Abstract
Anaerobic digestion (AD) is one of the most widely used processes to stabilize waste sewage sludge and produce biogas as renewable energy. This study investigated the effects of Fe3O4 NPs at different concentrations (0,100 and 300 mg/L) on AD. 100mg/L Fe3O4 NPs could increase gas production by 21.9% and reach the highest methane content of 66.75%. In addition, 100 mg/L Fe3O4 kept pH at an appropriate level. Scanning electron microscope (SEM) was used to study the changes in surface morphology in sludge. The dynamics of cumulative biogas production and daily biogas production were studied by using the Logistic model and modified Gompertz model respectively. Other indices also had changed in the whole process, which in the end lead to the variation of biogas production. These results suggested that Fe3O4 NPs could increase microbial activity and relevant enzyme activities, caused changes and transitions between different phases in the system.
Highlights
Due to the wide application of nanomaterials, which inevitably enter into the environment [1], the nanomaterials present in the wastewater were adsorbed by the sludge, trapped in sludge [2]
The daily biogas production of the three experimental groups reached the maximum value on the 9th day, the biogas production of the control group was 17.2mL, and the biogas production of the 100mg/L Fe3O4 NPs group was 30.3 L and higher than that of the control group
When the concentrations of Fe3O4 NPs increased from 100 mg/L to 300 mg/L, cumulative biogas production reduced from 247.2 mL to 190.5 mL. It suggested that adding an appropriate concentration of Fe3O4 NPs could increase biogas production at about 21.9% while adding excess Fe3O4 NPs had no significant effect on cumulative biogas production
Summary
Due to the wide application of nanomaterials, which inevitably enter into the environment [1], the nanomaterials present in the wastewater were adsorbed by the sludge, trapped in sludge [2]. Anaerobic digestion (AD) is an effective technique to treat solid waste and convert it into biogas consisting of carbon dioxide and methane. This biogas can be used as heating value or biomethane of the replacement to natural gas [3]. The AD is the cleanest and effective method to treat waste sludge, it referred to that in the absence of oxygen and microbial metabolism, through the degrading organic substances and produce clean combustible gases such as hydrogen and methanee [4] but there are so many limiting factors in the anaerobic digestion process that lead to a decrease in gas production, such as pH, temperature, oxidationreduction potential and the methanogens which have high environmental requirements. The traditional anaerobic digestion process has the characteristics of a long reaction cycle, low biogas production and low methane content in biogas, so adding additives to promote gas production has become a research hotspot
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