How To Expand Water Treatment Systems in Pulp And Paper Facilities

Should pulp and paper companies look to expand their operations, it is crucial that wastewater treatment plants also follow suit, while remaining robust and reliable. Here, Simon Emms, Business Development Manager at Veolia Water Technologies looks at how to approach this in a cost-effective manner.

The manufacture of pulp and paper is entirely reliant on a supply of water, with water required for nearly all parts of the process, from cleaning machinery to digesting wood chips. This, combined with the high concentration of solids and organic contaminants present in pulp and paper plants’ wastewater streams, make it critical for companies to have robust and reliable wastewater treatment systems in place.

Pulp and paper facilities looking to expand their operations, physically or in terms of efficiency, must ensure that their wastewater treatment processes have the capacity to treat growing quantities of effluent, while maintaining the required wastewater standards. As wastewater discharge regulations become more stringent, it is also crucial that companies ensure their wastewater treatment systems can cope with tightening contaminant consent levels, to prevent the need for further enhancement in the future.

For companies that need to update their treatment systems, the retrofitting of new technologies into current wastewater processes provides a viable alternative to investment in a new facility. Retrofitting technology can allow for increased flow or additional Biological or Chemical Oxygen Demand (BOD or COD) loads. It can also enable improved removal of Total Suspended Solids (TSS) or nutrients, and combat odour.

Whatever the requirement, there are number of technologies available that can help pulp and paper companies to expand their processes cost-effectively. When looking into the options, it is important for companies to consider the long and short-term goals of the facility and select a system that can adapt to future needs.

How to enhance COD/BOD removal

For companies that need to improve their plant’s ability to remove COD from its wastewater streams, advanced anaerobic digestion systems provide the ideal retrofit solution. Not only do the systems offer high removal rates, short retention times and low solids production, they are also incredibly reliable.

Capable of enhancing both COD and BOD removal levels, Biothane High-Rate Anaerobic wastewater treatment systems have been successfully implemented in pulp and paper industry facilities since the early 1980s. In fact, some of the first anaerobic applications in the sector were at recycled paper mills.

However anaerobic reactors have also successfully treated pulp mill effluents including Bleached Chemical Thermo-Mechanical Pulp (BCTMP), Neutral Sulphite Semi-Chemical (NSSC) and chemical pulp condensates.   

In particular, the retrofit installation of a Biothane anaerobic digestion system as a pre-treatment step can have a significant effect on the efficiency of a wastewater treatment plant. By installing ahead of any aerobic treatment method, the anaerobic system can ensure 70 to 90% removal of COD and BOD prior to entry into the next phase. This allows the aerobic treatment step and other downstream biological processes to be more efficient in their own COD and BOD removal and allow for increased capacity and removal rates across the entire plant.

Biothane High-Rate Anaerobic systems also have the added benefits of low sludge production and reduced energy demand. As such, retrofitting such a system generates little in terms of additional OPEX costs for a plant in comparison with alternative systems. Not only that, but these systems produce biogas as a by-product, which can be either sold to a combined heat and power (CHP) generator or used as an onsite fuel source.

Improving Aerobic Wastewater Treatment and Nutrient Control

Historically, aerobic biological treatment systems have been trusted to provide biological treatment at many pulp and paper facilities. In particular, activated sludge systems or aerated lagoons are commonplace. However, the need to expand capacity and ever tightening discharge limits has left many companies searching for a way to optimise their aerobic biological treatment systems into something more suited to their changing demands.

In this situation, Moving Bed Biofilm Reactor (MBBR) technologies are ideal, such as that produced by AnoxKaldnes™. A flexible and high-performance technology, MBBR systems utilise small plastic carriers, otherwise known as media, on which biofilm is grown. These carriers are then suspended and circulate within the MBBR reactor, maximising the removal of COD and BOD, nutrients and other pollutants.

MBBR systems can again be retrofitted and offer a great deal of flexibility. They can be installed in one of three ways: as a stand-alone system – pure MBBR, as a preliminary process upstream of an activated sludge system or as a hybrid process that combines both MBBR and activated sludge in the same tank. Finally, the technology can also be paired with existing lagoons to enhance removal rates and encourage nitrification, even at a low temperature.

Regardless of how it is integrated, the high-performance characteristics of MBBR technologies can help protect the activated sludge within the system from sludge bulking and improve sludge settleability. In turn, this results in superior removal rates. MBBR is also able to reduce the discharge of nutrients, such as nitrogen and phosphorus, helping plants to achieve strict discharge regulations.

Finally, in most installation cases, MBBR can take advantage of existing equipment, keeping CAPEX costs low but ultimately allowing increased capacity, stability and performance.

AnoxKaldnes™MBBR media on which biofilm is grown. These carriers are then suspended and circulate within an MBBR reactor, maximising the removal of COD and BOD, nutrients and other pollutants.

Enhancing Total Suspended Solids Removal

While biological treatment is an effective method of soluble contaminant removal, at pulp and paper facilities there are usually high concentrations of solids that also need to be removed prior to discharge to surface waters. Generally, clarification is the most common method of TSS removal. However, plants with particularly strict TSS discharge limits may need an additional tertiary treatment in order to meet the required removal levels.   

Microscreen discfilters provide the ideal retrofit solution in this case. Enabling a fine particle filtration using a woven media cloth, technologies such as VWT’s Hydrotech Discfilter can help pulp and paper companies with their TSS and also phosphorus discharge levels, regardless of the performance of their upstream technologies.

Existing Hydrotech Discfilter installations in the market, have helped facilities reduce their TSS, in normal operation, by 50 to 80%. In scenarios where the upstream clarifier is bulking, TSS removal levels can hit as much as 98%.

In addition, discfilters are also extremely compact in footprint. As such, retrofit installation can provide the desired robustness and discharge results without the costly refurbishment or upgrade of upstream systems.   

Enabling a fine particle filtration using a woven media cloth, VWT’s Hydrotech Discfilter can help pulp and paper companies with their TSS and also phosphorus discharge levels, regardless of the performance of their upstream technologies.

Need to expand and enhance your facility?

Pulp and paper facilities looking to expand their operations must consider how that will impact on the suitability of their wastewater treatment systems and make the appropriate alterations. However, expansion doesn’t always have to be costly.

Engaging with a wastewater treatment company, such as VWT UK, at an early stage of development will help plant managers consider what wastewater treatment enhancements may also be needed to cope with the expansion. Whether increased levels of BOD, COD or TSS are the issue, a water treatment expert will be able to recommend the most appropriate technology that can be retrofitted without extensive refurbishment or expense and help a facility achieve its wastewater goals.

For more information, please visit, www.veoliawatertechnologies.co.uk.