Bacterial Washout Research Articles

Advanced Bioconversion of sugary wastewater: Integrated polyhydroxybutyrate and hydrogen productions in a continuous airlift two-chamber bioreactor

This study utilized a novel Continuous Airlift Two-chamber Bioreactor (CATBR) for the co-production of hydrogen and polyhydroxybutyrate (PHB) from mixed microbial cultures in sugary wastewater. Hydrogen generation was investigated in a defined bacterial consortium that contained mainly Clostridium species, and diverse microbial communities were studied in relation to PHB production, demonstrating the ability of diverse microbial communities to form stable microbial consortia. The impact of hydraulic retention time (HRT), pH, and air flow rate on PHB production was evaluated with special emphasis on volatile suspended solids (VSS).Optimal conditions for hydrogen and PHB production were established at a pH of 5.5, an aeration rate of 1500 mL/h, and an HRT of two days. Hydrogen yield was determined to be 3.14 ± 0.92 mL/g COD, and PHB yield was 31.32% (g PHB/g VSS). Production rates for hydrogen and PHB peaked at 0.23 ± 0.07 L/L.d and 0.64 g PHB/L.d, respectively, with a COD removal efficiency of 85 ± 0.67%. At an HRT of two days, the PHB generation rate was found to be 6–10 times higher than previously reported rates. The application of immobilized cell technology effectively prevented bacterial washout from the reactor, thereby ensuring stable operational conditions.

Mutualistic symbiosis of fungi and nitrogen-fixing bacteria in halophilic aerobic granular sludge treating nitrogen-deficient hypersaline organic wastewater

Hypersaline organic wastewater is characterized as being nitrogen-deficient, and is easily prone to sludge bulking. In this study, the stability of halophilic aerobic granular sludge (HAGS) for the treatment of hypersaline organic wastewater is explored. Along with the decrease of influent ammonium, the bacterial population substantially reduced, whereas the fungal population continuously increased in HAGS. Saccharomycetales in fungi become the dominant sequence (99.78%) in HAGS bulking. Additionally, Halanaerobium (77.47%) remained prevalent in HAGS despite bacterial washout. Halanaerobium, a nitrogen-fixing genus of bacteria, provided nitrogen for ammonium-assimilating fungi. Saccharomycetales encapsulating HAGS reduced the transfer efficiency of dissolved oxygen, thereby creating favorable growth conditions for Halanaerobium. This paper for the first time highlights the mutualistic symbiosis of fungi and bacteria in HAGS treating the hypersaline organic wastewater. The study lays the foundation for the control and recovery of HAGS bulking.

Durable electrospun microtubes for encapsulation of bacteria in atrazine bioremediation

The operation of classic biological reactors under starvation conditions is ineffective due to bacterial washout and detachment. In this paper, an innovative approach to maintaining high cell concentrations in a continuous reactor under starvation conditions based on electrospun encapsulation is investigated. Pseudomonas sp. strain ADP (P. ADP) bacteria was encapsulated in core-shell electrospun microtubes and used as coverings on plastic carriers for bioremediation of atrazine without adding an external electron donor to minimise pollution. A microtube formulation consisting of polyvinylpyrrolidone (PVP) as the core solution and polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) as the shell material was investigated for the encapsulation of bacteria. Encapsulated P. ADP bacteria showed an initial inhibition to atrazine degradation mainly due to stress from electrospinning or solvents left over in the microtubes. However, atrazine degradation activity was regained after a number of consecutive batches. Microtubes containing bacteria were wrapped on plastic carriers, placed in a reactor and operated continuously without an external carbon source for 50days. Good atrazine degradation (83.1±3.9%) and ammonium recovery (75.5±5.9%) were observed in the reactor. Carrier samples taken at the end of the experiment showed no significant microtube deterioration, although biofilm growth appeared on the external surface of the microtubes due to the prevailing non-sterile conditions. The results show the potential for the application of this method in bioreactors.

Effect of flow and peristaltic mixing on bacterial growth in a gut-like channel

The ecology of microbes in the gut has been shown to play important roles in the health of the host. To better understand microbial growth and population dynamics in the proximal colon, the primary region of bacterial growth in the gut, we built and applied a fluidic channel that we call the "minigut." This is a channel with an array of membrane valves along its length, which allows mimicking active contractions of the colonic wall. Repeated contraction is shown to be crucial in maintaining a steady-state bacterial population in the device despite strong flow along the channel that would otherwise cause bacterial washout. Depending on the flow rate and the frequency of contractions, the bacterial density profile exhibits varying spatial dependencies. For a synthetic cross-feeding community, the species abundance ratio is also strongly affected by mixing and flow along the length of the device. Complex mixing dynamics due to contractions is described well by an effective diffusion term. Bacterial dynamics is captured by a simple reaction-diffusion model without adjustable parameters. Our results suggest that flow and mixing play a major role in shaping the microbiota of the colon.

