Activated Sludge Process

Because of the high BOD loads that remain in the wastewater following primary treatment, further treatment must be provided before the effluent may be discharged to the Hackensack River. The BCUA employs a biological treatment system known as the activated sludge process to achieve secondary treatment. During this process, the wastewater flows into an aerated and agitated tank containing a complex mixture of bacteria, fungi, protozoans, and other microorganisms which are referred to collectively as the biomass. The dissolved and suspended organic matter in the wastewater serves as a food source for the biomass which the organisms use to grow and reproduce.

Sufficient air must be provided to supply the biomass with the oxygen necessary for respiration. If too little air is introduced into the aeration tanks, the biomass will use anaerobic respiration to metabolize the organic matter, producing foul odors and poor effluent quality. The BCUA introduces air into the process tanks using one or two of its five 45,000 cfm capacity blowers.

The BCUA uses a variation of the activated sludge process known as contact stabilization. In the first step of this process, the wastewater is brought into contact with the biomass for a short period of time, in which the biomass absorbs the soluble BOD. The biomass is then settled and introduced into a stabilization tank where it is aerated for a longer period of time. In this step, the organic material is fully oxidized and the volume of the biomass increases.

After the wastewater and biomass have been aerated for a sufficient period to allow the soluble BOD to be incorporated into the cells of the biomass, the mixture flows to the final, or secondary settling tanks. Since these tanks are not aerated or agitated, the biomass is allowed to settle. The remaining effluent, which by this point in the process appears quite clear, is ready to be disinfected and discharged to the Hackensack River. The settled biomass is either reintroduced into a contact tank to serve as the inoculum for the process, or is wasted. Wasting the biomass, which is now designated as secondary sludge, refers to the removal of this material from the treatment process for final disposal. The wasted secondary sludge is pumped to the gravity thickener tanks and/or thickening centrifuge.

The BCUA utilizes thirteen aeration tanks, typically six as stabilization and seven as contact tanks. The aeration tanks are 31’ wide, 300’ long, and 15’ deep. There are sixteen secondary sedimentation tanks 37’ wide, 170’ long, and 12’ deep.

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