Sugar Factory as a Water Producer
Martin Čejka – Tereos TTD, a. s.
The Dobrovice sugar factory was built in 1831 by order of Karel Anselm Thurn Taxis, in an unoccupied castle. Because of its location, the factory lacked access to abundant water sources (such as rivers), available to many other sugar factories. In 1869/1870, the North-Western railway between Nymburk and Mladá Boleslav was built, including a station in Dobrovice, and a siding to the sugar factory. In 1874, the sugar factory was renovated: a battery of Robert diffusers, a new beet washer, and a lime kiln with a brick outer wall were installed; together with greater processed beet quantities, water consumption went up. For this reason, a cast-iron water-pipe system was built. This system included a steam-driven pumping station to bring water from the approximately 3-km distant Pěčice pond. In times of water shortage, use of underground water was considered; an artesian well was then installed in 1907–1908 by the company J. Thiele from Osek nad Duchcovem. It was drilled through a 385.2m-thick chalk layer, into the underlying Permian sedimentary rock formation 727.2m deep (1). Even though it was only used as a secondary water source, the well performed as per specification. A system whereby water was pumped from several ponds arranged in a cascade remained operational till the 1990s. Once water management - as well as other stations, including, but not limited to, pulp-pressing to increase dry matter of pulp - was made more efficient and processing capacity was increased, sugar beet itself became the main source of process water.
Today, the main source is water contained in the processed beet (a beetroot contains 76% of water on average). Steam from beet juice and syrup thickening is condensed; part of the water thus obtained is used to compensate for water losses in the boiler room where heating steam is produced (most of that water comes from heating steam condensed at the 1st evaporator stage); more steam is cooled in the barometric condenser, with water from the cooling system. Cooling water temperature is reduced in cooling towers. Some of the cooling water and condensate is accumulated in a tank, to be used as a water source for the distillery during its syrup-processing campaign. Another part of excess cooling water serves mainly to improve washing water quality. Soil contained in washing water is separated in sedimentation tanks. Adding clean water to the washing circuit increases the quantity of water accumulating in the sedimentation tanks. Excess water - i.e., beyond the quantity required to start the next processing campaign - is channelled to a biological waste-water treatment plant, then discharged into surface waters.

Waste-Water Treatment and Water Balance

The Dobrovice sugar factory waste-water treatment plant (WWTP) was commissioned in FY 1997/1998. Since then, the water management system underwent many changes: the most important ones include the building of a distillery, then of a distillery-slop treatment plant. A flowchart of the WWTP operation is shown in Figure 1.
The distillery operation was launched in 2006/2007. Waste water from the distillery includes bottoms liquid (from the distillation column and from the dehydration stage), and condensate from the slop evaporator. Together with water used for equipment cleaning, it is treated in a WWTP. Thank to the distillery waste water, the anaerobic stage of the WWTP can operate the year round.
A biological treatment plant with two anaerobic digesters for processing distillery slops was commissioned in the 2014/2015 processing campaign. During the beet-processing campaign, one of these (ICC 1) is used to pre-treat washing water containing organic impurities, so as to reduce the load on the anaerobic WWTP stage. Pre-treated water is recirculated to the sedimentation tank.
The anaerobic stage of the biological WWTP (anaerobic digestion) is fed with excess waste water, from which thick soil sludge has been removed in the sedimentation tank, as well as with distillery waste water - i.e., bottoms liquid (from distillation and dehydration columns) and condensate from the slop evaporator.
Organic-matter loaded water is pumped through the WWTP exchanger, to the anaerobic digester. The exchanger heats water to the required temperature. In the digester, organic matter undergoes anaerobic fermentation. This process releases biogas that is collected for further use. The mixture of pre-treated water from anaerobic digestion and small biomass particles overflows from the digester to a station with degassing tanks and lamella clarifiers, where biomass is separated from pre-treated water.
The separated anaerobic biomass is recirculated into the anaerobic digester; pre-cleaned water then flows by gravitation to the activation tank of the second WWTP stage.
The aerobic stage includes activation (nitrification) and denitrification steps, in an activated sludge system. Denitrification is the biological process by which nitrate is converted to gaseous nitrogen products, which are then removed from water in a stirred tank. Part of the entering organic load is thus removed, and more denitrification sludge is created. In the aerated nitrification reactor, reduced nitrogen forms are converted to oxidized forms. More organic impurities are thus removed from water, while nitrification sludge quantity increases.
Aerobic biomass is separated from treated water and is recycled into the denitrification stage. Excess biomass is extracted to a sludge sedimentation tank.
Cooling water and cleaned water from the aerobic-stage lamella clarifiers arrives into the denitrification stage, then to nitrification and to a final sedimentation tank, from which it is discharged. Between the nitrification and denitrification stages, the mixture is recycled through an inner recycling system. Separated biomass from the final sedimentation tank is then recycled through an outer recycling system.
As it has been stated above, the Dobrovice sugar factory operates with excess water, which needs to be first treated to achieve the required parameters, and then discharged to surface waters. The possibility of recirculation and waste water treatment in sugar factories was examined in detail by Lochman (2). Through calculation based both on theory and on real figures, this author promoted the idea that certain sugar factories have a positive water balance - as the Dobrovice sugar factory has had for years -, and therefore do not need to use extraneous water - superficial or underground - for their operation. A theoretical calculation with specific figures - a sugar factory operating 130 days, processing 15,000 tonnes of sugar beet per day on average - shows that the quantity of excess water to be discharged into a river is substantial (see Tab. I).

