Sludge management in wastewater treatment is key to achieving ROI in a landscape where funding is being cut.

Reducing costs, whether through reductions in CAPEX (capital expenditure) or OPEX (operational expenditure), is a primary consideration for utilities and their main consultants and contractors. Cost cutting has basic financial and regulatory drivers, as well as budget reductions and lack of funding. By focusing on wastewater sludge processing, it is possible to significantly improve return on investment (ROI).

The role of grit removal in reducing costs

The wastewater industry has placed an increasing emphasis on streamlining process performance, as the major CAPEX to meet regulatory drivers is largely completed. One of the basic considerations, which is now coming to the fore, is grit removal. Ensuring the best possible removal of primary sludge, and associated grit, can significantly reduce maintenance costs and increase returns.

This is because grit creates several important and costly downstream issues. The 50 to 70% of grit that is not trapped by traditional grit removal solutions:

• Damages downstream assets, particularly expensive pumps.
• Increases wear and tear of products, reducing their overall lifetime.
• Increases the risk that equipment will fail unexpectedly.

Grit also settles out at points in the process where flows slow, blocking pipes and channels and reducing the volume available in downstream treatment processes. The impact of this can be seen in increased aeration costs and reduced treatment effectiveness and efficiency. The costs of downtime and early replacement of vital assets must also be factored in.

Improving the settleability of sludge

Reducing solids handling costs is crucial when improving the settleability of sludge. The removal of unnecessary detritus and gross solids at the earliest possible stage reduces the impact on the downstream treatment train. By acting to remove these elements early on and improving the settleability of sludge at the primary stage, there will be less wear and tear on equipment and a higher quality of sludge going to the digester.

Improving downstream treatment efficiency is vital because of the significant amounts of energy involved in maintaining inefficient processes. US EPA estimates suggest that both water and wastewater treatment plants account for 40% of total energy consumed by municipal governments, and 2% of the overall energy use of the USA.

The EPA further notes that by incorporating energy efficiency practices, municipalities and utilities can save 15 to 30% of their energy use, saving thousands of dollars with payback at the scale of a few months to years. Undoubtedly, there are several different aspects to achieving energy efficiency, but grit removal and sludge screening improvements can be important contributors to this potential saving.

Choosing a grit removal system

There are various factors that must be considered when choosing a grit removal system, including:

• The amount and characteristics of the grit at the plant in question.
• The potential effects on downstream processes.
• Factors such as head loss, available space, removal efficiency and cost.

The grit removal system chosen for a treatment plant should balance these characteristics.

Primary scrapers play an important part in ensuring that the quality of sludge going to the digester is as high as possible; an effective primary settlement tank scraper system will increase the amount of carbon-rich early sludge that is fed to the digester.

Sludge screening provides an opportunity to capture grit in sludge brought onto the main site by tankers from smaller treatment works. These may not have effective (or any) grit removal systems.

Securing these improvements enables digesters to work more efficiently, producing more energy, and reducing maintenance, issues that are key to improving ROI and increasing profits.

Conclusion

With budget reductions and lack of funding common themes in today’s water industry around the world, alongside tightening discharge requirements, ensuring that maintenance costs are reduced is a vital part of wastewater treatment plant operations.

Takeaways

Reducing the maintenance requirements of wastewater sludge processing means ensuring that minimal grit enters the anaerobic digester and the profitable biogas yield increased.

Budget reductions and a lack of funding are common themes in the industry, driving the requirement to reduce maintenance requirements.

Grit removal systems, sludge screens and primary scrapers all play a vital role in enabling digesters to work more efficiently, so they can produce more energy, reduce maintenance and boost ROI.