bluuebunny/crossref_metadata_2025 huggingface dataset:
Coagulation-filtration of a secondary effluent by means of pre-hydrolyzed coagulants
Authors: Diamadopoulos Evangelos , Vlachos Christos
Published: May 2018

Jar tests were applied to a secondary effluent in order to determine optimal conditions for coagulation. The metal salts Al2(SO4)3, AlCl3 and FeCl3 were used as coagulants, and their efficiency under various degrees of pre-hydrolysis was examined. The variables under examination were the dose of the coagulant, the degree of pre-hydrolysis, B=[OH−]/[Me+3], and the pH at two different levels (pH=5.5 and pH=7.5). The efficiency of the various coagulants was evaluated for the removal of turbidity, phosphorous, COD and UV absorbance at 254 nm. The results showed that as far as turbidity removals are concerned, pre-hydrolysis of the aluminum and ferric chloride coagulants at values of B equal to 0.5 to 1 gave optimal results. However, for phosphorous removal, the higher the degree of pre-hydrolysis, the lower the removal of phosphorous. No remarkable differences were observed for the removal of organic matter measured as COD, while alum gave the best results for the reduction in UV absorbance at 254 nm. Direct filtration of the effluent showed that the coagulant dose required was an order of magnitude lower than that required for coagulation. 35 cm of filter bed were sufficient for effective filtration. All coagulants performed well, increasing the degree of turbidity removal as compared to the absence of coagulants. The lowest headloss rate was observed when alum was used, while the highest headloss rate, almost three times as much, when the aluminum chloride coagulants were used (with and without pre-hydrolysis). Ferric coagulants, with or without pre-hydrolysis, demonstrated intermediate headloss rates.
The roles of microbes in the removal and inactivation of viruses in a biological wastewater treatment system
Authors: Kim Tae-Dong , Unno Hajime
Published: May 2018

The objective of this research is to clarify the mechanism for virus removal in an activated sludge process. The roles of microbes, i.e. bacteria, protozoa and metazoa, which form activated sludge were investigated using poliovirus as a model virus. In a bacteria cultures, the virus concentration decreased in the first one hour after which no further decrease was observed. This phenomenon is explained by the interaction of bacterial floc and virus where virus was removed by reversible adsorption. On the other hand, in the mixed culture of bacteria and protozoa, or of bacteria and metazoa, the virus removal process was observed to proceed in two first-order processes. In the first stage, virus was removed from the liquid phase by adsorption onto the floc, whereas in the second stage, virus is removed by predation of the other microbes, i.e. protozoa or metazoa. Moreover, the floc-forming ability and the feeding manner of the microbes strongly affected the virus removal. Especially, a filter feeder microbe was more effective in virus removal than a detritus feeder microbe. Among the microbes used in the experiments, P. erythrophthalma which had a large mouth and a strong filter-feeding ability as well as a high floc-forming ability showed the most efficient virus removal.
Necessity and basis for establishment of European guidelines for reclaimed wastewater in the Mediterranean region
Authors: do Monte Maria Helena F. Marecos , Angelakis Andreas N. , Asano Takashi
Published: May 2018

The use of reclaimed wastewater for irrigation contributes to water conservation and, therefore, is an important component of a sound policy for water resources management in the Mediterranean region. With the exception of France and Germany, European Mediterranean countries have not established guidelines for the use of reclaimed wastewater for irrigation. The existence of such guidelines means an important step in the planning and implementation of safe use of reclaimed wastewater for irrigation, because it contributes to a sustainable development of landscape and agricultural irrigation. Guidelines for reclaimed wastewater use for irrigation must clearly define what is allowed and what is forbidden to execute. This can be defined in great detail or in a broad manner, but must take into account some important specific local conditions, such as the quality of reclaimed wastewater, soil, climate, relevant crops and agricultural practices. Consequently, experimentation means a key-support to establishing guidelines. The experience from a research project with different type of reclaimed wastewater, crops and irrigation methods carried out for several years in the climatic Mediterranean region of Portugal brings some contribution to the technical content of possible European guidelines. Other aspects to be included in the proposed guidelines, such as monitoring and institutional management are also presented.
Agronomic and public health assessment of reclaimed water quality for landscape irrigation
Authors: Mujeriego Rafael , Sala Lluís , Carbó Maria , Turet Josep
Published: May 2018

The Mas Nou golf course has been using disinfected secondary effluent for irrigation since September 1989. Although adjusted-SAR values and EC of irrigation water have generally fallen in the non-restricted irrigation categories, EC values were initially higher than desirable for turf irrigation, due to high effluent chloride concentration. A definite solution was reached in the summer of 1993 with completion of a new surface water transfer. Since 1993, EC values in summer effluent range from 1.2 to 1.5 dS/m. A new water and storage pond management system has been proposed to optimize both water and nutrients application, using only the most adequate water source available at a given time. The relatively low iron contributions of reclaimed water have resulted in occasional spots of ferric chlorosis, which have been recovered with localized application of iron compounds. Fertilizer savings have ranged from 0.06 to 0.12 US $/m3 of reclaimed effluent. Weekly analyses of reclaimed water show that faecal coliforms and faecal streptococci concentrations lower than 100 cfu/100 mL can be consistently achieved. By mechanical mixing of top oxygen-rich waters with bottom oxygen-depleted waters in the storage ponds, odor problems have been totally eliminated. Close collaboration with the greenkeeper has resulted in a more favorable attitude to the water quality requirements of reclaimed effluent and a more effective and economical fertilization program. The greenkeeper perception has gradually evolved from a passive acceptance of the requirements of using reclaimed water to a positive recognition of its benefits.
Issues in artificial recharge
Authors: Bouwer Herman
Published: May 2018

