International Water Association Research Articles

The concept of estimating the risk of water losses in the water supply network

One of the methods of increasing the availability of drinking water is to reduce water losses in existing water supply systems (WSS). The need to manage water losses in WSS is highlighted in the new Directive (EU) 2020/2184 of the European Parliament and of the Council of 16 December 2020 on the Quality of Water Intended for Human Consumption. It was indicated that the main cause of water losses is underinvestment in the maintenance and renovation of network infrastructure. The new legal provisions require a risk assessment to be carried out in the water supply system, taking into account the risk of leaks. The paper presents the concept of estimating the risk of water losses in the water supply network using the three-parameter risk assessment method and risk maps. The framework of the water balance proposed by International Water Association (IWA) were also presented, including the Infrastructure Leakage Index (ILI) for assessment of the water supply system Leakage Performance Category (LPC). The analysis was carried out for a water supply system used by 200,000 inhabitants. The LPC of the system was determined based on the ILI index. Then the water supply network pipes that could potentially be a source of leaks were identified. The analysis of the risk of water losses for the examined pipes allowed to determine which pipes should be first chosen to reduce the risk of water losses, i.e. active search for leaks.

Assessment of non-revenue water in the urban water distribution system network in Cameroon (Central Africa)

ABSTRACT This paper aims to assess non-revenue water (NRW) in the urban water distribution system in Cameroon. The methodological approach used in this study was based on online searches using the databases such as Google Scholar, Web of Science, PubMed, and the International Water Association. These online searches have been completed through field observations and interviews with institutional and non-institutional stakeholders in the urban water sector. Results indicate that the total volume of NRW in the urban area of Cameroon was 100.26 million m3/year, which represents 52.5% of the total system input volume. About 2 million people could be supplied by cutting Cameroon's NRW to half the present level. Findings also suggest that the water utility (Camwater) practices passive leakage control, meaning that Camwater repairs only those leaks that are visible. Reducing NRW can be achieved through leakage detection and pipe replacement, pressure management, water metering, and a program to identify, remove, and replace illegal connections.

Hydraulic and Utility Performance Evaluation of Ataye Town Water Distribution Network, Ethiopia: case for small towns in developing countries

Evaluating hydraulic and utility performance of water distribution network is a way to check the functionality degree of a system. Water CAD software was used in developing a model and evaluating the hydraulic performance of water distribution system of Ataye Town, Amhara Region, Ethiopia. Both steady state and extended period simulation analysis were carried out to determine hydraulic parameters (pressure and velocity). The model was calibrated using Darwin Calibrator and validity was checked by both correlation coefficient and scatter plot. The utility performance was also evaluated using international water association performance indicators. The simulated result for steady state analysis showed that 68.7% of the nodes operated within optimum adopted pressure (15-60 meter) and 93% of the distribution pipes had a velocity of <0.6 m/s which was a minimum adopted velocity. For extended period simulation 34.3% during maximum demand time and 16.8% during minimum consumption hours had pressure <15meters. 10.8% had negative pressure during maximum demand hours located at Sudan, Selama, and Zigba sefer and 14 nodes (8.4%) during low consumption time had a pressure greater than 60meter, which was a maximum adopted pressure. The areas of high pressure were located at around mosque, Worku Hotel and Hamus Gebaya. The distribution system performs within the adopted pressure at minimum demand time (74.7%) and maximum consumption hours (65.1%). 23.5% of the systems had a velocity of 0.6-2 m/s and the rest had a velocity less than 0.6m/s during high demand time. During low consumption hours, 100% of the system velocity was estimated to be <0.6m/s. Based on the IWA performance indicators, water utility of Ataye Town was evaluated and had low, technical, financial, personnel, and environmental performances. Finally, the distribution system was modified and optimized by providing alternative connections with pressure reducing valves and changing pipe diameter to improve the hydraulic performance and reduce system disruption of the Town.
 Keywords: Extended period simulation; Hydraulic performance; IWA Utility performance; Steady state analysis; Water CAD

Enhancing Methane Production through Anaerobic Co-Digestion of Sewage Sludge: A Modified ADM1 Model Approach

