This lecture discusses the difference between high solid digestion and low solid digestion and its design differences

1. High solid
digestion – design
parameters
By
Dr. S. PUGALENDHI & Er. T. AYISHA NAZIBA

2. HSD
● High solids digestion (HSD) is a type of anaerobic digestion that is
used to process waste materials with a high solids content (greater
than 20%).
● HSD is a relatively new technology, but it has the potential to be
more efficient and cost-effective than traditional anaerobic digestion
systems.
● HSD systems can process a wider range of waste materials - food
waste, manure, and agricultural waste.

3. Advantages
● Increased methane production
● Reduced digestate production
● Ability to process a wider range of waste
materials
● More environmentally friendly
● More cost-effective
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4. 4
Parameter High Solids Anaerobic Digestion (HSAD) Low Solids Anaerobic Digestion (Wet AD)
Solids Content in
Feedstock
Up to 35% 5-10%
Pre-processing
Requirement
Often extensive pre-processing required Typically requires less pre-processing
Biogas Volume
Output
Higher due to higher solids content. Lower due to lower solids content.
Water Usage Designed to reduce water usage. Higher water-to-feedstock ratio.
Organic Loading Rate
(OLR)
Designed to increase OLR. Lower OLR due to higher water content.
Nutrient Loss in
Digestate
Lower nutrient loss due to concentrated solids. Higher nutrient loss
Dewatering of
Digestate
Aims to avoid or reduce dewatering. Often requires dewatering
Methane Production
Efficiency
Lower rates and extents of methane
production due to low moisture and poor
mixing.
Typically more efficient methane
production due to higher moisture content
and better mixing.
Operational Costs Higher Generally lower operational costs.
Appropriate
Feedstock
Feedstocks with high solids content- non-
organic materials.
Organic waste with low solids content.

5. Design parameters
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6. Loading Rate (LR):
● The loading rate is the amount of organic solids added to the
digester per unit volume per unit time.
● It determines the organic loading capacity of the digester.
𝐿𝑅 =
𝑀𝑖𝑛
𝑉𝑡
- LR -loading rate (kg/m³/day)
- Min -mass of organic solids added (kg)
- V -volume of the digester (m³)
- t -digestion time (days) 6

7. Retention Time (RT):
● Retention time is the average time organic solids spend in
the digester and is a crucial parameter for achieving
effective digestion.
𝑅𝑇 =
ρ𝑉
𝑀𝑖𝑛
Where:
- RT -retention time (days)
- V -volume of the digester (m³)
- Min - mass of organic solids added (kg)
- ρ - density of organic solids (kg/m³)
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8. Biogas Production Rate
● The biogas production rate is the amount of biogas
produced per unit of organic solids added.
𝐵𝑖𝑜𝑔𝑎𝑠 𝑃𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑅𝑎𝑡𝑒, 𝑚3/𝑘𝑔 =
𝐵𝑖𝑜𝑔𝑎𝑠 𝑉𝑜𝑙𝑢𝑚𝑒
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑂𝑟𝑔𝑎𝑛𝑖𝑐 𝑆𝑜𝑙𝑖𝑑𝑠 𝐴𝑑𝑑𝑒𝑑
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9. Mixing and Temperature Control
● Proper mixing and temperature control are critical for
efficient digestion.
● Mixing can be assessed by the power input per unit volume
(W/m³), and temperature control involves maintaining the
digester at an optimal temperature for microbial activity.
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10. Hydraulic Retention Time (HRT)
● In some high-solid digestion systems, a liquid phase is
separated from the solid phase. The hydraulic retention time
is the average time the liquid phase remains in the system.
𝐻𝑅𝑇 =
𝑉𝑙𝑖𝑞
𝑄𝑖𝑛
Where:
- HRT - hydraulic retention time (days)
- Vliq - volume of the liquid phase (m³)
- Qin - flow rate of liquid feedstock (m³/day)
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11. Gas Production Potential and TS, VS
● The gas production potential of the feedstock is an essential
parameter for estimating biogas yield.
● TS and VS are used to characterize the composition of the
feedstock and are critical for determining the potential for
biogas production.
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12. • Fresh manure (FM)
• Pit manure (PM)
• Anaerobically digested
sludge (ADS)
• Inhibition of the methanogenesis was directly proportional to
the organic load.
• Anaerobic digestion at a total solids level of about 10% was
found feasible
• Anaerobically digested sludge was a superior seed to the pit
manure.
• 40% PM + 60% ADS -10% total solids range - methane
production
• The highest methane productivity was found with 100% fresh
manure diluted to 5% total solids.

13. Thank you!
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