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The Water Framework Directive (WFD) has drawn attention to a series of metals and organic compounds because of their demonstrated or potential harmfulness for aquatic environments. The aim of our work was to build and to process a "practical" database focused on the role of wastewater treatment plants for the removal of the 37 priority compounds that have to be reduced or stopped by 2015, and of 34 additional relevant contaminants. About 11,000 concentration values in raw and treated wastewater and sludge, from more than 100 peer-reviewed articles and six French national screening programs, were integrated. A systematic approach showed the global low quality of data for most of the compounds, with missing information about the treatment process, sampling and analysis, leading to 10% of the data available for removal efficiency calculations. A semi-quantitative analysis allowed the identification of 20 priority and 10 additional relevant substances more frequently quantified at significant concentrations in raw wastewater and treated wastewater. Conventional activated sludge was able to remove more than 70% of half of the studied compounds, leaving only 10% of them with less than 50% removal. Physical--chemical treatments appeared to be about 30% less efficient than biological treatments. In addition, very few data are available concerning some compounds and some processes, especially sludge treatment and tertiary wastewater treatment processes. Therefore, complementary on-site measurements and modeling are required to propose adapted solutions for the treatment of priority and emerging substances in wastewater treatment plants. [ABSTRACT FROM AUTHOR]

Thermal treatment applied in association with a biological system allows for a significant reduction in excess sludge production (~50%). In general, heat treatment is described as a sludge disintegration technique. This paper offers a thorough study on the impact of heat treatment, at temperatures below 100°C, on the solubilisation of the sludge COD and its biodegradability. Discontinuous heating experiments were performed on activated and digested sludge. At all temperatures tested the released COD for digested sludge was systematically higher than that for activated sludge (15 and 40%, respectively, at 95°C for 40 mm of contact time). For the first 30 mm, a 1st order kinetic, with respect to the residual COD, was systematically found. In the range of 40-95°C, digested sludge had a lower activation energy than activated sludge (26 kcal/mol compared to 70-160 kcal/mol). COD solubilisation is thus more positively influenced by temperature in the case of activated sludge. This may be due to the significant difference in the ratio of protein/carbohydrate in digested and activated sludge (1 -5 and 0.2-0.7, respectively). The increase in the COD/TKN ratio in the solubilised fraction after thermal treatment of activated sludge suggests a preferential solubilisation of proteins over carbohydrates. Respirometric tests performed on the solubilised COD showed that whatever the sludge origin, only 40-50% of released COD is biodegradable at a conventional hydraulic retention time (i.e. 24 h). Hence, heat treatment would act more through organic matter solubitisation rather than by a biodegradability increase. [ABSTRACT FROM AUTHOR]

Among the technologies aimed at reducing sludge production, the combination of thermal treatment at 95°C of sludge and the activated sludge process is a promising route. The feasibility of such a combined process is demonstrated (up to 60% sludge reduction) and the impacts of operating conditions on its efficiency are presented. Major emphasis was put on understanding the complex phenomena occurring within the thermal treatment: release and biodegradability of sludge organic matter, impact on the biological activity (decay, maintenance requirements, etc.). These effects were taken into account for the development of an ASM1-based model. Comparison between the modeling approach and experimental data (continuous and batch) showed that thermal treatment had three major issues partly explaining the reduction of sludge production: (i) a low release of organics; (ii) an immediate and reversible biological inactivation associated with additional maintenance energy requirements; and (iii) a potential inert production. [ABSTRACT FROM AUTHOR]

The effect of oxidative and thermo-oxidative co-treatment of excess municipal sludge was investigated. A mixture of primary and waste activated sludge was anaerobically treated using two different configurations: i) two stages and ii) a single stage with recycling. Oxidative or thermo-oxidative co-treatment placed in between the reactor or in the recycle line was studied. A two-stage configuration with no co-treatment served as a control and resulted in 50.1% overall solids removal. Compared to the control, an increase in solids removal of 10.8 and 2.7% was observed when oxidative co-treatment was placed between reactors and in the recycle line respectively. When thermo-oxidative co-treatment was placed between the two stages or in the recycle line an increase in solids removal of 25.1 and 26.9% respectively was observed. The performances of the different configurations were also evaluated with parameters such as COD, TKN, ammonia, and fecal coliform concentration. [ABSTRACT FROM AUTHOR]

