5TH International Congress on Technology - Engineering & Science - Kuala Lumpur - Malaysia (2018-02-01)

Photosynthesis Assisted Anaerobic Digestion: A Novel Technique For Wastewater Treatment And Highly Pure Methane Production

Anaerobic digestion was always used as a versatile technique for sustainable farming. Treatment of high strength wastewater, production of high quality fertilizers and most importantly biogas generation are the advantages of anaerobic digestion. On the other hand, specific process parameters such as pH, C/N ratio and temperature limits the effective application of conventional anaerobic digestion in modern farms. Leachate of cattle manure is one of the most abundant and hazardous materials exists in animal farms. This leachate has very low C/N ratio which made it to a hard to digest wastewater. In present study, photosynthesis assisted anaerobic digestion was used as a novel method for simultaneous wastewater treatment and biogas upgrading. For this purpose a combination of advanced bioreactors were used for compensation of C/N ratio of the leachate. Up-flow anaerobic sludge blanket reactor was used as anaerobic digester and up-flow anaerobic packed bed reactor was used as biogas upgrading unit. Biogas upgrading unit was based on photosynthesis process. In fact, photosynthesis process served as carbon recovery system by utilization of CO2. In this system, simple carbohydrates were synthesized through photosynthesis process and consumed by methanogens. This system was operated for more than 2 years and showed stable performance in very short retention times. The shortest stable HRT was 43.2h which resulted in highest COD removal of 88%. In addition 82% methane content and 0.3 m3.kg-1COD removed were achieved at this HRT. The performance of the system was evaluated at shorter HRTs. Up to 77% COD removal was obtained at 27.1h of HRT. Also methane content of 70% and methane yield of 0.27 m3.kg-1COD removed were acquired. The novel technique resulted in very efficient treatment of low C/N ratio wastewater. Finally, the obtained biogas had very high methane content and can be introduced as an energy carrier without any purification processes.
Soheil A. Neshat, Maedeh Mohammadi, Ghasem Najafpour