An anaerobic lagoon is a deep earthen basin with
sufficient volume to permit sedimentation of settlable
solids, to digest retained sludge, and to anaerobically
reduce some of the soluble organic substrate. Raw
wastewater enters near the bottom of the pond and
mixes with the active microbial mass in the sludge
blanket. Anaerobic conditions prevail except for a
shallow surface layer in which excess undigested
grease and scum are concentrated. Sometimes
aeration is provided at the surface to control odors.
An impervious crust that retains heat and odors will
develop if surface aeration is not provided. The
discharge is located near the side opposite of the
influent. The effluent is not suitable for discharge to
receiving waters. Anaerobic lagoons are followed by
aerobic or facultative lagoons to provide required
treatment