For a plant control scheme to provide accurate and efficient control, many process factors must be considered. The heart of the activated sludge process is located in the aeration basin. Many components are involved in the delicate balance of the micro-universe contained in an aeration basin. Some of these components are part of the original system design and are not controllable or changeable. Other components of the system that must be balanced are:
- Biomass – a blend of beneficial microscopic organisms, bacteria, and solids that convert nonsettleable solids (dissolved and colloidal matter) into settleable solids, carbon dioxide, water, and energy.
- Air – typically pumped from pure oxygen tanks or generated by blowers, fed into basin through bubble diffusers, and controlled by dissolved oxygen measurement.
- Return Activated Sludge (RAS) – most plants choose to keep mixed liquor suspended solids (MLSS) concentration in RAS line within a specific concentration range by monitoring suspended solids concentration in RAS line or sludge blanket level in secondary clarifier.
- Waste Activated Sludge (WAS) – how efficiently RAS concentration is controlled, directly effects amount of sludge being wasted. Regulating WAS is the most dramatic way to change the sludge and effluent quality.
- Throughput – the amount of wastewater that is passed through plant in specific time period.