Electrochemical valorization of waste activated sludge for short-chain fatty acids production

Abstract

A tremendous amount of waste activated sludge (WAS) ends up in landfilling even after a substantial retention time during anaerobic digestion. This leftover activated sludge is an organic-rich material with the high potential to produce value-added chemicals such as short chain fatty acids (SCFAs). In the present study, a novel electrochemical conversion of activated sludge (E-WAS) was carried out on the surface of non-precious electrodes (nickel, stainless-steel and copper) in alkaline media at low applied potential and temperature. Cyclic voltammetry showed that Cu (II)/Cu (III) and Ni (II)/Ni(III) redox couple catalyzed the WAS oxidation reaction to produce SCFAs and hydrogen. The results revealed that Cu(II)/Cu(III) has higher catalytic oxidation capability towards SCFAs. Yields of 48.7, 21.4, and 14.6 mg SCFAs per g of volatile solids were achieved by using copper, nickel and stainless-steel as working electrodes, respectively. Post analysis characterization techniques indicate that copper oxide films lead to WAS oxidation. Total volatile solid removal of 30% was obtained at 35°C and 1.65 V in 0.2 M NaOH after 2 h of operation in an electrochemical digestor with copper electrodes which is more efficient than a conventional alkaline treatment (24 h, 55%, 1M NaOH). Ammonia was produced as the by-product of E-WAS oxidation. The highest amount of ammonia (250 mg L−1) was obtained by using nickel as the working electrode after 2 h operation at 35°C and 1.35 V applied potential. The change in WAS morphology revealed that the copper oxide film is an effective electrocatalyst for WAS disinfection.

The Impact of Combinated Process of Electrolysis and Activated Sludge Process on Municipal Wastewater Treatment

“…The negative impact of electrolysis on activated sludge has also been utilized in studies where electrolytic decomposition was used for the production of volatile fatty acids [10] or to reduce its quantity and improve dewatering properties [11].…”

“…This process was also supported by the formation of hydroxyl and sulfate radicals. Study [10] suggests that electrolysis can valorize excess activated sludge and prepare valuable chemicals from it. The authors achieved the best results using copper electrodes, an applied voltage of 1.5 V, and a time of 2 hours, resulting in a 30% degradation of volatile suspended solids (VSS) and obtaining 48.7 mg of volatile fatty acids (VFA) per gram of degraded VSS.…”

Impact of Combined Electrolysis and Activated Sludge Process on Municipal Wastewater Treatment

“…The negative impact of electrolysis on activated sludge has also been utilized in studies where electrolytic decomposition was used to produce volatile fatty acids [10] or to reduce sludge quantity and improve dewatering properties [9].…”

“…This process was also supported by the formation of hydroxyl and sulfate radicals. Study [10] suggests that electrolysis can valorize excess activated sludge to prepare valuable chemicals. The authors achieved the best results using copper electrodes, applied voltage of 1.5 V, and time duration of 2 h, which resulted in a 30% degradation of volatile suspended solids (VSS) and provided 48.7 mg of volatile fatty acids (VFA) per gram of degraded VSS.…”

Electrocatalysts for Inorganic and Organic Waste Nitrogen Conversion

“…urea). While NH 3 production and recovery remain an emerging focus of the field, ,− there has been an abundance of literature examining electrochemical oxidation of organic matter for sludge treatment. − Common electrode materials include titanium-based catalysts, platinum, boron-doped diamond (BDD), and carbon. These are widely used to treat organic pollutants, including textile dyes, pharmaceuticals, and pesticides, and have been extensively covered in recent work. ,,, Other materials like Ni and Fe have well-established behaviors for organic oxidation and are currently being explored for real waste treatment. ,, The following section covers the possible electrochemical oxidation pathways and examples of catalysts being implemented in real waste matrices.…”