Wastewater management practices at the more than 15,000 publicly-owned treatment facilities in the United States historically have focused on producing liquid effluents to protect public health and the environment. Efforts to optimize the cost of accomplishing these treatment goals, as well as to achieve regulatory compliance, have been directed primarily toward the performance of the liquid processing systems.
However, with new and increasingly-stringent regulations governing solids generation and disposal practices mandated under the Clean Water Act, Resource Conservation and Recovery Act, and the Clean Air Act, wastewater plant managers now must place increased emphasis on biosolids management to maintain compliance and control their costs. Lack of a well-designed and executed sludge (biosolids) management program can result in excessive operating expenses, odor problems, regulatory fines, and poor relations with the community served. Undoubtedly, bio-solids handling and disposal gradually is becoming a bigger item in the municipal wastewater treatment budget.
The USEPA's 40 CFR Part 503 regulations, now included in virtually all treatment facilities' NPDES (National Pollutant Discharge Elimination System) permits, set standards for the use or disposition of municipal wastewater biosolids. These comprehensive rules address five major areas
- General permit requirements
- Reduction of pathogens and vector attraction
- Land application for a beneficial purpose
- Surface disposal
Provisions governing operational requirements, accepted management practices, pollutant limits, and monitoring, recordkeeping and reporting requirements also have been established by the 503 rules.
The 1990 Clean Air Act Amendments (CAAA) will significantly affect municipal biosolids management practices within the next few years. Titles I, III and V of the CAAA set limits for the release of numerous volatile organic compounds (VOCs) and hazardous air pollutants (HAPs) from wastewater treatment facilities. Furthermore, they mandate time-consuming and complex planning, permitting, monitoring and reporting requirements. In some cases facility modifications or operational changes will be required.
Evaluating biosolids practices
The operational success, as well as cost effectiveness, of a biosolids management program is dependent upon many variables, including
- Plant location and climate
- Influent quality
- Plant design
- Monitoring and reporting requirements
- Energy and labor costs
- Community acceptance
Each of these factors has to be evaluated. Then the "best-fit" program can be designed and executed to meet a treatment facility's unique biosolids management needs.
Certain basic questions should be asked at the start of any evaluation of a wastewater plant's biosolids management practices. What is the cost of biosolids management? Does that cost include all biosolids processing and disposal expenses? Is there potential for significant cost reductions? Can the quality of the biosolids be altered or improved to benefit or simplify the processing scheme, and to meet new regulatory requirements? Plant managers must also consider emerging technology issues, including the availability of different or new treatment processes; new management practices; the current outlook as to maintaining compliance with applicable biosolids regulations; and associated manpower and/or expertise requirements.
To help evaluate operational practices, a mathematical model of a facility's treatment systems can be developed using available computer modeling techniques. The benefits versus costs of altering systems and practices can now be weighed by making changes to the model's parameters (e.g., digester residence time, chemical feed rates or possible regulatory effects of the 503 rules) to explore "what if" scenarios.
Various operational parameters, alternative processing strategies and new disposal methods can be quickly and effectively investigated using such a model, without disrupting actual operations. Subsequently, an action plan can be developed to implement new solids management techniques, or correct performance limiting factors. Models are helpful in finding ways to utilize existing resources better and to cut costs.
A biosolids program may involve beneficial use, incineration or surface disposal, but certain conditions must exist if the program is to be cost-effective. It must include the balanced operation, maintenance and management (OM&M) of a facility's liquids and solids processes, which directly affect biosolids generation and quality. A contemporary program also may require additional resources to implement appropriate practices, and personnel with the necessary experience and/or training in those practices. At the same time, these operational considerations must be tailored to maintain compliance with the tightening regulations.
Interactive process management
Wastewater staffs, until recent years, generally regarded biosolids management as merely a secondary function, or at least secondary to the liquid treatment process. This view also has been almost universal among consulting engineers, who design the plants. It is essential, however, that operators and designers recognize the interactive nature of a facility's liquids and solids handling functions. Focusing solely on producing a high quality liquid effluent to meet discharge requirements, with little regard for the quality or volume of the biosolids, can easily overwhelm a plant's sludge handling capabilities, lead to offensive odors, contribute to regulatory violations, and necessitate costly capacity expansion projects.
