Showing papers in "Reviews in Environmental Science and Bio\/technology in 2004"

Assessment of the anaerobic biodegradability of macropollutants

Abstract: A variety of test procedures for determination of anaerobic biodegradability have been reported. This paper reviews the methods developed for determination of anaerobic biodegradability of macro-pollutants. Main focus is paid to the final mineralization of organic compounds and the methane potential of compounds. Hydrolysis of complex substrates is also discussed. Furthermore, factors important for anaerobic biodegradation are shortly discussed.

Recent Findings on the Phytoremediation of Soils Contaminated with Environmentally Toxic Heavy Metals and Metalloids Such as Zinc, Cadmium, Lead, and Arsenic

Abstract: Due to their immutable nature, metals are a group of pollutants of much concern. As a result of human activities such as mining and smelting of metalliferous ores, electroplating, gas exhaust, energy and fuel production, fertilizer and pesticide application, etc., metal pollution has become one of the most serious environmental problems today. Phytoremediation, an emerging cost-effective, non-intrusive, and aesthetically pleasing technology, that uses the remarkable ability of plants to concentrate elements and compounds from the environment and to metabolize various molecules in their tissues, appears very promising for the removal of pollutants from the environment. Within this field of phytoremediation, the utilization of plants to transport and concentrate metals from the soil into the harvestable parts of roots and above-ground shoots, i.e., phytoextraction, may be, at present, approaching commercialization. Improvement of the capacity of plants to tolerate and accumulate metals by genetic engineering should open up new possibilities for phytoremediation. The lack of understanding pertaining to metal uptake and translocation mechanisms, enhancement amendments, and external effects of phytoremediation is hindering its full scale application. Due to its great potential as a viable alternative to traditional contaminated land remediation methods, phytoremediation is currently an exciting area of active research.

Calcium carbonate scale formation and control

Abstract: This paper focuses on the complex problem of calcium carbonate scale formation on heated surfaces and the possibilities of controlling or reducing this problem. The development of scale is a multistage process and is affected by a number of factors, these include supersaturation, pH, temperature and flow velocity. Calcium carbonate deposition can be ameliorated by chemical, physical or biological methods with various level of effectiveness. These controls can be divided into three main categories: those that affect solubility, those that alter the growth mechanism of crystals, and those that change the potential of a surface to foul. One of the most effective methods of controlling crystallization fouling is the addition of chemical inhibitors to potentially scaling waters. There are a number of alternative non-chemical treatment options available, amongst these are the use of magnetic, electronic and electrolytic treatment devices. Scale formation is affected by the physical nature of the material on which it is forming, therefore it is possible to choose material to reduce scale formation. Each of these scale controlling methods has their advantages and a number of factors have to be considered before choosing the right option.

Biodegradability of chlorinated solvents and related chlorinated aliphatic compounds

Abstract: The biodegradability of chlorinated methanes, chlorinated ethanes, chlorinated ethenes, chlorofluorocarbons (CFCs), chlorinated acetic acids, chlorinated propanoids and chlorinated butadienes was evaluated based on literature data. Evidence for the biodegradation of compounds in all of the compound categories evaluated has been reported. A broad range of chlorinated aliphatic structures are susceptible to biodegradation under a variety of physiological and redox conditions. Microbial biodegradation of a wide variety of chlorinated aliphatic compounds was shown to occur under five physiological conditions. However, any given physiological condition could only act upon a subset of the chlorinated compounds. Firstly, chlorinated compounds are used as an electron donor and carbon source under aerobic conditions. Secondly, chlorinated compounds are cometabolized under aerobic conditions while the microorganisms are growing (or otherwise already have grown) on another primary substrate. Thirdly, chlorinated compounds are also degraded under anaerobic conditions in which they are utilized as an electron donor and carbon source. Fourthly, chlorinated compounds can serve as an electron acceptor to support respiration of anaerobic microorganisms utilizing simple electron donating substrates. Lastly chlorinated compounds are subject to anaerobic cometabolism becoming biotransformed while the microorganisms grow on other primary substrate or electron acceptor. The literature survey demonstrates that, in many cases, chlorinated compounds are completely mineralised to benign end products. Additionally, biodegradation can occur rapidly. Growth rates exceeding 1 d-1 were observed for many compounds. Most compound categories include chlorinated structures that are used to support microbial growth. Growth can be due to the use of the chlorinated compound as an electron donor or alternatively to the use of the chlorinated compound as an electron acceptor (halorespiration). Biodegradation linked to growth is important, since under such conditions, rates of degradation will increase as the microbial population (biocatalyst) increases. Combinations of redox conditions are favorable for the biodegradation of highly chlorinated structures that are recalcitrant to degradation under aerobic conditions. However, under anaerobic conditions, highly chlorinated structures are partially dehalogenated to lower chlorinated counterparts. The lower chlorinated compounds are subsequently more readily mineralized under aerobic conditions.