The International Water Association’s (IWA) established Anaerobic Digestion Model No. 1 (ADM1) was created to serve as a backup for experimental findings regarding the actual anaerobic digestion process. The previous model idea was adjusted and used to simulate an anaerobic digestion process in this study. Testing procedures, such as benchmark tests and balance checks, were performed in order to verify the accuracy of the implementation. These measures worked in tandem to ensure that the model was implemented flawlessly and without inconsistencies. The primary objective of this article is to construct a method that is based on the ADM1 for evaluating co-digestion and predicting the performance of the digestion process or methane yield based on the analyzed substrates’ physicochemical properties. Additional equations and simulations have been added to the standard model to create tools for evaluating the feasibility of anaerobic co-digestion. The study’s two most intriguing aspects are the optimal mixture and parameter dependence. The adjusted ADM1 is accurate in predicting the measured values of effluent COD, pH, methane, and produced biogas flows with a reasonable degree of accuracy, according to the validation results. This research shows how to use ADM1 in a wastewater treatment plant and other settings where anaerobic digestion is of interest.

Estimate measurement errors of household water meters using a large amount of on-site data feedback

Water meter measurement error is considered as one important component of non-revenue water by International Water Association. Its magnitude depends combinedly on users’ consumption behaviors (intake spectrum) and metrological characteristics of water meters (meter error curve). Most published researches have only analyzed the meter error curves without taking the users’ consumption behaviors into consideration. This study developed a practical approach by using the relative difference chart of master-meters and sub-meters groupings (i.e., RM-μz chart) to identify average metering errors for a major water utility company in Taiwan. About 120,000 sets of “master-meter and sub-meter grouping” data of Taipei Water Department were analyzed. The approach successfully estimated average metering errors of its 99.6% domestic meters (around 1.6 million water meters), the results are 9.9, 6.1, and 10.0% less than the actual water consumption recorded by the sub-meters, master-meters, and direct-meters, respectively.

ASSESSMENT OF ENERGY AND WATER AUDIT OF SELECTED SCHOOL OF AHMEDABAD

Climate change is one of the most significant environmental and societal issues of our time. This increase in temperature would have catastrophic consequences for the planet. To mitigate the impacts of climate change, urgent action is required at both the individual and societal levels. Energy audit is an essential process of identifying, analyzing, and evaluating the energy consumption patterns of a building or facility. Water audit is the process of analyzing water usage and identifying opportunities for conservation and efficiency improvements. A water audit can help individuals and organizations understand how much water they are using, this general structure of the energy assessment has undergone a few changes, It includes collecting data on water usage, identifying leaks and inefficiencies, and implementing measures to reduce water waste Which Was Created By American Water Works Association (AWWA) And International Water Association (IWA) In 2000.

An Approach to Assess the Water Resources Reliability and Its Management

One of the factors limiting the possibility of the development of urban agglomerations is access to drinking water. Due to progressive climate change, the available water resources are limited. The paper proposes new indicators of limiting the development of agglomerations related to the availability of water resources and the production capacity of water treatment plants, a method for assessing the diversification of water resources (using the Pielou index), and a water loss balance was prepared based on International Water Association (IWA) standards. On the basis of the obtained results, the potential increase in the number of inhabitants indicators (∆PR, ∆PP) and the time for the development of agglomeration indicators (TR, TP), the directions of development of the studied agglomerations in terms of the possibility of water supply were indicated. The main problems were reducing the amount of water losses, appropriate management of the migration policy of the population, and the necessity to look for alternative sources of water.

GIS-Integrated Approach for Non-Revenue Water Reduction in Sumbawanga Urban District, Tanzania

This study sought to determine daily water consumption in the three zones of Sumbawanga Urban district. The study applied the geographical information system (GIS) to map and quantify non-revenue water (NRW), and tested the use of geospatial database management strategy to reduce NRW. The study used water distribution networks of zone A (Majengo ward), zone B (Katandala and Mazwi wards), and zone C (Chanji and Kizwite wards) that are served by the Sumbawanga Urban Water Supply Authority (SUWASA). The study collected water flow and water loss data by recording and mapping the existing water networks using a GPS device. The methodology for determining the quantity of NRW abstracted from the International Water Association (IWA), and maps made through QGIS, were used to show the degree of water loss by zones. A geo-database that assists in maintenance, budgeting, planning and procurement of water assets to reduce NRW was developed using postgress and postGIS, and connected to QGIS for visualization. Experimental results and computations indicate that around 8787.6m3 , 10718.3m3 , 14637.1m3 of water are consumed monthly in zones A, B and C, respectively. Furthermore, the results show that averages of 15.15%, 40.2%, and 24.52% of water are lost as NRW in zones A, B, and C, respectively. The NRW in all the three zones were greater than the maximum NRW of 20% recommended by Energy and Water Utilities Regulatory Authority (EWURA), and key performance indicators suggested by the SUWASA. This study inform planners and decisionmakers that management strategies should employ GIS to establish optimal routes for effective and quick response to bursts before losing a lot of water, instead of using traditional auditing systems that results into high NRW levels.

