Optimal management of wastewater systems

Obiettivo

A.BACKGROUND

COST Action 682 entitled "Integrated Wastewater Management" was active from 1992 and will expire in February 1998. A new Action entitled "Optimal Management of Wastewater Systems" is proposed. This new Action covers all aspects of wastewater management systems (i.e. collection, treatment and disposal) with regard to optimizing the performance of the complete system and also focuses on the development of new sustainable wastewater management strategies.

The work done within COST Action 682 has improved considerably the understanding of many aspects of nutrient removal from wastewater, the standardization of measurement methods, the adoption of new structures for modelling and simulation of wastewater treatment plants and the development of methodologies for parameter identification and state variable estimation.

During the last few years the public awareness of urban water issues has increased considerably in many European countries. This has forced both the wastewater industry and the research community to take a more holistic view of the urban water system. It is not sufficient to sub-optimize individual processes. There is a need for further optimization of existing structures and to develop new systems and management policies. In order to promote such a development the need for more interactions, on the one hand, between engineers and system managers and, on the other hand, between engineers and microbiologists, is required. Furthermore, the concept of sustainability is coming up on the agenda in several countries. From a general point there seems to be an agreement on the definition of sustainability, as it is formulated in the UN Brundtland report. However, as soon as sustainability has to be more practically defined there is a big challenge. How to compare whether one solution is more sustainable than another one?

As a result of the discussions taking place in COST Action 682, the need for a new COST Action appeared. The anticipated new Action focuses on a better understanding and use of the biological processes involved in wastewater systems, on the integration of these systems and the development of overall control strategies.

The problems of water and wastewater management are general and similar throughout the European continent, although local conditions differ. COST offers a good platform for exchange between research projects in which Western and Eastern European countries share common interests. This new Action supports knowledge transfer and promotes field applications and full-scale implementation of the achieved results.

B.OBJECTIVES AND BENEFITS

The main objective of the Action is to optimize the performance and cost-effectiveness of wastewater management systems by increasing the knowledge of microbial systems and by implementation of integrated plant-wide control based on a description of the entire wastewater system, thereby providing new concepts for dealing with wastewater in a future sustainable society.

Presently wastewater management is organized as a series of units. There are several differently detailed mathematical models for many of these units. To accomplish integration in practice it is required to combine these models and to establish interfaces between them. Besides this, further development of missing or practically-not-applicable models for the different units of the water and sludge trains is also necessary. By using an integrated model of the entire wastewater management system it is possible to optimize the system as a whole instead of optimizing each unit process separately, which in turn leads to a sub-optimization of the larger system. It is also possible to predict effects of changes in the structures and the processes.

Several changes have lately occurred in society: there is today an increased public awareness with regard to the shortage of water and the impact of pollution release on the environment. The long-term effects of environmental pollution and the current waste of resources have put the issue of sustainability in the centre when developing new systems. Two major questions can be put forward in this respect:

-what would be an optimal wastewater management system if designed from scratch, i.e. without any consideration of existing structures and technologies;

-how can we - in a sustainable manner - deal with the huge resource investment made in existing infrastructures in order to move in the direction of such optimal wastewater management systems.

The secondary objectives of the proposed Action are:

-application of microbiological techniques and experimental approaches towards mixed cultures growing on mixed substrates. In recent years several new methods which could be used hereto have been developed (e.g. in vivo NMR-spectroscopy, gene probes and confocal microscopy);

-integration of models describing the sewer system, the treatment plant (from the point of view of the water train and of the sludge train) and the receiving body. The model inputs and outputs, as well as the time constants are different. Consequently, there is a need for developing interfaces between the existing unit models;

-further development of models for the different units on the water and sludge trains. For several units, no reliable models are available: for example biological processes in sewers, biofilm processes, sludge separation and handling, and physical/chemical (pre)treatment should be addressed;

-development of criteria (based on cost, environmental impact, energy and resource utilization, social economic conditions, etc.) for promoting the development of sustainable wastewater management systems. Such criteria are essential for application of methods such as Life Cycle Assessment and Environmental Impact Assessment of existing and future systems. Also essential is the explicitation of the goal to be aimed at in the wastewater management system;

-evaluation of new scenarios, including physical/chemical pre-treatment. This includes on the one hand to investigate how physical/chemical reactions and newly-discovered microbial conversions could be used in wastewater treatment and on the other hand whether new physical/chemical treatment steps and microbial conversion routes can be found in view of changing demands on the wastewater treatment systems.

In order to fulfil the above objectives there is a need for more cooperative research between engineers dealing with wastewater collection, treatment and disposal systems. Due to the central role of microbial processes a combined research effort of microbiologists and engineers leading to a better understanding of mixed populations occurring in wastewater management systems is needed. Due to the large practical implication of wastewater handling, a direct involvement of practitioners is required.

Dissemination of results

The research community has many established channels to publish the results of scientific work among researchers. All of these means are of course used, such as publications in journals, conferences, research reports and web-publications. Furthermore, interesting reports have been received from a number of earlier COST Actions.

