The aim of this project was to develop recommendations regarding how composting processes for the treat ment of source-separated food waste in Nordic countries should be designed and implemented in order to: Minimise the risk of odour problems with the process Minimise the risk of odour problems with the finished product Achieve an efficient and reliable process Achieve a high and uniform product quality. The hy pothesis for the project was th at total odour emissions from the composting process and the risk of odour from the finished com post product could be m inimised if the process turnover rate and decom position were to be maximised. In the project, incom ing biowaste and c omposting processes were investigated at three full-scale composting plants (NSR in Sweden, YTV in Finland and IVAR in Nor way) and at an experi mental reactor (S LU in Sweden). The results showed a strong correlation between pH an d odour in compost pore gas. At lo w pH values (below 6.0) the odour concentration was very high, from 70 000 to over 2 million ou E/m3 , whil e at pH >6.7 it was at most 44 000 ouE/m3 . The biowaste collected wa s consistently acidic, with pH between 4.7 and 6.0. Tests confir med previous results that the de composition process proceeds much more slowly at low pH (<6) if the tem perature is allowed to rise above 40°C. Howev er, if the temperature is kept below 40°C, decomposition is intensive, which causes the pH to climb rapidly. When the pH has incr eased to over 6.5, but not before, the te mperature should be allowed to increase to around 55°C, since this maximises the decomposition rate. The most im portant recommendation as regards decreasing o dour problems in composting of food waste is to control the process so that the pH is increased rapidly. This can be achieved by intensive ventilation at the beginning of the process, whic h promotes cooling and increases the oxygen suppl y. The pH can also be increased through addition of pHincreasing material such as co mpost or wood ash w ith a hi gh pH. This minimises the am ount of intensely m alodorous acidic com post in the system. In addition, it m aximises decomposition from the very beginning 12 of the process, which leads to m aximisation of the proportion of total odour em itted in the encl osed part of the co mposting plant, where the odours can be treated before being released to the environment. The am ount of readily av ailable energ y in fo od waste is very hi gh, while in stable and well-matured co mpost it is low. Therefore, a large amount of energ y m ust b e released during com posting. This energ y is largely used for evaporating water from the compost. Since food waste is very energy-rich, the amount of water in the inco ming waste is not sufficient to allo w evaporation of t he am ount required to cool the c ompost sufficiently to beco me sta ble. To ach ieve optimal p rocess speed in the enclosed part of the com posting plant, it should t herefore be possible to add water. Otherwise the degradation process halt s until a sufficient degree of cooling is achieved, e.g. through water in the form of rain or snow being added during post-process maturation.
|Place of Publication||Uppsala|
|Number of pages||93|
|Publication status||Published - 2009|
|MoE publication type||D4 Published development or research report or study|