ENVIRONMENT AND ENERGY
The dairy industry in the US produces large
amounts of wastewater: for every litre of milk, it
uses 1.5–3 litres of water. Typically, the wastewater
has approximately 10 times the organic loading
of municipal wastewater. Whey is a by-product of
cheese-making and commonly used for feeding pigs
or making other products.
However, there is a large surplus which is very energy-
intensive to treat as wastewater. The main ingredient of
whey is lactose and this can be fermented into ethanol in
a creative process of wastewater recycling. Carbery Milk
Products in Cork, Ireland, was the first dairy producer in
the world to do this.
The whey is put through microfiltration and reverse
osmosis and the lactose goes to a fermenter where it is
turned into beer before going on to a distillation system
to produce a 96% ethanol product for the bioethanol
fuel market. All the bioethanol in Ireland comes from this
one plant and it is the only European country not using
sugarcane-based ethanol from Brazil.
The steam from the distillation process is recovered and
used to pre-heat boiler water, heat water for clean-in-
place (CIP) and for pasteurisation, thus saving energy.
The waste stream from the fermentation is sent to an
anaerobic digester and produces biogas which is used to
produce additional heating.
The warm wastewater from the anaerobic digester
is passed through a heat exchanger to pre-heat the
incoming chilled milk.
Thus, the wastewater is cooled to a suitable
temperature for discharge into the local river without
affecting the environment. At the same time, the
wastewater has a large concentration of phosphorus
of which 99% must be removed before discharge. The
phosphorus is recycled back to agricultural land. The
company wants to expand the plant and the resulting
high-quality treated effluent is potentially suitable for
recycling at the site, particularly as boiler feedwater,
as the amount of water that the plant can withdraw
from the local river is limited.
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BOX 6.4: KALUNDBORG SYMBIOSIS IN KALUNDBORG, DENMARK
The Kalundborg Industrial Symbiosis is an ‘industrial ecosystem’ where the
by-products of one enterprise are used as a resource by other enterprises, in
a closed cycle. It began in 1961 with the development of a new project to use
surface water from Lake Tissø for a new oil refinery with the aim of saving the
limited supplies of groundwater.
The City of Kalundborg was in charge of building the pipeline while the refinery
was responsible for the financing. The Kalundborg Industrial Symbiosis has
developed gradually over several decades from initiatives and individual
cooperation between companies of different sectors driven by economic
advantages, with support from the Kalundborg Municipality. Nowadays, it is a
project mainly financed by the
symbiosis partners.
The symbiosis involves exchange of all sorts of materials, including wastewater,
as shown in the flow diagram. Water Cascading Initiatives: The Asnæs Power
Station receives 700 000m 3 of cooling water from Statoil each year, which it
treats to use as boiler feed water. It also uses about 200 000m 3 of Statoil’s
treated wastewater for cleaning each year.
The cooling water becomes steam that is provided back to Statoil, as well as to
other business, such as a local fish farm. The savings to local water resources
are considerable — nearly 3 million m 3 of groundwater and 1 million m 3 of
surface water per year (Domenech and Davis, 2011). The power plant uses salt
water from the fjord for some of its cooling needs. As a result, it reduces the
withdrawals of freshwater from Lake Tissø.
The resulting by-product is hot salt water, an amount of which goes to the fish
farm’s 57 ponds. Heat Cascading Initiatives: Asnæs started supplying the city
with steam for its new district heating system in 1981. Then, Novo Nordisk and
Statoil joined in as customers for steam. This system of district heating was
encouraged by the city and the Danish government and thus replaced about
3 500 oil furnaces.
Moreover, recycling would reduce discharges to the river,
particularly during seasonal low flow, when the dilution
capacity is lower. Polishing the already high-quality effluent
using advanced oxidation is being investigated, as it is
cheaper than buying potable water. The water would go
into the reverse osmosis plant, which demineralizes the
water. This has the added benefit of reducing membrane
fouling and reducing cross-contamination as it has no
direct contact with food products.
Continued on page 21 >>
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January 2019 Volume 25 I Number 1