Anaerobic co-digestion of cassava pulp and pig manure | |
| Author | Naraporn Glanpracha |
| Call Number | AIT Diss. no.EV-17-01 |
| Subject(s) | Cassava machinery Digestion |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of PhilosophyinEnvironmental Engineering and Management |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. EV-17-01 |
| Abstract | Cassava pulp (CP), a solid waste rich in organic carbon, is generated during the cassava starch production process. A small portion of CP is sold as a low-cost animal feed material the remaining amount is often left untreated. Biodegradation of CP under uncontrolled anaerobic conditions in a disposal area result in extensive environmental pollution affecting air, water, and soil quality. Anaerobic digestion (AD) is an alternative waste treatmentoption for CP due to it contains high starch and moisture content. However, low of nitrogen content, as well as, the presence of residual cyanide in CP limit its utility in AD process. Accordingly, the overall research aim was to enhance anaerobic co-digestion performance of CP with nitrogen rich co-substrate (pig manure (PM)). The performance of anaerobic co-digestion (AcoD) and cyanide content during the operation at various organic loading rates (OLRs) were investigated. Furthermore, the most suitable mathematical model was selected for estimating substrate treatment efficiency in term of effluent volatile solid (VS) concentration in AcoD of CP and PM.In this study, the anaerobic co-digestion experiment was carried out at ambient temperature (31±1oC)and in 10 L single stage semi-continuously stirred tank reactor with working volume of 7 L.The reactorwas operated in a semi-continuous mode with the mixed feedstock of CP and PM in the proportion of 80:20 (VS basis), corresponding to a C/N ratio of 35.Digester startup was accomplished in 60 days with the loading of 0.5–1 kgVS/m3d. Subsequently, the loading to digester was increased step-wise from 2 to 9 kgVS/m3d.During reactor operation under various OLRs, the reactor performance and cyanide concentration were evaluated.Digester performance was stable at OLR between 2 and 6 kgVS/m3d with an average VS removal and a methane yield of 82% and 0.38 m3/kgVSadded, respectively. The digester exhibited instability when OLR was increased in the range 7-9 m3/kgVSadded. During these loadings, the average biogas yield and methane yield decreased from 0.59 to 0.24 and 0.32 to 0.13 m3/kgVSadded, respectively since solubilization of particulate matter did not take place efficiently beyond loading of 7 kgVS/m3d. The soluble chemical oxygen demand (SCOD) production rate gradually increasedwith increasing OLR up to 7 kgVS/m3d and reached a steady value even OLR increased from 7 to 9 kgVS/m3d. The digester became unstable at OLR of 9 m3/kgVSaddedsince VFA concentration increased to over 3000 mg/L which was in the inhibition level leading to system failure.The average total cyanide content in fresh CP was 9.8 mg/(kg wet basis) which existed in the form of cyanohydrins (about 80%) and free hydrocyanic acid (HCN) (about 15 %). In anaerobic co-digestion system, the cyanide content in digester mainly in the form of HCN. The cyanide concentration in the digester increased and reached the maximum of about 6.5 mg/L as the OLR was increased from 2 to 5 kgVS/m3.d from day 70-110 of reactor operation. From the day 110 onwards,cyanideconcentrationdeclinedcontinuously tobelow 1 mg/L even OLR increased to9kgVS/m3.d indicated that sludge in digester was acclimatized and was capable of degrading cyanide in the system.Cyanide degradation in AD followed first-order kineticswiththe rate constant of0.0939 d-1. Thus, it can be concluded that CP can be successfully digested anaerobically with PM as co-substrate without any inhibitory effect of cyanide present in the CP. |
| Year | 2017 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. EV-17-01 |
| 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) | Annachhatre, Ajit P. |
| Examination Committee(s) | Thammarat Koottatep ;Anal, Anil Kumar ; |
| Scholarship Donor(s) | Rajamangala University of TechnologyThanyaburi(RMUTT), Thailand |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2017 |