks, reducing tank overflows and an improvement in condensate recovery
  • Ngodwana Mill: Improved efficiencies because of increased production rates
  • Stanger Mill: Sugar mill off-crop shut (the mill uses sugar cane waste residue – bagasse), process water was replaced with recovered water in the pulp mill, process optimisations, improved water use in the bagasse depithing plant.
  • Tugela Mill: Improved water balance controls on the paper machine to reduce unnecessary makeup; improved stability on paper machine and spray dryer; further water reduction especially on PM2 with cleaning processes and reduced overflowing of backwater tank; increased stability on the digester; reduced make-up water by stopping waste plant when PM2 was not operating.

CASE STUDY

Reducing water use at Stanger Mill

In reviewing ways to reduce water use, the mill focused on the significant water users in the mill—the pulp and wet depithing operations. We have replaced processed freshwater with recovered water at the screw feeder and rock cyclone in the pulp mill. This was followed by optimisations on the pith clarifier and belt washer. The pulp mill water use reduced from an average volume of 6.8 m3/min in 2018 to 6.1 m3/min in 2019.

 

CASE STUDY

Getting more from less

Ngodwana Mill identified an opportunity for cost-efficient improvement in its steam generation process: Investigations indicated that the quality of feed and boiler water was good enough to allow the boiler to operate at the 'sweet spot' in terms of its most optimal ratio—total dissolved solids (TSS) concentration of the blowdown water to TSS concentration of the feedwater. This ratio is known as the cycles of concentration (COC). The steam generation process optimisation at Ngodwana Mill focused on maximising the boiler COC, bringing significant improvements in economies of treatment chemicals, water and fuel.

The boiler COC optimisation required no capital investment. The first step was to understand the system dynamics and determine the baseline: The proposal to increase the boiler COC was done through the Ngodwana Mill standard trial procedure. The boiler COC was increased from 80 to 90 COC for a one-month period. The quality of boiler water was monitored very closely during the trial period and a trial review was done completing the first three-month stage.

Following this, the COC was increased from 90 to 100 COC 12 months. Samples of boiler tubes were taken as per standard practice during the annual shut within the course of the extended trial period to assess the general impact of water quality on the tubes. Results indicated that the water quality was good and had no abnormal impact on the tubes. A decision was made to keep the boiler COC permanently at 100 COC until the next shut while continuing with the regular water analysis.

Key process indicators were identified as follows:

  • Boiler water quality (silica iron and conductivity)
  • Boiler blowdown rate and chemical use reduction
  • Boiler water make-up rate and energy input reduction
  • 2020 shut inspections.

The commissioning of the new condensate polisher plant at Ngodwana Mill has improved the feed water quality sufficiently and created an opportunity to maximise the boiler cycles. By implementing the concept of getting more from less, we optimised steam boiler cycles and were able to reduce the annual total cost of boiler water treatment by 10-15% without negatively impacting water quality or putting the system at risk.

Since we have increased the boiler cycles, the combined boiler blow-down has reduced by 2.5 tons (demineralised make-up at elevated temperature and effluent reduction). The boiler chemical dispersant consumption which affects the annual rand cost was reduced by 16.5%, which meant 5 tons less was disposed to effluent drains.

 

CASE STUDY

Pioneering innovation in wastewater treatment

Sappi Europe's re-build of PM8 at Lanaken Mill put a number of elements in place to produce bulky wood-free sheets. During the project, investments were made to achieve environmental benefits throughout the mill's assets. Through the PM8 redesign and technology, improved energy efficiency will be realised once the machine is fully online. The wastewater treatment plant was another area of focus to prepare the mill for the new pulp and production capacity.

The mills wastewater treatment plant incorporated a series of innovative technologies, many never deployed previously in the paper industry and all developed on site at Lanaken Mill. The treatment plant uses a series of anaerobic and aerobic systems, together with advanced oxidation technology which reduces lignin in the final effluent. The state-of-the-art facility optimises the limited space available and triples capacity. The new wastewater plant gives the water clarity and reduces the Chemical Oxygen Demand (COD) levels.

