Sludge bulking impact on relevant bacterial populations in a full-scale municipal wastewater treatment plant

We have investigated the changes of microbial community structures and the concomitant performance in two biological wastewater treatment systems (conventional and inverted A²/O processes) over a whole cycle of sludge bulking. A low level of filament abundance was observed during non-bulking period, with types 0092 and 0041 as the dominant filamentous bacteria. With the increase of the sludge volume index values from 76 (73) to 275 (300) mg/L, the filament abundance estimated by microscopic examination increased from 1 (few) to 5 (abundant), with Microthrix parvicella becoming the dominant filament bacteria. Sludge bulking resulted in a significant shift in bacterial compositions from Proteobacteria to Actinobacteria dominance, characterized by the significant presence of filamentous M. parvicella (from not detected to higher than 60% of clones) and decrease of the dominant Betaproteobacterial population (from higher than 40% to less than 1%). Important relevant bacterial populations including polyphosphate-accumulating organism (PAO, Candidatus Accumulibacter phosphatis), ammonia-oxidizing bacteria (AOB, Nitrosomonas), nitrite-oxidizing bacteria (NOB, Nitrospira) and denitrifying bacteria (Thauera) were absent under the serious bulking condition. Accumulation of nitrite and ammonia was observed during serious bulking, while the phosphorus removal performance was not decreased because M. parvicella could behave as a PAO.     

Nitrogen removal in a wastewater treatment plant through biofilters: nitrous oxide emissions during nitrification and denitrification

In order to estimate N₂O emissions from immersed biofilters during nitrogen removal in tertiary treatments at urban wastewater treatment plants (WWTPs), a fixed culture from the WWTP of “Seine Centre” (Paris conurbation) was subjected to lab-scale batch experiments under various conditions of oxygenation and a gradient of methanol addition. The results show that during nitrification, N₂O emissions are positively related to oxygenation (R ² = 0.99). However, compared to the rates of ammonium oxidation, the percentage of emitted N₂O is greater when oxygenation is low (0.5–1 mgO₂ L⁻¹), representing up to 1% of the oxidized ammonium (0.4% on average). During denitrification, the N₂O emission reaches a significant peak when the quantity of methanol allows denitrification of between 66% and 88%. When methanol concentrations lead to a denitrification of close to 100%, the flows of N₂O are much lower and represent on average 0.2% of the reduced nitrate. By considering these results, we can estimate, the emissions of N₂O during nitrogen removal, at the “Seine Centre” WWTP, to approximately 38 kgN-N₂O day⁻¹.     

Study of operational conditions of simultaneous nitrification and denitrification in a Carrousel oxidation ditch for domestic wastewater treatment

The study on the operational conditions of simultaneous nitrification and denitrification (SND) in the channel of oxidation ditch (OD) without the need for a special anoxic tank was carried out based on lab-scale and pilot-scale experiments using real domestic wastewater. The influence of sludge loading and component proportion in influent, temperature, hydraulic retention time (HRT), dissolved oxygen (DO) and operational mode on SND was investigated. The result indicated that the optimal DO (ODO) of SND occurrence was confirmed majorly by the sludge loading of influent and temperature, the high TCOD/NH₃–N and short HRT can enhance the occurrence of SND. A new operational mode was proposed that achieved a higher removal efficiency of 60–70% for total nitrogen by SND with HRT of 4–6 h, and the concentrations of NH₃–N and TN in effluent are less than 5 and 15 mg/L, respectively.     

Characterization of bacterial diversity in two aerated lagoons of a wastewater treatment plant using PCR-DGGE analysis

Aerated lagoons are commonly used for domestic and industrial wastewater treatment due to their low cost and minimal need of operational requirements. However, little information is known regarding microbial communities that inhabit these ecosystems. In this study, a 16S-DGGE approach was used to estimate bacterial diversity and to monitor community changes in two aerated lagoons from a wastewater treatment plant receiving urban and industrial effluents. Pronounced shifts between bacterial communities collected in winter–spring and summer–autumn months were detected. Temperature, dissolved oxygen (DO) and pH were the variables that most influenced the bacterial communities. Phylogenetic affiliation of predominant members was assessed by the determination of the 16S rDNA sequence of correspondent bands. Affiliations to Cytophaga–Flexibacter–Bacteroides (CFB) group, Firmicutes, and β- and ε-proteobacteria were found.     

