South Korea Mandarin orange juice production - residues used to produce biogas

Jeju is a subtropical, volcanic island  located  100 kilometres south  of the Korean peninsula. It is about  half the  size of Majorca and,  due  to  its  mild  climate, it offers optimum  conditions for cultivating citrus  plants. Moreover, thanks  to its lush and  diversified  natural  setting  and  its ex- pansive beaches, it is a popular port of call on cruises  through East Asia.

With a market share of 55 percent, China is by far the world’s largest producer  of man- darin oranges.  South Korea, where cultiva- tion is limited to Jeju, is in tenth place, with a production total of just about two percent. Due to the mild climate, more than 40 dif- ferent  varieties  thrive  on this  island.  On Jeju,  the  mandarin orange  harvest  takes place  from October through  February.  Be- cause  of its high content of vitamins A and C, calcium  and potassium, this well-known winter fruit is also a very healthy food. But primarily due  to strict  regulations, which stipulate that  mandarin orange juice must consist  of 100 percent fruit,  the  oranges are seldom processed into juice.

The only production site  for mandarin or- ange juice in Korea is located  on Jeju.  Its production capacity  has increased steadily in recent  years. The pressing  residues ac- cumulated from juice production are processed further in a dewatering  system.  The press  cakes  produced in this way are used in cattle  feed and the thin,  liquid phase  is used to feed the biogas plant.

Because the  requirements for the  quality of fresh  water  and  processing   water  are high in the beverage industry,  the increase in juice  production pushed the  cleaning performance of the  aerobically  operated wastewater  treatment plant  to its  limits. Consequently, treating  the water such  that its quality  is sufficient  for discharge into receiving  waters  has  become  more  com- plex and  expensive  in  recent  years.  The reason  was that  at 165 grammes  per litre, the  biochemical oxygen demand (BOD), which represents the amount  of oxygen re- quired by bacteria for the biological decom- position  of the  organic compounds in the wastewater, was significantly  higher  than the permissible limit value. On the island of Jeju,  the state’s  environmental require- ments  are high.  Compliance  necessitated that solutions be found.


Plant construction and operating experience

Mandarin  orange juice is not produced all year long; instead, it is a seasonal business that  starts  at the beginning  of the harvest and lasts somewhat longer than half a year. For this reason,  to ensure  uniform operat- ing performance for the biogas plant  to be constructed, four vertical  containers with a total  storage  capacity  of 20,000 cubic metres were required to store the mandarin orange residue. To achieve  maximum  leak tightness, these  containers, as well as all of the others  supplied by the Lipp compa- ny, were manufactured with the  patented double-seam system using a stainless steel composite material.

The other containers include a universal di- gester (850 cubic metre) for the anaerobic treatment of the highly polluted wastewater before further aerobic treatment in the mu- nicipal  wastewater  treatment plant  as well as a mixing tank and a buffer tank. Each of these tanks has a volume of 100 cubic me- tres.
The biogas  produced in the  digester is used  for heat  generation for the  waste- water treatment plant  and the production site.  The entire  plant  was commissioned in 2019. Since  then  it has been  operating successfully and  achieves  very good BOD values of less than  3 grammes  per litre for the wastewater.