Discussion for Session 3

pp. 167-170 in Traditional Technology for Environmental Conservation and Sustainable Development in the Asian-Pacific Region

Proceedings of the UNESCO - University of Tsukuba International Seminar on Traditional Technology for Environmental Conservation and Sustainable Development in the Asian-Pacific Region, held in Tsukuba Science City, Japan, 11-14 December, 1995.

Editors: Kozo Ishizuka, D. Sc. , Shigeru Hisajima, D. Sc. , Darryl R.J. Macer, Ph.D.


Copyright 1996 Masters Program in Environmental Sciences, University of Tsukuba. Commercial rights are reserved, but this book may be reproduced for limited educational purposes. Published by the Master's Program in Environmental Science and Master's Program in Biosystem Studies, University of Tsukuba, 1996.

Yang : I am from the University of Hawaii. I will chair this session with Dr
mura. The first speaker is Dr Liu from China. The commentary is from Dr Maekawa. Dr Maekawa gave some very real examples, which helps us. The floor is open.

Ryan : Information about the use of water hyacinth is given in one of our manuals. A practical suggestion for making biogas is, if you take the water from a coconut, chop a potato up and soak it in that water for two or three days, it becomes very concentrated yeast. If you introduce this into the chamber, plenty of gas can be produced. You must have a system to stir the mixture inside the gas chamber. The anaerobic process takes place mostly at the bottom of the heap in the chamber, so there also needs to be a system for churning inside the chamber.

Yang : Thank you, this is another alternative. I think Dr. Liu has given us the clear policy for China, will be developed in the near future. Chinese policy is useful to developing countries in the area, on an very urgent issue. It is useful to pass this information onto other countries. Dr Ryan has given us another alternative, the composting issue is also useful. Are there any other questions?

Wiloso : At the end of your presentation you mentioned that your treatment procedures will be applied mainly to landfill and incineration. Prof. Maekawa mentioned that incineration produced gas pollution, so would landfill be a better choice? Maybe China has enough land to allow this?

Liu : A good question. In China the strategy has four parts: one is minimization; second is recycling and reutilisation; third decontamination , for example secure landfill and incineration.

Yang : The landfill approach is another area to discuss. Prof. Maekawa pointed out that there are other affects of landfill. Since there are no more questions let us move to Dr Wiloso from Indonesia, who will discuss biogas production. Dr Matsumura will give a commentary.

Yang : We now have some time for discussion.

Maekawa : In Figure 1 you showed us a type of fermentor. Hot water is used, because Indonesia is very hot. In Hokkaido in the winter the temperature is very low, so psychophilic methane producing microorganisms should be developed for this type of fermentor. For biogas production to use a water hyacinth directly as a substrate and carbon source. In the southern area of Japan, for example, Kagoshima, this is used for dairy and cattlefeed. Their waste is supplied to the methane fermentor. What do you think of this system.

Wiloso : First I want to respond to the comments of Prof. Matsumura. We have natural gas production however in rural areas transportation is a problem. The collection of agricultural waste from the rural areas point of view, as I mentioned in one of my examples, is not a problem for those with cow manure. In response to Prof. Maekawa, the work shown here is done in Bandoon , which in the morning can be 15 degrees Celsius, so we want to make sure mesophilic bacteria are dominant. We make the temperatures constant at 35 degrees Celsius. We also use water hyacinth as a feed supplement for animals, and the work which has been done at Houjuganis University is looking at other alternatives, because the production rate of water hyacinth is so high, as I mentioned, about 50 tonnes per day.

Matsumura : You mentioned many examples of methane production, however its low production rate is always a problem. When you use cassava, the fermentation time is 30-100, don't you have any good ideas to enhance this production rate?

Wiloso : It is very difficult for crop residues because crop residue contains starch, and easily degradable materials are contained in a matrix of cellulose and hemicellulose which are not easily attacked by microorganisms, so the liquefaction process, the first step, is the limiting one. Long retention times are typical for crop residues, and there are some references in my paper, using elephant grass or grass. The may have 50-60 day retention times. As I mentioned before using cassava solid waste can be operated at both long or short retention time, depending on the objective. If you want to treat the organic waste than high organics loading rate will be the objective, but for producing gas a lower organics loading rate is better to have a better percentage of methane. This can be higher than 50%. For other uses we need pretreatment for the gases, because it contains so much carbon dioxide or hydrogen sulfide.

Matsumura : I would also like to make sure, your main purpose is to make a compact system suitable for domestic use?

