Thermophilic aerobic granular biomass for enhanced settleability.

Aerobic biological wastewater treatment at thermophilic (ca. 55 degrees C) temperatures notoriously produces biomass that flocculates poorly or not at all. Contrary to this, thermophilic aerobic biomass that settled well in sequencing batch reactors was cultured with sludge volume index (SVI) values as low as 60mL/g. A mixture of granular and flocculant biomass resulted when closed reactors were sparged with recirculated reactor headspace gas containing some air, whereas a conventionally aerated control reactor sparged with air alone contained dispersed growth that did not flocculate. Maximum granule diameter was from 1.2 to 1.9mm, and granule resistance to disintegration was comparable to aerobic mesophilic granules. Two bacteria were isolated and identified as Anoxybacillus flavothermus and Pseudoxanthomonas taiwanensis as determined by partial 16S rDNA sequencing. Anoxybacilli species are alkaliphilic or alkalitolerant, with the type species having an obligate requirement for carbonate, even when grown on glucose. We postulate that high alkalinity and CO(2) may select for a population of aerobic thermophilies that flocculates and granulates.

The inhibitory effects and removal of dieldrin in continuous upflow anaerobic sludge blanket reactors.

The inhibitory effects and removal efficiency of dieldrin (DLD) in anaerobic reactors were investigated. Anaerobic toxicity assay (ATA) experiments conducted in batch reactors revealed that 30 mg/l DLD had inhibitory effects on the unacclimated mixed anaerobic cultures. Continuous reactor experiments performed in a lab-scale two-stage upflow anaerobic sludge blanket (UASB) reactor system which was fed with ethanol as the sole carbon source, indicated that anaerobic granular cultures could be successfully acclimated to DLD. Chemical oxygen demand (COD) removal efficiencies were 88-92% for the two-stage system. The influent DLD concentration of 10 mg/l was removed by 44-86% and 86-94% in the second stage and overall UASB system, respectively. Biosorption of DLD on granular anaerobic biomass was found to be a significant mechanism for DLD removal in the UASB system. The maximum DLD loading rate and minimum HRT achievable for the first stage UASB reactor were 0.5 mg/lday (76 microg DLD/g VSS.day) and 10 h, respectively, which resulted in the overall COD removal efficiency of 85%.