Competition between two microbial populations in a sequencing fed-batch reactor: theory, experimental verification, and implications for waste treatment applications

Competition between two microbial populations for a single pollutant (phenol) was studied in a sequencing fed-batch reactor (SFBR). A mathematical model describing this system was developed and tested experimentally. It is based on specific growth rate expressions revealed from pure culture batch experiments. The species employed were Pseudomonas putida (ATCC 17514) and Pseudomonas resinovorans (ATCC 14235). It was found that both species biodegrade phenol following inhibitory kinetics which can be described by Andrews' expression. The model predicts that the dynamics of a SFBR, and the kinetics of biodegradation, result in a complex set of operating regimes in which neither species, only one species, or both species can survive at steady cycle. The model also predicts the existence of multiple outcomes, achievable from different start-up conditions, in some domains of the operating parameter space. Experimental results confirmed the model predictions. There was excellent agreement between predicted and measured concentrations of phenol, total biomass, and the biomass of each individual species. This study shows how serious discrepancies can arise in scale-up of biodegradation data if population dynamics are not taken into account. It also further confirms experimentally the theory of microbial competition in periodically forced bioreactors. (c) 1993 John Wiley & Sons, Inc.     

Denitrification in the periphyton associated with plant shoots and in the sediment of a wetland system supplied with sewage treatment plant effluent

Seasonal variation in denitrification and major factors controlling this process were determined in sediment, microbial communities attached to plant shoots (periphyton) and in the water of a Phragmites and an Elodea-dominated stand of a constructed wetland system between May 1997 and February 1998. The wetland was supplied with effluent from a sewage treatment plant. The denitrification rate in periphyton on plants shoots (expressed per shoot area) was always considerably higher than in the sediment and varied with the chlorophyll-a content of the periphyton in the course of the year. The algae in the periphyton provided attachment surfaces and probably also organic compounds to the denitrifying bacteria. Decreases in periphyton biomass and denitrification rate in the Phragmites and Elodea-dominated stands during the growing season were associated with enhanced shading by Phragmites shoots or a floating layer of macro-algae and Lemna spp., respectively. Light availability and the denitrification rate of periphyton increased again after the Phragmites shoots were cut in October. Nitrate appeared to limit the denitrification rate in the sediment. Periphyton denitrification rates were mostly lower on Elodea shoots than on Phragmites shoots, in spite of the higher living algal biomass on Elodea shoots. This difference was associated with lower nitrate concentrations in the Elodea-dominated stand. In the two stands, the daily denitrification rates in periphyton on shoots of Phragmites australis (44.4–121 mg N m^–2 stand area d^–1) and Elodea nuttallii (14.8–33.1 mg N m^–2 d^–1) were clearly more important than rates in the sediment (0.5–25.5 mg N m^–2 d^–1) or the water (0.4–3.9 mg N m^–2 d^–1). The presence of few bacteria attachment sites or low organic carbon availability possibly resulted in low denitrification rates in the water. Denitrification appeared to be a major process in nitrate removal from the through-flowing water in this wetland system.     

Estimate of life-cycle greenhouse gas emissions from a vertical subsurface flow constructed wetland and conventional wastewater treatment plants: A case study in China

This study aims to estimate the three greenhouse gas (GHG) emissions (i.e. CO₂, CH₄, N₂O) from a vertical subsurface flow constructed wetland (VSSF CW, 1000 m²) and a cluster of conventional wastewater treatment plants (WWTPs) in the city of Changzhou, China. The two estimated emissions are set up for comparison. The results show that the WWTP system emits 7.3 kg CO₂-eq to remove 1 kg BOD in the studied life cycle, while the VSSF system only emits 3.18 kg CO₂-eq, which is only half of the amount given off by the WWTP system. Especially at the treatment stage, the WWTP system's GHG emissions are almost 7 times higher than the VSSF system's. N₂O emissions in both systems are only a minor fraction of the total emissions. Therefore, this study has concluded that the VSSF system is an effective option for GHG emissions mitigation in the wastewater sector. The study further suggests that developing countries like China should extensively build up VSSF systems for decentralized wastewater treatment, which could also potentially reduce GHG emissions by 8-17 million ton CO₂-eq per year compared with the centralized scenario.     

