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PubMedDate not supplied

Characterization of selenate removal from drainage water using rice straw.

Removal of selenium (Se) from agricultural drainage water is very important for protecting wildlife in wetland systems. We conducted a series of experiments on selenite [Se(IV)] adsorption and selenate [Se(VI)] reduction to determine Se removal from drainage water amended with 1000 microg/L of Se(VI) or Se(IV) and 5 g of rice (Oryza sativa L.) straw. Under sterile conditions, the added Se(IV) was not adsorbed to the rice straw within 2 d of the experiment and the added Se(VI) was not reduced within 14 d. In contrast, added Se(VI) in a nonsterile rice-straw solution was reduced rapidly, from 930 microg/L at Day 3 to 20 microg/L at Day 5, with an increase in unprecipitated elemental Se [Se(0)] and total Se(0). In the last several days of the experiments, unprecipitated Se(0) was the major Se form in the rice-straw solution, with a small amount of organic Se(-II). This study showed that Se removal from drainage water in the presence of rice straw involves a two-step process. The first is the microbial reduction of Se(VI) to Se(IV) and then to colloidal Se(0). The second is flocculation and precipitation of colloidal Se(0) to the bottom of the experimental flasks and the surface of rice straw.

Adsorption↗

PubMed2005

Disturbance of water-extractable phosphorus determination by colloidal particles in a heavy clay soil from the Netherlands.

Water extraction methods are widely used to extract phosphorus (P) from soils for both agronomic and environmental purposes. Both the presence of soil colloids in soil water filtrates, and the contribution of colloidal P to the molybdate-reactive phosphorus (MRP) concentration measured in these filtrates, are well documented. However, relatively little attention has been given to the direct disturbance by colloids of MRP measurement. The objective of this paper is to show this influence found for water extracts with a soil to solution ratio of 1:60 (v/v) (P(w)), obtained from a heavy clay soil in the Netherlands. Colloidal particles, which passed a 0.45-mum filter, caused a large overestimation of MRP. The low ionic strength of the P(w) filtrates (on average 0.64 mmol(c) L(-1)) probably caused soil dispersion and increased detachment of colloids from soil during extraction. After NaCl addition, followed by 0.45-mum filtration, MRP was on average 93% lower. This can be ascribed to flocculation of colloids and removal by filtration. A low ionic strength can thus lead to the direct disturbance by colloidal particles of MRP measurement in waters from soils sensitive to release of colloids.

Aluminum Silicates↗

PubMed2006

Effects of velocity gradient and mixing time on particle growth in a rapid mixing tank.

Effects of velocity gradient (G value) and mixing time (t) on the coagulation of particles were investigated by monitoring particle counts in a rapid mixing process. Total particle counts after mixing of 30 s at G value of 200 s(-1) were similar to the summation of clay particles and alum precipitates at alum dose of 30 mg L(-1). Although small particles (microflocs less than 5 microm) were formed within the mixing time of 30 s, macroflocs larger than 8 microm did not increase significantly until the mixing time of 60 s. However, macroflocs larger than 8 microm started to increase after mixing of 75 s and they reached the maximum counts at 150 s. On the other hand, macroflocs larger than 8 microm decreased after mixing time of 180 s due in breaks of the macroflocs, which resulted in resuspension of small particles. The rapid mixing conditions for the maximum growth of macroflocs were the G value of 200 s(-1) and the mixing time of 150 s, which confirmed the best performance of turbidity removal in jar tests. Growth and break of particles and flocs in a rapid mixing step would influence significantly on the sequential flocculation and sedimentation processes for turbidity removal.

Alum Compounds↗

PubMed2006

Floc size distribution in a stirred suspension.

This paper focuses on the distribution of alumino-humic flocs found in a stirred suspension. Distributions were scaled using the transformation u = d/dL in which d is floc diameter and dL its arithmetic mean value and fitted by a gamma distribution. Flocs were treated as monofractal with solids mass concentration specified by C = A'rhos (d/do)D-3 in which A' is a packing coefficient, rhos the density of the floc solids, D the fractal dimension and do a reference size. It was shown that the overall solids concentration (M) complies with the dependence M proportional to NA'dDL-S(D) in which N is the number of flocs per unit volume and S(D) a distribution moment. Initial estimates of A' and D were obtained from analysis of floc sedimentation behaviour. From knowledge of the base parameters, the calculated value of M did not match the measured M and varied with shear. This was attributed to a kinematic influence on C over and beyond changes associated with the response of dL to shear. Issues of self-similarity were examined and it was concluded that distributions did not display strict self-similarity. Data are provided on the size distribution found in the flocculators of a treatment works at full scale.

