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November 2015
Biogas production potential
for South African sugar cane industry
PRIMROSE MAGAMA
and
KHUTHADZO MUGODO,
both from the ARC-Institute of Agricultural Engineering and
SALOME MODISELLE,
Economic Analysis Unit, ARC-Agricultural Economics and Capacity Development
FOCUS
Natural resources and energy
Special
T
he aim of this article is to present the potential for local
biogas production from the sugar cane industry in South
Africa. The review of biogas production potential in this
article was done alongside the analysis of the possibil-
ity of biogas production from different other agricultural and
agro-waste streams in the country (such as the livestock industry,
abattoir waste, the fruit processing sector as well as the brewery and
winery industry).
Sugar cane industry outlook
The sugar cane industry makes a significant contribution to the South
African economy. This is attributed to its agricultural and industrial
investments, foreign exchange earnings, high employment and its
linkages with major suppliers, support industries and customers.
However, for the past decade the South African sugar cane indus-
try has been grappling to come to terms with much tighter profit
margins, mainly due to stagnant and in some areas even declining
yields, combined with rising input costs.
In the coastal regions, the prevalence of Eldana (the African sugar
cane borer) has forced growers to shorten their cutting cycles,
impacting negatively on yields as well as the quality of cane
delivered (BFAP, 2015).
In recent years yields have also been affected by exceptionally low
rainfall conditions. Particularly during 2014 and 2015, the rainfall
levels have dropped well below long-term average levels. Hence,
the year 2015 will be remembered as the worst year of drought in
103 years.
The severity of the drought has impacted heavily on yield levels
and consequently, the total cane production is projected to drop
to 14,2 million tons in 2015, compared to 17,7 million tons in 2014 and
20,3 million tons in 2013 (BFAP, 2015).
There are 14 sugar mills operating in South Africa and they are
owned by six companies. The mills operate for approximately
36 weeks of the year between April and December. The recent
drought comes at a time where a number of mills have already been
struggling with lower throughput and consequently lower profit
margins for the past several years. Currently the energy supply is
unreliable and energy costs have been increasing in South Africa.
This adds pressure to an already troubled sugar cane industry.
Pressures on the industry have forced sugar cane industry partici-
pants to find ways to offset high operational costs. The industry has
already invested in the renewable energy sector by producing en-
ergy from bagasse. Meanwhile, there are other kinds of by-products,
such as filter cake and wastewater, which have been largely unused
from an energy point of view.
It is estimated that the sugar cane industry generates 0,2 m
3
/ton -
1,8 m
3
/ton of wastewater with a high biological demand. Sugar
wastewater, if disposed of in water bodies and left untreated, can
contaminate surface and subsurface waters.
Current mainstream technologies for wastewater treatment, such
as aerobic activated sludge and tertiary nutrient removal processes
have a limitation of not recovering valuable energy contained in
the wastewater.
Calculation of the amount of biogas
produced
Methodology
The theoretical amount of biogas presented by this desktop study
is merely a guideline. It should be noted that the actual amount of
biogas that can be realised will differ from that which are calculated.
This is due to factors such as biogas digester efficiency, fluctuations
in production levels and assumptions made during calculations.
Lastly, literature gave varying values of waste generation rates,
chemical oxygen demand and biogas yields for the same waste resi-
due. Hence in most cases the values used for calculations was at
the discretion of the authors and conservative values were favoured.
Data regarding the amount of sugar cane crushed annually by each
of the 14 mills was obtained from the South African Sugar Associa-
tion (SASA) website.
For the 2014/2015 production season an estimate of 17,76 million
tons of sugar cane was crushed. The amount of solid and liquid waste
AGRO-
SECTOR
NUMBER
OF MILLS
ANNUAL
PRODUCTION
(MILLION TONS)
TYPE OF
WASTE
WASTE
GENERATED
THEORETICAL
BIOGAS GENERATION
POTENTIAL (MILLION
m
3
/ANNUM)
POTENTIAL
ENERGY
RECOVERY
(GWH/ANNUM)
POTENTIAL
ELECTRICITY
GENERATION
CAPACITY
(GWH/ANNUM)
Sugar mills
14
17,76
Solid
(filter cake)
887 775,20
tons/annum
22,19
133,16
39,95
Liquid
(wastewater)
3,2 million
litres/annum
2,56
15,34
4,60
Total
24,75
148,5
44,55
TABLE 1: THEORETICAL BIOGAS PRODUCTION FOR THE SOUTH AFRICAN SUGAR CANE INDUSTRY.
The potential of biogas production from the sugar cane industry is calculated based on the methodology given in this article.