Factors implicated in pathogenesis of urinary tract infections in neurogenic bladders: some revered, few forgotten, others ignored

To comprehensively review factors implicated in the pathogenesis of urinary tract infection in patients with neurogenic bladders, and to stimulate research, especially in the somewhat ignored and forgotten areas of this important clinical subject. In addition to reviewing relevant articles on pubmed, some important articles from previous times which were not available online were also procured and reviewed. Intrinsic defence mechanisms including protective flora, anti-adherence mechanisms, urothelial, and immunological responses to bacterial binding and the blood supply to the urinary bladder may be impaired in patients with neurogenic bladders. Further, bacterial washout mechanisms may be compromised as a result of inefficient voiding, reflux, and altered hydrokinetics. Finally, catheterization itself contributes to urinary tract infection in patients with neurogenic bladders. In order to address the issue of urinary tract infection in patients with neurogenic bladders, multiple factors need to be looked into and corrected. Further research is required, especially in the area of compromised host defence mechanisms. An individualized approach, which attempts to optimize each factor is recommended.

Effect of feed characteristics on the organic matter, nitrogen and phosphorus removal in an activated sludge system treating piggery slurry

Piggery wastewater is characterized by its high content in nitrogen and phosphorus, as well as by a low C/N ratio. This type of wastewater is traditionally spread to croplands (with its subsequent leaching to groundwater) or rarely discharged into natural water bodies, which ultimately cause severe episodes of eutrophication in aquatic ecosystems. In this context, activated sludge systems constitute a robust and efficient treatment option. The performance of an activated sludge process using a pre-denitrification configuration treating both sieved and flocculated swine slurry at a hydraulic retention time (HRT) of 7.7 days was evaluated. In order to avoid bacterial wash-out, sludge from the settler was recirculated to the anoxic tank to accomplish denitrification. Once the biomass was acclimatized, the reactor was fed with swine slurry containing 19, 2.6, and 0.27 g/L of total chemical oxygen demand (COD), total Kjeldhal nitrogen (TKN), and soluble P, respectively. Nitrogen removal showed a clear dependency on the influent composition. When the influent TKN/total COD and soluble COD/total COD ratios were respectively 0.12-0.15 and 0.7, the reactor exhibited good removal efficiencies (up to 99 and 91 for N-NH(4)(+), TKN, respectively) while PO(4)(3-) was removed up to 65%. However, when the influent TKN/total COD ratio rose to 0.26 and soluble COD/total COD decreased to 0.3, the denitrification process was severely hindered concomitant with and accumulation of nitrite. Nevertheless, organic matter degradation was not affected by influent composition. At the last stage of the experiment, removals of dissolved phosphorus fell to 40% when the redox potential (ORP) profile showed a constant value of -400 mV, likely due to phosphate released from bacterial sludge.

Failure of antibiotic treatment in microbial populations

The tolerance of bacterial populations to biocidal or antibiotic treatment has been well documented in both biofilm and planktonic settings. However, there is still very little known about the mechanisms that produce this tolerance. Evidence that small, non-mutant subpopulations of bacteria are not affected by an antibiotic challenge has been accumulating and provides an attractive explanation for the failure of typical dosing protocols. Although a dosing challenge can kill the susceptible bacteria, the remaining persister cells can serve as a source of population regrowth. We give a condition for the failure of a periodic dosing protocol for a general chemostat model, which supports the simulations of an earlier, more specialized batch model. Our condition implies that the treatment protocol fails globally, in the sense that a mixed bacterial population will ultimately persist above a level that is independent of the initial composition of the population. We also give a sufficient condition for treatment success, at least for initial population compositions near the steady state of interest, corresponding to bacterial washout. Finally, we investigate how the speed at which the bacteria are wiped out depends on the duration of administration of the antibiotic. We find that this dependence is not necessarily monotone, implying that optimal dosing does not necessarily correspond to continuous administration of the antibiotic. Thus, genuine periodic protocols can be more advantageous in treating a wide variety of bacterial infections.

Activated Sludge Process Modification for Sludge Yield Reduction Using Pulp and Paper Wastewater

Implications of conventional activated sludge (CAS) process modification to a low sludge production (LSP) process have been studied for treating pulp and paper wastewaters. The activated sludge process is modified to a two-stage design to establish a microbial food chain that would result in reduced sludge production. The return activated sludge in the LSP process bypasses the first (dispersed growth) stage to be received only by the second (predatory) stage. The resulting once-through operation of the dispersed growth (DG) stage makes it potentially susceptible to bacterial washout under hydraulic shock conditions. A sensitivity analysis of the DG stage operation was performed by varying its hydraulic residence time. The experimental data revealed that the optimal DG stage hydraulic residence is between 3 and 5 h, with bacterial washout likely to be initiated within 2 h. Based on laboratory results, it appears that a well-designed LSP system is likely to be able to handle day-to-day variations in hydraulic and organic loading rates. The LSP process produced 36% less sludge than the CAS process while consuming approximately 25% more oxygen. The treatment performance of the two systems was comparable except that the LSP sludge had much better settling and dewatering properties.

