In situ observation of suspended solid aggregates in rivers

Suspended solids are a major pathway of the biogeochemical fate of many contaminants in aquatic systems. Aggregation processes of particles are poorly reported in rivers but they are likely to exist at low flow, mostly because of sticky polysaccharides produced by living organisms. These processes affect suspended particle transport by changing particle sizes and densities and may also limit exchanges of matter between solid and dissolved phases. The main difficulty in floc studies is aggregate fragility, which requires the use of specialized in situ techniques to analyze aggregated suspended solids.We describe two in situ methods for observing suspended particles which do not need heavy field equipment. The first one is based on the filtration of a thin water layer in the natural flow through a membrane which can subsequently be observed by microscope. The second one is based on in situ video snapshots of suspended solids by an endoscope. The video camera linked to the microscope or the endoscope supplies images which are automatically analyzed by image processing to give size distributions.Procedures and validation for both methods are described and results compared with a standard method. The filtration method has been used to trace suspended solids from sewer overflows in the Seine River downstream of Paris. Freshwater flocs are described and a discussion of the fate of aggregates is presented.

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Résumé Les matières en suspension sont déterminantes dans le cycle biogéochimique de nombreux polluants des systèmes aquatiques. Les phénomènes d'agrégation des particules sont encore mal connus en rivière, mais peuvent se produire dans les fleuves urbains du fait de la lenteur des écoulements et vraisemblablement de l'importance des processus bactériens. Ces phénomènes influencent directement le transport des suspensions en modifiant les tailles et les densités des particules. Ils peuvent également limiter les échanges chimiques entre phase dissoute et particulaire.Le problème de la fragilité des flocs et la complexité des équipements habituellement utilisés in situ nous ont conduit à développer deux méthodes d'observation non destructives des flocs. La première consiste à filtrer une mince lame d'eau directement dans l'écoulement naturel puis à observer les suspensions au microscope. La deuxième méthode est l'observation directe des suspensions dans l'écoulement, grâce à un endoscope. Une caméra vidéo reliée au microscope ou à l'endoscope fournit des images que l'on traite automatiquement (dénombrement et mesure des particules) pour obtenir la granulométrie des agrégats naturels.Nous comparons les résultats des deux méthodes à ceux d'une méthode de référence, puis nous comparons les deux méthodes entre elles. La filtration in situ a été utilisée en Seine à l'aval de gros rejets de temps de pluie de l'agglomération parisienne pour étudier les matières en suspension issues des rejets. La caractérisation des flocs de Seine permet de discuter de leur devenir dans le fleuve.

     

Investigation of the electro-coagulation treatment process for the removal of total suspended solids and turbidity from municipal wastewater

In this work, raw municipal wastewater was electro-coagulated for the removal of total suspended solids (TSS), turbidity, and particulate BOD using stainless steel electrodes. The removal efficiency of TSS and turbidity is shown to depend on the amount of iron generated from the anode of the reactive electrode used in this study, when applying the lower currents of 0.05 A and 0.1A. For such lower currents, the results suggested that the removal is consistent with charge neutralization coagulation mechanism. When applying higher currents of 0.2 A, 0.4 A, and 0.8 A, the results suggested that the dominant removal mechanism is sweep-floc coagulation as the generated soluble ferrous ions are converted to insoluble ferric ions due to oxidation with chlorine generated during the electrochemical process at the higher currents. The highest TSS removal efficiency of 95.4% occurred at a current of 0.8A and contact time of 5 min. The effect of electro-coagulation on the removal of particulate BOD was shown to depend on the TSS removal efficiency.     

污染底泥原位覆盖技术综述

从污染底泥的危害入手,提出简单、有效且低成本的底泥原位覆盖技术.该技术将无污染的清洁材料铺盖到污染底泥上,通过覆盖材料对污染物的阻隔、稳固和吸附作用来有效控制底泥污染物.覆盖材料的粒径、比表面积和孔隙率、密度等特性关系到材料的吸附能力和对底泥污染物的阻隔和稳固作用,从而决定覆盖效果.选取覆盖材料及确定最佳覆盖厚度需要依据材料的这些特性.本文分析了原位覆盖技术的优缺点及适用条件和适用范围.介绍了几种常用的原位覆盖工程的施工方式及每种方式的优缺点,列举了大量的国内外覆盖工程实例,并就覆盖技术在我国良好的应用前景进行了分析.     

