Extant Biodegradation Testing With Linear Alkylbenzene Sulfonate in Laboratory and Field Activated Sludge Systems

Two 1-L porous pot (65 μ stainless steel mesh) reactors were fed synthetic wastewater with a COD of 200 mg/L including 2 mg/L linear alkyl benzene sulfonate (LAS) to evaluate the influence of specific operating conditions (i.e, hydraulic retention time, HRT, and solids retention time, SRT) on the measured rate of LAS biodegradation. The reactors were operated in parallel under a constant SRT of 10 d, and HRTs of 2, 4, 6, and 12 h. Subsequently, the reactors were operated under a constant HRT of 6 h, and SRTs of 3, 6, 10, and 15 d. The biodegradation responses of LAS were measured using a respirometric method, and the extant kinetic parameters were evaluated using the Monod model. The extant kinetic parameters obtained from these experiments suggest that the HRT had little impact on the measured kinetic parameters (μ̂ = 0.14 ± 0.06 h, KS = 0.4 ± 0.3 mg COD/L, and Y = 0.67 ± 0.02 mg biomass COD formed/mg LAS COD utilized) at a constant SRT of 10 d. The SRT had a more noticeable effect on the measured biodegradation kinetics (e.g., Y increased from 0.50 ± 0.08 to 0.66 ± 0.05 mg/mg when the SRT increased from 3 to 10 d at a constant HRT of 6 h). Extant kinetics for LAS biodegradation were measured in the field at two activated sludge wastewater treatment plants operated at different conditions. The field results were similar to the results from laboratory systems operated to simulate the field conditions (μ̂ values ranged from 0.02 0.05 h, KS values ranged from 0.11 0.39 mg COD/L, and yield values ranged from 0.46 0.50 mg biomass COD formed/mg LAS COD utilized). The week to week variability in measured LAS kinetic parameters was greater with the field samples than with the laboratory samples, possibly due to the non-steady state nature of the treatment plants. The long term variability in the field kinetic parameters was comparable to the laboratory variability. These results confirm the efficacy of the extant respirometric technique to measure biodegradation rates of surfactants in laboratory and field systems operated at a range of HRT and SRT conditions.