Data Interpretation, Statistical↗

PubMed2006

Effects of surface charge, micro-bubble size and particle size on removal efficiency of electro-flotation.

Flotation is a water treatment alternative to sedimentation, and uses small bubbles to remove low-density particles from potable water and wastewater. The effect of zeta potential, bubble size and particle size on removal efficiency of the electro-flotation process was investigated because previous model-simulations indicated that these attributes are critical for high collision efficiency between micro-bubbles and particles. Solutions containing Al3+ as the metal ion were subjected to various conditions. The zeta potentials of bubbles and particles were similar under identical conditions, and their charges were influenced by metal ion concentration and pH. Maximum removal efficiency was 98 and 12% in the presence and absence of flocculation, respectively. Removal efficiency was higher when particle size was similar to bubble size. These results agree with modelling simulations and indicate that collision efficiency is greater when the zeta potential of one is negative and that of the other is positive and when their sizes are similar.

Aluminum Chloride↗

PubMed2006

Intermittent vs continuous operation of upflow anaerobic sludge bed reactors for dairy wastewater and related microbial changes.

This work compares continuous vs intermittent UASB reactors inoculated with flocculent sludge for the treatment of dairy effluents. The effects of effluent recirculation on the performance of intermittent reactors were assessed as well as the differences in specific methanogenic activity (SMA) with different substrates for the biomass from continuous and intermittent UASB reactors. Compared to the continuous operation the intermittent operation resulted in higher methanization of the removed COD (64-78% and 65-88%, respectively) whilst the effluent recirculation presented beneficial effects when applied during the stabilization period and was clearly detrimental when applied during the feed period of the intermittent operation. The SMA tests showed that the intermittent operation causes a shift in the microbial populations towards a better adaptation for the degradation of complex substrates confirmed by the meaningfull contribution of methane production through a pathway other than acetoclastic methanogenesis observed in the biomass taken from intermittent UASB reactors.

Anaerobiosis↗

PubMed2006

Evaluation of conditioning responses of thermophilic-mesophilic anaerobically and mesophilic aerobically digested biosolids using rheological properties.

One of the most crucial processes in biosolids management is stabilisation, which is typically accomplished using either anaerobic or aerobic digestion processes. Although there are many advantages to both of these methods--such as reduction of volatile organic matter, pathogen content, and offensive odours--one common disadvantage is that digested biosolids exhibit poor dewaterability characteristics. The deterioration in dewaterability of digested biosolids leads to increases in polymer requirements, connoting higher conditioning costs. Many studies have examined this phenomenon based on conventional filterability tests such as capillary suction time and specific resistance to filtration. However, these test methods are limited in their ability to predict full-scale dewatering behaviour (particularly in centrifugation), and do not regard handling properties as being important for sludge transport. For this purpose, new rheometric methods may assist in predicting sludge behaviour, potentially allowing optimisation of stabilisation and conditioning processes relative to the desired sludge properties. This paper investigates the possible utility of these methods. Classical methods for characterising biosolids, such as filtration tests, are compared with yield stress values and other rheological properties as determined using the steady-shear rate sweep test. The rheological behaviours are compared for different sludge types, including raw and polymer conditioned thermophilic anaerobically, mesophilic anaerobically, and mesophilic aerobically digested biosolids. The paper demonstrates the determination of specific energy values associated with breakdown of the flocculated matrix. Robust modelling approaches are employed to optimise the conditioning of the digested samples, and to shed light on commonly used rheological models such as Bingham, Herschel-Bulkley, and Ostwald equations.

Aerobiosis↗

PubMed2006

A different approach for predicting reaeration rates in gravity sewers and completely mixed tanks.

A new semiempirical approach is presented for predicting air-to-water oxygen transfer rates in mixed tanks and gravity sewers, using methods adopted from mixing theory. First, a flocculation unit was used to impart selected mean velocity gradients (G) into a completely mixed tank, from which oxygen was first removed, and dissolved oxygen concentrations were measured with time. Regression analysis was used to fit the rate of oxygen transfer equation against G. The reaeration rate in completely mixed reactors was found to be proportional to G2 (R2 = 0.987). Subsequently, G was linked to headloss in sewers, and the equation was calibrated using a slope-adjustable, 27-m-long, gravity-flow, experimental sewer (internal diameter, D = 0.16 m). Here, the reaeration rate was proportional to G1 (R2 = 0.981). The equation was compared with existing oxygen transfer models and validated against experimental data from the literature, to which the overall mass transfer coefficient for oxygen, K(L)a, derived by the new approach, conformed well.