In situ bioremediation of contaminated aquifers and subsurface soils

Bioremediation, the use of microorganisms to detoxify and degrade hazardous wastes, is an emerging in situ treatment technology for the remediation of contaminated aquifers and subsurface soils. This technology depends upon the alteration of the physical/chemical conditions in the subsurface environment to optimize microbiological activity. As such, successful bioremediation depends not only upon an understanding of microbial degradation processes, but also upon an understanding of the complex interactions that occur between the contaminants, the subsurface environment, and the indigenous microbial populations at each site. At present, these interactions are poorly understood. Site‐specific evaluation and design therefore are essential for bioremediation. In this paper, we review microbiological, hydrological, and geochemical factors that should be considered in evaluating the appropriateness of bioremediation for hazardous waste‐contaminated aquifers and subsurface soils.     

In situ removal and purification of biosurfactants by automated surface enrichment

Erysipelothrix rhusiopathiae, the causative agent of swine erysipelas, was cultivated in a 5-L stirred and aerated bioreactor under different dissolved oxygen tensions (0%, 5%, and 30% of saturation) for evaluation of the influence of oxygen on cell growth as well as on the production of the main antigenic component of the vaccine against erysipelas, a 64–69 kDa protein (SpaA). The microorganism presented different growth profiles for different aeration conditions. However, at the end of the batch cultivations, similar cell concentrations were obtained under the studied conditions. In order to maximize biomass titers and antigen production, the microorganism was cultivated in fed-batch operation mode under aerobic conditions. Under this condition, there was a fivefold increase in biomass production in comparison to the results attained in batch cultivations. To follow up antigen expression, samples collected during batch cultivations were concentrated and treated with choline for antigen extraction. Antigen expression was then assessed by sodium dodecyl sulfate polyacrylamide gel electrophoresis and by murine immunization tests. It was observed a direct influence of oxygen availability upon antigen expression, which is favored in the presence of oxygen. Analysis of the samples collected throughout the fed-batch process also revealed that antigen production is growth associated.     

In situ filtration of Anchusa officinalis culture in a cell-retention stirred tank bioreactor

Summary The effect of agitation and aeration on filtration of Anchusa officinalis culture in a stirred tank bioreactor integrated with an internal filter unit was investigated. Increases in suction head of the pump that drove the filtration process were measured at impeller speeds of 100 and 200 rpm. Surprisingly, suction head attained at 200 rpm was about 40% higher than at 100 rpm. Direct observation of the cake deposition process in the reactor using a dilute cell suspension revealed that the filter cake formed at 100 rpm was thicker, but less compact. Aeration at 0.4 vvm was shown to have little effect on the filtration rate, since the bulk fluid flow was dominated by the impeller hydrodynamics. The initial flux can be recovered by filter backwashing with compressed air at a flow rate of 0.6 vvm for a duration of 5 minutes.     

Ammonia removal from freshwater using nitrifying bacteria enriched from a seawater aquaculture pond

Intensively cultured fish stock when fed protein-rich feeds typically excrete high concentrations of total ammoniacal-nitrogen (TAN) into the water column which can have adverse effects on productivity, and upon the environment when aquaculture water is discharged. An immobilized culture of nitrifying bacteria isolated from prawn pond water and known to effectively remove TAN from saline water was tested for its ability to remove TAN from freshwater. The culture was readily adaptable to non-saline conditions and maintained TAN at less than 0.25 mg l^–1, even with a daily addition of 3.2 to 4.2 mg TAN l^–1 per d. The use of the immobilized culture of nitrifying bacteria represents an innovative and economical in situ treatment technology for removal of TAN in both saline and freshwater.     

In situ nitrogen removal in phase-separate bioreactor landfill

The feasibility of in situ nitrogen removal in phase-separate bioreactor landfill was investigated. In the experiment, two sets of bioreactor landfill systems, namely conventional two-phase and in situ nitrogen removal bioreactor landfills, were operated. The in situ nitrogen removal bioreactor landfill (NBL) was comprised of a fresh-refuse filled reactor (NBLF), a methanogenic reactor (NBLM) and a nitrifying reactor (NBLN), while the two-phase bioreactor landfill (BL) used as control was comprised of a fresh-refuse filled reactor (BLF) and a methanogenic reactor (BLM). Furthermore, the methanogenic and nitrifying reactors used aged refuse as bulk agents. The results showed that in situ nitrogen removal was viable by phase-separation in the bioreactor landfill. In total 75.8 and 47.5 g of nitrogen were, respectively, removed from the NBL and the BL throughout the experiment. The methanogenic reactor used the aged refuse as medium was highly effective in removing organic matter from the fresh leachate. Furthermore, the aged refuse was also suitable to use as in situ nitrification medium. The degradation of fresh refuse was accelerated by denitrification in the initial stage (namely the initial hydrolyzing stage) despite being delayed by denitrification in a long-term operation.     

