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|Sharon J. Ostrander||Sharon J. Ostrander is a laboratory technician and N.H. Grade IV operator with the Keene Municipal Wastewater Treatment Plant in New Hampshire, and was recently honored as the New Hampshire Operator of the Year..
Filament outbreaks can be controlled with a little help
|1.Permit limit demand
||To meet its permit limit on total oxygen demand, the Keene, N.H., Wastewater Treatment Plant Figure1 nitrifies from May 1 to October 1. Each year, while operating in a mode that encourages nitrification, the plant suffers from filament outbreaks. The microorganisms are also affected by the nitrification process: the predominant stalked ciliates and free swimmers are replaced by flagellates.|
|2. Microorganism ratio||Through staining, Microthrix parvicella was identified as the main culprit. This filament was caused by a low food-to-microorganism ratio (F:M), a necessary condition when nitrification is required. An evaluation of deficiencies that lead to filament problems revealed that the Keene facility was not suffering from any of the common ones: the dissolved oxygen in the aeration basin exceeded 2.0 mg/L, the biochemical oxygen demand (BOD)/nitrite/phosphorus ratio of the influent to the aeration basin was adequate, and heavy metals were not present in toxic amounts .
|3.Begin of the study||Controlling M. parvicella through chlorination was unsuccessful; it resulted in inhibition of the nitrifying bacteria and thus increased the effluent ammonia nitrogen. Chlorination also increased the effluent BOD and suspended solids. More importantly, the filament populations were not reduced satisfactorily and would increase again once chlorination was discontinued.
It was suspected that nitrification was depleting a trace nutrient that is essential for a healthy microorganism population. Research data from Europe on the use of a folic acid supplement indicated that this might be the deficient nutrient. Therefore, a study was conducted to monitor the effects of folic acid on filament populations, microorganisms, sludge volume index (SVI), and overall activated-sludge system performance.
At the beginning of the study Figure2, two secondary clarifiers were on line and polymer was added at the end of the aeration basin. The extra clarifier and the polymer addition were necessary to avoid solids carryover at the weirs.
|3.1 Study Procedure||The folic acid solution (DOSFOLAT®) was diluted in two, 300-gal fiberglass tanks. A metering pump delivered the diluted solution at the inlet channel to the head of the aeration basin. The folic acid was diluted 300 to 1 and was fed at a rate of 0.2 ppm (180 gpd of diluted solution) from August 1 through 7. From August 8 through September 4 the folic acid feed was lowered to 0.1 ppm (90 gpd of diluted solution). Then, from September 5 through 10, the feed was again lowered to 0.075 ppm (67.5 gpd diluted solution). On September 11, the feed was returned to 0.1 ppm (90 gpd diluted solution) and was kept at this rate until its use was discontinued on October 19. The process was monitored closely for changes in activated sludge filament populations, treatment efficiency, and settling characteristics.
Filamentous staining was done on August 2 and 6, and September 7 and 24. A quantitative microorgansim count and settleometer and suspended solids tests were conducted daily on the mixed liquor. Suspended solids tests were also conducted on the return activated sludge. The final effluent was monitored daily for turbidity and three times a week for BOD, total suspended solids, and ammonia nitrogen. Dissolved oxygen levels in the aeration basin and the blanket levels in the final clarifier were closely monitored.
By the end of the first week, flagellates were no longer predominant. Free-swimmers had replaced them, with stalked ciliates in second place. After the second week, stalked ciliates became the predominant microorganism, with the free-swimmers in second place. The flagellates comprised only a small percentage of the overall microorganism propulation.
Once the stalked ciliates became predominant, the oxygen demand within the aeration basin decreased. After the shift in microorganism predominance, the aeration basin weir was lowered by 35%. (Mechanical aerators supplied the oxygen, with the rate being controlled by motor speed and aeration basin weir level.) The oxygen uptake rate also increased.
The SVI dropped slightly after the first week. At the end of the second week, settling improved enough to allow the polymer feed to be discontinued. After 21 days, the SVI improved dramatically it had dropped to less than 200 from greater than 570. One clarifier was removed from service because of the improved settling. By Day 27, the SVI had fallen to less than 150.
At the beginning of the study, staining showed the filamentous organisms were abundant to excessive. They caused bridging between flocs and an open floc that was irregular and diffuse Figure 3. M. parvicella comprised about 99% of the filament population. After 5 weeks of the folic acid supplement, the floc had become firm and M. parvicella were present in very small quantities Figure 4 . The turbidity and the effluent suspended solids increased slightly because of the decrease in filaments. The effluent suspended solids were still well below the permit requirement, so this was not a problem.
When folic acid feed was reduced to 0.075 ppm in early September, the SVI and the effluent ammonia nitrogen began to increase. Because of this trend, the folic acid feed was returned to 0.1 ppm after only a week.
