Showing papers on "Enhanced biological phosphorus removal published in 1995"

Bacterial community structures of phosphate-removing and non-phosphate- removing activated sludges from sequencing batch reactors

Abstract: The bacterial community structures of phosphate- and non-phosphate-removing activated sludges were compared. Sludge samples were obtained from two sequencing batch reactors (SBRs), and 16S rDNA clone libraries of the bacterial sludge populations were established. Community structures were determined by phylogenetic analyses of 97 and 92 partial clone sequences from SBR1 (phosphate-removing sludge) and SBR2 (non-phosphate-removing sludge), respectively. For both sludges, the predominant bacterial group with which clones were affiliated was the beta subclass of the proteobacteria. Other major groups represented were the alpha proteobacterial subclass, planctomycete group, and Flexibacter-Cytophaga-Bacteroides group. In addition, several clone groups unaffiliated with known bacterial assemblages were identified in the clone libraries. Acinetobacter spp., thought to be important in phosphate removal in activated sludge, were poorly represented by clone sequences in both libraries. Differences in community structure were observed between the phosphate- and non-phosphate-removing sludges; in particular, the Rhodocyclus group within the beta subclass was represented to a greater extent in the phosphate-removing community. Such differences may account for the differing phosphate-removing capabilities of the two activated sludge communities.

A structured metabolic model for anaerobic and aerobic stoichiometry and kinetics of the biological phosphorus removal process.

Abstract: A structured metabolic model is developed that describes the stoichiometry and kinetics of the biological P removal process. In this approach all relevant metabolic reactions underlying the metabolism, considering also components like adenosine triphosphate (ATP) and nic-otinamide-adenine dinucleotide (NADH(2)) are describedbased on biochemical pathways. As a consequence of the relations between the stoichiometry of the metabolic reactions and the reaction rates of components, the required number of kinetic relations to describe the process is reduced. The model describes the dynamics of the storage compounds which are considered separately from the active biomass. The model was validated in experiments at a constant sludge retention time of 8 days, over the anaerobic and aerobic phases in which the external oncentrations as well as the internal fractions of the relevant components involved in the P-removal process were monitored. These measurements include dissolved acetate, phosphate, and ammonium; oxygen consumption; poly-beta-hydroxybutyrate (PHB); glycogen; and active biomass. The model satisfactorily describes the dynamic behavior of all components during the anaerobicand aerobic phases.(c) 1995 John Wiley & Sons, Inc.

A metabolic model of the biological phosphorus removal process: I. Effect of the sludge retention time

Abstract: The biological phosphorus removal process is a process which depends basically on three internal storage compounds. Poly-beta-hydroxybutyrate (PHB) produced during the anaerobic phase is used as substrate for biomass, polyphosphate, and glycogen formation. The reaction rates of the aerobic processes are primarily determined by the PHB content of the cells. This PHB content is highly dynamic due to the conversions during the anaerobic and aerobic phase of the cycle and the ratio between substrate addition and biomass present in the reactor. The amount of biomass present in the reactor is determined by the sludge retention time and growth rate. A metabolic model of the biological phosphorus removal process was developed and verified over a wide range of growth rates. The effect of different growth rates on the internal fractions of stored components was determined and described mathematically. One set of kinetic parameters was capable of describing the measured conversions of all components observed in the reactor as a function of the sludge retention time.

The availability of phosphorus in municipal wastewater sludge as a function of the phosphorus removal process and sludge treatment method

Abstract: The objective of this study was to determine the availability of phosphorus contained in different wastewater sludges and sluge-soil mixtures. The sludges studied included raw and aerobically digested sluges frm activated sludge treatment plants using four different methods of phosphorus removal: alum addition, ferric chloride addition, anaerobic/oxic biological phosphorus removal, and no provision for excess phosphorus removal. test methods used to determine phosphorus availability of the sludges included the equilibrium phosphorus concentrationt est and soil-incubation tests. The soil-incubation studies consisted of soil and soil-sand mixtures spiked with sludges. Testing on the pots compared initial pots to final pots after leaching with distilled water. Results showed that based on most measures, phosphorus was the most available from fertilizer. Phosphorus was also highly available from sludges generated without using chemical addition for phosphorus removal. Phosphorus availability of digested sludges versus raw sludges varied, depending on the method of analysis

Treatment of phosphorus containing sewage

Abstract: PROBLEM TO BE SOLVED: To recover phosphorus as resources from sewage and also to sharply reduce the generated quantity of sludge by adding an new idea to a conventional flocculant addition activated sludge process. SOLUTION: After an iron based/aluminum based phosphorus removing agent is added to a biological treatment process for biologically treating phosphorus containing organic sewage to adsorb or flocculate phosphorus, a part of sedimented sludge which a biological treatment process outflow liquid is subjected to sedimentation to form is returned to the biological treatment process, and the other part of the sedimented sludge or sludge drawn from the biological treatment process is oxidized by ozone under alkaline conditions. Next it is subjected to solid-liquid separation, and to the formed separated liquid, Ca or Mg ions are added to remove phosphorus, and then it is returned to the biological treatment process together with the separated sludge after oxidation by ozone. COPYRIGHT: (C)1997,JPO

