The effects of direct enzyme cocktail addition and other pretreatment methods on VFA production through cofermentation of primary sludge and external organic waste were studied under initial alkaline (pH 10) and acidic (pH 5) conditions. Besides the direct enzymes addition, 24-h enzymatic, ultrasonic, ultrasonic+24-h enzymatic and thermal were the other pretreatment methods employed. Under the alkaline condition, direct addition of enzymes enhanced VFA production by 29-39%, attaining VFA yields of 364-633 mg COD g(-1) VS throughout the experimental period, whereas there was 37-43% increase in VFA production under the acidic condition only at retention days 1 and 2, achieving VFA yield of 207 and 215 mg COD g(-1) VS, respectively. VFA composition was dominated by acetic acid (54-67%) and propionic acid (31-46%) under alkaline and acidic conditions, respectively. Direct enzyme addition increased the percentage of caproic acid from 8 9% to 16-17%, under the acidic condition. While 24-h enzymatic pretreatment didn't show any improvement on VFA production, thermal, ultrasonic+24-h enzymatic and ultrasonic pretreatment methods increased VFA production by only 18,14 and 4%, reaching maximum VFA yields of 512,486 and 445 mg COD g(-1) VS, respectively. On the other hand, these pretreatment methods significantly increased biogas production. Experiment without pretreatment achieved maximum biogas production of 392 NmL CH4 at day 9 while experiments with pretreatments achieved a maximum of 679-954 NmL CH4 in the order of no pretreatment < ultrasonic < thermal < 24-h enzymatic < ultrasonic+24-h enzymatic. The study gives insight into how pretreatment strategy can influence VFA production and composition.

Selective leaching of Li from spent LIBs thermally pretreated by pyrolysis and incineration between 400 and 700 °C for 30, 60, and 90 min followed by water leaching at high temperature and high L/S ratio was examined. During the thermal pretreatment Li2CO3 and LiF were leached. Along with Li salts, AlF3 was also found to be leached with an efficiency not higher than 3.5%. The time of thermal pretreatment did not have a significant effect on Li leaching efficiency. The leaching efficiency of Li was higher with a higher L/S ratio. At a higher leaching temperature (80 °C), the leaching of Li was higher due to an increase in the solubility of present Li salts. The highest Li leaching efficiency of nearly 60% was observed from the sample pyrolyzed at 700 °C for 60 min under the leaching condition L/S ratio of 20:1 mL g−1 at 80 °C for 3 h. Furthermore, the use of an excess of 10% of carbon in a form of graphite during the thermal treatment did not improve the leaching efficiency of Li.