4. Conclusions
Taken as a whole, the moderate addition of ZVI can promote COD
removal and methane production of the anaerobic system treating
swine wastewater. The corrosion-induced H2 could improve
the hydrogenotrophic methanogenesis and dissolved ferrous ions
also could stimulate the microorganism activity. In addition, the
abiotic reactions such as flocculation, adsorption and precipitation
were inevitable to removal some suspended COD. However,
large numbers of ZVI added was not beneficial to biodegradation
mainly due to the increasing amount of solid iron species in sludge,
which appeared to encapsulate the cells and even damage the cellular
structure. According to the results, it was advised to choose
the optimum rZVI/VSS between 0.32 and 2.63, based on the processing
requirements and economic costs. The most promoting effect
induced by ZVI was observed at the rZVI/VSS of 2.63, while the maximum
utilization of per ZVI adding occurred at the rZVI/VSS of 0.74.
And the rZVI/VSS of 5.26 was proved not suitable to microorganism
and thus weaken the enhancing effect.