Development of an operational performance indicator system for activated sludge wastewater treatment plants

The aim of this system is to provide a continuous performance assessment and improvement framework for small-to-medium sized urban activated sludge (AS) wastewater treatment plants (WwTPs) in Ireland. The fundamental objective of this system is to facilitate the implementation of best practice sustainable AS WwTP operation, monitoring and management by integrating performance measures/indicators into this overall framework. The term ‘sustainable optimisation indicator’ (SOI) was devised to describe the system in relation to optimising the performance of AS WwTPs and highlight the stakeholder consultation focus of the system. The framework was developed and modified using comprehensive stakeholder consultation to incorporate the needs and views of both technical and general stakeholders. Gordon & McCann (2015) reported that currently there is no system to monitor AS WwTP operational performance in Ireland that would assist with improving plant operating performance and sustainability.

Sustainable operation, optimisation and performance evaluation of municipal WwTPs in Ireland is topical due to the transfer of water and wastewater operational and capital delivery functions from 34 individual local authorities (LAs) to a single national water utility. The new national water utility is regulated by the Environmental Protection Agency (EPA) and economic regulator. LAs are now working as contractors under a 12 year service level agreement with the national water utility for WwTP operations and management. Private contractors (e.g. design, build & operate) contracts have transferred from LAs to the national water utility. Applicable legislation for urban wastewater treatment in Ireland includes the European Union Water Framework Directive (OJEC 2000), the 1991 Urban Wastewater Treatment Directive (OJEC 1991) and the associated Regulations. The EPA (2014) report outlined that 534 urban areas (359 areas with a population equivalent from 500–2,000 PE, 118 areas from 2,000–10,000 PE and 57 areas with over 10,000 PE) in Ireland were subject to the wastewater discharge licensing process in 2013. There are in excess of 500 WwTPs in Ireland with a size of less than 500 PE that operate under a certificate of authorisation and are not eligible to be licensed. A single national water utility means reduced variation in operation and management systems when compared to the previous local authority controlled system, making a performance assessment and improvement framework more practicable.

A comprehensive literature review of best practice AS WwTP operating, management and optimisation guidance was carried out in order to assist with initial optimisation fieldwork. The aim of the optimisation study fieldwork was primarily to identify the scope for improved economic and environmental performance of urban AS WwTPs in Ireland and to identify a methodology which would be useful for continuous performance assessment and improvement of plant operations. This fieldwork was carried out by engaging with operators, managers and senior managers of urban AS WwTPs and working alongside them in their day-to-day role, assisting with process management, troubleshooting and the implementation of optimisation studies and performance improvement measures. Typical physical (assets), technical (operational) and organisational plant performance limiting factors associated with small-to-medium sized AS WwTPs were identified during this fieldwork. This field research allowed the various stakeholders associated with wastewater services provision to be identified and their characteristics, views and work practices assessed. A national survey of plant managers, wastewater service providers’ organisational structures and overview of treatment assets was also carried out to determine the overall characteristics of the wastewater industry.

A literature review was carried out to determine the range and scope of existing performance assessment, indicator and benchmarking guidance systems used to assess and monitor wastewater services and plant operational performance. Key themes were identified to assist with the development of indicator categories and indicators that could be applicable or adaptable to individual AS WwTPs in Ireland. This review contributed to the formulation of the Preliminary SOI Set which is the first main stage in the development process. The relevance of the performance measurement areas identified in the literature were evaluated in conjunction with findings from the initial optimisation field studies, the current status of the urban wastewater treatment sector in Ireland and the objectives of the SOI system being developed. This literature review also contributed to setting the goals for sustainable AS WwTP operation and management which are used in the formulation of appropriate performance measures to measure goal attainment as discussed by Quadros et al. (2010) and others.

The SOI system being developed aims to improve both plant operational performance and the level of service to external stakeholders. ISO 24511:2007 refers to water as a social good and that water services activities support the social, economic and environmental aspects of sustainable development. This Standard also emphasises the need for water utilities to be transparent to and inclusive of all relevant stakeholders. A stakeholder-based participatory approach was used in the development process of this SOI system similar to that used by Amajirionwu et al. (2008) in the development of Sustainable Development Indicators for managing biosolids in Ireland. The concepts outlined in the Aarhus Convention (UNECE 1998) relating to access to information and public participation in decision making on activities that may affect the environment are integrated into the development of this SOI system. All relevant stakeholders (in particular external stakeholders such as environmental groups and individuals) were included in the various consultation phases. Ultimately, this system can be utilised by stakeholders for determining plant performance and levels of service. This could provide accountability for and transparency of WwTP operations to stakeholders. Main et al. (2008) indicate that in contrast to a private water utility, which may be most concerned about financial indicators relating to return to shareholders, public bodies typically have a much wider set of objectives including social, economic, environmental and financial performance.

