Chulabhorn Research Institute and Mahidol UniversityA thesis submitted in partial fulfillment of the requirements for the Degree of Master of Science, Asian Institute of Technology; Inter-University Program on Environmental Toxicology, Technology and Management,

Thesis (M.Sc.) - Asian Institute of Technology, 2004

Bio-extract product (BE) is a liquid solution resulting from a fermentation process of different organic materials such as food waste, residual vegetables, and fruits mixed with molass under anaerobic condition. A mixing period required at least one month. In this study different organic wastes from three markets in Bangkok areas were investigated as starting or raw materials to produce BE. They could be divided into two groups, one as mixed organic waste, and the other is a mixture of vegetables and fruit waste only. After completed digestion, the BEs produced were chemically analyzed whether they are safe and can be used equivalent to organic fertilizers for agricultural use or not. Their nutrient concentrations (mainly N, P, K) and potential harmful substances namely toxic elements as well as some micronutrients and pathogens remained were evaluated using seed germination test and earthworm acute toxicity test, respectively. For their nutrient values mainly P and K, two groups of BEs are quite similar. Whereas mixed organic waste gave higher N content (0.94%N), almost double than mixed vegetable with fruit wastes. Note should be made here that all BEs products are very diluted as compared with inorganic fertilizers. So they are good enough to be used as nutrient supplement rather than basal fertilizers. Concentrations of lead (Pb) and c.admium (Cd) toxic elements found in liquid BEs as well as in solid residue (SR) of BE were extremely low even lower than any organic fertilizers. Besides when liquid BEs will be applied to the crops they will be diluted with water at 1 :500 ratio. So those toxic elements contents would be further reduced. Similar with SR that needs to be mixed with the soil when it is used. Both iron (Fe) and zinc (Zn) content representing micronutrients present in BE and SR products were within sufficient range for plant requirement. Focusing on microbial contamination, only one sample of SR contained fecal coliform which derived from non-registered market source. This type of market is not access for the food safety program. Further study on what loading rate of the products of BE is safe to the soil environment. Results show that at 1: 1 dilution ratio if applied to soil would be at risks (10 earthworms were killed within 24 hrs). However at higher dilution of BEs to water at 1 :500 ratio, all those tested worms survived with increasing weight. This ratio of both BEs was also safe to use for watering seeding plants (Cosmos and Pak-choi) similar manner to tap water based upon our seed germination test. Likewise BE residuals (solids parts) could be incorporate with soil and used as a seed bed without causing any problem in seed germination (Cosmos and Pak-choi). However the liquid extract and residue from vegetable mixed with fruit waste was more friendly to the environment over the organic market wastes.