However, the results have to be more directly aimed at specific end-users. It is already a routine in some countries to:

-collaborate with the water authorities;

-work on a regular basis with wastewater treatment plant engineers and operators;

-participate in short courses for consultants, operators or process engineers;

-publish in national engineering newsletters and magazines aimed at operators or process engineers.

The Management Committee (MC) works out a procedure for publishing results outside the scientific community during the Action. At each MC meeting every participant is reminded about this, and the MC requires reports on the dissemination efforts.

The group is aware that many results have to be exchanged with other groups, like the Technical Committee on Urban Civil Engineering and the ad hoc Working Party on Environment. Members of these groups will be invited to the MC meetings and be informed about the activities. Furthermore, it may be suitable to invite members from these other groups to general seminars in order to transfer knowledge. In particular, issues on sustainability have to be addressed by different groups.

C.SCIENTIFIC PROGRAMME

In the course of COST Action 682, the cooperation of the various European specialists resulted in a better understanding of the processes taking place in the activated sludge units. Based on that experience, an extension to include the whole of the wastewater system is beneficial.

(a)Processes in wastewater systems

-In wastewater treatment the organic pollutants are transformed into sludge. The structure of activated sludge flocs affects the dewatering and settleability of sludge. Separation and further treatment of the sludge are therefore always necessary. These processes are influenced in a complex manner by the microbial population present (e.g. settling in the presence of filamentous bacteria, or dewatering in the presence of specific biopolymers).

-Biofilms play a dominant role in the conversions within the sewer system and modern high-rate treatment processes. The main unknown factor in the description of biofilm processes is the form of the biofilm obtained under different operational conditions (mixing intensity, loading rate, etc.).

-Nitrogen removal is a dominant conversion process in environmental biotechnological processes. The possible formation of intermediates such as NO or N2O have to be understood in order to prevent their emission into the environment.

-In the wastewater several compounds that are either difficult to degrade or have toxic effects may be present. It is important to understand the toxicity mechanisms and the way xenobiotics can be degraded. The addition of iron and aluminium salts for chemical P removal is becoming more and more common. The effect of these metals on the activity of the micro-organisms is not yet clearly understood. This knowledge will lead to better design and understanding of treatment processes.

-Microbiological research is usually performed in systems with continuous feeding of the organisms. In wastewater processes the feeding is always temporary (feast-famine regimes). It has been recognized from activated sludge studies that storage polymers (i.e. fat reserves) play a dominant role in the adaptation of micro-organisms towards these conditions. A better microbiological understanding and description of these processes will help improve the systems with respect to bulking sludge control, phosphorus and nitrogen removal and digestibility of the sludge.

(b)Tools for integration

The tools presented below are necessary for integration of new as well as existing infrastructures.

-Methods for integration of models describing the behaviour of the different units in wastewater treatment - primary (grit, oil, sand removal, etc.), secondary and tertiary treatment, sludge dewatering, anaerobic digestion, incineration, etc. - are taken into account (including energy consumption/production). Models for the sewer system and for the receiving body are taken into account. Each of these models has its specific set of state variables and inputs. For integration it is necessary to develop interfaces between the models.

-Characterization techniques Development of microbial characterization methods (activity tests, probes, guidelines). For the characterization of microbial processes and the use of models it is necessary to have specific tests available that can give reliable insight into the process performance. Methods originally developed on pure cultures for identification of micro-organisms (gene probes), activity (microelectrodes), physiology (in vivo NMR-spectroscopy), microbial structure analysis (confocal microscopy) have to be adapted and transferred for use with mixed cultures. Using these techniques requires specialized persons and equipment. In this COST Action these techniques are adopted for the study of mixed microbial populations. Moreover, these techniques are made available to all participants. The COST Action offers a platform for the validation of these methods under different working conditions.

Guidelines for standard methods for sludge, wastewater and surface water characterization. This item is strongly connected to the information required by the models.

Development of new methods (e.g. pattern recognition for spectrum-based analysis). In bioengineering the analysis of spectra obtained by spectroscopy (ultra-violet, infra-red, etc.), by mass spectrometry (with or without sample preparation such as chromatographic separation or pyrolysis), or simply by an array of mono-output sensors of different types have been used to monitor complex fermentations using new data analysis techniques (artificial neural networks, principal component analysis, etc.).

-Benchmarking: in order to evaluate the control strategies proposed by different control research groups in a standardized way, the benchmark project initiated in COST Action 682 has to be expanded. The benchmark consists of a dynamic plant simulation employing a selected number of inlet wastewater scenarios depicting normal and disturbed situations. The library of models and the reference database for inputs and disturbances are made available over the internet. Control strategies could then be compared, on the basis of various criteria, using the same input scenario and the same plant described by the same models.

-Model analysis: the different models involved are highly complex, non-linear and are aiming at different purposes. Steps, such as parameter identification, sensitivity analysis and model reduction, are necessary to ensure proper integration and allow for practical use of the models. In the field of control and system engineering such tools are available, mostly for linear systems. There are developments for non-linear and distributed parameter systems that should be adapted and further investigated in the context of wastewater systems.

-Optimization: in complex integrated models (like those proposed) the use of algorithms for mathematical optimization is essential to estimate the optimum operational strategies that minimize the global "cost criterion" under different objectives.

