Abstract
The objective of the present study is to investigate the different effects on the oxygen transfer of fine-bubble aeration systems in saline water. Compared to tap water, oxygen transfer increases due to the inhibition of bubble coalescence. In Part I of the present study, we investigated in laboratory-scale experiments the effect of design of diffuser membrane. The objective of Part II is the assessment of effects of different salts, diffuser type and diffuser density. We measured the concentration of various salts (MgCl2; CaCl2; Na2SO4; NaCl; KCl) above which coalescence is fully inhibited and oxygen transfer reaches its maximum (referred to as the critical coalescence concentration; CCC). For this purpose, we developed a new analytical approach, which enables investigation of the coalescence behaviour of any aeration system and (mixed) salt solution quickly and easily by evaluating the results of oxygen transfer tests. To investigate the transferability to large scale and the effect of diffuser type and density, we repeated lab-scale experiments in a 17,100 L pilot-scale test tank and carried out additional tests with tube and plate diffusers at different diffuser densities. The results show that despite the higher pressure drop, diffusers with dense slit density and smaller slits are to be recommended in order to improve efficiency of aeration systems in saline water.
Highlights
If only the coalescence concentration (CCC) is considered as the molar concentration of the salts investigated in all the different studies, the following order emerges for most
The highest fS values could be reached in the middle of the operation range (3.0– 4.0 Nm3/h per diffuser) given by the diffuser manufacturer (1.5–8.0 Nm3/h per diffuser) which corresponds to the results of Sander et al ( )
The experiments presented in Part I of this paper (Behnisch et al ) were continued to investigate the oxygen transfer of fine-bubble aeration systems and their influencing factors in saline water
Summary
In biological wastewater treatment plants, mainly fine-bubble aeration systems are used to satisfy the oxygen demand of microorganisms in activated sludge Air is introduced via diffusers installed at the bottom of the aeration tank. From the rising air bubbles, the oxygen is transferred to the liquid phase. Oxygen transfer from ascending air bubbles to the liquid phase is described by the volumetric mass transfer coefficient (kLa), which represents. Behnisch et al | Improving aeration systems in saline water (part II)
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