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High-rate stormwater clarification with polymeric flocculant addition
J Wood1, C He, Q Rochfort
1Environment Canada, National Water Research Institute, Burlington, Ontario, Canada L7R 4A6. Jim.Wood@cciw.ca
Summary
Urban stormwater treatment using lamellar clarification with flocculants effectively removes pollutants. Modifications allowed plate removal without losing efficiency, enabling higher surface loads for effective stormwater management.
Area of Science:
- Environmental Engineering
- Water Treatment Technologies
Background:
- Urban stormwater runoff is often polluted and requires effective treatment.
- Lamellar clarification with flocculants showed promise for stormwater treatment but faced challenges with plate cleaning.
Purpose of the Study:
- To assess the treatability of urban stormwater using lamellar clarification.
- To improve clarifier design to eliminate the need for lamellar plate cleaning.
- To evaluate the efficiency and effluent toxicity of a modified clarifier system.
Main Methods:
- Characterization of approximately 90 urban stormwater runoff events.
- Numerical modeling to optimize clarifier inlet hydraulics.
- Retrofitting the pilot-scale clarifier with hydraulic improvements.
- Testing the modified clarifier with cationic polymeric flocculant addition.
Main Results:
- The modified clarifier achieved 77% total suspended solids (TSS) removal at surface loads up to 43 m/h.
- Lamellar pack removal was possible without compromising treatment efficiency.
- No increase in acute toxicity was observed in the treated effluent.
- Generated sludge was heavily contaminated with heavy metals, necessitating special disposal.
Conclusions:
- Hydraulic improvements enabled efficient stormwater treatment without lamellar plates.
- The modified process is suitable for intensive stormwater treatment in compact areas.
- Sludge management is a critical consideration for this treatment approach.