Biodegradation and microbial diversity within permeable pavements

Permeable Pavement Structures (PPS), designed to improve drainage of urban paved areas, have been demonstrated to function as hydrocarbon traps with 98.7% efficiency and as powerful in-situ aerobic bioreactors. A mesocosm constructed like one of these pavements and inoculated with microorganisms with the aim of increasing hydrocarbon biodegradation was found not to retain a viable population of organisms derived from the inoculum, although the protozoan fauna initially increased in diversity more quickly than in an identical non-inoculated mesocosm. The source of protozoan diversity in oil cultures containing different components used in pavement construction, was revealed to be primarily the granite sub-base which contained flagellates, gymnamoebae, ciliates and testate amoebae. Other components only provided cosmopolitan genera such as Colpoda and Heteromita. Biodegradation was facilitated to a similar degree by bacteria or fungi, as demonstrated by inhibition with tetracycline and cycloheximide, respectively. A full microbial community, without inhibition by antibiotics, degraded the greatest mass of oil. Elucidating the role of protozoa assists in fully understanding and optimising the function of PPS in hydrocarbon degradation.