Using the Excess Water Potential

In today's world, it might be worthwhile to consider finding a use for this excess water, instead of treating it at high cost, then irreversibly discharging it into surface waters. According to Government Decree No. 528 of 24 July, 2007 (3), a Drought Impact Protection Policy for the Czech Republic (4) was drawn up. It provides a number of measures intended to attenuate drought impact on our countryside, specific to individual sectors such as industry or agriculture. These include saving actions to prevent water being wasted, and to better protect water supply in the countryside. In my opinion, it would be also useful to look into more productive use of certain types of water, now considered as waste water under Czech law. This applies, among other, to excess water from the sugar production process, which some West-European countries use for irrigating adjoining fields; this keeps water in the countryside better than treating it and discharging it into a river.

Bibliography

1.	Hynie, O.: Návrh na definitivní úpravu artézské studně cukrovaru Dobrovice. 1941, 18 s. 

2.	Lochman, V.: Krajní možnosti recirkulace odpadních vod v cuk rovarech. Listy cukrovarnické, 103, 1987, s. 184–192. 

3.	Usnesení vlády č. 528 o Koncepci ochrany před následky sucha pro území České republiky. 2017. 

4.	Koncepce ochrany před následky sucha pro území České republiky. 

2017, 65 + 26 s. 

5.	Vodní právo cukrovaru Dobrovice. 1892. 

Coagulating agent

Sludge sedimentation tank

Sedimentation tank

Aerobic sludge extracted

Washing water

Final sedimentation tank

Anaerobic digester

Discharge

Condensate

Outer recycling

Anaerobic recycling

OT – degassing tanks
LU – lamella clarifiers
AN – anaerobic
AE - aerobic

Cooling water

Flocculating agent

Activation tank

Sugar factory

Distillery

Anaerobic stage output

Fig. 1 Dobrovice Sugar Factory Wastewater Treatment Plant Flowchart

Fig. 2 Dobrovice Sugar Factory Wastewater Treatment Plant

Fig. 3 Biological WWTP Treating Dobrovice Distillery Slops

Tab. I. Dobrovice Sugar Factory and Distillery Water Balance

Type	Water Quantity		
				
	per day (m3)	campaign (m3)		
				
Incoming water in sugar beet	11,426	1,485,380		
Water in pulp	1,980	257,400		
Water in molasses	152	19,760		
Evaporation and loss in cooling circuit	3,898	506,740		
Total losses	6,030	783,900		
Residual water	5,396	701,480		
Distillery water consumption	2,215	287,950		
Excess water - discharged	3,181	413,530