Improvement of carbon usage for phosphorus recovery in EBPR-r and the shift in microbial community.

Enhanced biological phosphorus removal and recovery (EBPR-r) is a biofilm process that makes use of polyphosphate accumulating organisms (PAOs) to remove and recover phosphorus (P) from wastewater. The original process was inefficient, as indicated by the low P-release to carbon (C)-uptake (Prel/Cupt) molar ratio of the biofilm. This study successfully validated a strategy to improve the Prel/Cupt ratio by at least 3-fold. With an unchanged supply of carbon in the recovery stream, an increase in the hydraulic loading in stages I, II and III (7.2, 14.4 and 21.6 L, respectively) resulted in a 43% increase in the Prel/Cupt ratio (0.069, 0.076 and 0.103, respectively). The ratio further increased by 150% (from 0.103 to 0.255) when the duration of the P uptake period was increased from 4 h (stage III) to 10 h (stage IV). Canonical correspondence analysis showed that, correlated to the 3-fold increase in the Prel/Cupt ratio, there was an increase in the abundance of PAOs ("Candidatus Accumulibacter" Clade IIA) and a decrease in the occurrence of glycogen accumulating organisms (GAOs) (family Sinobacteraceae). However, the four stage operation impaired denitrification, resulting in a 5-fold reduction in the Nden/Pupt ratio. The decline in denitrification was consistent with a decrease in the abundance of denitrifiers including denitrifying PAOs (family Comamonadaceae and "Candidatus Accumulibacter" Clade IA). Overall, a strategy to facilitate more efficient use of carbon was validated, enabling a 3-fold carbon saving for P recovery. The new process enabled up to 80% of the wastewater P to be captured in a P-enriched stream (>90 mg/L) with a single uptake/release cycle of recovery.

Simultaneous phosphorus uptake and denitrification by EBPR-r biofilm under aerobic conditions: effect of dissolved oxygen.

A biofilm process, termed enhanced biological phosphorus removal and recovery (EBPR-r), was recently developed as a post-denitrification approach to facilitate phosphorus (P) recovery from wastewater. Although simultaneous P uptake and denitrification was achieved despite substantial intrusion of dissolved oxygen (DO >6 mg/L), to what extent DO affects the process was unclear. Hence, in this study a series of batch experiments was conducted to assess the activity of the biofilm under various DO concentrations. The biofilm was first allowed to store acetate (as internal storage) under anaerobic conditions, and was then subjected to various conditions for P uptake (DO: 0-8 mg/L; nitrate: 10 mg-N/L; phosphate: 8 mg-P/L). The results suggest that even at a saturating DO concentration (8 mg/L), the biofilm could take up P and denitrify efficiently (0.70 mmol e(-)/g total solids*h). However, such aerobic denitrification activity was reduced when the biofilm structure was physically disturbed, suggesting that this phenomenon was a consequence of the presence of oxygen gradient across the biofilm. We conclude that when a biofilm system is used, EBPR-r can be effectively operated as a post-denitrification process, even when oxygen intrusion occurs.

A direct pre-screen for marine bacteria producing compounds inhibiting quorum sensing reveals diverse planktonic bacteria that are bioactive.

A promising new strategy in antibacterial research is inhibition of the bacterial communication system termed quorum sensing. In this study, a novel and rapid pre-screening method was developed to detect the production of chemical inhibitors of this system (quorum-quenching compounds) by bacteria isolated from marine and estuarine waters. This method involves direct screening of mixed populations on an agar plate, facilitating specific isolation of bioactive colonies. The assay showed that between 4 and 46 % of culturable bacteria from various samples were bioactive, and of the 95 selectively isolated bacteria, 93.7 % inhibited Vibrio harveyi bioluminescence without inhibiting growth, indicating potential production of quorum-quenching compounds. Of the active isolates, 21 % showed further activity against quorum-sensing-regulated pigment production by Serratia marcescens. The majority of bioactive isolates were identified by 16S ribosomal DNA (rDNA) amplification and sequencing as belonging to the genera Vibrio and Pseudoalteromonas. Extracts of two strongly bioactive Pseudoalteromonas isolates (K1 and B2) were quantitatively assessed for inhibition of growth and quorum-sensing-regulated processes in V. harveyi, S. marcescens and Chromobacterium violaceum. Extracts of the isolates reduced V. harveyi bioluminescence by as much as 98 % and C. violaceum pigment production by 36 % at concentrations which had no adverse effect on growth. The activity found in the extracts indicated that the isolates may produce quorum-quenching compounds. This study further supports the suggestion that quorum quenching may be a common attribute among culturable planktonic marine and estuarine bacteria.

