Combined fluorescence in situ hybridization and microautoradiography (FISH-MAR)

Cultivation independent studies have revealed, that due to the complexity of natural ecosystems such as activated sludge, rhizosphere, rumen etc., the pure cultivation of all related micro-organisms in these diverse ecosystems is quite unsuccessful [2]. Accordingly, the small subunit ribosomal RNA (SSU rRNA, i.e. 16S and 18S rRNA) or genes, obtained from these ecosystems without cultivation has become a widely accepted approach to describe the phylogenetic diversity of microbial communities present in these ecosystems [1, 6]. The rapid growth of the rRNA gene (rDNA) sequence data bank, accessible via the Internet (http://www.ncbi.nlm.nih.gov/BLAST/) has enabled us to compare microbial diversities across the globe without cultivation. However, these rRNA gene sequences provide very few direct clues regarding the interactions and the metabolic capabilities of the identified micro-organisms [9]. Accordingly, the knowledge available on the in situ physiology of the inhabitants of most microbial ecosystems is quite remote and the availability of such knowledge will enable our ability to manipulate ecosystems (e.g. activated sludge) to achieve better process performances with the aid of improved mathematical models

Ano-cathodophilic biofilm catalyzes both anodic carbon oxidation and cathodic denitrification

Biocathodic denitrification using bioelectrochemical systems (BES) have shown promise for both wastewater and groundwater treatment. Typically, these systems involve anodic carbon oxidation and cathodic denitrification catalyzed by two electroactive biofilms located separately at an anode and a cathode. However, process efficiencies are often limited by pH drifts in the respective electrode-biofilms: acidification (pH 8.5) in the biocathode. Here, we describe for the first time a single electroactive biofilm that acts as a bioanode and a biocathode, alternately catalyzing anodic acetate oxidation (Coulombic efficiency (CE) 85.3%) and cathodic denitrification (CE 87.3%) (−400 mV Ag/AgCl). Our results indicate that the ano-cathodophilic biofilm denitrified autotrophically using the electrode (−200 to −600 mV Ag/AgCl) as a direct electron donor. Further, the alkalinity produced from cathodic denitrification partially (19%) neutralized the acidity of the anodic reaction. Switching the electrode potential to temporarily favor either an anodic or cathodic reaction may represent a unique method for removing carbon and nitrate from contaminated liquors. This study offers new insights into the development of sustainable BES-based nutrient removal processes

Biological recovery of phosphorus from municipal wastewater

Today’s agriculture is largely dependent on phosphorus (P) fertilisers mined from rock. Phosphate rock is a non-renewable resource and reserves that do exist, are under the control of a handful of countries, including China, US and Morocco. Given the fact that agriculture is based on non-renewable P, its consumption would ultimately lead to a depletion of P resources. Hence, P recovery and recycling are of considerable importance to sustain a profitable agricultural industry and to ensure the long-term, equitable use and management of P resources. If a sound recycling strategy could be developed, municipal wastewater could be a source from which Australia could approximately recover 22,000 tons of P annually. Recently, a novel biological strategy based around polyphosphate accumulating organisms (PAOs) was developed to concentrate P in municipal wastewater. The cost-effective and environmentally friendly approach to concentrate P in municipal wastewater has enabled the wastewater industry to contribute towards recycling of P. In this communication, we outline this novel biological process and discuss its potential benefits to Australia and to the wastewater industry

Microbially catalysed selenate removal in an inverse fluidised bed reactor

Selenate removal from mine waters is required to mitigate human and environmental health impacts. In this study, the performance of an inverse fluidised bed reactor (IFBR) for the biological removal of selenate from synthetic mine water (pH 6.0-7.0) was evaluated. A laboratory-scale IFBR was set up with floating biomass carriers. Selenate reducers were enriched from environmental samples and anaerobic sludge. The synthetic medium contained ~10 mM (~1.4 g L-1) selenate, nutrients and 10 mM ethanol as electron donor. During stable performance the bioreactor achieved 94 % removal of selenate representing a removal rate of 251 mg L-1 d-1 at a hydraulic retention time of 5 d. Selenite concentration remained < 1 mg L-1 during stable performance, and the formation of a red precipitate indicated that selenate was reduced to elemental selenium. The biological selenate reduction generated alkalinity, increasing the wastewater pH from 6.0 to 8.6. The redox potential gradually approached a value ranging from -300 mV to -400 mV against standard hydrogen electrode. Overall, the results showed that the IFBR can be used for removing selenate and acidity from mine waters. Moreover, it has potential to facilitate recovery of elemental selenium. Therefore, the bioprocess provides an opportunity to reduce the costs and liabilities associated with selenium containing mine drainage and the associated environmental impacts