New concepts of microbial treatment processes for the nitrogen removal in wastewater

Many countries strive to reduce the emissions of nitrogen compounds (ammonia, nitrate, NOx) to the surface waters and the atmosphere. Since mainstream domestic wastewater treatment systems are usually already overloaded with ammonia, a dedicated nitrogen removal from concentrated secondary or industrial wastewaters is often more cost-effective than the disposal of such wastes to domestic wastewater treatment. The cost-effectiveness of separate treatment has increased dramatically in the past few years, since several processes for the biological removal of ammonia from concentrated waste streams have become available. Here, we review those processes that make use of new concepts in microbiology: partial nitrification, nitrifier denitrification and anaerobic ammonia oxidation (the anammox process). These processes target the removal of ammonia from gases, and ammonium-bicarbonate from concentrated wastewaters (i.e. sludge liquor and landfill leachate). The review addresses the microbiology, its consequences for their application, the current status regarding application, and the future developments.     

A state of the art review on microbial fuel cells: A promising technology for wastewater treatment and bioenergy

A microbial fuel cell (MFC) is a bioreactor that converts chemical energy in the chemical bonds in organic compounds to electrical energy through catalytic reactions of microorganisms under anaerobic conditions. It has been known for many years that it is possible to generate electricity directly by using bacteria to break down organic substrates. The recent energy crisis has reinvigorated interests in MFCs among academic researchers as a way to generate electric power or hydrogen from biomass without a net carbon emission into the ecosystem. MFCs can also be used in wastewater treatment facilities to break down organic matters. They have also been studied for applications as biosensors such as sensors for biological oxygen demand monitoring. Power output and Coulombic efficiency are significantly affected by the types of microbe in the anodic chamber of an MFC, configuration of the MFC and operating conditions. Currently, real-world applications of MFCs are limited because of their low power density level of several thousand mW/m2. Efforts are being made to improve the performance and reduce the construction and operating costs of MFCs. This article presents a critical review on the recent advances in MFC research with emphases on MFC configurations and performances.     

Effect of the concentration of suspended solids on the enzymatic activities and biodiversity of a submerged membrane bioreactor for aerobic treatment of domestic wastewater

A pilot-scale submerged membrane bioreactor was used for the treatment of domestic wastewater in order to study the influence of the variations in the concentration of volatile suspended solids (VSS) on the enzymatic activities (acid and alkaline phosphatases, glucosidase, protease, esterase, and dehydrogenase) and biodiversity of the bacterial community in the sludge. The influence of VSS concentration was evaluated in two separated experiments, which were carried out in two different seasons of the year (experiment 1 through spring–summer and experiment 2 through autumn–winter). Cluster analysis of the temperature gradient gel electrophoresis (TGGE) profiles demonstrated that the community composition was significantly different in both experiments. Within the same experiment, the bacterial community experienced sequential shifts as the biomass accumulated, as shown by the evolution of the population profiles through time as VSS concentration increased. All enzymatic activities studied were significantly lower during experiment 2, except for glucosidase. Concentrations of VSS over 8 g/l induced a strong descent of all enzymatic activities, which overlapped with a significant modification of the community composition. Sequences of the major TGGE bands were identified as representatives of the Alpha-proteobacteria, filamentous bacteria (Thiotrix), and nitrite oxidizers (Nitrospira). Some sequences which were poorly related to any validated bacterial taxon were obtained.     

Development of an efficient process for the treatment of residual sludge discharged from an anaerobic digester in a sewage treatment plant

In order to reduce the discharge of residual sludge from an anaerobic digester, pre-treatment methods including low-pressure wet-oxidation, Fenton oxidation, alkali treatment, ozone oxidation, mechanical destruction and enzymatic treatment were evaluated and compared. VSS removal efficiencies of greater than 50% were achieved in cases of low-pressure wet-oxidation, Fenton oxidation and alkali treatment. Residual sludge from an anaerobic digester was pre-treated and subjected to thermophilic anaerobic digestion. As a result, the process of low-pressure wet-oxidation followed by anaerobic digestion achieved the highest VSS removal efficiency of 83%. The total efficiency of VSS removal of sewage sludge consisting of primary and surplus sludge would be approximately 92%, assuming that the VSS removal efficiency of sewage sludge is 50% in the anaerobic digester of the sewage treatment plant.     

