43    SEQUENCING BATCH AND HYBRID ANAEROBIC
REACTORS TREATMENT OF DAIRY WASTES
Veysel Eroglu, Associate Professor
Izzet Ozturk, Associate Professor
Ibrahim Demir, Research Assistant
Lutfi Akca, Associate Professor
Kadir Alp, Associate Professor
Environmental Engineering Department
Istanbul Technical University
Maslak, Istanbul 80626 Turkey
INTRODUCTION
The wastewater treatment alternatives for diary wastes produced from a Turkish Milk Industry
Association (SEK) plant located in Istanbul producing bottled milk, cheese, yogurt and butter were
investigated. Sequencing batch and hybrid pilot reactors (SBR and HPR) were constructed and the
operation of these two systems were tested using the wastewater from the SEK plant. Intermittent
sequencing reactors possess operational flexibility. The number of reactors in operation can be altered
depending on the daily and seasonal flow rate changes. Since aeration and sedimentation takes place
in the same tank, there is no need for recycling facilities and the system is not affected by shock loads.
Since the effluent is discharged intermittently, the effluent can be kept in the reactor till the effluent
standards are fulfilled. Organic carbon removal, nitrification and the denitrification processes can all
be achieved in a single reactor. Also during the filling and discharging, operation schemes can be
changed to control the overgrowth of filamentous microorganisms.
The pilot plant sequencing batch reactor was operated for a duration of 6 months at different
organic loads and operational modes. The COD of the inlet was varied between 1 000 and 4 000 mg/L.
The response of the reactor to various filling times as long as 3 hours was investigated. One cycle that
included the filling, aeration, mixing, settling, draining and resting operations was taken as 24 hours.
The aeration time was 13 hours. For each mode of operation, SVI and the BOD removal efficiencies
were measured. The SVI range was 38 to 105 mg/L and the COD removals of 91-98% were achieved.
The concentration of the suspended solids in the effluent was between 30 and 110 mg/L.
The anaerobic processes are comparatively more difficult to operate and the microorganisms in
anaerobic reactors are more sensitive to temperature, pH and other environmental changes. However,
the anaerobic reactors have less operating costs, and the methane produced can be utilized as a
valuable by-product. Following the period of start up the hybrid anaerobic reactor was operated at the
loading rate varying between 1 and 8 kg COD/m3/d. The operating parameters including suspended
solids, biogas volumes and compositions were measured. COD removal efficiencies of 60% to 90%
were achieved depending on the varying organic loading rates, for an operating period of four
months.
PRODUCTION PROCESSES
The Turkish Milk Industry Association (SEK) is a state establishment. It has over thirty plants in
different cities distributed throughout Turkey. The total capacity of all these plants is about 200,000
tons/year. In the last decade, private industry has also contributed to the production. The plant that
was the subject of this investigation was SEK located in Kuleli, Istanbul. The plant's capacity is 60,000
ton/year. In the year 1989, the unprocessed milk entering the plant was 59,000 tons/year (40,000 tons
of pasteurized bottled milk, 5,600 tons of yogurt, and 310 tons of butter, 28 tons of cheese).
The first step in the processes is receiving the unprocessed milk. The milk passes through quality
control and centrifuged. Then it is stored after cooling to 4°C. After clarification and standardization
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