Biodiesel Producers Limited (BPL) - A 3 Month Grease Eradication System (GES) Trial

Bioremediation project at Biodiesel Producers Limited, Barnawatha, Victoria.
The project involved the remediation of a large covered anaerobic lagoon (CAL) and the downstream aerobic reactor (SBR). The ponds downstream of the SBR were also heavily loaded with a thick grease cap. The CAL was believed to have a 1metre plus grease cap (GHD) and the SBR had developed a thick foam cap that has prevented aeration and mixing.

The inflow to the CAL was designed for a flow of 210 KL per day with a loading of 6,900 mg/L BOD and FOG of 425 mg/L. Actual load was 100KL with 20,000 mg/L BOD and 1,800 mg/L FOG. This load was made up in two parts: - Approximately two thirds of the flow was from a rendering plant adjacent to the Biodiesel plant and the balance from BPL. Each site was tested weekly by grab sampling. Both sites reported erratic results varying from 490,000mg/L to as low as 1,600mg/L. Auto sampling was commenced during the trial.

The CAL had been in use for over 2 years and had been generating methane. It was assumed that it was working well in the breakdown of the COD and fat. In December 2009 the quality of the effluent began to decrease, overloading the SBR with fat. The average discharge from the CAL of the first quarter of 2010 was 28,300mg/L COD, 4000mg/L VFA’s, 6,429mg/l TSS and 1278mg/L FOG. This overloading caused the formation of dense foam on aeration and mixing. The foam would not breakdown and would overflow from the SBR. This foam formation prevented the use of the mixers and aerators and the tank became anaerobic. Fat in the discharge then flowed into the subsequent ponds. The formed foam had a unique texture similar to fine mica flakes that was very dense and stable. It also had little to no odour. Its identity or cause was not initially determined.

Due to the foaming issue the SBR became a large holding tank for the fat and because of the reduced mixing, the solids were settling on the bottom of the tank. The average discharge from the SBR for the first quarter of 2010 was 22,550mg/L COD and 5,992 mg/l TSS. This is a reduction of 20%in the COD and only 6.8% reduction in TSS. This was possibly in part due to the creation of the dense foam and settling of solids to the bottom of the SBR.

The goal of Environmental Biotech was to bioremediate both ponds with initial criteria to reduce the FOG in the CAL discharge to less than 150mg/L and reduce/eliminate the stable foam in the SBR to allow the sequencing program to be reinstated

Initial treatment. 14 April 2010.

The CAL was initially dosed with 400 Litres of GES bacteria and a dosing rate of 400 litres per fortnight.

The SBR was initially dosed with 200 litres of GES bacteria followed by a dosing rate of 400 litres of aerated bacteria per fortnight. 1000 litre UBC storage drums were fitted with 300 watt aquarium heaters to keep the bacteria at a temperature between 22-25 degrees C.

Mixing and aeration of the SBR was provided on an "as much as possible" basis using the two large impellors with injected air and two smaller mixer/aerators. This was extremely limited due to rapid formation of foam which quickly covered the pontoons on which the mixing motors are mounted.

Results and Observations after 4 weeks. (15 April - 10 May 2010)

No continual trend reduction in any of the measured chemical parameters in the CAL or SBR. However the averages show some decrease in discharge from the CAL. The CAL discharge averaged 21,250 mg/L COD (25% drop*), 5,650 mg/L TSS (12% drop*), 780 mg/L FOG (39% drop*) and 3600mg/L VFA’s (10%drop*). The foam in the SBR appeared to be slightly less dense and more mixing/aeration was able to be undertaken. SBR discharge averaged 18,660 mg/L COD (17% drop*) and 4,575 mg/L TSS (17% drop*). There were no obvious changes in the appearance of the secondary pond.

* = % drop compared to average results in the calendar year prior to commencement of GES trial.

Results after 7 weeks. (11 May - 3 June 2010)

There is now a clear trend downwards of the measured discharged parameters for the CAL. The reduced load to the SBR will aid in the bioremediation progress. Foaming in the SBR has reduced allowing for much more mixing and aeration. The CAL discharge averaged 15,000 mg/L COD (47% drop*), 5,000 mg/L TSS (23% drop*), 450 mg/L FOG (65% drop*) and 3,000 mg/L VFA’s (25% drop*). The SBR discharge averaged 18,750 mg/L COD (17% drop*) and 5,375mg/L TSS (10% drop*).

The second pond has a large amount of volcanoes releasing gas from under the grease cap indicating significant biological activity occurring.

Results after 12 weeks. Lab results 4 - 30 June 2010 , Observations 12 July 2010.

Large drops in all measured chemical parameters in the effluent from both the CAL and SBR. FOG from the CAL has dropped to below 150mg/l to achieve one of the initial primary goals.

The thick mica like foam in the SBR has all been removed and replaced with coarse, large bubble soft foam that easily collapses on itself. The odour of the SBR is now earthy and inoffensive. A second slug dose of bacteria was added during this period as the solids in the bottom of the tank began to break up releasing fats that had been trapped with the sediments. This caused some very erratic behavior of the SBR as the anaerobic fat/solid material was suddenly “liberated” from the bottom of the SBR. One weekend the mixing was accidentally turned off and on recommencing mixing a thick hard “Styrofoam like” foam formed that lasted for 2 days. This foam then broke down to leave the current coarse “normal” froth.

The CAL discharge averaged 5,025 mg/L COD (82 % drop*), 1,247 mg/L TSS (81% drop*), 85 mg/L FOG (93% drop*) and 2,335 mg/L VFA’s (42% drop*). The SBR discharge averaged 7,760 mg/L COD (66% drop*) and 2,067mg/L TSS (66% drop*).

The 2nd pond was observed with the once hard grease cap breaking down. Open water gaps could be observed.

Conclusion.

The introduction of the GES bacteria has been successful in the breakdown of the FOG/BOD/COD/TSS within the CAL to historically low values. This has reduced the load going to the SBR allowing for more mixing and aeration as the foam production diminished.

The bacteria have also broken down the solids formation on the bottom of the SBR further reducing the FOG leaving the SBR. All measured effluent parameters are in downward trend with pH trending upwards.

The secondary pond is also in the process of being cleaned up by bacterial activity and decreased load from the SBR. The hard grease cap was breaking up and pieces of fat were flowing out through the overflow pipe work. Outlet T’s were being installed to prevent this free floating fat from being discharged to the final discharge pond.