Flocculation Tests↗

PubMed1998

Preliminary evaluation of shilajit as a suspending agent in antacid suspensions.

The efficacy of shilajit, a gummy exudate of the plant Styrax officinalis Linn (Family: Styraceae), was evaluated as a suspending agent for the formulation of antacid preparations. Shilajit produced effects on sedimentation volume similar to those produced by sodium carboxymethyl cellulose (CMC), but at lower concentrations. It induced better flocculation with a moderate increase in viscosity compared to CMC. It did not interfere with the acid-consuming capacity of the suspensions.

Aluminum Hydroxide↗

PubMed1978

Evaluation of serodiagnostic tests for visceral larva migrans.

Four serologic techniques for the diagnosis of visceral larva migrans caused by Toxocara canis, namely indirect hemagglutination (IHA), bentonite flocculation (BF), enzyme-linked immunosorbent assay (ELISA), and double diffusion in agar (Ouchterlony), were evaluated using sera sent to the Center for Disease Control from patients with a presumptive diagnosis of visceral larva migrans (VLM). Patients having 5-6 of the clinical or laboratory criteria for VLM were designated as cases while those with 0-2 criteria served as controls. The sensitivity of the ELISA was 78.3% compared to 18.2%, 25.8% and 65.2% for the IHA, BF, and Ouchterlony, respectively; the sepcificity of all four tests was greater than 92%. The predivtive value of positive test was greater than 85% for all tests except the IHA, while the predictive value of a negative test was greater than 85% only for the ELISA. The results of a ELISA were reproducible in different laboratories. Based on these findings, the ELISA using a larval antigen appears to be the serodiagnostic method of choice for VLM.

Adolescent↗

PubMed2001

Enhancement of nitrifying biofilm formation using selected EPS produced by heterotrophic bacteria.

The possibility of enhancing nitrifying biofilm formation rate with the aid of selected EPS produced by heterotrophic bacteria was investigated. When EPS production characteristics were examined for four kinds of heterotrophs isolated from a domestic wastewater treatment reactor, two strains obtained from biofilms (B1, B2) exhibited a higher polysaccharide production rate than those from suspended flocs (A1, A2). Among EPS components, the concentration of uronic acids gave a good correlation with flocculation ability, which suggests that acidic polysaccharides play a major role in bioaggregate formation. Addition of 1 g/L D-glucuronic acid as an EPS substitute enhanced the homocoagulation rate of autotrophic Nitrosomonas europaea and altered its zeta potential from ñ30.4 mV to +4.3 mV, which indicates a possibility that particular EPS components produced by heterotrophs are utilized as neutralising reagents for nitrifying biofilm formation. Moreover, when heterotrophic isolates with Nitrobacter winogradskyi were cultured in batch with fabric supports, biofilm formed on the substratum. These experimental results suggest the application of selected EPS for enhancing nitrifying biofilm formation.

Bacteria↗

PubMed2001

[Characterization of speciation distribution of IPF-PFSi].

The preparation and speciation distribution characteristic of a new kind of inorganic polymer flocculant(IPF)-PFSi were investigated in detail by the combination of direct and indirect speciation analysis methods. The experimental results show that the speciation distribution of PFSi is decided significantly with basicity, kinds of silica and Si/Fe ratio. Among them, the basicity is one of the main factors. SilicaA and silicaB exhibit a similar effect, while silicaC has limited effect on the hydrolysis of Fe(III). The typical speciation distribution and transformation property of PFCl changes limitedly with the introduction of silica species.

Chlorides↗

PubMed2001

Modelling of floc-bubble aggregate rise rates in dissolved air flotation.

The use of relatively simple, but conceptually sound mathematical models, is a powerful tool to identify and understand parameters that are critical to a process. In this paper, a model is presented which addresses the rise rate of floc-bubble aggregates in the DAF separation zone. The model uses Stoke's Law as a point of departure, which is then progressively extended to incorporate the non-sphericity of the aggregates, the non-laminar nature of their movement, the fractal nature of the flocs, the physical constraints of attaching bubbles to a floc, and the limit on bubble numbers imposed by a typical air dosing system. The main findings are: There are two distinctly different DAF domains, namely a small floc domain and a large floc domain. In the small floc domain, the bubble size, the air volume, chemical dosing and the degree of flocculation have to be optimized and accurately controlled, while the large floc domain is less sensitive to these parameters. The calculated rise rates are significantly lower than some of the latest pilot testing results reported from the USA; a surprising finding at first. There are, however, numerous modelling simplifications that may explain this discrepancy. The most probable reasons are the further agglomeration of the aggregates in the separation zone due to differential rise rates or the recirculating flow within the white-water blanket, and the complex and poorly understood flow patterns within the separation zone.