A facility can optimize its treatment effectiveness and costs of biosolids management, as well as liquids management, by maintaining a balance between liquid and solids process objectives through interactive process management. An example is the establishment of clarifier flow and wasting rates that produce a suspended solids content which meets liquid effluent standards. But they also must generate underflows with high solids content to reduce the volume of biosolids for further treatment or disposal. This type of give-and-take among treatment objectives should be incorporated into all process sections.
Several other interactive practices must be in place to ensure successful biosolids management. Lack of an effective industrial pretreatment monitoring and enforcement program, for example, can increase treatment costs, hamper regulatory compliance activities, and restrict disposal options. Likewise, a thorough program of preventive maintenance is especially important if the solids processing systems are to operate efficiently, since they tend to incur more wear and tear than their liquids processing counterparts in other plant sections.
Standard operating procedures (SOPs) and performance goals also should be developed for each process to help ensure proper OM&M practices are in place for both solids and liquid functions. The SOPs should reflect a combination of process design, standard treatment practices and in-the-field operator experience. It should be noted that while such guidelines are important, flexibility is equally important for meeting performance goals while controlling process expenses. Rigid adherence to the "status quo" of SOPs can stifle an operator's ability to find innovative process improvements and solutions to problems.
Numerous municipal wastewater treatment facilities do not possess the resources to implement modern solids management programs. Many were built as part of the Construction Grants Program, begun in the 1970s, when the main regulatory goal was to produce an acceptable liquid effluent to meet set limits. In general, a lower priority was given to the biosolids quality control and management function, particularly at smaller plants.
Accepted practices today, however, can require additional financial resources to operate cost-effectively and meet federal, state and local regulations. Substantial capital investment in new, often sophisticated, systems using chemical stabilization, dewatering, odor reduction, or other technologies often is dictated by overriding community acceptance and regulatory issues.
The increasingly-used method of agricultural land application, for example, may require the addition of advanced processes, or transportation and application equipment. Although financially challenging for some municipalities, a return on investments in such programs can be realized from both reduced costs and long-term, environmentally-friendly strategies. Approximately 50 percent of the wastewater biosolids generated in the United States are now land applied through beneficial use programs.
The implementation of additional chemical, physical and biological monitoring also is important, and often is regulated. The more solids processing and quality control data available to an operator, the more informed is the decision that can be made addressing operational trends and maintaining process objectives. For example, where communities incinerate biosolids, treatment plants may have to install additional equipment to monitor pollutants or by-products in their atmospheric emissions.
Thorough operator training, as in all wastewater OM&M areas, helps ensure that the various biosolids management tasks are carried out properly. While some skills are required for other plant operations, many are new and different. Biosolids programs, depending upon the combination of practices utilized, can require personnel with expertise in a wide variety of disciplines, including
- Odor control
- Regulatory permitting
- Product marketing
Biosolids composting, for example, requires knowledge of complex process management, as well as marketing skills for dealing with the biosolids product classified as "exceptional quality" under the new 503 rule.
Expertise in community relations also also has become more important due to the growing influence of organized environmental, local community and other citizen groups. Beneficial use provides a good example of the need for community relations skills. Increased truck traffic, real or perceived odor problems, and highly-visible distribution activities often require ongoing and sometimes intensive public education programs. Acceptance by the community, once a less important concern than program costs and regulatory compliance, is now absolutely essential for successful biosolids management.
Modern solids management
It is clear that wastewater biosolids OM&M practice should be approached as a production process, rather than merely as a treatment process. In the case of "exceptional quality" biosolids, OM&M should, in fact, be viewed in the same light as a product manufacturing operation. Facility managers should incorporate this operating philosophy and work toward producing the highest-quality product possible, balanced against available resources and costs. Many of the quality-control techniques used successfully in private-sector process industries can be adapted to the production of biosolids.
About the Authors:
John Nelson is a senior technical specialist and Peter Wernsdorfer is director of residuals management for Professional Services Group, Inc. (PSG), in Houston, Texas.