1,721,004 research outputs found
Filamentous activated sludge bulking, Environmental Waste Management : a European Perspective
No full textBiodegradable polymers from wastes by using activated sludges enriched by aerobic periodic feeding
No full textDesign and Integrated management of WWTP’S with low energy consumption and cost reduction of waste disposal.
No full textThe design and operation of the wastewater treatment plant is usually based on the conceptual separation between the wastewater and the sludge streams of the plant. It is important to consider both these aspects of the water purification process in order to achieve the maximum environmental benefits complying with the effluent standards using simple technologies with low energy consumption. Moreover the integration between water and sludge treatment streams could be used to reduce the energy demand of the whole treatment plant as long as the sludge is a potential energy source.
The aims of the design and integrated operation with low energy consumption and cost reduction of waste disposal are: to minimize the energy demand of the biological oxidation phase; to maximize the biogas production during the anaerobic stabilization of primary and secondary sludge; to obtain a secondary sludge rich of nutrients, without pathogens and organic micropollutants and with high biological stabilization level in order to use it in agriculture; to obtain the nutrient recovery from liquid side-streams.
These objectives can be achieved with a number of improvements on the wastewater treatment plant scheme, such as:
1) Optimization of the COD removal and of the primary sludge production in the primary assisted sedimentation.
Inorganic coagulants and/or polyelectrolytes were used in the primary treatment to increase the COD removal efficiency up to 60% and the suspended solids up to 80%. Alternatively lime was used because the coagulant dosage control can be made with a simple pH measure, because the flocs have high settlement velocity and this allows decreasing the settler area and the sludge obtained is more dewatered. The major problem of using lime was the excessive sludge production from the precipitation of the calcium carbonate. The optimization of the exercise conditions was carried out minimizing the lime dosage in the primary treatment and the sludge production operating with pH < 10.
2) Biological treatments.
The attached biomass processes can be considered a valid alternative to the traditional activated sludge treatments: they have the benefit of the high removal efficiency of the suspended solids in the primary assisted settler. A biological aerated filter (BAF) was used in order to obtain a highly polished effluent in terms of removal of organic matter, suspended solids and ammonia. Moreover the influence of temperature, pH and nitrite accumulation on the nitrification process were analyzed.
Other important improvements are: differentiated treatment for primary and secondary sludge and mechanical or thermal pre-treatment of secondary sludge before the anaerobic stabilization.
Since the last two objectives require further research, in this paper we will discuss only the first two topics
Comment on “Microbiology and biochemistry of the enhanced biological phosphate removal process. Review Paper” by T.Mino, M.C.M. Van Loosdrecht and J.J.Heijnen
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Bulking control methods in Activated sludge separation problems: theory, control measures, practical experience
No full textComparison of carbon storage under aerobic and anoxic conditions
No full textIn various activated sludge systems, the biomass grows under transient (unbalanced) conditions and the storage response (formation of internal polymers as the fastest adaptation to the changing environment) becomes important. Till now the role of storage on population dynamics has been deeply investigated under anaerobic (EBPR processes) or aerobic (bulking control) conditions. Little attention has been given to processes including anoxic conditions even though in many of them storage phenomena are likely to occur (anoxic selectors, nitrogen removal processes with addition of an external source of readily biodegradable COD or with aerobic contact/anoxic stabilization). For these reasons, the aim of the present work was to investigate storage and succeeding use of stored products under anoxic and mixed (anoxic/aerobic) conditions. Batch experiments have shown that a mixed culture selected under aerobic conditions and intermittent feed (acetate-limited medium), was also able to take up acetate (90-100 mgCOD/gCOD h) and store it as PHB (35-40 mgCOD/gCOD h) under anoxic conditions. After acetate depletion, the stored PHB was used for growth and maintenance. The NUR on acetate in the presence of storage was 20 mgN/gVSS h (which corresponded to a COD removal of 6.9 mgCOD/mgN) while it dropped to 10-3 mgN/gVSS h in the "endogenous phase" when denitrification was on the stored PHB. The presence of aerobic conditions instead of anoxic ones had a major positive effect on the rate and yield of PHB storage while it had only a minor effect on the rate of PHB consumption. The latter observation can be explained by assuming that the hydrolysis of the stored product is the rate limiting step of the "endogenous" metabolism and that the hydrolysis rate is not highly dependent on aerobic-anoxic conditions. Cross-comparison of PHB storage and consumption under aerobic/anoxic conditions made it possible to determine that, in the particular mixed culture under investigation, all aerobic heterotrophs able to store were also able to denitrify. (C) 1998 Published by Elsevier Science Ltd. All rights reserved
Effect of culture residence time on substrate uptake and storage by a pure culture of Thiotrix (CT3 strain)under continuous or batch feeding
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Dynamics of Phosphorus and Organic Substrates in Anaerobic and Aerobic Phases of a Sequencing Batch Reactor
No full textThis paper describes a lab-scale experimentation carried out to study enhanced biological phosphate removal (EBPR) in a sequencing batch reactor (SBR). The synthetic feed used was based on peptone and glucose as organic substrate to simulate the readily biodegradable fraction of a municipal wastewater (Wentzel et al., 1991). The experimental work was divided into two runs, each characterized by different operating conditions. The phosphorus removal efficiency was considerably higher in the absence of competition for organic substrate between P-accumulating and denitrifying bacteria. The activated sludge consisted mainly of peculiar microorganisms recently described by Cech and Hartman (1990) and called “G bacteria”. The results obtained seem to be inconsistent with the general assumption that the G bacteria are characterized by anaerobic substrate uptake not connected with any polyphosphate metabolism. Supplementary anaerobic batch tests utilizing glucose, peptone and acetate as organic substrates show that the role of acetate in the biochemical mechanisms promoting EBPR may not be so essential as it has been assumed till now.</jats:p
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