48    UPGRADING THE ANAEROBIC CONTACT PROCESS
CAPACITY USING POLYURETHANE CARRIERS
Veysel Eroglu, Associate Professor
Izzet Ozturk, Associate Professor
Department of Environmental Engineering
Istanbul Technical University
80626 Maslak, Istanbul —Turkey
Erol Bircan, Environmental Engineer
Sahan Kimya A.S., Inonu Caddesi No. 70
80090, Gumussuyu, Istanbul —Turkey
INTRODUCTION
In recent years extensive investigations have been carried out all over the world on industrial
wastewater treatment. The organic conventional parameters such as BOD, COD and TOC which are
significant indicators in wastewater pollution are usually removed by biological methods. Among
these methods aerobic biological ones are preferred over the anaerobic systems due to simplicity in
their operation and control. However, for strong organic wastewaters anaerobic treatment systems
become increasingly preferable over the aerobic methods since anaerobic processes are bioenergy
producers. Consequently, anaerobic biological treatment methods are being continuously developed.
The most important points in the anaerobic processes are the preservation of sufficient biomass
within the system and the maintenance of necessary contact between the substrate as well as biomass.
For this purpose, in recent years it has been practiced to keep the micro-organisms at fixed surfaces by
putting carriers into the main reactors.
In this study, the effect of the polyurethane (PUR) carriers was investigated on the anaerobic
treatment of wastes from a citric acid plant in Turkey. Since the company has planned to double the
capacity of the factory without any extension in the existing treatment plant, two model anaerobic
digesters were used to test the feasibility of the PUR carriers for upgrading the existing treatment
system.
PRODUCTION OF CITRIC ACID
Citric acid is produced by surface fermentation method from the sugar-beet molasses at the FUR-
SAN factory which is the subject of this research. The yearly production of this plant is 3500 tons
composed of citric acid monohydrate, citric acid anhydrate and trisodium citrate dehydrate. Under
the suitable conditions the molasses is transformed to citric acid and oxalic acid. With the treatment
of lime the oxalic acid is settled as calcium oxalate and hence it is separated from the system.
Subsequently, calcium citrate is also settled and filtered. Sulphuric acid is added and the calcium
sulphide precipitates are removed from the system.The citric acid solution passes through an active
carbon bed, cationic and anionic ion exchangers. Then it is evaporated and crystallized. Finally, the
crystals are dried and packed for commercial purposes.
SOURCES AND CHARACTERISTICS OF WASTEWATERS
The wastewaters produced during the citric acid production the wastewater can be classified five
groups.
1. Wastewater from calcium citrate filter.
2. Wastewater from the washing of molasses tanks and connections.
3. Wastewater from the activated carbon filter, anionic and cationic ion-exchangers.
4. Cooling waters, and
5. Domestic wastewaters
45th Purdue Industrial Waste Conference Proceedings, © 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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