Microbial dynamics and properties of aerobic granules developed in a laboratory-scale sequencing batch reactor with an intermediate filamentous bulking stage.

Aerobic granules offer enhanced biological nutrient removal and are compact and dense structures resulting in efficient settling properties. Granule instability, however, is still a challenge as understanding of the drivers of instability is poorly understood. In this study, transient instability of aerobic granules, associated with filamentous outgrowth, was observed in laboratory-scale sequencing batch reactors (SBRs). The transient phase was followed by the formation of stable granules. Loosely bound, dispersed, and pinpoint seed flocs gradually turned into granular flocs within 60 days of SBR operation. In stage 1, the granular flocs were compact in structure and typically 0.2 mm in diameter, with excellent settling properties. Filaments appeared and dominated by stage 2, resulting in poor settleability. By stage 3, the SBRs were selected for larger granules and better settling structures, which included filaments that became enmeshed within the granule, eventually forming structures 2-5 mm in diameter. Corresponding changes in sludge volume index were observed that reflected changes in settleability. The protein-to-polysaccharide ratio in the extracted extracellular polymeric substance (EPS) from stage 1 and stage 3 granules was higher (2.8 and 5.7, respectively), as compared to stage 2 filamentous bulking (1.5). Confocal laser scanning microscopic (CLSM) imaging of the biomass samples, coupled with molecule-specific fluorescent staining, confirmed that protein was predominant in stage 1 and stage 3 granules. During stage 2 bulking, there was a decrease in live cells; dead cells predominated. Denaturing gradient gel electrophoresis (DGGE) fingerprint results indicated a shift in bacterial community composition during granulation, which was confirmed by 16S rRNA gene sequencing. In particular, Janthinobacterium (known denitrifier and producer of antimicrobial pigment) and Auxenochlorella protothecoides (mixotrophic green algae) were predominant during stage 2 bulking. The chitinolytic activity of Chitinophaga is likely antagonistic towards Auxenochlorella and may have contributed to stage 3 stable granule formation. Rhodanobacter, known to support complete denitrification, were predominant in stage 1 and stage 3 granules. The relative abundance of Rhodanobacter coincided with high protein concentrations in EPS, suggesting a role in microbial aggregation and granule formation.

Influence of COD:N ratio on sludge properties and their role in membrane fouling of a submerged membrane bioreactor.

The effect of COD:N ratio on sludge properties and their role in membrane fouling were examined using a well-controlled aerobic membrane bioreactor receiving a synthetic high strength wastewater containing glucose. Membrane performance was improved with an increase in the COD/N ratio (100:5-100:1.8) (i.e. reduced N dosage). Surface analysis of sludge by X-ray photoelectron spectroscopy (XPS) indicates significant differences in surface concentrations of elements C, O and N that were observed under different COD/N ratios, implying changes in the composition of extracellular polymeric substances (EPS). Fourier transform-infrared spectroscopy (FTIR) revealed a unique characteristic peak (CO bonds) at 1735 cm(-1) under nitrogen limitation conditions. Total EPS decreased with an increase in COD/N ratio, corresponding to a decrease in the proteins (PN) to carbohydrates (CH) ratio in EPS. There were no significant differences in the total soluble microbial products (SMPs) but the ratio of PN/CH in SMPs decreased with an increase in COD/N ratios. The results suggest that EPS and SMP composition and the presence of a small quantity of filamentous microorganisms played an important role in controlling membrane fouling.

Hydrodynamic treatment of wastewater effluent flocs for improved disinfection.

Hydrodynamic forces generated by an orifice plate under low pressure were examined as a means of disrupting flocs, in order to improve disinfection of treated wastewater effluents. Changes in cavitation conditions were found to have little impact on the extent of particle breakage in this experimental setup. The rate of strain (flow rate divided by the hole radius cubed), however, was found to be the best predictor of floc breakage. Floc breakage was not affected by changes in floc concentration, but was very sensitive to differences between flocs collected from different sources. Larger flocs (90 to 106 microm) were broken apart to a greater extent than smaller ones (53 to 63 microm). Hydrodynamic treatment decreased the viability of bacteria associated with large flocs, and also increased the ultraviolet dose response by up to one log unit (i.e., a factor of ten). Subjecting final effluent wastewaters to hydrodynamic treatment, therefore, provides a treatment strategy for conditions in which the presence of flocs limits the level of disinfection that can be achieved.

Modelling sediment-microbial dynamics in the South Nation River, Ontario, Canada: Towards the prediction of aquatic and human health risk.