Pseudomonas laurylsulfatovorans sp. nov., sodium dodecyl sulfate degrading bacteria,isolated from the peaty soil of a wastewater treatment plant

Pseudomonas are known from their flexible degradation capabilities and their engagement in xenobiotic biotransformation and bioremediation in habitats like soil, active sludge, plant surfaces, and freshwater or marine environments. Here we present taxonomic characterization of three efficient sodium dodecyl sulfate degrading strains: AP3_10, AP3_20 and AP3_22^T belonging to the genus Pseudomonas, recently isolated from peaty soil used in a biological wastewater treatment plant. Sequence analyses of 16S rRNA and housekeeping genes: gyrB, rpoD and rpoB showed that the three closely related isolates classify within the Pseudomonas jessenii subgroup. ANIb or dDDH genomic comparisons of AP3_22^T (type strain DSM 105098^T = PCM 2904^T) supported by biochemical tests showed that the isolates differ significantly from their closest relatives. The combined genotypic, phenotypic and chemotaxonomic data strongly support the classification of the three strains: AP3_10, AP3_20 and AP3_22^T as a novel species of Pseudomonas, for which we propose the name Pseudomonas laurylsulfatovorans sp. nov. with AP3_22^T as the type strain.     

The use of sub-surface constructed wetlands for wastewater treatment in the Czech Republic: 10 years experience

Wetlands have been intensively studied in the Czech Republic for more than 30 years, but the first full-scale constructed wetland (CW) for wastewater treatment was built in the Czech Republic in 1989. By the end of 1999, about 100 CWs were put in operation. The majority of the systems are horizontal subsurface flow (HSF) CWs and are designed for the secondary treatment of domestic or municipal wastewater. The size of CWs ranges between 18 and 4500 m² and between 4 and 1100 population equivalent (PE). Most frequently used filtration media are gravel and crushed rock with size fractions of 4/8 and 8/16 mm and Phragmites australis is the most commonly used plant. The treatment efficiency is high in terms of BOD₅ (88.0% for vegetated beds) and suspended solids (84.3% for vegetated beds). The removal of nutrients is lower for vegetated beds, and averages 51 and 41.6% for total phosphorus and total nitrogen, respectively.     

Alginate from the macroalgae <Emphasis Type="Bold">Sargassum sinicola</Emphasis> as a novel source for microbial immobilization material in wastewater treatment and plant growth promotion

Alginate extracted from the macroalgae Sargassum sinicola was used as the raw material for co-immobilization of the microalgae Chlorella sorokiniana and growth-promoting bacterium Azospirillum brasilense for wastewater treatment and as an inoculant carrier of A. brasilense for plant growth promotion. The composition, structure, viscosity, color, and phenolic compound content of the alginate were analyzed and compared with commercially available alginate produced from the macroalgae Macrocystis pyrifera. From ¹H NMR analysis of alginate, S. sinicola was found to have more guluronic acid (F _G=0.64) than it had mannuronic acid (F _M=0.38) and had a viscosity of 13.5 m Pa s compared to 50 m Pa s for M. pyrifera. The S. sinicola alginate had dark brown color, reducing light penetration, with more phenolic compounds than M. pyrifera alginate. Nonetheless, growth of C. sorokiniana and A. brasilense in S. sinicola alginate was not significantly different than the growth in M. pyrifera alginate beads. Nutrient removal from wastewater by the co-immobilized microorganisms was similar for both types of alginate beads, and so was the growth enhancement of tomato plants inoculated with microbeads containing A. brasilense. This study shows the potential use of S. sinicola alginate as a raw material for cell immobilization for wastewater treatment and plant growth promotion.     

Effects of phase vector and history extension on prediction power of adaptive-network based fuzzy inference system (ANFIS) model for a real scale anaerobic wastewater treatment plant operating under unsteady state

A conceptual neural fuzzy model based on adaptive-network based fuzzy inference system, ANFIS, was proposed using available input on-line and off-line operational variables for a sugar factory anaerobic wastewater treatment plant operating under unsteady state to estimate the effluent chemical oxygen demand, COD. The predictive power of the developed model was improved as a new approach by adding the phase vector and the recent values of COD up to 5–10 days, longer than overall retention time of wastewater in the system. History of last 10 days for COD effluent with two-valued phase vector in the input variable matrix including all parameters had more predictive power. History of 7 days with two-valued phase vector in the matrix comprised of only on-line variables yielded fairly well estimations. The developed ANFIS model with phase vector and history extension has been able to adequately represent the behavior of the treatment system.     

