A potato processing factory in the north of England with a throughput of some 70,000 tons of potatoes p.a. was unable to meet its effluent discharge consent levels after increasing the variety and volume of items it prepared for retail sale. In August Cleveland Biotech was asked to review the factory’s effluent treatment system and to propose solutions.
As a result of the additional processing being undertaken in the factory the level of fat being discharged had increased significantly. Fat leaving the factory first passes through a fat trap and balance tank before going to a primary clarifier and then to a high rate tower. The fat which is not recovered in the initial treatment process goes to the high rate tower where it is distributed over media and is biologically degraded. As a result of the increase in fat being discharged the high rate tower was unable to cope with the volume of fat within the available residence time. This resulted in high fat levels passing to the aeration tank and to an increase in COD levels in the final effluent. The factory, because the effluent is discharged directly into a river, has a COD discharge consent level of a low 250 mg/l. This level was not being met.
A further problem existed. Because of the increase in activity in the factory it had proved difficult during normal working hours effectively to carry out the regular hygiene routines required by law. The management had therefore decided to work the factory continuously for two weeks (2 x 12 hour shifts) and then to shut down for one week for cleaning. As a result of the break in processing the activated sludge in the treatment plant lost activity and it took two/three days after start-up before it achieved its normal efficiency levels. This also effected the COD levels in the effluent discharge.
Cleveland Biotech recommended bioaugmentation of both the high rate tower and the aeration tank. The proposal was accepted.
The High Rate tower was dosed with Amnite S150L Fat Digester at a rate of 40g/m3 as an initial dose followed by a weekly maintenance dose of 8g/m3 during the working weeks. This has re-established and maintained a good microbial population on the media within the tower. The immediate effect has been that the tower is now coping effectively with the increased fat levels and the loading on the aeration tank has been greatly reduced. Effluent readings have shown that the final effluent has been well within the COD consent levels apart from a short period at the end of November when, through an error, a large quantity of untreated fat was released into the treatment system. The management has however commented very favourably on the speed which the plant has recovered from this shock which would not have been the case prior to the bioaugmentation.
The aeration tank has been dosed with 10g/m3 of Amnite S100 Organic Solids Digester every three weeks, 24 hours before restarting processing in the factory. This has been successful in eliminating the problems caused by loss of activity in the treatment plant as a result of the shut-down. The plant now functions efficiently directly on start-up.
The management remain extremely satisfied with the results achieved. For a small recurring cost and no capital expenditure the plant is now working well within its effluent consent levels. The outlay on bioaugmentation is modest in relation to the potential charges/fines which might have been incurred.