A combination of the suspended carrier biofilm process and the activated sludge process (biofilm-activated sludge--BAS) has been shown to be very successful for the treatment of different types of pulp and paper mill effluents. The robust biofilm pre-treatment in combination with activated sludge results in a stable, compact and highly efficient process. Recent findings have shown that nutrient limited operation of the biofilm process greatly improves the sludge characteristics in the following activated sludge stage, while minimising sludge production and effluent discharge of nutrients. The nutrient limited BAS process was implemented at full scale at the Södra Cell Värö kraft mill and taken into operation in July 2002. After start-up and optimisation over about 5 months, the process meets all effluent discharge limits. The removal of COD is close to 70% and the removal of EDTA greater than 90%. Typical effluent concentrations of suspended solids and nutrients during stable operations have been 20-30 mg/L TSS, 0.3-0.5 mg/L phosphorus and 3-5 mg/L nitrogen. The sludge production was 0.09 kgSS/kg COD removed and the sludge volume index was 50-100 mL/g.
The City of Los Angeles, Bureau of Sanitation has a long history of implementing proactive and innovative measures to control sewer odors from its wastewater collection system. The North Outfall Replacement Sewer has presented challenges to the City due to on-going air pressurization generated from within the sewer, which have migrated to the surrounding communities. The City has examined and identified mitigation measures to address the positive ventilation conditions on the NORS. These measures include: Hydraulic Flow Management; Construction and operation of air treatment facilities (ATF), Installation of air curtains, and Replacement and upgrade of trap maintenance holes. Implementation of these mitigation measures have significantly reduced and controlled the air pressure from the NORS and has alleviated the odor impacts to the surrounding communities.
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