Leachate after aerobic stabilization of municipal solid waste supplemented by waste glycerine from saponification to improve biogas production during co-digestion

Co-digestion of leachate from aerobic stabilization of OFMSW (leachateOFMSW) with waste glycerine (WG) from saponification is a promising approach for municipal waste and wastewater treatment. The effect of feedstock composition on co-digestion efficiency was examined. Two feedstocks with different contents of WG (6%, 13%) were used, which affected the COD:TKN ratios in those feedstocks (60, 100). LeachateOFMSW provided nitrogen and the microand macroelements. In both feedstocks, the N-NH4:TKN ratio was low (0.08), indicating that the dominant form of nitrogen was organic nitrogen (Norg). Co-digestion was carried out in upflow anaerobic-sludge blanket reactors (37 +/- 2 degrees C; OLR, 4 kg COD m(-3) d(-1)). This process ensured highly effective COD removal (over 97%). At a feedstock COD:TKN ratio of 60, specific biogas production (SBP) was ca. 0.22 m(3) kg(-1) COD, and methane content, 61.6%. Increasing the COD:TKN ratio to 100 significantly increased SBP to ca. 0.36 m(-3) kg(-1) COD, but reduced biogas quality (54.2% CH4). Although Norg had to be ammonified to ammonium because of the low N-NH4:TKN ratio in the feedstocks, the ammonium concentration in the post-processing wastewater remained low. Moreover, the low ammonium concentrations meant that the pH (8.8) did not have a toxic effect on anaerobic co-digestion (free ammonia concentrations were merely ca. 28 and 5.5 mg L-1, respectively). However, at higher feedstock COD:TKN ratios than those tested, ammonium could be exhausted, which would impede methane production. These results indicate that WG is an effective co-substrate for leachateOFMSW if an appropriate amount of WG is added to the feedstock.

Automated summary

Co-digestion of leachate from aerobic stabilization of organic solid waste (leachateOFMSW) with waste glycerine (WG) from saponification process is an efficient method for simultaneous treatment of municipal waste and wastewater, achieving high COD removal and biogas production. Adjusting the feedstock composition can affect the specific biogas production and methane content.