Interest in artificial recharge with normal water and sewage effluent continues to increase. Issues discussed in this paper include recharge with infiltration basins, soil-aquifer treatment of sewage effluent, potable use of water from aquifers recharged with sewage effluent, nitrogen removal, pre-treatment of sewage effluent, disinfection, well recharge, clogging parameters, superchlorination, disinfection byproducts, vadose zone wells, seepage trenches, and constructed aquifers used as intermittent sand filters.
Pilot-plant experiments with moving-bed biofilm reactors
Authors: Pastorelli G. , Andreottola G. , Canziani R. , de Fraja Frangipane E. , De Pascalis F. , Gurrieri G. , Rozzi A.
Published: May 2018

A flexible pilot plant, fed with primary settled wastewater, was used to study (1) organic carbon and nitrification in a two(three)-stage continuous-flow aerobic process and (2) organic carbon and nitrogen removal in a heterotrophic moving-bed sequencing batch biofilm reactor (MBSBBR) for denitrification and in a continuous-flow autotrophic moving-bed biofilm reactor (MBBR) for nitrification. In both experiments the same polyethylene biofilm carriers were used. Filtered COD removal rates in aerobic conditions appear to be proportional to the corresponding loading rates up to 8 gCOD m−2 d−1. Nitrification tests, performed in oxygen limiting conditions and ammonia limiting conditions, showed that the reaction rate was nearly first order with respect to dissolved oxygen due to liquid film diffusion. Denitrification tests, performed without external carbon sources, showed that the denitrification rate never fell below 0.3 gNO3−-N m−2 d−1 even at very low biodegradable filtered COD loading rates.
Experience with nutrient removal in a fixed-film system at full-scale wastewater treatment plants
Authors: Borregaard Vibeke R.
Published: May 2018

In the upgrade of wastewater treatment plants to include biological nutrient removal the space available is often a limiting facor. It may be difficult to use conventional suspended growth processes (i.e. activated sludge) owing to the relatively large surface area required for these processes.

Recent years have therefore seen a revived interest in treatment technologies using various types of attached growth processes. The “new” attached growth processes, like the Biostyr process, utilise various kinds of manufactured media, e.g. polystyrene granules, which offer a high specific surface area, and are therefore very compact.

The Biostyr plants allow a combination of nitrification-denitrification and filtration in one and the same unit. The results obtained are 8 mg total N/l and an SS content normally below 10 mg/l. The plants in Denmark which have been extended with a Biostyr unit have various levels of PLC control and on-line instrumentation.
Biological upflow fluidized bed denitrification reactor demonstration project - Stamford, CT, USA
Authors: Semon Jeannette , Sadick Thomas , Palumbo Dennis , Santoro Marylee , Keenan Peter
Published: May 2018

The discharge of nitrogen in wastewater treatment plant effluent has been identified as a receiving water quality issue throughout the United States and in the European Community. Regulatory agencies are evaluating discharge limits for total nitrogen (TN) as low as 3 to 5 mg/l. To attain these limits at treatment plants with little or no space for expansion, technologies which can remove large quantities of nitrogen with relatively small space requirements are required. Biological upflow fluidized bed (BFB) technology appears to be well suited to these regions. This paper describes the results of a demonstration project using a fluidized bed reactor. The reactor was operated at a flow rate of 15 l/s and an average daily loading of 1843 kg NO3/1000 m3/d and maximum loadings of 6407 kg NO3/1000 m3/d. At steady-state conditions, effluent total nitrogen concentrations averaged 2.5 mg/l over a temperature range of 11 to 25°C. At high nitrate loading rates, effluent total nitrogen concentrations averaged 4.1 mg/l. Approximately 3 mg of methanol per mg of influent nitrate was used as a carbon source. Reactor empty bed contact time averaged 5.7 minutes.
Studies on the dechlorination of tetrachloroethene to cis-1,2-dichloroethene by dehalospirillum multivorans in biofilms
Authors: Eisenbeis Martina , Bauer-Kreisel Petra , Scholz-Muramatsu Heidrun
Published: May 2018

