EVN 6114May 1, 2023

Anaerobic digestion

--a biological solid waste treatment technology—Presented by

Emmanuel George

Overview▪ What is Anaerobic

Digestion?▪ Process– Process stages

1. Hydrolysis 2. Acidogenesis 3. Acetogenesis 4. Methanogenesis

– Batch and continuous process

– Residence time.

▪ Application ▪ Products ▪ Conclusion ▪ Reference

What is anaerobic digestion?

▪ Anaerobic digestion is a collection of processes by which microorganisms break down biodegradable material in the absence of oxygen.

▪ Used both industrially and domestically to produce fuel

▪ Anaerobic digestion is widely used as a source of renewable energy

mechanical biological treatment plant

in Germany

Process

▪ Bacteria break down biomass (food waste)in the absence of oxygen, in temperature controlled sealed vessels and produce biogas which is typically made up of 60% methane and 40% carbon dioxide .

▪ microorganisms responsible for digesting the sludge's anaerobically are often classified in two groups, the acid formers and the methane formers.

▪ There are basically 3 steps1. Preparing the waste , by

reducing the size.2. Constantly mixing the

sludge with moisture, nutrients and pH neutralizers while heating it to 60 degree Celsius and holding it for the required time.

3. Collecting the generated gas and disposing the digested solids.( for each pound of undigested solids we get 8- 12 cubic feet of gas in which 60% is methane.

Anaerobic Digestion process

Process stages

Batch & continuous process ▪ Continuous process – Organic matter is constantly

added or added in stages.– Here the end products are

completely removed. Resulting constant production of biogas.

– Single or multiple digesters in sequence may be used .

– Continuous gas supply and fast process residence time is less.

– More equipment , more design work

▪ Batch process – Biomass added at the start of the

process, then the reactor is sealed for the duration of the process.

– Simple batch process needs inoculation, with the already processed material to start digestion.– this will have odor issues if opened before process is complete.

– Advanced batch process has less odor issues because it uses the after digested biomass is kept in the reactor for composting.

– Lower design work, less equipment , more than one tank ensures constant gas production.

Residence time

▪ The residence time in a digester varies with the amount and type of feed material, the configuration of the digestion system, and whether it be one-stage or two-stage

▪ residence times may be in the region of 14 days ▪ In two stage it may vary from 15- 30 days.

Application

▪ Waste treatment▪ Power generation▪ reduce the emission of greenhouse gases – Reduce fossil fuels– Displacing industrially produced chemical fertilizers – Reducing usage of LP Gas for cooking.

Products

1. Biogas– Methane --60-80%– Carbon dioxide – 20-40%– Nitrogen – 0-10%– Oxygen -- 0-1%

2. Digestate– used as fertilizers replacing the industrially produced fertilizers

3. Waste-Water– this is because of the moisture content present that was introduced in the preparation stage and this is reused/recycled back to the preparation process.

Conclusion– What is anaerobic digestion

References

▪ http://en.wikipedia.org/wiki/Anaerobic_digestion#Process_stages

▪ http://www.omafra.gov.on.ca/english/engineer/facts/07-057.htm#1

▪ http://www.ionacapital.co.uk/page/95/Anaerobic-Digestion-Adoption.htm

▪ Anaerobic Digestion--Gregory D. Boardman. Environmental Encyclopedia.

▪ https://www.youtube.com/watch?v=5dErUHBjR0o