Effluent odours

I have not yet produced any slurry from my BioDigesters (largest is 10 m³ and operating for about 2 months now). Influent is 20 litres of manure per day soaked in an equal amount of water for 4 hours prior to feeding into the Digester.

In response to a recent discussion with Paul and Simon, Influent was increased 4 days ago to 40 litres of manure per day soaked in 60 liters of water for 4 hours prior to feeding. This to double Biogas production rate and give the BioDigester sufficient incoming liquid volume to push out effluent or slurry.

I expect the slurry to smell BAD -- like sewer water. If this is to be used as a fertilizer, shouldn't something be done to keep it from stinking the area where it is used?

If allowed to settle for awhile, the effluent should separate into a muddy sediment and free-flowing liquid. Do you have any suggestions on handling the free flowing liquid? I want to pass it through a simple waste water treatment process (again to remove its foul odour) before using it to irrigate plants in the farm.

Codigestion

Hi Gerry,
I was not suggesting codigestion as being essential to the well-being of your biodigester. It is just common for the larger biodigesters to take in the scraps from the local markets or whatever else is available.

After all, you have a permanent source of feedstock, but anything else is just extra. You are getting rid of the rubbish for them and doing something useful with it. All the big ones in Switzerland are codigesters.

Simon

large-scale biodigester

Hello again,

my little presentation went very well except for the fact that my audience thought my radical ideas were backed by a lot of in-experience compared to PhilBIO’s track record for building HUGE digesters. Patience and practical examples, however, gave my audience something to think about. I can only hope at this stage that they keep my ideas to themselves, give me some credit and allow me to build their digester.

The “model” confirms that my proposal is on the right track. PhilBIO is proposing a HUGE 20,000 m³ digester because they have to process 9,000 liters of manure + 80,000 liters of wastewater everyday. I propose a 5,000 m³ BioDigester because I want to settle, collect and only allow wet manure of approximately 19,000 liters into the digester. PLH proposes a VERY small 1,451 m³ digester and there seems to be a typo on the dilution rate. I believe should be 0.30 (not 3.0). If PhilBIO’s 20,000 m³ digester costs 4 million pesos, my 5,000 m³ BioDigester will cost less than HALF that (or less than 2 million pesos). The PLH digester at 1,451 m³ will cost less than 1 million pesos. The savings ARE SUBSTANTIAL if the digester is sized correctly.

My audience eventually appreciated the ingenuity of NOT HAVING TO DIGEST ALL the wastewater.

Again based on the “model”, if:PhilBIO’s 20,000 m³ digester will produce 668 m³ of biogas/day,My 5,000 m³ BioDigester will produce 669 m³ biogas/day; and,PLH’s 1,451 m³ digester will produce 562 m³ biogas/day, my BioDigester is PREFERABLE to PhilBIO because it is CHEAPER!

Simon, I anxiously await your two cents. Btw, does codigestion mean feeding the digester with something other than pig manure? If so, its safe to say this system will use 100% pig manure on a regular basis. However, I might advise them to occasionally add chopped grass or the like to feed the system some carbon.

Salamat at mabuhay kayong dalawa!

Gerry

Biogas and codigestion

To produce 1 m³ of BIOGAS, to cook 3 meals daily for a small family of 4 to 6, you need at least 5 litres of pig manure/day. 8 sows will produce 5+ litres/day easily and your 36 heads total will probably give you at least 15 litres. A 2 m³ digester wil produce 1 m³ of BIOGAS/day -- good for experimental purposes. I suggest your first digester be at least 5 m³. This will produce more BIOGAS when needed and accommodate your farm's growth.

The China Fixed Dome, India Floating Cover and DOST-PSTC designs are the most popular here in the Philippines. Download drawings from the internet but I suggest you get professional help as the building process is not easy.

Here are people who can help:

Roberto Bajenting Trained at Asia-Pacific Biogas Research and Training Center, Chengdu City, Sichuan, China.
Provincial Agrarian Reform Officer, Cebu CityCell No: +63920-923-6930

Engr Orlando Anselmo. Has installed 35+ DOST-PSTC digesters in Aurora Province
DOST Officer, Baler, Aurora ProvinceCell No: +63915-569-9631

The BioDigester I designed is made of 1.5 mm HDPE or High Density Polyethylene. It’s the same material used for landfills worldwide. Working with HDPE requires special equipment and trained technicians. Building just one or two is not cheap and economical.

