BK100 Bio-System)

A biological inoculation procedure was designed and implemented to significantly reduce sludge solids content in a municipal sewage sludge lagoon. The inoculation program, utilized a unique, proprietary facultative (anaerobic/aerobic) Canadian-made inoculant.  The trial [in Australia] ran for 32 days consecutively and resulted in a measured 53.4% reduction in wastewater sludge solids. The procedure succeeded in eliminating gaseous odors from the system in less than 8 days and significantly reduced other measurable parameters, such as supernatant (liquid from wastewater) BOD, TSS,  and Ammonia content. 
(See Table 1)

Test lagoon was designed to contain digested sludge from various sources including high strength industrial waste, septic tanks, and Municipal Sewerage. The sludge typically had the following treatment characteristics: Total Solids Residue (TSR): 7%; Fixed Residue (FR):40% of TSR.Historically, the dewatering and disposal procedure normally incurred very high capital and environmental costs. A specialized biological inoculation procedure, using a unique bacterial spore and enzyme product which had been used with great success in industrial waste treatment pond applications, was offered as a very attractive and low cost option to substantially reduce the sludge solids content of sewerage lagoons and thereby provide equally substantial maintenance cost savings.

The objective of the procedure was to significantly reduce the sludge solids content of the pond (by up to 40%) and thereby achieve equivalent savings in sludge dewatering and disposal costs.

Historically the sludge pond has been de-sludged every three years and data accumulated over many years indicates that the rate of buildup of sludge and the sludge depth after a set period of time is predictable. (The population supplying the plant is relatively constant). Prior to the start of the inoculation program, an electronic sludge depth monitoring device showed that the average sludge depth was 600mm. Subsequently during the course of the study, sludge depths were measured using a hollow Perspex tube, sealed off with a core of clay. This was necessary as soon after the study commenced; the sludge depth measuring device became unreliable. However, historical sludge accumulation/depth records indicate that the depth of sludge at the start of the study would be between 580 and 620mm. The client wanted the study to indicate quickly whether the inoculant would be successful as the contractor booked to de-sludge the pond in the conventional manner would not be able to do so before the seasonal heavy rains commenced. We were given 4-6 weeks to demonstrate the [inoculant’s] ability to achieve an adequate result.
SIZE OF SLUDGE POND: 260 m x 140 m x 1.5 m deep [54,600 m3 volume]

[Suspended Inoculant preparation]
was added to the pond via a 90,000 litre tank. Over a 32 day period, 134 Kg of the inoculant was dosed into the pond via the tank, and multiplication of the bacteria in the tank was facilitated using some added nutrients. After the first two doses via the tank, only sewage sludge from the system was used as nutrient, with water from a clarifier having been used to “top” up the dosing tank.

At the beginning of the program and during, the sludge was sampled at a depth between 120 and150mm from the clay bottom of the pond. Composite samples were tested between 30 x 50 sampling points. The municipal district regularly tested the parameters of BOD, TSS, NH3, and Nitrates in the supernatant wastewater above the sludge layer. In addition, measurements were made on the Chlorophyl A, Pheophytin A levels in the supernatant wastewater to show the reduction in algae that could be achieved. E.coli measurements were performed to demonstrate the reductions in E. coli that occurred through competition from the unique bacterial and enzyme plethora.

Table 1 – RESULTS: 32 day process


% Reduction


% Reduction





BOD Unfiltered Supernatant




BOD Filtered Supernatant 




TSS Supernatant 




COD Supernatant 




NH3 Supernatant


Chlorophyll A (Algae)


Chromium (Sludge) 


Pheophytin A (Algae)


Sludge Depth 


E-coli (Supernatant)


NB:     Dewatering of pond 4 commenced on 2/26/92.

As at 5/3/92 considerable biological activity was still evident, with vigorous bubbling and bubble/ froth formation on the surface of the supernatant. It was quite clear that given time, further reductions in many of the above parameters would likely occur and less inoculant would be required in a maintenance phase. 

No sludge was discharged to pond 4 subsequent to 24/10/91.  The bacterial formula inoculation commenced on 12/30/91 and the bacterial [slurry] was tankered to pond 4 and pumped into the pond at various locations around the edge. From that time on the inoculant was pumped into one end of the pond only. In the short time given for the reduction in sludge to occur there was evidence in the sludge depth/solids profile that it would have been preferable to add inoculant more frequently. However, after 7 weeks, the bacteria and dispersement and sludge layer parameter distribution appeared to be becoming more uniform.

The sludge solids in pond 4 were reduced by 53.4% during the period from 12/30/90 to 2/26/92 whilst the control sample of the sludge composite taken on the commencement of the program reduced in solids by only 3.2%. All of the green algae color in pond 4 was lost within 7-8 days of the inoculation commencing.

As at 2/12/92 some greenish algae color returned to pond 4. The unfiltered BOD rose by 27 mg/l from its lowest point reached of 40 mg/l. However, the filtered BOD continued to drop to around 5-7 mg/l. The continuing aggressive biological activity meant that some suspended solids rose with the gas bubbles and continued to contribute to the unfiltered BOD. This was also confirmed by the fact that on 2/27/92, the filtered COD was 571, and the unfiltered COD was 303 and both were still falling. The incoming sludge, in this location, can have very high BOD, COD and heavy metal concentration. Consequently, the relatively shallow sludge ponds presented quite a challenge to the [bacterial-enzyme] culture.

The program of inoculation has been shown to achieve a large 53.4% reduction in sludge solids with substantial reductions in all key parameters in both the sludge blanket and in the covering supernatant, even when the conditions were not completely suited to anaerobic processes. The reduction was achieved in a very short time period of seven (7) weeks with absolutely no odour creation. The plant reported that the entire unpleasant odour associated with the pond water at the commencement of dosing, was eliminated within 4-5 days of dosing commencement. It is anticipated that the remaining sludge residue will display greatly enhanced dewatering characteristics, and will remain free of unpleasant odour.

The same accelerated dewatering characteristics were duplicated again in Utah, USA where an aerobic bioreactor system which previously took months to complete wastewater processing was easily converted to an anaerobic process, which reduced the inoculated sludge de-watering time to a few days.   Subsequently, the number of de-watering (drying) beds was reduced from 15 to 3 through the action of the inoculant process.  (See Video Clips)