Determination of the methanogenic potential of an apple processing wastewater treatment system
Date
2006-12
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
The food and beverage industry generates large volumes of wastewater annually. The
disposal of factory effluent from the fruit processing industry has always been a cause of
concern to both the fruit processors and controlling bodies responsible for effluent
management. Traditional disposal of wastewater into sewerage works has become
undesirable due to its economical and environmental impacts. Therefore, on-site
anaerobic treatment of wastewater has received considerable interest due to lower capital
outlays and energy recovery possibilities. Thus, the aim of this study was to establish an
operational treatment profile for an anaerobic pond system treating fruit-processing
wastewater. The specific activity of the microbial populations was also monitored to
determine the effect of the fruit processing seasons (peak and off-peak season). The
biogas production potential at various temperatures was also assessed to determine the
viability of methane recovery.
The influence of the processing and environmental conditions on the ponds’
performance was established by monitoring various process parameters. The results
showed that the chemical oxygen demand (COD) levels decreased during the off-peak
season but the pond pH remained relatively stable between 6.0 and 6.4 during the entire
year. Pond alkalinity was found to be dependent on the regular lime dosing to maintain
the necessary alkalinity. The volatile fatty acid (VFA) concentrations indicated that the
microbial populations of the pond were functioning well. However, a decrease in microbial
activity and VFA concentrations were observed at the lower temperatures during the winter
months. The temperature profile of the pond showed that the pond temperature was
impacted by the fluctuations in the ambient air temperature. The general trend established
by the operational treatment profile clearly showed the impact of the peak and off-peak
season.
The sludge activity of the anaerobic pond was evaluated to determine the effect of
the apple-processing peak and off-peak season on the specific activity of the acidogenic
and methanogenic populations within the sludge. An activity test using four different test
media was used during the activity assays. Sludge samples were taken at four different
sampling positions across the pond’s sludge bed. The sludge was also subjected to a
biogas formation study, which was designed to simulate pond conditions on laboratory scale in order to evaluate the biogas production potential of the anaerobic pond. The
cumulative biogas volume and total CH4 composition showed little or no difference
between the four sludge sampling sites. A major difference was found between the activity
of the microbial populations during the peak and off-peak seasons. The overall trend
regarding the biogas production rate (SB) and the methane production rate (SM) values
showed an increased activity during peak-season and a decreased activity during off-peak
season. For the biogas formation test the highest incubation temperature (25°C) resulted
in the most biogas being produced, followed by 18°C, and with 10°C resulting in the lowest
biogas volume. The biogas formation tests indicated that microbial activity and therefore
biogas production was dependent on especially favourable temperature conditions. The
pond and activity of the microbial populations are therefore influenced by factors like
environmental changes such as decreased air temperatures and substrate changes such
as decreased COD concentrations during the off-peak season. This in turn influences the
rate of biogas production as well as the methane production rate.
The theoretical CH4 calculations and estimates based on the results obtained during
the biogas formation tests indicated that CH4 recovery from the anaerobic pond would
definitely be a worthwhile consideration. If it were assumed that the estimated CH4
volumes (based on only 15% of the pond volume for practical reasons) obtained could be
applied as an energy source, the minimum yearly savings in coal usage would amount to
about R 665 000.
This study was valuable in evaluating the factors such as pond conditions, pond
activity and air temperatures and the effect on the biogas production potential as well as
more importantly, CH4 production for the purpose of energy recovery.
Description
Thesis (Msc Food Sc (Food Science))--University of Stellenbosch, 2006.
Keywords
Methanogenic potential, Apple wastes, Digestion, Wastewater, Dissertations -- Food science, Theses -- Food science, Apples -- Processing -- Waste disposal, Factory and trade waste -- Purification