This study was conducted to examine the application of the anaerobic bacterium Dehalospirillum multivorans in a biofilm reactor for the reductive dechlorination of tetrachloroethene (PCE) via trichloroethene (TCE) to cis-1,2-dichloroethene (DCE). A laboratory scale fluidized-bed reactor, operated under continuous flow conditions at 20°C, converted PCE to TCE at an apparent maximum reaction rate of 55 nmol/min/mg protein and TCE to DCE at 90 nmol/min/mg protein. These high rates should be even higher with an improved reactor performance since the apparent maximum reaction rates of the suspended cells (30°C) were by a factor of about 3.5 higher. With respect to its technical application D. multivorans is quite insensitive against unfavourable conditions, e.g. the presence of oxygen and low temperature. Natural groundwater components like nitrate and sulfate did not interfere with the dechlorination process up to a concentration of 5 mmol/l. Possible co-contaminants like chlorinated methanes, however, strongly inhibited PCE-dechlorination of the suspended cells, whereas chlorinated ethanes had no influence up to a concentration of 800 μmol/l. Experiments are presently being carried out to study the influence of biofilm immobilization on the protection of the dechlorination process against organic and inorganic inhibitors.
Development of a membrane biofilm reactor for the degradation of chlorinated aromatics
Authors: Peys Kurt , Diels Ludo , Leysen Roger , Vandecasteele Carlo
Published: May 2018

Many wastewaters generated by industry contain a limited amount of very toxic and recalcitrant pollutants which can upset biological treatment systems. A new membrane biofilm reactor concept is studied to treat these wastewaters. A biofilm is grown on an ultrafiltration membrane supporting layer that separates wastewater from an additional nutrient stream. The biofilm bacteria are in close contact with the wastewater which allows an efficient degradation of organic pollutants. Meanwhile, the diffusion of specific nutrient compounds keeps the bacteria active. The study is focused on modelling and optimization of the reactor operation considering both mass transfer and degradation kinetics. The biofilm structure and characteristics are very important in this optimization study.
Characterization of suspended solids in/out airlift biofilm-reactors
Authors: Roessink Roy , Eikelboom Dick H.
Published: May 2018

In airlift reactors the biomass is immobilized on small (200-300 μm) carrier particles, suspended in the water phase. If domestic wastewater is treated in these systems, the soluble and colloidal compounds are generally removed with an efficiency of 75±5%. However, the overall treatment results are negatively affected by the high amount of suspended material in the effluent. Different fractions in influent and effluent were analyzed using microscopic techniques and chemical analyses to collect more information about the behavior of suspended solids. Settlable (Se), centrifugable (C), filterable (F) and soluble (So) fractions were obtained by sequential settling, centrifugation and filtration. After correction for sorbed soluble compounds the fractions C, F, and So contributed 30%, 20% and 50% respectively to the COD of presettled wastewater. During periods when biofilms were compact/smooth and the population of protozoa in the reactor was small, size and composition of the C-fraction only slightly changed when passing the reactor. The removal efficiency of this fraction increased from less than 10% to 15-25% if large populations of protozoa were present, which were able to consume more than 99% of the free cells. Additionally, a small amount of settlable compounds (< 20 mg COD/l) was formed in the reactor. This amount increased to 40-60 mg COD/l as soon as the surface of the films changed from smooth to very irregular due to growth of “streamers” and/or filamentous bacteria. Retention of this suspended biomass under these circumstances resulted in the development of an activated sludge process under these circumstances. The advantages of the biofilm process were thus partly lost.
Nitrifying biotower upsets due to snails and their control
Authors: Palsdottir Gudny , Bishop Paul L.
Published: May 2018

The primary purpose of this study was to find the proper operating parameters for successful operation of the nitrification biotowers at the North Regional Wastewater Treatment Plant in Dayton, Ohio, and to recommend an operational protocol to prevent future failures. This plant is subject to regular, periodic biotower upsets. It was found that these upsets are correlated with blooms of snails (Physa gyrina) which it is believed graze the biofilm and devour the nitrifying organisms. Snail control mechanisms are under investigation.
Structure and function of a nitrifying biofilm as determined by microelectrodes and fluorescent oligonucleotide probes
Authors: Schramm A. , Larsen L. H. , Revsbech N. P. , Amann R. I.
Published: May 2018

Microelectrodes for O2 and NO2−/NO3− and fluorescently labelled 16S rRNA-targeted oligonucleotide probes were combined to examine the activity and stratification of nitrifying bacteria in a trickling filter biofilm. Microprofiles showed that O2 consumption and NO3−/NO2− production were restricted to the upper 50-100 μm of the biofilm. The vertical distribution of the nitrifying bacteria Nitrosomonas sp. and Nitrobacter sp. was investigated by fluorescent in situ hybridisation (FISH) with specific oligonucleotides. Nitrifiers formed a dense layer of cells and cell clusters in the upper part of the biofilm. This correlates well with the measured activity profiles.

Ammonia- and nitrite-oxidisers occurred in close vicinity to each other supporting a fast sequential metabolism from ammonia to nitrate. Both species were not restricted to the oxic part of the biofilm, but also appeared -in lower numbers- in the anoxic layers on the bottom of the biofilm.

