Effects of newly prepared alkaline ferrate on sludge disintegration and methane production: Reaction mechanism and model simulation

Sewage sludge can be a potential energy source, but its digestion rate is restricted by the poor availability of biodegradable contents in the sludge. Disintegrating sludge floc and microbe cell can improve the sludge digestion potential and facilitate methane production. Here, the effects of newly prepared alkaline ferrate (NPAF) on sludge disintegration and methane production were investigated. When 200 mg Fe(VI)/L of NPAF was applied, the content of soluble chemical oxygen demand (SCOD), total nitrogen (TN), total phosphorus (TP), protein and polysaccharide in sludge supernate increased to 11, 17, 6.5, 4, and 30 times respectively as compared with the raw sludge. However, when the dosage of NPAF surpassed 300 mg Fe(VI)/L, the content of SCOD, biochemical oxygen demand (BOD), and protein in sludge was decreased. Low level of NPAF could effectively destroy sludge floc and improve its solubilization, leading to the release of cell contents. High level of NPAF may oxidize the easy biodegraded components (such as protein) in the supernate and deteriorate its biodegradation property. For sludge anaerobic digestion, the highest methane production was achieved with a 200 mg Fe(VI)/L pretreatment, increasing methane production by 42.5% compared to the raw sludge. Further increases in the NPAF dosage inhibited methane production, probably because partially solubilized compounds were oxidized, and superfluous potassium inhibited the activity of methanogens. The biochemical methane potential (BMP) assays suggest that low NPAF doses [< 200 mg Fe(VI)/L] could improve the hydrolysis rate (k) and biochemical methane potential (B-0) of sludge.