This study investigated the impact of spent brewery grains and spent mushroom compost on the development of phenanthrene biodegradation in soil. Two aspects were considered: (i) the influence of increasing waste-to-soil ratios (1:10, 1:5, 1:2, 1:1 & 2:1) and (ii) the impact of soil-PAH contact time (1 -100 d). Biodegradation was quantified by measuring changes in the lag phase, the fastest rates and extents of mineralization of 14 C-phenanthrene, as well as changes in the number of total heterotrophic and phenanthrene degrading bacteria and fungi. The amendment of smaller amounts of the wastes (1:10 & 1:5) resulted in greatest levels of biodegradation. Microbial numbers increased in all of the amended soils but phenanthrene-degrading numbers in most amended soils did not correlate with the rates and extents of 14 C-phenanthrene mineralization. This investigation highlighted the value of waste organic materials as nutrient sources to stimulate microbial degradation of contaminants in soil.

Biochar is a by-product from the pyrolysis of biomass and has a great potential in soil amendment due to its carbon and nutrient-rich properties. The aim of this study was to investigate the impact of increasing amounts (0, 0.01, 0.1, 0.2, 0.5 and 1.0%) of two types of biochar (so-called enhanced and non-enhanced) to soil on the biodegradation of 14 C-phenanthrene. Enhanced biochar contains inoculants which are designed to potentially stimulate microbial activity and promote biological function in soil. After 100 d of incubation, the addition of 0.5% and 1% enhanced (EbioC) and non-enhanced biochars (NEbioC) led to longer lag phases, reduced rates and extents of 14 C-phenanthrene in amended soil. However, in soils amended with 0.01%, 0.1% and 0.2% amendments, extents of mineralisation of 14 Cphenanthrene increased and were found to be higher in the EBioC-as compared to the NEbioC-amended soils. Increasing soil-phenanthrene contact time also increased 14 C-phenanthrene mineralisation in soil which had received smaller amounts of EBioC. Application of both EbioC and NEbioC also enriched the soil microbial populations during the incubation. However, it was found that phenanthrene-degrading microbial populations declined as soil contact time increased; this was particularly true for soils receiving larger amounts of due to reduction in the mobile/bioaccessible fraction of the phenanthrene in soil. The findings revealed the importance of the type and amount of biochar that may be added to soil to stimulate or enhance organic contaminant biodegradation.

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