The treatment plant at this Midwestern City is a well operated facility treating approximately 1.1 mgd municipal waste from the surrounding community. Over the past several years the publicly owned treatment works has consistently been able to produce an excellent quality effluent with respect to BOD, suspended solids, ammonia and phosphate. To achieve this level of treatment, the authority operates an activated sludge plant with no primary clarification and tertiary sand filtration. The activated sludge systems comprises an oxidation and secondary clarifier with suction mechanism. Sludge treatment is an aerobic digestion of secondary sludges followed by dewatering.
Since the commissioning, the plant has run well and produced good effluent. In January 1988, the treatment plant experienced filamentous infestation which continued through March, resulting in poor settlement properties and high effluent BOD and suspended solids.
In March 1988, a field trial of the product Bio-Systems was undertaken to see if the amount of filamentous infestation in the system could be reduced, and at the same time observe operational improvements achieved by Bio-Systems.
The program was commenced on March 16,1988. Visual observation of the filamentous infestation in the activated sludge confirmed that the build-up was significantly reduced within a thirty (30) day period. Settling properties as measured by SDI and % settling improved to normal levels within 20 days and stabilized within forty (40) days. The treatment plant has continued to operate well using a maintenance dose of Bio-Systems at the rate of 1 lb/day, 5 days/week.
Sludge Density Index
The sludge density index is a measure of how well the sludge settles. A SDI of 0.4 indicates extremely poor settling at the plant, with increasing value indicating better settling. The average SDI value for January and February was 0.4, indicating very poor settling. Shortly after BIO-SYSTEMS was added the SDI gradually increased to normal levels.
Settlement % is again a measurement of settlement properties and is useful as a parameter in this case because at times of poor settlement (i.e. settlement %=100% and SD =0.4) slight improvements can be detected in the settlement % data before they appear in improved SD. Within a few days of adding Bio-Systems, the settlement % lowered, with continued improvement.
Other municipal treatment plants have documented reduced grease build-up in digesters and sludge processing equipment when using Bio-Systems on a regular basis. The cleaner belts and easier operation of the belt press have been noted since use of Bio-Systems was started. Lower polymer consumption on the belt press was also rated.
The D.A.F. sludge pumped to digester was used as a measure of waste activated sludge generated, and the following table provides the results for 1987 and 1988.
The amount of sludge treated by the D.A.F. unit total 129 tons for April through July 1988 compared to 172 tons for the same period of 1987.
In conclusion, the addition of Bio-Systems to the wastewater treatment plant has shown benefits as follows:
- Reduced filamentous infestation build-up in the plant, resulting in less maintenance.
Improved sludge settling characteristics.
- Reduced sludge production.