Chelate-Enhanced Phytoremediation of Soils Polluted with Heavy Metals

Abstract: In general, hyperaccumulators are low biomass, slow-growing plants. High biomass non-hyperaccumulator plants by themselves are not a valid alternative for phytoextraction as they also have many limitations, such as small root uptake and little root-to-shoot translocation. In this context, chemically-induced phytoextraction (based on the fact that the application of certain chemicals, mostly chelating agents, to the soil significantly enhances metal accumulation by plants) has been proposed as an alternative for the cleaning up of metal polluted soils. But chelate-induced phytoextraction increases the risk of adverse environmental effects due to metal mobilization during extended periods of time. In order to minimize the phytotoxicity and environmental problems associated with the use of chelating agents, nowadays, research is being carried out on the gradual application of small doses of the chelating agent during the growth period. However, EDTA utilization in the future will most likely be limited to ex situconditions where control of the leachates can be achieved. There are other mobilizing agents which are much less harmful to the environment such as citric acid, NTA, and particularly EDDS. Research should also be aimed towards more innovative agronomic practices. Environmentally safe methods of chelate-induced phytoextraction must be developed before steps towards further development and commercialization of this remediation technology are taken. Most importantly, more applied projects in this field are needed to clarify the real potential and risks of this technology.

Methods of assessing microbial activity and inhibition under anaerobic conditions: a literature review

Abstract: This work reviews the existing methodologies for assessing microbial activity and inhibition under anaerobic conditions. The anaerobic digestion process consists of several metabolic steps–the Anaerobic Digestion Model No. 1 (ADM1) has attempted to describe these steps in the form of a mathematical model with the intention of providing a reference base for all further efforts in the modelling of anaerobic processes. The existence of a reference point for modelling has highlighted the fact that there is a lack of coherence between the many different methodologies for experimentally assessing anaerobic activity and inhibition. A working group of the International Water Association was recently founded to harmonise the existing methodologies with the ultimate intention of developing a unified reference procedure– a primary objective of the group will be the establishment of a standard terminology in the field of anaerobic digestion, activity and inhibition assessment. Secondly, it will compare the existing methodologies and develop standard protocols for assessing the kinetic parameters (e.g. maximum uptake rate, half-saturation constant) of anaerobic processes that may be entered directly into ADM1 and its successors. This paper revises and enlarges a contribution presented by the authors at the workshop “Harmonisation of anaerobic biodegradation, activity and inhibition assays” (Ligthart & Nieman 2002, Proc. workshop held in Orta (Italy) June 7–8, 2002) and aims to promote a clear understanding of the currently established methodology. Numerous methods have been developed over the past 30 years, since Van den Berg et al. (1974, Biotechnol Bioeng 16(11)– 1459–1469) measured methanogenic activity, by using a manometric device equipped with a photoelectric sensor to quantify the gas production. Methanogenesis is often the rate limiting step of the entire process and since the quantification of gas flowrate is relatively easy to perform, most of the methods reported in literature monitor the production of biogas. These methods can be termed volumetric or manometric methods, as the volume of biogas produced or the pressure increase due to gas production inside a close vessel are assessed, respectively. However, this same concept can be employed to assess activity or inhibition of individual metabolic steps preceding the methanogenic one, providing that they are rate limiting for the whole process. The reliability of activity assessment through gas measurement has been proven to be strongly dependent on the equilibrium between liquid and gas phase in a closed vessel. This can be influenced by many factors, e.g. the amount and characteristics of the test substrate; the concentration of the biomass; the gas-to-liquid ratio– all these aspects will need to be addressed in the standard procedure. Other direct or indirect methods, targeting physico-chemical or microbiological parameter exist and have been investigated by many authors. Besides the interest for research purposes, the definition of reference methods to assess activity and inhibition can be of great interest for engineers, both phy. Specific reference procedures might be needed for particular applications, e.g. the (kinetic) study of rate limiting microbial steps and might require ad-hoc methodologies to be devised. A microbiological technique such as FISH, coupled with microsensors have been reported to have a great potential in the near future.

