**4. Conclusions**

24 Management of Organic Waste

The third important factor is presence of nitrogen. Several authors have reported that the optimal C/N ratio is between 25/1 and 30/1 although operation at low C/N ratios of 10/1 are also possible. With such low C/N ratios the undesirable emission of ammonia can be significant (Matsumura et al., 2010). Characteristic values of organic matter content and total nitrogen in the digested sludge are 50-70% and 1.5-2.5%, respectively. In the first week of the digested sludge composting the total carbon is reduced by between 11% and 27% and total

**Parameter Test method Limit value** 

EN 13650 EN 13650 EN 13650 ISO 16772 EN 13650 EN 13650 EN 13650

EN 13654 EN 13650 EN 13650 EN 13652 EN 13652 EN 14346 EN 15169 EN 13037

Table 6. Control parameters of digestate quality for application in agriculture (WRAP 2010) Highest degradation rates in the compost pile are achieved with air oxygen concentration above 15% which also prevents formation of anaerobic zones. The quality of aeration depends primarily on structure and degree of granulation of the composting material; finer materials generally provide better aeration of the compost pile (Sundberg and Jönsson, 2008). In the first stages of degradation, acids are generated, and these tend to decrease the pH in the compost pile. The optimum pH range for microorganisms to function is between 5.5 and 8.5. Elevated temperature in the compost material during operation is a consequence of exothermic organic matter degradation process. The optimum temperature for

ISO 16649-2 1000 CFU/g fresh matter

GC -

Absent in 25 g fresh matter

1.5 mg/kg d.m. 100 mg/kg d.m. 200 mg/kg d.m. 1.0 mg/kg d.m. 50 mg/kg d.m. 200 mg/kg d.m. 400 mg/kg d.m.

0.25 l/gVS

0.5 %m/m d.m. 8 %m/m d.m.


nitrogen is reduced by between 13% and 23% (Pakou et al., 2009; Yañez et al., 2009).

1. Pathogens Escherichia coli Salmonella sp.

2. Toxic elements Cd Cr Cu Hg Ni Pb Zn

3. Stability Volatile faty acids Residual biogas potential

4. Physical contaminants Total glass, metal, plastic and other manmade fragments Stones >5 mm

> 5.Parameters for declaration Total nitrogen Total phosphorus Total potassium Water soluble chloride Water soluble sodium Dry matter Loss on ignition pH

The chapter entitled "Sustainable Treatment of Organic Wastes" presents principles and techniques for treatment of wet biodegradable organic waste, which can be applied in order to achieve environmental as well as economic sustainability of their utilisation.

The chapter mostly focuses on organic wastes generated in the municipal sector; however it may well apply to similar wastes from agriculture and industry. The main focus is aimed at matching the anaerobic treatment process to the selected type of waste in order to maximize the biogas production, a valuable renewable energy resource. The chapter also focuses on technological aspects of the technology used in such treatments and presents and elaborates several conventional treatments (such as semi-continuous processes, two stage processes, sequencing batch processes, etc.) as well as some emerging technologies which have only recently gained some ground (such as anaerobic treatment in solid state). The basic conditions are presented which are required to successfully design and operate the treatment process. Organic loading rates, biogas production rates, specific biogas productivity, biogas potentials and specific concerns for certain technologies and waste substrates are presented. The main influencing factors such as environmental conditions (pH, temperature, alkalinity, etc.) have been addressed as well as inhibitors that can arise in such processes (heavy metals, ammonia, salts, phenolic compounds from lignocellulosic degradation, organic overload etc.). The biogas treatment and use, such as power

Anaerobic Treatment and Biogas Production from Organic Waste 27

ISO (1998) EN ISO 11734 (1998) Water Quality – Evaluation of the »Ultimate« Anaerobic

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production and natural gas grid injection, have been presented as well as the use of parasitic energy, options for biogas production enhancement through waste pre-treatment (mechanical, chemical, physical, etc.) and treatment of residues of anaerobic digestion, which may have an important impact on the environment. Special attention is given to further treatment of digested solid residues as well. Due attention is paid to aerobic stabilization processes (open and closed composting), taking into account physical form of the waste, its composition, pollution, degradability and final deposition and use.
