Wastewater Treatment
SAGR system allows First Nation communities to meet federal effluent regulations By Merle Kroeker, Martin Hildebrand, Kevin Vieira
T
he Government of Canada is participating in an ongoing effort to clean up polluted and problem waters from coast to coast. Canada currently dumps over 150 billion litres of untreated and undertreated wastewater directly into waterways annually. In response, the Government of Canada has worked with provinces, territories, municipalities, and Aboriginal communities to create the first set of national standards for wastewater treatment. The Wastewater Systems Effluent Regulations (WSER) were established in the summer of 2012. The goal is to transition all new and existing wastewater facilities across Canada to secondary treatment levels. Secondary treatment uses physical or biological processes to treat dissolved contaminants (soluble CBOD, NH3), which are not removed in primary treatment. Effluent discharged into water frequented by fish must now meet specified deposit pollutant limits under the Fisheries Act. Prior to the WSER coming into effect, many provincial discharge licenses did not include ammonia limits. This meant many lagoon facilities were unknowingly exceeding the allowable federal ammonia toxicity requirements while still meeting their carbonaceous biochemical oxygen demand (CBOD) / total suspended solids (TSS) discharge permits. Ammonia toxicity Total ammonia in wastewater is comprised of un-ionized ammonia (NH3) and ionized ammonia (NH4+). These two forms of ammonia are collectively referred to as TAN (total ammonia – nitrogen). For lagoon operators in Canada, complying with ammonia limits is a challenge because of low water temperatures and the fact that ammonia toxicity is a misunderstood parameter. Generally, the un-ionized portion (NH3) is a concern, as it is toxic to fish at low levels. (NH4+) is generally not considered toxic except at very high
40 | May/June 2015
Alum dosing equipment at Misipawistik for total phosphorus removal.
levels. The portion of total ammonia that is in the toxic form rises as pH and temperature increases. An effluent TAN concentration that is non-toxic in winter can cause fish kills at higher pH and temperature conditions in summer. To account for this, seasonal ammonia discharge limits are common, with higher
Designed for cold climate treatment, the SAGR removes ammonia through biological nitrification. Ideally it follows secondary lagoons to provide full nitrification and partial disinfection in climates where water temperatures can be near freezing for extended periods of time. TAN concentrations allowed during colder weather. Ammonia toxicity in wastewater is
addressed through nitrification. This is the conversion of ammonia to nitrates by attached growth nitrifying bacteria. In a typical lagoon, however, the lack of available surface area means that populations of nitrifying bacteria are relatively low. Without significant biomass, nitrification levels are low at best, and can be negligible at low temperatures. Effluent water temperatures from lagoons in Canada are typically less than 1°C for about five months of the year. Nitrification only begins once CBOD levels are reduced to approximately 25 mg/l. During cold weather, by the time water in the treatment process reaches a point where CBOD levels are low enough to allow nitrification, the water has typically cooled to a point where nitrifying bacteria are ineffective. Over winter and early spring, many lagoon facilities will discharge toxic effluent due to minimal nitrification. Submerged attached growth reactor Over the last 10 years, Nelson Environmental has conducted significant research and development to provide a solution for cold temperature nitrification within lagoon based treatment facilities. To address this issue without abandoning existing lagoon infrastructure, the firm developed the Submerged Attached Growth Reactor or SAGR®. Designed for cold climate treatment, the SAGR removes ammonia through biological nitrification. Ideally it follows secondary lagoons (facultative/ aerated), to provide full nitrification and partial disinfection in climates where water temperatures can be near freezing for extended periods of time. The SAGR can handle a wide range of influent water qualities without upset. This allows it to be used as a final CBOD and TSS polishing technology in addition to nitrification for lagoons that are exceeding their original design loads and flows. In some cases, utilizing existing facultative lagoons in place of continued overleaf...
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