Preliminary consultations were held through meetings, phone calls and email communication with key wastewater sector stakeholders. Stakeholders were identified based on optimisation field studies, referrals from other stakeholders, literature review and exploring the extended relationships between the various actors from a technical plant operation/management level to a community and environment level. Stakeholders who have an interest in and/or an influence on the operating performance of urban AS WwTPs were identified for the main consultation phase involving an online survey.

An online survey questionnaire was developed and administered to stakeholders via email to determine stakeholder knowledge and identify issues that they consider to be important in relation to the operating performance of urban AS WwTPs in Ireland. This information, in conjunction with findings from optimisation field studies, literature review and the goals developed for sustainable AS WwTP operation and management contributes to the development of indicators. The potential issues raised in the survey were formulated based on field optimisation studies, plant operator/manager consultation and literature review. These issues (10 general and 24 technical issues) were grouped into categories including ‘General Issues’, ‘Environmental Performance’, ‘Plant Technical Personnel’, ‘Plant Monitoring’ and ‘Plant Operation and Maintenance’. Stakeholders that indicated that they did not have any technical experience/knowledge of urban AS WwTPs were directed to answer only the ‘General Issues’ rating type question. Participants were asked to rate the importance that they place on each of the prescribed issues on a 5-point Likert-type scale from ‘Not at all important’ to ‘Extremely important’ with an option to state ‘Don't know’. Respondents were requested to participate in the next phase of stakeholder consultation for selection and ranking of the draft set of indicators. The survey was pre-tested, before full-scale circulation to all stakeholders, with a selection of key respondents from each stakeholder category to ensure that survey instructions, questions and prescribed answers were easily understood, the layout and functionality of the survey was acceptable and that it could be completed in a reasonable time-frame of approximately 10–15 minutes. Questions with open answers were included typically after closed questions to afford stakeholders the opportunity to explain or provide context for any of the answers provided. Fowler (2009) described that the advantages of open survey questions are that unanticipated answers can be obtained, the real views of the respondents may be more closely described and that respondents like the opportunity to answer some questions in their own words rather than being limited to prescribed answers alone. Purposive and snowball sampling techniques were used to solicit the participation of stakeholders. The research project description and details of this stakeholder consultation survey were made available on the IT Sligo Research Webpage by means of a link to the research project webpage.

Stakeholder survey results and follow-up consultation will be used to modify the Preliminary Set to form the Draft SOI Set. The follow-up stakeholder consultation meetings and discussions are currently taking place to determine additional information relevant to the development of indicators and to clarify any issues raised in the survey responses. The development process of this Draft Set includes careful selection of indicator numerator and denominator variables as well as indicator measurement periods. A key consideration of this stage was to ensure that a comprehensive but concise set of indicators was developed that would facilitate effective performance assessment, enable the identification of sustainable performance improvement measures and provide the desired information in a comprehensible format to external stakeholders. As with other performance indicator type systems, this SOI system is designed to comply with the requirements of ISO 24511:2007.

The planned methodology for selection of the Final SOI Set involves another stage of consultation with the stakeholders who identified themselves in the initial survey as being willing to participate in the next stakeholder consultation phase. Other key organisations and individuals may also be utilised. The next consultation phase will consist of an online survey which will present each of the indicators including information relating to its purpose, description of variables, units and frequency of calculation. Stakeholders will be invited to rate the importance of each indicator in terms of several criteria including data availability, relevance, accuracy, significance, validity and practicality. The dynamic nature of this research methodology in terms of its reaction to stakeholder requirements means that the planned final stage of indicator selection is subject to minor changes.

