Regular articleCarbon and nutrient-limiting conditions stimulate biodegradation of low concentration of phenol

•Kinetic constraints limit biological removal of low phenol concentration (< 5 ppm).•C, N and/or P limiting conditions stimulate uptake of low concentration of phenol.•The bacteria make self-adjustments of N and P on prolonging the incubation time.•C-limitation is better option to increase hydrocarbon degrading bacteria.•Two-staged biological process is proposed for improved phenol uptake.

Biological removal of phenol in wastewater is kinetically constrained if its initial concentration is low (<5 mg/L) making compliance of environmental norms (≤0.35 mg/L) difficult. Taking a cue from the soil matrix where bio-remediation of very low concentrations phenol is possible under nitrogen (N), phosphorus (P) and carbon (C) limiting conditions, the present study was carried out to stimulate phenol biodegradation in a low-phenolic (<5 mg/L) refinery wastewater. Experiments with nutrient limiting conditions showed that N-limited and P-supplemented conditions were necessary to stimulate phenol uptake if the initial concentration of phenol is <1 mg/L or is between 2.5-5.8 mg/L. Further studies revealed that instead of manipulating nutrients, enforcing the C-limited condition on the microorganisms through a two-staged reactor process, not only did the phenol removal efficiency improve but also eliminated the need to externally manipulate N and P concentrations in the system. The high abundance of hydrocarbon degrading gram-negative bacteria and Pseudomonas species in the second stage of the two-staged process, further confirmed that C-limitation was a better option than the nutrient manipulation. The study thus illustrates methods of acclimatizing microorganisms to remove very low concentration of target substrate (here phenol) in low strength wastewater.

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