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Sand based system for physiochemical and biological treatment of winery wastewater
Author(s)
Holtman, Gareth Alistair
Date Issued
2023
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
In South Africa, many wineries use cellar effluent for irrigation after primary settling and pH
adjustment. This poses an environmental risk as winery effluent can contain high concentrations
of organic and inorganic pollutants. Most vine growing countries, including South Africa, are
water-stressed, so it is important that winery effluent is remediated to the extent that it is safe
for reuse as irrigation water. In order to align the South African wine industry with global views
to achieve sustainable development, there is a need for low maintenance, low cost and effective
solutions for treating winery wastewater which can be easily integrated into the existing
infrastructure. This body of work presents the results of a number of fundamental and applied
studies used to determine the validity of biosand reactors as a potential solution to fulfil this
winery wastewater treatment function in small to medium sized cellars.
In the first study, chapter 3, a pilot biosand reactor with a nodal design was installed, operated
and monitored for 2 years at a medium sized winery (crushing 1600 tons of grapes per annum)
in the Stellenbosch area, Western Cape. Two reactors were operated in alternating continuous
and pulse modes, with COD removal efficiencies of 70% achieved in each mode. Higher hydraulic
and organic loading rates were achieved in continuous mode (113 L.m-3sand.day-1 and 279
gCOD.m-3sand.day-1, respectively) than in pulse mode (90 L.m-3sand.day-1 and 192 gCOD.m-
3sand.day-1). In comparison to other passive systems treating winery effluent, the biosand
reactor system achieved significantly higher loading rates with a smaller spatial footprint.
This applied study was followed by three fundamental studies to elucidate the biodegradation,
neutralization and hydraulic mechanisms involved in remediating winery wastewater in biosand
reactors. These studies were conducted using a series of columns containing raw sand and
various sized fractions of sand from the Philippi quarry site in Cape Town.
Biosand reactors have been shown to effectively neutralize winery wastewater, and it was
assumed that the major neutralization was via dissolution of calcite sand particles. The first flowthrough
column experiment was conducted to determine whether there may be a biotic
contribution to pH adjustment. Sand cores containing functional microbial communities were
extracted from an operational biosand reactor system. One half of the cores were sterilized by
irradiation and used to determine the abiotic contribution, while the biotic contribution was calculated by deducting the results obtained from the irradiated columns from those obtained
from the non-irradiated columns. The cores were dosed with synthetic winery wastewater and
hydrochloric acid at the same pH. Using the hydroxide ion concentration in the effluent as a
proxy, it was found that the major neutralization mechanism was abiotic (average 95.5±0.16%)
due to the dissolution of calcite, with a small biotic contribution (average 4.5±0.13%).
The second series of column experiments was conducted in order investigate calcite dissolution
kinetics and the effect of calcite dissolution on the hydraulic conductivity of the Philippi sand.
The results were used in conjunction with those obtained from an operational pilot biosand
reactor system to determine the temporal abiotic neutralization capacity of biosand reactors.
Flow-through experiments using hydrochloric acid were conducted using columns containing
sand with a variety of particles sizes. The larger particles (>0.425 mm) contained lower amounts
of calcite (using Ca as a proxy), but exhibited higher hydraulic conductivities before and after
calcite dissolution (3.0 ± 0.05 %Ca and 2.57 to 2.75 mm·s−1, respectively) compared to the
fractions containing smaller particles and/or raw sand (4.8 ± 0.04 to 6.8 ± 0.03 %Ca and 0.19 to
1.25 mm·s−1, respectively). By measuring the amount of Ca removed from the sand as a proxy for
calcite dissolution, a temporal abiotic neutralization capacity of 37 years was calculated for
biological sand reactor systems containing Philippi sand with 5.4 % wt.wt Ca and an influent with
a pH ranging from 2 to 3 and a hydraulic loading rate of 150 L·m−3 of sand.d−1.
