Anaerobic digestion of poultry slaughtering wastes

The feasibility of anaerobic digestion of poultry slaughterhouse wastes com bined with wastes from a food packing plant was studied using semi-continuo usly fed, laboratory-scale, continuously-stirred digesters at 35 degrees C and 55 degrees C. Furthermore, factors affecting anaerobic digestion were s tudied using batch assays with digested material from the digesters. In the mesophilic digester, inoculated with mesophilic digester sewage sludge, an d with a loading of up to 4.6 g volatile solids (VS) 1(-1) d(-1) (a hydraul ic retention time (HRT) of 18 days), the specific methane yield was 330 ml g(-1)VS(added). Nitrogen in the feed was organic nitrogen with a slight amo unt of ammonium present, while ammonium nitrogen in the digested material a ccounted for 50 to 70 % (up to 3.9 g 1(-1)) of total nitrogen. The total so lids and VS removals were 58 and 68 %, respectively With the highest loadin g, however, methane production was apparently curtailed at the end of the s tudy period, and sustainability of a long-term operation of the process rem ains to be proven. In contrast, under similar conditions the digesters inoc ulated with mesophilic and thermophilic granular sludge both failed after 4 0 to 50 days of operation, their failure being due apparently to inhibition (unadapted inocula or overloading). The results show that up to 100 m(3) o f methane can be produced from ton (wet weight) of the waste mixture studie d. The process may be inhibited by ammonium nitrogen and some other inhibit ory compounds, most likely long-chain fatty acids.