Arsenic removal technologies for drinking water treatment

Abstract: Arsenic contamination as a consequence of human activities such as mining and pesticide use is affecting the water resource quality worldwide. Because of the high risk of arsenic exposure, specific water treatment processes are required to meet the anticipated more severe water quality standards. Better understanding of presently available processes is necessary to develop economic, efficient and effective methods for arsenic removal. Arsenic could either be coagulated, adsorbed using a wide range of materials both mineral and organic or could be directly rejected by membrane processes such as reverse osmosis and nanofiltration. The recent development of submerged hybrid membrane systems, such as membrane bioreactor in wastewater treatment, offers alternative technologies for arsenic treatment. The membrane in hybrid systems allows a better phase separation between the particles binding the arsenic and the treated water. The effect of pH and contact time, and the existence of other ionic compounds must be taken into account when designing the system for optimum arsenic rejection. Further research on both hydraulic and removal performances of hybrid adsorption/membrane technology is still required to assess the full potential of this technology for arsenic removal.

Bioremediation of petroleum hydrocarbons through landfarming: Are simplicity and cost-effectiveness the only advantages?

Abstract: The biological removal of petroleum products using landfarming has been applied commercially in large scale with relative success. The technology has been widely used due to its simplicity and cost-effectiveness. However, together with these advantages, there are physical, chemical and biological aspects of the technology that can hamper the remediation process. The dominant pollutant removal mechanisms involved in landfarming are volatilisation of low molecular weight volatile compounds during the early days of contamination or treatment, biodegradation and adsorption. However, volatilisation, leaching of the petroleum products and the remaining ‘recalcitrant’ hydrocarbon residues present both health and environmental challenges to the rehabilitation practitioners when designing the landfarming technology. Bioaugmentation and biostimulation are promising bioremediation approaches involving landfarming. However, due to the inherent problems related to bioaugmentation such as poor survival of augmented strains, biostimulation should be preferred in contaminated sites with indigenous pollutant-degrading bacteria. Although simplicity and cost-effectiveness are the major advantages for using landfarming, other factors generally regarded as disadvantageous to implementing the technology can be addressed. These includes requirements for large land area for treatment, availability of the pollutant degrading bacteria, effectiveness of the technology at high constituent concentration (more than 50,000 ppm), improved concentration reductions in cases requiring more than 95% of pollution reduction and the flexibility of the technology in integrating the removal of petroleum hydrocarbons with other contaminants that may occur with the petroleum products.

Removal of inorganic anions from drinking water supplies by membrane bio/processes

Abstract: This paper is designed to provide an overview of the main membrane-assisted processes that can be used for the removal of toxic inorganic anions from drinking water supplies. The emphasis has been placed on integrated process solutions, including the emerging issue of membrane bioreactors. An attempt is made to compare critically recently reported results, reveal the best existing membrane technologies and identify the most promising integrated membrane bio/processes currently being under investigation. Selected examples are discussed in each case with respect to their advantages and limitations compared to conventional methods for removal of anionic pollutants. The use of membranes is particularly attractive for separating ions between two liquid phases (purified and concentrated water streams) because many of the difficulties associated with precipitation, coagulation or adsorption and phase separation can be avoided. Therefore, membrane technologies are already successfully used on large-scale for removal of inorganic anions such as nitrate, fluoride, arsenic species, etc. The concentrated brine discharge and/or treatment, however, can be problematic in many cases. Membrane bioreactors allow for complete depollution but water quality, insufficiently stable process operation, and economical reasons still limit their wider application in drinking water treatment. The development of more efficient membranes, the design of cost-effective operating conditions, especially long-term operations without or with minimal membrane inorganic and/or biological fouling, and reduction of the specific energy consumption requirements are the major challenges.

