bluuebunny/crossref_metadata_2025 huggingface dataset:
Full-scale evaluation of an integrated fixed-film activated sludge (IFAS) process for enhanced nitrogen removal
Authors: Randall Clifford W. , Sen Dipankar
Published: May 2018

One of the two trains of the 37,000 m3/d Annapolis, Maryland step aeration activated sludge treatment plant was modified for single-sludge anoxic-aerobic operation, and then fixed-film media were integrated into the aerobic zone to enhance nitrification. Rope-like Ringlace media was selected for integration, and 30,000 meters were installed in a volume of 475 m3 for a pilot demonstration. The purpose of the integrated fixed-film media was to upgrade the short hydraulic retention time (HRT) basin (6 hrs nominal) for efficient, year-round nitrogen removal without construction to increase basin volume. An engineering study had concluded that upgrading the facility for year round complete nitrification, without nitrogen removal, would cost US$24 million. The modified train was operated for 12 months, six in the plug-flow MLE configuration, and six in a step-feed configuration. The integrated Ringlace media increased the nitrification rate per unit volume to 225% of that observed in the control section, attaining a value of 1.75 kg/d NH3-N per linear meter at 15°C. The media also increased denitrification in the aerobic media section to the extent that between 30 and 88% of the nitrates formed in the section were denitrified within it, permitting a potential 25% or more reduction in the volume of the anoxic zone. An IFAS retrofit design was developed which incorporated step-feed operation, and reduced the projected construction cost to US$9.2 million.
Municipal wastewater treatment in Berlin with deep tanks and flotation for secondary clarification
Authors: Gnirss R. , Peter-Fröhlich A. , Schmidt V.
Published: May 2018

For municipal wastewater treatment, space-saving 10m deep activated sludge tanks are an interesting alternative to conventional tanks of shallow construction. Results from pilot tests in the Berlin-Ruhleben WWTP have shown that the biological P-elimination, nutrification and denitrification processes can be implemented as in shallow tanks. However, the activated sludge did not settle satisfactorily. Flotation was implemented in the process for secondary clarification and in the meanwhile has shown to be advantageous. Tests run over a period of some years with the pilot plant have proven the feasibility of this process. Energy requirements for both systems were found to be approximately the same. A cost estimate based on a preplan revealed a 10% advantage in favour of the 10m WWTP with flotation. For these reasons, one 10m WWTP with flotation for secondary clarification and a capacity of 80,000 m3/d will be built in Berlin in the near future.
Developing acceptable sewage screening practices
Authors: Clay Stephen , Hodgkinson Andrew , Upton John , Green Maurice
Published: May 2018

Severn Trent Water screens approximately 1.9 million cubic metres of sewage every day, producing 46000 m3 of screenings annually. Although the company's sludge incinerators are able to burn small quantities of screenings most of the material has to be landfilled.

Over the last few years the company has investigated the areas relating to the development of an environmentally sound disposal strategy at minimum cost. These areas have included the volume and “quality” of screenings produced, the costs of collection, treatment and disposal and the variation of screenings production rates under high flow conditions. Various items of screenings handling equipment have been assessed to identify acceptable options for permanent installations.

The required quality of screenings for economic disposal has been established and a “Quality Factor”, combining biological oxygen demand, density and dryness developed to provide a scientific basis to judge the aesthetic and commercial acceptability of a screenings product. This factor has been tested widely and found to coincide with visual assessment.

Data on the variation of screenings production with sewage flow have been collected to assist with the sizing of future installations.

The information obtained has been used to develop an application matrix for screenings handling equipment at large sewage treatment works.
Simulation of nitrogen removal by step feeding for Istanbul wastewaters
Authors: Görgün E. , Artan N. , Orhon D. , Sözen S.
Published: May 2018

The Metropolitan Area of Istanbul is the major polluter in the Marmara Sea which shows all the indications of a sensitive zone. The adopted wastewater management policy involves biological nitrogen and phosphorus removal at all the discharge points in the area. The Riva plant at the Black Sea coast is designed as a two-stage step feeding system. A model simulation shows that the proposed design cannot meet the effluent standard of 10 mgl−1 total N for the sewage character assessed on the basis of an experimental study, totally different from the one adopted for design.
Volatile organic compounds (VOC) at some sewage treatment plants in Poland
Authors: Suschka Jan , Mrowiec Bozena , Kuszmider Grazyna
Published: May 2018

Volatile organic compounds have been measured at two relatively large sewage treatment plants. Quantitative estimation of benzene, toluene, m.p-xylene, o-xylene and isopropylbenzene have been made for raw sewage, sewage after primary treatment and after biological treatment. Also measurements of 14 different volatile organic compounds in the ambient air, close to screens, and the air above (0.5 m above) aeration tanks have been done. Tests on air stripping of added volatile organic compounds to clean water have been performed in parallel in the laboratory. The removal of examined VOCs in full scale treatment plants was very much below the expected level. In the low loaded activated sludge process the removal was between 2 and 56%, depending on the compound considered. The behavior of volatile organic compounds in laboratory tests was very much different. The concentration of VOCs in the air of rooms where bar racks have been installed was found to be very high. The concentration of toluene in the ambient air could be as high as 460 μg/m3.
Recovery of biological phosphorus removal after periods of low organic loading
Authors: Temmink H. , Petersen B. , Isaacs S. , Henze M.
Published: May 2018

