A field-scale assessment of the efficacy of bioremediation of petroleum hydrocarbon-contaminated soils using two biostimulants

Nutrients are known limiting factors for the successful bioremediation of soil contaminated with petroleum hydrocarbons (PHCs). Thus, two biostimulants, soil bioremediation nutrients (SBNs) and nutrient solution (NS), were tested to assess their effects on the degradation of PHCs and changes in bacterial community compositions, functions and functional genes using third generation sequencing, Tax4Fun2 and qPCR at the field scale. The addition of SBNs or NS significantly increased and accelerated the degradation of total petroleum hydrocarbons (TPH). The highest TPH degradation rate (96%) and k (0.134/day) were shown for biopiles with SBNs addition (particularly for 0.5% SBNs), indicating that SBNs were a good biostimulant for bioremediation of PHCcontaminated soil in the field. After different operations, rapid reconstruction of bacterial communities and functions for 5 biopiles was found with relatively high metabolic function and a change in dominant PHC degraders from Rugosibacter aromaticivorans and Novosphingobium aromaticivorans to Immundisolibacter cernigliae and Dyella ginsengisoli. The results of Tax4Fun2 prediction revealed that the addition of SBNs and water with soil turning enhanced and accelerated bacterial metabolic functions and related functional genes for degrading aromatic compounds. The qPCR results indicated that most samples contained a relatively high abundance of alkB, alkB1, XylE and PHE, and high expression of XylE and PHE, while the addition of SBNs and NS enhanced the expression of XylE and PHE for degrading catechol and phenol. Concentrations of TPH and nutrients were major environmental factors influencing the degradation of TPH, alkane and aromatic compounds and changes in bacterial communities, functions and functional genes (e.g., alkB, alkB1, XylE, NAH, PHE and BPH4). Biostimulation by the addition of SBNs proved an effective strategy for increasing the degradation of PHCs and facilitating the growth and metabolic activity of PHC degraders.