Analysis and modeling of suspended solids from high-frequency monitoring in a stormwater treatment wetland

Tools for modeling pulsed flows and constituent fluxes in wetlands, although well developed in theory, have not been well tested in practice. High-frequency monitoring of suspended solids and flows in a stormwater treatment wetland enabled application and analysis of these tools. A dynamic flow- and volume-weighted time variable, analogous to the retention time in steady-flow systems, is one important tool tested in this study. Cross-correlations with time lags demonstrated that the dynamic time variable was a better predictive variable of pulsed events than was the standard, static time variable. Although plug-flow models are typically used for steady-flow wetlands, residence time distribution (RTD) models are indispensable for describing pulsed flows and constituent fluxes in wetlands. This study demonstrated that RTD modeling with reaction kinetics of suspended solids during storm events produces a better explanation of outflow data than possible with steady, plug-flow models. Using only input and output data, an RTD model explained sedimentation rates with less unexplained variance than the standard, plug-flow model. The results of this study underscore the importance and utility of RTD modeling for complex flows.     

Simultaneous phenanthrene and cadmium removal from contaminated soil by a ligand/biosurfactant solution

Surfactants and inorganic ligands are pointed as efficient to simultaneous removal of heavy metals and hydrophobic organic pollutants from soil. However, the biosurfactants are potentially less toxic to soil organisms than other chemical agents. Thus, in this study the efficiency of combinations of iodide (I⁻) ligand and surfactants produced by different bacterial species in the simultaneous removal of cadmium (Cd²⁺) and phenanthrene in a Haplustox soil sample was investigated. Four microbial surfactants and the synthetic surfactant Triton X-100 were tested with different concentrations of ligand. Soil samples contaminated with Cd²⁺ and phenanthrene underwent consecutive washings with a surfactant/ligand solution. The removal of Cd²⁺ increased with increased ligand concentration, particularly in solutions containing biosurfactants produced by the bacterial strains Bacillus subtilis LBBMA155 (lipopeptide) and Flavobacterium sp. LBBMA168 (mixture of flavolipids) and Triton X-100. Maximum Cd²⁺ removal efficiency was 99.2% for biosurfactant produced by Arthrobacter oxydans LBBMA 201 (lipopeptide) and 99.2% for biosurfactant produced by Bacillus sp. LBBMA111A (mixed lipopeptide) in the presence of 0.336 mol iodide l⁻¹, while the maximum efficiency of Triton X-100 removal was 65.0%. The biosurfactant solutions removed from 80 to 88.0% of phenanthrene in soil, and the removal was not influenced by the presence of the ligand. Triton X-100 removed from 73 to 88% of the phenanthrene and, differently from the biosurfactants, iodide influenced the removal efficiency. The results indicate that the use of a single washing agent, called surfactant-ligand, affords simultaneous removal of organic contaminants and heavy metals.     

In situ determinations of bacterial selectivity and filtration rates by five cladoceran zooplankters in a hypertrophic subtropical reservoir

Cladoceran in situ feeding rates on natural bacteria labelledwith [methyl-³H] were studied in parallel with feeding ratedeterminations on ¹⁴C-labelled Chlorella in a hypertrophic subtropicalreservoir (Lake Hartbeespoort) through spring and summer (1986/87).Community filtration rates (CFR5) on bacteria and algae weresimilar, but selection for Chlorella (relative to natural bacteria)increased from midsummer in association with declining bacterialdensity and increasing dominance of ‘inedible’ componentsof the natural phytoplankton. Species-specific filtration rates(SSFRs) were determined for Daphnia pulexllongispina, Ceriodaphniareticulata, Diaphanosoma excisum, Bosmina longirostris and Moinamicrura during their respective seasonal occurrence in the studyperiod. SSFRs on algae and bacteria increased with body length(L, mm) in all species apart from Bosmina. Species-specificdifferences in absolute feeding rate (FR, ml animal^–1day^–1), the slope of the FR-L relationship and bacteriaselectivity were evident. The feeding rate of all cladoceranson bacteria is described by the power equation FR 5.231L^1.42FR values on bacteria relative to FR values on algae averaged     

