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Engineering

Municipal Treatment

Introduction

The Municipal Wastewater Treatment Facility (MWWTF) consists of a primary treatment building, a sequencing batch reactor, a disinfection facility and a lagoon system.

Primary Treatment

Primary treatment begins in the Main Lift Station which receives all of the wastewater generated in the City of Brandon. The first step in primary treatment is screening which is accomplished by bar screens with a bar spacing of 12 mm. The waste collected on the bar screens is disposed of at the City’s landfill. The next step in the primary treatment occurs in the Primary Treatment Building which houses the “head-end works” for the MWWTF. This step includes grit removal, which is accomplished by a gravity vortex grit removal unit, further screening is accomplished by fine screens with an effective opening size of 4 mm. All of the grit and screenings are disposed of at the City’s landfill. Once the partially treated wastewater leaves the primary treatment building it enters the Sequencing Batch Reactors.

Sequencing Batch Reactor

Sequencing Batch Reactors (SBR)s are a fill-and-draw, non-steady state activated sludge process in which one or more reactor basins are filled with wastewater during a discrete period and operated in a batch treatment mode. The SBR accomplishes equalization, aeration, and clarification in a timed sequence in a single reactor basin. By varying the operating strategy aerobic, anaerobic, or anoxic conditions can be achieved to encourage the growth of desirable microorganisms. SBR’s are ideally suited when nitrification, denitrification, and biological phosphorous removal are necessary.

Varying the operating strategy enables aerobic, anaerobic or anoxic conditions to be achieved. Precise control of these conditions allows organism selection to take place which is the encouragement of the proliferation of specific desirable microorganisms, while the growth of undesirable microorganisms is inhibited. Microorganisms can also be acclimated to a wide range of industrial and chemical processing wastes and temperatures.

A single cycle for each reactor consists of five discrete periods, Fill, React, Settle, Decant and Idle. The purpose of each phase is described below.

Fill Phase

The reactor is filled with wastewater, the fill phase can be aerated, anoxic, or a combination of aerated and anoxic. Biodegradation is initiated during the fill phase. During anoxic fill, influent is distributed throughout the settled sludge through the influent distribution manifold. Influent is not diluted by mixing, making biological nutrient removal much more reliable.

React Phase

After the fill phase influent flow is diverted to another reactor. In the full reactor aeration continues until allowing for biodegradation of the reactor contents. Mixed liquor is drawn through the aeration header and is used as the motive liquid for the jet aerator.

Settle Phase

The air supply to the aeration header is shut off and the biomass is allowed to settle, leaving the treated supernatant above.

Decant Phase

Treated effluent is removed from just below the liquid surface by the floating solids excluding decanter.

Idle/Waste Sludge Phase

Once the decant phase has been completed the reactor waits, or idles, to receive the next batch of influent. Settled sludge is drawn though the header and is pumped to the sludge receiving and holding cells located at the City’s lagoons.

Disinfection

The partially treated effluent from the SBR’s is then sent to the disinfection facility for disinfection utilizing ultraviolet light technology. Once the effluent has passed through the UV facility it is ready for final disposal into the Assiniboine River or further treatment in the lagoon system.

Lagoon System

The lagoon system was constructed in 1963 and acted as the City’s wastewater treatment facility until 1975. In 1975 an aeration facility was constructed that increased wastewater treatment during the coldest months of the year. In 1994 the SBR’s were added and the need for the lagoons was reduced. The existing anaerobic treatment lagoon cells were converted into sludge receiving cells and sludge isolation cells. The aerobic lagoon cells were retained for excess wet weather flow treatment as well as a treatment facility to accommodate any treatment that could not be achieved in the SBR’s.

One of the aerobic cells was also converted to an aeration treatment facility to accommodate industrial waste. This waste stream is transported to this isolated cell via truck, therefore the lagoon cell is separate and distinct from the other cells. A clarification cell was added inside the isolated cell which can transfer any solids to the sludge receiving and isolation cells.

Today the lagoon cells are used extensively for both the treatment of excess wet weather flows as well as acting as a clarifier for the final effluent from the UV facility.

 

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