Primary effluent is then pumped up to eight gravity filters. Filter effluent is pumped by four 6.67 mgd high- head pumps up through the carbon columns. The six carbon columns remove soluble BOD and other contaminants by adsorption as the wastewater travels upward through the carbon media. The upflow mode was selected to avoid plugging problems and allow for better contact with the carbon. The flow to the columns is split into two paths so that they may operate singly or two in series with the third column acting as a standby unit.
Operational flexibility allows any column to be operated as lead column in the series.
The online columns periodically require cleaning by air scouring and hydraulic backwashing. Carbon column effluent flows into twin chlorine contact chambers, each with a capacity of 212,000 gallons. The disinfected plant effluent is finally discharged through a submerged diffuser in the Niagara River. The sludge that is removed by the primary clarifiers is pumped to two, high-rate heated primary digesters. Organic solids are broken down by the digester microbes, producing carbon dioxide and methane.