Standard Biochemical Oxygen Demand Research Articles

Resilience of anodic biofilm in microbial fuel cell biosensor for BOD monitoring of urban wastewater

Efficient wastewater treatment monitoring is vital for addressing water scarcity. Microbial fuel cells (MFCs) have emerged as real-time biosensors for biochemical oxygen demand (BOD) in urban wastewater. Discrepancies in signal generation may arise due to changes in the composition and metabolism of mixed-culture electroactive biofilms stemming from different wastewater compositions. In this study, 3D-printed MFC-based biosensors were employed to assess the BOD of sterile complex artificial wastewater and untreated urban wastewater. Alterations in the microbial composition of the anode were evaluated using 16S rRNA sequencing and metagenomics analysis. Results show that MFC-based biosensors can be effectively recalibrated for diverse types of wastewater, maintaining consistent sensitivity (0.64 ± 0.10 mA L mg−1 m−2 with synthetic wastewater and 0.78 ± 0.13 mA L mg−1 m−2 with urban wastewater) and limit of detection (49 ± 8 mg L−1 for synthetic wastewater and 44 ± 7 mg L−1 for urban wastewater). Crucially, pre-sterilization, conductivity adjustments, and nitrogen purging of wastewater are not required before its introduction into the biosensor. However, the presence of native aerobic microorganisms in the wastewater might affect the current output. Metagenomics and taxonomic analyses revealed that the alterations in biofilm composition are predominantly in response to the varied chemical and microbiological compositions of different substrates. Despite variations in anodic biofilm composition, the MFC-based biosensor maintains a relative error comparable to the standard BOD test. This highlights the resilience and flexibility of the biosensor when directly used with a variety of wastewater types before full biofilm adjustment.

Bioburden proliferation in vehicle air filters waste: the use of gamma radiation on fungal decontamination

This study aimed to analyze the fungal contamination of air-conditioning filters waste (n=20) as an indicator of Quality Air Indoor from different car models, that were collected from 10 exchange stations located in the South, North, West, Downtown and East, of the city of São Paulo in São Paulo State, Brazil, during the period from October 2017 to November 2018. Sampling of filter particles (33 fragments of 10 × 10-mm size) were plated onto solidified Potato Dextrose agar in Petri dishes. The samples were incubated for 7 days at 25 °C and were stored in a standard Biochemical Oxygen Demand incubator, for growth of fungal cultures. After incubation, the fungal culture in the plates was evaluated, and the total counting of infected fragments was expressed as a percentage. The fungi were examined by Lactophenol blue solution staining for microscopy. All samples were contaminated with various fungal genera, including Aspergillus, Alternaria, Cladosporium, and Penicillium. The study also aimed to evaluate the fungal enumeration in the samples that were irradiated with dose of 10 kGy to fungal decontamination of air-conditioning filters waste. Of total samples, 50% were completed decontaminated, but some genera such as Aspergillus, Penicillium, Rhizopus, Cladosporium and yeasts demonstrated radioresistance at the dose of 10 kGy. The only yeast called Rhodotorula showed an increase in growth after the irradiation process.

Bacterial Cellulose Immobilized S. cerevisiae as Microbial Sensor for Rapid BOD Detection

As one of the most important parameters to characterize the organic pollution of water, biochemical oxygen demand (BOD) determined through a rapid, in situ and on line method is very attractive. In this paper, a new BOD biosensor has been developed, which are composed of the ecofriendly precursor of Saccharomyces cerevisiae (S. cerevisiae) embedded in bacterial cellulose (BC) matrix and the Ketjen Black (KB) modified glassy-carbon electrode. Furthermore, a doublemediator system is constructed using potassium ferricyanide and menadione in reaction cell to transfer electron from the microbe to electrode. The responses of glucose glutamic acid (GGA) standard solutions are amperomertrically measured with an applied potential of 0.25 V versus Hg/Hg2Cl2 in a three-electrode system. Under the optimum conditions, the (BC/S. cerevisiae-menadione)/KB modified electrode shows a high operational stability with relative standard deviation (RSD) of 4.16% (fourteen assays), a good repeatability (RSD=3.10%), a fast response time (in 20 minutes) and a wide linear range (from 10–220 mg O2l−1). The BOD values measured by this method have been highly correlated with the standard BOD 5-day method for wastewater samples (R2=0.9859, n=3), indicating that it can meet the requirement of BOD rapid measurement.