Runoff from agricultural watersheds can carry a number of agricultural pollutants and pathogens; often associated with the sediment fraction. Deposition of this sediment can impact water quality and the ecology of the river, and the re-suspension of such sediment can become sources of contamination for reaches downstream. In this paper a modelling framework to predict sediment and associated microbial erosion, transport and deposition is proposed for the South Nation River, Ontario, Canada. The modelling framework is based on empirical relationships (deposition and re-suspension fluxes), derived from laboratory experiments in a rotating circular flume using sediment collected from the river bed. The bed shear stress governing the deposition and re-suspension processes in the stream was predicted using a one dimensional mobile boundary flow model called MOBED. Counts of live bacteria associated with the suspended and bed sediments were used in conjunction with measured suspended sediment concentration at an upstream section to allow for the estimation of sediment associated microbial erosion, transport and deposition within the modelled river reach. Results suggest that the South Nation River is dominated by deposition periods with erosion only occurring at flows above approximately 250 m(3) s(-1) (above this threshold, all sediment (suspended and eroded) with associated bacteria are transported through the modelled reach). As microbes are often associated with sediments, and can survive for extended periods of time, the river bed is shown to be a possible source of pathogenic organisms for erosion and transport downstream during large storm events. It is clear that, shear levels, bacteria concentrations and suspended sediment are interrelated requiring that these parameters be studied together in order to understand aquatic microbial dynamics. It is important that any management strategies and operational assessments for the protection of human and aquatic health incorporate the sediment compartments (suspended and bed sediment) and the energy dynamics within the system in order to better predict the concentration of indicator organism.

Performance and fouling characteristics of a submerged anaerobic membrane bioreactor for kraft evaporator condensate treatment.

Submerged anaerobic membrane bioreactor (SAnMBR) technology was studied for kraft evaporator condensate treatment at 37 +/- 1 degrees C over a period of 9 months. Under tested organic loading rates of 1-24 kg COD/m3/day, a chemical oxygen demand (COD) removal efficiency of 93-99% was achieved with a methane production rate of 0.35 +/- 0.05 L methane/g COD removed and a methane content of 80-90% in produced biogas. Bubbling of recycled biogas was effective for in-situ membrane cleaning, depending on the biogas sparging rate used. The membrane critical flux increased and the membrane fouling rate decreased with an increase in the biogas sparging rate. The scanning electron microscopy images showed membrane pore clogging was not significant and sludge cake formation on the membrane surface was the dominant mechanism of membrane fouling. The results suggest that the SAnMBR is a promising technology for energy recovery from kraft evaporator condensate.

Sludge properties and their effects on membrane fouling in submerged anaerobic membrane bioreactors (SAnMBRs).

Two submerged anaerobic membrane bioreactors (SAnMBRs) (thermophilic vs. mesophilic) were operated for a period of 3.5 months with kraft evaporator condensate at a feed chemical oxygen demand of 10,000 mg/L. The results show that the filtration behavior of the two systems was significantly different. The filtration resistance in the thermophilic SAnMBR was about 5-10 times higher than that of the mesophilic system when operated under similar hydrodynamic conditions. Comparison of sludge properties and cake layer structure from the two systems was made to elucidate major factors governing the different filtration characteristics. There were more soluble microbial products (SMP) and biopolymer clusters (BPC) produced and a larger portion of fine flocs (<15 microm) in the thermophilic SAnMBR. Analysis of bound extracellular polymeric substances (EPS) showed that the thermophilic sludge had a higher protein/polysaccharide ratio in EPS, as compared to that in the mesophilic sludge. A series of analyses, including Fourier transform infrared (FTIR) spectroscopy, energy dispersive X-ray spectroscopy (EDX), confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and particle size analyzer showed that the cake layer formed in the thermophilic SAnMBR contained higher levels of both organic and inorganic foulants, smaller particle sizes, and especially, a denser and more compact sludge cake structure. These results indicate that floc size, SMP, BPC, bound EPS as well as cake layer structure are the major factors governing membrane fouling in SAnMBR systems.

Effect of oxygen partial pressure and chemical oxygen demand loading on the biofilm properties in membrane-aerated bioreactors.

