Evolution of lagoon effluent enhancement
to meet stringent effluent criteria

Aerial view of Dundalk lagoon system following 1984 expansion. Photo - Bob Willcocks

Articles in ES&E magazine as well as papers at technical conferences have provided an insight into the use of open air intermittent sand filters to enhance effluent quality from facultative lagoons. In Ontario, this is known generically as the New Hamburg process, as it was first applied in the early 1980s in New Hamburg in the Region of Waterloo, Ontario. It is known from papers presented that similar technology has been applied in other jurisdictions.

Effluents from facultative lagoon cells can have problems with elevated ammonia and hydrogen sulphide (H₂S) levels in the spring, after the ice comes off, until aerobic conditions return. In the summer, algae blooms elevate suspended solids levels in the effluent and, as blooms die off in the late Fall, there can be an increase in BOD levels. Both conditions make the effluent unacceptable under the Ontario surface water quality objectives. The addition of the intermittent sand filter as an add-on effluent treatment was designed to address these issues. The intermittent sand filter exposes lagoon effluent to open air to provide oxygen and to coarse sand media to provide a growth site for bacteria which promotes the conversion of ammonia in the effluent to nitrate through nitrification. Exposure to oxygen also removes the H₂S. The media acts as a physical barrier to the migration of effluent solids into the final effluent.

The Ontario Ministry of the Environment has accepted the process as a lagoon enhancement which allows for continuous discharge of effluent which has been accepted as Best Available Technology (BAT). With this enhancement, some projects allow for continuous effluent discharge for an extended period instead of the twice yearly seasonal discharge which requires a 180-day retention period. The limiting factor to the process was established as the need to retain effluent for the coldest winter months when the nitrification treatment could not be maintained because ambient liquid temperatures fall to less than 4°C. This is the lowest viable temperature for maintaining nitrification, established in pilot testing at McMaster University. Depending upon the location in Ontario, the original treatment and storage requirement of 180 days has been reduced to a three or four month storage period, effectively increasing the 'capacity' of the same lagoon volume by 33 - 50%.

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