Co-digestion of petrochemical wastewater with activated manure in continuous stirred tank reactor for methane production / Md. Nurul Islam Siddique

Faculty of Engineering Technology

Thesis (Doctor of Philosophy (Civil Engineering)) -- Universiti Malaysia Pahang -- 2015

Bibliography : p. 110-130

The combined challenges of environmental crisis and declining fossil fuel supplies are driving intensive research focused on alternative energy production. Particularly, today’s generation is facing two coexisting problems: the proper management of wastes generated from the industrial sectors, and the scarcity for novel resources of gasoline to meet up energy demand of civilization. Anaerobic co-digestion, a sustainable green technology, presents an outstanding opportunity for both energy conversion and pollution control. Therefore, it has become a core method treating organic wastes on account of its economic benefits of energy generation. The continuous stirred tank reactor (CSTR) can be defined as a sealed-tank digester equipped with mixing facility. Chemical pretreatment coupled with anaerobic co-digestion technology was applied on petrochemical wastewater using CSTR focusing on enhanced hydrolysis and methanogenesis. Batch experiments were performed, with applied H2O2 doses of 0.5%, 1% and 1.5% for contact times of 5, 10 and 15 min. Results revealed that 1% H2O2 dose (1.0mM Fe3+) for 5 min exposure elevated biodegradability index (BOD/COD) up to 35%. Subsequently, batch experiments were employed with various mixing proportions of petrochemical wastewater (PWW): dairy cattle manure (DCM): beef cattle manure (BCM), such as 25: 37: 38, 40: 30: 30, 50: 25: 25, 60: 20: 20, and 75: 12: 13. Results revealed that PWW: DCM: BCM ratio (50: 25: 25) provided maximum methane production. Although methane production is considered to get introverted by VFA accumulation leading to reactor instability during anaerobic digestion, a 10 mg/L of NH4HCO3 dosing and the co-digestion of PWW together with BCM and DCM caused 50% enhancement in methane production, followed by a 98±0.5% reduction in COD at 10 days hydraulic retention time. No VFA buildup was identified. In comparison with the digestion of PWW alone, methane yield increased by 50–60% under mesophilic conditions and 50–65% under thermophilic conditions due to co-digestion. This was induced by an optimum C: N ratio (30:1) of the feed stock ensuring microbial growth and buffering capacity. The anaerobic digestion, biogas generation, and energy assessment were analyzed for ten flow rates; 170, 220, 300, 370, 410, 475, 540, 600, 640 and 680 mL/day. The analytical data revealed that the environmentally complied optimum flow rate was 170 mL/day, for maximum methane generation. As the F/M proportion varied from 0.25 to 2.0 and organic loadings from 6.31-27.14 (g VS/L), however, it has been observed that the methane yield increased from 451.9±15 to 461.5±17 and 519.8±15 to 520.9±16 mL/ g VS as the F/M ratio increased from 0.25 to 0.5 for mesophilic and thermophilic states respectively but decreased gradually even when the F/M ratio increased up to 2. However, considering all the factors F/M ratio of 0.5 was observed to be the optimum to avoid system imbalance. This work may help in minimizing the environmental issues of petrochemical wastewater treatment in the future