Bioavailability of dissolved organic matter in biogas slurry enhanced by catalytic ozonation combined with membrane separation.

Large molecular weight pig biogas slurry (L-PBS) and small molecular weight pig biogas slurry (S-PBS) were separated from original pig biogas slurry (O-PBS) using a 100 kDa membrane. The original bioavailability and biosafety of L-PBS was very low. In order to enhance the total bioavailable dissolved organic nitrogen (TB-DON) and total bioavailable dissolved organic phosphorus (TB-DOP), optimum catalytic ozonation of L-PBS conditions were determined using Box-behnken design models (P < 0.0001) and intersection tests. The optimal values for ozone concentration, pH value, active catalyst concentration and reaction time were 2.63 mg·L, 6.48, 1.43 g·L and 40 min, respectively. Catalytic ozonation can effectively decompose and transform 68.07% of L-PBS into S-PBS to improve content organic bioavailability, with a molecular weight distribution of 0-1 kDa (13.53%), 1-5 kDa (16.62%), 5-10 kDa (11.16%), 10-30 kDa (11.73%), 30-100 kDa (15.04%). Catalytic ozonation of L-PBS can reduce protein levels from 85.28% to 47.18%, but increases the proportion of fulvic and humic components from 10.22% to 32.67% and 4.51%-20.15%, respectively. Because catalytic ozonation changes the internal components and molecular weights of L-PBS, both saw increases in TB-DON and TB-DOP from 3.33% to 41.12% and 2.43%-37.88%, respectively, with a large number of TB-DON and TB-DOP derived from hydrophilic organic components during catalytic ozonation. These important internal mechanisms changed by catalytic ozonation can effectively reduce the ecotoxicity (IR, from 76.5% to 33.1%) and phytotoxicity (GI, enhanced from 35.4% to 70.3%) of L-PBS. Therefore, catalytic ozonation combined with membrane separation is a choice technology in improving the nutrition of biogas slurry and reduce its ecological risk.