Membrane-aerated biofilms with oxygen and nutrients diffusing from the opposite sides possess distinct properties, including the ability to couple aerobic and anaerobic processes. The objective of this study was to examine the effects of oxygen partial pressure and chemical oxygen demand (COD) loading on biofilm properties. Two laboratory-scale membrane-aerated bioreactors were operated for a total of 283 days, with one reactor operated at 42, 60, and 89 kPa (0.41, 0.59, and 0.88 atm) oxygen, and the other reactor at 25 kPa (0.25 atm) oxygen (air control). The biofilm detached at the oxygen partial pressures of 60 and 89 kPa (0.59 and 0.88 atm) at a COD loading of 11.3 kg COD/1000 m2/d, but was sustained at the oxygen partial pressures of 25 and 42 kPa (0.25 and 0.41 atm), with a porous structure at the membrane interface at the COD loading of 11.3 kg COD/1000 m2/d. Biofilm formation was improved at a higher COD loading. It is proposed that the loss of extracellular polymeric substances at the biofilm bottom is the cause for the biofilm detachment subjected to a higher oxygen partial pressure.

The impact of reduced phosphorus levels on microbial floc properties during biological treatment of pulp and paper wastewaters.

The effect of limiting P in activated sludge was investigated in laboratory scale sequencing batch reactors (SBRs) fed effluent from a container board mill. Floc characterization included measurement of hydrophobicity, surface charge, and analysis of extracellular polymeric substances (EPS). Reactor performance was assessed by monitoring COD and inorganic P removal, MLSS, and sludge settleability (SVI and batch settling flux) over a period of eight months. Control reactors (BOD:N:P of 100:5:1) were compared to reactors run under P-limited conditions (100:5:0.3; 100:5:0.1). Reactor performance at lower temperatures (14 degrees C; control = 26 degrees C) was also studied to assess the impact of P-limitation. Changes in floc structure and the composition of EPS occurred within 1 to 3 days following a reduction in P levels. There was an insignificant increase in SVI; however, gravitational settling velocity and batch settling flux values for low P floc were consistently higher than for floc generated under control conditions. Lower temperatures (14 degrees C) resulted in a deterioration in floc settling properties at a BOD:N:P of 100:5:1. This impact on settling was significantly reduced at a BOD:P of 100:0.1. Reducing P concentrations in the wastewater treatment system has the potential to improve sludge settleability and reduce final P discharges.

Effect of phosphorus limitation on microbial floc structure and gene expression in activated sludge.

The effect of limiting phosphorus (P) in activated sludge was investigated in laboratory-scale sequencing batch reactors (SBRs). Correlative microscopy revealed that P-limitation (COD:N:P = 100:5:0.05) leads to morphological changes in floc structure and the composition of extracellular polymeric substances (EPS). This was found to be accompanied by expression of quorum-sensing in an acyl homoserine lactone bioassay. Differential gene expression in relation to P-limitation was examined in a global profile using the Affymetrix Escherichia coli antisense genomic microarray. Three separate experiments were conducted where the impact of P-limitation was examined under batch conditions and in SBRs at stable operating conditions and within 3-7 days following a down-shift in P. Significant changes in open reading frames (ORF) and intergenic regions based on the E. coli microarray were observed. Several genes associated with cell structure, including slt, wbbH, fimH, amB, rfaJ and slp were found to be expressed. Quorum regulated genes were also found to be expressed including psiF which is known to be induced by P-starvation (92% confidence level; 1.45 log ratio).

Effect of solids retention time on structure and characteristics of sludge flocs in sequencing batch reactors.

The effect of solids retention time (SRT) (4-20 d) on sludge floc structure, size distribution and morphology in laboratory-scale sequencing batch reactors receiving a glucose-based synthetic wastewater was studied using image analysis in a long-term experiment over one year. Floc size distribution (>10 microm) could be characterized by a log-normal model for no bulking situations, but a bi-modal distribution of floc size was observed for modest bulking situations. In each operating cycle of the SBRs, the variation in food /microorganisms ratio (0.03-1.0) had no significant influence on floc size distribution and morphology. The results from a long-term study over one year showed that no clear relationship existed between SRT and median floc size based on frequency. However, sludge flocs at the lower SRTs (4-9 d) were much more irregular and more variable in size with time than those at higher SRTs (16 and 20 d). The level of effluent-suspended solids at lower SRTs was higher than that at higher SRTs.

A review of biofouling and its control in membrane separation bioreactors.

Membrane separation technology is increasingly becoming an important innovation in biological wastewater treatment. Biofouling of the membrane is a major factor affecting the efficient and economic operation of membrane separation bioreactors (MBRs). This review summarizes the state-of-the-art progress in understanding the mechanisms and factors affecting membrane biofouling and the strategies for biofouling control. Biofouling mechanisms include the adsorption of soluble and suspended extracellular polymers on membrane surfaces and in membrane pores, the clogging of membrane pore structure by fine colloidal particles and cell debris, and the adhesion and deposition of sludge cake on membrane surfaces. Design and operating conditions of membrane modules and materials, hydrodynamic conditions in MBRs, process and environmental conditions of activated sludge systems, and the physicochemical properties of the wastewater are the dominant factors determining membrane biofouling. Current strategies to control biofouling include periodic relaxation, backwashing, chemical cleaning, and possible manipulation of hydrodynamic conditions and sludge properties. Achieving full integration of MBRs in wastewater treatment technology requires further research and development. Fundamental information on the bacteria, colloid, and membrane interaction, developed through multimethod and multiscale approaches, is particularly needed.

