**2. Characteristics of food industry wastewaters**

Considering the legislation of wastewater purification, total suspended solids (TSS), organic matter, total nitrogen (Ntot) and phosphorus (Ptot) must be removed from both municipal and industrial wastewaters before being released into the watercourse (Metcalf & Eddy, 2003).

In 2008 in Finland, the amount of food processing industry wastewater was 4.1 million m3 and the total amount of industrial wastewaters was 1130 million m3 (Table 1) (Finnish Environment Institute, 2009).

In 2008, the amount of total suspended solids was 83 tonnes, Ptot 4 tonnes, Ntot 87 tonnes whilst the proportion of food industry wastewater of the total industry wastewaters was around 0.4 %. However, the volume of organic matter in food industry wastewater was notable: 0.024 kg m-3 when for example, compared to BOD7 in the pulp and paper industry (0.015 kg m-3) (Finnish Environment Institute, 2009).

oxygen demand (BOD), chemical oxygen demand (COD) and total organic carbon (TOC)

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The most widely used parameter for the determination of organic matter in wastewater is BOD. In this method, the biodegradable organic matter of wastewater is measured. The biochemical oxygen demand is the amount of oxygen which organic matter (solid or dissolved) in the water is consumed when biodegradation occurs in biological oxygen containing states (SFS-EN 1899-1). There are numerous standards for the determination of BOD such as SFS-EN 1899-1 (SFS-EN 1899-1), APHA standard 5210 B (APHA, 1998) and OECD 301 F-guide (OECD, 1992). For wastewater samples, the standard measuring time is five days (BOD5) at 20 °C, but other lengths of time and temperatures can also be used. In Finland, for example, the typical measuring time is seven days (BOD7) (Karttunen,

Although there is a high content of organic matter in food industry wastewaters, the organic compounds, such as fats and proteins, are usually easily biodegradable. Furthermore, the large amount of micro-organisms, for example in the slaughterhouse and meat processing industry wastewaters, facilitates the decomposition of organic compounds (Hiisvirta, 1976). However, there are also some exceptions such as food industry wastewaters containing salts, disinfectants and cleaning agents (Finnish Food and Drink Industries` Federation,

Chemical oxygen demand describes the number of chemically oxidising organic compounds of wastewater (SFS 3020). The COD value can be determined according to APHA standard 5220 "Chemical oxygen demand (COD)". For wastewaters, the oxidising agent is dichromate in an acid solution (APHA, 1998). The ratio of the BOD and COD can provide more information about the wastewater sample. Usually, for industrial wastewaters, COD is higher than BOD because many organic substances which are difficult to oxidise biologically can be oxidised chemically. If the COD value is much bigger than the BOD value, the organic compounds in wastewater are slowly biodegradable (Hiisvirta, 1976). In food industry wastewaters, the COD and BOD values are often closely matched to each other due to the easily biodegradable organic compounds of the effluent (Finnish Food and Drink

Total organic carbon (TOC) describes the amount of organic compounds in wastewater and is used as a more convenient and directs expression of the total organic content than either BOD or COD. TOC analysis provides different information to BOD or COD because the unit of the TOC value is [mg C L-1] while measuring BOD and COD uses the unit of mg O2 L-1. TOC is also independent of the oxidation state of the organic matter and does not measure other organically bound elements, such as nitrogen and hydrogen, and inorganic compounds that can contribute to the oxygen demand measured by BOD and COD (APHA, 1998). The analysing methods for TOC utilises heat and oxygen, UV radiation, chemical oxidants, or a combination of these to decompose the organic compounds of the sample to

(Metcalf & Eddy, 2003).

2003).

2005).

**2.2.1 Biochemical oxygen demand**

**2.2.2 Chemical oxygen demand**

Industries` Federation, 2005).

**2.2.3 Total organic carbon** 


Table 1. Industrial discharge into the watercourse in 2008 in Finland (Finnish Environment Institute, 2009).