Activated sludge plants for enhanced biological phosphorus removal (EBPR) are often disturbed by short periods of low organic loading. Depending on the exact nature of the disturbance this may result in a partial or complete depletion of the internal PHB stores. PHB and phosphate measurements in a pilot-scale EBPR process show that recovery from such disturbances is slow and temporarily results in high phosphate concentrations. The measurements strongly suggest that the main reason for this slow recovery is a dependency of P-uptake on a slowly rising level of PHB. In a number of batch experiments this dependency of P-uptake on PHB was clearly shown. Also, based on the results of these batch experiments, a more detailed analysis was made of the effect of organic loading and aeration time on EBPR recovery. It is concluded that to obtain EBPR recovery, the aeration time should be carefully adjusted to the organic loading, particularly if the organic loading is low.
Enhanced biological phosphate removal: modelling and design in theory and practice
Authors: Scheer Holger , Seyfried Carl F.
Published: May 2018

The need for Enhanced Biological Phosphorus Removal (EBPR) in wastewater treatment plants (WTP) is increasing so that the development of steady state design models for WTPs using nitrification, denitrification and EBPR becomes more and more important. In developing such a model, theoretical and practical aspects must be considered if the qualitative and quantitative statements regarding the influence of various wastewater conditions (e.g. substrate composition) and surrounding conditions (e.g. influence of nitrate, duration of the anaerobic contact time) affecting EBPR shall be described. The presented EBPR design model is verified using data from various WTPs (e.g. Berlin-Ruhleben) currently using EBPR practices. Sensitivity studies for the most important influencing parameters and surrounding conditions are done, using fictious plant data. Recommendations are given, based on these studies, for the optimization of the EBPR process. These recommendations illustrate the most effective means towards improving the surrounding conditions for EBPR (e.g. increase of amount of readily available organic substrate, decrease of sludge age) with regard to an increase of the biologically removed phosphorus concentration.
Operational factors affecting enhanced biological phosphorus removal at the waste water treatment plant in Helsingborg, Sweden
Authors: Jönsson Karin , Johansson Per , Christensson Magnus , Lee Natuscka , Lie Ewa , Welander Thomas
Published: May 2018

Enhanced biological phosphorus removal (EBPR) has since 1992 been run as a full-scale UCT-process in a part of the waste water treatment plant in Helsingborg. Between June 1993 and July 1994 an extended operational and microbiological investigation was conducted. It was shown that the major phosphorus removal mechanism was biological and that at the most 10% of the soluble phosphorus entering the biological reactor, was removed due to chemical reactions. The VFA-potential in pre-treated waste water has been found to be a key factor. At the waste water treatment plant in Helsingborg 1 mg phosphorus is removed for each 14 mg VFA-potential added. COD, soluble COD and BOD1 are correlated to the VFA-potential, which means that these measurements can be used as operational parameters. If enough VFA-potential is present, the concentration of soluble phosphorus will be lower than 0.3 mg/l in the effluent even at temperatures below 10°C. The mean concentration of soluble phosphorus in the effluent has been 0.29 mg/l during the period October 1993-July 1994. Effluent nitrogen concentration was during the evaluation period between 8–10 mg/l and it was found that PHA was one of the major carbon sources for denitrification. Compared with a pre-denitrification process in combination with simultaneous precipitation, both the filament index and the DSVI were lower in the EBPR process. Other operational factors that affect the process are oxygen and nitrate concentrations in flows to the anaerobic reactor and the degree of internal recirculation from the aerobic to the anoxic reactor.
Biofilm development in a nitrifying trickling filter
Authors: Thörn Marina , Mattsson Ann , Sörensson Fred
Published: May 2018

Two start-ups with a nitrifying trickling filter carrying different substratum densities (157 and 226 m2 m−3) have been made during winter time. The biofilm development time in both cases was approximately 100 days (nitrification rates between 0.6–1.6 gN m−2 d−1 when fully developed) and the pattern of the increase of the nitrification rate was similar during both the biofilm development periods. The substratum density did not affect the nitrification rate, and thus the total amount of ammonium nitrified in the denser material was higher. Microbial parameters were measured during biofilm development in the denser material. The bacteria were more loosely attached to the surface at the beginning of the biofilm development (50% firmly attached), while 80-100% were firmly attached after 20 days. Irreversible attachment was achieved after 20 days. The bacterial size decreased during the initial phase. Microscopic examination showed that the film consisted of both densely populated and empty areas during the biofilm development period, which indicates that the area was not fully used by the microorganisms. The maximum nitrification rate was reached at around 10 gram biofilm dry weight per square metre.
Development of a combined BAC and BZ reactor for removal of nitrogen in wastewater from sludge drying process
Authors: Nishimura Fumitake , Somiya Isao , Tsuno Hiroshi , Iwabu Hideki
Published: May 2018

