Automation of Water Resource Recovery Facilities. Water Environment Federation

solids in the sludge feed and centrate. This system resulted in a savings of 11.7% of polymer usage, lower recycle rates, a higher percentage of dry solids in the cake, and higher consistency in the cake (Bates and Montoya, 2010).

2.1.4 Additional Savings

      There are other areas of a WRRF that represent potential savings that depend on unique characteristics of the utility. Effective automation can reduce capital costs by allowing staff to maximize existing treatment capacity and facilities, enhance maintenance, reduce equipment wear and damage, reduce chemical usage resulting in reduced chemical storage requirements, and minimize chemical hazards.

      Energy efficiency improvements can also yield environmental benefits by reducing greenhouse gas emissions and improving a utility’s carbon footprint. The magnitude of the effect of energy reduction measures on a utility’s carbon footprint is highly dependent on local conditions and the amount of greenhouse gases attributed to the electrical energy source. For example, utilities that obtain electricity from coal-fired power plants will typically have a higher effect than those that obtain a significant amount of energy from renewable sources such as hydroelectric generation.

2.2 Intangible Economic Benefits

      2.2.1 Compliance Monitoring

      Monitoring of several key process parameters is required under water-quality regulations. State and federal discharge permits, for example, require WRRFs to record their daily flowrates and report average monthly and maximum daily flows. Most WRRFs also must collect flow-weighted composite samples for analysis. The samples may be collected by an operator and composited manually based on the flowrate during sampling or collected by an automatic sampler paced by a flow meter’s signal.

2.2.2 Improved Process Performance and Reliability

      Automation can allow for more accurate and consistent control of a process, resulting in improved performance. Improved performance can take the form of better yields, in terms of the amount of wastewater treated for a given unit of chemicals or energy, or fewer unwanted byproducts. While an operator can occasionally adjust a process based on changing facility conditions, automation can continually adjust the process to more closely track an optimal operating condition. Reliability can also be improved as regular adjustments to alarm conditions and fault handling can be programmed into the control system.

      As an example, the Water Environment Research Foundation (2002) presented five case studies of facilities that implemented automatic solids retention time (SRT) control. Significant benefits were demonstrated by the facilities, including improved process performance. Figure 2.1 shows an example of the effects on several process parameters of changing from manual control to automatic SRT control of an activated sludge process. The graph shows more consistent mixed liquor suspended solids and mass of wasted sludge. This affects not only the activated sludge process, but also sludge consistency, thereby improving operation of downstream thickening.

      Another advantage to the improved control is the potential to maximize unit performance, potentially delaying upgrades.

2.2.3 Improved Responsiveness

      With automation, operators can often respond to situations faster as they arise. Better information is available to more quickly troubleshoot issues, and action can be immediately taken through the control system instead of travelling to the affected location. Improved responsiveness can also result in reduced travel time and labor. It is important to point out that, for many utilities, operators are required to travel to the location of an alarm to investigate the problem. However, proper automation can help identify problems, improve data collection, and increase the ability to “fail” in a predictable manner, thereby improving the overall response to upsets or alarm conditions.

      FIGURE 2.1 Performance comparison for a WRRF with manual and automatic SRT process control (Tchobanoglous, 2003).

2.2.4 Enhanced Decision Making

      Improved measurement and data collection can lead to better information being available for planning, management, and operational decisions; engineering studies; and maintenance and troubleshooting. For example, if appropriate power monitoring is put in place at a WRRF, then data can be collected and used to evaluate the actual energy consumption of particular pieces of equipment or unit processes. Energy consumption data combined with operational data such as pressure and flow can be used to evaluate equipment efficiency and performance for a wide range of operating conditions. If the data indicate that the equipment is not operating at peak efficiency, this can help identify what the issues could be. For example, it could point to a degradation of equipment performance over time or that the equipment is being operated under condition changes that are less than optimal for the particular equipment. In many instances, minor operational or automation changes can improve energy efficiency or energy costs. Power monitoring should be evaluated so that metering, or submetering, is installed at the correct locations required to understand where energy is being consumed in the facility.

2.2.5 Reduced Risk

      Today, penalties for improper risk management include fines; incarceration; wasted resources; and public outrage at facility odors, unsightly receiving waters, and discharged toxics. Instrumentation and controls can reduce the risk of permit violations, which are very costly. By automating repetitive tasks, potential entry errors can be reduced, thereby reducing the potential for accidents (e.g., chemical spills, fires, electric hazards, human fatalities, etc.). Control systems and associated security improvements can improve a utility’s ability to identify security issues and to respond faster.

2.2.6 Workforce Morale and Aging

      Automation allows operators to focus on optimizing a facility as opposed to “being” the control system. In addition, institutional knowledge can be incorporated to operating control strategies, reducing labor requirements, and preparing a utility for the loss of long-term knowledgeable staff.

2.2.7 Customer Satisfaction

      Automation can help identify potential system upsets earlier, thereby helping to avoid issues and improving overall operational efficiencies of a utility. These issues, in turn, can affect overall end-user satisfaction.

3.0 AUTOMATION COSTS

      Automation equipment, including sensing instrumentation, control elements, controllers, software, and programming, typically adds at least 4 to 12% to the total cost of building a treatment facility. Project costs are site-specific and depend on the treatment processes involved and managers’ decisions about the tradeoffs between automation and labor. Once installed, an automation system has ongoing maintenance costs. Such costs should be considered early in the design phase because an automation system that is not maintained properly will eventually fail and fall into disuse.

      It is worthwhile to note that many of the benefits identified in the previous section may only be achieved through the application of complex automation solutions with the associated costs. For example, tighter process control may require additional instrumentation, field devices, sophisticated software algorithms, and ongoing operations and maintenance support.

      There have been studies that look at correlating the cost of SCADA systems to facility-production capacity (U.S. EPA, 1999). Although the data in these studies indicated a rough correlation, the wide deviation makes it difficult to develop a reasonable cost estimate without completing a detailed analysis.

      The American Association of Cost Engineers (Christensen et al., 2011) has established five categories of estimates. Each category includes