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

Ammonium-oxidizing bacteria facilitate aerobic degradation of sulfanilic acid in activated sludge

Sulfanilic acid (SA) is a toxic sulfonated aromatic amine commonly found in anaerobically treated azo dye contaminated effluents. Aerobic acclimatization of SA-degrading mixed microbial culture could lead to co-enrichment of ammonium-oxidizing bacteria (AOB) because of the concomitant release of ammonium from SA oxidation. To what extent the co-enriched AOB would affect SA oxidation at various ammonium concentrations was unclear. Here, a series of batch kinetic experiments were conducted to evaluate the effect of AOB on aerobic SA degradation in an acclimatized activated sludge culture capable of oxidizing SA and ammonium simultaneously. To account for the effect of AOB on SA degradation, allylthiourea was used to inhibit AOB activity in the culture. The results indicated that specific SA degradation rate of the mixed culture was negatively correlated with the initial ammonium concentration (0-93 mM, R²= 0.99). The presence of AOB accelerated SA degradation by reducing the inhibitory effect of ammonium (≥ 10 mM). The Haldane substrate inhibition model was used to correlate substrate concentration (SA and ammonium) and oxygen uptake rate. This study revealed, for the first time, that AOB could facilitate SA degradation at high concentration of ammonium (≥ 10 mM) in an enriched activated sludge culture

Aerobic degradation of sulfanilic acid using activated sludge

This paper evaluates the aerobic degradation of sulfanilic acid (SA) by an acclimatized activated sludge. The sludge was enriched for over three months with SA (>500 mg/L) as the sole carbon and energy source and dissolved oxygen (DO, >5 mg/L) as the primary electron acceptor. Effects of aeration rate (0–1.74 L/min), DO concentration (0–7 mg/L) and initial SA concentration (104–1085 mg/L) on SA biodegradation were quantified. A modified Haldane substrate inhibition model was used to obtain kinetic parameters of SA biodegradation and oxygen uptake rate (OUR). Positive linear correlations were obtained between OUR and SA degradation rate (R2 ≥ 0.91). Over time, the culture consumed more oxygen per SA degraded, signifying a gradual improvement in SA mineralization (mass ratio of O2: SA at day 30, 60 and 120 were 0.44, 0.51 and 0.78, respectively). The concomitant release of near stoichiometric quantity of sulphate (3.2 mmol SO42− released from 3.3 mmol SA) and the high chemical oxygen demand (COD) removal efficacy (97.1%) indicated that the enriched microbial consortia could drive the overall SA oxidation close to a complete mineralization. In contrast to other pure-culture systems, the ammonium released from the SA oxidation was predominately converted into nitrate, revealing the presence of ammonium-oxidizing bacteria (AOB) in the mixed culture. No apparent inhibitory effect of SA on the nitrification was noted. This work also indicates that aerobic SA biodegradation could be monitored by real-time DO measurement

Long-term performance of a full-scale intermittently decanted extended aeration (IDEA) plant: The effect of dissolved oxygen and the relocation of alum dosing to bioselector

Dosing alum to remove phosphorus (P) from wastewater is a common practice. However, the dosing-location and quantity of alum required to meet P discharge limits are vaguely defined. As such, utilities overdose alum to avoid noncompliance, but this leads to wastage and costs. This study aimed to address this issue through a long-term evaluation of an alum-assisted full-scale intermittently decanted extended aeration (IDEA) plant. Specifically, the effects of relocating alum dosing from a low P containing IDEA-tank to a bioselector containing elevated P concentrations were examined. The plant is fitted with two IDEA-tanks, each retrofitted with a bioselector at the inlet end. Over 359 d, key parameters (dissolved oxygen (DO), NH4+-N, NO2−-N, NO3−-N, PO43–-P) were quantified to account for the effects of switching alum-dosing into the bioselector and varying dosages (429, 643, 1072 and 1286 g-Al3+ per treatment cycle). Results indicated a 52% reduction of alum usage with no impact on discharge limit (≤0.85 mg-P/L). As expected, a failure to maintain DO setpoint (1.6 mg/L) reduced both NH4+-N and PO43–-P removal. Increasing alum dosage simply could not alleviate this problem, but maintenance of DO at least 85% of setpoint enabled effective rectification. This 15% DO buffer zone offers operators an opportunity to rectify imminent operational failures related to DO, prior to escalating alum dosage. An operational framework to manage DO related failures is proposed. Overall, this study offers insights on how to cost effectively apply alum and manage DO failures to achieve P discharge limits in IDEA plants

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