Wiloso : Yes, for rural areas.

Bertram : I would like to ask you about the adoption of this technology. You've mentioned in your paper that the competitive technology is kerosene, which is high quality and very consistent, it is easy to get appliances which use kerosene, and there is no explosion risk. Biogas therefore has some competitive disadvantages to overcome.

Wiloso : We have to compare the biogas to the available fuel. While kerosene is cheap there is not enough pressure to make this biogas acceptable for rural areas, this is my point.

Yang : One more point we can add, is that this is essentially for the environmental benefit.

Wiloso : Yes, the process stabilizing the organic waste, and unlike aerobic digestion which produces sludge which must further be disposed of, this process produces a low waste volume.

Alexandrov : I think there are good possibilities for the use of biogas in Indonesia because it is warm for the whole year. Maybe in the Russian winter it is not so effective. What is your perception about the period which is needed before it can be put in practice? I understand this is experimental, but how many years do you think it will take before the economic or traditional barriers and obstacles are overcome?

Wiloso : I think the obstacles is that kerosene is cheap, and the capital investment to install the digester is expensive, for the rural family and farmer. However, Indonesia still is a net exporter of oil, but in the near future, we will be a net oil importer. I think there will be some changes because maybe kerosene will no longer be available so cheaply so people will look for other alternatives.

Mazid : To continue Dr Bertram's point, you said the use of kerosene is less expensive than the use of biogas, from the farmer's point of view. Which is more convenient, the biogas plant or the use of kerosene? What is the actual cost for a family of 6 persons? Do you think you will be able to commercialize the biogas in rural areas of Indonesia in the future?

Wiloso : I cannot give exact costs, or a figure because this work has been done by another group. From the farmers' point of view I think the kerosene would be easier. because the biogas has to be pretreated in storage, and storage will be effective if it is in a huge amount. For a family of 6 persons it is good only for direct usage, not for collection and storage. This is another problem. It must be community based with as big raw material supply.

Yang : If there are no other questions, I have a question. I think that cassava is a good approach, but this is a rural approach so it should be as simple as possible. I think this has followed the original Indian style of digester. Have you done any literature search on this. The second approach is the central level, using cotton, water hyacinth, cassava, and other plants which may need to be pretreated if it is to be degraded quickly. Pretreatment costs money, so it is very difficult unless you have a special central plant to develop a rural approach. So nationwide there are two approaches, the rural or the centrally coordinated approach, like in Denmark there is a central processing plant. You have nitrogen deficient type of crop waste, so water hyacinth or cow manure which contains high nitrogen can be digested together. There also needs to be economic assessment with the extra handling.

Wiloso : I agree.

Ryan : I want to add to the comment of Dr Wiloso, and my earlier comments on biogas production. In my book and as published by CAPART of the Indian Government, a 3 drum biogas generator has been developed, using kitchen and dining table waste. This was published by the Swedish Invention Society as one of their 100 best innovations in the world in 1990. It is just 3 drums, with one drum filled with waste and left for 15-20 days. We also add some vinegar, some yeast, some yoghurt curds, or country brewed alcohol to accelerate production of the gas. This keeps producing gas for 15-20 days. The middle drum collects the gas. The plastic tubes reveal gas production, and the tube will explode if there is too much gas, so there is no danger. from the bulge of the tube we can tell how much gas is made. We keep it outside of the kitchen, so there is no fire danger, we use another tube to feed into the kitchen for cooking. It is experimental, and has not been commercially made so far, although the Indian and Swedish governments have recommended it. Every home has waste, and every few days the gas can be used. In some villages there are no drums, so a chamber can be made out of bricks and mortar. We build the houses without cement, but we use mortar, and allow every house to use it.

Yang : Thank you, we need to combine different ideas. Dr Wiloso, could I just ask why you don't go through the combustion approach to disposal.

Wiloso : There is no particular reason. In the ASEAN region there is a working group on food waste management, others are doing work on other applications.

Yang : Next we have Dr Huang from Taiwan, and a commentary from Prof. Maekawa.

Maekawa : Taiwan ROC has achieved prosperity in economics as you mentioned, on the other hand, the environmental degradation Taiwan has been widely spread, serious and steadily increasing. So the Taiwan EPA has made many efforts in every area for protecting this situation, and introduced environmental education, polluter - pay -principles, green label program and has been obtained the effects. In Taiwan for the solid waste treatnent, the landfill method has occupied 89% of all, but the composting method is not used much at all, only about 0.02%. So please comment on why the composting ratio is at a lower level than the others.