Bacterial ferrous iron oxidation of acid mine drainage as pre-treatment for subsequent metal recovery

Mining activities at Falu copper mine in Sweden started around the year 1080 AD and continued until 1993. During all these centuries, the acid mine drainage has caused low pH values and high metal levels in the nearby Falu river and it's surroundings. This work is part of a plan to achieve a long-term solution to this environmental problem, where the aim is to treat the mine water overflow in such a way that a neutral pH and an essentially metal free aqueous effluent is obtained. The idea is to first oxidise the ferrous iron with bacteria, in order to be able to make a selective ferric iron precipitation at a pH of around 3. One possible process option is to use the precipitated ferric hydroxide for the production of red pigment. Thereafter, zinc will be recovered in such a way that it will be suitable for recycling. In this paper, only the initial stage of bacterial ferrous iron oxidation is discussed. The ferrous iron oxidation was initially studied in laboratory scale using batch cultures of mesophilic (35°C), moderate thermophilic (45°C) and extreme thermophilic (65°C) microorganisms. The ferrous iron oxidation kinetics was determined with two different concentrations of ferrous iron. The moderate thermophilic culture did not grow well on ferrous iron only. Since the mesophilic and extreme thermophilic microorganisms showed approximately the same oxidation kinetics, the mesophilic bacteria was selected for further studies in pilot scale, due to their lower operating temperature which reduces the heating cost. A pilot plant was erected at the mine site with three 500 l reactors in series with a treatment capacity of up to approximately 500 l h −1. The reactors were filled with plastic bodies in order to support the formation of a permanent biofilm to avoid bacterial washout. The pilot plant has been operating continuously for several months and the influence of flow rate, ferrous concentration, pH and temperature was investigated. The feasibility for a biological ferrous iron oxidation step was successfully demonstrated. With a ferrous concentration of 3.5 g l −1, 35°C, pH 1.8 and a flow rate of 330 l h −1 a ferrous iron oxidation rate of 750 mg l −1 h −1 was achieved. The results obtained will be used to calculate the capital and operating cost for a full scale plant, capable of treating 25 m 3 of acid mine drainage per hour. Before the final decision, regarding the ferrous iron oxidation step is made, alternative processes such as hydrogen peroxide and ozone oxidation will be evaluated.

Methane production from low solid concentration liquid swine waste using conventional anaerobic fermentation

A study was conducted to determine the methane production characteristics of low concentration liquid swine waste using conventional dispersed growth anaerobic fermentation at 35°C. Raw waste was obtained from a conventional under floor flushing system and screened using an 18 mesh vibrating liquid–solid separator. The volatile solid (VS) concentration of the influent waste used in the study was 15 g/l. Hydraulic retention times (HRTs) of 5, 3, 2, and 1 days were replicated three times with one 300 l bench scale fermenter. Results from the study show that conversion to methane is practical for the 5 and 3 day HRT but that considerable stress occurred at the 2 day HRT. One replicate failed during the 2 day HRT and all three replicates failed at the 1 day HRT. Failure of digestion was determined based on steady-state gas production. Methane productivity (LCH 4/g VS added) ranged from 0.36 to 0.22 for the 5 and 2 day HRTs, respectively. VS reduction showed a high of 51.6% for the 5 day HRT and a low of 34.5% for the 2 day. Steady-state operating levels of ammonia and total volatile fatty acids (TVFA) suggest no inhibition from either at any of the HRTs. Alkalinity levels were low (1200–2000 mg/l as CaCO 3) when compared to digestion studies using longer HRTs. Although foaming occurred at the 2 and 1 day HRT, TVFA levels remained low (<700 mg/l as acetic) and pH was >7. This suggests the failure mechanism was bacterial washout, not organic overloading.