A combined biological activated carbon (BAC) and biological zeolite (BZ) reactor is under development to remove organics and nitrogen from wastewater which contains both inhibitory organics to nitrification and high concentration of ammonium nitrogen. In this study, the combined BAC and BZ reactor was applied to treatment of scrubber-washed wastewater from sludge drying process. Successful treatment performance was accomplished by decreases in concentrations of the inhibitory organics (in BAC tank) and ammonium nitrogen (in BZ tank) occurred by both adsorption to the mediums and biological reaction. Appropriate nitrogen loading rate for fine and stable treatment was shown to be less than 7 mgNOx−-N · (gGAC · d)−1 for denitrification in BAC tank less than 4 mgHN4+-N · (gZeolite · d)−1 for nitrification in BZ tank. DOC/NOx−-N loading ratio to BAC tank is required to be more than 2.0 mgDOC · (mgNOx−-N)−1 for successful denitrification.
Phosphorus removal by hydrotalcite-like compounds (HTLcs)
Authors: Hang-Sik Shin , Mi-Joo Kim , Se-Yong Nam , Hi-Chung Moon
Published: May 2018

Hydrotalcite-like compounds (HTLCs), which are also called anionic clay minerals or Layered Double Hydroxides (LDHs), can be formulated by M(II)1−xM(III)X(OH)2(An−)X/nyH2O. This chemical, which has anoin exchange capacity, could be an alternative chemical for phosphorus removal. The phosphate uptake by HTLcs containing C1− as the interlayer anion was found to be 2.35-2.83 meq of P/g. The most serious obstacle anion against phosphate uptake was bicarbonate because the selectivity of carbonate by LDH is the highest. To investigate the possibility of LDH's recycle employing the “Memory effect”, calcined LDH (CLDH) was repeatedly used for 6 times. From the fifth time, the final phosphate uptake capacity decreased. The consecutive reconstruction mechanism of CLDH is not yet known but it is certain that the possibility of LDH's recycle is promising.
Biological nutrient removal from a phosphorus-rich pre-fermented industrial wastewater
Authors: Comeau Yves , Lamarre Daniel , Roberge François , Perrier Michel , Desjardins Gaétan , Hade Claude , Mayer Raymond
Published: May 2018

The objective of this work was to demonstrate the feasibility and to quantify the maximum extent of enhanced biological phosphorus (bio-P) removal from a phosphorus-rich (60 to 100 mg P/L) wastewater originating from a cheese factory (2100 mg total COD/L; 57 mg total TKN-N/L). An existing wastewater treatment plant at the industrial site consisted of an anaerobic equalization tank followed by an anaerobic upflow sludge blanket (UASB) and aerated lagoons. In a bench-scale sequencing batch reactor, bio-P removal was better achieved by treating the effluent from the equalization tank in which a high level of volatile fatty acids were produced (1230 mg as HAc/L) rather than the effluent from the UASB. The effluent orthophosphates concentration reached as low as 5 mg P/L. An intracellular polyphosphates content in the biomass greater than 5% (g P/g MLVSS) was observed which demonstrated without doubt that bio-P removal, and not just normal metabolic phosphorus accumulation, took place. Optimizing industrial bio-P removal should consider prior acidogenesis of the influent wastewater, acetate or chemical addition, and an efficient control over effluent suspended solids.
Nitrous oxide emission during nitrification and denitrification in a full-scale night soil treatment plant
Authors: Itokawa Hiroki , Hanaki Keisuke , Matsuo Tomonori
Published: May 2018

Nitrous oxide (N2O) emissions from nitrification-denitrification processes in a full-scale night soil treatment plant were measured, and patterns and control of the N2O production were investigated. Estimated N2O emissions ranged from 4.4 to 1,190 gN/(m3 of influent), corresponding to a conversion ratio of influent nitrogen to N2O-N of 0.24-55%. N2O was produced in the intermittent aeration tank (IAT) where nitrification and denitrification were carried out alternately. The produced N2O was either stripped out to the off-gas or remained in the effluent in dissolved form. The former accounted for more than 99.5% of the total emissions. The latter flowed into the following anoxic tank, where 60-98% of N2O was reduced. A significant difference in the extent of N2O supersaturation in mixed liquor of IAT was observed between the cases of high and low N2O emissions. In IAT, N2O tended to be produced discretely either in aerobic or in anoxic phases. It seemed that the completeness of nitrification and denitrification in IAT, indicated from a mass balance between NH4-N and NO3-N and from NO2-N accumulation in mixed liquor of IAT, was one of the important factors affecting the N2O production. This completeness was decided by the time ratio of aerobic and anoxic phases. External addition of methanol to IAT seemed to reduce N2O emissions.
Thermal hydrolysis for the production of carbon source for denitrification
Authors: Barlindhaug John , Ødegaard Hallvard
Published: May 2018