In situ remediation of aquifers contaminated with dense nonaqueous phase liquids by chemically enhanced solubilization

Chemically enhanced solubilization (CES) is an advanced variant of pump‐andtreat that results in more effective and more rapid remediation of groundwater contaminated with organic solvents and other dense nonaqueous‐phase liquids (DNAPLs). Attempts to remediate DNAPL‐contaminated groundwater by pump‐and‐treat have generally not been successful, due to the low aqueous solubility of most DNAPLs. Regions of undissolved, organic liquids slowly release additional contamination to surrounding groundwater, in effect acting as in situ sources of contamination and hindering the progress of remediation attempts. Cleaning up an aquifer can take many decades or more of pump‐and‐treat. CES accelerates pump‐and‐treat by using surfactants at low concentration to increase the solubility of organic contaminants by up to three orders of magnitude, while maintaining hydraulic control. The surfactants are chosen to maximize contaminant solubilization while minimizing decreases in the DNAPL/ water interfacial tension in order to prevent mobilization of DNAPL to uncontaminated regions. The surfactants are also selected to be nontoxic and biodegradable (many are U.S. Food and Drug Administration‐ (FDA‐) approved food additives). After the contaminants have been solubilized, they are pumped to the surface and treated by air stripping and other methods as in traditional pump‐and‐treat operations. CES has had extensive laboratory development and is now being field tested at three sites. The first field test is at Canadian Forces Base Borden, a military facility in Ontario, Canada. The field test involves the controlled contamination of a shallow sand aquifer with approximately 240 L of tetrachloroethylene (PCE). CES increased the contaminant concentration in the extracted water to over 10,000 ppm of PCE, compared with an aqueous solubility of 200 ppm. At latest report, more than 80% of the residual PCE has been removed. A second field test is currently in preparation at a chlorinated solvent manufacturing facility in Texas and a third at a DOE site with PCE, 1,1,1‐trichloroethane (TCA), and trichloroethylene (TCE) contamination.     

High-performance microbial removal of ethanol from contaminated air

Ethanol vapour from air was removed using a bioreactor (2.7 m 3 ) packed with a novel engineered material consisting of a highly porous inorganic matrix coated with activated carbon. The system was operated over a period of two months varying the inlet ethanol between 90 and 2200 mg m –3 . Removal efficiencies ranging from 80 to 99.9% were obtained. A simplified kinetic model of the bioreactor was developed and used to estimate the maximum degradationrate and to predict thermal effects resulting from ethanol oxidation.     

Giardia and Cryptosporidium removal from waste-water by a duckweed (Lemna gibba L.) covered pond

AIMS: To determine the ability of duckweed ponds used to treat domestic waste-water to remove Giardia and Cryptosporidium. METHODS AND RESULTS: The influent and effluent of a pond covered with duckweed with a 6 day retention time was tested for Giardia cysts, Cryptosporidium oocysts, faecal coliforms and coliphage. Giardia cysts and Cryptosporidium oocysts were reduced by 98 and 89%, respectively, total coliforms by 61%, faecal coliforms by 62% and coliphage by 40%. There was a significant correlation between the removal of Giardia cysts and Cryptospordium oocysts by the pond (P < 0.001). Influent turbidity and parasite removal were also significantly correlated (Cryptosporidium and turbidity, P=0.05; Giardia and turbidity, P=0.01). CONCLUSIONS: The larger organisms (parasites) probably settled to the bottom of the pond, while removal of smaller bacteria and coliphages in the pond was not as effective. SIGNIFICANCE AND IMPACT OF THE STUDY: Duckweed ponds may play an important role in wetland systems for reduction of Giardia and Cryptosporidium.     

Microbe removal in secondary effluent by filtration

A study was carried out to assess the efficiency of filtration in reducing microbial contamination in municipal secondary effluent. After primary and secondary treatments, the wastewater underwent filtration through sand/hydroanthracite filters. A total of 20 samplings were made, each consisting of two instant samples (secondary effluent and filtered effluent). Each of the 40 samples was tested for: total and faecal coliforms,Escherichia coli, enterococci and somatic coliphages. The mean concentrations detected in the secondary effluent were in the order of 5 log for the total and faecal coliforms, 4 log for enterococci andEscherichia coli, and approx. 3 log for the coliphages. The filtration showed a higher efficacy in the reduction of feacal coliforms,Escherichia coli and in particular total coliforms. The results obtained for enterococci and coliphages were significanty lower. Filtration alone was not enough to reduce the bacterial indicators to within Italian legal limits, and showed a poor capacity to abate coliphages. However, by performing the filby-products and a consequent reduction in the chemical risk for the general population.     

