Effect Of Trace Elements Addition On The Anaerobic Digestion Performance Of Food Waste And Chicken Manure

Anaerobic digestion of biomass is a multi-stage process involving different types of microorganisms. In this process, in addition to macronutrients such as carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur, trace elements also play crucial roles in the growth and metabolism of anaerobic microorganisms. Trace elements, such as iron (Fe), cobalt (Co), nickel (Ni), and selenium (Se) among others, may promote the growth of methanogens and are known to be crucial for the activity of enzymes involved in methanogenic systems to increase the rate of methane bioconversion. The stimulation and antagonism by trace elements plays a significant role in the performance and stability of biogas digesters. Based on the anaerobic digestion (AD) characteristics of food waste and chicken manure as the main substrates, as well as the special functions of trace elements, we studied the role of trace elements in AD performance of food waste and chicken manure. In addition, the function of trace elements in the recovery of the initially acidified AD system was investigated. We provide a theoretical foundation for the efficient and stable operation of biogas plants for treating high solid content organic matters. The main conclusions are as follows:Trace elements (TEs) may improve the operational performance of AD processes with high organic loading rates (OLR). For the moon mosphiiic AD of food waste, the highest OLR for the AD system without adding TEs was 3.0 gVS/L/d, which was increased to 5.0 gVS/L/d by supplying TEs (Fe, Co, and Ni). In addition, the highest OLR treatment further increased this value to 5.5 gVS/L/d when Fe, Co, Ni, and Se were added to the AD systems. This study indicated that the addition of only Fe, Co, or Ni could not maintain the high performance of the AD system at an OLR of 5.5 gVS/L/d. However, when Se was supplied with Fe, Co, and Ni, the performance of methane fermentation was recovered. For the initial acidified mosphilic AD systems without external TEs supplied, adding Fe, Co, and Ni accelerated the degradation of VFAs, which had decreased to 2260 mg/L. This suggests that the TEs improved the conversion of VFA. At an OLR of 4.5 gVS/L/d, except for Fe, addition of only Co and Ni could not maintain the stability of the AD process. These results indicate that Co and Ni are not limiting factors in maintaining the stability of the AD process. Further analysis revealed that when only Fe was added, the system showed good performance and relative stable specific methane production and volume methane production rate. This suggests that Fe is necessary for stabilizing the AD system.According to these characteristics of high ammonia and sulfide in the AD process of Chicken manure (CM), the effect of TEs on the AD of CM was evaluated in batch and semi-CSTR tests. The batch experimental results reflected that in a specific iron concentration range, adding the appropriate amount of iron enhanced biogas production. The relatively appropriate iron addition concentrations were 300, and 750 mg/L. Based on the batch test, a long-term semi-continuous CSTR test was carried out to evaluate the effects of Fe and Ni on the AD of CM. The results showed that TEs improved processing capacity, which increased the OLR from 5.0 to 6.0 gVS/L/d. The biomass balance model indicates that TEs enhanced the metabolism of anaerobic micro-organisms and that the biomass concentration increased by 25.5% following the addition of TEs.