Thermal hydrolysate is the liquid fraction (supernatant) of thermally treated wastewater sludge. Based on a literature study, a factorial design experiment was carried out in order to investigate important condition-variables in the thermal hydrolysis step. The objective of the study was to investigate the influence on composition and amount of produced thermal hydrolysate, as well as the influence on the quality of hydrolysate as carbon source for denitrification, from varying hydrolysis conditions. The thermal hydrolysis experiments demonstrated that carbohydrates are the organic fraction that is most easily decomposed, while proteins are most easily solubilized. A small increase in the content of VFA was found during thermal hydrolysis, while fat did not seem to be affected. The varying hydrolysis conditions resulted in varying content of the produced hydrolysate, but the quality of the hydrolysate as carbon source did not vary dramatically with varying hydrolysis conditions.
Nitrogen removal from digester supernatant - comparison of chemical and biological methods
Authors: Siegrist H.
Published: May 2018

Physical/chemical elimination of ammonium from digester supernatant with magnesium-ammonium-phosphate (MAP) precipitation and with air stripping is investigated in pilot scale and compared with separate intermittent denitrification, denitrification in wastewater treatment and in tertiary filtration. MAP-precipitation is feasible but most expensive due to required chemicals as well as dewatering and drying of the precipitate. Air stripping is slightly cheaper, but still more expensive than biological treatment due to the complex process, cost of chemicals and reconditioning of the ammonium sulfate solution to a fertilizer product. In nutrient removal plants the additional nitrogen from the digester supernatant can be eliminated by increasing the anoxic volume or using a carbon source. Denitrification with methanol will be the cheapest solution with today's methanol price. If digester supernatant inhibits nitrification substantially or if the anoxic zone is too small for organic carbon addition a separate intermittent denitrification with addition of a carbon source, as used in some treatment plants in Scandinavia, might be a good solution.
Nutrient removal using a combined process with activated sludge and fixed biofilm
Authors: Su J. L. , Ouyang C. F.
Published: May 2018

A new nutrient removal system combining activated sludge with fixed biofilm was developed in this work. Fully and partially submerged rotating biological contactors (RBC) were added in the anaerobic, anoxic and aerobic reactors, respectively. The pilot-scale plant was fed synthetic municipal wastewater with the different operating parameters (i.e., hydraulic retention time, return sludge ratio and mixed liquid recycle ratio) to evaluate its performance. High degree performances of nutrient removal were obtained in the experiments. The specific substrate utilization rates in each reactor were also conducted in this work. The kinetic behaviours presented in the combined process were similar to the performance in a single sludge system. The biokinetics of a single sludge system can also be applied to the system that combines biofilm and activated sludge.
Separate management of anthropogenic nutrient solutions (human urine)
Authors: Larsen Tove A. , Gujer Willi
Published: May 2018

Anthropogenic Nutrient Solution (ANS, Urine) adds about 75% of the nitrogen and 50% of the phosphorus to domestic wastewater. It is proposed to collect ANS at the source and release it sequentially, so that it arrives all at the same time at the treatment plant where it could be treated separately. The proposed system would have many advantages relative to the conventional technology. A stepwise transition from the conventional to the proposed technology would slowly improve system performance.
Predictive control of sewer systems by means of grey-box models
Authors: Carstensen Jacob , Nielsen Marinus K. , Harremoës Poul
Published: May 2018

Grey-box modelling is a new methodology which can be used for obtaining important information from on-line data. This information can be used in control for optimizing the performance of the sewer system as well as the treatment plant during rain events. The objective is to minimize the effect from discharges on the receiving water without increasing the risk of flooding. This is the concept used in the control part of the EUREKA-financed project MUST.
Nitrogen removal upgrade of a wastewater treatment plant within existing reactor volumes: A simulation supported scenario analysis
Authors: Coen F. , Vanderhaegen B. , Boonen I. , Vanrolleghem P. A. , Van Eyck L. , Van Meenen P.
Published: May 2018

A simulation supported scenario analysis for the upgrading of a municipal WWTP Hoogstraten (Belgium) with nitrogen removal is presented. The most cost-effective solution is to create optimal aerobic and anoxic conditions within the existing reactor volumes. The IAWQ-model No. 1 was used for the simulation of the biological reactor. A measuring campaign and some specific respirometric tests provided the necessary information for calibration and verification of the biological model.

The study consisted of two parts: 1) increase of the denitrification capacity, and 2) optimisation of operation. First, the impact of three measures, i.e. creation of anoxic zones, implementation of step feeding and introduction of internal recirculation, was evaluated by means of simulation. For this purpose a standard time variant influent was defined based on the measuring campaign. This approach made it easy to compare the different scenarios.

In the second part of the study some specific problems were handled. To avoid high nitrate concentrations during weekends three possible control actions were simulated. The simulation study also evaluated the usefulness of the primary clarifier in the upgraded design and the effect on the biological process of first flush during intensive rainfall.
A full-scale operation of a novel activated sludge process without excess sludge production
Authors: Yasui H. , Nakamura K. , Sakuma S. , Iwasaki M. , Sakai Y.
Published: May 2018

