Preservation techniques and carbon and nitrogen growth enhancement of batch cultivated UASB granules

[摘要] ENGLISH ABSTRACT:The potential use of the upflow anaerobic sludge blanket (UASB) bioreactor islimited by the extended start-up periods due to the time-consuming granulationprocess and the fact that seeding inoculum is not freely available in mostdeveloping countries like South Africa. The mass cultivation of granules wouldprovide the waste water treatment industry with suitable seeding inoculum and,therefore, an efficient waste water treatment option would be more easilyavailable. By applying 'stress' conditions on a bioreactor system seeded with rawanaerobic sludge, the population dynamics of the anaerobic community changeand the acidogens start to produce extracellular polymers, which in turn enhancethe granulation process by providing a matrix for the bacterial cells to adhere to.These environmental stress conditions include changes in the C:P:N ratio's. Theaim of this study was, therefore, to assess the impact of different carbon andnitrogen sources on the enhancement of granulation in a batch system, and todetermine the best preservation technique in terms of retainment of activity.It was found that the carbon source and concentration had a significantinfluence on batch granule enhancement. Low concentrations (2.g.l ̄ ¹)of glucosegave the best granule enhancement over a 14 day incubation period. Fruitcocktail effluent was found to be a cheap and effective carbon source for batchgranule cultivation. It was found that different nitrogen sources did not have thesame impact on granule enhancement, however, urea, at all concentrationstested, gave the best granule enhancement.A major problem encountered during the study was the standardisation ofthe inoculum. Significant granule enhancement comparisons between thedifferent carbon sources were impeded by the lack of a suitable and reliable formof sludge standardisation. Future research needs to address this problem of thestandardisation of the sludge inoculum as this would lead to more kineticallycomparable results.Mass granule culturing will require granule preservation without risking theloss of activity. In the second study, six different preservation techniques andstorage periods were evaluated in terms of the retainment of activity. Theseinvolved freeze-drying, vacuum freeze-drying, vacuum-drying, freezing, coldstorage and room temperature preservation. Activity testing was used forcomparing the efficiency of the different preservation techniques in terms of thetempo of biogas and methane production. Freeze-drying the granules, withstorage for up to 90 days was found to give the best retainment of activity,followed by vacuum freeze-drying. The room temperature preserved samplesshowed a sudden increase in activity by day 120, which could possibly beexplained by cell hydrolysis of the granules after day 90.The highest activity was achieved after 10 h of incubation, and it was,therefore, suggested that activity testing for evaluation purposes should use anincubation time of only 10 h. Furthermore, only the basic test medium with addedglucose should be used for activity testing as it was observed that the addition oflactate and acetic acid played no decisive role in determining the level of activity ofthe granules.This study recommends the use of low concentrations of glucose foroptimum granule enhancement during the mass cultivation of granules, and theaddition of low concentrations of lactate to ensure a stable system with noacidification. It is also advisable to use a standardised sludge inoculum, as thiswill allow more efficient comparisons. Freeze-drying is recommended aspreservationtechnique as this technique showed the best retainment of activity. Astorage period of 90 days is, however, too short to be of much use for the industry.This will have to be investigated, together with the phenomenon of increasedactivity after 90 days as shown by the room temperature preserved granules.

[发布机构] Stellenbosch University