Application, eco-physiology and biodiversity of anaerobic ammonium-oxidizing bacteria

Abstract: The demand for new and sustainable systems for nitrogen removal has increased dramatically in the last decade. It is clear that the conventional systems cannot deal with the increasing nitrogen loads in a cost effective way. As an alternative, the implementation of the anammox (anaerobic ammonium oxidation) process in the treatment of wastewater with high ammonium concentrations has been started. The compact anammox reactors can sustain high nitrogen loads without any problems. The highest observed anammox capacity is 8.9 kg N removed m-3 reactor day-1. The first 75 m3 anammox reactor is operating in Rotterdam, the Netherlands, combined with the partial nitrification process Single reaction system for High Ammonium Removal Over Nitrite (SHARON). Partial nitrification and anammox can also be combined in one reactor systems like Completely Autotrophic Nitrogen removal Over Nitrite (CANON) or Oxygen Limited Ammonium removal via Nitrification Denitrification (OLAND) where aerobic ammonium-oxidizing bacteria (AOB) and anammox bacteria cooperate under oxygen-limitation. These systems remove about 1.5 kg N m-3 reactor day-1. In addition to ammonium, urea can also be converted in the CANON system after a two-week adaptation period. The ecophysiological properties of the anammox bacteria make them very well suited to convert ammonium and nitrite. The Ks values for ammonium and nitrite are below 5 μM. However, nitrite above 10 mM is detrimental for the anammox process, and oxygen reversibly inhibits the process at concentrations as low as 1 μM. Acetate and propionate can be used by the anammox bacteria to convert nitrite and nitrate, whereas methanol and ethanol severely inhibit the anammox reaction. The enzyme hydroxylamine/hydrazine oxidoreductase (HAO), one of the key enzymes, is located in the anammoxosome, which is a membrane bound organelle. The membranes of the anammox bacteria contain unique ladderane lipids and hopanoids. The bacteria responsible for the anammox reaction are related to the Planctomycetes. The first anammox bacteria were isolated via Percoll centrifugation and characterized as Candidatus “Brocadia anammoxidans”. Survey of different wastewater treatment plants using anammox specific 16S rRNA gene primers and anammox specific oligonucleotide probes has revealed the presence of at least three other anammox bacteria, which have been tentatively named Candidatus “Kuenenia stuttgartiensis”, Candidatus “Scalindua wagneri” and Candidatus “Scalindua brodae”. A close relative of the latter, Candidatus “Scalindua sorokinii” was found to be responsible for about 50% of the nitrogen conversion in the anoxic zone of the Black Sea, making the anammox bacteria an important player in the oceanic nitrogen cycle.

Modeling composting kinetics: A review of approaches

Abstract: Composting kinetics modeling is necessary to design and operate composting facilities that comply with strict market demands and tight environmental legislation. Current composting kinetics modeling can be characterized as inductive, i.e. the data are the starting point of the modeling process and determine the type of model used. It is argued that the inductive empirical approach has been developed to its limit of practicality. Further progress is not expected because of limits in measurement techniques and the resources needed to perform all experiments needed.Contrary to the inductive, the deductive modeling approach uses the existing theory as its starting point for model development. Deductive models of realistic situations contain many basic parameters representing the theoretical basis. These basic parameters however tend to be non-identifiable, limiting practical application. To overcome this problem, it is proposed that the basic parameters in the deductive model must be combined to a smaller number of so-called combined parameter that are identifiable. In this way a model is developed that can incorporate both the theoretical knowledge introduced via the basic parameter and the information of data as represented by the identifiable combined parameters. As an example of how information of both theory and data can be used, the case of the temperature effect on the composting rate is analyzed. The temperature effect is quantified as the activation energy E, a parameter derived from the well-known Arrhenius equation. The theoretical analysis shows that the E-value changes strongly during the process, which is very remarkable, as the E value of basic parameter remains constant. These results are in accordance with literature findings. The results suggest that the multiplicative approach used in first-order modeling should be reconsidered, as both the literature findings as well as the theoretical analysis of the model predict a shift in E-value. Missing a shift in the E-value could lead for instance to instability in temperature control algorithms.

Equipment used for testing anaerobic biodegradability and activity

Abstract: Recently there has been a growing demand for information on the biodegradability and microbial toxicity of xenobiotic compounds. The environmental fate and effect of these chemicals in aerobic and anaerobic conditions has been extensively studied using a variety of different methods. This paper reviews the different protocols, equipment and instruments used in anaerobic biodegradation and activity tests, including the more sophisticated automated techniques recently developed. The different systems for detecting biogas production are given particular attention. As well as gasometric methods, the different instrumental techniques used to follow the fate of compounds under anaerobic conditions, via analysis of substrate consumption and product formation are evaluated.

