Viscous and filamentous bulking in activated sludge: Rheological and hydrodynamic modelling based on experimental data.

Although achieving good activated sludge settleability is a key requirement for meeting effluent quality criteria, wastewater treatment plants often face undesired floc structure changes. Filamentous bulking has widely been studied, however, viscous sludge formation much less investigated so far. Our main goal was to find relationship between sludge floc structure and related rheological properties, moreover, to estimate pressure loss in pipe networks through hydrodynamic modelling of the non-Newtonian flows in case of well settling (ideal-like), viscous and filamentous sludge. Severe viscous and filamentous kinds of bulking were generated separately in continuous-flow lab-scale systems initially seeded with the same reference (ideal-like) biomass and the entire evolution of viscous and filamentous bulking was monitored. The results suggested correlation between the rheological properties and the floc structure transformations, and showed the most appropriate fit for the Herschel-Bulkley model (vs. Power-law and Bingham). Validated computational fluid dynamics studies estimated the pipe pressure loss in a wide Reynolds number range for the initial well settling (reference) and the final viscous and filamentous sludge as well. A practical standard modelling protocol was developed for improving energy efficiency of sludge pumping in different floc structure scenarios.

How the nature of the compounds present in solid and liquid compartments of activated sludge impact its rheological characteristics.

Although the role of the solids concentration on the rheological characteristics of sludge is greatly documented in the literature, few studies focused on the impact of the nature of these solids. How the nature of solutes can modify the solid-liquid interactions and thus the rheological properties of the sludge are also slightly explored. Thus, the objective of this study is to investigate the rheological characteristics of activated sludge in relation with the nature of the compounds present in the solid and liquid phases. Rheological measurements were carried out on raw sludge and on sludge modified by mechanical actions and/or addition of solids or solutes. The rheological properties of raw and modified sludges were measured according to flow and dynamic measurements. Results demonstrated that if suspended solid concentration affected sludge rheological parameters, the nature of the solids was quite of importance. The key role of nature and molecular weight of solutes was also highlighted. The results contribute to a better knowledge of the relationship between sludge composition and its rheological properties, which is useful for the optimization of sludge mixing, pumping or aeration and also for the improvement of sludge dewatering, notably by a relevant choice of adjuvant.

Lab-scale experimental strategy for determining micropollutant partition coefficient and biodegradation constants in activated sludge.

The nitrifying/denitrifying activated sludge process removes several micropollutants from wastewater by sorption onto sludge and/or biodegradation. The objective of this paper is to propose and evaluate a lab-scale experimental strategy for the determination of partition coefficient and biodegradation constant for micropollutant with an objective of modelling their removal. Four pharmaceutical compounds (ibuprofen, atenolol, diclofenac and fluoxetine) covering a wide hydrophobicity range (log Kow from 0.16 to 4.51) were chosen. Dissolved and particulate concentrations were monitored for 4 days, inside two reactors working under aerobic and anoxic conditions, and under different substrate feed conditions (biodegradable carbon and nitrogen). We determined the mechanisms responsible for the removal of the target compounds: (i) ibuprofen was biodegraded, mainly under aerobic conditions by cometabolism with biodegradable carbon, whereas anoxic conditions suppressed biodegradation; (ii) atenolol was biodegraded under both aerobic and anoxic conditions (with a higher biodegradation rate under aerobic conditions), and cometabolism with biodegradable carbon was the main mechanism; (iii) diclofenac and fluoxetine were removed by sorption only. Finally, the abilities of our strategy were evaluated by testing the suitability of the parameters for simulating effluent concentrations and removal efficiency at a full-scale plant.

Removal of xenobiotics from effluent discharge by adsorption on zeolite and expanded clay: an alternative to activated carbon?