Modeling and optimization of the anaerobic digestion system for domestic waste water treatment with the development of monitoring techniques

Water scarcity and wastewater management are two most serious environmental problems faced by developing countries like India. Recycling and reuse of the treated wastewater for non-potable purpose may significantly reduce the stress on fresh water requirement. Anaerobic digestion methods are used to treat wastewater discharge from various fields. Software tools provide an opportunity for engineers to create models which represent activities, resources, and the environment in powerful, affordable and user-friendly way. Modeling and simulation results serve as an important guideline in the optimization and process control for plant operators and other specialists in the field of engineering. Model-based development of software using tools such as Math Works Simulink has become common in the engineering. The Anaerobic Digestion Model (ADM1) from the International Water Association might be used for modeling and optimization of digestion operations. This research reveals the study of domestic wastewater treatment using ADM1. The process equations are solved using the input data, and output is generated. The results show that the proposed method is capable of predicting process parameters of excellent stream with high degree of accuracy (R2=0.945).

A critical analysis of water economics in public water and sanitation services in Morocco

PurposeThe objective of this article is to propose a panel of management performance evaluation indicators at operator level. This panel would be the tool to be made available to an observatory that should be set up by regulation. The proposal comes at the right time given that Morocco is planning a major reform of the sector very soon. A framework law has already been promulgated for this purpose (Law 51-21 relating to the reform of public establishments).Design/methodology/approachThe proposed panel is the result of (1) a review of the literature dealing with public management theories, in particular those relating to industrial and commercial public services and whose character is captive. The management of the latter requires a great deal of caution to preserve their economic balance and consequently their sustainability. (2) A review of experiences of countries is chosen because of contextual their similarities with Morocco like France having a similar legal background, Tunisia and Algeria chosen for geographical and economic similarities. The British experience is also discussed for what it represents as a liberal model in the management of public water and sanitation services, as opposed to the German model also studied and which stands as the only country where the management of public services has almost always been a communal prerogative. The analysis of these models has made it possible to identify management evaluation practices that could be adapted to the Moroccan context. (3) Research work by practitioners and reports from specialized international institutions (International Water Association [IWA]). (4) A critical analysis of a multitude of management and activity reports from 12 autonomous authorities and 4 private delegates covering 16 million inhabitants of the urban environment. A total of 15 indicators are developed. They aim to assess the effectiveness of management in terms of saving drinking water and preserving the natural environment from the pollution of water resources.FindingsApproximately, 15 indicators for assessing water resource management in public water and sanitation services are proposed. These indicators relate to the efficiency of pipe networks, the performance of storage systems and losses in users' homes. Indicators specific to liquid sanitation systems, particularly with regard to the control of wastewater overflows into the public highway and their treatment before discharge into the natural environment, are also proposed.Research limitations/implicationsThe application of the results of this research could be confronted with its appropriation by the operators. Indeed, the investment involved in setting up the proposed evaluation system, as well as the conflict of interest that may arise in the process of formalizing and standardizing the system at the national level, may slow down the process of setting it up.Practical implicationsIn practice, the implementation of a system for evaluating the performance of water resource management in public drinking water and liquid sanitation services would make it possible to optimize the volume of water to be mobilized. Substantial savings are expected both at the level of the resource itself and at the level of the investments that accompany the realization of the mobilization and distribution infrastructures. These savings will be very useful for the creation of other similar services and to serve more people.Social implicationsThe distribution of drinking water and liquid sanitation is a vital human need. These services are extremely captive. They are key factors in the socioeconomic development of the territory and the citizen. The impact is transversal and affects the lifestyle of the populations. On the one hand, it favors the sedentarization of the populations and on the other hand, preserves their health by fighting against the diseases of water origin. In addition, the comfort that it provides in the daily life of users is highly coveted when they are delivered in a modern way and arranged with modern technologies.Originality/valueThe regulation of public drinking water and liquid sanitation services in Morocco is the weakest link in the sector. The Ministry of the Interior is legally responsible for setting up a standard system for evaluating the management of these services to fill this gap (organic law 113-14 on municipalities). Unfortunately, this initiative is not yet underway. The opportunity to apply the results of this research is well timed. Morocco plans to launch a global reform of the sector starting in 2022–2023 (Law 50-21 on the reform of public institutions).

