Background
A large malting company, located in Minnesota, utilizes a sequential batch reactor (SBR) to treat incoming wastewater. The wastewater treatment facility treats approximately 1.5 MGD of the 1.9 MGD total effluent pursuant to the discharge limits of the operating permit. The treated effluent is discharged to the Minnesota River, with the remaining untreated wastewater and the waste activated sludge (WAS) being discharged to the municipal sewer line.
Study Design
On October 6, 2003, a 90 day field trial was initiated at the malting wastewater facility to determine if ACCELL could reduce the amount of sludge being sent to the municipal sewer, with a goal established as a 30% decline in sludge production. The initial dose of 5.2 gallons per day (GPD) ACCELL for the first 30- days were initiated based on average influent BOD and TSS levels of approximately 800 ppm and 100 ppm, respectively. The targeted operating MLSS level for the SBR was 4,000 mg/L.
Results
When initiating treatment of activated sludge processes with ACCELL, there is an acclimation period during which the biology experiences an adaptation of its metabolic activity. Some of the effects are seen within the first 10-15 days, such as improved oxygen transfer and reductions in BOD, TSS and ammonia levels in the treatment facility’s effluent levels. However, optimal sludge reductions are generally not seen until about 60 days (1-2 sludge ages) into the trial.
The reduction of sludge disposal is deemed the primary objective of this study. Data from September through December 2002 were used as baseline for sludge reduction because historical data showed seasonal trends for sludge production.
| 2002, No ACCELL | |
| Time Period | Avg. Gal. Discharged |
| September | 71.910 GPD |
| October | 80,900 GPD |
| November | 82,400 GPD |
| December | 89,322 GPD |
| 2003, with ACCELL | |
| Time Period | Avg. Gal. Discharged |
| September | 71.910 GPD |
| ACCELL treatment starts - October | 70,115 GPD |
| November | 67,060 GPD |
| December | 60,245 GPD |
The third month’s treatment data yielded a 32.6% decline in sludge disposal levels, therefore meeting the stated goal of achieving a 30% minimum sludge reduction.
While sludge reduction was designated as the primary goal of this study, other factors were being monitored to further demonstrate improvements of the wastewater treatment operating process. ACCELL’s primary effect of a reduced sludge production led to an accelerated and more complete digestion of nutrients, increased dissolved oxygen and lower effluent ammonia and phosphate. The following results show an improvement of operating parameters accompanying the reduced sludge production:
| Reduction: July – September 2003 compared to October 2003 – January, 2004 | |
| Biological Oxygen Demand | 13.4% |
| Total Suspended Solids | 15.6% |
| Ammonia | 30.4% |
| Phosphate | 45.0% |
These improvements also have a significant impact on oxygen transfer rates, which led to a reduction of the compressor aeration output requirements. Two compressors, which normally operated within 45% - 55% of output, could be reduced to an output range of 38% - 40%.
In addition, oxygen uptake rates (OUR) were examined. An OUR less than 25 mg/l/h has been deemed to be optimal and, therefore, the aeration cycle time at which OUR <25 is attained, is the point at which the aeration cycle could be terminated. Extrapolation of the obtained OUR’s indicates that it would be possible to reduce the aeration cycle time by up to 60 minutes or approximately 33%. The reduction of aeration cycle time, coupled with decreased compressor output, resulted in a potential 33% to 50% savings of aeration operating expense.