Huang : To respond to the question of Prof. Maekawa, the reasons why the composting method shares only 0.002% of the waste management in Taiwan are due to the limited land. There is also resistance to this method due to secondary pollution like the smell, air pollution or water pollution. It is also negative from the cost and efficiency point of view. They cannot see any benefit from the past 20 years. I cannot see it commercialized in Taiwan for 20 years.

Yang : Perhaps marketing of the composted products might be a problem.

Alexandrov : The incentives are very essential to your program. In Russia we have used incentives for bottle recycling in Russia, so that for beer or milk bottles, if you return four empties you can receive one full bottle. It has been working well, but now we have many imported beverages so there are problems. It does create links between shops and consumers.

Yang : This is part of waste minimization. I think one of the key issues is raised by Prof. Maekawa, the balance between incineration and composting.

Matsumura : I would like to call Prof. Yang from Hawaii to address us. I have a common interest to Prof. Yang as described in my commentary.

Yang : I think nitrous oxide is related to greenhouse gases, and is a very important issue. Our system creates some release of nitrous oxides, there is also work by Dr Hanaki of the Dept. of Urban and Environmental Engineering at the University of Tokyo.

Ryan : I must admit that I am lost in the technicalities of the subject. I have a question to ask Prof. Yang. You mentioned about aquatic weeds. I am particularly interested in information about the Duck Weed, which is used in several cities in the USA to purify drinking water. Does it eliminate excess nitrogen, carbon, bacteria, alkalinity, salinity, iron content, etc.? I have received information from the FAO that several cities only use this weed.

Yang : I think this duck weed was used in Georgia, as seen in one of my slides. If we are to use this weed, we first need pretreatment. Also UV or chlorination will be done on the water to purify it sufficiently.

Matsumura : Are there any questions or comments.

Alexandrov : I would like to give a case study from Russia, and maybe you can evaluate it from the viewpoint of the current technology, as you have provided a very excellent review of many different methods. About five years ago one of our scientists, Prof. Boach lay a tube to transfer sewage water from pig farms into the bog, a peat bog near St. Petershurg. As an output she received very clear water, which could be drunk. When we put it into our simulation model, we considered that this biological system cannot sustain this high load of nitrogen, because there is no room for disposition of the nitrogen in the biological system. Nevertheless, this bog nor the mosses in it did not seem to suffer.

Yang : There are various methods to purify water and I am sure that pig water can become drinking water, but the cost is high. Last month I was in Taiwan, and a closed or complete recycling biological process was needed. Part of this system can be incorporated into a system, to remove nitrogen or phosphate. If you have enough land you can do anything. Hawaii, Japan and Taiwan are short of land.

Wiloso : My first question is what is being trapped, is it a pure culture or a mix.

Yang : In 1984 we initiated this process after reading literature which mainly cited pure culture to remove N and P. But wastewater treatment never uses pure, it is always mixed so I called it EMMC, with MM meaning mixed microorganisms. A mixed culture is needed to create the appropriate environment for each.

Wiloso : Your method of immobilization, the entrapment method (EMMC) is quite different to the cellulose carrier of Prof. Matsumura. The cellulose carrier has a high porosity, so the microorganism has easy contact to the medium. Your system could have some diffusion limitation problem for nutrients, what do you think?

Yang : Yes, we also considered this question at the beginning of our design. The reason we use the entrapped system are, if you open any textbook you will see the comment you need to have high SRT - solid retention time. In other words you want to keep the bugs inside the reactor. As long as you entrap the starting up process is very short. For example how long is the start up time to steady state?

Matsumura : Less than 10 days.

Yang : Our is less than 10 days, about the same time. Of course diffusion mechanism may result in deficiency, but we are still researching this and have not found any problem. Our system is different, the same as the grant system is different.

Seki : I agree to the comment of Prof. Yang showing that mixed culture is very effective for purifying water. We have the same case in Tsukuba. Probably on the way to the National Institute for Environmental Studies you will see many paddy fields with Lotus plants. There, many scientists have studied how nitrogen will be removed by organisms in the fields, and they found that the Lotus plant will make a very good environment to encourage the activity of denitrifying bacteria, and of course Lotus plant will consume a lot of nitrogen, and their roots and stems will make the mud condition to encourage these activities. This is also an example of cooperation between macroorganisms and microorganisms.

Matsumura : Yes, thank you. Now we must close this session, thank you to all the speakers.


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