Polymer electrolyte membrane fuel cells: Principles and advances

Abstract: Polymer electrolyte membrane fuel cells (PEMFC) are currently under intensive development for a range of power generation application in transportation, stationary and portable power. The PEMFC can produce electricity at high fuel efficiency and high energy density. The PEMFC is typically based on Nafion® or similar polymers and operates at low temperatures of less than 80 °C. This article reviews the design principles of the PEMFC, the advances made in their performance and considers their limitations in relation to the source and types of fuel used to generate power.

Reverse logistics in effective recovery of products from waste materials

Abstract: Technical solutions for the recovery of products from waste materials become more and more available. To have these new technologies implemented in a real world, a feasibility study is indispensable. For this purpose, it is often imperative to adopt the viewpoint of an individual firm and ask whether it would be wise to engage in product recovery activities or not. Aspects of economics and logistics are of prime importance here. Some important frameworks, models, and insights that have been developed in recent years are described in this paper.

The value of compost

Abstract: Sub-department Environmental Technology, Wageningen University, P.O.B 8129, 6700 EV, Wageningen, TheNetherlands (* author for correspondence, e-mail: aad.termorshuizan@wur.nl)1. IntroductionComposting is the controlled decomposition oforganic matter resulting in stabilized and sanitizedorganic matter that can be used as soil conditionerin agriculture. There exist multiple compostingmethods, varying from the small, home-madereactors used by individual households, to therelatively simple, on-site reactors used by farmers,to the large, simple to complex reactors used byprofessional composters to which the biowaste hasto be transported.If organic matter is targeted for agriculturaluse, the major reason for composting is sanitation(i.e. the inactivation of pathogens) of the material.In addition, apart from the presence of pathogensin fresh organic matter, returning great amounts ofuncomposted, fresh organic matter to agriculturalfields may have a stimulatory effect on plantpathogens already present in soil. The value ofcompost is difficult to summarize in one sentence,as its amendment to soil essentially has multiplepositive effects, which in turn also affect eachother. For example, an increase of soil organicmatter content improves the water holdingcapacity, which makes plants less prone to condi-tions of dry weather. As a result of that, they maybecome more resistant against pathogens thatspecifically affect plants under stress.Thisreviewaimstosummarizethemainwaysinwhich compost affects the functioning of the soil.Wefocusmainly oncompostedbiowaste,which weuse in its broad sense, including organic householdwaste, green waste and crop residues, but manyaspects also apply to composted manures.2. SanitationA major goal of composting is the removal ofpathogens. Although much emphasis is often puton the potential survival of some plant, human oranimal pathogens during compositing, it must berealized that the majority of pathogens is promptlyand completely killed during the heat phase ofcomposting (e.g. Bollen et al. 1989). Moreover,many pathogens that are known to have some po-tential to survive normal composting conditionsoccuronlyrarely,whichresultsinaverylowchanceofoccurrenceinbiowaste.TobaccoMosaicVirusisanexampleofsuchapathogen.Thisviruscancauselargecroplosseswhenintroducedintoacrop,butitis virtually absent in Dutch agriculture. The com-mon presence of this virus in tobacco of cigarettessmoked in the Netherlands (pers. comm. D. Peters,Virology, Wageningen University) is most likely ofsubstantial greater risk for agriculture than itspresence in compost. So, not only the fate ofpathogens during composting needs to be includedin a risk assessment, but also the probability ofpathogen incidence in biowaste and the probabilitythat presence in compost leads to phytosanitaryproblems.The scale of composting is an issue that af-fects phytosanitary aspects: large compostingfacilities collect organic matter from a multitudeof sources and one compost heap may thereforecontain various pathogens. Moreover, such largefacilities also distribute the compost to a largearea. So, the need for inactivating the pathogensin such large facilities is therefore great, asotherwise there would be uncontrolled spread ofpathogens. At the other extreme, on-farm com-posting facilities do not introduce pathogensfrom elsewhere, but reduced ability to controlthe composting process (relative to large com-posting facilities) may lead to limited survival ofsome plant pathogens. Although such a survivalis unwanted, the consequences for farm man-agement may be limited as these pathogens useto be all soil-borne, and their possible presence

