Energy Efficient WWTP
WWTP and Energy Efficiency
Wastewater treatment plants are energy intensive and account for a large percent of municipal energy consumption. Particularly pumps and aeration consume a significant portion of energy in water and wastewater plants and should therefore be a special focus. In many cases water and wastewater treatment plants are operated without optimised devices or measures for processes optimization. However, an optimized system consumes less electrical power, results in reduced maintenance work and increased life time of the operational units. A detailed study of the energy consumption should be executed in order to determine the optimisation potential.
The energy efficiency of a wastewater treatment plant is determined by a ration of the consumption of energy and the performance. The power consumption can be considered as electric energy consumption, as heat energy consumption or as the sum of these two forms of energy. The cleaning performance can expressed in eliminating fload (z. B. tons COD/a) or in the form of population equivalents.
For example, the results in the electrical energy efficiency of a sewage treatment plant, with a external purchase of electric energy of 2 GWh/a, having a COD load of 4,380 t/a - with a COD load of 120 g COD/ (person * d) corresponds to a cleaning performance 100,000 PT (total number of inhabitants and population equivalents).
It is obvious that the energy efficiency improves with decreasing consumption of external energy. Ideally, a water treatment plant does not require external energy (see e.g. Kunz, 2009). From the above equations, we can assume that the energy efficiency is not only improved due to external energy consumption reduction, but also with an increase in cleaning efficiency.
The terms of external energy can in principle be reduced in two ways, by:
energy savings in plant operation
in-house generated energy
The possibilities for self or alternative energy generation should be taken into consideration, they consist but not restricted to the followings:
chemical energy of the wastewater
heat energy of the waste water
potential energy of the wastewater
other sources of energy (solar, wind…)
These relationships are summarised in the following figure: