AEROBIC COMPOSTING AND ANAEROBIC-DIGESTION OF PULP AND PAPER-MILL SLUDGES

The feasibility of aerobic vessel composting and anaerobic digestion f or the treatment of pulp and paper mill sludges were studied. The comp osting studies made use of primary and secondary sludge from a de-inki ng and paper mill. In six parallelly aerated 500 1 vessels with variou s carbon 1 nitrogen (C:N) -ratios, the most optimal performance was ob tained with C:N -ratios of c. 22-35, while higher and lower ratios del ayed the temperature increase. With the optimal ratios, the thermophil ic stage was reached within 36 h, and the stage lasted for about seven days, In the scale-up study (18 m(3) compost vessel), the thermophili c stage was reached within 24 h. An effective dehydratation of the mas s was obtained as the total solids (TS) content of the compost increas ed from 31.3% to 63.8% within 21 days. The anaerobic digestion of pulp and paper mill sludges was studied using two mesophilic 5 1 digesters , their feed sludges consisting of a mixture of municipal sewage sludg e and primary and secondary sludge from a pulp and paper mill. With th is feed mixture and with a loading rate of about 1.0 kg volatile solid s (VS)/m(3)d a removal of about 27 to 40% VS and methane production of about 180 l/kgVS(added) feed sludge were achieved during the 80 d stu dy period. The study showed that pulp and paper mill sludges are amena ble to both aerobic composting and anaerobic digestion. (C) 1997 IAWQ. Published by Elsevier Science Ltd.