Operational Strategies for Thermophilic Anaerobic Digestion of Organic Fraction of Municipal Solid Waste in Continuously Stirred Tank Reactors

Abstract

Three operational strategies to reduce inhibition due to ammonia during thermophilic anaerobic digestion of source-sorted organic fraction of municipal solid waste (SS-OFMSW) rich in proteins were investigated. Feed was prepared by diluting SS-OFMSW (ratio of 1:4) with tap water or reactor process water with or without stripping ammonia. Three continuously stirred tank reactors were operated at 55 degrees C with 11.4 gVS d(-1) loading rate and 15 d retention time. Total ammonia nitrogen (TAN) level in the reactor fed with recirculated water alone was spiked to 3.5 and 5.5 g-N l(-1) through ammonium bicarbonate additions. Dilution of SS-OFMSW with fresh water showed a stable performance with volatile fatty acids of < 1g l(-1) and methane yield of 0.40 m3 kg(-1) volatile solids (VS). Use of recirculated process water after stripping ammonia showed even better performance with a methane yield of 0.43 m3 kg(-1) VS. Recirculation of process water alone on the other hand, resulted in process inhibition at both TAN levels of 3.5 and 5.5 g-N l(-1). However, after a short period, the process recovered and adapted to the tested TAN levels. Thus, use of recirculated process water after stripping ammonia would not only evade potential inhibition due to ammonia but could avoid the use of fresh water for dilution of high solids protein-rich SS-OFMSW.

Anaerobic digestion of selected Italian agricultural and industrial residues (grape seeds and leather dust): combined methane production and digestate characterization

“…As a theoretic calculation supporting this hypothesis, it can be considered realistic for substrates rich in organic nitrogen that the ammonium nitrogen in the digestate accounts for 50 to 70% of total nitrogen [43,52]. Consequently, on the basis of the nitrogen content in the original leather dust and of the average temperature and pH conditions in the pertinent tests T1 and T2, the free ammonia concentration in the digestion of leather dust -as derivable with the appropriate equilibrium relation depending on pH and temperature [4,28,53] -was expected to be in the range from about 146 to about 205 mgN L −1 . This estimated range results above the concentrations of 100-150 mgN L −1 that have been reported for ammonia inhibition of an unadapted digestion process [54], although there is still uncertainty in the technical-scientific literature concerning the effective threshold levels and conditions at which ammonia becomes inhibitory to methanogenesis [38,41,48].…”

The effect of upper mesophilic temperature and feed-to-seed ratio on batch anaerobic digestion systems

“…It is evident that there is a considerable increase in the gas generated with an increase in the F/S ratio from 10/90 to 50/50; however, a further increase in the F/S ratio resulted in a steady and remarkable decline in gas formation, which is an indication that reactors with high F/S content were susceptible to organic overloading. [35,36] Accumulation of VFAs (as mentioned earlier) and the associated reduction in gas production have been frequently linked to batch reactor imbalance. [29,30] Furthermore, the methane content of the biogas averaged 53 ± 13%, which compares well with the generally accepted range (i.e., 55 to 70%) for full-scale anaerobic digesters.…”

Production of biogas from solid organic wastes through anaerobic digestion: a review

“…The authors found out that both reactors gave a comparably high performance when treating organic matter. Angelidaki et al (2006) evaluated how different operational strategies could minimize the process inhibition due to ammonia accumulation during the anaerobic digestion of Source-Sorted Organic Fraction of Municipal Solid Waste (SS-OFMSW) in a thermophilic CSTR. At an OLR of 11.4 kg VS m −3 day and a 15-day HRT, a stable performance was observed when SS-OFMSW was diluted with fresh water and when process water was recirculated after ammonia stripping.…”