A BRIEF OVERVIEW OF BENCHMARKING AS A MANAGEMENT TECHNIQUE IN THE FIELD OF WATER IN ROMANIA

Given the public and permanent nature, of the public utility services, as a continuous operation, coupled with the dynamics of changes in technology, communication, labor market and last but not least the many changes in recent years of legislation and tax regulations in Romania, lead to increased pressure on decision-makers in the field of public utility services with an impact on housing. This topic was chosen in the context of the economic realities in Romania in the field of public utility services with an impact on housing, an area that reflects the ongoing concerns for a development that will ensure technological reform and integration into European financial structures. It is of real interest for any entity in the field of public utility services with an impact on housing concerned about the need to implement a decision-making and financial mechanism that provides a clear and relevant picture of the performance of services provided. In this context, the opinion of the International Water Association Group of Specialists that “benchmarking is a tool for improving performance through systematic research and best practice” has motivated many water companies to introduce benchmarking as a method of management. This article provides an overview of benchmarking as a water management technique for European Benchmarking Co-operation (EBC) compared to the national benchmarking exercise called H2Obenchmark. Due to the fact that both are based on the methodology developed by the International Water Association (IWA), the most important advantage of these benchmarking techniques is that they ensure comparability at any time with any water company in the world that uses the same system. By ensuring the opportunity for knowledge transfer, operators are able to identify and implement best practices and innovative solutions to the realities they face in the field of management, operations and investment projects. The brief diagnosis of water benchmarking in Romania highlights the fact that H2OBenchmark is a mature benchmarking exercise, with experience gained and maintained both in the water sector (ARA, CEB, OR, ANRSC, etc.) and partner consultants.

Water Supply and Management System of Urban City: Santiago City Case

Goal 6 of the 17 Sustainable Development Goals (SDGs) set out by the United Nations 2030 Agenda and SDGs is a national call for Clean Water and Sanitation. For society's demographic, social, and economic development, reliable and outstanding water quality and long-term water supply services are deemed essential. The study aimed to evaluate the effectiveness of Santiago City's Local Water Utility (LWU) system in terms of water supply and wastewater management. The performance evaluation was based on the following domains – (a) sustainability of water supply; (b) consumers satisfaction; and (c) waste management practices; including compliance of the local government unit and service units by water security and management. The International Water Association's assessment framework and indicators were employed (IWA). The method used to collect information and/or data for this study, key informant interviews, and field surveys were conducted, with a total of 395 respondents drawn from 12 active barangays using stratified random sampling. The results showed that in terms of water sustainability for the next 30-year considering the future population and based on the present demand as of 2019, water demand will skyrocket with an equivalent percent increase of 8.97%, 17.95%, and 28.20% for 2030, 2040, and 2050 respectively. The result analysis does not include the agricultural demands or groundwater withdrawal for agricultural purposes and individual domestic wells within the City of Santiago. Overall acceptability on water quality was acceptable with a rating of 52% wherein 66%, 67%, 65% and 56% acceptability ratings were attributed to quality, taste, odor, color, and pressure, respectively. The Santiago water district has two water treatment facilities located within the city. For the water waste disposal, it is observed that there is direct disposal of waste to water bodies specifically to farms and drainage. The city of Santiago along with SANWAD has implemented ordinances and enabling laws on water/wastewater management for sustainable water resources utilization. Furthermore, on the issue of sustainability, it is highly recommended to develop alternative water resources that could increase water distribution efficiency, eliminate or lessen illegal tapping/ connection, increase coverage area, and maintain water quality valuation as a sustainable approach to sufficiently and dependably supply water demand for future generations.

