Esitetään Jyväskylän yliopiston matemaattis-luonnontieteellisen tiedekunnan suostumuksella julkisesti tarkastettavaksi yliopiston Ylistönrinteellä, salissa YAA303 toukokuun 23. päivänä 2014 kello 12.Academic dissertation to be publicly discussed, In this thesis, the anaerobic digestion of industrial by-products from meat and pulp and paper industry were studied. These materials, which are treated mainly like wastes, were seen to be potential substrates for anaerobic digestion. Methane yields of ca. 700 dm 3 kg volatile solids (VS)added -1 were obtained for slaughterhouse wastes, alone and in co-digestion with rendering wastes. On the other hand, methane yields of 190-240 dm 3 kgVSadded -1 were obtained in the monodigestion of pulp and paper industry primary sludge, and 150-170 dm 3 kgVSadded -1 in the co-digestion of primary sludge with secondary sludge. In the digestion of slaughterhouse and rendering wastes, mesophilic conditions were more stable, and the feasible organic loading rates (OLRs) were 1-1.5 kgVS m -3 d -1 and hydraulic retention times (HRTs) were 50 d. For pulp and paper mill wastewater sludge, thermophilic conditions were more stable with the feasible OLRs of 1-2 kgVS m -3 d -1 and the HRTs of 14-32 d. The digestion processes of these industrial by-products can easily turn unstable. In the digestion of slaughterhouse and rendering wastes, process imbalance may occur due to inhibition from intermediate products like volatile fatty acids, long-chain fatty acids and ammonia. On the contrary, in the digestion of pulp and paper mill wastewater sludge, the low nitrogen content and low pH may cause problems. It was observed that the more stable digestion process of slaughterhouse waste is achieved by additive of Co, Ni, Se, W, Fe and HCl. In addition, in pulp and paper mill secondary sludge digestion, hydrothermal pretreatment, among the studied 12 single or combined pre-treatments, increased the methane yield by 19-31 %. In conclusion, the digestion of two different kinds of industrial by-products was seen to be feasible, although operational conditions should be optimised and possibly enhancement methods used to ensure the stable digestion processes of these vulnerable organic materials.
