Abstract
Experiments with the degradation of morpholine (MO), sulphanilic acid (SA), nitrilotriacetic acid (NTA) and methanol (MA) were carried out in completely-mixed systems at constant volumetric loading ( B v) and variable solids retention time (SRT). In the first series, a mixed substrate composed of the above compounds was used (each compound formed 25% of the total COD), in the second, each of the above compounds was used as a sole source of organic carbon and energy. Respirometric studies were carried out with excess biomass in order to determine the following kinetic parameters: yield coefficient ( Y), half-velocity coefficient ( K s), maximum volumetric removal rate ( q v,max) and maximum specific removal rate ( q max). It has been found that both q v,max and q max depend on the SRT of a mixed culture. A method of determining the critical solids retention time, π x,cr, at which q v,max = B v, was developed. The values of π x,cr found were 2.4, 1.5 and 0.62 d in the first series for SA, NTA and MA, respectively, and 3.8, 3.6, 1.3 and 0.52 d in the second series for MO, SA, NTA and MA, respectively. Below π x,cr, there is q v,max < B v, and a tested compound behaves as only partially degradable or nondegradable. Above π x,cr, there is q v,max B v and a system has the potential capability for shock loading treatment. At the minimum solids retention time, π x,min, all microorganisms responsible for the degradation of a given compound are washed out from the cultivation system. The developed method makes it also possible to determine q max, μ max and the decay coefficient, b, of the microorganisms in a mixed culture responsible for the degradation of xenobiotics. The results indicate that the microorganisms responsible for the degradation of the xenobiotics are slow-growing. A kinetic equation based on q v,max and K s was derived and shown to predict well effluent concentrations of the tested compounds at all SRT. None of the tested compounds supported filamentous bulking in completely-mixed reactors under the technological parameters used.
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