Application of Effective Microorganisms in a New Hybrid System of Biogas Production

A new hybrid system of biogas production was developed for treating the piggery wastes at Kasetsart University Animal Research Farm. The system is a combination of a settler, a low rate anaerobic digester (generally known as biogas plant) and a newly developed aerobic digester (namely bio-contact aeration system). The settle separates piggery waste water into two parts : a low-volume solid portion with high TS concentration flowing into the low rate digester and a high-volume liquid portion with low TS concentration flowing into the aerobic digester. After one month of successful operation of the system, EM (in form of Bokashi has been added in feed at 1%) for pigs to control the odor problem at source of production. When the system operation was continued, no adverse effect was found both on the biogas production and the performance of the aerobic digester. The results of this experiment clearly demonstrated that EM can be used in coupling with anaerobic digester and aerobic digester for treating animal wastes. Introduction Kasetsart University (KU) is involved in research, development and consulting in animal waste management technology on the family farm and industrial scales. In cooperation with the Asia Institute of Technology (AIT), two pilot plants of biogas production were successfully constructed and operated for research and demonstration purposes. A new hybrid system of biogas, consisting of a low rate anaerobic digester (generally known as biogas plant) and a newly developed aerobic digester, is currently being designed for treating highly diluted pig manure. Effective Microorganisms (EM) technology is another animal waste treatment system being studied and disseminated by KU. Research works at KU have shown that EM is practicable for treating pig wastes, particularly for controlling the odor problem (Chantsavang et al., 1993). Laboratory scale research results in KU also revealed that EM can be applied in combination with biogas digester (Sawanon, 1996). The main objective of this study was to evaluate the combination effects of biogas and EM technologies for environmental control and biogas recovery at farm scale. Materials The treatment system was designed to recover wastes from 20 sows, 200 finishers and and 200 weaners and was built for research, training and demonstration purposes at Methods the Kasetsart University Animal Research Farm. The system consists of a fiberglass sedimentation tank, a low rate anaerobic digester or biogas digester (50 m hemispherical fixed-dome type digester is used in this system) and an aerobic digester of a particular type called Bio-contact Aeration System (constructed from cylindrical fiberglass tank with a diameter of 3.5 m and a length of 8 m packed with newly developed plastic media). The configuration and system layout are depicted in Figure 1. The slurry is flushed out of the manure pit inside the house once a day. This minimizes the emissions of noxious gases and also ensures a good climate inside the house. Next, the slurry is pumped into the sedimentation tank where it is separated into a low volume portion with high total solids concentration (solids fraction) and a high volume portion with low total solids concentration (liquid fraction). Treatment of the solids fraction is performed at ambient temperature in the biogas digester. The liquid fraction from the sedimentation tank is treated in the Bio-contact aeration tank. The treated effluent from the biogas digester and the aeration tank is led to a holding lagoon. The effluent, which still contains some fertilizer compounds, is used for biofertigation and recycling to the piggery unit as washing and flushing water. The biogas produced is used in the process of pig and chicken slaughtering in the Animal Research Farm. After one month of successful operation of the system, EM, in form of Bokashi, was added in to feed for pigs at 1 percent to control the odour problem at source of production. Samples of raw waste water, influent and effluent at different stages of the system were collected for chemical analyses, after the system operation was continued for one more month. Determination of standard parameters were mainly performed according to APHA (1971). Results Fresh pig waste has a TS concentration of approximately 10 percent. The degree of and dilution of the incoming pig waste to the treatment plant influenced by the amount Discussion of was washing and flushing water. In the present study, the average composition of the raw pig waste is shown in Table 1. The mean values of BOD and COD of raw pig waste were 1,600 and 10,321 mg/l, respectively. The COD/BOD ratio of 6.45 indicated that the biodegradability of the organic material was relatively low. The TSS content of raw pig waste was 6,675 mg/l and the VSS content 1,375 mg/l, which showed that the content of suspended organic material in raw pig waste was relatively low. The nitrogen content of raw pig waste was found to be 324 mg/l. Table 1. Composition of the Raw Pig Waste, the Influent to Digester, the Effluent from the Digester and the Treatment Efficiency in the Digester Parameter Raw Pig Waste Biogas Digester Efficiency(%)