Operating conditions and performance analysis of anaerobic digestion of poultry manure

Anaerobic digestion (AD) enables the valorization of organic waste, such as poultry manure (PM), into biogas and nutrient-rich digestate. However, the high total ammonia nitrogen (TAN) content of PM is a significant bottleneck, as high free ammonia (FA) levels inhibit methanogenesis. This review provides a quantitative synthesis of reported batch and continuous AD trials to identify operating conditions associated with high methane yields, focusing on the effects of FA concentrations and HRT on methane yield. Data from 55 continuous-reactor trials were consolidated and filtered by methane yield percentile to focus on high-performance cases, with mono-digestion and co-digestion systems analyzed separately. The novelty of this review lies in the integrated analysis of operational parameters to identify practical operating windows associated with high methane yields. For mono-digestion, methane yields above 300 L CH₄/kg VS_added were achieved when systems were operated with an organic loading rate (OLR) and hydraulic retention time (HRT) that ranged between 1-4.67 g VS/L·d and 12-14 d, respectively. Under these conditions, FA concentrations were maintained between 450-780 mg N/L. For co-digestion of PM, methane yields raised 388 to 608 L CH₄/kg VS_added using OLR and HRT windows ranged between 2.0-4.2 g VS/L·d and 15-30 d. The presence of other organic waste and carbonaceous additives improves the C/N ratio, thereby increasing the methane yield. These operating windows proposed in this review are indicative and should be validated under long-term continuous operation and integrated with techno-economic and life-cycle assessments to guide deployable PM valorization schemes.