Lagoons are widely used in small communities for wastewater treatment, due to their comparatively low life-cycle costs and treatment efficacy for small systems. Lagoons effectively remove biochemical oxygen demand and total suspended solids in wastewater.
Historically, nitrification for ammonia removal was typically not considered for lagoon design. In recent years, the federal government’s Wastewater Systems Effluent Regulations (WSER) has mandated more stringent effluent requirements, particularly for un-ionized ammonia to a concentration below 1.25 milligrams per litre. In addition, the discharge must not be acutely toxic. These new requirements have posed significant challenges for existing lagoon-based systems, especially during cold weather.
Process Engineer, Kevin Yu, tells us, “One of the approaches to achieve ammonia removal is to increase and retain the nitrifier bacteria population that oxidize ammonia by growing the bacteria on and inside biofilm carriers or media to compensate for the low nitrification rates in winter.” This can be done on existing lagoons by retrofitting the systems with a post-BOD removal Moving Bed Biofilm Reactor (MBBR), a Membrane Aerated Biofilm Reactor (MABR), or a Submerged Attached Growth Reactor (SAGR).
Moving Bed Biofilm Reactor adopts features of two wastewater treatment processes: activated sludge and attached growth nitrification. An MBBR system is versatile and can be used to provide consistent ammonia removal throughout the year, as demonstrated by many pilot studies and full-scale applications. Associated Engineering is currently retrofitting two lagoon systems using MBBR technology, at the Town of Camrose Wastewater Treatment Plant and the Town of Neepawa Wastewater Treatment Plant.
Wastewater lagoons retrofitted with Biofilm technology meet new regulations for treated effluent quality
Membrane Aerated Biofilm Reactor uses hollow gas permeable membranes as a biofilm growth medium to the bacteria growing attached to the membrane and in the bulk liquid. Kevin says, “Oxygen is transferred directly to the microorganisms growing on the membrane and can result in up to seven times higher aeration efficiency than traditional fine bubble diffusers.” MABR has been operating successfully at treatment plants outside of Canada. In Ontario, MABR has been piloted in the City of Guelph, City of London, and Region of Waterloo.
MBBRs and MABRs can considerably improve nitrification rates of lagoon systems in cold weather. They are promising technologies to help small communities meet the new WSER requirements.