Sludge Production and Management

The management of biosolids from treatment plants is a growing problem in New Zeland and world-wide. A notable feature of the Packed Bed Reactor is its ability to perform without generating any appreciable volumes of sludge or biomass.  This is achieved by maintaining the aerobic microorganisms living on the textile media well into the endogenous respiration phase, meaning birth and death rates are in equilibrium regardless of incoming flow rates. Figure 2 presents sludge production correlated to position on the bacterial growth curve. Approximate positions are indicated for activated sludge, extended aeration and packed bed filters.The primary tanks in the effluent sewer, if properly designed, provide considerable pretreatment, reducing organic and solids loading on downstream treatment processes. The septic tanks comprise the major sludge handling system, sludge separation and storage in these tanks is a passive process, requiring no operator intervention until the tank is pumped. The recirculation tank will accumulate a small amount of sludge which is essentially the inorganic component of the 30 ppm TSS derived from the STEP tanks once they have passed through the Biotube effluent filters.  This sludge is pumped from the recirculation tank once the level reaches 300 mm above the base of the tank.  We expect this to occur at a minimum of 7 to 10 years.This can not be said for aerated wastewater plants which generate much higher volumes of activated sludge.