A short term decrease in the O2 concentration of the bulk water resulted in a quick decrease in O2 penetration and metabolic rates inside the biofilm. However, neither the stratification nor the cellular ribosome content of nitrifiers changed within a few hours.
Determination of oxygen profiles and diffusivity in encapsulated biomass k-carrageenan gel beads
Authors: Zhou Qin , Bishop Paul L.
Published: May 2018

Biofiltration is a popular method for removing volatile organic compounds (VOCs). One promising medium for biofilters is biomass encapsulated gel beads. Like any other biodegradation system, oxygen concentration is an important factor affecting microbial activities in gel beads and thus the VOC removal efficiency. This paper summarizes the studies on oxygen distribution and diffusivity in k-carrageenan gel beads using oxygen microelectrodes to measure oxygen profiles. By using a reaction-diffusion model and the concentration measurements obtained, a homogeneous diffusivity constant and an oxygen consumption rate constant in k-carrageenan gel beads were estimated. The estimated oxygen diffusivity in the gel bead is 46.3% of the value in water when the bead is immersed in water and 53.9% that of water when the bead is in air with a thin liquid film surrounding it. To provide more information for the design and operation of biofilters using biomass-loaded gel beads, we also investigated and report on effects of biomass immobilization time, TCE influent concentration and TCE gas flow rate on oxygen concentrations in the gel bead.
Kinetic and mechanistic aspects of the oxidation of chlorophenols by ozone
Authors: Boncz M. A. , Bruning H. , Rulkens W. H. , Sudhölter E. J. R. , Harmsen G. H. , Bijsterbosch J. W.
Published: May 2018

In Advanced oxidation processes (AOPs) radicals are considered to play an important role. Organic contaminations can in AOPs generally be converted to carbon dioxide, water, etc. The most important limitation to the application of AOPs, however, is their high costs, especially when complete mineralisation of the pollutants is pursued. The costs can be reduced by using the oxidant more efficiently, which can be achieved by introducing selectivity. Kinetic and mechanistic data are the basic requirements for optimization of the process. In this work, the influence of several different parameters (temperature, pH, UV irradiation and carbonate concentration) on the kinetics of the degradation ofortho -chlorophenol and para-chlorophenol by ozone was investigated. The pH is the most important parameter. Strongly related to the pH is the degree of ionisation of the phenol, which might be of importance since the shift from a slow to a fast reaction occurs at a higher pH in the case of para-chlorophenol as compared to the case with the more acidic ortho-chlorophenol. A strong indication for a radical mechanism is found in the decrease of the reaction rate in the presence of carbonate, a well known radical scavenger. A further indication is seen in the first step of the reaction, which is dechlorination of the aromatic compound.
Effect of properties of polyelectrolytes on their interaction with particulates and soluble organics
Authors: Lurie M. , Rebhun M.
Published: May 2018

In many situations, the purpose of water and effluent treatment by flocculation-sedimentation or flocculation-filtration is to remove the suspended particulates and not necessarily the “dissolved” macromolecular organics. Flocculation of above mentioned systems by “traditional” (low molecular mass, high charged) cationic polymers as primary flocculants is limited because of high flocculants requirement, caused by polymers chemical binding with anionic organic substances in liquid phase. Effects of matrix, molecular mass and ionic value of polymers on their interaction with SS and DOM were investigated in this research. Significant differences were discovered in interaction of the low molecular mass polymers and high molecular mass polymers with particulates in the presence of soluble organics.
Incidence of wave-frequency on the reaction rates during ultrasonic wastewater treatment
Authors: Petrier Christian , Francony Anne
Published: May 2018

Organic compounds in aqueous solution submitted to an ultrasonic irradiation behave differently according to their physical and chemical properties. In this work, degradation rate of phenol and carbon tetrachloride, has been studied at different frequencies, 20 kHz, 200 kHz, 500 kHz and 800 kHz. Whatever the frequency, it's easier to decompose CCl4 than phenol by means of ultrasonic waves. It is shown that the rates of reactions involving hydroxyl radicals (hydrogen peroxide formation and phenol degradation) have a maximal value at 200 kHz. The best yield observed at 200 kHz for the phenol degradation may be the result of a better HO° radicals availability outside of the bubble of cavitation. The degradation rate for carbon tetrachloride which decomposes into the bubble of cavitation increases with the frequency.
Particle counts and size distribution in system design for removal of turbidity by granular deep bed filtration
Authors: Hatukai S. , Ben-Tzur Y. , Rebhun M.
Published: May 2018

Surface water treatment plants are required to reduce filtered water turbidities down to 0.1 NTU. Turbidity measurement is not sensitive to particles in the size range of Giardia cysts and Cryptosporidium oocysts; furthermore, low treated water turbidity does not necessarily indicate their absence in the water. Particle removal measurement in the Giardia and Cryptosporidium size range was used for treatment process evaluation and optimization. Pilot plant experiments demonstrated that preoxidant type and dosing rate of alum and a cationic polymer affected removal efficiency of particles during direct filtration process more than any other process parameter.
Particle removal in different filtration systems for tertiary wastewater treatment - a comparison
Authors: Kobler Daniel , Boller Markus
Published: May 2018

