Anaerobic digestion of two biodegradable

municipal waste streams

Presented by: Milagro Chavez

Municipal solid waste (MSW) Waste type consisting of everyday items discarded by the public.

Food waste (FW) Garbage: food that is discarded

Methane potential (MP) Methane biogas produced during anaerobic degradation

Calorific value(CV) Energy released as heat, when a compound undergoes complete combustion with oxygen.

Nutrients A substance that provides nourishment essential for growth and the maintenance of life.

Toxic elements (TE) Elements with an abnormally high, toxic doses.

Background information

As you may have read this experiment was performed in the UK due to several laws that were implemented in 1999 to 2009, these laws gave researchers an opportunity to investigate ways in which to incorporate waste products as fuel and fertilizers from the digested waste materials.

By using anaerobic digestion of solid wastes under batch and semi-continuous digestion to eliminate or reduce the amount of waste produce by humans and animal byproducts.

Rather than continue to put all these waste product in landfills , why not find ways to recover the natural energy of these materials.

Background info. cont.

food wasteRoughly 222 million ton of waste per year is created in the United states.

Landfill and a sewage treatment plant

To be able to extract energy out of municipal waste.

The focus of the study was to test for energy yield and digestion characteristics of two fraction of municipal waste plants in the UK.

Using different types of experiments (testing for biochemical methane, digestion experiment, and analytical methods)

The purpose of this study was

The physical and chemical properties used were:◦ ss-FW Source segregated domestic food waste.

◦ mr- OFMSW Mechanically-recovered organic fraction of municipal solid waste.

These two samples were done through anaerobic digestion.

Study continue .

1st sample was from a mixed organic leftover waste that was taken from a post-collection mechanical sorting…(meaning a mixture of all kinds of garbage).

2nd sample was from household food waste collected separately (in biodegradable cornstarch bags)…(citizens were asked to separate the food waste content in biodegradable bags).

Study continue

A 210 kg sample of the ss-FW was collected from the Bio-recycle anaerobic digestion plant in the UK

This sample was removed from biodegradable cornstarch bags which were process on a commercial shear shedder

This material when through further shedding until it became a homogeneous solution.

Methods

◦ 100 kg sample of mr-OFMSW was collected and further hand-sorted to remove large non organic contaminants.

◦ This sample was taken from Bursom Recycling centre, in the UK

◦ These materials were pulverized and than separated in two size fractions that were screen to remove excess water.

Methods continue

Particle size distribution (PSD)◦ The mr-OFMSW was analyzed with different mesh

sizes to determine the byproduct in this sample.

To determine the particle size of ss-FW, the sample was diluted and used different mesh size to separate the particle.

Methods continue.

Particle size distribution of ss-FW and mr-OFMSW.

The batch digesters were used to test for biochemical methane potential (BMP).

Digestate liquor from semi-continuous digesters were used to inoculate the batch digesters.

Semi-continuous digesters were monitor on a daily basis for biogas production and pH.

The biogas production and pH was monitored 2 to 3 times per week for the following:◦ Total solids (TS)◦ Volatile solids (VS)◦ Volatile fatty acids (VFAs)◦ Total Ammonia nitrogen (TAN)◦ Alkalinity◦ Biogas composition

Results

The analysis of the chemical contents of the waste product were carried out in both batch and semi-continuous anaerobic digestion.

They looked for:

◦ Methane production◦ Solids destruction◦ process stability◦ digestate quality-meaning how much toxins or nutrient the

waste materials produced.◦ Also the elemental composition and calorific values of the

wastes-can be compared to theoretical predictions of biogas yield

Results cont.

Results cont.

Physico-chemical characterization of MSW streams◦ The ss-FW had much higher water content, volatile

solids, and lower total solid basis.

◦ It also contain higher % of carbohydrates, lipids, and proteins on a volatile solids because of the higher calorific value.

◦ The ss-FW indicated longer biogas yield with higher methane concentration in a volatile solids basis.

Result cont.

The mr-OFMSW had a higher carbon-to-nitrogen ratio than the ss-FW, even though ss-FW is considered to be nitrogen rich.

Mr-OFMSW had concentrations that were potentially toxic elements, metals such as(Cd, Cr, Cu, Ni, Pb and Zn) much higher than found in ss-FW.

Results cont.

Result cont.

The physico-chemical characteristics of ss-FW and mr-OFMSW selected for this experiment were very different, and directly impacted the methane potential and the digestate quality

mr-OFMSW had a higher proportion of lignin and other products that can not be degraded in anaerobic conditions.

Conclusion

In the semi continuous digestion both samples showed good methane yield for the wet weight.

The mr-OFMSW digestate produced potentially toxic elements (PTE) and it was too high to be used in the agriculture fields.

It was also lower in nutrient content than ss-FW

Conclusion cont.

Although ss-FW had higher nutrient content, It also cause the most stability trouble during the experimental process. Making the process more complex to obtain methanogenic products, because the increase build up in the TAN and VFA.

(the build-up of VAF reduces the pH which allows the TAN to shift equilibrium from free ammonia causing consumption of accumulated VAF therefore increasing methane % in biogas)

TAN Total ammoniacal nitrogen VAF Volatile fatty acids

Conclusions cont.

The limitations and problems for each of the samples were:◦ The waste that was mechanically separated (mr-OFMSW)

had very high consecrations of a toxic component which could not be used as a fertilizer.

◦ The waste that was sorted in biodegradable starch-based

bags (ss-FW) this waste would be ideal for fertilizer used. However, they had problems controlling the reaction.

So in their final conclusion: more testing needs to be done to make anaerobic digestion a viable option for waste reduction.

Critique

This experiment was important because of need to keep human waste and animal by-product from contaminating fresh water reservoirs.

Waste product materials is an ongoing problem that needs to be resolve.

The need to conserve resources is very important.

New ways need to be discover and implemented in order to recycle more and used less.

Take home message

Anaerobic digestion of two biodegradable municipal waste streams

Yue Zhang*, Charles J. Banks, Sonia Heaven The movement is on for the recycling human

waste|pleaseConserve.com…www.pleaseconserve.com/the-mivement-is-on-for recycling-human

http://blog.friendseat.com/food-waste-study-worldwide/

Reference