Xenobiotics such as pesticides and pharmaceuticals are an increasingly large problem in aquatic environments. A fixed-bed adsorption filter, used as tertiary stage of sewage treatment, could be a solution to decrease xenobiotics concentrations in wastewater treatment plants (WWTPs) effluent. The adsorption efficiency of two mineral adsorbent materials (expanded clay (EC) and zeolite (ZE)), both seen as a possible alternative to activated carbon (AC), was evaluated in batch tests. Experiments involving secondary treated domestic wastewater spiked with a cocktail of ten xenobiotics (eight pharmaceuticals and two pesticides) known to be poorly eliminated in conventional biological process were carried out. Removal efficiencies and partitions coefficients were calculated for two levels of initial xenobiotic concentration, i.e, concentrations lower to 10 µg/L and concentrations ranged from 100 to 1,000 µg/L. While AC was the most efficient adsorbent material, both alternative adsorbent materials showed good adsorption efficiencies for all ten xenobiotics (from 50 to 100 % depending on the xenobiotic/adsorbent material pair). For all the targeted xenobiotics, at lower concentrations, EC presented the best adsorption potential with higher partition coefficients, confirming the results in terms of removal efficiencies. Nevertheless, Zeolite presents virtually the same adsorption potential for both high and low xenobiotics concentrations to be treated. According to this first batch investigation, ZE and EC could be used as alternative absorbent materials to AC in WWTP.

Modelling of micropollutant removal in biological wastewater treatments: a review.

Modelling the fate of micropollutants through wastewater treatment plants is of present concern. Indeed, such a tool is useful to increase the removal of micropollutants and reduce their release to the environment. In this paper, 18 literature models describing micropollutant removal in activated sludge processes were reviewed. Investigated micropollutants were mainly volatile organic compounds, metals, surfactants, pesticides and pharmaceutical compounds. This work provides a detailed insight about the main mechanisms leading to the micropollutant removal (volatilisation, sorption, biodegradation, cometabolism), the associated mathematical equations and the parameter values found in the literature. A critical analysis was carried out to evaluate the conditions and the domain of validity for which each model was set-up. We also propose (i) an inventory of the experimental methodologies applied to determine the values of model parameters, (ii) a critical study of the main differences between models and (iii) suggestions for a standardisation of calibration methodologies. Finally, this review highlights the lack of explanation concerning the domain of validity of the models and proposes future developments to improve modelling of micropollutant removal in wastewater treatment plants.

Sludge drying reed beds for septage treatment: towards design and operation recommendations.

This paper focuses on the feasibility of septage treatment by sludge drying reed beds (SDRB). Different designs and operation conditions of SRDB pilot-scales were tested on system efficiencies such as the top filtration layer (sand or compost) and the organic load (30 and 50 kg SSm(-2)y(-1)). Results focus on the obtained performances considering sludge characteristics, filtration efficiencies, percolate qualities, and sludge deposit properties. Although results show better filtration efficiency for activated sludge (e.g. SS removal around 98.4%) than for septage (e.g. SS removal around 87.5%), the feasibility of septage treatment with SDRB has been demonstrated with, at 50 kg SSm(-2)y(-1) sludge accumulation, and dry matter about 7.9 cm y(-1) and 70% (summer period), respectively. Further design and operation condition recommendations for SDRB treating septage are proposed.

Biomass adaptation to complex substrate degradation in membrane bioreactors: appropriated operating conditions.

The aim of this work is to analyse the biological performances of two immersed membranes bioreactors focusing on the biomass adaptation to complex substrate degradation and the performance in term of permeate quality. Two influents were selected: a synthetic complex influent (acetate/Viandox, MBR1) and a real seafood processing wastewater (surimi product, MBR2). The MBR systems were operated for long periods without any sludge extraction except for sampling. Organic matter removal, sludge production and quality of the treated wastewater were analysed and studied. COD removal efficiencies after a period of biomass adaptation were higher than 97% and 95% for the synthetic and real wastewater respectively. In both cases, the COD of the treated wastewater was lower than 50 mg.L(-1). In spite of salt concentration in the real wastewater a biomass adaptation process occurs. In the overall operational period, a 0.058 gCOD P.gCOD T(-1) and a 0.12 gCOD P.gCOD T(-1) observed sludge yields were obtained for the MBR1 and MBR2 respectively. These values are approximately 5 to 10 times lower than those measured in conventional activated sludge process. These results showed that the presence of particular and some of non-easily degradable compounds in the influent of MBR2 didn't limit the performance of MBR in term of COD removal achieved. The results have also confirmed the excellent permeate quality for water reuse from MBRs systems.

