There are many opportunities in the wastewater industry to respond to climate change challenges. This includes improving energy efficiency, reducing greenhouse gases, and generating own energy. In an advanced wastewater treatment plant, the energy cost is around 25 to 40% of the operations and maintenance budget (Water Research Commission, 2021). The National Green Drop Report of 2022 indicates that very few water services authorities (WSAs) conducted a baseline energy audit, or can account for their wastewater treatment plant CO2 footprint. In addition there are limited energy efficiency initiatives in place, except for some municipalities in Gauteng, KwaZulu-Natal and Western Cape.
The first step towards improving a wastewater treatment plant’s efficiency, including energy efficiency, is to capacitate operations and maintenance staff, and managers, with adequate training relevant to plant and process efficiency. The second is to measure, capture and monitor data in real time. Using this data will present the WSA with the opportunity to reduce costs through process optimisation and improved energy efficiency, through the beneficial use of sludge and other energy resources.
Route to improved energy efficiency
One of the important ways of making energy usage more transparent is by calculating key performance indicators (KPIs). These highlight overall energy consumption, and help operators to identify energy-saving potential. Analysing the performance and energy consumption of a wastewater treatment plant helps to:
• Detect savings potential through constant monitoring of energy-relevant areas of the treatment plant.
• Benchmark efficiency of treatment plants with similar plants to create transparency and define further activities.
• Track energy usage, and determine the cost of wastewater treatment.
• Evaluate equipment, system, and control performance to find the ideal point of operation, avoid downtimes and ensure plant safety.
• Quantify benefits of system modifications and improvements.
• Verify predicted performance.
• Improve KPA in Green Drop audits.
Aeration performance
Depending on the type of aeration in the bioreactors, the power consumption of the aerators or blowers can be up to 50% of the plant’s power consumption. Typical causes for inefficiencies of blowers relate to pressure loss through leaks in piping, blockages in air piping, or blocked aeration elements. This will increase the power consumption of the blowers. Through monitoring pressure, air flow and power consumption measurements, it will indicate where the optimum operational point of the blowers is and when maintenance is required on the aeration elements.
To calculate this KPI, it is required to measure and monitor the blower air flow, air pressure, COD value, inflow into aeration basin and blower power consumption.
By using in-line dissolved oxygen and ammonia measurements we can determine the optimum air required for nitrification to take place, which supports energy efficiency gains within the process.
Electricity generation
Increase of electricity production is often easier to achieve and less expensive than electricity-saving measures. Key process parameters such as gas to chemical oxygen demand ratio or electrical and thermal efficiency of combined heat and power (CHP) plants are essential parameters for optimisation and verification of electricity production or quantifying effects of co-fermentation. Here it is necessary to focus not only on single processes but to monitor the complete system to discover related effects of interactions between processes. For a CHP plant to produce heat and electricity optimally, the CHP efficiency and sludge gas production efficiency must be analysed and optimised. The following measurements would be required to optimise CHP and sludge gas production efficiency: sludge flow into digesters; COD value; biogas volume flow; biogas pressure; biogas temperature; power production; and total power consumption.
Pump performance monitoring
Key performance area benchmarking based on power consumption, flow and pressure are useful to discover weak performance and maintain pumps in time. For example, centrifugal pumps require regular impeller adjustment to avoid significant efficiency loss.
In some of the more advanced wastewater treatment plants, most of these process measurement points might already exist, which decreases the capital cost for this investment. Endress+Hauser can assess existing instrumentation and analyse what additional measurement points are required to achieve efficiency goals and gains to improve the plant’s Green Drop rating. A simple solution could be to centralise KPA calculations on an RSG45 data manager, or create a dedicated consumption monitoring solution hosted in Endress+Hauser’s Netilion ecosystem. Endress+Hauser understands the importance of efficiency and sustainability in the sub-Equatorial African wastewater industry, and remains committed to supporting you in achieving these KPAs.
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