Results of benchmarking at 7 larger WWTP operators in Denmark

In this ongoing project, the process at 15 medium to large WWTPs is compared using benchmarks. The influent COD load was found to be the best predictor of the sludge TS amount in the dewatered sludge. The best predictor of the total electricity use was the total N influent load. The BOD5 load was a poor predictor of both. The standard population equivalents were also found to be poor predictors of the influent loads. For some plants, the influent load can be much as 4 times greater than the load predicted by the PE. For other plants, the influent load was 30-50% less than the load predicted by the PE. This load variation is due to the industrial load. A comparison of the type of aeration equipment used showed that the electricity consumption of diffuser aerators was about 35% lower than for surface aerators. More than 40% of electricity used is for aeration. Therefore there is a large potential for saving electricity by switching to diffuser aeration.