M.C.M. van Loosdrecht

Activated Sludge Models ASM1, ASM2, ASM2d and ASM3

This book has been produced to give a total overview of the Activated Sludge Model (ASM) family at the start of 2000 and to give the reader easy access to the different models in their original versions. It thus presents ASM1, ASM2, ASM2d and ASM3 together for the first time. Modelling of activated sludge processes has become a common part of the design and operation of wastewater treatment plants. Today models are being used in design, control, teaching and research. Contents This title belongs to Scientific and Technical Report Series ISBN: 9781900222242 (Print) ISBN: 9781780402369 (eBook)

Microbiology and biochemistry of the enhanced biological phosphate removal process

Abstract This paper reviews microbiological and biochemical aspects of the enhanced biological phosphate removal (EBPR) process. The discussion includes: microorganisms responsible for EBPR, isolation of polyphosphate accumulating organisms (PAOs), microbial diversity of the EBPR sludge, biochemical metabolisms of PAOs, energy budget in PAOs metabolism, denitrification by PAOs, glycogen accumulating non-poly-P organisms (GAOs), etc. Since pure cultures which possess complete characteristics of PAOs have not been isolated yet, the biochemical mechanism cannot be definitively described. The criteria to obtain a pure culture isolate are proposed. Based on the review, essential characteristics of PAOs are summarized in a table and directions for future research are identified.

Sewage Treatment with Anammox

Wastewater treatment including high rate anammox processes have the potential to become energy-neutral or even energy-producing. Organic matter must be removed from sewage to protect the quality of the water bodies that it is discharged to. Most current sewage treatment plants are aimed at removing organic matter only. They are energy-inefficient, whereas potentially the organic matter could be regarded as a source of energy. However, organic carbon is not the only pollutant in sewage: Fixed nitrogen such as ammonium (NH4+) and nitrate (NO3−) must be removed to avoid toxic algal blooms in the environment. Conventional wastewater treatment systems for nitrogen removal require a lot of energy to create aerobic conditions for bacterial nitrification, and also use organic carbon to help remove nitrate by bacterial denitrification (see the figure). An alternative approach is the use of anoxic ammonium-oxidizing (anammox) bacteria, which require less energy (1) but grow relatively slowly. We explore process innovations that can speed up the anammox process and use all organic matter as much as possible for energy generation.

Aerobic granular sludge in a sequencing batch reactor

In a laboratory scale sequencing batch reactor (SBR) granules were cultured under aerobic conditions. To enhance the growth of granular sludge the SBR was operated with very short sedimentation and draw phases resulting in the washout of slow settling biomass. Fast settling granules were retained in the reactor and thus had an advantage over flocs with a slower settling velocity. After 40 days of operation granules were the dominant form of microbial aggregates in the reactor, even though some pin-point flocs remained in the system. Granules taken from the reactor were stored for weeks without disintegrating. After about 130 days of operation the granule quality and COD-removal worsened. The reasons for that are yet to be investigated.

Biological wastewater treatment: Principles, modelling and design

For information on the online course in Biological Wastewater Treatment from UNESCO-IHE, visit: http://www.iwapublishing.co.uk/books/biological-wastewater-treatment-online-course-principles-modeling-and-design Over the past twenty years, the knowledge and understanding of wastewater treatment have advanced extensively and moved away from empirically-based approaches to a first principles approach embracing chemistry, microbiology, physical and bioprocess engineering, and mathematics. Many of these advances have matured to the degree that they have been codified into mathematical models for simulation with computers. For a new generation of young scientists and engineers entering the wastewater treatment profession, the quantity, complexity and diversity of these new developments can be overwhelming, particularly in developing countries where access is not readily available to advanced level tertiary education courses in wastewater treatment. Biological Wastewater Treatment addresses this deficiency. It assembles and integrates the postgraduate course material of a dozen or so professors from research groups around the world that have made significant contributions to the advances in wastewater treatment. The book forms part of an internet-based curriculum in biological wastewater treatment which also includes: * Summarized lecture handouts of the topics covered in book * Filmed lectures by the author professors * Tutorial exercises for students self-learning Upon completion of this curriculum the modern approach of modelling and simulation to wastewater treatment plant design and operation, be it activated sludge, biological nitrogen and phosphorus removal, secondary settling tanks or biofilm systems, can be embraced with deeper insight, advanced knowledge and greater confidence.

Wastewater treatment with particulate biofilm reactors

The review presented in this paper focuses on applications of particulate biofilm reactors (e.g. Upflow Sludge Blanket, Biofilm Fluidized Bed, Expanded Granular Sludge Blanket, Biofilm Airlift Suspension, Internal Circulation reactors). Several full-scale applications for municipal and industrial wastewater treatment are presented and illustrated, and their most important design and operation aspects (e.g. biofilm formation, hydrodynamics, mass transfer, mixing) are analysed and discussed. It is clear from the review that this technology can be considered a grown up technology for which good design and scale-up guidelines are available.

