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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 (

Ruokajätteen kompostointi aiheuttaa usein ongelmallisia hajupäästöjä. Tässä projektissa kehitettiin suositukset hajuhaittojen riskin minimoimiseksi ja tehokkaan prosessin sekä korkean ja tasaisen tuotteen laadun saavuttamiseksi. Kolmea täyden mittakaavan laitosta ja yhtä koereaktoria tutkittiin. Tulokset osoittavat voimakkaan korrelaation pH:n ja hajuemissioiden välillä, lämpötila ja hajoamisnopeus ovat myös tärkeitä tekijöitä. Pääsuositus hajuhaittojen vähentämiseksi on prosessin hallinta siten, että pH nousee nopeasti ilman, että lämpötila nousee, joko ilmastuksen avulla taikka lisäämällä kompostia tai korkean pH:n omaavaa puutuhkaa. Vettä voidaan käyttää lämpötilan säätämiseen. Ruokajätteessä on paljon energiaa ja suuri osa energiasta vapautuu kompostoinnissa. Jos energiaa käytetään veden haihduttamiseen, komposti pysyy viileänä. Ruokajätteen sisältämä vesi ei yleensä riitä saamaan aikaan riittävää haihtumista ja viilentämistä. Sen vuoksi olisi voitava lisätä vettä prosessiin lämpötilan ja pH:n säätämiseksi.

A laboratory scale composting reactor was constructed for systematic studies of the effects of oxygen levels and temperature on carbon and nitrogen turnover in household waste compost. The reactor was equipped for independent control of oxygen level and temperature. The results presented showed that the performance of the reactor concerning uniform regulation of temperature and O2 level in the compost matrix, gas and over time was good. The effect of three temperature regimes performed at the constant level of 16% O2 in the compost gas was studied in eight experimental runs in the compost reactor. The effect of reduced O2 levels of 2.5 and 1% in the compost gas was studied in two experimental runs for one of the above temperature regimes. It was found that the highest rate of degradation was achieved when the temperature was actively regulated to below 40°C during a low pH phase. The lowest degradation was obtained when the temperature was already regulated to 55°C from the start. It was further found that reduced O2 levels of 2.5 and 1% in the compost gas reduced the degradation rate and enhanced methane emission.