Processes and systems using a modular multi-stage anaerobic digester
Some variations provide a multi-stage process for anaerobic digestion of animal manure, comprising: providing a feedstock comprising animal manure; introducing feedstock with a hydrolytic microorganism to a hydrolysis stage; introducing feedstock with an acidogenic microorganism to an acidogenesis stage; introducing feedstock with a methanogenic microorganism to a methanogenesis stage; forming an anaerobic environment in each stage; monitoring the gas composition and the ratio of volatile fatty acids to total alkalinity in each of the hydrolysis stage, the acidogenesis stage, and the methanogenesis stage; and feeding a steady-state amount of the feedstock into the hydrolysis stage, and processing the steady-state amount of the feedstock, continuously or intermittently, through the hydrolysis stage, the acidogenesis stage, and the methanogenesis stage, thereby generating a product comprising biogas. There are numerous advantages of the disclosed process and system compared to the prior art, including faster processing speed, higher biomethane yield, and lower capital costs.
1 . A multi-stage process for anaerobic digestion of animal manure, wherein said multi-stage process comprises:
(a) providing a feedstock comprising animal manure, wherein said animal manure is in liquid form dissolved in water and/or slurry form suspended in water;
(b) introducing a first start-up amount of said feedstock and a hydrolytic microorganism to a hydrolysis stage, wherein said first start-up amount of said feedstock and said hydrolytic microorganism are introduced batchwise, wherein said hydrolytic microorganism is contained with said first start-up amount of said feedstock, and wherein said hydrolysis stage is operated in step (g) at a hydrolysis temperature selected from about 50° C. to about 65° C.;
(c) introducing a second start-up amount of said feedstock and an acidogenic microorganism to an acidogenesis stage, wherein said second start-up amount of said feedstock and said acidogenic microorganism are introduced batchwise, wherein said acidogenic microorganism is contained with said second start-up amount of said feedstock, and wherein said acidogenesis stage is operated in step (g) at an acidogenesis temperature selected from about 50° C. to about 70° C.;
(d) introducing a third start-up amount of said feedstock and a methanogenic microorganism to a methanogenesis stage, wherein said third start-up amount of said feedstock and said methanogenic microorganism are introduced batchwise, wherein said methanogenic microorganism is contained with said third start-up amount of said feedstock, wherein said methanogenesis stage is operated in step (g) at a methanogenesis temperature selected from about 50° C. to about 75° C.;
(e) forming an anaerobic environment in each of said hydrolysis stage, said acidogenesis stage, and said methanogenesis stage;
(f) monitoring gas composition and ratio of volatile fatty acids to total alkalinity in each of said hydrolysis stage, said acidogenesis stage, and said methanogenesis stage; and
(g) feeding a steady-state amount of said feedstock into said hydrolysis stage, and processing said steady-state amount of said feedstock, continuously or intermittently, through said hydrolysis stage, said acidogenesis stage, and said methanogenesis stage, thereby generating a product comprising biogas, wherein step (g) is triggered based on both monitored gas composition obtained during step (f), and monitored ratio of said volatile fatty acids to said total alkalinity obtained during step (f).
2 . The multi-stage process of claim 1 , wherein said animal manure is swine manure.
3 . The multi-stage process of claim 1 , wherein said hydrolytic microorganism has a genus selected from the group consisting of Coprothermobacter, Acetomicrobium , and Thermoanaerobacterium.
4 . The multi-stage process of claim 1 , wherein said hydrolysis stage is operated in step (g) at a hydrolysis-stage residence time selected from about 1 day to about 5 days.
5 . The multi-stage process of claim 1 , wherein said acidogenic microorganism has a genus selected from the group consisting of Acetitomaculum, Acetoanaerobium, Acetonema, Anaerovorax , Candidatus Phosphitivorax, Dehalobacterium, Moorella , Romboutsia, Ruminococcus , and Terrisporobacter.
6 . The multi-stage process of claim 1 , wherein said acidogenesis stage is operated in step (g) at an acidogenesis-stage residence time selected from about 5 days to about 14 days.
7 . The multi-stage process of claim 1 , wherein said methanogenic microorganism has a genus selected from the group consisting of Methanobacterium, Methanoculleus, Methanothermobacter, Methanosarcina, Methanothrix , and Methanospirillum.
8 . The multi-stage process of claim 1 , wherein said methanogenesis stage is operated in step (g) at a methanogenesis-stage residence time selected from about 7 days to about 14 days.
9 . The multi-stage process of claim 1 , wherein total residence time is about 30 days or less, wherein said total residence time is defined as the sum of hydrolysis-stage residence time, acidogenesis-stage residence time, and methanogenesis-stage residence time.
10 . The multi-stage process of claim 9 , wherein said total residence time is about 15 days or less.
11 . The multi-stage process of claim 1 , wherein step (f) includes monitoring concentration of H 2 S to indicate a transition from hydrolysis to acidogenesis.
12 . The multi-stage process of claim 1 , wherein said biogas produced in step (g) has a biomethane yield of at least 80%, wherein said biomethane yield is calculated as a ratio, expressed as a percentage, of biomethane in said product divided by total biomethane potential associated with said feedstock.
13 . The multi-stage process of claim 12 , wherein said biomethane yield is at least 85%.
14 . The multi-stage process of claim 12 , wherein said biomethane yield is at least 90%.