A plant-wide model describing GHG emissions and nutrient recovery options for water resource recovery facilities

In this study, a plant-wide model describing the fate of C, N and P compounds, upgraded to account for (on-site/off-site) greenhouse gas (GHG) emissions, was implemented within the International Water Association (IWA) Benchmarking Simulation Model No. 2 (BSM2) framework. The proposed approach includes the main biological N2O production pathways and mechanistically describes CO2 (biogenic/non-biogenic) emissions in the activated sludge reactors as well as the biogas production (CO2/CH4) from the anaerobic digester. Indirect GHG emissions for power generation, chemical usage, effluent disposal and sludge storage and reuse are also included using static factors for CO2, CH4 and N2O. Global and individual mass balances were quantified to investigate the fluxes of the different components. Novel strategies, such as the combination of different cascade controllers in the biological reactors and struvite precipitation in the sludge line, were proposed in order to obtain high plant performance as well as nutrient recovery and mitigation of the GHG emissions in a plant-wide context. The implemented control strategies led to an overall more sustainable and efficient plant performance in terms of better effluent quality, reduced operational cost and lower GHG emissions. The lowest N2O and overall GHG emissions were achieved when ammonium and soluble nitrous oxide in the aerobic reactors were controlled and struvite was recovered in the reject water stream, achieving a reduction of 27% for N2O and 9% for total GHG, compared to the open loop configuration.

How elevation dictates technology selection in biological wastewater treatment

Most wastewater treatment facilities are built using procedures from previous designs which are predominantly from sites and regions not located at high elevation. Recognizing this limitation, we assessed the effects of elevation above sea level on the suitability of process configurations and technologies as well as their associated energy costs. Using the International Water Association (IWA) benchmark simulation model No. 2 (modified Ludzack-Ettinger process layout) as a reference, we simulated scenarios including different activated sludge process configurations, operating under different environmental and process conditions. In order to include a wide sample of environmental conditions, data on atmospheric pressure, wastewater temperature, air temperature, and relative humidity (for average, warmest, and coldest months) were collected from municipal wastewater treatment plants located at different latitudes and elevations. The results confirm that elevation is a driver against the selection of diffused aeration technologies. Aeration costs for aerobic wastewater treatment are highly influenced by local project conditions, particularly by elevation and wastewater temperature, which together influence the driving force for oxygen transfer into water. When the driving force is low, operating costs are high. Recommendations for designing treatment processes effectively, including diffused aeration systems operating at high elevations above sea level, are proposed.

Probabilistic Minimum Night Flow Estimation in Water Distribution Networks and Comparison with the Water Balance Approach: Large-Scale Application to the City Center of Patras in Western Greece

Quantification of water losses (WL) in water distribution networks (WDNs) is a crucial task towards the development of proper strategies to reduce them. Currently, WL estimation methods rely on semi-empirical assumptions and different implementation strategies that increase the uncertainty of the obtained estimates. In this work, we compare the effectiveness and robustness of two widely applied WL estimation approaches found in the international literature: (a) the water balance, or top-down, approach introduced by the International Water Association (IWA), and (b) the bottom-up or minimum night flow (MNF) approach, based on a recently proposed probabilistic MNF estimation method. In doing so, we use users’ consumption and flow-pressure data from the 4 largest pressure management areas (PMAs) of the WDN of the city of Patras (the third largest city in Greece), which consist of more than 200 km of pipeline, cover the entire city center of Patras, and serve approximately 58,000 consumers. The obtained results show that: (a) when MNF estimation is done in a rigorous statistical setting from high resolution flow-pressure timeseries, and (b) there is sufficient understanding of the consumption types and patterns during day and night hours, the two approaches effectively converge, allowing for more reliable estimation of the individual WL components. In addition, when high resolution flow-pressure timeseries are available at the inlets of PMAs, the suggested version of the bottom-up approach with probabilistic estimation of MNF should be preferred as less sensitive, while allowing for confidence interval estimation of the individual components of water losses and development of proper strategies to reduce them.

Application of IWA standard water balance in strategic water loss analysis: Benefits and problems

Water losses occurring in distribution systems have effect on the operating cost, water and energy efficiency, service quality, customer satisfaction, maintenance and new resource demand. The standard water balance recommended by International Water Association (IWA) were used for defining, analyzing, regularly monitoring the water balance and sub-components, and determining the weakness and strengths of system. Water Utilities in Turkey are required to fill the water balance annually in order to analyze and monitor the performance with the regulation published in year 2014. However, in the use of this table, important problems are experienced due to the lack of technical, technological, personnel and economic conditions, data representing the field are not used and in many cases the real performance of the system is not revealed. In this study, the importance of IWA water balance in water loss management and monitoring system performance is emphasized, and the benefits and advantages are detailed by analyzing the pilot regions. In addition, problems encountered during filling the water balance, mistakes made, incomplete or incorrectly filled data and other problems were discussed. It is thought that this study will constitute a reference for the technical personnel in Utilities for measuring the data, analyzing the components and interpreting the results.

