Enhanced biohydrogen production from waste activated sludge in combined strategy of chemical pretreatment and microbial electrolysis

• Combined strategy of chemical pretreatment and MEC was applied for WAS utilization.
• Four kinds of chemical pretreatments were tested to enhance VFAs accumulation in WAS.
• Cascade utilization was proved in combined strategy which affected H2 production.
• SDS get high acetic and propanoic accumulation for best H2 yield in combine strategy.

Cascade conversion methods are required to treat waste sludge (WAS) targeting at abundant biomass embedded in its cells and extracellular polymer. Two limiting factors have to overcome to obtain efficient conversion: (i) low release of soluble organics in raw WAS; (ii) limited conversion rate from organics to energy. Combined strategy of effective chemical pretreatment and microbial electrolysis was tested. Four kinds of chemicals (SDS, NaOH, peracetic-acid and β-cyclodextrin) were chosen to enhance volatile fatty acids (VFAs) production and following effects on hydrogen production and energy recovery by microbial electrolysis was further studied. The highest VFAs concentration was accumulated to 4712.69 mgCOD/L by β-CD within 3 days, which was increased to 4 times of unpretreated WAS. Other three chemicals respectively achieved ∼2.5-fold increase by SDS and PAA, and ∼2-fold increase by NaOH. However, the highest hydrogen yield was 8.5 mgH2/gVSS with energy efficiency of 138% ± 8% by SDS pretreatment. The pretreatment substantially affects VFAs components, reflected on cascade changing of current and hydrogen production rate. The cascade conversion indicated that accumulation of acetate and propionate in SDS pretreatment benefited the most hydrogen production in combined strategy.