The review of literature on best practice plant operation and optimisation in conjunction with field studies informed the development of a methodology for carrying out plant audits to determine the current operating status of urban AS WwTPs. Key publications included the US EPA (1984) Composite Correction Programme, WEF (2008) Manual of Practice and WEAO (2010) Optimization Guidance Manual for Sewage Works. Field studies and preliminary plant manager/operator surveys indicated the need for a more consistent and sustainable operational approach and the requirement for performance evaluation and optimisation of existing AS WwTPs in Ireland. Field studies assisted in identifying the type of performance assessment system that would be appropriate for the Irish context and to select key parameters for incorporation into the SOI system. Plant operation and optimisation field studies were a cornerstone in the development of the stakeholder consultation methodology due to the practical experience gained from working with WwTP operators. Key findings of these optimisation field studies, which are outlined in more detail in Gordon & McCann (2015), include the implementation of effective sampling, data management and analysis methodologies that enabled the identification of cause and effect relationships. Operators were trained in the application of appropriate measures to cost effectively improve the operating performance of urban AS WwTPs while maintaining consistent or improved treatment performance. A survey of plant operators/managers provided further insight into their role and in particular the priority that they place on monitoring (e.g. influent & effluent quality parameters), measuring (e.g. settled sludge volume) and calculating various process parameters (e.g. mean cell residence time). A survey of AS WwTP operational and management organisational structures and the characteristics of the treatment assets found inconsistencies relating to personnel (e.g. reporting structures) and assets (some plants did not have basic inlet/outlet flow meters installed) that were not conducive to satisfactory performance. A plant without inlet/outlet flowmeters may be meeting the required discharge requirements for final effluent but, in terms of operational performance, the plant would be seen to perform poorly from a due diligence viewpoint due to the lack of data for accurate data-based process control decision making. A key point raised by Matos et al. (2003) was that performance indicator systems require a lot of data and therefore provide an incentive for good data management. When it comes to performance assessment of urban AS WwTPs, it was clear from various site visits and optimisation studies that just because a particular parameter can't be measured or isn't currently being measured doesn't mean that it shouldn't be measured. This concept is extended to the SOI system being developed. This stage of the research found that the lack of consistency in organisational structures and managing treatment assets in Ireland highlights the importance of a plant audit as a key component in the performance assessment and improvement process. This applied research phase also provided the relevant contacts for further stakeholder consultation and contributed to the formulation of the SOI stakeholder consultation survey.

A comprehensive literature review of existing performance measurement systems assisted in focusing the development of this SOI system on plant operational performance and in the identification of key performance measurement areas or categories. Key publications include Matos et al. (2003), ISO 24511:2007, Main et al. (2008), Lindtner et al. (2008), Quadros et al. (2010), Cabrera et al. (2011), Balmér & Hellström (2012) and Matichich et al. (2014). Quadros et al. (2010) reported that preliminary field testing results of the Performance Assessment System (PAS) system were described as encouraging in terms of the adequacy of the system as a management instrument for the continuous improvement of WWTP performance. Many indicator systems focus on the wastewater utility level whereas this SOI system focuses on performance assessment and improvement at the treatment plant operations and management level. This literature review was a useful step in framing the scope of indicator categories and also in identifying relevant indicators that could be adapted to a WwTP level for the Irish context. Much of the literature relates to performance measurement over relatively long measurement periods in the region of one year at the utility level rather than at a treatment plant level. Field studies and preliminary consultation with Irish municipal wastewater treatment sector personnel has pointed towards a system that utilises performance assessment at a treatment plant operations level. This type of system is expected to achieve cost-effective optimised operating performance from existing AS WwTPs using existing assets whilst facilitating increased levels of service to all stakeholders.

The definition of objectives/goals for sustainable AS WwTP operations and management is a key step in the SOI development process. A literature review of performance assessment and benchmarking systems for wastewater services identified various objectives of water utilities including those set out by Main et al. (2008), Quadros et al. (2010) and others. This literature review was used with the findings from field studies and best practice plant operation literature review to set out the objectives for the provision of sustainable AS WwTP operations and management in the context of Ireland. These goals are used as the basis for indicator formulation in the Preliminary SOI Set. The specific goals of sustainably operated and managed AS WwTPs (to meet the stakeholder requirements) are to:

• Provide diligent, capable and supported plant operation and management personnel with adequate training, knowledge, experience and resources to facilitate effective and efficient data-based process operational decision making

• Ensure that effective sampling, testing and data-management regimes are in place

• Ensure optimal pollutant removal efficiencies and environmental compliance

• Minimise energy, chemicals and fresh water usage in a sustainable manner

• Enhance reliability using effective asset management and maintenance practices

• Protect the safety and health of the public and persons on site

• Proactively communicate, consult and cooperate with all relevant stakeholders

• Make efficient use of financial resources

• Ensure sustainable management and disposal of biosolids, residuals and other waste

• Provide service continuity and consistency using capable human and physical infrastructure in a sustainable manner

These goals are subject to refinement/modification on completion of a comprehensive analysis of the SOI stakeholder survey results.