Hibernations of electroactive bacteria provide insights into the flexible and robust BOD detection using microbial fuel cell-based biosensors

Microbial fuel cell (MFC) biosensors have been suggested as an alternative detection method for biochemical oxygen demand (BOD). However, it is absolutely essential to develop maintenance procedures for MFC biosensors` because in practice the lay-up period cannot be avoided. In this work, setting electroactive bacteria (EAB) under hibernation condition was demonstrated to be a feasible maintenance method, which provided important insights into the flexible and robust BOD detection using MFC biosensors. Standard BOD solution containing 500, 200, and 20 mg/L BOD were used to evaluate the detection performance after EAB hibernations. Results demonstrated quick recovery of voltage output and high-accuracy BOD detection after hibernations up to 30 days in MFC biosensors detecting 500 mg/L and 200 mg/L BOD. Identical anode potentials after the EAB hibernations suggested intact bacterial ability of current generation. Non-turnover cyclic voltammetry immediately collected after the hibernations suggested multiple redox couples and the presence of cytochromes that played key roles in EAB metabolism and functioned as temporary electron sinks during the hibernations, leading to the increased detected BOD concentration in the restarting cycles. Generally, setting EAB under hibernation condition is a simple and convenient maintenance method for MFC-based BOD biosensors, which not only provides insights into flexible and robust BOD detection, but also be helpful for other MFC biosensing instruments.

Impact of heterotrophic denitrification on BOD detection of the nitrate-containing wastewater using microbial fuel cell-based biosensors

Microbial fuel cell (MFC)-based biosensors are promising alternative biochemical oxygen demand (BOD) detection method. However, the presence of alternative electron acceptor such as nitrate will interfere BOD detection because of the heterotrophic denitrification. So, it is essentially important to investigate how nitrate influences BOD detection and to make correction. In this work, standard BOD solution containing 20–500 mg/L BOD was used to evaluate performance of MFC biosensors impacted with 0–50 mg/L NO3−-N. Results demonstrated the underestimated BOD concentration detected using biosensors with impact of nitrate reduction. Graphical and mathematical method was proposed to make correction, and the corrected BOD concentration accurately indexing the organic matter concentration of the nitrate-containing sample could be obtained. Voltage output, polarization curve and cyclic voltammetry collectively suggested that denitrifying bacteria outcompeted over electricity-generating bacteria for electron donors, and that heterotrophic anodic denitrification was the priority process compared to current production. Generally, the more nitrate in standard solution, the more electron donors consumed for nitrate reduction and the less left for current production. The main nitrogen removal processes in MFC biosensors involved heterotrophic denitrification and ammonification at anode, ammonium transport to cathode chamber, and bioelectrochemical autotrophic denitrification at cathode. Phyla Bacteroidetes, Proteobacteria and Firmicutes were the dominant bacteria, accounting for more than 92% of the whole population in the anode chamber, while the phyla Bacteroidetes, Proteobacteria and Actinobacteria accounted for more than 84% in cathode chamber. The findings in this work provide important insights into BOD detection of nitrate-containing wastewater using MFC biosensors.

Biochemical Oxygen Demand Microelectrode for Quantifying Concentration Gradients in Anaerobic Biofilms

Biochemical oxygen demand (BOD) is one of the widely used parameter to determinate the level of organic pollution in water. The standard method, BOD5 assay, is commonly used to measure BOD concentration but it takes a long time and cannot be integrated for online measurements. Additionally, BOD5 cannot be used to measure BOD in microscale systems, especially in anaerobic biofilms where the oxygen is absent. Because of the limitation of available tools for quantifying BOD concentration within anaerobic biofilms, a new, simple and miniaturized tool is needed for measuring local BOD concentrations in biofilms. The goal of this work is to develop a BOD microelectrode for quantifying concentration gradients in anaerobic biofilms. The developed BOD microelectrode uses an anaerobic mixed-culture-anodic biofilm as a transducer, which is grown on a carbon fiber tip diameter. The carbon fiber microelectrode acts as the working electrode, which is polarized using a potentiostat. A 100 µm platinum wire counter electrode and a Ag/AgCl-wire pseudo reference electrode are used to complete the electrochemical cell. The BOD microelectrode components are enclosed in a glass outer case. The BOD microelectrodes were calibrated using a standard BOD solution. The performance of the BOD microelectrode was assessed including response time and the linear BOD concentration range. Finally, concentration profiles in an anaerobic biofilm were measured to demonstrate its use.

Microbial BOD sensors based on Zr (IV)-loaded collagen fiber.

Biochemical oxygen demand (BOD) sensors based on Zr (IV)-loaded collagen fiber (ZrCF), a novel material with great porous structure, were developed. This novel material shows adsorbability by microorganisms. Saccharomyces cerevisiae and Escherichia coli were used for the construction of BOD sensors. Factors affecting BOD sensor performance were examined. The ZrCF-based BOD sensor showed different sensitivities and linear response ranges with different biofilm densities. The amount of microorganisms strongly affected the performance of the BOD sensor. Poor permeability of previously reported immobilization carriers were greatly circumvented by ZrCF. The service life of the ZrCF-based BOD sensor was more than 42 days. The immobilized microorganisms can be stored for more than 6 months under 4°C in PB solution. There was good correlation between the results of the sensor method and the standard 5-day BOD method in the determination of pure organic substrates and real water samples.

