The wastewater treatment process produces biogas, a form of renewable energy, but typically this biogas is burned off. However, if this useful energy byproduct could be harnessed, this would result in significant fossil fuel energy savings. Therefore, biogas conservation can be both cost-effective and energy efficient. 

The Portinho da Costa Wastewater Treatment Plant was designed to harness this biogas byproduct. The cogeneration system of the plant consists of two power units (motors and alternators) that feed on the biogas stored in two double membrane floating gasometers.

The power units allow for converting approximately 33 percent of the energy contained in the biogas into electricity. About 60 percent of its energy is recovered in the form of heat (steam and hot water) using heat exchangers to profit from the thermal energy present in the exhaust gases and engine cooling circuits. The loss of energy in the cogeneration process amounts to just 7 percent.

The cogeneration system of Portinho da Costa covers about 40 percent of the energy needs of the facility, equivalent to about 550 MWh per year. These energy savings translate into a decrease of 40 percent of GHG emissions, which in absolute terms represents a reduction of 180 tons of CO2.

The technology used in the Portinho da Costa WWTP is all commercially available and poses no obstacles to use. Existing WWTPs that already have anaerobic digestion in place to treat sludge, but which are not yet harnessing the energy potential of biogas, can potentially replicate elements of the Almada model.

Harnessing biogas reduces operating costs with the acquisition of energy while it also avoids GHG emissions. The major costs towards such a WWTP are those associated with the acquisition and installation of equipment, which are recoverable within its life span, and are thus not a financial burden.

Photo by John Cameron on Unsplash