The oxygen input of fine-bubble pressurized aeration systems is (positively) influenced by salts in (industrial) wastewater. Long-term measurements of the oxygen input will generate empirical values to further develop the current design methods for aeration systems. This will save costs and energy in later stages.
As part of the WaReIp project, the IWAR Institute at the Darmstadt Technical University investigated the biological treatment of saline wastewater. The focus was on the aeration system and the influence of increased salt concentrations on the oxygen input. Elevated salt concentrations in wastewater inhibit coalescence, resulting in a decrease in bubble size in pressurized aeration systems as compared to pure water. As a result, the oxygen input or aeration coefficient (kLa) increases. This effect is insufficiently taken into account in current planning standards for pressurized aeration systems, which results in higher investment costs during plant construction and increased energy consumption in wastewater treatment during subsequent operations.
Saline wastewater comes mainly from industry. However, due to the targeted use of seawater, e.g. for toilet flushing, or infiltration of seawater through leaky sewer systems, wastewater with elevated salt concentrations is also increasingly found in the municipal sector.
In measurements at the IWAR Institute using conventional aeration elements, limit concentrations (cG) of various salts were determined for the first time. A cG value is the concentration of a salt above which the coalescence of a system is completely inhibited. It was found that cG depends on the salt type and concentration as well as on many other factors (e.g. air flow rate, aerator design and type, etc.). The measurement results will be used for the further development of design methods for ventilation systems, so that in future, the influence of increased salt concentrations can be taken into account when planning. The energy efficiency of both aeration systems and the entire cleaning process can thus be significantly increased.
