A novel green substrate made by sludge digestate and its biochar: Plant growth and greenhouse emission

Abstract

Anaerobic digestion of sludge produces a large amount of sewage sludge anaerobic digestate (SSAD) that can be reused. A novel green substrate was prepared by mixing SSAD and its biochar (SSBC) filled with perlite and quartz sand for plant growth, as a replacement of soil. We carried out pot experiment, measured ryegrass biomass, seedling survival rate, and evaluated the emission of greenhouse gas (GHG), NH3 volatilization. The results showed that the seedling survival rate and individual biomass of ryegrass in green substrate were 100% and 100.02 mg, which were 14.4% and 231.4% higher than those in only SSAD, but were 1.3% and 19.6% higher than those in soil. SSBC significantly reduced N2O and CO2 emission, inhibited the NH3 volatilization, but increased CH4 emission. However, the cumulative emission of N2O and CH4 was approximation to that in soil. Global warming potential of CH4 and N2O (GWP(CH4+N2O)) green substrate was 11,842.01 kg CO2·hm-2, which was 1.35-fold higher than that of soil. Microbial community structure analysis showed that fermentative bacteria and methanogenic archaeal had a higher abundance in green substrate than in soil, which caused the different gas emission. This study will provide an effective and economical way to dispose excessive SSAD.