Standardized methods for anaerobic biodegradability testing

Abstract: The European Community Directive 67/548/EEC (adopted in 1967), Annex V, contains about 85 testing methods, legally binding for all EU-Member States. They are regularly updated, or new methods are introduced in a formal procedure. Until 2002, no anaerobic biodegradability testing methods have been explicitly included either in the EU Directive 67/548/EEC or in the OECD-Guidelines adopted. However, a ‘hidden’ EU-document with a testing scheme exists which recommends when anaerobic testing may be applied, without specifying in detail which legally binding method is to be used. In order to give an impression of the spectrum available, anaerobic test schemes proposed by ASTM, CEN, DIN, ISO, ECETOC, and OECD, are classified according to temperature, test environment, test purposes, and the equipment used. Some problems with the equipment and the methodology such as permeation phenomena, reproducibility, and the medium composition are addressed. With this, the difficulty to reach a satisfying carbon balance can be better understood. Finally, some recommendations are given on how to improve knowledge on the test equipment and the test procedure.

Olfactory and chemical analysis of taste and odor episodes in drinking water supplies

Abstract: This paper evaluated the presentknowledge of taste and problems in drinkingwater supplies in the form of a ``Taste and OdorWheel'' which organises the relationshipsbetween specific taste and odor problems andtheir causes. The Flavor Profile Analysis (FPA)method enabled the development of the odordescriptors on the wheel. The abilities andshort-comings of the FPA method for odorevaluation by taste and odor panels wereevaluated. The present state of development oftaste and odor standards for drinking water wasthen discussed.

Recent developments on biological nutrient removal processes for wastewater treatment

Abstract: The need for preserving the environment is tightening regulations limiting the discharge of contaminants into water bodies. Nowadays most of the effort is done on the removal of more specific contaminants such as nutrients (N and P) and sulfurous compounds since they are becoming of great concern due to its impact on the quality of water bodies. There have been two recent discoveries of microbial conversions of nitrogenous compounds. One consisting on the capability of ammonia oxidizers of denitrify under certain conditions resulting in a new one-step method for the removal of N-compounds. The second has been named the ANAMMOX process, wherein ammonium is oxidized to dinitrogen gas with nitrite as the electron acceptor. Other developments consist of operational strategies aiming at obtaining the highest efficiency at removing nitrogen at lowest cost. One strategy consists of the partial nitrification to nitrite (only successful in the SHARON process) and subsequently either the heterotrophic denitrification of nitrites or its autotrophic reduction by ANAMMOX microorganisms. Another strategy consists of the coexistence of nitrifiers and denitrifiers in the same reactor by implementing high frequency oscillations on the oxygen level. The recent developments on biological phosphorous removal are based on the capacity of some denitrifying microorganisms to store ortho-phosphate intracellular as poly-phosphate in the presence of nitrate. These microorganisms store substrate (PHB) anaerobically which is further oxidized when nitrate is present. By extracting excess sludge from the anoxic phase, phosphate is removed from the system. Removing phosphate using nitrate instead of oxygen has the advantage of saving energy (oxygen input) and using less organic carbon. The microbial conversions of sulfurous compounds involve the metabolism of several different specific groups of bacteria such as sulfate reducing bacteria, sulfur and sulfide oxidizing bacteria, and phototrophic sulfur bacteria. Some of these microorganisms can simultaneously use nitrate, what has been reported as autotrophic denitrification by sulfur and sulfide oxidizing microorganisms. More recently, the anaerobic treatment of an industrial wastewater rich in organic matter, nitrogen and sulfate, reported a singular evolution of N and S compounds that initially was hypothesized as SURAMOX (SUlfate Reduction and AMmonia OXidation). The process could not have been verified nor reproduced and further investigations on the proposed SURAMOX mechanism have given no additional insights to those initial observations.

Improvement of biohydrogen production and intensification of biogas formation.