The action mechanisms and performances of a combined system associating activated sludge and mechanical treatment (High Pressure Homogenizer) were evaluated for urban wastewater. Discontinuous experiments showed that the energy applied at the first pass was high enough to modify the sludge particulate fraction (high COD release) but without cell lysis. The applied shear forces led to a progressive cell break up (maximal COD release 90% total COD). Continuous experiments showed less than 20% reduction in sludge production (compared to a control run under the same loading conditions YTSS = 0.35 g TSS.g-1CODremoved) through the application of mechanical treatment (stress frequency = 0.2 d-1). Recycling of mechanical treated sludge to the aeration tank induced a slight increase in effluent TSS, but the biological performance seemed to be maintained. Significant improvements in sludge settling characteristics were observed. [ABSTRACT FROM AUTHOR]

The release performances of an organic and mineral activated sludge matrix were studied for a wide range of disintegration treatments like mechanical, thermal, thermal-chemical and oxidative disintegration techniques. The maximal COD release was 35% of total COD after 24 hours contact time at 95°C. A limiting value of 60% COD release was obtained for 500 and 700 bars after 10 passes. Concerning the oxidative disintegration techniques (O3 and H2O2), a limiting value of around 60-65% of TOC release was observed. Therefore, it was hypothesised that thermal and mechanical treatments allow mainly for breaking apart the micro-organisms while the oxidative treatment destroys the sludge flocs and disrupts the micro-organisms. A release effect of the mineral fraction is observed only oxidative disintegration techniques. [ABSTRACT FROM AUTHOR]

Presents results of physico-chemical and biological characterization of wastewater samples. Activated sludge; Biodegradability of physico-chemical fractions; Chemical oxygen demand; Coagulation; Hydrolysis; Respirometry.

Discusses how physical-chemical and biological fractionation methods were used at different parts of the Evry WWTP in order to assess the influence of effluents recycled from the primary settling tanks and sludge treatment processes on the characteristics of the wastewater. Consideration of the primary sludge gravity thickener effluent; Findings that significant variations of RBCOD across the plant were not caused by fluctuations of the physical-chemical COD fractions.

Examines the ability of enzymatic activities extracted from activated sludges to hydrolyse the organic colloidal fraction of wastewaster. Enzymatic activity of extracellular polymeric substances; Presence of glycolytic activity in the organic colloidal fraction of the wastewater; Concentration of bacteria by wastewater microfiltration.

Despite its importance, relatively little is known about the composition and fate of wastewater organic matter (OM) in treatment plants. Monitoring the chemical changes in OM during activated sludge treatment can improve our knowledge of the processes involved in the biological elimination of OM. Direct chemical analyses of treated water OM typically account for about 20% of the OM, and structural information was obtained in this study using Nuclear Magnetic Resonance (NMR) andFourier Transform Infrared (FTIR) spectroscopic techniques. Distinctchanges in the OM during wastewater biological treatment were underlined. 13C and 1H NMR showed that aromatic carbons were minor constituents of the samples. Alkyl chains exhibited a more highly branched character in treated water, as compared to long chain aliphatic carbons present in wastewater. Carboxyl signals in the13C NMR spectrum of wastewater could be due to peptide bonds in proteins, whereas in the treated water spectrum, this signal could be related to the presence of non-proteinaceous nitrogen. Besides the non-degraded compounds, treated water OM could contain recondensation products of simple molecules. Their refractory character probably derives from their complex structures rather than from particularchemical functions, as suggested by the lack of fundamental differences in the chemical structures of wastewater and treated water OM. [ABSTRACT FROM AUTHOR]

A new respirometric method for COD fractionation was applied to various wastewaters collected on French treatment plants. Great variations were observed especially in the readily biodegradable fraction (RBCOD) ranging from 1 to 16% of total COD. Variability of the results among the origin can be explained by the reactions occurring in the sewers. In one of the towns studied, the wastewater samples collected directly in the sewer show COD characteristics very different from the sewage which reaches the treatment plant. By analysing the same wastewater after aerobic and anaerobic storage, it was proved that RBCOD respectively decreased or increased significantly. Seasonal fluctuations were also quantified, showing that RBCOD fraction decreased from 75 mg/L to -15 mg/L during the summer whereas the variation of solublefraction was less important. [ABSTRACT FROM AUTHOR]

The paper presents a concise overview of respirometric experiments for the calibration of ASM1. First, the popularity of respirometry is explained by its historical impact and its sensitivity and robustness. The body of the text consists of a systematic overview of existing methods for assessment of nearly all ASM1: (i) component concentrations in sludge and waste water; and (ii) biokinetic and stoichiometric parameters. Real life examples illustrate the methods. A difference is made between direct methods that use explicit calculations and optimisation methods that require numerical optimisation algorithms. It is stressed that the latter approach is especially useful to extract multiple parameters and component concentrations from single respirometric experiments. Finally, the importance of reflecting on the translation of lab-scale respirometric results to a full-scale model is stressed. (c) 1999 IAWQ Published by Elsevier Science Ltd. [ABSTRACT FROM AUTHOR]