Dry anaerobic digestion of municipal solid waste and digestate management strategies | |
| Author | Zeshan |
| Call Number | AIT Diss. no.EV-12-06 |
| Subject(s) | Refuse and refuse disposal Sewage--Purification--Anaerobic treatment |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Environmental Engineering and Management |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. EV-12-06 |
| Abstract | Global solid waste generation is continuously rising. Improper disposal of the gigantic amount of solid waste seriously affects the environment and contributes to climate change by release of green house gases (GHGs). Practicing anaerobic digestion for organic fraction of municipal solid waste (OFMSW) can reduce emissions to environment and thereby alleviate the environmental problems together with production of biogas, an energy source, and digestate, a soil amendment . Dry anaerobic digestion has gained much attention because of its advantages of lesser water addition, lower reactor volume and higher volumetric biogas production than wet digestion. However, one of its problems is accumulation of ammonia which is more common in digesters fed with improper C/N ratio wastes and needs to be corrected. This study was carried out to evaluate the performance of a pilot - scale thermophilic dr y anaerobic reactor for biogas production and to analyze the management options for the digestate. This was achieved by investigating substrates of different C/N ratio to get a correct feedstock for dry anaerobic digestion (to minimize ammonia accumulation ) and by investigating different organic loading rates (OLRs) of the correct feedstock. Moreover, GHG emission potential of digestate was calculated (based on its characteristics) with and without storage and curing and different digestate management optio ns were analyzed. In first experiment, t he effect of C/N ratio and total ammonia - N accumulation in a dry anaerobic digestion was studied effectively. T wo simulations of OFMSW were prepared to attain C/N ratio 27 and C/N ratio 32 using biodegradable feeds tocks such as food waste, fruit and vegetable waste, leaf waste and paper waste . Results showed that the simulation with C/N ratio 32 had about 3 0 % less ammonia - N in digestate as compared to that with C/N ratio 27. Moreover, a free ammonia accumulation/inh ibition effect was documented and methods to overcome the adverse effects were discussed . In another experiment, correct feedstock from the first experiment (C/N ratio 32) was used as substrate to improve the performance of the same reactor. The effect of different OLRs, such as 4.55, 6.30 and 8.50 kg VS/m 3 d, was studied on the parameters like biogas production, VS removal and VFA accumulation. Results showed that increase in OLR proportionally increased the gas production rate (5, 6.37 and 7.55 m 3 /m 3 react or vol /d for three OLRs respectively) of reactor, but the specific methane production reduced (330, 320 and 266 L CH 4 /kg VS). Similarly, VS removal also reduced (78, 75 and 67%) with increase in OLR. The system performed well at OLR and RT of 6.40 kg VS/m 3 d and 24 days respectively, however, purpose of treatment also determines the optimum operating conditions. Digestate from the reactor was characterized and its C/N ratio and GHG emission potential was calculated. It was found that the C/N ratio of diges tate was 15 - 20 for most of the study period, which is safe range for its application to agricultural land without further treatment. The GHG potential calculation shows that storage of the digestate for 2 months decreased its GHG potential by 10%, hence, s torage was found to be a source of GHG emission. Moreover, application of digestate directly to land has minimum net GHG emission (i.e. - 11 gCO 2 - eq/kg digestate). Therefore, digestate should be applied to land immediately after digestion to minimize GHG em ission from the storage system. |
| Year | 2012 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. EV-12-06 |
| 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 and Management (EV) |
| Chairperson(s) | Visvanathan, Chettiyappan |
| Examination Committee(s) | Annachhatre, Ajit P. ;Salam, P. Abdul |
| Scholarship Donor(s) | Higher Education Commission (HEC) Pakistan ;Asian Institute of Technology Fellowship |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2012 |