Effluent

The raw effluent from St. Marys Paper Corp. is cleaned through both Primary and Secondary Treatment before it is discharged to the St. Mary’s River.

Primary Treatment is intended to reduce the amount of suspended solids, mainly pulp fibre in the mill effluent and is strictly a mechanical process. All mill effluent flows through a bar screen to remove any large material and then is it pumped to the influent well of the primary clarifier. In the primary clarifier, the suspended solids (pulp fibre, clay, etc.) settle to the bottom and are scraped into the sludge mix tank.

Secondary Treatment involves the use of naturally occurring micro-organisms to reduce the amount of dissolved organic matter BOD (biochemical oxygen demand) in the effluent. By controlling the temperature, pH, dissolved oxygen, nutrient residuals, retention time, and other characteristics of the effluent in this level of treatment, the micro-organisms are encouraged to reduce the BOD at a much faster rate than in the natural environment.

The effluent flows by gravity to an anoxic selector tank, and then to the aeration basin. For micro-organisms to be able to break down the organic matter present in the effluent, nutrients and oxygen are required. Nutrients are added at the selector stage in the form of Urea Ammonium Nitrate and Phosphoric Acid, air is added to the aeration basin by means of blowers.

The retention time throughout the process is approximately 12 hours. The treated sludge flows from the aeration basin to the secondary clarifier where the biosolids settle to the bottom and the clarified effluent is discharged to the river. A portion of the settled solids is re-circulated back to the aeration basin to continually grow and reproduce and a portion is pumped to the sludge mix tank where it is blended with the primary solids. The mix tank sludge is pumped to the sludge blend where a polymer is added to flocculate the sludge and aid in drainage of the material on the Komline drum filter. The resulting product is termed biosolids.

The effluent that is discharged to the river passes through our final discharge flume where it is monitored on a 24 hour basis for several government regulated parameters including pH, BOD, tss, toxicity, and residual chemicals. There has been no problem in meeting these regulations as we continue to report test results well below the allowable limit.