Energy Efficiency

A change in the energy tariff from constant charge to time of use resulted in high energy costs at a UK Water Company’s large activated sludge plants. TruSense Process Engineering was awarded the contract to undertake the investigation of optimum operational and control methods to save energy under the new tariff while ensuring final effluent compliance at the 158,000 m3/d sctivated sludge plant.

Comprehensive process audit and mathematical modeling were applied to evaluate various options of reducing energy use in the activated sludge process . Modelling results predicted savings in aeration costs of ~25% through implementing optimized aeration control and up to 52% through implementing both influent flow balancing and optimized aeration control. Site implementation of optimization of current control strategies through introduction of variable DO setpoints achieved immediate savings on aeration costs of 25% aeration costs without incurring substantial capital expenditure but only changes in control protocols. More complex measures such as implementing flow balancing within the collection system are under review for site trialsuSense Process Engineering was engaged by Yorkshire Water.

TruSense acted as process specialist sub-consultant for a project to assess the energy consumption and efficiency improvement potential of wastewater treatment plants in five small municipalities (population range 2 000 to 12 000) in southeastern British Columbia. The goal of the assignment was to provide recommendations to reduce energy consumption, greenhouse gas emissions, and operating costs, as well exploring opportunities for renewable energy generation. The facilities were unique with different capacities and treatment processes as follows:

• SBR activated sludge plant
• Package plant activated sudge process
• Aerated and polishing lagoon plant
• Rotating biological contactor
• Oxidation ditch

For the five plants, eighteen measures were identified with a savings value of $175,000 per year and an overall payback of less than ten years, with many measures in the two to three year range. Many communities are working on plans to implement the measures.

TruSense were the project leader for this project which forms part of the Water Research Commission’s energy efficiency in the water sector initiative. The objective of the project was to determine feasible practical aeration energy conservation measures that can be implemented at typical South African BNR activated sludge plants that not only result in aeration energy use reduction but also ensure final effluent compliance with permit requirements.Two BNR activated sludge plants Zeekoegat was (85 Ml/d) and JP Marais (15 Ml/d) were used as case studies.

The main tasks involved collection and analysis of data, energy audits and benchmarking, evaluation of aeration energy use reduction strategies through advanced modelling and simulation as well as financial analysis.

The Key findings from the project were:

• Identified aeration ECMs can potentially save 9-40% of aeration energy consumption and cost.
• Implementing the identified ECMs which include optimal process and aeration control results in improved biological nutrient removal and compliance with final effluent nitrogen and phosphorus limits.
• In order to realise these savings local authorities, need to develop a clear energy management strategy and put in place robust systems and structures towards achieving this strategy.

Knowledge dissemination workshops were carried out to communicate the project findings to key stakeholders.

The project was undertaken in collaboration with the City of Tshwane and ERWAT who provided the case study plants as well as collection of wastewater data and analysis services

TruSense is the project leader for this Water Research Commission project to evaluate and compare appropriate sludge-to-energy technologies that can be applied by the South African wastewater industry. Sludge treatment and management is a widely acknowledged challenge in SouthAfrica. While the Department of Water and Sanitation Guidelines for the Utilisation and Disposal of wastewater Sludge recommend beneficial use, there are very few wastewater treatment plants that recover energy from sludge or have a cradle to grave approach to sludge management. To provide information needed by municipalities to make informed long term sludge management strategies, the project will implement life cycle assessment to evaluate three technologies that have been identified as appropriate to South Africa:

• Anaerobic Digestion (conventional and advanced)
• Thermal Gasification
• An innovative emerging technology, Polymeric Carbon Solid (PCS).

The study will involve a combination of desk top evaluation of full scale plants as well as laboratory and pilot scale studies for the PCS technology. By adopting this approach, the project will address the gaps in knowledge on sludge-to-energy technologies identified in previous research and provide valuable information on both established and innovative emerging technologies that South African municipalities can use to formulate long term sludge management strategies.

The project is being undertaken in collaboration with the University of Stellenbosch who are carrying out the laboratory scale investigation for the PCS technology and ERWAT who are providing the case study plants for anaerobic digestion and for the PCS pilot scale study.