In seven wastewater installations in the area of Zürich, Switzerland, four different filtration systems for tertiary wastewater treatment (deep bed, cloth drum, continuous up-flow and cell filters) were investigated with special attention to particle size distributions in the in- and outflow of the flocculation and the filtration step. Flocculation and filter performance was characterised by the shift of particle number curves. For each filter, particle number, surface and volume removal as a function of particle size was determined and revealed to be an excellent tool to evaluate the filter plants under practical conditions. The number removal efficiency for small particles in the colloidal size range proved to be the most sensitive parameter and could be related to operating parameters such as flocculant dose and filtration rate. The results of the particle analysis were compared to quality parameters related to small particles such as micro-organism and heavy metal concentrations. A good agreement between the removal of small size particles (< 8 μm) and bacteria counts as well as copper was found in the different filter systems. The filters were finally classified according to their particle removal performance.
Homogeneous and heterogeneous advanced oxidation of a bleaching effluent from the pulp and paper industry
Authors: Mansilla Héctor D. , Cristina Yeber M. , Freer Juanita , Rodríguez Jaime , Baeza Jaime
Published: May 2018

The degradation of phenolic and polyphenolic compounds present in a bleaching ECF effluent for different advanced oxidation systems is described. Photocatalysis with O2/ZnO/UV, O2/TiO2/UV were demonstrated to be the best systems to oxidize the effluent in a short period of time. The homogeneous systems O3 and O3/UV also degrade the organic matter but at a lower extent considering the same time of reaction. Reactions were monitored by color changes, pH, COD and BOD.
On-line measurements of settling characteristics in activated sludge
Authors: Rasmussen Michael R. , Larsen Torben
Published: May 2018

An on-line settling column for measuring the dynamic variations of settling velocity of activated sludge has been developed. The settling column is automatic and self-cleansing insuring continuous and reliable measurements. The settling column was tested on sludge from a batch reactor where sucrose was added as an impulse to activated sludge. The continuous measurement of settling velocity revealed a highly dynamic response after the sucrose was added. The results were verified with simultaneous measurement of the initial settling rate. A 200 hour experiment showed variations in settling velocity, which was not apparent in the DSVI (Diluted Sludge Volume Index).
Characterization of activated sludge flocs structure
Authors: Snidaro D. , Zartarian F. , Jorand F. , Bottero J.-Y. , Block J.-C. , Manem J.
Published: May 2018

Activated sludge is the most widely used process for wastewater treatment. However basic properties such as floc structure or settling properties, still remain unknown. In order to describe activated sludge floc structure, four investigation methods were used: (i) size distribution analysis associated with sonication, (ii) transmission electron microscopy (iii) laser scanning confocal microscopy and fractal dimension analysis, and (iv) three dimensional modelling.

The evolution of floc size distribution in dispersed samples was used to build a model of floc showing that the predominating microflocs (125 μm) are formed from 13 μm aggregates, which are made up of smaller particles (2.5 μm). By transmission electron microscopy it was assumed that the 2.5 μm sub-units could correspond to microorganisms and that exopolymers form a gel-like matrix which holds the structure of the aggregates together.

The microfloc (13 μm) structure was investigated by confocal scanning light microscopy and image processing. The analysis of the mass distribution pointed out that the microfloc is a fractal object (fractal dimension around 3). The total number of cells in these aggregates was found to be 2n number. These two results suggest that division of microorganisms explained the formation of 13 μm units which are microcolonies.

A mass fractal dimension 2.5 ± 0.15 was measured for the microfloc. Its external surface was reconstructed by using interpolating software (GOCAD). It appeared that the surface is also a fractal object with a dimension 2.3 ± 0.1. According to the fractal theory, it seems that diffusion limited aggregation via monomer-cluster collision is the mechanism which describes the formation of macroflocs.
The design of wetland systems for the treatment of urban run off
Authors: Shutes R. B. E. , Revitt D. M. , Mungur A. S. , Scholes L. N. L.
Published: May 2018

The results of studies of the pollution removal performance of constructed wetlands for urban runoff treatment are discussed. The design of urban runoff wetlands including primary treatment components, substrate composition and flow rate regulation are considered.

The use of front-end treatment systems such as oil interceptors, spillage containment facilities and wetland forebays or lagoons are recommended to provide an initial pollutant removal capacity as well as attenuating the impact of high discharges. Design criteria which will ensure inlet flow velocities do not exceed 0.7m/s and which will achieve optimum retention times (10-15 hours) for maximum pollutant removal are described. The relative advantages of different soil types are discussed and an overall minimum substrate depth of 0.6m is recommended for sub-surface systems. Two case studies of urban runoff wetlands in the UK which are currently being monitored are described.
A stochastic model for two-station hydraulics exhibiting transient impact
Authors: Jacobsen J. L. , Madsen H. , Harremoès P.
Published: May 2018

The objective of the paper is to interpret data on water level variation in a river affected by overflow from a sewer system during rain. The simplest possible, hydraulic description is combined with stochastic methods for data analysis and model parameter estimation. This combination of deterministic and stochastic interpretation is called grey box modelling.

As a deterministic description the linear reservoir approximation is used. A series of linear reservoirs in sufficient number will approximate a plug flow reactor. The choice of number is an empirical expression of the longitudinal dispersion in the river. This approximation is expected to be a sufficiently good approximation as a tool for the ultimate aim: the description of pollutant transport in the river.