Abstract: H2 is considered as the ultimate cleanest energy carrier to be generated from renewable sources. This minireview intends to point out that in addition to this function, biologically produced hydrogen is important for environmental biotechnological applications. The purple sulphur phototrophic bacterium, Thiocapsa roseopersicina BBS contains several NiFe hydrogenases. These enzymes can be used e.g., as fuel cell H2 splitting catalyst or in photoheterotrophic H2 production. Microorganisms that supply H2 in situ facilitate the biodegradation of organic material and concomitant biogas production. Fast, efficient, and economic treatment of organic waste, sludge, manure is achieved and generation of significant amount of renewable fuel from waste is intensified. The technology has been field tested under mesophilic and thermophilic conditions with positive results.

Improved understanding of the interactions and complexities of biological nitrogen and phosphorus removal processes

Abstract: Nitrogen and phosphorus removal from wastewater is now considered essential for the protection of our waterways. Biological nutrient removal processes are generally the most efficient and cost-effective solution to achieve this. While the principles of these processes are well known, intriguing and useful details are being discovered with the recent advances in bio-process engineering and microbial sciences. Phosphorus accumulating organisms have only been identified in recent years, and there are now competing glycogen accumulating organisms being found in biological phosphorus removal systems. These can possibly explain the reasons for the variable phosphorus removal performance of certain systems, and their control can help in the development of more stable and better performing processes. Detailed investigations of the traditional nitrification-denitrification systems, but also of novel developments for nitrogen removal, reveal a more complex and diverse range of processes involved in these transformations. Increasingly, linked phosphorus and nitrogen removal processes are being developed, creating further opportunities to optimise the technologies. However, this might also bring certain risks such as the potential to produce the greenhouse-gas nitrous oxide (N2O) rather than nitrogen gas as the final denitrification product. A range of recent developments in these areas is covered in this paper.

Role of oxidants and disinfectants on the removal, masking and generation of tastes and odours

Abstract: This paper summarises theadvantages and disadvantages effects of themost commonly used oxidants and disinfectants:chlorine, ozone, advanced oxidation withozone/hydrogen peroxide, chlorine dioxide,potassium permanganate and chloramines, ontastes and odours present in natural anddrinking waters. Case studies are presentedwhich illustrate the generation of odorousby-products such as chlorophenols, iodinatedtrihalomethanes, aldehydes, the masking effectbetween earthy-musty and chlorinous odours andthe removal of odorous algal metabolites oranthropogenic pollutants by ozone alone orozone coupled with hydrogen peroxide.

Separate collection and biological waste treatment in the European Community

Abstract: Group 1: The national conditions and prescriptions have been worked out before the EU guidelines were published. Germany, Austria, Denmark, Luxembourg, the Netherlands and Belgium (Flanders) belong to this first group. Group 2: The EU standards have been adopted as a target in the national law, the realisation already converted: France, Italy, Sweden, England and Finland Group 3: The EU standards are acknowledged as a future target, the realisation is on the way: Greece, Ireland, Portugal and Spain.

Effects of materials of construction on tastes and odours in drinking water

Abstract: Products and materials used incontact with drinking water have the potentialto cause tainting of drinking water. Whilsthealth effects are not necessarily associatedwith such effects, for consumers, flavour orodour are the main parameters they use toassess the wholesomeness of their drinkingwater. There are a number of possible causes oftainting from products and materials and theseare discussed. In many countries products usedin contact with drinking water are screened toavoid odour or flavour problems. However,despite these safeguards tainting problems canand do still occur. Some relate tomisapplication of products in distributionsystems, poor domestic plumbing practices orthe use of domestic appliances after the pointof supply.

Electronic sensory systems for taste and odour monitoring in water – Developments and limitations

Abstract: Taste and odour causingchemicals in drinking water supplies can bedetected and identified using a variety ofanalytical techniques and sensory methods.Currently limitations exist in applying thesetechniques and methods to the continuousmonitoring of taste and odour episodes.Electronic sensory systems so called``electronic noses'' using non-specific gassensors could offer a rapid and relative simpletechnique for continuous monitoring of waterquality. Laboratory and field-based continuouswater monitoring showed that introducedpollutants such as 2-chlorophenol and geosmincould be detected by a sensor array, howeverthe detection limits were significant higherthan the odour threshold concentrations (OTC)for the respective compounds. The conditioningof the monitoring system in a temperaturecontrolled environment for on-line headspacegeneration and transfer reduced the impact ofenvironmental fluctuations on the sensorresponse profiles. At present, a sensor arraybased monitoring system could be applied to theintake protection of taste and odour causingcompounds in water supplies with a minimum OTCof 10 ppm.