An example of an issue of importance to plant operation, management and monitoring stakeholders can be seen in Figure 5 for issue ‘B2 - Insufficient plant operating data for process control decision making’ where over 80% of stakeholders in this category view this potential issue as being either ‘Extremely important’ or ‘Very important’. This issue is inherently relevant to the ‘Process Monitoring and Treatment Efficiency’ indicator group category. Some examples of potential performance assessment indicators derived from this verified issue of importance, in combination with the identified goals and the field study findings include the following:

• The ratio of the number of daily quality parameter tests (e.g. influent Chemical Oxygen Demand (COD)) carried out per month to the desired target number of tests prescribed for effective monitoring.

• The ratio of the number of daily process parameter tests (e.g. SSV₃₀) carried out per week to the desired target number of tests prescribed for effective monitoring.

• The ratio of the number of daily process parameter calculations (e.g. Mean Cell Residence Time (MCRT)/Sludge Age, F/M ratio) carried out per week to the desired target number of tests prescribed for effective monitoring.

This system is aimed at the plant manager/operator level for operational performance measurement, tracking and oversight purposes but also provides plant performance metrics relevant to the needs of all stakeholders. The survey questionnaire results are in the process of being analysed in detail. The Preliminary SOI Set is being adapted based on survey findings to formulate the Draft SOI Set. The Draft SOI Set will consist of nine indicator categories. These categories are performance assessment areas relating to the main operation and management components of municipal AS WwTPs. These categories and an overview of the performance measures incorporated into this system are shown in Table 1.

The assessment period over which indicators are calculated is critical to the utility of this SOI system. It is important to ensure that measurement periods are appropriate to ensure sufficient data to enable the identification of areas of poor performance and the derivation of improvement measures is collated. The assessment period proposed for this system will facilitate effective monitoring and control to ensure that sustainable process operation and management strategies are consistently implemented. Frequent indicator assessment allows for more accurate decision making by facilitating the identification of cause and effect relationships. The nature of this system in terms of its fundamental linkages to process oversight and the incorporation of the plant audit and target setting stages means that, where possible, many of the indicators are ratios between variables where the denominator is the pre-set desired target value for that variable. This type of system would be most relevant for application and calculation of indicators by water services providers as they are best placed to source and collate the requisite data pertaining to plant operations and performance. The indicators could be used by:

• Utility/contractor operations and management personnel to assess and monitor AS WwTP operating performance, identify performance improvement measures, and assist with sustainable decisions and strategies.

• Environmental enforcement and assessment personnel to monitor AS WwTP operations and environmental compliance.

• Non-Governmental Organistations (NGOs), individuals and other government organisations to monitor plant operations, management and plant operating performance, and to assist with facilitating the drafting of submissions to the water services provider during the stakeholder consultation phase.

• Industry experts and academics to focus on and identify information, design, research and innovation needs of the wastewater sector and its stakeholders.

• Economic regulator to protect the interests of people served by a water utility.

The recent significant changes in the water sector in Ireland have increased the awareness of issues surrounding provision, operation, maintenance and cost of running treatment assets. Increasingly the general public, environmental groups and other affected and influential stakeholders require a higher level of accountability, transparency and responsiveness from the new water utility and regulatory authorities. The national water utility and service providers responsible for operating, managing and monitoring treatment plants require mechanisms to actively monitor performance in a systematic and consistent way for all plants, irrespective of operating context and resources. There is a need to optimise personnel, physical and financial resource use and improve plant operating performance from an operations and management point of view. A further objective is to ensure that a satisfactory level of service is being provided to all key stakeholders, including the environment. Field studies, review of literature and comprehensive engagement with all relevant stakeholders identified the characteristics and concerns of the Irish wastewater treatment sector. Best practice plant operations and international performance assessment and improvement frameworks are identified, and a solution for Irish AS WwTPs based on consistent monitoring and improving wastewater treatment operations and management has been devised. The SOI system under development will allow the implications of current operational practices to be evaluated, assist with future planning of resources/funding to plants and provide a rationale for sustainable decisions and strategies. It is also a first step towards benchmarking of AS WwTP operations in Ireland and incorporates a sustainable approach, incorporating the views, concerns and requirements of a range of relevant stakeholders in its development and application.

This research is funded by the Irish Research Council ‘Embark Initiative’.