A metabolic model of the biological phosphorus removal process: II. Validation during start‐up conditions

Abstract: A metabolic model of the biological phosphorus removal process has been developed and validated previously for complex conversions during the process under anaerobic and aerobic conditions at different growth rates in sequencing batch reactors in steady state. For additional validation of the metabolic model, the model was applied to the dynamic conditions which occur during the start-up phase of the biological P removal in the presence and absence of non-polyP heterotrophic microorganisms. In a laboratory scale sequencing batch reactor, experiments were performed to examine the enrichment of the population with polyphosphate organisms during the start-up and the subsequent shift from non-polyP, heterotrophic organisms to polyP organisms in the sludge. The effect of different influent loading patterns for acetate and phosphate was studied. In these experiments, the maximal growth rate of the polyP organisms and the behavior of the internal storage compounds could be derived. The metabolic model was capable of describing the experimental results, without the need to adjust the kinetic or stoichiometric parameters obtained under steady state conditions.

Biological Nutrient Removal: Design Snags, Operational Problems and Costs

Abstract: The EC urban waste water treatment Directive will lead to some sewage-treatment works in the UK having to remove nitrogen and phosphorus. The paper reviews the basic biological processes which are available for retrofitting existing activated-sludge plants to achieve this removal, and then points to some of the problems which are encountered with these processes in other countries. The authors make suggestions as to how these problems can be overcome in design and operation. The paper also provides a cost comparison of different ways of uprating an existing nitrifying activated-sludge plant to achieve nitrification/denitrification and phosphorus removal

Fate of nutrients during anaerobic co-digestion of sludges from a biological phosphorus removal process

Abstract: Pilot scale (160 L) research on enhancement of anaerobic co-digestion of combined primary and high-phosphorus waste activated sludge (WAS) was performed, using low-level alkaline solubilization of WAS. Solubilization was performed by the addition of 15 meqL−1 of calcium hydroxide or sodium hydroxide, using a mechanical anoxic mixing time of 5 hours. The research examined the effects of decreasing solids retention time (SRT) on digester operational efficiency, as well as the fate of various nitrogen and phosphorus species in both the sludge and supernatant. The overall performance of three pilot scale digesters, including a control unit was monitored. Nitrogen and phosphorus species demonstrated somewhat different response patterns for each chemical. Generally, both chemicals were responsible for significant release of soluble TKN and ammonia during both the solubilization and actual anaerobic digestion steps. Similarly, sodium hydroxide addition to WAS caused a significant release of soluble phosphorus du...

Phosphate uptake by immobilized Acinetobacter calcoaceticus cells in a full scale activated sludge plant

Abstract: Anin situ study of the P-uptake ability ofAcinetobacter calcoaceticus was carried out using the alginate immobilization technique. ImmobilizedA. calcoaceticus cells displayed a high P-uptake ability (>97% P-accumulating cells) when immersed in the aerobic zone of an activated sludge system for 30–240 min. The overall P-accumulation pattern of the anaerobic zone depicted a typical P-release mechanism. However, limited P-accumulation was also observed at this stage. Growth and anaerobiosis were not prerequisites for P-uptake. The immobilized cell retention time in the anaerobic zone did not affect remarkably the inherent P-uptake ability of immobilizedA. calcoaceticus when exposed to the aerobic stage. P-uptake and release were reversible and depended on the environmental conditions to which immobilized cells were exposed. Immobilization ofA. calcoaceticus using alginate can be regarded as a reliable method of studying pure cultures in the activated sludge process.

Influence of the Addition of Different Metals to an Activated Sludge System on the Enhanced Biological Phosphorus Removal

Abstract: Activated sludge systems can be operated to select bacteria which accumulate phosphorus as polyphosphate. By these means, phosphate can be removed without the addition of chemical precipitants. This contribution presents results of experiments with a bench-scale purification plant for domestic sewage. The goal was to find the concentrations of relevant metal cations at which the biological P removal may be affected by competing chemical (precipitation) or physical (adsorption) processes. For this goal, increasing amounts of iron and calcium, respectively, were added into the pilot plant. During the addition of iron, the proportion of chemically (iron-) bound phosphorus increased from 10 to more than 50%. The P-release rate substantially decreased with increasing amount of added iron. An addition of small amounts of iron enhanced the long-term stability of the P elimination as a whole. During the experimental period with addition of calcium, the proportion of Ca-bound phosphorus increased from 1 to 2% to almost 15%. In batch experiments a measurable Ca-phosphate precipitation took place at a pH value of at least 8.0 and a Ca-concentration of at least 100 mg/l. The increase in hardness of the influent waste water didn't produce any positive effect on the stability of the enhanced biological phosphorus removal. The metal ions Ca2+, Mg2+ and K+ serve as counter-ions in the polyhosphate chains. They were identified and quantified by X-ray spectrometry in combination with scanning transmission electron microscopy. A release of Mg2+ and K+ occured simultaneously with the degration of polyphosphates (PP). The PP bound to Ca was not redox sensitive.

An ORP screening protocol for biological phosphorus removal in sequencing batch reactors

Abstract: This research discusses two strategies for adding acetate to sequencing batch reactors operating as biological removal (Bio-P) systems. The control (fixed-time) reactor adds the acetate at a set ti...