QUALITY MANAGEMENT SYSTEMS
Current U.S. and European regulations and guidance on biosolids are based on the concept of multiple barriers to the prevention of transmission of pathogens when treated sludge is applied to agricultural land. These barriers are (i) sludge treatment, which will reduce pathogen content; (ii) restrictions on which crops may be grown on land to which sludge has been applied, and (iii) minimum intervals before grazing or harvesting. Although not explicitly stated in either set of regulations, there is a balance between the degree of pathogen reduction achieved by treatment and the severity of post-application controls. Treatments achieving lower pathogen reduction are coupled with greater restrictions on post-application activities and vice versa. The overall effect is to provide a similar degree of safety in terms of human and animal health. Realizing the health goals necessitates controlling the end to end process of sludge treatment, biosolids application, and post-application restrictions. Restrictions subsequent to land application may prove difficult to enforce because they rely on the recipient to observe specified minimum time periods between land spreading and allowing grazing by livestock or the harvesting of food crops. This provides greater pressure on sludge treatment operators to achieve Class A or enhanced status for their biosolids products.
Obtaining the necessary pathogen reduction and/or end product standard requires assurance that treatment processes operate consistently within the specified parameters. In the UK, operators are employing quality management systems (QMS) as a means of demonstrating compliance. These are based on the HACCP principle. The HACCP system, as applied to food safety, originated in the 1960s. It was developed jointly by the Pillsbury Company, the U.S. Army, and the National Aeronautics and Space Administration (NASA) with the objective of ensuring the safety of foods being developed for the manned space program. The starting point was Failure Mode and Effect Analysis, an engineering system that looks at a process in its entirety (components and manufacturing stages) and seeks to identify what can go wrong. The HACCP system has become the universally accepted strategy for ensuring food safety (National Advisory Committee on Microbiological Criteria for Foods, 1997). Briefly, HACCP is a systematic approach to the identification, evaluation, and control of food safety hazards based on the following seven principles:
- Principle 1: Conduct a hazard analysis (including five preparatory steps).
- Principle 2: Determine the critical control points (CCPs).
- Principle 3: Establish critical limit(s).
- Principle 4: Establish a system to monitor control of the CCP.
- Principle 5: Establish the corrective action to be taken when monitoring indicates that a particular CCP is not under control.
- Principle 6: Establish procedures for verification to confirm that the HACCP system is working effectively.
- Principle 7: Establish documentation concerning all procedures and records appropriate to these principles and their application.
The first-stage hazard analysis is common for treatment works producing biosolids for land application and the scope can be reduced to the production of a process flow diagram. This should include all inputs into the sludge treatment, including imports such as primary sludges from smaller outlying facilities or other organic materials.
Determination of Critical Control Points
A critical control point (CCP) is defined as a step (in the treatment process) at which control can be used to prevent or eliminate a hazard, or reduce it to an acceptable level. The CCPs depend on the type of sludge treatment being used and the configuration of the works. Stressors used to inactivate pathogens include heat, pH, time, and moisture content.
Setting Critical Limits
A critical limit is one that separates acceptability from unacceptability. The critical limit may be specified within the definition of processes to significantly reduce pathogens (PSRPs) or processes to further reduce pathogens (PFRPs) (USEPA, 1993) or the UK Code of Practice (Department of the Environment, 1989). Where these are not specified, it will necessary to conduct a statistically robust program of sampling and analysis. In preparation for the proposed UK regulations, operators of sludge treatment facilities have performed sampling of the E. coli content of raw and treated sludges over typically a 28-d period. Data on potential CCPs is collected over the duration of the trial using spot measurements or the output from continuous monitors (e.g., temperature or pH).
Critical Control Point Monitoring
Each CCP requires defining a monitoring program to assess whether the CCP is under control. Ideally, this should make use of continuous, real-time measurements. This minimizes the requirement for additional sampling and analysis, but more importantly it allows for early warning that process conditions are moving out of specification.
Corrective Action
Under the proposed UK regulations, failure to achieve the critical limits for a CCP must trigger an action specified in the site HACCP plan. This may be to analyze the batch(es) of sludge for E. coli content to determine whether it complies with the microbiological standards for treated or enhanced sludge (Table 6). Biosolids not achieving the minimum end product standard are not permitted to be land-applied. In the absence of microbiological results, biosolids produced at times that the critical limits have not been achieved cannot be land-applied until such time as the process comes back into control. The options available for disposal of noncompliant biosolids include return to the sludge treatment process, landfilling, incineration, or application to nonagricultural land.
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