Using AI and BES/MFC to decrease the prediction time of BOD5 measurement.

Biochemical oxygen demand (BOD) is one of the most important water/wastewater quality parameters. BOD5 is the amount of oxygen consumed in 5 days by microorganisms that oxidize biodegradable organic materials in an aerobic biochemical manner. The primary objective of this research is to apply microbial fuel cells (MFCs) to reduce the time requirement of BOD5 measurements. An artificial neural network (ANN) has been created, and the predictions we obtained for BOD5 measurements were carried out within 6-24 h with an average error of 7%. The outcomes demonstrated the viability of our AI MFC/BES BOD5 sensor in real-life scenarios.

Microbial fuel cell biosensor for the determination of biochemical oxygen demand of wastewater samples containing readily and slowly biodegradable organics.

OBJECTIVES: Single-chamber air cathode microbial fuel cells (MFCs) were applied as biosensors for biochemical oxygen demand (BOD) measurement of real wastewaters with considerable suspended and/or slowly biodegradable organic content. RESULTS: The measurement method consists of batch sample injection, continuous measurement of cell voltage and calculation of total charge (Q) gained during the biodegradation of organic content. Diverse samples were analyzed: acetate and peptone samples containing only soluble readily biodegradable substrates; corn starch and milk samples with suspended and colloidal organics; real domestic and brewery wastewaters. Linear regression fitted to the Q vs. BOD5 measurement points of the real wastewaters provided high (> 0.985) R2 values. Time requirement of the measurement varied from 1 to 4 days, depending on the composition of the sample. CONCLUSIONS: Relative error of BOD measured in the MFCs comparing with BOD5 was less than 10%, thus the method might be a good basis for the development of on-site automatic BOD sensors for real wastewater samples.

Single chamber air-cathode microbial fuel cells as biosensors for determination of biodegradable organics.

OBJECTIVES: Single chamber air cathode microbial fuel cells (MFCs) were investigated with sodium-acetate and peptone as test substrates to assess the potential for application as biosensor to determine the concentration of biodegradable organics in water/wastewater samples. RESULTS: MFCs provided well-reproducible performance at high (> 2000 mg COD l-1-Chemical Oxygen Demand) acetate concentration values. Current in the cells proved to be steady from 25 to 35 °C, significant decrease was, however, revealed in the current below 20 °C. Direct calculation of non-toxic biodegradable substrate concentration in water/wastewater from the current in MFCs is possible only in the non-saturated substrate concentration range due to the Monod-like dependence of the current. This range was determined by a fitted and verified Monod-based kinetic model. Half saturation constant (KS) values were calculated at 30 °C applying different external resistance values (100 Ω, 600 Ω and 1000 Ω, respectively). In each case KS remained below 10 mg COD l-1. CONCLUSIONS: Biosensors with this particular MFC design and operation are potentially applicable for detecting as low as 5 mg COD l-1 readily biodegradable substrates, and measuring the concentration of these substances up to ~ 50-70 mg COD l-1.

Enhancing substrate utilization and power production of a microbial fuel cell with nitrogen-doped carbon aerogel as cathode catalyst.

OBJECTIVES: Catalytic efficiency of a nitrogen-doped, mesoporous carbon aerogel cathode catalyst was investigated in a two-chambered microbial fuel cell (MFC) applying graphite felt as base material for cathode and anode, utilizing peptone as carbon source. RESULTS: This mesoporous carbon aerogel containing catalyst layer on the cathode increased the maximum power density normalized to the anode volume to 2.7 times higher compared to the maximum power density obtained applying graphite felt cathode without the catalyst layer. At high (2 and 3) cathode/anode volume ratios, maximum power density exceeded 40 W m-3. At the same time, current density and specific substrate utilization rate increased by 58% resulting in 31.9 A m-3 and 18.8 g COD m-3 h-1, respectively (normalized to anode volume). Besides the increase of the power and the rate of biodegradation, the investigated catalyst decreased the internal resistance from the range of 450-600 to 350-370 Ω. CONCLUSIONS: Although Pt/C catalyst proved to be more efficient, a considerable decrease in the material costs might be achieved by substituting it with nitrogen-doped carbon aerogel in MFCs. Such cathode still displays enhanced catalytic effect.

Substrate concentration dependence of voltage and power production characteristics in two-chambered mediator-less microbial fuel cells with acetate and peptone substrates.

OBJECTIVES: Power production characteristics and substrate concentration dependence of voltage have been investigated together with the determination of kinetic constants in two-chambered mediator-less microbial fuel cells (MFC) for acetate and peptone substrates. RESULTS: At 500 mg DOC l-1 (dissolved organic carbon), power densities normalized to the anode surface of 112 mW m-2 with acetate and 114 mW m-2 with peptone as electron donor were attained by applying cathodes with a Pt catalyst layer. Related anode surface specific substrate removal rate was 44 g DOC m-2 h-1 for acetate and 52 g DOC m-2 h-1 for peptone. Substrate concentration dependency of the voltage suggests Monod-like kinetics with extremely low, <1 mg DOC l-1, half saturation constants and with final DOC concentrations of 6-10 mg l-1. CONCLUSIONS: Acetate and peptone are equivalent substrates for the exoelectrogenic bacteria both from the point of view of biodegradation kinetics and power production characteristics.

Short-sludge age EBPR process - Microbial and biochemical process characterisation during reactor start-up and operation.

The new paradigm for used water treatment suggests the use of short solid retention times (SRT) to minimize organic substrate mineralization and to maximize resource recovery. However, little is known about the microbes and the underlying biogeochemical mechanisms driving these short-SRT systems. In this paper, we report the start-up and operation of a short-SRT enhanced biological phosphorus removal (EBPR) system operated as a sequencing batch reactor (SBR) fed with preclarified municipal wastewater, which is supplemented with propionate. The microbial community was analysed via 16S rRNA amplicon sequencing. During start-up (SRT = 8 d), the EBPR was removing up to 99% of the influent phosphate and completely oxidized the incoming ammonia. Furthermore, the sludge showed excellent settling properties. However, once the SRT was shifted to 3.5 days nitrification was inhibited and bacteria of the Thiothrix taxon proliferated in the reactor, thereby leading to filamentous bulking (sludge volume index up to SVI = 1100 mL/g). Phosphorus removal deteriorated during this period, likely due to the out-competition of polyphosphate accumulating organisms (PAO) by sulphate reducing bacteria (SRB). Subsequently, SRB activity was suppressed by reducing the anaerobic SRT from 1.2 day to 0.68 day, with a consequent rapid SVI decrease to ∼200 ml/g. The short-SRT EBPR effectively removed phosphate and nitrification was mitigated at SRT = 3 days and oxygen levels ranging from 2 to 3 mg/L.