Continuous and sequencing membrane bioreactors applied to food industry effluent treatment.

This work focuses on the performances of two immersed membrane bioreactors used for the treatment of easily biodegradable organic matter present in food industry effluents, for the purpose of water reuse. Two reactor functioning modes (continuous and sequencing) were compared in terms of organic carbon removal and of membrane permeability. For each working mode, pollutant removal was very high, treated water quality presented a low COD concentration (< 125 mg x L(-1)), no solids in suspension and low turbidity (< 0.5 NTU). The quality of the treated water (including germ removal) enabled its reuse on site. Moreover, by developing high biomass concentrations in the reactor, excess sludge production remained very low (< 0.1 gVSS x gCOD(-1)). The performances appeared slightly better for the continuous system (lower COD concentration in the effluent, < 50 mg x L(-1), and lower sludge production). In terms of filtration, a distinct difference was observed between continuous and sequencing systems; transmembrane pressure showed a small and constant evolution rate in continuous membrane bioreactor (CMBR) although it appeared more difficult to control in sequencing membrane bioreactor (SMBR) probably due to punctually higher permeate flow rate and modified suspension properties. The rapid evolution of membrane permeability observed in SMBR was such that more frequent chemical cleaning of the membrane system was required.

Effects of starvation conditions on biomass behaviour for minimization of sludge production in membrane bioreactors.

The behaviour of an activated sludge system in starvation conditions was examined in batch according to substrate impulses defined by different S0/X0 ratio. The answer was characterised by an exogenous phase followed by a starvation one. If at high S0/X0 ratio, bacterial cell multiplication was the main synthesis process during exogenous phase, at low S0/X0 ratio the observed phenomenon was compound storage. In starvation conditions, for the lowest S0/X0 ratio, a rapid decrease in the MLVSS without soluble proteins production was observed. No bacterial lysis occurred and this phenomenon was due to consumption of the storage compounds with a decrease rate equal to 0.74d(-1). For high S0/X0 ratio, as soon as the exogenous phase was completed, a decrease of the MLVSS simultaneously to a soluble protein production was observed. An immediate bacterial lysis occurred with a decay rate equal to 0.53 d(-1). Because MBR systems work generally in low F/M conditions, the activity of the present microbial population is close to the one observed in starvation phase. This work points out that these conditions do not allow net bacterial growth and cells just use lysis products to satisfy their maintenance requirements. These assumptions confirm the feasibility of a decrease of the net biomass production in a MBR when high sludge retention time is operated.

Effect of calcium replacement on the hemodynamic changes associated with high dose interleukin-2 therapy.

Administration of high-dose IL-2 results in hemodynamic changes that are similar to those seen in septic shock. These include a decrease in systemic vascular resistance (SVR) with a resultant drop in mean arterial pressure (MAP). Hypocalcemia is seen in septic shock and with IL-2 administration. Calcium replacement in septic shock has been reported to result in hemodynamic improvement; we therefore administered calcium to patients receiving high dose IL-2 to correct ionized hypocalcemia. Five consecutive patients underwent invasive hemodynamic monitoring before and during IL-2 administration. Calcium chloride was administered to correct ionized hypocalcemia, and hemodynamic parameters were monitored before and after calcium administration. Ionized hypocalcemia was associated with an elevation in parathyroid hormone levels. There was no toxicity related to the administration of calcium. An improvement in the MAP and SVR was seen early and late (after a dose of IL-2 was held) in the IL-2 treatment cycle; there were minimal effects at other points. Because of the potential hemodynamic benefit of calcium replacement, we recommend that ionized hypocalcemia be corrected in patients receiving high-dose IL-2.