Effect of solids retention time on floc structure.

Correlative microscopy was applied to study the influence of solids retention time on activated sludge floc structure. Conventional optical microscopy revealed flocs at lower SRTs (4 and 9 days) to be irregular in shape while flocs at higher SRTs (16 and 20 days) had a more spherical and compact structure. Flocs were examined by environmental scanning electron microscopy (ESEM) and by transmission electron microscopy (TEM) coupled with energy-dispersive spectroscopy (EDS). Distinctive differences in floc structure and the arrangement of EPS were revealed. Flocs from higher SRTs were less hydrated and were found to possess a dense EPS layer that covers much of the surface. Extracellular osmiophilic granules present in these flocs indicate that the cells at the higher SRT may produce more lipid-like material. This EPS layer appears to decrease the floc surface roughness and protects the interior cells from disruption by changes in the external environment. Sludge flocs at higher SRTs were found to be physically more stable than those at lower SRTs.

Interparticle interactions affecting the stability of sludge flocs.

Interparticle interactions affecting the stability of sludge flocs taken from laboratory-scale sequencing batch reactors at different solids retention times (SRTs) were investigated in batch experiments by varying the pH, ionic strength, cation valence, and urea and ethylenediaminetetraacetate concentrations of suspending solutions. The ultrastructure of sludge floc surfaces was observed by transmission electron microscopy. Changes in dissociation constants of sludge flocs under different conditions indicated that ionic interactions and hydrogen bonds held flocs together and compensated for the negative influence of electrostatic interactions on the stability of sludge flocs. Ionic interactions and hydrogen bonds were two dominant forces that maintained the stability of sludge flocs at lower SRTs; other mechanisms, such as physical enmeshment and van der Waals and/or hydrophobic interactions, were more important in controling the stability of sludge flocs at higher SRTs. Sludge flocs at higher SRTs (16 and 20 days) were physically more stable than those at lower SRTs (4 and 9 days). A conceptual model of floc structure, based on interparticle interactions, for describing the stability of sludge flocs is proposed. The floc matrix is proposed to consist of two physically distinct regions that are defined by the arrangement of extracellular polymeric substances (EPS). These are likely to be differentially affected by the agents applied to manipulate interparticle forces. Thus, the heterogeneity in the packing of and the type of EPS reflects the stability of the floc.

Emotional impact of retirement on physicians.

The current study sought to identify the factors underlying physicians' decision to retire, describe the emotional impact of retirement on physicians, measure quality of life in retirement, and identify coping strategies used by retired physicians. A questionnaire was sent to all 689 retired members of the Harris County Medical Society, and 323 (47%) responded. Data were analyzed using SPSS. Physicians overwhelmingly indicated positive reasons for retirement, although one third said that loss of autonomy and control in medical practice were factors. Participants were satisfied with retirement and enjoyed low levels of stress and depression. Spousal and personal health had the largest negative impact on retirement. Being prepared emotionally significantly affected physicians' attitudes. Longitudinal studies and research on the impact of managed care on the retirement experience are needed. Younger physicians need to be prepared for the emotional impact of retirement.

Insights into physician retirement.

Most physicians in this study retired because they thought the time was right, and they did not feel forced to do so. This situation may not be the case in the future with changes occurring in the practice of medicine. Most of the physicians were pleased with their retirement after they had completed an adjustment period, often lasting about a year. The most important factor involved in successful retirement was the health of the physician and his or her spouse. A good relationship with the spouse was important. Typically, relationships with spouses improved. If a physician has no spouse or poor spousal support, some other method of replacing the support network previously provided by staff, patients, and practicing colleagues is necessary. After retirement, the physicians in our study became comfortable with living on their savings. Strategies employed after retirement were diverse. Many of the retired physicians took advantage of increased time to exercise for enjoyment and for health. Although some of the retired physicians continued to pursue medical interests, many others discovered rewarding activities away from medicine, but rarely for financial compensation.

Surface properties of sludge and their role in bioflocculation and settleability.

