The treatment plant at this midwest city is a well operated facility treating approximately 1 mgd municipal waste from the surrounding community and a high grease load from a local dairy. Over the past several years the publicly owned treatment works has had difficulty producing an excellent quality effluent with respect to BOD 5, and suspended solids.
To achieve this level of treatment, the authority operates a trickling filter plant with primary clarification. Sludge treatment is anaerobic digestion of both primary and secondary sludges followed by disposal to land.
For several years there have been consistent operating problems related to meeting the effluent BOD and suspended solids.
In May 1989, a field trial of the Bio-Systems product was undertaken to see if the effluent BOD and suspended solids could be reduced and at the same time observe operational improvements achieved by Bio-Systems.
The program was commenced on May 25, 1989.
The graph shows an increase in suspended solids followed by a steady decline after the addition of Bio-Systems B500A was commenced.
Effluent Total BOD and Soluble BOD
The effluent total and soluble BOD both increased significantly for about ten days after the addition of Bio-Systems B500A was commenced.
The soluble BOD in the effluent has consistently been low (approx. 5 mg/l). Five days after the addition of Bio-Systems B500A, the effluent soluble BOD had risen to 20 mg/l and stayed at an elevated level.
Effluent Organic Nitrogen
Before the Bio-Systems program was commenced, the effluent organic NH4 was consistently around 10 mg/l. After the program was commenced, the level steadily declined.
The data is widely scattered, however, there is a general increase in the amount of ammonia removed across the trickling filter from 2 mg/l to 4 mg/l.
The addition of Bio-Systems to a trickling filter treatment facility is normally evaluated over a one year period, compared to shorter evaluations for activated sludge facilities. The reason for this is the build up of organics and grease in the trickling filter act as a buffer, making measurement of the increased biological activity due to Bio-Systems B500A difficult. The dairy component of the wastewater would normally cause an even larger build up than usual of grease in a trickling filter installation. This particular facility had not consistently met the effluent BOD standard of 30 mg/l and suspended solids standard of 30 mg/l prior to May 1989. Changes to the process were made and an improved effluent standard was achieved by May 1989.
The break down of grease by Bio-Systems occurs in two steps. First, a liquefaction to soluble BOD and then conversion to biological solids. When the product is first used on a trickling filter, the generation of soluble BOD normally exceeds the conversion to biological solids for a period of time. At this midwest city, this occurred within days of starting the program. The soluble BOD increased to 20 ppm at the maximum and has stabilized at approximately 10 mg/l. This level of soluble BOD can be expected to lower further as the organic build up in the trickling filter is reduced.
The improved conversion of grease to biological solids is also demonstrated by the improved effluent suspended solids. Solids leaving the trickling filter are separated in the final clarification, relying on natural settlement properties. By increasing the biological component of the solids there is a better floc forming characteristic. By reducing the grease content, the density of the solids increase.
It is interesting to note that the peaks of BOD stock loading pouring through the trickling filter have been lowered each month and this should be expected to continue.
Another good indicator of increased biological activity in the trickling filter is the amount of ammonia removed across the filter. Each 10 lbs. of BOD converted to biomass requires 2 to 10 lbs. of ammonia, and there is no storage mechanism for ammonia in the trickling filter. At this midwest city, both the organic nitrogen and ammoniacal nitrogen removal increased significantly after the Bio-Systems program was commenced.