Acetic acid inhibition of biological phosphorus removal

The effects of high acetic acid concentrations on biological phosphorus removal (BPR) in single‐sludge, three‐stage biological nutrient removal systems were studied using two bench‐scale units fed with mixtures of domestic wastewater increments plus increments of either a high acetic acid industrial wastewater or additions of sodium acetate. Incremental additions varying from 25 to 800 mg/L acetic acid delivered to the anaerobic reactor. The systems were maintained at 20°C and operated at a solids retention time of 5 days. The total nominal hydraulic retention time was either 6 or 12 hours, depending on the total chemical oxygen demand of the influent. The results showed that high concentrations of either acetic acid or sodium acetate can cause failure of BPR, with the progression of failure being typical of bacterial washout. The industrial wastewater was considerably more inhibitory to BPR than equivalent amounts of sodium acetate, probably because of other organic chemicals in the industrial wastewater, such as isopropyl alcohol and acetone, although high concentrations of inorganic chemicals such as magnesium and sulfate also were present. Other inorganic chemicals such as nickel, copper, lead, and chromium also were monitored but were present only in trace, nontoxic concentrations.

Kinetic measurement of bacterial adherence to eukaryotic cells

We developed a kinetic assay using a monolayer of differentiated respiratory epithelium in culture to assess bacterial adherence. Mean residence time of bacteria in the tissue culture chamber was estimated from a model-independent (moment) analysis of the rate of bacterial washout from perfused Rose chambers. Results with this method compared favorably with visual assessment of adherence and double radiolabel method with H. influenzae. Adherence was assessed with low inoculae of H. influenzae, P. cepacia and P. aeruginosa avoiding cytotoxic effects seen when large inoculae are added to eukaryotic cells. This method will provide a means of assessing adherence of pathogenic respiratory bacteria to their cellular target at low inoculae.

Mathematical Simulation of Upflow Anaerobic Fixed Bed Reactors

ABSTRACT ANAEROBIC digestion of agricultural wastes using conventional stirred-reactor technology has been unsuccessful in treatment of dilute waste streams. The development of *'fixed bed anaerobic reactors has provided an effective method of utilizing dilute waste for methane production. Anaerobic fixed bed reactors (AFBR), or anaerobic filters, are unique among anaerobic reactor designs in that a fixed support medium is placed inside the reactor vessel, allowing attachment of active bacterial mass responsible for substrate conversion. The resulting attached biofilm allows high hydraulic flow through the reactor vessel without causing bacterial washout and subsequent digester failure, a significant advantage over conventional reactor designs. A mathematical model was developed which simulates dynamic upflow AFBR response to waste characteristics, loading, flow rate, surface area and porosity of the support medium, and temperature. Computer simulations with the model indicate that the AFBR is superior to conventional stirred reactor designs for treatment of dilute wastes. The AFBR provides stable operation, rapid response to transient operational and environmental conditions, and effective treatment at reduced temperatures (20C to 30C).

Bladder Mucin: A Scanning Electron Microscopy Study in Experimental Cystitis

Scanning electron microscopy has been used to assess surface mucin changes following an induced Escherichia coli urinary tract infection in the rat bladder. The principal changes seen following bacterial challenge were bacterial adherence to the urothelium, swelling of epithelial folds, disruption of the mucin layer, and increased adherence of bacteria to the sub-surface epithelium. The bladder mucin before infection appeared as an even, whitish, viscous layer which covered epithelial cells and cell junctions. Bacteria appeared to become enmeshed in mucin strands after infection and this process may facilitate bacterial washout from the bladder. A recovery phase showed reversal of the scanning electron microscopy changes. These findings support other studies in suggesting that mucin may play a role in protecting the bladder from invading and adhering bacteria.

Modeling Toxicity in Methane Fermentation Systems

Wastewater treatment using anaerobic methane fermentation offers several significant advantages over aerobic methods, but is considered unreliable when treating wastewaters containing toxicants. Three models describing toxicity phenomena are given to help engineers develop more rational design and operational strategies. The first model describes the recovery pattern of methane fermentation systems from slug addition of toxicants as a function of toxicant type and concentration, and time. This model allows for prediction of periods of zero gas production and threshold toxicant concentrations. The second two models incorporate the effect of toxicity on the fundamental Monod-type expressions. Unsteady-state behavior is effectively described by both models and the importance of providing proper biological solids retention time is emphasized. The primary effect of toxicant addition is to alter process kinetics by temporarily or permanently increasing bacterial washout time. Therefore, to minimize the severity of both transient and chronic toxicity, a sufficiently large solids retention time is required.

Nitrification in a column reactor: Limitations, transient behaviour and effect of growth on a solid substrate

Metabolic inhibition, insufficient O 2, CO 2 and trace metals, pH and bacterial wash-out were investigated as potential causes of incomplete nitrification of ammonium supplied to column reactors containing Nitrosomonas europaea and Nitrobacter agilis. Of these only the last two factors offered a partial explanation of the phenomenon. The transient behaviour of the columns after flow rate and nutrient perturbations could be classified as either short term (< 10 h) or long term (>20h). The major properties conferred by adhesion of the nitrifiers to a solid substrate in a nitrification column were the ability to respond rapidly to environmental changes, asymmetric transient responses and increased likelihood of multiple steady states.