Phosphorus and nitrogen removal with minimal cod requirement by integration of denitrifying dephosphatation and nitrification in a two-sludge system

Abstract Denitrifying dephosphatation enables the removal of phosphorus and nitrogen with minimal use of COD, minimal oxygen consumption and minimal surplus sludge production. Moreover it would make aeration only necessary for nitrification. Therefore we have studied an anaerobic-anoxic (A2) sequencing batch reactor (SBR) coupled to a nitrification SBR. Denitrifying phosphorus removing bacteria (DPB) and nitrifiers were completely separated in two sludges in these two SBRs. The nitrified supernatant was recirculated from the nitrification SBR to the A2 SBR where nitrate was utilized by DPB as an electron acceptor for phosphorus removal. The technical feasibility for simultaneous phosphorus and nitrogen removal in the proposed two-sludge system was evaluated. The benefits of two-sludge systems over single-sludge systems were also discussed. It could be concluded that the separation of the nitrification step leads to an optimal process design for the application of denitrifying dephosphatation. The two-sludge system showed stable phosphorus and nitrogen removal, and enabled the removal of 15 mg-P/1 and 105 mg N/1 at the expense of only 400 mg-COD/1 acetic acid. Stoichiometric calculations showed that, in the two-sludge system the required COD can be up to 50% less than for conventional aerobic phosphorus and nitrogen removal systems. Moreover oxygen requirements and sludge production can be decreased in significant amounts of about 30 and 50%, respectively.

Influence of dissolved oxygen concentration on nitrite accumulation in a biofilm airlift suspension reactor

The biofilm airlift suspension (BAS) reactor can treat wastewater at a high volumetric loading rate combined with a low sludge loading. Two BAS reactors were operated, with an ammonium load of 5 kg N/(m(3) d), in order to study the influence of biomass and oxygen concentration on the nitrification process. After start-up the nitrifying biomass in the reactors gradually increased up to 30 g VSS/L. Due to this increased biomass concentration the gas-liquid mass transfer coefficient was negatively influenced. The resulting gradual decrease in dissolved oxygen concentration (over a 2-month period) was associated with a concomitantly nitrite build-up. Short term experiments showed a similar relation between dissolved oxygen concentration (DO) and nitrite accumulation. It was possible to obtain full ammonium conversion with approximately 50% nitrate and 50% nitrite in the effluent. The facts that (i) nitrite build up occurred only when DO dropped, (ii) the nitrite formation was stable over long periods, and (iii) fully depending on DO levels in short term experiments, led to the conclusion that it was not affected by microbial adaptations but associated with intrinsic characteristics of the microbial growth system. A simple biofilm model based on the often reported difference of oxygen affinity between ammonium and nitrite oxydizers was capable of adequately describing the phenomena.Measurements of biomass density and concentration are critical for the interpretation of the results, but highly sensitive to sampling procedures. Therefore we have developed an independent method, based on the residence time of Dextran Blue, to check the experimental methods. There was a good agreement between procedures.The relation between biomass concentration, oxygen mass transfer rate and nitrification in a BAS reactor is discussed. (c) 1997 John Wiley & Sons, Inc.

Stoichiometry and kinetics of poly-β-hydroxybutyrate metabolism in aerobic, slow growing, activated sludge cultures

This paper discusses the poly-beta-hydroxybutyrate (PHB) metabolism in aerobic, slow growing, activated sludge cultures, based on experimental data and on a metabolic model. The dynamic conditions which occur in activated sludge processes were simulated in a 2-L sequencing batch reactor (SBR) by subjecting a mixed microbial population to successive periods of external substrate availability (feast period) and no external substrate availability (famine period). Under these conditions intracellular storage and consumption of PHB was observed. It appeared that in the feast period, 66% to almost 100% of the substrate consumed is used for storage of PHB, the remainder is used for growth and maintenance processes. Furthermore, it appeared that at high sludge retention time (SRT) the growth rate in the feast and famine periods was the same. With decreasing SRT the growth rate in the feast period increased relative to the growth rate in the famine period. Acetate consumption and PHB production in the feast period both proceeded with a zero-order rate in acetate and PHB concentration respectively. PHB consumption in the famine period could best be described kinetically with a nth-order degradation equation in PHB concentration. The obtained results are discussed in the context of the general activated sludge models.

Hydrophobic and electrostatic parameters in bacterial adhesion

Recently it has been shown that the initial stages of bacterial adhesion to a model-surface of sulphated polystyrene can best be described using hydrophobic and electrostatic parameters. In the present study it is tested whether these parameters can generally be applied to predict bacterial adhesion by using (i) glass, as a model for hydrophilic and natural surfaces of silicates and oxides, (ii) polystyrene coated with proteins, as a model for a surface coated with an organic layer, and (iii) river Rhine sediment, as an example of a natural surface. Adhesion to glass was dominated by electrostatic interaction, whereas adhesion to polystyrene coated with various types of proteins depended on the surface characteristics of the bacteria and the type of protein. By relating Van der Waals interactions to hydrophobicity of the interacting species, the adhesion of bacteria to the various surfaces including the river Rhine sediments could be interpreted in terms of the DLVO-theory. It is therefore concluded that the conceptual principles of the DLVO-theory (interplay of Van der Waals and electrostatic interactions) are suitable to describe, at least qualitatively, the initial processes of bacterial adhesion to a wide range of surfaces.