The authors have presented a new concept of excess sludge elimination treatment with recirculation of sludge via ozonation in the activated sludge process. This paper is intended to clarify the potential application of the process to municipal and industrial wastewater treatments. In a full-scale operational experiment lasting 10 months under 550 kg/d of BOD loading, no excess sludge was needed to be withdrawn and no significant accumulation of inorganic solids occurred in the aeration tank. Most of the inorganic compounds in the sludge were released to the soluble phase. Material balance indicated that one-third of ozonated sludge was mineralized via the recirculation treatment, and thereby the requirement of sludge mass to be treated was 3.3 times as much as sludge to be eliminated. Effluent TOC was slightly higher than under the conventional activated sludge process, indicating that refractory TOC was released from the sludge eliminated by treatment. The amount of released TOC corresponded to less than 2 weight % of eliminated sludge under recirculation rates below 30% of total biomass in the aeration tank in a day, but increased at higher recirculation rates. The operation costs associated with the process were estimated to be lower than those of conventional dewatering and disposal.
Capillary suction time (CST) as a measure of sludge dewaterability
Authors: Chen G. W. , Lin W. W. , Lee D. J.
Published: May 2018

The feasibility of employment of capillary suction time (CST) for characterizing the dewaterability of excess activated sludges was examined. The CST was shown as a good index for sludge filterability, if only the product of solid concentration and average specific resistance is of interest. On the other hand, the bound water content cannot be directly evaluated from the CST data.
Case study involving using fluidised bed incinerator sludge ash as a partial clay substitute in brick manufacture
Authors: Anderson Michael , Skerratt R. Glynn , Thomas Julian P. , Clay Stephen D.
Published: May 2018

Earlier work at Staffordshire University revealed encouraging results when sewage sludge ash from a fluidised bed incinerator was added to a series of common commercial brickclays used in the United Kingdom. The results of this work led a United Kingdom brick manufacturer to the identification of this material as a possible replacement for the sand addition to the bricks produced at one of their factories. As a result, an experimental programme was formulated at Staffordshire University's Ceramic Technology Laboratory which used the factory's current mix-design as a control standard against a mix-design in which the sand component was replaced weight-for-weight with sewage sludge ash. Comparative bodies were fabricated and both laboratory and factory firings undertaken. Physical testing results have revealed that the experimental mix-design containing the sewage sludge ash contributes positively to the ceramic properties of the control product in both the unfired and fired condition. Moreover, the fired colour of this experimental product has also been found to be indistinguishable from the control.
Physical properties of dewatered wastewater sludge for landfilling
Authors: Koenig A. , Kay J. N. , Wan I. M.
Published: May 2018

In the context of landfilling dewatered wastewater sludge in Hong Kong, with landfills up to 140 m high, one of the most significant properties of sludge is its physical nature with regard to moisture characteristics and associated geotechnical stability. Commonly, lower limits are set on total solids content, but no geotechnical stability criteria are applied with the exception of Germany where a minimum requirement for vane shear strength is set at 25 kN/m2. The purpose of this study was to determine and evaluate dewatered wastewater sludge from three Hong Kong municipal wastewater treatment plants with regard to the following physical and geotechnical properties: (i) vane shear strength; (ii) consolidation characteristics such as compression index, compressibility factor, coefficient of consolidation and compressibility coefficient; and (iii) hydraulic characteristics such as permeability and intrinsic resistance. Although dewatered sludge exhibits quite different characteristics as compared to soils, predictive logarithmic relationships may be established between various properties which are consistent with the critical state model for soils, conventional filtration and consolidation theory. Such representation provides a valuable basis for understanding the sludge characteristics and behaviour to landfill design.
Biological treatment of airstreams contaminated with VOCs: an overview
Authors: Edwards Findlay G. , Nirmalakhandan N.
Published: May 2018

Biological treatment of contaminated airstreams is a technology which has been used successfully in Germany and The Netherlands for twenty years. The technology can be utilized in a wide array of industries to treat numerous volatile chemicals. There are three categories of air phase bioreactors: biofilters, biotrickling filters, and bioscrubbers. Addition of nutrients and buffer capacity may be required. Many different types of support media can be used. Currently, design of airphase bioreactors is based upon guidelines, pilot studies, and experience gained from similar applications.
The potential impact of soil carbon content on ground water nitrate contamination
Authors: Adelman D. D. , Tabidian M. A.
Published: May 2018

A potential buildup of nitrate in the ground water resources of the eastern Sandhills of Nebraska has been projected to occur due to the intensive use of nitrogen fertilizer on irrigated cropland. A root-zone nitrate leaching study in this area revealed that soils with a high carbon concentration had minimal leaching compared to soils with lower concentrations. Soils high in carbon have an active population of denitrifying bacteria possibly causing denitrification and in turn reduction of nitrate leaching. Denitrifying bacteria are principally heterotrophic using soil organic carbon for both an energy and carbon source. The objective of this research was to interpret how root-zone denitrification affected nitrate leaching and ground water contamination by nitrate. A modified version of a solute transport model developed for the Eastern Sandhills was used to assess the risk of nitrate contamination for combinations of fertilizer and irrigation rates and for various soil carbon levels.

