The effect of substrate/inoculums ratio on the kinetics of methane production in swine wastewater anaerobic digestion

VERÓNICA CÓRDOBA; MONICA FERNANDEZ; ESTELA SANTALLA

Buenos Aires

Simposio; 5th International Symposium on Environmental Biotechnology and Engineering; 2016

Universidad Nacional de San Martín

Methane production from swine wastewater was evaluated by using sewage sludge asinoculums in three SIR (A: 1/1, B: 3/1, C: 6/1), with the objective to identify the ratio thatoptimizes the performance of the process. Duplicated batch bioreactors of 1 L capacityunder mesophilic conditions were used to carry out the experience. The highest biogasyield was observed in A treatment (554±75 mL/g VS) followed by B (394±25 mL/g VS)and C (466±7 mL/g VS). Cumulative methane production decreased from (382±22) to(232±5 ml/g SV) when SIR increased from 1/1 to 6/1. Modified Gompertz equation wasused to model the experimental cumulative methane yield. The effect of the SIR wasanalyzed based on the kinetic parameters methane production potential, maximummethane production rate and lag-phase time. The obtained results showed thatGompertz equation adjusted adequately the experimental data (R2>0.99). The bestperformance in terms of the kinetic parameters was obtained for treatment A howevertreatment B could still ensure a stable process. The use of higher inoculumsconcentration generated 469.2% higher methane production rate and required 77.2%lower adaptation time (lag-phase) in the SIR range employed. When higher SIR is used(e.g.14/1, previous work) it could be observed that Gompertz equation also adjustedadequately the experimental data (R2>0.99) although the lag-phase time did not remainin a linear relationship with SIR but exponential above SIR=6/1. These resultsdemonstrated that when low amount of inoculums was used, the adaption time ofmicroorganisms resulted much higher than expected delaying the methane production,extending the processing time needed to achieve adequate methane production.