Maintenance for wastewater systems can either be preventive/predictive or corrective activity. Effective maintenance programs are based on knowing what components make up the system, where they are located and the condition of the components. With that information, preventive/predictive maintenance can be planned and scheduled, rehabilitation needs identified, and long-term improvement programs planned and budgeted. High-performing agencies have all developed performance measurements of their maintenance program and track the information necessary to evaluate performance.

Commonly accepted types of maintenance include the following classification:

Corrective Maintenance (Those maintenance activities are also called reactive):

Maintenance classified as corrective, including emergency maintenance, is reactive. Only when equipment or system fails maintenance is performed. A corrective maintenance is characterized by the inability to plan and schedule work, the inability to budget adequately, the poor use of resources and a high incidence of equipment and system failures.

Preventive / Predictive Maintenance (Those maintenance activities are also called proactive):

Preventive Maintenance being defined by a programmed, systematic approach. This type of maintenance will always result in improved system performance except in the case where major chronic problems are result of design and/or construction flaws that can not be corrected by operation and maintenance activities. Major elements of preventive maintenance programs are planning and scheduling, records management, spare parts management, cost and budget control and training program for the involved personnel.

Predictive maintenance is a method of establishing baseline performance data and monitoring performance criteria over a period of time so that failure can be predicted and maintenance can be performed on a planned, scheduled basis.

In reality, every agency operates their system using a combination of corrective and emergency maintenance, preventive maintenance and predictive maintenance methods. The goal should be to reduce the corrective and emergency maintenance efforts by performing preventive maintenance that will minimize or even eliminate system failures and optimize operation cost.

Optimizing the operating costs, however, does not only mean having an optimum treatment process. Working effectively also means to optimize the operation of each individual part of the facility – for example, considering the cost of a measuring point is comprised of only 25% investment costs (planning, purchasing, commissioning) but 75% general operating costs, preventive and reactive maintenance costs: Obviously, there is great potential for cost reduction over the entire life cycle of the whole treatment system (see figure 6)

Figure 6: Costs and maintenance seen as a whole; the optimum is achieved from the best relationship between costs and availability [Müller, 2003]