The first attempt was to make risk assessment with eight farm management practices for cells with increasingly greater carbon levels until only those cells with the greatest carbon level were kept in production. Results of this assessment showed that even with excessive fertilizer and irrigation rates, risk of nitrate leaching was reduced as the minimum carbon level was increased. However, since less cropland was leaching nitrate with each successive risk calculation, the impact that root-zone denitrification had in nitrate leaching reduction could not be definitively determined. This prompted a model modification of the risk calculation procedure which kept all cropland in production and computed nitrate leachate risk for increasingly higher artificial carbon levels during successive risk calculations. Changing carbon levels was still more detrimental on nitrate leaching rates than changing farm management practices.
Incorporation of spatial variability in modeling non-point source groundwater nitrate pollution
Authors: Goderya F. S. , Dahab M. F. , Woldt W. E. , Bogardi I.
Published: May 2018

A methodology for incorporation of spatial variability in modeling non-point source groundwater nitrate contamination is presented. The methodology combines geostatistical simulation and unsaturated zone modeling for estimating the amount of nitrate loading to groundwater. Three dimensional soil nitrogen variability and 2-dimensional crop yield variability are used in quantifying potential benefits of spatially distributed nitrogen input. This technique, in combination with physical and chemical measurements, is utilized as a means of illustrating how the spatial statistical properties of nitrate leaching can be obtained for different scenarios of fixed and variable rate nitrogen applications.
Influence of acid deposition on water quality in the sous reservoir
Authors: Macek Lubomír , Grünwald Alexander
Published: May 2018

The article deals with the changes of water quality in the surface water of the Jizera Mountains in the period of 1982–1993, caused by atmospheric deposition of sulphur. This northern part of Czech Republic is very sensitive to acidic deposition. In the central area of the mountains the artificial planted spruce monocultures had to be cut down. The comparison of pH, aluminium and sulphate concentrations is presented. The changes of water quality were studied also by the linear correlation coefficient applying on two period: 1983–1987 and 1988–1992. Finally the simple model for reacidification of the water in the reservoir is used to demonstrate the effect of liming.
Impact of acidification on structural organization of phytoplankton community in the forest lakes of the north-western Russia
Authors: Korneva L. G.
Published: May 2018

The response of the phytoplankton to different degree of pH was studied by the example of 7 shallow weakly mineralized forest lakes located in the Darwin National reserve on the north shore of the Rybinsk reservoir (north-western Russia). With a decrease of pH the number of phytoplankton species decreased especially among centric diatoms,blue-greens and Euglenophyta, total biomass of phytoplankton and its seasonal dispersion declined. Green algae, chrysomonades and cryptomonades biomass correlated negatively with pH but diatoms and blue-greens biomass were related positively to pH. The drop in pH produced a decrease of Shannon-Weaver diversity index, obtained from biomass and cell volume of algae, increase of Simpson index and algae size. The growth of phytoplankton did not correspond the total phosphorus. The necessary modifications to the structural characteristics of phytoplankton by the acidification came about in the pH range from 6 to 5.
Sludge production and oxygen demand in nutrient removal activated sludge systems
Authors: Barker P. S. , Dold P. L.
Published: May 2018

Results of model simulations indicate that without the assumption of COD loss, predictions of oxygen consumption and volatile suspended solids production are significantly over-estimated for biological excess phosphorus removal (BEPR) activated sludge systems (and to a lesser extent anoxic-aerobic systems). These systems apparently consume less oxygen and produce less volatile solids than aerobic systems for the same amount of COD removal. A general model for biological nutrient removal systems has recently been presented by Barker and Dold. Three mechanisms for COD loss are suggested, based on results of COD balances for different types of activated sludge system. Model simulation results with and without the assumption of COD loss are discussed, as well as the influence of influent COD composition on predictions of volatile suspended solids concentration/production and oxygen consumption.
Symbiosis and competition among sulfate reduction, filamentous sulfur, denitrification, and poly-p accumulation bacteria in the anaerobic-oxic activated sludge of a municipal plant
Authors: Yamamoto-Ikemoto Ryoko , Matsui Saburo , Komori Tomoaki , Bosque-Hamilton E. J.
Published: May 2018

Symbiosis and competition were examined among sulfate reducing bacteria (SRB), filamentous sulfur bacteria (FSB), denitrification bacteria (DNB) and poly-P accumulation bacteria (PAB) in the activated sludge of a municipal plant operated under anaerobic-oxic conditions. Batch experiments were carried out using settled sewage from the same plant as the substrate under several conditions. Under oxic conditions, both sulfate reduction and sulfide oxidation occurred simultaneously, making a symbiotic relationship of SRB and FSB for establishment of a sulfur cycle sustaining the energy requirements. Under anoxic conditions, denitrification was dominant because DNB outcompeted PAB and SRB for organic acids. Under anaerobic conditions, phosphate release and sulfate reduction occurred simultaneously. SRB produced for moles of acetate from four moles of propionate and/or unknown substances by reduction of three moles of sulfate. PAB competed with sulfate-reducing bacteria for organic acids such as propionate. However, PAB utilized acetate produced by SRB.
Accumulation of DNA in the exopolymeric matrix of activated sludge and bacterial cultures
Authors: Palmgren Rikke , Nielsen Per Halkjær
Published: May 2018