The mill is now well positioned to deal with future challenges by ensuring that increased pulp production and different species mix or other changes will not impact the ability of the mill's effluent to meet and exceed expectations laid out in Belgium's water regulations.

Going forward, there are also new opportunities that the wastewater treatment plant can provide to move the installation from cost to earning. From producting biogas to creating new material streams from the alginates recovery, collaboration with R&D and the academic community is now ongoing to explore this circular economy opportunity.

 
Specific COD (kg/adt) (excluding Saiccor Mill)

Comment:

Globally, there was an increase, attributable mainly to SEU: Alfeld Mill increased pulp integration and also increased spruce wood input from 50% to 65%, which had a negative effect on the biodegradability of COD. The increase at Gratkorn Mill reflects to a higher amount of bleach plant wastewater with low biodegradability due to increased pulp production and increased sludge losses. Levels at Stockstadt Mill rose due to increased pulp production and lower performance in the anaerobic reactor. An electric power outage in July 2019 caused neutralisation disturbances and acidified the reactor, decreasing efficiency. Ehingen Mill somewhat offset the increase with a decrease in COD due to the improved evaporation of spent liquor. Wastewater treatment at Lanaken Mill is expected to stabilise following the major rebuild in 2019.

In SNA, total COD was stable year on year, however specific COD improved based on increased pulp sales at Somerset Mill. There was a decrease in SSA, due largely to commissioning a new chlorine dioxide plant and resulting effluent improvements.

Note:

SEU aims to increase pulp integration, which will lead to increased specific COD load. To mitigate this increase, the following plans are in place:

  • Alfeld Mill will increase its pulp mill evaporation capacity and the capacity of the anaerobic part of its effluent treatment plant. This will be realised through two projects to be completed before the end of June 2021. This will increase the process stability of biological effluent treatment and lead to decreased values for TSS and COD in the final effluent.
  • At Gratkorn Mill, we are investigating magnesium oxide-based pre-bleaching with recirculation to brown stock washing in according with best available technology (BAT) requirements. In addition, a capacity increase of the sludge-handling equipment is in the planning stages.
Specific TSS (kg/adt) (including Saiccor Mill)

Comment:

Globally, there was an increase across all regions: In SEU, emissions increased at Gratkorn Mill due to hydraulic peaks and bottlenecks in the sludge-handling capacity. At Lanaken Mill, following the rebuild of PM8, there was a change in wood species which led to increased organic load in the wastewater treatment plant. However, wastewater treatment at the mill is expected to stabilise in 2020. At Stockstadt Mill, the increase was due to problems with the recovery plant.

In SNA, at Cloquet Mill, inefficiencies in the on- and offsite wastewater treatment plants contributed to the increase. TSS increased at Somerset due to high sludge volumes and a high level of sludge in the polisher pond. The increase at Westbrook Mill was due to several one-time events.

The increase in SSA was due to unstable conditions (plant trips and shut) at Saiccor Mill which contributed to a higher level of fibre in the effluent. At Tugela Mill, the additional solids to effluent and high fibre loss from the paper machines and waste plant were caused by instability during and after the plant shut and clarifier 2 not functioning optimally.

Note:

Going forward, action plans in each region include:

  • SEU: Alfeld Mill will increase its pulp mill evaporation capacity and the capacity of the anaerobic part of its effluent treatment plant. This will be realised through two capex projects which will be completed before the end of June 2021. This will increase the process stability of the biological effluent treatment and lead to decreased values for TSS and COD in the final effluent. Gratkorn Mill is planning a capacity increase of the sludge-handling equipment.
  • SNA: Dredging the polishing pond in FY20 and an increase in the food-to-mass ratio in the waste treatment aeration basins to lower sludge volumes.
  • SSA: Increased plant stability at Saiccor and Tugela Mills will decrease TSS to effluent.