Efficiency of integrated electrooxidation and anaerobic digestion of waste activated sludge
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-04-01 |
| Journal | Biotechnology for Biofuels |
| Authors | J.A. Barrios, A. Cano, Fernando F. Rivera, M. E. Cisneros, U. DurĂĄn |
| Institutions | Center of Research and Technologic Development in Electrochemistry, SecretarĂa de Ciencia, Humanidades, TecnologĂa e InnovaciĂłn |
| Citations | 19 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research validates the integration of Electrooxidation Pre-treatment (EOP) using Boron-Doped Diamond (BDD) electrodes with Anaerobic Digestion (AD) to significantly enhance biogas recovery from Waste Activated Sludge (WAS).
- Value Proposition: EOP effectively overcomes the rate-limiting hydrolysis step in AD by disintegrating microbial cell walls, making particulate organic matter bio-available.
- Optimal Conditions: Maximum performance was achieved by pre-treating WAS at 3% Total Solids ([TS]) concentration using a Current Density (CD) of 21.4 mA/cm2.
- Methane Yield: The integrated system produced a maximum Biochemical Methane Potential (BMP) of 305 N-L CH4/kg VS, representing a 65% increase compared to non-pretreated sludge (109 N-L CH4/kg VS).
- Energy Feasibility: The process demonstrated a strong positive energy balance of 1.67 kWh/kg VS, confirming that the energy invested in EOP is recovered through increased methane production.
- Mechanism: The BDD electrodes efficiently produce strong oxidants (hydroxyl radicals, OH) that facilitate the solubilization of Chemical Oxygen Demand (COD) and Volatile Solids (VS) from the WAS.
- Conversion Efficiency: The pre-treatment resulted in high COD and VS removal, indicating effective conversion of sludge mass into usable biogas.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Optimal Total Solids ([TS]) | 3.0 | % (w/v) | Condition for maximum CH4 production |
| Optimal Current Density (CD) | 21.4 | mA/cm2 | Condition for maximum CH4 production (305 N-L/kg VS) |
| Maximum Methane Production (BMP) | 305 | N-L CH4/kg VS | Achieved with EOP pre-treatment |
| Baseline Methane Production (Control) | 109 | N-L CH4/kg VS | Non-pretreated WAS |
| Net Energy Balance (Positive) | 1.67 | kWh/kg VS | Energy recovered minus EOP electrical consumption |
| EOP Electrical Consumption (Optimal) | 0.38 | kWh/kg VS | Consumption at 21.4 mA/cm2, 30 min |
| COD Removal (Maximized) | 61.6 | % | Optimized theoretical maximum (at 3.5% [TS], 31.03 mA/cm2) |
| VS Removal (Control) | 14.2 | % | Non-pretreated WAS baseline |
| Electrode Material | p-Si-BDD | N/A | Boron-Doped Diamond (Anode and Cathode) |
| Electrode Surface Area | 70 | cm2 | Circular electrodes (100 mm diameter) |
| EOP Treatment Time | 30 | min | Fixed duration for electrooxidation |
| AD Operating Temperature | 36 ± 2 | °C | Mesophilic digestion conditions |
Key Methodologies
Section titled âKey Methodologiesâ- Sludge Sourcing and Preparation: Waste Activated Sludge (WAS) was collected from a municipal WWTP. Initial characterization showed Total Solids (TS) of 80 ± 4.3 g/L and a VS/TS fraction of 59.5 ± 11.4%.
- Inoculum Conditioning: Anaerobic sludge from a brewery WWTP was used as inoculum. It was incubated for 24 hours in a vacuum chamber to eliminate residual biogas production interference prior to use in BMP assays.
- Electrooxidation Pre-treatment (EOP):
- A DiacleanÂź single-compartment electrochemical reactor was utilized.
- Electrodes were p-Si-BDD (Diamond-based material) used for both anode and cathode, providing a 70 cm2 surface area.
- Current densities (CD) were tested at three levels: 14.3, 21.4, and 28.6 mA/cm2.
- The treatment time was fixed at 30 minutes, and the temperature was maintained at 25 °C using a water bath.
- Biochemical Methane Potential (BMP) Assays:
- Assays were conducted in 250-mL flasks using the OxiTopÂź Control OC 110 system, with an 80 mL working volume.
- The Substrate/Initial Biomass (S/X) ratio was maintained at 0.5 g VSfed/g VSbiomass.
- Digestion was performed under mesophilic conditions (36 ± 2 °C) for 16 days, with continuous shaking at 150 rpm.
- Optimization and Analysis: A 3-level full factorial design and Analysis of Variance (ANOVA) were used to assess the influence of [TS] and CD. Mathematical optimization (nonlinear complex method) was applied to the fitted models to determine the conditions maximizing CH4 production and COD/VS removal.
Commercial Applications
Section titled âCommercial ApplicationsâThe successful integration of BDD-based electrooxidation with anaerobic digestion provides a robust, energy-positive solution for sludge management, relevant to several engineering sectors:
- Wastewater Treatment Plants (WWTPs): Implementation of EOP as a pre-treatment step to increase biogas yield and reduce the volume of sludge requiring disposal, moving WWTPs toward energy self-sufficiency.
- Renewable Energy Generation: Utilizing the enhanced methane production (biogas) for combined heat and power (CHP) generation, contributing to the interconnected energy infrastructure.
- Advanced Oxidation Processes (AOPs): Leveraging the high stability and strong oxidant generation capacity of BDD electrodes for industrial wastewater purification and degradation of refractory organic compounds.
- Sludge Minimization and Disposal: Reducing Volatile Solids (VS) and sludge mass, thereby lowering transportation and disposal costs associated with excess WAS.
- Electrochemical Reactor Design: Development and scaling of flow reactors utilizing BDD technology for high-efficiency, low-maintenance electrochemical hydrolysis applications.