New System Targets Ammonia in Cold Environments

A new wastewater treatment system designed around the Submerged Attached Growth Bioreactor (SAGB) concept is being used successfully to remove CBOD and ammonia from wastewater in lagoons, retention basins and tanks.

The Bio²-Bloc™ system from FBC Technologies uses a bed of media submerged in the wastewater and then aerated from the bottom. As air passes up through the media bed, it carries with it a flow of water which contains the food and nutrients eaten by the film which attaches to the media. This environment is highly productive for the removal of CBOD and ammonia.

The media bed is suspended under a floating compartment filled with waterproof foam. The bed is continuously aerated by an array of fine-bubble diffusers under the media bed. A second, coarse-bubble system is also fitted on each unit for periodic scouring and flushing of sediments from the media bed.

The Village of Elverson, PA, plant uses seven Bio² Block floating modules.

The patented Bio²-Bloc system installs quickly, as the units are floated into place and air connections are made from a shore-based blower.

Traditionally, most discharge permits have been very relaxed regarding ammonia limits during wintertime. The bacteria which convert ammonia are notoriously slow as wastewater temperatures dip in winter months. However, when the same bacteria (nitrifiers) are immobilized and protected in an attached-growth environment, their productivity at low water temperatures is enhanced.

The Bio²-Bloc system protects nitrifiers in a fixed-film environment and warm air from the blower is flushed through the media bed to keep the bacteria aerated, fed and productive.

FBC has installed the system specifically for the removal of ammonia during cold weather at municipal wastewater treatment plants in Pennsylvania and New York. At all locations, the nitrification was maintained down to temperatures as cold as 4 degrees C.

As the ammonia is cleared from wastewater during warmer weather, the system has also shown benefits in sharply reducing algae growth.

Case Study

The Village of Elverson, PA, recently installed the system to meet new, tougher ammonia limits. The Elverson wastewater treatment plant serves a small rural community. The plant was built with a designed flow rate of 75,000 gpd. BOD coming into the system averages 240 mg/L and influent ammonia averages 30 mg/L.

The plant had performed successfully for many years. It only encountered a problem when the Pennsylvania Department of Environmental Protection reduced ammonia discharge limits to 1.5 / 4.5 mg/L (summer/winter).

The plant's flow is channeled through three lagoons. Total plant capacity between the lagoons is 3.6 million gallons. Given its low average daily flow, the plant enjoys a retention time of 48 days. Each of the lagoons is equipped with a small 10 hp splasher. The system has never failed to accomplish BOD removal within permit limitations.

With the reduction in NPDES limits for effluent ammonia, however, the village had to seek a method of removing the extra ammonia, particularly during cold weather months when the system effluent can contain as much as 20 mg/L of ammonia.

Working with the village's engineers, Spotts, Stevens & McCoy, Reading, PA, the decision was made to install FBC's Bio²-Bloc system.

The installation involved the use of seven Bio²-Bloc floating modules. Powered by a single 5 hp positive displacement blower, the system was installed in three days by a factory installation crew. It was designed to provide sufficient fixed-film nitrification capacity to bring effluent ammonia below NPDES limits. The media beds were pre-seasoned for faster formation of the biofilm favored by nitrifying organisms.

The FBC system was installed in mid-March 2002, with water temperatures at 4 degrees C and NH3 effluent at 15 mg/L. Within 10 days, the ammonia had dropped below winter permit levels, bringing the plant within NPDES limits.