Air↗

PubMed2001

Using lessons learned and advanced methods to design a 1,500 Ml/day DAF water treatment plant.

The paper describes the method that led to the design of the 1,500 Ml/day dissolved air flotation (DAF) water treatment plant for Boston's water supply. In particular, the topics of flocculation techniques, floated solids removal and DAF recycle as they relate to very large capacity plant design are covered in detail. The use of mathematical models, including computational fluid dynamics (CFD) software, to refine the design is described.

Air↗

PubMed2001

Control measures for wastewater treatment plants during storm flow.

In the context of the development of treatment plant control techniques, three measures for maintaining a high efficiency of treatment plants during rainfall events were tested. The three measures are increasing the nitrification volume by operating a facultative aeration, bypassing the primary sedimentation and adding flocculants before secondary sedimentation. Ammonia concentrations and ammonia loads were used in combination with rainfall forecasts as the criteria for putting the measures into operation. A simulation based on the Activated Sludge Model No. 1 and a pilot scale plant were used for testing the measures. The results show that all three measures may be suitable to cope with peak loads of treatment plants during rainfall events.

Air↗

PubMed2001

What to do after nutrient removal?

In the Netherlands, interest in advanced treatment is increasing now that almost all wastewater treatment plants apply full biological treatment and nutrient removal. The resulting effluents have an excellent quality which can be improved further by applying advanced treatment processes like flocculating filtration, membrane filtration, UV or activated carbon, and others. The treated effluent can be re-used for various purposes, as process water, household water, urban water, for groundwater suppletion and drinking water. Nowadays many applications are investigated. In order to confirm the applicability pilot test investigations are done at various WWTPs. The results are promising; the cost estimations show increasing prospects. This will finally lead to the maturity of the advanced treatment. It will certainly contribute to a more sustainable water cycle.

Cities↗

PubMed2001

Municipal wastewater sludge dewaterability and the presence of microbial extracellular polymer.

Dewatering of sewage sludge is an essential and costly part of the wastewater treatment process. The presence of microbial extracellular polymer (ECP) is important for sludge flocculation, but ECP has also been shown to have a detrimental effect on the dewaterability of certain sludge types. This paper investigates the relationship between sludge dewaterability and the level of ECP present in a range of sludges obtained from 8 full-scale municipal treatment works in the UK. Sludge dewaterability was determined using the capillary suction time (CST) test, and a thermal extraction process followed by solvent precipitation was used for ECP extraction. The results indicate that for each type of sludge examined there appears to be an optimum level of ECP (raw sludge 20 mg ECP/g SS; activated sludge 35 mg ECP/g SS; digested sludge 10 mg ECP/g SS) at which the sludge should exhibit maximum dewaterability. The establishment of a trend between sludge dewaterability and the quantity of ECP present opens up the possibility of manipulating the level of microbial polymer present to aid sludge dewatering, and hence reduce plant operating costs.

Flocculation↗

PubMed2001

Flotation technique with coagulant and polymer application applied to the post-treatment of effluents from anaerobic reactor treating sewage.

This paper presents the results of a study performed with a lab-scale batch DAF unit fed with previously coagulated (with FeCl3 and/or cationic polymer) effluent from a pilot-scale expanded bed anaerobic reactor treating domestic sewage. The association between ferric chloride and polymers was studied, aimed at sludge reduction. Ferric chloride dosages ranging from 15 to 65 mg.l-1, and polymer dosages from 0.25 to 7.0 mg.l-1 were investigated. Flocculation conditions were kept constant: 20 min of time (Tf) and 80 s-1 of mean velocity gradient (Gf). Air requirement was kept to 19.0 g of air.m-3 wastewater, using 20% recycle ratio and saturation pressure at 450 kPa. When the anaerobic reactor was operating at steady state conditions, it was possible to reduce the FeCl3 dosage from 65 to 30 mg.l-1 after applying 0.4 mg.l-1 of non-ionic polymer, before the DAF process. For these dosages, 79% COD removal (residual of 23 mg.l-1), 86% total phosphate removal (residual of 0.9 mg.l-1) and 98% turbidity removal (residual of 2.6 NTU) were observed. Furthermore, the use of adequate polymer together with 30 mgFeCl3.l-1 leads to the production of high rising rate flocs.

Bacteria, Anaerobic↗