More deoxyribonucleic acid (DNA) was measured than could be accounted for by cell counts in activated sludge flocs, a mixed culture of sludge bacteria, and a pure culture of Pseudomonas putida. This means that estimations of cell number or biomass by measurement and correlation with DNA content will result in an overestimation of the cell number or biomass by up to a factor 10. There could be four reasons for the fact that the DNA was present: There were no specific enzymes present that degrade DNA (DNAses), DNAses were inhibited by humic or humic-like substances, the DNA was protected by coiling with metal ions or the turnover of DNA was very high. For activated sludge it is unlikely that there were no DNAses present but inhibition of DNAses and protection of DNA by metal ions are the most probable reasons why the DNA stays in the systems. The DNA was found in the activated sludge floc exopolymeric matrix whereas DNA from the bacterial cultures was found mainly in the bulk phase (in the slimes).
Minimisation of biomass in an extractive membrane bioreactor
Authors: Strachan L. F. , Freitas dos Santos L. M. , Leak D. J. , Livingston A. G.
Published: May 2018

Many traditional biological methods for the treatment of wastewater cope poorly with toxic, volatile organic compounds. The extractive membrane bioreactor is a novel process for the treatment of industrial wastewaters containing such compounds which combines extraction across a silicone rubber membrane with biodegradation. Previous work has shown that there is a problem in this system with excess biofilm growth on the membrane surface, resulting in reduced flux of organic substrate across the membrane. The work presented here shows that addition of sodium chloride to the biomedium increases the maintenance energy requirement of the degradative microorganisms and results, in a carbon-limited situation, in a reduction in biofilm growth. Flux of organic substrate was shown to remain high under reduced biofilm growth conditions.
Bulking and foaming caused by microthrix parvicella at three large sewage treatment plants in the greater stockholm area
Authors: Westlund Åsa Dillner , Hagland Eva , Rothman Maria
Published: May 2018

Microbiological studies of the activated sludge have been performed continuously at three of the largest sewage treatment plants in Stockholm (Bromma, Henriksdal and Himmerfjärdsverket). All three plants are operated with nitrogen removal. The filamentous organism Microthrix parvicella has been observed at all plants during the study. Large bulking and foaming problems have only been observed at Himmerfjärdsverket although Himmerfjärdsverket is operated at a higher F/M ratio and a lower aerated sludge age than Henriksdal. Bulking has mainly occured at filament abundances above 3 (relative scale 0-6, 0; none, 6; excessive). Large variations in the settleability of the sludge have been observed in the case of sludge collected from different periods but with the same filamentous abundance. The structure of the flocs and the location of the filaments within the flocs have a major impact on the final settleability of the sludge. Foaming in the activated sludge caused by Microthrix parvicella has only been observed at filamentous abundance above 3. During this study, Microthrix parvicella has been observed in the activated sludge when the plant is operated with an aerated sludge age above 3 days and F/M ratios below 0.3 kg BOD7/kg MLSS, day. Operation with a low F/M ratio can be obtained without excessive growth of Microthrix parvicella.
A mathematical model for the optimal design and operation of an anaerobic co-digestion plant
Authors: Bozinis N.A. , Alexiou I.E. , Pistikopoulos E.N.
Published: May 2018

The anaerobic co-digestion of high strength industrial wastewaters in centralised plants receiving effluents from various local small scale industries is considered to be superior than individual small scale treatment plants. An approach is proposed to systematically tackle co-digestion problems, with respect to both biological and engineering models. In a steady-state mathematical model presented, the effect of combining wastewaters in mixtures, based on major component groups (i.e. lipids, hydrocarbons and proteins), is systematically accounted for. The model is then solved via a non-linear optimisation program (NLP) which results in the determination of an optimal design of the necessary reactors and their respective layout, by balancing the natural trade-offs between reactor and post-treatment costs (due to high pollutants emissions). The preparation of appropriate mixtures is the major parameter controlled. The applicability and potential of the model are demonstrated with a small example.
Methanogenic activity and performance of UASB, DSFF and USFF reactors
Authors: Jawed Mohammad , Tare Vinod
Published: May 2018

This paper presents correlation of methanogenic activity with performance of bench scale models of UASB, DSFF and USFF reactors at varying OLRs while maintaining EBHRT in the range of 0.80-1.10 d. At lower OLR, performance of the reactors appears to be similar. However, at higher OLR, the performance of DSFF and USFF reactors is fairly steady whereas UASB reactor shows poor performance in terms of methane production. This is in conformity with methanogenic activity test results. The results of AMA and TMA tests also reveal that at higher OLR, acetoclastic methanogens population decreases considerably in UASB reactor and a large fraction of methane is produced due to the activity of non-acetoclastic methanogens.
Prediction of dissolved oxygen concentration along sanitary sewers
Authors: Matos J. Saldanha , de Sousa E. Ribeiro
Published: May 2018

The oxygen balance in wastewater collection systems is important in respect to the degree of biological oxidation that occurs within the stream and in respect to the control of septicity and its effects. In this paper, a simple mathematical model is presented, in order to predict dissolved oxygen concentration profiles along sanitary sewers.

The mathematical model was developed based on an analytical solution of the simple differential equation of dissolved oxygen balance in sewers, and includes an empirical expression for prediction of dissolved oxygen transfer to the slime layer on the pipe walls.

