You work at a very high OLR!

You should start at a much lower OLR (

Sera Aidan,

I agree with Nicolas, 15 Kg/m3 are quite high for a batch test on organic waste.

If you had problems of VFA accumulation it means that the buffer capacity of the system is not sufficient and the methanogenic activity is lower than the fermentative (acidogenic) one.

Follow the suggestion of Nicolas and try to start from 2 kgBs/m3.

The I:S ratio you used is correct. It is the normal I:S ratio suggested for succesful BMP tests.

Whether also 2 KgVS/m3 results too high you can increase the amount of inoculum, say 3:1 or even 4:1. In this way you increase the amount if methanoges and speed up VFA consumption.

You can also increase the alkalinity of the system addin CaCO3 or K2CO3.

Fruit and vegetable waste are easily biodegradable and can easily create rapid VFA production. In case of slower metanogenic activity and insufficient alkalinity, pH drops to unfavourable conditions.

I normally run BMP test on similar waste at 5gVS/L with I:S ratios of 2 or 3.

Search for papers on BMP tests!

Anyway the main possibilies you have are:

-reduce the substrate concentration;

-improve inoculum concentration;

-add an alkalinity source.

Hope that will help!

Ciao!

Luca

We have found that we can process about 20% of active volume per day using the Managed Ecosystem Fermentation which is a managed anaerobic digestion process. The key issue is what do you wish to produce out of the process. We are focused on converting the waste into high value chemicals as methane production (via anaerobic digestion) in no longer economically viable in the United States. Our business math goes something like this, methane (C2H4O2) is converted into methane (CH4) and carbon dioxide (CO2). Immediately you have let 50% of the carbon that could have been sold be wasted as carbon dioxide. Acetic acid sells fro about $600 per ton, methane (in the US) goes for about $150 per ton. The MEF process produces the acetic acid in less than 24 hours.. which is less than the general anaerobic digestion.

Edward, what if my interest is to produce cooking gas in a developing country, should acetic acid be my choice. off course the answer is No. The aim/needs determines the target product.

The question may revolve around the economic principal of substitution. Since acetic acid is worth more, you can sell it and buy the methane/gas and still have funds left over to invest in other materials to better the community. The big difference in this case may be the ability of the MEF process to produce both protein and gas. The production of protein would make feed available for feeding chickens or fish/prawns.

what if viewed from the point of view of scarcity. A scenario where fossil fuel becomes scares, i bet you, the equilibrium would be driven to find more renewable power sources, then the maths would change completely in favor of biogas. i strongly believe that the economics of the future may vest more profit on methane than acetic acid.

Lets start with the original question; the amount of material that can be input into an anaerobic process. Our work has shown it can range between 15% and 30% of the active volume. Active volume being defined as the size of the fermentation vessel less the head space allowing for holding gas and allowing for the rise and fall of the material in the fermentation process. The rate at which the input feed is converted is a function of the microbial community in place, the nutrients available to it, the physical conditions under which the fermentation occurs, fluid levels, and extraction rate of gases and digestate.

Now lets look at anaerobic digestion in the context of its use in society. As practiced today anaerobic digestion generates a single product; a one carbon molecule (methane) which as value to the community. It also generates carbon dioxide which is a greenhouse gas.

In a rural community in a developing country anaerobic digestion provides an economical source of clean fuel. It also produces a digestate which is easily put back into the soil. The digestate permits the recycling of the nutrients and microbes back into the soil thereby maintaining its fertility. The best examples of this can be seen in rural India. Thy have the process well developed. There books available on how they do it.

In an urban environment (in both the developing world and developed world) the waste biomass used in anaerobic digestion is a known disease vector. Urban society requires more complex carbon compounds beyond a single carbon molecule (methane). Waste biomass is capable of producing carbon compounds ranging from one to twenty-two carbons. Many of these longer chain carbon compounds are currently derived from petroleum. The economics of carbon are in general the longer the carbon chain the higher its economic value. These compounds are used to produce lubricants, sealants, adhesives, cosmetics and pharmaceuticals. So the key question is why take a resource that is capable of providing these compounds (currently derived from petroleum) and produce only a single product which has the lowest value. The point I am trying to make is it is not the resources you have to use, but rather how you uses those resources determines how well you and society live. Waste biomass is a valuable resource that is better used to extend the life of petroleum through more efficient use of the petroleum by displacing the materials that can be produced from biomass.

Our views can be captured in this parable, "one sitting from the top of a giraffe would see the world view differently from one sitting on a turtle".

Your economy is far advance and marketplace well developed for these by-products you have enumerated. Many developing countries lack the infrastructure for adequate marketing of products such as acetic acid, ...... etc . such technology requires products of high purity making it some what too technical and it can hardly be a one man show as biogas technology can be. Hence, i would say the more developed the economy, the more practicable the production and marketing of acetic acids and its fermentative counterparts, while the less developed the economy, the more impractical the production and marketing of fermentative by products of waste streams.

But here is the difference between anaerobic digestion and Managed Ecosystem Fermentation, in the developed world the production of higher chemicals can be accomplished with existing technology. In the developing world, the MEF process output is modified to better the local economy. In developing countries, there is a great need to improve the diet of the people as well as dispose of the organic waste. Both actions are needed to improve the public health. Using, MEF, the output is protein that can be used as animal feed for chickens, fish or prawns. Thereby providing a sustainable source of farm raised protein (Chicken, fish or prawns). It also now reduces the need to import animal feed thereby making more funds available for other needed infrastructure projects. The MEF process is designed to provide the most benefit to the local economy by focusing on the local needs for resources that can be derived from biomass.