ALTERNATIVE APPROACHES FOR UPGRADING EFFLUENT QUALITY FOR LAGOON BASED SYSTEMS

The province of Ontario is Canada's most populous province with over 8 million residents out of a total population of 27 million. The provin ce has 512 sewage treatment plants of which 137 or 27% are lagoons. Im proved environmental effluent quality standards since the introduction of the lagoons has resulted in many of these being unable to achieve proper effluent quality. Typical effluent quality requirements across the province require a minimum of secondary treatment, that is 15 mg/l of BOD and suspended solids and 1 mg/l of total phosphorus. The movem ent towards a clean environment has resulted in phosphorus levels as l ow as 0.3 mg/l TP and in an increasing number of cases, full nitrifica tion year round. Because many of these lagoons serve small populations in the 100 - 3 population equivalents category, the cost of upgrading such lagoons to tertiary quality effluent is significant. Two approac hes for upgrading conventional lagoon systems were evaluated. They are called the Sutton and New Hamburg processes after the towns in Ontari o where they were first installed. The Sutton process consists of exte nded aeration plant, followed by polishing lagoons with waste sludge s ent directly to the lagoons, while the New Hamburg process consists of conventional lagoons followed by intermittent sand filtration.