The grey box modelling involves a statistical tool for estimation of the parameters in the deterministic model. The advantage is that the parameters have physical meaning, as opposed to many other statistically estimated, empirical parameters. The identifiability of each parameter, the uncertainty of the parameter estimation and the overall uncertainty of the simulation are determined.
A thermal analysis of a sub-surface, vertical flow constructed wetland
Authors: Smith Ian D. , Bis George N. , Lemon Edgar R. , Rozema Lloyd R.
Published: May 2018

Since November of 1991, an experimental constructed wetland has successfully treated municipal sewage effluent on a year round basis in a cool climate. The sub-surface, vertically pulsed flow system is located at a latitude of approximately 43 degrees, 15 minutes north latitude in south-central Canada. The 5 metre long by 5 metre wide by 1.2 metre deep constructed wetland cells were designed to operate through extended freezing periods via a number of specific features. The most important features being the allowance of thatch accumulation atop the system, ice accretion within the upper cell strata both acting as insulating layers, and the transfer of thermal energy to the system from warmer deep soils. The cells were hydraulically loaded below this frozen layer of granular matrix six times a day. A dense three dimensional array of thermocouples was planted within the first of the three constructed wetland cells in a series to allow for the assessment of thermal data at a high level of temporal and spatial resolution. Thermal data were sampled every five minutes and averaged and stored every hour over a two year period (1994 and 1995). The data were reviewed statistically to determine the operating envelope experienced at the Niagara-On-The-Lake experimental constructed wetland site. A detailed review of winter thermal data was made to provide parameters for the use of the HEATFLOW density-dependent ground water flow and thermal energy transport numerical model (Molson and Frind, 1995). The use of this coupled Darcy flux, thermal transport model has allowed for a better understanding of the importance of various thermal design considerations, and has allowed for the undertaking of sensitivity analyses for design assessment and optimization. The sensitivity analyses indicate that the retention of deep soil heat and top insulation from plant thatch are the most important thermal features. It is likely that this technology can be used in areas colder than Niagara-On-The-Lake.
A procedure for selecting best identifiable parameters in calibrating activated sludge model no. 1 to full-scale plant data
Authors: Weijers Stefan R. , Vanrolleghem Peter A.
Published: May 2018

A systematic procedure for selecting identifiable parameter subsets for a given set of measured outputs is proposed. The aim is to only select those parameters which can be estimated uniquely from the dataset used. The proposed procedure consists of first selecting a reduced set of most sensitive parameters by sensitivity analysis and subsequently selecting identifiable parameter subsets using the Fisher information matrix.

For a particular set of outputs obtained from a typical calibration exercise at a carrousel-type nitrogen removal plant, parameter subsets ranging from two to eight parameters were selected by this procedure. The procedure proved successful as the parameter subsets thus selected could be estimated accurately from simulated data without and with noise as well as from real data.

However, the procedure is based on a property which is local in parameter space. Consequently, as an a priori assumption on the parameter vales has to be made at the start of the procedure, the selection results might be different from the results which would have been obtained by using the a posteriori parameter values. Hence, the sensitivity towards this a priori assumption was tested explicitly. For this purpose, the parameter space was sampled according to a Latin hypercube sampling scheme and the selection procedure was applied in all sampling points as if these were a priori estimates. From this extensive study it could be concluded that the results of the procedure were not too severely influenced by the a priori assumption on the parameter values. Therefore, the proposed procedure appears to be a powerful and practical tool for efficient and reliable model calibration.
The use of Leca (Light Expanded Clay Aggregates) for the removal of phosphorus from wastewater
Authors: Johansson Lena
Published: May 2018

Increasing attention is being focused on the phosphorus retention capacity of wetlands. Several attempts have been made to improve the reduction of phosphorus in wastewater by the use of constructed wetlands. One way of improving the phosphorus reduction capacity is to use efficient filter materials in the wetland. Leca® (Light Expanded Clay Aggregates) has been tested in Norway, where laboratory and field investigations gave promising results. To further study the chemical removal mechanism of Leca, an experiment utilising five columns was performed. A phosphate solution was applied to the columns intermittently and samples were taken twice a week. Parallel to this study, a P-fractionation experiment was conducted to find out how the phosphate was sorbed to various components of the material. Both experiments showed that only a small amount of the applied phosphate was sorbed by the Leca. The amount sorbed was primarily attached to Al-complexes. In a second column experiment Opoka, a reactive medium rich in CaCO3, was added to Leca and sand to investigate the P-sorption capacity. The results from this investigation showed a higher P-uptake than in the previous column experiment. The lime additive clearly increased the P-sorption and, in this study, Leca in its pure form could be considered as chemically non-reactive.
Recent advances in the data-based modelling and analysis of hydrological systems
Authors: Young Peter C. , Jakeman Anthony J. , Post David A.
Published: May 2018

Hydrological systems present several difficulties for modellers. A data-based approach utilizing objective statistical analysis of output and/or input-output time series behaviour has much to offer, both for understanding of the response dynamics of systems and future hypothesis formulation for improved model structure, as well as good predictive capacity. In this paper, the essential elements and tools of a data-based approach, using an Unobserved Components (UC) model, are presented and illustrated with two examples.
On the necessity of using imprecise probabilities for modelling environmental systems
Authors: Reichert Peter
Published: May 2018

