S. Zahedi

Changes in microbial community during hydrogen and methane production in two-stage thermophilic anaerobic co-digestion process from biowaste.

In this paper, the microbial community in a two-phase thermophilic anaerobic co-digestion process was investigated for its role in hydrogen and methane production, treating waste activated sludge and treating the organic fraction of municipal solid waste. In the acidogenic phase, in which hydrogen is produced, Clostridium sp. clusters represented 76% of total Firmicutes. When feeding the acidogenic effluent into the methanogenic reactors, these acidic conditions negatively influenced methanogenic microorganisms: Methanosaeta sp., (Methanobacteriales, Methanomicrobiales, Methanococcales) decreased by 75%, 50%, 38% and 52%, respectively. At the same time, methanogenic digestion lowered the numbers of Clostridium sp. clusters due to both pH increasing and substrate reduction, and an increase in both Firmicutes genera (non Clostridium) and methanogenic microorganisms, especially Methanosaeta sp. (208%). This was in accordance with the observed decrease in acetic (98%) and butyric (100%) acid contents. To ensure the activity of the acetate-utilizing methanogens (AUM) and the acetogens, high ratios of H2-utilizing methanogens (HUM)/AUM (3.6) were required.

Hydrogen production from the organic fraction of municipal solid waste in anaerobic thermophilic acidogenesis: Influence of organic loading rate and microbial content of the solid waste

Hydrogen production (HP) from the organic fraction of municipal solid waste (OFMSW) under thermophilic acidogenic conditions was studied. The effect of nine different organic loading rates (OLRs) (from 9 to 220 g TVS/l/d) and hydraulic retention times (HRTs) (from 10d to 0.25 d) was investigated. Normally, butyrate was the main acid product. The biogas produced was methane- and sulfide-free at all tested OLR. Increasing the OLR resulted in an increase in both the quantity and quality of hydrogen production, except at the maximum OLR tested (220 g TVS/l/d). The maximum hydrogen content was 57% (v/v) at an OLR of 110 g TVS/l/d (HRT=0.5 d). HP was in the range of 0.1-5.7 l H2/l/d. The results have clearly shown that the increase in OLR was directly correlated with HP and microbial activity. The bacterial concentration inside the reactor is strongly influenced by the content of microorganisms in the OFMSW.

Optimisation of single-phase dry-thermophilic anaerobic digestion under high organic loading rates of industrial municipal solid waste: Population dynamics

Different high feed organic loading rates (OLRs) (from 5.7 g to 46.0 g TVS/l/d) or hydraulic retention times (HRTs) (from 15 d to 2 d) in single-phase dry-thermophilic anaerobic digestion (AD) of organic fraction municipal solid waste (OFMSW) were investigated. The specific gas production (SGP) values (0.25-0.53 m(3)/kg TVS) and the percentages of Eubacteria, Archaea, H2-utilising methanogens (HUMs) and acetate-utilising methanogens (AUMs) were stable within the ranges 80.2-91.1%, 12.4-18.5%, 4.4-9.8% and 5.5-10.9%, respectively. A HUM/AUM ratio greater than 0.7 seems to be necessary to maintain very low partial pressures of H2 required for dry AD process. Increasing OLR resulted in an increase in all the populations, except for propionate-utilising acetogens (PUAs). Optimal conditions were obtained at 3d HRT (OLR=30.7 g TVS/l/d), which is lower than the doubling time of acetogens and methanogens. The methane production (MP) was clearly higher than those reported in AD of OFMSW.

Optimisation of the two-phase dry-thermophilic anaerobic digestion process of sulphate-containing municipal solid waste: Population dynamics

Microbial population dynamics and anaerobic digestion (AD) process to eight different hydraulic retention times (HRTs) (from 25d to 3.5d) in two-phase dry-thermophilic AD from sulphate-containing solid waste were investigated. Maximum values of gas production (1.9 ± 0.2 l H2/l/d; 5.4 ± 0.3 l CH4/l/d and 82 ± 9 ml H2S/l/d) and microbial activities were obtained at 4.5d HRT; where basically comprised hydrolysis step in the first phase (HRT=1.5d) and acidogenic step finished in the second phase as well as acetogenic-methanogenic steps (HRT=3d). In the first phase, hydrolytic-acidogenic bacteria (HABs) was the main group (44-77%) and Archaea, acetogens and sulphate-reducing bacteria (SRBs) contents were not significant; in the second phase (except to 2d HRT), microbial population was able to adapt to change in substrate and HRTs to ensure the proper functioning of the system and both acetogens and Archaea were dominated over SRBs. Decreasing HRT resulted in an increase in microbial activities.

Dark fermentation from real solid waste. Evolution of microbial community

The purpose of this paper was to study the evolution of microbial community and its relation to the hydrogen production (HP) steps in thermophilic-dry dark fermentation from real organic fraction of municipal solid waste (OFMSW). Nine organic loading rates (OLRs) (from 9 to 220 g TVS/l/d) were investigated. Population dynamics study showed that increasing OLR (between 9 and 110 g TVS/l/d) resulted in an increase in the relations between Eubacteria:Archaea and hydrolytic-acidogenic bacteria (HABs):acetogens. This was strongly influenced by the microbial content of the OFMSW. The presence of acetogens and Archaea was due to contribution of these microorganisms in the substrate (the biogas produced was methane-free). The maximum value of hydrolysis (63±7%) was observed at 110 g TVS/l/d OLR according to maximum HP and HAB activity. The highest average values of acidification yields (57-60%) were achieved for OLR between 28 and 43 g TVS/l/d.

Biochemical conversion of fruit rind of Telfairia occidentalis (Fluted Pumpkin) and poultry manure

Environmental pollution by solid wastes and inadequate energy supply are some of the major challenges facing the developing world. This study evaluated the potentials of Fluted pumpkin fruit rind and poultry manure for biogas generation. Mechanical and thermo-alkaline pre-treatments were applied to two samples labeled ‘O’ and ‘P’ while the third sample (Q) had no thermo-alkaline treatment. The physicochemical characteristics of the substrates revealed richness in nutrients and mineral elements. The results showed that use of a combination of pre-treatment methods enhanced the biogas yield in the pre-treated substrates. Analysis of the gas composition showed 66.5 ± 2.5% Methane, 25 ± 1% Carbon dioxide; 58.5 ± 2.5% Methane, 26 ± 1% Carbon dioxide; 54.5 ± 1.5% Methane, 28 ± 2% Carbon dioxide for the three experiments, respectively. All the obtained values show the models had a high predictive ability. The substrates should be further used for energy generation. ARTICLE HISTORY Received 9 June 2018 Revised 4 July 2018 Accepted 16 July 2018