This study examines the performance and fouling potential of flat sheet (FS) and hollow fiber (HF) membrane bioreactors (MBRs) during the treatment of high strength landfill leachate under varying solid retention times (SRT = 5-20 days). Mixed-liquor bacterial communities were examined over time using 16S rRNA gene sequence analysis in an attempt to define linkages between the system performance and the microbial community composition. Similarly, biofilm samples were collected at the end of each SRT to characterize the microbial communities that evolved on the surface of the FS and HF membranes. In general, both systems exhibited comparable removal efficiencies that dropped significantly as SRT was decreased down to 5 days. Noticeably, ammonia and nitrite oxidizing bacteria were not detected at the tested SRTs. This suggests that the nitrifiers were not enriched, possibly due to the high organic and ammonium content of the leachate that led to low TN and NH removal efficiency. The steady-state fouling rate of both membranes increased linearly with the decrease in SRT at an estimated factor of 1.1 and 1.2 for the FS- and HF-MBR, respectively, when the SRT was reduced from 15 to 10 days and from 10 to 5 days. Similar dominant genera were detected in both MBRs, including Pseudomonas, Aequorivita, Ulvibacter, Taibaiella, and Thermus. Aequorivita, Taibaiella; Thermus were the dominant genera in the biofilms. Hierarchical clustering and non-metric multidimensional scaling revealed that while the mixed liquor communities in the FS-MBR and HF-MBRs were dynamic, they clustered separately. Similarly, biofilm communities on the FS and HF membranes differed in the dynamic bacterial community structure, especially for the FS-MBR; however this was less dynamic than the mixed liquor community.

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Historically, municipal solid waste landfills have been designed and operated as storage facilities with suboptimal degradation under anaerobic conditions resulting in slow waste stabilization, gaseous emissions and leachate formation. This article examines the aerobic bioreactor alternative combining the recirculation of high strength leachate [chemical oxygen demand (COD): 89,000-95,600 mg/l; biological oxygen demand (BOD): 75,700-80,000 mg/l)] with low aeration rates (0.0125-0.05 l/min.kg) at high initial waste compaction (657-875 kg/m3) to promote and control biodegradation of solid waste in laboratory-scale columns (diameter = 60 cm, height = 1 m). Low aeration rates coupled with high initial density demonstrated improved performance with increased levels of stabilization with COD and BOD attenuation reaching up to 96%, final C:N ratio of 25 and waste settlement up to 55%.

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