One of the most important problems in the application of methods of parametric statistics to environmental systems is the impossibility of verifying the assumptions on probability distributions (e.g. the assumption of normally distributed measurements is usual but hardly exactly true). If Bayesian techniques are applied, the knowledge of probability distributions is even worse, because also vague prior knowledge (typical in modelling environmental systems) must be formulated in the form of (precise) prior probability distributions of model parameters or model structures. These two examples demonstrate the necessity of using imprecise probabilities in order to avoid arbitrariness in the choice of probability distributions. In spite of these well-known problems, imprecise probabilities are rarely used in environmental systems analysis and prediction. In order to motivate a change of this situation, this paper briefly reviews various techniques for the formulation of imprecise probabilities, and it demonstrates the advantages of using imprecise probabilities in a Bayesian context (for prior distributions and for measurement distributions) with a simple didactical example.
The use of constructed wetlands to upgrade treated sewage effluents before discharge to natural surface water in texel island, The Netherlands – pilot study
Authors: Schreijer M. , Kampf R. , Toet S. , Verhoeven J.
Published: May 2018

Since 1988 experiments have been carried out on a pilot scale on polishing of sewage treatment plant (STP) effluent in a constructed wetland system, a combination of a macrophyte bed and a lagoon. The hydraulic retention time (HRT) has been between one and ten days. At HRTs of 2-3 days a favourable oxygen regime and a high degree of removal of E. coli bacteria could be obtained. The natural alternation of low and high oxygen levels resulted in an extra nitrogen removal from the low levels of nitrogen in the effluent of the STP. Phosphorus removal in the wetland system under these conditions was low, therefore chemical precipitation has to take place in the STP.

The favourable results of the study have led to the construction of a full scale 3.5 ha wetland system for the treatment of 3500 m3 effluent day−1 in 1994. The HRT is 2.1 days at dry weather flow. The purpose of this wetland is to further polish the STP effluent in order to match the water quality of the natural local surface waters.
Nitrogen removal and cycling in restored wetlands used as filters of nutrients for agricultural runoff
Authors: Comín Francisco A. , Romero Jose A. , Astorga Valeria , García Carmen
Published: May 2018

Four restored wetlands dominated by Phragmites australis, Typha latifolia and Scirpus lacustris were used to improve the quality of agricultural runoff in the Delta of the Ebro River (NE Spain) in 1993. The wetlands were continuously flooded with water from a ricefield irrigation network during the growing season and received water with between 0-270 mg m−2d−1 of total nitrogen, 29-105 mg m−2d−1 of dissolved inorganic nitrogen and 0-27 mg m−2d−1 of dissolved organic nitrogen. Surface outflows contained between 0-80 mg m−2d−1 of total nitrogen, 0-12 mg m−2d−1 of dissolved inorganic nitrogen and 1-19 mg m−2d−1 of dissolved organic nitrogen. The nitrogen retention efficiency was close to 100% of the input, except for dissolved organic nitrogen at the end of the growing season. The denitrification rates measured by the acetylene reduction in the sediment ranged between 0 and 3.46 mg N m−2 d−1 and represented between 0 and 12% of the inflowing dissolved inorganic nitrogen. Emergent macrophytes accumulated between 20 and 100 mg N m−2 d−1, which accounts for between 66 and 100% of the inflowing dissolved inorganic nitrogen. The wetland sediment accumulated between 111 and 250 mg N m−2 d−1 during the six month growing season. The removal rate constants calculated according to a first - order plug - flow kinetics, were between 0.01-0.075 m d−1 for total nitrogen and 0.01-0.3 m d−1 for dissolved inorganic nitrogen. Plant uptake, detritus accumulation and decomposition, and nitrogen recycling in the sediment are major processes for nitrogen retention and recycling in the wetlands. This type of wetlands, restored from ricefields, act as highly efficient water polishing filters for agricultural runoff and, at the same time, can contribute to increase the habitat biodiversity of large areas where rice is cultivated extensively.
Constructed wetlands for sludge dewatering
Authors: De Maeseneer Jean L.
Published: May 2018

Helophytes such as the common reed can be used for removing excess water from sludges from different sources such as municipal and industrial wastewaters and from dredging. Several pilot and full-scale studies indicate that the original dry-weight content of municipal wastewater sludge can be increased from about 1% to 40%. Reeds can grow in substrates polluted by several heavy metals without taking up and concentrating excessive amounts of these elements in their above-ground parts. In contrast with terrestrial plants and similar woody plants (willows) reeds can be at the origin of food-chains and so constitute a safe species for dumping sites. Sludge drying by reeds constitutes a sustainable procedure since it does not make use of manmade energy nor chemicals. Being atmosphere driven it is a reliable procedure but, in the short-term, of low predictability.
A critical evaluation of a pilot scale subsurface flow wetland: 10 years after commissioning
Authors: Batchelor Allan , Loots Pierre
Published: May 2018