In situ bioassessment of dredging and disposal activities in a contaminated ecosystem: Toronto Harbour

The contamination of Toronto Harbour is a very serious problem. The major sources of pollution are the Don River and sewer outflows, as well as industrial, and municipal effluents. The problem is further compounded by perturbations of the toxic sediment caused by dredging, dredge-disposal, navigation, and recreational activities. The impact of contamination and nutrient enrichment was reflected in the size-fractionated primary productivity experiments. Generally, microplankton/netplankton (> 20 µm) productivity was enhanced whereas ultraplankton (< 20 µm) productivity was inhibited. These observations are attributable to interactions between ameliorating nutrients and toxic contaminants as well as to the differential sensitivity of natural phytoplankton size assemblages to the bioavailable chemical regime. In situ environmental techniques applied in Toronto Harbour were effective, sensitive, and rapid, and provided a better understanding of the impact of dredging/disposal activities under natural conditions. These techniques have great potential in the assessment of the ecotoxicology of harbours and other stressed environments.     

In situ product removal using a crystallization loop in asymmetric reduction of 4-oxoisophorone by Saccharomyces cerevisiae

In situ product crystallization was investigated for solid product crystals that were obtained during fermentation. The model reaction was the asymmetric reduction of 4-oxoisophorone (OIP) using baker's yeast (S. cerevisiae) as a biocatalyst. The target product was 6R-dihydro-oxoisophorone (DOIP), also known as levodione, a key intermediate in carotenoid synthesis. DOIP was degraded by baker's yeast mainly to (4S,6R)-actinol, an unwanted byproduct in the process. Actinol formation reached up to 12.5% of the initial amount of OIP in the reactor during a batch process. However, better results were obtained when the dissolved DOIP concentration was controlled using an integrated fermentation-crystallization process because: (a) actinol formation was reduced to 4%; and (b) DOIP crystal formation in the reactor was avoided. DOIP productivity was improved by 50% and its selectivity was raised from 87% to 96% relative to the batch process. In the integrated process, most of the product was recovered as pure crystals; this may already minimize, if not eliminate, the need for organic solvents in the final purification steps. An almost sixfold reduction in biocatalyst consumption per kilogram product was achieved, which also can contribute to the minimization of waste streams.     

In situ filtration responses of Daphnia galeata to changes in food quality

In the stoichiometric study of phyto–zooplankton interactions,a controversy exists about how Daphnia species regulate theirfeeding rate when submitted to low-quality food (i.e. high dietarycarbon:phosphorus [C:P] ratio). In this study, we gathered dataover 3 years on in situ clearance rates of a Daphnia galeatapopulation, by conducting grazing experiments from April 1998to October 2000 in the Esch-sur-Sûre reservoir (Grand-Duchyof Luxembourg). Observed clearance rates (2.5–13.5 mLindividual^–1 day^–1, mean 7.0 mL individual^–1day^–1) were correlated with population and environmentalvariables. Mean body size of Daphnia individuals was the bestpredictor of clearance rate (r² = 0.639), followed by watertemperature (r² = 0.262) and P concentration in the seston (r²     

Poliovirus removal from primary and secondary sewage effluent by soil filtration.

Adsorption of poliovirus from primary sewage effluent was similar to that from secondary sewage effluent in both batch soil studies and experiments with soil columns 240 cm long. Virus desorption by distilled water was also similar in a soil column that had been flooded with either primary or secondary effluent seeded with virus. These results indicated that absorption of poliovirus from primary effluent and virus movement through the soil were not affected by the higher organic content of primary sewage effluent.     

Poliovirus removal from primary and secondary sewage effluent by soil filtration.

Adsorption of poliovirus from primary sewage effluent was similar to that from secondary sewage effluent in both batch soil studies and experiments with soil columns 240 cm long. Virus desorption by distilled water was also similar in a soil column that had been flooded with either primary or secondary effluent seeded with virus. These results indicated that absorption of poliovirus from primary effluent and virus movement through the soil were not affected by the higher organic content of primary sewage effluent.