Biogas EnergyRenewable Energy, Sustainable Living

What is Biogas

Biogas is generated through the anaerobic digestion of organic matter. This can be done either under mesophilic (35 to 38°C) or thermophilic (50 to 55°C) conditions.

There are several anaerobic digester or reactor designs – those commonly found in Asia are shown here. We strongly recommend the use of steel tank designs with limited gas storage capacity to enhance both efficiency and safety. We also suggest a fully automated design to improve reliability and reduce the potential for human intervention or error.

Reactor NameAliasCharacteristicsRangeSafetyEfficiency
Continuously Stirred Tank Reactor CSTR Good for moderate to high TS TS<12% High High
Upward Flow Anaerobic Sludge Blanket UASB Good for wastewater with low to moderate COD COD < 30k mg/l
SS < 1k mg/l
High High
Covered in Ground Anaerobic Reactor CIGAR Good for moderate to high COD (or low TS) TS < 3% Low Low

 

The basic feedstock or required production capacities for various agricultural byproducts and livestock manure are listed here.

FeedstockVolumeUnitWaste NameSuggested Biogas Reactor Technology
Cassava 70  TPD of Starch  Wastewater  Mesophilic EGSB or UASB 
Cassava 70  TPD of Starch  Pulp or Wetcake  Thermophilic CSTR 
Cassava  40  TPD of Ethanol  Stillage  Thermophilic CSTR 
Palm  30  TPH of FFB  POME  Thermophilic CSTR 
Dairy, Cow  10,000  Head  Manure  Mesophilic CSTR 
Dairy, Buffalo  13,000  Head  Manure  Mesophilic CSTR 
Beef Cattle  15,000  Head  Manure  Mesophilic CSTR 
Sow  100,000  Head  Manure  Mesophilic CSTR 
Layer/Broiler  1,000,000  Head  Manure  Mesophilic CSTR 
Food Waste  100  TPD of Waste (at 12-15% TS)  Restaurant Disposal  Mesophilic CSTR 
Sorted MSW  125  TPD of Waste (at 25-35% TS)  Kitchen Disposal  Mesophilic CSTR 
Industrial  28  TPD of COD  Wastewater  Mesophilic or Thermophilic CSTR 
Sewage  850  TPD (at 6% TS)  Surplus Activated Sludge  Mesophilic CSTR 
Napier Grass  100  Hectare  Fresh Grass  Mesophilic CSTR 

It is of paramount importance to understand that in biogas reactor designs, there is no such thing as one-size-fits-all. Each feedstock needs to be managed differently and each needs different pretreatment before it goes into the digester. The criticality of pretreatment cannot be underestimated. Additionally, if the biogas is to be further utilized, then post-treatment is required, generally involving the reduction of hydrogen sulfide (H2S) and moisture. This can be easily managed with automated, properly sized and reliable scrubbers and dryers.

Furthermore, each plant needs to be sized differently if there are issues with seasonality of the feedstock. Proper design and optimization of the biogas plant size and type are keys to technical, commercial and financial success and project continuity.

In general, a mesophilic or thermophilic continuously stirred tank reactor (CSTR) steel tank design provides high robustness and reliability. Initial capital expenditures (CAPEX) maybe be higher, but in the long run, with a proper, safer, more efficient, more reliable and more robust design, the payback should be quicker and more consistent.