High solid anaerobic digestion and management of distillers grains from cassava-ethanol production | |
| Author | Phonthida Sensai |
| Call Number | AIT Diss. no.EV-14-03 |
| Subject(s) | Cassava industry--Waste disposal Alcohol as fuel |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Environmental Engineering and Management |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. EV-14-03 |
| Abstract | Due to the shortage in global oil stocks, countries are pursuing alternative fuel such as biodiesels, gasohol and blending them with gasoline to potentially reduce their dependence on fossil fuel. Currently fossil fuel is also being blended with ethanol for commercial fuel consumption. Ethanol can be produced by distillation fermentation of corn, molasses or cassava. Cassava is an attractive raw material for ethanol produc tion, as it is more tolerant to all year around climatic variations than other plants. In ethanol production besides the product, the process generates huge quantities of wastewater called whole stillage. Generally, there are two options for stillage treat ment and management. First, it can be treated directly by upflow anaerobic sludge blanket (UASB). Another option can be solid - liquid separation which separate whole stillage into liquid (or thin stillage) part and solid part (distillers grains). Thin still age can be successfully treated by using UASB. However treatment of distillers grains, needs a suitable treatment options which can reduce GHG emissions with energy co - benefits. Consequently the objective of this research was to investigate the characteris tics of waste from cassava ethanol production namely whole stillage, thin stillage and distillers grains. Thus, methane production potential of the three samples (whole stillage, thin stillage and distillers grains) was investigated to assess their potenti al feasibility for high solid anaerobic digestion (HSAD). Moreover, methane yield optimization was studied for HSAD with distillers grains. The suitable option for waste management was analyzed in view of minimizing GHG emissions. The imperative character istics of whole stillage and thin stillage are low pH and nitrogen, thus creating a deficient nutrient conditions in anaerobic system, which were observed in this study with C/N ratio of 40/1. Methane production potential of whole stillage, thin stillage a nd distillers grains were 175, 194 and 144 NmLCH 4 /gVS respectively. Using BMP tests, the optimum C/N ratio for distillers grains treatment was found to be 30/1 for HSAD operation. Distillers grains treatment with HSAD had a balanced VFA/Alk ratio. However, HSAD operation for distillers grains eventually had insufficient nutrient in the system after long operation. Therefore, C/N ratio was adjusted to 30/1 by co - digestion using swine manure. Thus system performance was stabilized for further testing. The OLR was varied from 3.5 - 14 kgVS/m 3 .day to determine the optimum loading rate. The system showed stability during operation at OLR 3.5 to 8 kgVS/m 3 .day. But system instability was observed after OLR 8 kgVS/m 3 .day. This was due to the incremental change in OLR of 1.5 to 2 kgVS/m 3 .day during the operation at OLR 10 - 14 kgVS/m 3 .day. Consequently causing system instability and reduced methane yield. Thus concluding that operation at higher OLR required longer time for acclimatization. A suitable treatment options comprising of landfill, composting, RDF, animal feed and HSAD for distillers grains was investigated by comparing of GHG emission and energy benefit. GHG emission and energy calculation tool were developed to analyze the potent ial of each option. HSAD was found to be a suitable option for distillers grains treatment while comparing GHG emission and energy benefit. |
| Year | 2014 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. EV-14-03 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering (EV) |
| Chairperson(s) | Visvanathan, Chettiyappan |
| Examination Committee(s) | Salam, Abdul ;Thammarat Koottatep |
| Scholarship Donor(s) | Kasetsart University Chalermphrakiat Sakon Nakhon |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2014 |