Utilization of water hyacinth (Eichhorniacrassipes) as a substance for biogas production employing Rumen microorganisms

The degradation of dry entire water hyacinth plant {WHE), water hyacinth shoot (WHS), water hyacinth shoot-cowdung (WHS-CD) mixture and fresh whole water hyacinth (FWH) plant was studied in batch cultures with rumen microorganisms. After 132 hours of incubation, total fibre (NDF) degradation efficiencies ranged between 25 and 69% far all substrates. The extents of degradation showed the order: FWH > WHS-CD > WHS > WHE. Average specific productions of methane and volatile fatty acids (VFA) ranged between 0.071 and 0.095 1 and 8.45 and 11.22 mural. per gram NDF digested, respectively. The effect of substrate concentration on substrate degradation. VFA and methane productions was also examined in batch cultures with WHE and WHS. Methane and VFA produced after 132 h of incubation increased with increasing substrate concentration, whereas fibre degradation decreased with increasing substrate concentration. At ail substrate concentrations tested, WHS gave relatively higher values of all measured factors than WHE. It was concluded that the degradability of the water hyacinth can be improved to some extent by excluding the root biornass, using fresh material and mixing with cowdung. The capability of rumen microorganisms to digest WHS and WHS-CD mixture in a continuous culture (an artificial rumen reactor) was investigated. Under standard rumen conditions (SRT and HRT.of 60 and 12 h, respectively) and at a loading rate of 11.6 g VS I----1 d......1 , the extents of volatile solids (VS) degradation of WHS and WHS-CD mixture were 38 and 42 % respectively. An apparent degradation of lignin of about 17 and 12 % was observed in cultures of WHS and WHS-CD mixture, respectively. Mean specific productions of biogas and VFA were 0.26 and 0.18 1 and 6.95 and 7.92 mmoles g-1 VS digested, respectively. An average of 18 x 10..3 protozoans ml ..1 were maintained in both experiments. Because the artificial rumen reactor was operated under standard conditions, a higher degradation was expected to be obtained by choosing appropriate conditions. In order to optimize conditions for the degradation of the WHS-CD mixture in an artificial rumen reactor, the effects of various combinations of loading rate (LR), solid retention time (SRT) and dilution rate (D) were examined. The optimal conditions were found to be a LR of about ,15.4 g VS l.....1 d......1 , SRT of not less than 60 h and a D of about 2.0 fermenter volume d l. At these conditions about 50 % of VS was digested. The optimal conditions of LR, SRT and D for acidogenesis of the WHS-CD mixture were employed in the conversion of the substrate in a two-phase Rumen Derived Anaerobic Digestion (RUDAD-) process. Degradation efficiency of about 52% VS was obtained. All the VFA produced in the acidogenic phase (about 32 mM) were completely converted to biogas in the methanogenic phase. The methane content of the gas was about 78%. These results demonstrate that coupling of an artificial rumen reactor to a high rate (UASB) methane reactor is a more efficient way of converting the substrate into methane than by employing the artificial rumen reactor alone.