The influence of sludge retention time (SRT) on the extracellular polymeric substances (EPS) and physicochemical properties (hydrophobicity and surface charge) of sludge was studied using laboratory-scale sequencing batch reactors (SBRs) fed a synthetic wastewater containing glucose and inorganic salts. Sludge surfaces were more hydrophobic (larger contact angle) and less negatively charged at higher SRTs (16 and 20 d) than at lower SRTs (4 and 9 d). The ratio of proteins to carbohydrates within the EPS of the sludges increased as the SRT increased from 4 to 12 d corresponding to the changes in the physicochemical properties of the sludge. The protein:carbohydrate ratio remained constant at SRTs of 16 and 20 d. A transition in sludge properties appeared to occur between the upper range of low- (9 d) and lower range of high-SRTs. The total EPS content, however, was independent of the SRT. A higher sludge volume index (SVI), an indication of poorer settleability or compression, was associated with a larger amount of total EPS but no significant correlation between SVI and the surface properties of sludge was observed. A more hydrophobic and less negatively charged surface corresponded to lower levels of ESS. These results indicate that it is the surface properties, hydrophobicity, surface charge and composition of EPS, of sludge, rather than the quantity of EPS, that govern bioflocculation. In contrast, the EPS content is more important in controlling the settleability of sludge.

Toluene removal in an automated cyclical bioreactor.

A control scheme was developed for the automation of toluene removal in a cyclical bioreactor. Toluene was added to the self-cycling fermentor by diffusion across a silicone membrane. Transient dissolved oxygen, carbon dioxide evolution, and oxidation-reduction potential (ORP) were screened as potential control variables. Through experimentation, ORP was deemed most effective. Control algorithms based on real-time estimates of the first and second derivatives of the ORP signal were tested. Although both approaches resulted in stable operation of the reactor, average toluene removal efficiencies of 95% were realized when control was based on the second derivative. This was significantly higher than the 77% efficiencies obtained when the control scheme centered on the first derivative of the transient ORP signal. The system developed was self-regulating, ensuring that a high toluene removal rate, on the order of 1.1 g h(-1), was maintained from cycle to cycle.

Microbiology and biodegradation of resin acids in pulp mill effluents: a minireview.

Resin acids, a group of diterpenoid carboxylic acids present mainly in softwood species, are present in many pulp mill effluents and toxic to fish in recipient waters. They are considered to be readily biodegradable. However, their removal across biological treatment systems has been shown to vary. Recent studies indicate that natural resin acids and transformation products may accumulate in sediments and pose acute and chronic toxicity to fish. Several resin acid biotransformation compounds have also been shown to bioaccumulate and to be more resistant to biodegradation than the original material. Until recently, the microbiology of resin-acid degradation has received only scant attention. Although wood-inhabiting fungi have been shown to decrease the level of resin present in wood, there is no conclusive evidence that fungi can completely degrade these compounds. In contrast, a number of bacterial isolates have recently been described which are able to utilize dehydroabietic or isopimaric acids as their sole carbon source. There appears to be an unusually high degree of substrate specificity with respect of the utilization of abietane congeners and the presence of substituents. Pimaranes do not appear to be attacked to the same extent as the abietanes. This paper reviews the occurrence, chemistry, toxicity, and biodegradation of resin acids in relation to the biological treatment of pulp and paper mill effluents.

Floc stabilization for multiple microscopic techniques.

A nondestructive stabilization technique for the characterization of microbial flocs which permits the application of correlative microscopic techniques is described. Flocs embedded in agarose are retained in a porous, resilient medium which allows for the transport, staining, washing, and subsampling of the flocculated material directly within a plankton chamber with minimal or no destructive forces. A single agarose disc can be subdivided into numerous sections for analysis by several microscope types and associated techniques.

Physiological and therapeutic effects of high frequency electrical pulses.

The results of stimulating human subjects with the LISS Cranial Stimulator (LCS) and the LISS Body Stimulator (LBS) include an increase or decrease in the activities of certain neurotransmitters and neurohormones and the reduction of associated pain, insomnia, depression, and spasticity. The effects were documented in human subjects with measurements of the serum concentration of the various agents and assessments of the symptoms being performed before and after stimulation. The stimulators had a carrier frequency of 15,000 hz, which utilizes the bulk capacitance of the body, and a 15 hz modulating bioactive frequency. The second modulating frequency presently used, 500 hz, reduces the energy input to the patient by half. Significant increases in levels of CSF serotonin and beta endorphin were recorded post stimulation. There were also elevations in the levels of plasma serotonin, beta endorphin, GABA and DHEA together with diminished levels of cortisol and tryptophan. Concomitant with these changes were significant improvements in the symptoms of pain, insomnia, spasticity, depression, and headache.