Evolution of an Intelligent Biosolids System

Introduction Clean Water Services (CWS) is a wastewater, stormwater, and watershed management utility serving the populous of Washington County, Oregon through implementation of a watershed based NPDES permit. CWS operates 4 water resource recovery facilities (WRRF), of which two are advanced treatment facilities producing Class B biosolids through mesophilic anaerobic digestion and centrifuge dewatering. Struvite fertilizer is manufactured from thickening and dewatering liquors. The NPDES permit requires phosphorus removal to 0.10 mg/L from May to October, accomplished with a combination of enhanced biological phosphorus removal (EBPR) and chemical phosphorus removal by alum addition in primary and tertiary processes. The ramification in solids processing is that there exists significantly different sludge dewaterability characteristics between the summer and winter months. In the winter of 2014, faced with outlandish polymer doses (~80 lbs. active/dry ton) CWS completed a consultant assisted (The Centrifuge Guy) optimization of the dewatering process that led to a new sensibility in centrifuge operation focused on achieving the lowest total cost for biosolids production. The subsequence of this original optimization has been the development of an intelligent biosolids system that appropriates technology, software, and human resources to achieve total cost efficiency in the biosolids management program, in both materials and labor. Centrifuge Operation Dewatering operators are burdened by triumvirate goals; high cake solids, low centrate or filtrate solids, and polymer dose control. Relationships between the three are not simple and site specific. Maximizing one parameter often leads to sacrificing the others. When the goals are aggregated and presented as the component costs of haul, polymer, and recycled solids and as the total cost, the job becomes clear. Beginning with simple spreadsheet tools, CWS has advanced cost driven centrifuge operation to real-time SCADA displays and trending. A centrifuge replacement project offered the opportunity to add instrumentation to the process to advance real-time analysis to real-time control. Process analyzers (Valmet) were installed on the feed sludge line and cake chute for total solids (TS) and on the centrate drain line for total suspended solids (TSS). Previous iterations of cost calculations relied on daily laboratory data and operator analysis of cake solids by moisture analyzer Technology employed in the new system enabled true real-time information. It has also enabled new control automation modes. In TSS control, the polymer dose is adjusted by the PLC to maintain a centrate TSS setpoint for quality control in the feed to fertilizer manufacturing. Data and Report Automation An immense amount of data must be generated, transformed, analyzed and maintained to meet the requirements in the 40 CFR Part 503 regulations as well as to comply with biosolids management plans required by state agencies. An immensity of human resources can be expended to manage this flow of data. Manual transmission of data between databases is not only time consuming but also increases the odds of erroneous data. CWS has implemented smart technologies and digital solutions to automate much of this data management. A prime example of this is the installation of smart scales used to weigh biosolids trucks. Previously weigh tickets would be collected at the end of the month and hand entered into a spreadsheet on an individual hard drive. Utilizing the smart scale, all the ticket data is automatically imported into a SharePoint site that tracks each load as it happens, including weight, vehicle number, and application site destination. Field reports are provided by the applier as they happen and field completion status is continuously updated. The biosolids annual report required by Oregon DEQ contains 21 sections of information to be filled in and an additional 40 pages of supporting documentation. With all the information now located in Hach WIMS and SharePoint databases, the report is largely auto-populated, requires little manual entry, and a final review. Communication and Visualization Power BI has been deployed extensively for communication to managers and stakeholders, but also for visualization of operational efficiency by process control analysts. These dashboards display information ranging from average monthly cake solids to fuel price history and transactions to financial information like budget to actual expenditures. The value of these dashboards is that they aggregate data from different data generators and make it easily accessible to anyone inside or outside CWS. Ongoing Development Efficiencies are continuing to be found by CWS staff. Integration of GIS software is underway to facilitate field application planning that will minimize the distance and number of times that application equipment must be moved to a new site. GIS systems can also be used as visual interfaces providing an array of data on application sites as well as for customizing application rates down to the detailed level of specific sections of an individual field. CWS is also undertaking the agronomy aspect of land applying biosolids as an in-house function. Although it is a small part of the total cost of biosolids utilization, there is the potential for cutting a high amount of waste from the process. Empowering the biosolids management staff with agronomy education and skills can make it possible for a single individual to make a single site visit and accomplish a suite of tasks; field inspection, soil sampling, meeting with hauling and application operators, and developing the personal relationships with landowners that are vital to the success and future of beneficial reuse of biosolids.