I have 5 m³ BioDigesters available as ready-to-install kits because I had them pre-fabricated and mass-produced, resulting in lower costs. You can have a complete 5 m³ BioDigester system for about P20,000.00 (a 10 m³ unit for about P30,000.00) plus P5,000 max for delivery and installation. To compute SAVINGS just remember: 1 m³ BIOGAS/day replaces one 11 kg tank of LPG worth P400.00 per month. Using 2 m³ BIOGAS/day will save P800.00 per month.

The CFD, IFC and DOST-PSTC digesters all cost over P25,000.00. For this reason, I have asked Bobby Bajenting and Engr Anselmo to help me promote the BioDigester. I avoided bagasse despite its energy potential for two reasons. It is not readily available and its near-solid nature will probably fill-up and clog my digester. As you said, there are lots of other wastes available. I have used grass cuttings from the local golf course, spoiled vegetables from the "palengke" and all our kitchen scraps.I am currently installing a 10 m³ BioDigester at my brother’s restaurant. I am also talking with local officials about a 10 m³ BioDigester for the "palengke" to digest vegetable scraps and provide some kitchenettes with cheap cooking gas.

When I started my BIOGAS experiments, I checked temperatures and pH. First with an expensive kit from BioResearch and eventually with plain litmus papers. I measured quantities of manure used, volumes of BIOGAS produced, etc. It was a lot fun – but largely unnecessary -- I think. Conditions for digestion in the Philippines are ideal. Its so EASY to produce BIOGAS here! Just follow some tried and tested procedures.

Biomass and codigestion

You can gasify material. You will find information on it if you check around under pyrolysis as it is generally called. The big disadvantage of pyrolysis is that you have to put a lot of energy into it to get a result, and the gas you get is mainly a mixture of carbon monoxide and hydrogen. It is very combustible but equally toxic. Pyrolysis has the advantage that it works on wood, which is indigestible for anaerobic bacteria. Lignin, the wood fibre material, just will not decompose without oxygen. Probably there was not much wood around when these bacteria evolved, many millions of years ago! If bagasse will decompose, and I have no idea, never having seen the stuff, then you will get more energy more safely this way.

I have been reading up on the codigestion projects in Switzerland, and they have all been chopping the vegetable matter and pasteurising it before use. Perhaps there are residual conservation chemicals (antibacterials?) that have to be removed before it will work properly.

The question of H₂S is one that comes up more when you are storing the gas or feeding it into the mains gas supply. It is corrosive and there are strains of bacteria that thrive in it. We are permitted to keep it at work in concentrations less than 50 ppm. This is not considered dangerous, but you can definitely smell it!The traditional method of removing it is either washing or passing it over iron, usually both are used. The problem only really occurs with manure, vegetable matter has little sulphur in it, and it is very diluted. That is another advantage of codigestion, the manure is diluted, so the production of H₂S and NH₃ is also diluted. For small scale use I would simply ignore it.

Biodiesel

Biodiesel is a clean burning alternative fuel, produced from domestically grown, renewable resources. Biodiesel contains no petroleum products, but can be blended at any concentration with diesel from traditional sources to create a biodiesel blend. It can be used in compression-ignition engines with little or no modification. Biodiesel is simple to use, biodegradable, non-toxic, and intrinsically free of sulphur compounds and aromatics.

Biodiesel is made in a chemical process called transesterification, where glycerine is separated from the vegetable oil. The process results in two products -- methyl esters (the chemical name for biodiesel) and glycerine (a by-product used in soap manufacture).

Looking at the disadvantages, biodiesel does not supply the same energy yield per unit area that simple green plants used in a biodigester would. The biogas produced there would give about twice the energy that the same area devoted to oil plants for biodiesel production.
Biodiesel is so attractive because it can be used in existing engines with very little needed in the way of adaptation. At very low temperatures it will probably prove impossible to use pure biodiesel (B100), but mixtures up to 20 % biodiesel (B20) should cope with most climates. This advantage means that the technology can be applied generally without any preparation stage. Converting fleets of vehicles to gas propulsion is a very costly and time-consuming business, to say nothing of the down-time caused.