Body weight and coronary disease risk: patterns of risk factor change associated with long-term weight change. The Normative Aging Study.

Previous studies have suggested that excess body weight increases coronary disease risk by modification of the levels of other risk factors and in addition may contribute to overall risk independently. Few studies, however, have systematically characterized long-term change in risk factors with specific changes in overall weight while they have controlled for the effects of multiple potential confounders. Also, very little information is available on the differential impact of weight change on risk factor changes with advancing age. The present investigation used 15 years of longitudinal data collected on 1,396 men participating in the Veterans Administration Normative Aging Study in Boston, Massachusetts. Multiple regression analysis was used to predict change in each of eight putative coronary disease risk factors from change in weight and the interaction between weight change and age. These included blood pressure, serum cholesterol, triglycerides, fasting and two-hour postprandial blood glucose, uric acid, and forced vital capacity of the lungs. After controlling for initial levels of the risk factor, weight, age, and smoking status, change in weight remained a significant predictor of long-term change in each of the risk factors studied. In addition, the interaction between weight change and age was significant for fasting glucose, uric acid, and forced vital capacity, indicating that the effect of weight gain on uric acid and forced vital capacity was greater in younger men whereas the effect of weight gain on fasting glucose was greater in older men.

Relationship of fat distribution to glucose tolerance. Results of computed tomography in male participants of the Normative Aging Study.

Computed tomography (CT) scanning was used to assess the relationship of glucose tolerance to fat distribution in men. Three cross sections [chest (including upper arms), abdomen, and thigh] were scanned in 41 men randomly selected from the Normative Aging Study, a longitudinal study of aging. Greater amounts of fat in the upper body and greater ratios of upper-body fat to lower-body fat were significantly correlated with higher 2-h serum glucose levels after adjustment for age and body mass index. In particular, intra-abdominal fat, a feature uniquely measured by CT, was a significant correlate of 2-h glucose. Largely parallel results were obtained when we compared a sample of male diabetic subjects (N = 8) with the male normal subjects from our random sample. This investigation demonstrates that body fat distribution, adjusted for overall degree of obesity, is a significant correlate of glucose tolerance even in a sample unselected for extremes of physique.

The efficacy of response prevention on avoidance behavior in young and adult rats with prefrontal cortical injury.

Five days prior to one-way active avoidance training, 36 rats of 18-20 days of age and 36 rats of 110-130 days received dorsomedial, ventrolateral or sham lesions. During acquisition, the CS consisting of the raising of a guillotine door was followed 5 sec later by footshock US onset unless a response was emitted. After acquisition, subjects of each surgical condition were given 1 of 3 extinction treatments. Twelve pups and 12 adults received 5 response prevention trials, in which a second door blocked responses upon CS onset. The same number of subjects was given a delay prior to extinction, and the remaining subjects began extinction immediately following acquisition. Both lesion conditions interfered with adult acquisition, but produced superior acquisition in the lesioned pups, as measured by trials to criterion and trial speeds. In extinction, response prevention seriously disrupted the sham adults, as did the delay condition to a lesser extent. Resistance to extinction decreased to an equivalent extent after both response prevention and delay in the sham pups. An overall disruption in extinction was found in the adult lesioned groups, although there was some evidence of response prevention and delay equivalency in the medial adults. The lesioned pups showed a dramatic persistence responding. A test of passive avoidance to the previous shock compartment was administered 24 h later. Both response prevention and delay treatments in the adults produced residual fear, which was not found in the pups. Rather, all pups behaved with characteristic response inhibitory deficits. The results were considered in light of the prefrontal mediation of response inhibitory centers during ontogeny.