Enhancement of the biodegradability of grain distillery wastewater to improve upflow anaerobic sludge blanket reactor efficiency
Date
2007-12
Authors
Gie, Lowna-Marie
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
The distillery industry generates large volumes of heavily polluted wastewater and thus
effective wastewater treatment is essential. It has been reported that a chemical oxygen
demand (COD) reduction of more than 90% can be achieved when wine distillery wastewater
(WDWW) is treated in an upflow anaerobic sludge blanket (UASB) reactor. The first objective
of this study was to investigate UASB treatment of WDWW and to try to enhance the
efficiency by using ozonation treatments. Secondly, the impact of grain distillery wastewater
(GDWW) on UASB granules was determined. The third objective was to determine whether
ozonation and enzymatic treatment combinations might improve the biodegradability of
GDWW and thus make GDWW more amenable to UASB treatment.
It was found that UASB treatment combined with ozonation improved the WDWW
treatment efficiency. When diluted WDWW (chemical oxygen demand COD = 4 000 mg.L-1)
was ozonated (dose = 47 mg.L-1) in a 50 L venturi circulating contactor system, the COD
reduction was 7%. When WDWW was treated in a laboratory-scale UASB reactor (substrate
pH = 7.0, COD = 4 000 mg.L-1 and organic loading rate (OLR) = 4.0 kg COD.m-3.d-1), the
COD reduction was 92%. When the UASB treatment was combined with either pre- or postozonation,
the COD reduction was 94 and 96%, respectively. When UASB treatment was
combined with pre- and post-ozonation, a COD reduction of 98% was achieved. The activity
of the UASB granules was also found to improve over time, despite the addition of the
ozonation treatment.
It has been reported that operational problems occur when GDWW is treated in an
UASB reactor as a result of the encapsulation of the granules. This was confirmed when
granules from a full-scale UASB treating WDWW became encapsulated in a layer after being
exposed to GDWW (COD = 4 000 mg.L-1) for 24 d. The results showed that the lipid content
of the granules increased from 1.25 to 60.35 mg lipid.g-1 granule over the 24 d exposure
period. Therefore, granules exposed to GDWW were encapsulated in a lipid-rich layer and as
a result the contact between the GDWW and microbial consortium in the granules was
reduced. The operational problems found during the industrial UASB treatment of GDWW
were ascribed to the encapsulation of the granules.
Combinations of ozonation (dose = 1 476 mg.L-1) generated in a 2 L bubble column
and enzymatic treatments (1% FogFreeTM (FF) dosage and 2 d incubation at 35°C) were found to improve the biodegradability of GDWW. This improvement was in terms of lipid
reduction in GDWW, granule activity and visual appearance of the encapsulating layer of the
granules. The highest lipid reduction (90%), highest granule activity, lowest lipid content of
the granules (3.74 ± 0.10 mg.g-1 granule) and best visual appearance were achieved in
ozonated GDWW treated with 1% FF, followed by just ozonation. The higher lipid reduction
and subsequent higher granule activity were ascribed to the reduction in lipids which resulted
in the fact that fewer lipids were available to encapsulate the granules. As a result of the lipid
reduction, the granule activity improved and the GDWW was made more amenable to UASB
treatment.
This study proved that UASB treatment combined with ozonation led to an
enhancement of the treatment efficiency of WDWW. It was also found that the cause of the
operational problems during UASB treatment of GDWW was as a result of the granules being
encapsulated in a lipid-rich layer. It was established that treating GDWW prior to UASB
treatment improved the biodegradability of GDWW. The data from the study showed that
high lipid reduction in the GDWW directly led to better granule activity, lower granule lipid
content and a thinner encapsulating layer. Based on the data from this study, it is
recommended that GDWW be ozonated prior to other treatments because it can be done inline
and the costs would be lower than that of enzymatic treatments.
Description
Thesis (Msc Food Sc (Food Science))--University of Stellenbosch, 2007.
Keywords
Anaerobic digestion, Upflow anaerobic sludge blanket, Ozone, Dissertations -- Food science, Theses -- Food science, Distilleries -- Waste disposal, Factory and trade waste -- Biodegradation, Sewage -- Purification -- Anaerobic treatment, Ozonization