Combustion efficiency

Combustion efficiency is one of those terms which are bandied about and sound as if everybody should know what is meant. The problem is that combustion efficiency is only one small part of the total efficiency of a heating system. Particularly with old systems, the radiation losses from the boiler and the poor lagging on the pipe-work can lead to losses far in excess of any stack loss or loss by incomplete combustion.

Combustion efficiency is, as the name suggests, purely a measure of the amount of energy that is lost up the stack and, perhaps, lost by unsatisfactory conversion of fuel and air to carbon dioxide and water. As such, it is a good measure of what can be gained by tuning a boiler, or better still, what has been gained by tuning a boiler, but it does not and cannot take the other factors into consideration.

It is a value readily measured by a combustion analyzer, and this makes it very useful for boiler maintenance technicians, who cannot be expected to take radiation losses into account. These losses can only be altered by changing to a newer boiler anyway.

More news from the Philippine biodigester

I have managed to test a few carbon based feedstocks as we last discussed.
They are:
1. lawn-mower grass cuttings from the greens of a nearby golf course
2. shredded sweet potatoes (yams) - from waste bin in vegetable market
3. shredded potatoes - from waste bin in vegetable market
4. sliced tomatoes - from waste bin in vegetable market
5. pressed coconut meat - from a native cake bakeshop

The sliced tomatoes and pressed coconut meat did not appear to produce biogas.d(When fed to a working biodigester, biogas output continued to decline as if no feedstock was added.)

Worse, the pressed coconut meat floats and may be floating inside the digester impeding digestion.

With the grass cuttings, gas production did not drop. In fact, there was a small noticeable increase for a few days.

The yams and potatoes, however, gave a surge in biogas production for a few days. Yams and potatoes (apparently, vegetables that cause one to fart) are good for biogas production.

In all instances, approximately 5 % feedstock by volume was added once and production was observed for two weeks.

I plan to repeat the tests and validate the results.
I have also been keeping track of the listserv forum. The composting of biomass wastes before using it as feedstock is a good idea specially for wastes that tend to float.


Returning from a vacation, we passed a little remote-community that had signs saying they were using biogas. We stopped, interviewed two users and examined their set-ups. Though they invested heavily when their digesters were built in 2001, they are very happy to have them now that LPG prices have almost tripled.

I was able to track down one of the technicians who happily reported that he has built 41 digesters ranging from 5 to 10 m³ since 2000 -- with funding assistance from UNDP.

It was great to find that community with home-type or family-type biodigesters. The find affirms that biogas WORKS!

My biodigester which only costs about 80 % today for what they paid for in 2001 continues to appear to be a great idea for the Philippines. The DOST tech I mentioned above agrees and plans to try my units in his next projects.

The 10 m³ HDPE units installed in our farm are now full of biogas. We are going to test burning the biogas when I go there tomorrow.

I also have a couple of relatives interested in 10 m³ units for their farms. This is getting interesting.

Biomass

Biomass is another of those topics that is becoming more and more interesting these days. Basically, there are two ways in which biomass may be used directly: Direct combustion to produce heat or power and gasification to produce a gas that can be used to power vehicles etc. The version chosen will depend on the needs of the local industry. Biomass can also be used to feed a methane digester, but we are talking about the direct uses here. Biomass can be defined as any waste vegetable matter, such as straw, wood branches or other leftovers, very similar to what our ancestors were burning 10000 years ago. So what has changed? Modern combustion technology can use this biomass to produce electricity on a small scale without leaving a trail of smoke across the landscape, supplying a single village or smaller group of houses with their own power. The combination of a combustion plant with a gasification unit is equally possible, allowing a number of vehicles to be run without the need for imported gasoline. Biomass is the up and coming technology in many outlying areas in Europe, where the supply of piped fuel is not available and liquid fuel must come a long way across difficult terrain.

Renewable energy is a recognised goal for the future, and one of the most successful routes is via the use of fuels that can be grown or collected from nature, where they will be replaced in a reasonable period of time. Perhaps the best description is “second-hand solar energy”.