Based on the promising results obtained with the larger sand particles in the second series of
columns experiments, a third set of column experiments was used to compare the raw
(unfractionated) sand to fractionated sand (<0.425 mm removed) in terms of operational
performance. The flow in biosand reactors slows down after start-up due to the growth of
functional biomass within the sand pores that decreases the hydraulic conductivity. In this study,
initial hydraulic conductivities of 0.285 mm.s-1 and 2.504 mm.s-1, were measured in the columns
containing raw and fractionated sand, respectively. After operating the columns by feeding with
winery effluent for 3 months, the hydraulic conductivities reduced to 0.129 mm.s-1 and 1.116
mm mm.s-1, respectively. Similar organic removal efficiencies were obtained with raw (94%) and
fractionated (95%) sand, and both sands were able to effectively neutralize the acidic (pH 4.9)
winery wastewater. It was calculated that one 5.6 m3 biosand reactor containing the fractionated
sand can potentially treat 8102 L.d-1 of winery wastewater, which surpasses the design flow rate
of raw sand of 1000 L.d-1. During the applied pilot study, it was noted that copious amounts of primary wastewater sludge
is generated at the study site. Currently, the winery contacts a commercial company to remove
this waste to landfill which is an economic and environmental burden. Biochemical methane
potential tests were used to determine the potential for valorisation of this organic-rich wastestream
via anaerobic digestion. The highest specific methane yield of sludge harvested during
the crush season (206 ± 2.7 mLCH4/gVSadded) was obtained under mesophilic (37°C) conditions.
The composition of the digestate compared favorably with commercial organic agricultural
fertilizers.
Finally, building on the results obtained, a zero-waste model is presented for treatment of winery
effluent based on the use of biosand filters. This includes: (i) using fractionated sand in the filters
and the sifted smaller sand particles in the concrete industry, (ii) remediating the winery
wastewater in biosand filters, and using the treated effluent for safe irrigation, (iii) valorizing the
primary wastewater sludge via anaerobic digestion and using the digestate as an agricultural
fertilizer.
adjustment. This poses an environmental risk as winery effluent can contain high concentrations
of organic and inorganic pollutants. Most vine growing countries, including South Africa, are
water-stressed, so it is important that winery effluent is remediated to the extent that it is safe
for reuse as irrigation water. In order to align the South African wine industry with global views
to achieve sustainable development, there is a need for low maintenance, low cost and effective
solutions for treating winery wastewater which can be easily integrated into the existing
infrastructure. This body of work presents the results of a number of fundamental and applied
studies used to determine the validity of biosand reactors as a potential solution to fulfil this
winery wastewater treatment function in small to medium sized cellars.
In the first study, chapter 3, a pilot biosand reactor with a nodal design was installed, operated
and monitored for 2 years at a medium sized winery (crushing 1600 tons of grapes per annum)
in the Stellenbosch area, Western Cape. Two reactors were operated in alternating continuous
and pulse modes, with COD removal efficiencies of 70% achieved in each mode. Higher hydraulic
and organic loading rates were achieved in continuous mode (113 L.m-3sand.day-1 and 279
gCOD.m-3sand.day-1, respectively) than in pulse mode (90 L.m-3sand.day-1 and 192 gCOD.m-
3sand.day-1). In comparison to other passive systems treating winery effluent, the biosand
reactor system achieved significantly higher loading rates with a smaller spatial footprint.
This applied study was followed by three fundamental studies to elucidate the biodegradation,
neutralization and hydraulic mechanisms involved in remediating winery wastewater in biosand
reactors. These studies were conducted using a series of columns containing raw sand and
various sized fractions of sand from the Philippi quarry site in Cape Town.
