Treatment and valorization of anaerobic digestate

Ülgüdür, Nilüfer
Anaerobic digestion is a widely applied process for the stabilization and treatment of high-strength wastes. The process has two outputs, biogas and digestate. Even though biogas produced during the treatment is a renewable energy source and has positive impacts on improving the economics of the plant, the treatment and disposal of the digestates present a challenge. The treatment methods offered so far are either costly or low yielded which drives off these uneconomic and non-viable treatment processes from being solutions for digestate management. Digestates are still commonly applied on land as a fertilizer or soil conditioner. However, the land application of the digestate is exposed to several concerns regarding pollution, limited applicability and regulatory aspects. In this thesis study, a residual biogas potential (RBP) test was initially conducted on six digestate samples with the aim of developing a new approach for digestate management. The test indicated that significant biogas yields (0.111-0.326 Lbiogas/g VS) and total chemical oxygen demand (CODt) removal (21-84%) could be obtained from digestates in 70 days. The high-rate anaerobic treatment was then applied on the digestate having the highest residual biogas yield to reduce the time required to digest the residual organics. CODt was removed by 56-63% in 1.3-1.4 days of hydraulic retention time (HRT). A subsequent process of microalgal nutrient removal resulted in 92.7-93.7% of ammonium nitrogen and 95.6-97.8% of dissolved phosphorus reduction. The results were promising and verified the applicability of the high-rate anaerobic and microalgal nutrient removal processes for the digestate management.
Citation Formats
N. Ülgüdür, “Treatment and valorization of anaerobic digestate,” Ph.D. - Doctoral Program, Middle East Technical University, 2019.