Because the factors controlling dissolved oxygen balance in sewers are so complex, it would be unrealistic to expect, that with this rather simple model, dissolved oxygen concentrations can be accurately predicted. Nevertheless, it is reasonable to suppose that the predictions may be adequate for some design and operation purposes.
Genotoxicity of influents and effluents of the wastewater treatment plant
Authors: Filipic M. , Toman M. J.
Published: May 2018

Wastewaters are treated through different processes of wastewater treatment procedures. Nevertheless they often contain mutagens especially when the proportion of industrial wastewater in comparison to municipal wastewater is high.

In this study we evaluated mutagenic potential of influents and effluents from a wastewater treatment plant that is processing both industrial and domestic wastewater. The mutagenicity of XAD-2 extracts of influent and effluent was evaluated by means of Ames test using S. typhimurium strains TA100 and TA98 in the presence and in the absence of metabolic activation. Extracts that were mutagenic to strain TA98 without metabolic activation were suspected to contain nitropolyaromatic hydrocarbons (nitro-PAHs). To confirm this hypothesis they were tested with nitroreductase (TA98NR) and O-acetiltransferase (TA98/1,8DNP6) deficient derivatives of strain TA98, that are resistant to nitropolyaromatic hydrocarbons. The nitroreductase deficient strain TA98NR was less sensitive to the mutagenic extracts of influent than the parent strain TA98. The O-acetiltransferase deficient strain TA98/1,8DNP6 was resistant to the mutagenic extracts of influent. The mutagenic extracts of the effluent were nearly equally mutagenic to the parent strain TA98 and both deficient strains TA98NR and TA98/1,8DNP6.

On the basis of the responses of nitroreductase deficient strains on the influent and effluent it was concluded that the influent contained nitro-PAHs. These were not removed or inactivated during the biological treatment of the wastewater, but activated to the final nucleophylic form able to induce mutations strain TA98 and in its nitroreductase deficient derivatives TA98NR and TA98/1,8DNP6.
A laboratory study of sediment phosphorus flux in two tropical reservoirs
Authors: Appan Adhityan , Ting Ding-Sie
Published: May 2018

The prevailing levels of dissolved oxygen, pH and temperature in a sediment-water interface largely influence the sediment nutrient flux in waterbodies. The main objective of this study is to appraise the interaction between the aquatic sediment in two tropical reservoirs and the overlying water in simulated laboratory conditions. In actuality, these two reservoirs were subjected to highly varying nutrient inputs. Sediment and water samples were collected from both the reservoirs for laboratory simulation tests. Perspex columns were used as reaction chambers to study the effect of dissolved oxygen levels and pH values on sediment nutrient flux over a period of 60 days under controlled conditions. In the oxic chambers, DO levels were maintained within 7.5 mg/L to 7.7 mg/L whereas DO levels of less than 1 mg/L were maintained in anoxic chambers using argon gas. The concentrations of orthophosphate and total phosphorus in the overlying waters increased significantly in the anoxic chambers for both reservoirs though release rates in Kranji Reservoir sediments were 1.5 to 19.5 times greater than those in MacRitchie Reservoir. The highest total phosphorus release rates prevailed in Kranji and were 13.5 to 14.8 mg/m2.d at pH values of 5 and 9, respectively. These release rates are marginally lower than those reported in other in situ experiments. It can be concluded that the DO and pH are important in controlling the sediment nutrient flux, particularly in anaerobic or highly alkaline conditions, and hence will influence considerably the quality of the overlying waters in tropical reservoirs.
General characteristics and fractions of phosphorus in aquatic sediments of two tropical reservoirs
Authors: Ding-Sie Ting , Appan Adhityan
Published: May 2018

The availability of phosphorus (P) for the growth of phytoplankton in waterbodies is generally believed to be the controlling factor in eutrophication. The objective of this study was to quantify fractions of phosphorus so as to determine the potential of aquatic sediment as a source of phosphorus supply. Surface sediments from two of the reservoirs in Singapore were collected, analyzed and the general characteristics investigated. Fractionation of phosphorus was carried out to determine the various components such as NH4Cl-P, NAI-P, Apatite-P and Residual-P. In the sediments from MacRitchie Reservoir, total phosphorus (TP) concentrations, in terms of dry weight (dw) of sediment, ranged from 211 μg P/g dw to 448 μg P/g dw. Besides, Residual-P formed the major component in the sediments (74.4% to 81.8% of TP). The P bound with Fe and Al varied from 18.0% to 25.1%. But, in the Kranji Reservoir, the TP concentrations in the sediments were found to be four-to eight-fold higher (1640 μg P/g dw to 1885 μg P/g dw) than that from MacRitchie Reservoir, and the Residual P only accounted for 28.2% to 39.2% of TP. However, the P bound with Fe and Al, was the dominant component (53.0% to 63.0%) of TP. This fraction of phosphorus could be released for the growth of phytoplankton when anoxic conditions prevail at the sediment-water interface. It can be concluded from this fractionation study that sediments in Kranji Reservoir have a larger pool of potential phosphorus supply to support the growth of phytoplankton in the waterbody.