Biosand reactors have been shown to effectively neutralize winery wastewater, and it was
assumed that the major neutralization was via dissolution of calcite sand particles. The first flowthrough
column experiment was conducted to determine whether there may be a biotic
contribution to pH adjustment. Sand cores containing functional microbial communities were
extracted from an operational biosand reactor system. One half of the cores were sterilized by
irradiation and used to determine the abiotic contribution, while the biotic contribution was calculated by deducting the results obtained from the irradiated columns from those obtained
from the non-irradiated columns. The cores were dosed with synthetic winery wastewater and
hydrochloric acid at the same pH. Using the hydroxide ion concentration in the effluent as a
proxy, it was found that the major neutralization mechanism was abiotic (average 95.5±0.16%)
due to the dissolution of calcite, with a small biotic contribution (average 4.5±0.13%).
The second series of column experiments was conducted in order investigate calcite dissolution
kinetics and the effect of calcite dissolution on the hydraulic conductivity of the Philippi sand.
The results were used in conjunction with those obtained from an operational pilot biosand
reactor system to determine the temporal abiotic neutralization capacity of biosand reactors.
Flow-through experiments using hydrochloric acid were conducted using columns containing
sand with a variety of particles sizes. The larger particles (>0.425 mm) contained lower amounts
of calcite (using Ca as a proxy), but exhibited higher hydraulic conductivities before and after
calcite dissolution (3.0 ± 0.05 %Ca and 2.57 to 2.75 mm·s−1, respectively) compared to the
fractions containing smaller particles and/or raw sand (4.8 ± 0.04 to 6.8 ± 0.03 %Ca and 0.19 to
1.25 mm·s−1, respectively). By measuring the amount of Ca removed from the sand as a proxy for
calcite dissolution, a temporal abiotic neutralization capacity of 37 years was calculated for
biological sand reactor systems containing Philippi sand with 5.4 % wt.wt Ca and an influent with
a pH ranging from 2 to 3 and a hydraulic loading rate of 150 L·m−3 of sand.d−1.
Based on the promising results obtained with the larger sand particles in the second series of
columns experiments, a third set of column experiments was used to compare the raw
(unfractionated) sand to fractionated sand (<0.425 mm removed) in terms of operational
performance. The flow in biosand reactors slows down after start-up due to the growth of
functional biomass within the sand pores that decreases the hydraulic conductivity. In this study,
initial hydraulic conductivities of 0.285 mm.s-1 and 2.504 mm.s-1, were measured in the columns
containing raw and fractionated sand, respectively. After operating the columns by feeding with
winery effluent for 3 months, the hydraulic conductivities reduced to 0.129 mm.s-1 and 1.116
mm mm.s-1, respectively. Similar organic removal efficiencies were obtained with raw (94%) and
fractionated (95%) sand, and both sands were able to effectively neutralize the acidic (pH 4.9)
winery wastewater. It was calculated that one 5.6 m3 biosand reactor containing the fractionated
sand can potentially treat 8102 L.d-1 of winery wastewater, which surpasses the design flow rate
of raw sand of 1000 L.d-1. During the applied pilot study, it was noted that copious amounts of primary wastewater sludge
is generated at the study site. Currently, the winery contacts a commercial company to remove
this waste to landfill which is an economic and environmental burden. Biochemical methane
potential tests were used to determine the potential for valorisation of this organic-rich wastestream
via anaerobic digestion. The highest specific methane yield of sludge harvested during
the crush season (206 ± 2.7 mLCH4/gVSadded) was obtained under mesophilic (37°C) conditions.
The composition of the digestate compared favorably with commercial organic agricultural
fertilizers.
Finally, building on the results obtained, a zero-waste model is presented for treatment of winery
effluent based on the use of biosand filters. This includes: (i) using fractionated sand in the filters
and the sifted smaller sand particles in the concrete industry, (ii) remediating the winery
wastewater in biosand filters, and using the treated effluent for safe irrigation, (iii) valorizing the
primary wastewater sludge via anaerobic digestion and using the digestate as an agricultural
fertilizer.
Additional information
Thesis (DEng (Civil Engineering))--Cape Peninsula University of Technology, 2023
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