Keene attempted to lower the sludge age in late June (in an attempt to reduce the filaments), which resulted in poor settling; solids washout in the clarifiers; and an increase in effluent ammonia, BOD, and suspended solids. However, after settling had improved in October, Keene was able to lower the sludge age and thus the mixed liquor concentration with no adverse affect on the effluent quality.
Addressing Keens filament problem as nutrient deficiency allowed the plant to narrow the scope of its search for a solution. Keeping eyes and ears open and looking beyond typical treatments for settling and filament problems, Keene was able to find a remedy for this chronic ailment while maintaining effluent quality.
Sharon J. Ostrander is a laboratory technician and N.H. Grade IV operator with the Keene Municipal Wastewater Treatment Plant in New Hampshire, and was recently honored as the New Hampshire Operator of the Year.
The graphs on these two pages supply additional information that was not included in the January, 1992 article in Operations Forum on the Keene, NH municipal wastewater treatment plant.
Each graph includes data from the periods before and after folic acid was used, as well as data showing how folic acid helped the Keene plant. On each graph, diagonal lines show the duration of Keenes summer nitrification requirement. The late summer period when Keene used dosfolat®, Bioprimes folic acid additive for wastewater treatment, is marked in gray. The different shades of gray are labeled to show the different folic acid dosage rates that Keene used over the course of their trial.
|4 Microorganisms||The Microorganism Counts chart shows the results of the Keene plants microscopic examination of their mixed liquor. In the early spring, before the required nitrification period, the graphs show a stable population dominated by ciliates only a few flagellates are present. When the sludge age was increased in late April to promote the nitrifiers, the populations became unstable and flagellates replaced ciliates as the dominant life form. Flagellates remained the dominant protozoa during May, June and July. The wild swings on the Microorganism Count graphs and the other graphs opposite are indications of the operating problems that Keene experienced during these three months. The Keene plant has experienced similar problems each summer since the nitrification requirement was introduced in 1986.
After one week of applying folic acid, free swimming ciliates had replaced flagellates as the dominant microorganism. At the end of the following week, stalked ciliates were dominant and remained so for the balance of the test. A predominance of stalked ciliates is generally viewed as an indicator of a well-running plant and Keene is no exception. Shortly after the stalked ciliates became predominant, Keenes bulking problem cleared up and settleability remained good for the rest of the summer and early fall. In addition, the oxygen requirements of the mixed liquor dropped significantly after the flagellates were replaced with stalked ciliates, thus saving the city significant electrical costs.
|5 Sludge Volume Index||The primary problem at the Keene plant was sludge bulking. When the sludge age was increased in the spring to promote nitrification, the filament Microthrix parvicella took hold and the SVI quickly shot up over 1000 ml/g.
After three months of adjustments by plant operators, the SVI was still above 400 ml/g. Three weeks of treatment with folic acid brought the SVI down below 200 and allowed the Keene personnel to remove one clariefier from service. The SVI remained below 250 for the rest of the summer and early fall. When the folic acid dosage was reduced after Labor Day, the SVI began to rise but this problem was quickly resolved by returning the folic acid dose to the correct value.
|.6 Oxygen Uptake||The Oxygen Uptake Rate is a gauge of sludge activity. Higher oxygen uptake rates indicate that the metabolism of the microorganisms in activated sludge is accelerated. The Oxygen Uptake Rate chart shows that the addition of dosfolat®, Bioprimes folic acid additive, increased oxygen uptake rates by over 50%.
|7. Folic Acid: More Evidence||Supplementing secondary treatment with folic acid, a member of the B vitamin complex, significantly improves the performance of wastewater treatment plants. A micronutrient and coenzyme, folic acid is essential for the growth and metabolism of all cells. Folic acid increases the variety, population and activity of the microorganisms that are the heart of all secondary treatment processes, leading to improved performance, better settling and cleaner effluent, especially in systems subject to overloads or toxic shocks.
Results include reduced effluent suspended solids, COD and BOD5; less sludge; and more stable operation. Benefits have been substantiated with research at the University of Karlsruhe, Germany, through parallel tests, by field trials, and in continuing operational applications.
|8. Using DOSFOLAT®||Bioprimes dosfolat® is the most efficient means for addingg folic acid to secondary wastewater treatment systems because the vitamin is already in aqueous solution, thus ensuring efficient utilization by the activated sludge microorganisms.
Dosfolat® is diluted before use and then metered continuously into the treatment plant. Activated sludge, lagoon, sequenced batch and fixed film systems have all exhibited excellent results when treated with folic acid.
|Figures||Figure 1: The Keene, New Hamshire WWTP
Figure 2: Keene Treatment Process Flow
Figure 3: Filaments and floc before floc improved (August 2)
Figure 4: Filaments and floc after conditions improved (September 7)
|References|| A. Anderl, " A vitamin for biological sewage treatment plants",BIOTECHNOLOGIE,Issue 7,
 H. Mohr, " Folic acid-a micronutrive and promoter of growth for bacteria and fungus ",
BIOTECHNOLOGIE,Issue 10, (1987)