A pilot scale subsurface flow wetland, commissioned in 1986, has been continuously operated since 1990 at a hydraulic load of 330 mm/day and a corresponding organic load of 1200 kg/ha·day. At these loading rates preliminary evidence suggests that the microbial biomass in the wetland was dominated by anaerobes. Attempts to increase the hydraulic load resulted in surface flooding which was attributed to suspended solids clogging the surface. Despite short circuiting, revealed by tracer studies, COD removal exceeded 70%. The hydraulic flow through the wetland was modelled and was described as modified plug flow with a degree of back mixing. A comparative costing exercise revealed that the unit treatment cost of a combination of a subsurface flow wetland/nitrification column, surface flow wetland was lower than that of an activated sludge system treating the same volume of effluent.
Evaluation of sludge dewatering reed beds: a niche for small systems
Authors: Kim B. J. , Smith E. D.
Published: May 2018

The U.S. Army Construction Engineering Research Laboratories (USACERL) has been developing and adopting improved sludge dewatering systems for U.S. Army wastewater treatment plants. USACERL selected reed beds as the best alternative for future Army sludge dewatering systems based on the system's economical and technical feasibility and on a demonstration of the technology at Fort Campbell, KY, USA.

This paper compares the Army's options for upgrading Fort Campbell's sand-drying beds, analyzes costs, discusses sludge hydraulic and solids loading rate data from existing reed bed operations in the United States, and presents 5 years' operational data from Fort Campbell. Options considered for comparison included: land application of sludge at training fields, wedgewater beds, vacuum-assisted beds, wedgewater beds and composting, mechanical dewatering systems, and a “no change” option in which sand-drying beds would have been retained.

In conclusion, this paper summarizes advantages and limitations of reed bed sludge dewatering. Advantages of reed beds may include: low investment especially when sand-drying beds are converted to reed beds, savings of sludge removal costs, and the benefits inherent to using a simple and economical technology. Limitations may include: large land requirements and little scientific understanding of this empirical technology. The challenge will be to further develop appropriate disposal technologies to meet new U.S. sludge regulations.
Optimum operation of a small sequencing batch reactor for bod and nitrogen removal based on on-line our-calculation
Authors: Johansen N. H. , Andersen J. S. , la Cour Jansen J.
Published: May 2018

A full-scale Sequencing Batch Reactor designed for 200 P.E. has been operated with nutrient removal. In aerated periods of the operational cycle the Oxygen Utilization Rate has been calculated on-line based on a standard oxygen probe which is also used for the control of the oxygen supply. It is described how a simple OUR process control strategy can be applied in order to obtain energy savings and optimization of the plant capacity. OUR has been found to be very valuable for on-line and off-line process control at small nutrient removing waste water treatment plants. A true batch system as the SBR provides the optimum conditions for the installation of OUR process control, but it can also be applied in other alternating activated sludge plants.
Effects of temperature and volatile fatty acids on nitrification-denitrification activity in small-scale anaerobic-aerobic recirculation biofilm process
Authors: Takai T. , Hirata A. , Yamauchi K. , Inamori Y.
Published: May 2018

The purpose of this study is to clarify effects of temperature, volatile fatty acids (VFAs) and recirculation on nitrification-denitrification activity and biota such as nitrifying bacteria in a small-scale domestic wastewater treatment process. Effects of VFAs produced in anaerobic biofilm reactors under various flow-rates and recirculation ratios on nitrifying bacteria were also investigated with laboratory-scale plants on a long-term stable conditions. As a result, at a temperature of 10°C, nitrification activity could be increased about 65% by recirculation and nitrogen removal efficiency was also surely raised. Temperature coefficients of nitrification rate at recirculation ratios of 0 and 4.0 were 1.039 and 1.090, respectively, and that of denitrification was 1.065 at recirculation ratio of 4.0.

High concentrations of VFAs were found in anaerobically treated effluent, especially at 10°C without recirculation, and inhibition of nitrite oxidation and nitrite accumulation were observed in the aerobic biofilm reactor. From batch experiments, VFAs' inhibition constants γ in nitrification activity of aerobic biofilm was calculated, and consumption rates of each VFA was investigated on the condition that denitrification was progressed or not. It was clarified that each VFA did not inhibit ammonium oxidation in observed concentration, but slightly inhibited nitrite oxidation. Acetic acid was used as a carbon source of denitrification at the rate of 17.3mg/mg-SS/hr. On the other hand, propionic acid was not used effectively and denitrification did not occur. It was concluded that the recirculation was indispensable to promote nitrification-denitrification activity and biodegradation of VFAs in the small-scale anaerobic-aerobic biofilm process.
Evaluation of granular activated carbon adsorber design criteria for removal of organics based on pilot and small-scale studies
Authors: Wang Chang-Keun , Lee Sang-Eun
Published: May 2018

The major objective of this research is to determine engineering GAC adsorber design criteria for removal of various organic contaminants found in the 3 drinking water sources in the Keum river basin. Dissolved Organic Carbon (DOC) and UV absorbance at 254 nm were chosen as parameters for overall organics level in raw and treated water. Removal of micropollutants including organophosphorus pesticides, MBAS, volatile organic chemicals (VOCs), phenol and NH3-N were also taken into consideration in bench and/or pilot studies. Treatment efficiencies for target contaminants in three different pilot plants with different raw water quality in the same Keum river basin were compared. Identification and decision of the treatment objectives were found to be important factors for determining design parameters such as GAC bed depth. Range of appropriate bed depth and reactivation frequency for different treatment levels were suggested based on pilot studies.