Operational and technical performance of a water distribution network in Oman

Abstract A water distribution network in an urban area in Muscat region (the capital city of Oman) is assessed for operational performance using the widely accepted methodology proposed by the International Water Association (IWA). The technical performance of this network was assessed using global performance index methods after modifying the performance levels as per local guidelines. A total of 37 operational performance indicators for the network were selected to carry out assessment. Overall operational performance showed high scores whereas some indicators showed unacceptable performance values. The network showed very high technical performance considering nodal pressures. The lower performance for pipe velocity may be attributed to the fact that the network is currently being utilized by 70% of the population for which it was designed. The residual chlorine levels were within the acceptable range of the Public Authority for Water (PAW), showing a very good performance by virtue of water quality. This study will be useful for decision makers to assess the operational, technical and water quality performance of urban networks and take actions for improvements.

Intermittent water supply systems and their resilience to COVID-19: IWA IWS SG survey

Abstract There is limited information about the current state of intermittent water supply (IWS) systems at the global level. A survey was carried out by the Intermittent Water Supply Specialist Group of the International Water Association (IWA IWS SG) to better understand the current state of these systems and challenges that water companies may have faced under COVID-19 pandemic and to capture successful management strategies applied by water utilities. The survey consisted of three parts: (1) general information about IWS systems, (2) current state of IWS and (3) resilience of IWS under COVID-19 conditions, as well as some questions about potential interventions in order to improve system performance in general and under future uncertain conditions. The survey responses were evaluated based on the Safe & SuRe resilience framework, assessing measures of mitigation, adaptation, coping and learning, and exploring organisational and operational responses of IWS utilities. Infrastructure capacity and water resources availability were identified as the main causes of intermittency in most water distribution systems, while intermittent electricity was considered as the main external cause. Participants indicated that some risk assessment process was in place; however, COVID-19 has surpassed any provisions made to address the risks. Lessons learnt highlighted the importance of financial resources, e-infrastructure for efficient system operation and communication with consumers, and the critical role of international knowledge transfer and the sharing of best practice guidelines for improving resilience and transitioning towards continuous water supply.

Indicator-based rural water service sustainability assessment: a review

Abstract The aim of this paper is to present the state of the art on the sustainability indices of rural water services in order to identify gaps in knowledge. The methodological approach used was to conduct online searches using the databases of Google Scholar, Web of Science, Pub Med, the International Water Association, and ResearchGate. Several indices have been identified in the literature including the Canadian Water Sustainability Index, Index of Drinking Water Adequacy, the Sustainable Water Governance Index, equity index in water and sanitation, WASH performance Index, Sustainable Water Management Index, and Index of water service quality. However, these indices do not provide an integrative, contextualized and prospective analysis of the sustainability of water services. In addition, these indices select only a few evaluation criteria deemed relevant. In other words, these indices choose to make visible certain phenomena and therefore make others invisible, according to the logic of action of each and to certain social compromises. These difficulties therefore encourage the development of a new index to provide an integrative, contextualized and prospective analysis of the sustainability of rural water services.

Modeling interspecific competition of the microbial community during anaerobic digestion based on cellular automata and ADM1.

Interspecific competition for substrate and space gives rise to considerable variation in biomass distribution within the microbial community. To study microbial community in depth, we used several research methods as sampling and analytical measurements, and developed a cellular automata (CA) model that would facilitate a description of the microbial growth process based on Anaerobic Digestion Model No. 1 (ADM1) of the International Water Association (IWA). Using the CA model, we aimed to determine whether interspecific competition occurs among acidogens, acetogens and methanogens, and to examine the influence of interspecific competition on the spatial structure of microbial communities. We found that acetogens and methanogens competed for core space, resulting in a multi-layer structure. Butyrate-degrading acetogens increased in number, resulting in inhibition of propionate-degrading acetogens. Hydrogenotrophic methanogens showed stronger competitive advantage than acetotrophic methanogens. The simulation showed that the multi-layer structure of the microbial community was formed by interspecific competition.