The experimental design of AD in this study is shown in Table 2.
Briefly, varying amounts of homogenized PPW and PPW-FR samples were mixed with sodium bicarbonate and water to adjust pH to 7 and total solid (TS) content. After releasing of all the CO2 bubbles, varying amounts of inoculum was added into each reactor.All tests were conducted in batch mode using 800 mL serum bottles fitted with a rubber septum and incubated in a water bath at 35 C for 40 days with manually shaking twice a day. The digesters, PPW-1 and PPW-FR-1, have the same TS content of 6.4%, volatile solid (VS) content of 5.2%, and feedstock/inoculum (F/I, the amount of feedstock VS per amount of inoculum VS) ratio of 2.6.