Tangled up in two: a burst of genome duplications at the end of the Cretaceous and the consequences for plant evolution

Genome sequencing has demonstrated that besides frequent small-scale duplications, large-scale duplication events such as whole genome duplications (WGDs) are found on many branches of the evolutionary tree of life. Especially in the plant lineage, there is evidence for recurrent WGDs, and the ancestor of all angiosperms was in fact most likely a polyploid species. The number of WGDs found in sequenced plant genomes allows us to investigate questions about the roles of WGDs that were hitherto impossible to address. An intriguing observation is that many plant WGDs seem associated with periods of increased environmental stress and/or fluctuations, a trend that is evident for both present-day polyploids and palaeopolyploids formed around the Cretaceous–Palaeogene (K–Pg) extinction at 66 Ma. Here, we revisit the WGDs in plants that mark the K–Pg boundary, and discuss some specific examples of biological innovations and/or diversifications that may be linked to these WGDs. We review evidence for the processes that could have contributed to increased polyploid establishment at the K–Pg boundary, and discuss the implications on subsequent plant evolution in the Cenozoic.     

Simulating the effects of localized red:far-red ratio on tillering in spring wheat (Triticum aestivum) using a three-dimensional virtual plant model

The outgrowth of tiller buds in Poaceae is influenced by the ratio of red to far-red light irradiance (R:FR). At each point in the plant canopy, R:FR is affected by light scattered by surrounding plant tissues. This paper presents a three-dimensional virtual plant modelling approach to simulate local effects of R:FR on tillering in spring wheat (Triticum aestivum). R:FR dependence of bud outgrowth was implemented in a wheat model, using three hypothetical responses of bud extension to R:FR (unit step, curvilinear and linear response). Bud break occurred when a threshold bud length was reached. Simulations were performed for three plant population densities. In accordance with experimental observations, fewer tillers per plant were simulated for higher plant population densities. The linear and curvilinear responses caused a delay in the increase in tiller number compared with experimental data. The unit step response approached experimental results best. It is suggested that a model based on relatively simple relations can be used to simulate degree of tillering. This study has shown that the virtual plant approach is a promising tool with which to address crop morphological and ecological research questions where the determining factors act at the level of the individual plant organ.     

Nutrient requirements differ in two Pedicularis species in the absence of a host plant: implication for driving forces in the evolution of host preference of root hemiparasitic plants

Background and Aims

Facultative root hemiparasitic plants generally have a wide host range, but in most cases show an obvious host preference. The reasons for the marked difference in growth performance of hemiparasites when attached to different hosts are not fully understood. In this study, the hypothesis was tested that hemiparasites showing a preference for different hosts have different nutrient requirements.

Methods

Two facultative root hemiparasitic Pedicularis species (P. rex and P. tricolor) with a different host dependency and preference were used to test their responses to inorganic solutes. The effects of nitrogen, phosphorus and potassium on growth of the hemiparasitic plants not attached to a host were determined, using an orthogonal design in pot cultivation under greenhouse conditions. Variables including biomass, shoot nutrient concentration, root:shoot (R:S) ratios and the number of haustoria were measured.

Key Results

As in autotrophic plants, nutrient deficiency reduced dry weight (DW) and nutrient concentrations in the root hemiparasites. Nitrogen and phosphorus significantly influenced growth of both Pedicularis species, while potassium availability influenced only shoot DW of P. rex. Nitrogen had far more effect on growth of P. rex than on P. tricolor, while phosphorus deficiency caused more marked growth depression in P. tricolor than in P. rex. Pedicularis rex grew faster than P. tricolor in a range of nutrient supplies. Different patterns of biomass allocation between the two Pedicularis species were observed. While P. rex invested more into roots (particularly fine rootlets) than P. tricolor, the number of haustoria produced by P. rex was relatively much lower than that produced by P. tricolor, which had a much smaller root system.

Conclusions

The two Pedicularis species differ in nutrient requirements and biomass allocation. Distinct interspecific traits in growth and nutrient requirements can be driving forces for the differential interactions between hemiparasites and their hosts.