Adaption of Different Operation Strategies for a Sequencing Batch Reactor Plant Working at Seasonal Load Variations
A small SBR-plant (Sequencing Batch Reactor) operating at substantial load variations has been examined with respect to performance at changing load conditions. The plant serves a ski resort area about 200 km north of Stockholm. The plant has a capacity equivalent to 700 pe and a daily flow of 100 m3/d. The results have been examined closely both by a one year follow-up study of the plant performance and also by a Master Thesis. The analysis of the performance study demonstrates how flexible an intermittently operated biological reactor is in treating varying loads, but also indicates possible operational strategies. It is important to keep in mind that the inlet concentrations of the main pollutants far exceed the “normal” values in untreated municipal wastewater. This circumstance is mainly attributed to a new and concentrated sewer system. Thus the amounts of diluting water are very limited.
The treatment chain is built up by a pre-treatment stage, a biological and chemical treatment stage in an SBR-reactor and a final polishing stage where the water passes a fine grade screening filter.
The requirements set for effluent water by the Environmental Protection Division on the Environmental Testing Advisory Board at the Swedish Environmental Agency are:
• BOD7 < 10 ppm;
• Total P < 0.3 ppm;
No formal requirements have been addressed for COD, suspended solids (SS) or nitrogen. However, these pollution indicators have also been examined during the follow-up session. Typical performance results during the intense period (ski season) were as follows:
• BOD7 < 3 ppm, equivalent to a removal efficiency of around 99%;
•COD < 40 ppm, equivalent to a removal efficiency of around 96 %;
• SS < 5 ppm, equivalent to a removal efficiency of around 99 %;
• Total P < 0.3 ppm, equivalent to a removal efficiency of around 98 %; and
• Total N < 40 ppm, equivalent to a removal efficiency of around 77 %.
Abbreviations: BOD7 means Biochemical Oxygen Demand measured during 7 days; COD means Chemical Oxygen Demand; SS means Suspended Solids, as captured on a filter with 0,45mm; SRT means Solids Residence Time.