(c)Tools for strategy assessment

Any new strategy for integrated wastewater management must be evaluated not only from a cost-benefit perspective but, more importantly, from a sustainability perspective. Life Cycle Assessment (LCA) is a method for analysis and assessment of the environmental impact of a material, product or service throughout its entire life cycle. A life cycle includes raw material extraction, processing, transportation, manufacturing, distribution, use, re-use, maintenance, recycling and waste treatment. LCA allows a standardized comparison of different products performing the same function, different process alternatives or different waste handling alternatives, etc. Environmental Impact Assessment (EIA) aims to serve as a decision support at different levels, ranging from daily operation to strategic decisions for an entire system. Both these methods and others must be adapted before their application within the context of wastewater management systems.

(d)Development of sustainable water management systems

The goal is to plan, manage and operate the water systems in such a way that there is no over-use of the available resources defined as:

-primary resources (water, nutrients, energy);

-secondary resources used to fulfil the assignment (energy, space, material);

-recipients (ground and surface waters, soil and air);

-anthropogenic resources (capital, qualified labour, public acceptance, etc.).

A comprehensive method to identify these different resources and to structure them needs to be developed.

A proper definition and organization of the variables to be considered during the development phase should be proposed. The variables should describe the availability of the resources, the pollution discharge, the water consumption, the different costs associated with the management as well as macro-economic, geographical, social and ecological indicators.

Based on evaluation of future changes in the wastewater composition (due to the implementation of a more sustainable water management system) new processes need to be developed; in general these rely on microbial conversions. The application of microbial conversions under conditions different from the present day processes need to be evaluated. Moreover, it will be investigated which of the existing microbial processes could be exploited in future wastewater management systems (e.g. thermophilic or halophilic micro-organisms).

In recent years there have been proposals of new microbial processes dealing with nitrogen removal (e.g. aerobic denitrification, anaerobic ammonium oxidation). The question is whether these new processes can be used in practice. They require thorough evaluation.

Within this framework, new water management strategies based on existing or innovative water rehabilitation processes can be proposed and assessed. A close cooperation will be established with the proposed COST Action C8 on sustainable urban infrastructure on this research topic if this Action is approved by the CSO.

(e)Operational optimization

The development of integrated management strategies is aimed at the optimization of the operation of the entire wastewater system, taking into account the performance in terms of effluent water quality but also the economical and resource-saving aspects based on exergy (i.e. total energy and quality of energy), consumption of chemicals, reutilization of sludge products, etc. The management is aimed at improving both the daily and long-term practice and should consequently cover the case of specific events such as extended rain, storm events and accidental discharge of toxins.

The different items of the scientific programme have clear interactions, such as:

-characterization methods are needed to define and use the models which will rely partly on a better understanding of the microbial fundamentals. Some new techniques such as gene probes can be used for sludge characterization;

-to develop strategies in response to toxic events, a better knowledge is needed of how such events affect the microbial processes;

-if the role of storage polymers and the formation of biofilms are better understood, it will lead to better models for wastewater management and consequently better control;

-the future wastewater management strategies may require new microbial processes and new conversion routes may open new possibilities in wastewater management.

D.ORGANIZATION AND TIMETABLE

The Management Committee of the new Action is organized and operates according to document COST 400 "Rules and Procedures".

The work is organized around Working Groups. Due to the amount of work which is performed the proposed Action is carried out over a period of five years (1998-2003). A General Meeting is organized every 18 months. Each General Meeting contains Plenary Sessions with all the participants and Parallel Meetings for focusing the work to be done in the following months. At the first General Meeting (6 months after the start of the Action), the Working Groups are defined. During the first six months the research projects and demonstration projects dealing with the Action objectives in the various participating countries are collected and made available on a Web Site, to facilitate contacts between research teams and to increase cooperation.

The duration of the Action seems to be adequate for the following main reasons:

-in the initial phase a learning period between the different scientific field communities of microbiologists, engineers and practitioners is necessary, before integration can be successfully made;

-practical tests in real systems take time due to the large time-constants of activated sludge processes and the dependency on weather conditions.

E.ECONOMIC DIMENSION

The following COST countries have actively participated in the preparation of the Action or otherwise indicated their interest: Belgium, Czech Republic, Denmark, Finland, France, Germany, Hungary, Italy, the Netherlands, Norway, Portugal, Spain, Slovenia, Sweden, Switzerland.

On the basis of national estimates provided by the representatives of these countries and taking into account the coordination costs to be covered over the COST budget of the European Commission, the overall cost of activities to be carried out under the Action has been estimated, in 1997 prices, at roughly ECU 10 million for a five-year period.

This estimate is valid under the assumption that all the countries mentioned above but no other countries will participate in the Action. Any departure from this will change the total cost accordingly.

Programma(i)

IC-COST - European cooperation in the field of scientific and technical research (COST), 1971-

Argomento(i)

3 - Environment

Invito a presentare proposte

Data not available

Meccanismo di finanziamento

Data not available

Coordinatore

N/A

Contributo UE

Nessun dato

Indirizzo

Danimarca

Costo totale