Enrichment of anodophilic nitrogen fixing bacteria in a bioelectrochemical system.

We demonstrated the ability of a bio-anode to fix dinitrogen (N2), and confirmed that diazotrophs can be used to treat N-deficient wastewater in a bioelectrochemical system (BES). A two-compartment BES was fed with an N-deficient medium containing glucose for >200 days. The average glucose and COD removal at an anodic potential of +200 mV vs. Ag/AgCl was 100% and 76%, respectively. Glucose removal occurred via fermentation under open circuit (OC), with acetate as the key byproduct. Closing circuit remarkably reduced acetate accumulation, suggesting the biofilm could oxidise acetate under N-deficient conditions. Nitrogen fixation required an anode and glucose; removing either reduced N2 fixation significantly. This suggests that diazotroph utilised glucose directly at the anode or indirectly through syntrophic interaction of an N2-fixing fermenter and an anodophile. The enriched biofilm was dominated (68%) by the genus Clostridium, members of which are known to be electrochemically active and capable of fixing N2.

A novel post denitrification configuration for phosphorus recovery using polyphosphate accumulating organisms.

Enhanced biological phosphorus removal (EBPR) has been widely used to remove phosphorus (P) from wastewater. In this study we report a novel modification to the EBPR approach, namely enhanced biological phosphorus removal and recovery (EBPR-r) that facilitates biological recovery of P from wastewater using a post denitrification configuration. The novel approach consists of two major steps. In the first step, a biofilm of phosphorus accumulating organisms (PAOs) is exposed to a wastewater stream in the absence of active aeration, during which P is taken up by the biofilm using nitrate and residual dissolved oxygen as electron acceptors. Thus, P and nitrogen (N) removal from wastewater is achieved. During the second step, the P enriched biofilm is exposed to a smaller recovery stream supplemented with an external carbon source to facilitate P release under anaerobic conditions. This allows P to be recovered as a concentrated liquid. The EBPR-r process was able to generate a P recovery stream four time more concentrated (28 mg-P/L) than the wastewater stream (7 mg-P/L), while removing nitrate (denitrification) from the wastewater stream. Repeated exposure of the biofilm (10 P-uptake and release cycles) to a recovery stream yielded up to 100 mg-P/L. Overall, EBPR-r is the first post denitrification strategy that can also facilitate P recovery during secondary wastewater treatment.

Comparison of microbial communities in pilot-scale bioreactors treating Bayer liquor organic wastes.

Western Australian bauxite deposits are naturally associated with high amounts of humic and fulvic materials that co-digest during Bayer processing. Sodium oxalate remains soluble and can co-precipitate with aluminium hydroxide unless it is removed. Removal of sodium oxalate requires a secondary crystallisation step followed by storage. Bioreactors treating oxalate wastes have been developed as economically and environmentally viable treatment alternatives but the microbial ecology and physiology of these treatment processes are poorly understood. Analysis of samples obtained from two pilot-scale moving bed biofilm reactors (MBBRs) and one aerobic suspended growth bioreactor (ASGB) using polymerase chain reaction- denaturing gradient gel electrophoresis of 16S rRNA genes showed that members of the α-, ß- and γ-Proteobacteria subgroups were prominent in all three processes. Despite differing operating conditions, the composition of the microbial communities in the three reactors was conserved. MBBR2 was the only configuration that showed complete degradation of oxalate from the influent and the ASGB had the highest degradation rate of all three configurations. Several strains of the genus Halomonas were isolated from the bioreactors and their morphology and physiology was also determined.