Degradation of organics extracted from dewatered sludge by alkaline pretreatment in microbial electrolysis cell

Abstract

Waste activated sludge in China are mostly subjected to dewatering process before final disposal without stabilization. This study investigated the feasibility of organics degradation and H production from non-stabilized dewatered sludge (DS) by microbial electrolysis cells (MECs). Alkaline pretreatment was used to disintegrate sludge matrix and solubilize organic matters in DS. Then, the treatment performance of DS supernatant in a single-chamber MEC at various applied voltages was investigated. The COD (chemical oxygen demand) removal rate increased with increasing voltage, which ranged from 26.35 to 44.92% at 0.5-0.9 V. The average coulombic efficiency was 75.6%, while the cathodic hydrogen recovery was not satisfied (15.56-20.05%) with H production rates of 0.027-0.038 m H/(m day). The reasons could be ascribed to the complexity of the substrate, H loss, and the confinement of configuration in scale-up. The organic matter degradation was influenced by the composition of DS. The carbohydrates could be readily used; meanwhile, the major component of the DS supernatant, i.e. proteins, was difficult to be utilized, which resulted from the low biodegradability of the transphilic fractions during the MEC operation.

Combined freezing-thawing pretreatment and microbial electrolysis cell for enhancement of highly concentrated organics degradation from dewatered sludge

“…Previous studies have shown that a minimum external voltage of 0.4-0.6 V is required to produce a significant amount of hydrogen, but further increase in voltage beyond 0.8 V is incapable of improving current density [13]. Moreover, our previous study [12] has observed a notable difference in organics degradation at 0.5 V and 0.7 V when treating WAS. So, herein, the variations of 0.5 V and 0.7 V were chosen to investigate the impact of the applied voltage.…”

“…The F/T-treated DS was fed with nutrient solution [11] into long-term running single-chamber MECs. Each MEC was constructed according to the previous report [12] with effective volume of 400 mL.…”

“…The properties of MECs fed with raw and F/ T-pretreated DS are summarized in Table 2. Several previous studies [12,24,25] on the MEC performance fed with highly concentrated organics were compared with this study ( Table 3).…”

“…To date plenty of studies focused on the pretreatment to enhance the digestion performance [8][9][10], few researches were reported for the influence of the pretreatment method on the MEC in terms of sludge [11,12]. Our previous study [12] demonstrated the efficiency of alkaline pretreatment for DS as this process affected soluble organic matter content and microbial community structures during electrogenesis. Unfortunately, for highly concentrated organic matters, efforts to develop optimal and efficient pretreatment methods are still at the early stage.…”

Microbial electrolysis cell as an emerging versatile technology: a review on its potential application, advance and challenge

“…In China, most WWTPs were not built with or run anaerobic digesters due to technical hurdles and capital and operational cost. Most often, the sewage sludge is only subjected to concentrating and dewatering treatment processes . Li et al .…”