Geobacter-dominated biofilms used as amperometric BOD sensors

The biochemical oxygen demand (BOD) of a given water sample is typically measured using a conventional BOD5 assay, which requires 5 days of incubation at 20°C of the sample with mixed communities of bacteria. The study presents a new type of BOD sensor using a Geobacter-dominated biofilm selected with ethanol as the sole carbon source. Ethanol selected for biofilms with a broader substrate usage than those selected with acetate, making them better for BOD biosensing applications. The biosensor was operated at room temperature with a voltage input of −0.08V vs SHE (−0.36V vs Ag/AgCl) and calibrated using several dilutions of synthetic wastewater with known BOD concentrations ranging from 174mg/L to 1200mg/L. The charge transferred by the biofilm over a reaction time of 17.5h was linearly correlated (R2=0.96) with BOD. Once calibrated, the biosensor was used to measure the BOD of cow’s milk with a reproducibility of 94% and an error of only 7.4% compared to BOD5 values. In contrast to the 5 days incubation currently required by standard BOD methods our novel biosensor offers a rapid monitoring alternative for assessments of the BOD of dairy effluent.

Impairment in water quality of Ganges River and consequential health risks on account of mass ritualistic bathing

Effect of mass ritualistic bathing was studied on the water quality of Ganges River during Maha Kumbh festival in India. Significantly higher values of biochemical oxygen demand (BOD) (14 mg/L), chemical oxygen demand (67 mg/L), total suspended solids (55 mg/L), and ammonia nitrogen (2.15 mg/L) were observed during mass ritualistic bathing. The BOD values were observed to surpass the standard BOD criteria (≤3 mg/L) of outdoor bathing. Similarly, higher number of total coliforms (792 most probable numbers [MPN]/100 mL) and fecal coliforms (482 MPN/100 mL) were observed in water samples, which show the alarming level of fecal contamination according to Indian and European (100 MPN/100 mL) standards of outdoor bathing. Furthermore, total 5,368 cases of water borne infections were observed during the epidemiological survey. In order to protect the public health and water quality of river, it is recommended to strictly regulate the bathing practices with continuous disinfection at upstream of bathing spot. Moreover, a comprehensive health-based investigation should be performed to facilitate the development of a suitable model.

Oxygen Demand of Aircraft and Airfield Pavement Deicers and Alternative Freezing Point Depressants

Aircraft and pavement deicing formulations and other potential freezing point depressants were tested for biochemical oxygen demand (BOD) and chemical oxygen demand (COD). Propylene glycol-based aircraft deicers exhibited greater BOD5 than ethylene glycol-based aircraft deicers, and ethylene glycol-based products had lower degradation rates than propylene glycol-based products. Sodium formate pavement deicers had lower COD than acetate-based pavement deicers. The BOD and COD results for acetate-based pavement deicers (PDMs) were consistently lower than those for aircraft deicers, but degradation rates were greater in the acetate-based PDM than in aircraft deicers. In a 40-day testing of aircraft and pavement deicers, BOD results at 20°C (standard) were consistently greater than the results from 5°C (low) tests. The degree of difference between standard and low temperature BOD results varied among tested products. Freshwater BOD test results were not substantially different from marine water tests at 20°C, but glycols degraded slower in marine water than in fresh water for low temperature tests. Acetate-based products had greater percentage degradation than glycols at both temperatures. An additive component of the sodium formate pavement deicer exhibited toxicity to the microorganisms, so BOD testing did not work properly for this formulation. BOD testing of alternative freezing point depressants worked well for some, there was little response for some, and for others there was a lag in response while microorganisms acclimated to the freezing point depressant as a food source. Where the traditional BOD5 test performed adequately, values ranged from 251 to 1,580 g/kg. Where the modified test performed adequately, values of BOD28 ranged from 242 to 1,540 g/kg.

A BOD monitoring disposable reactor with alginate-entrapped bacteria

Biochemical oxygen demand (BOD) is a measure of the amount of dissolved oxygen that is required for the biochemical oxidation of the organic compounds in 5 days. New biosensor-based methods have been conducted for a faster determination of BOD. In this study, a mathematical model to evaluate the feasibility of using a BOD sensor, based on disposable alginate-entrapped bacteria, for monitoring BOD in situ was applied. The model considers the influences of alginate bead size and bacterial concentration. The disposable biosensor can be adapted according to specific requirements depending on the organic load contained in the wastewater. Using Klein and Washausen parameter in a Lineweaver-Burk plot, the glucose diffusivity was calculated in 6.4 × 10(-10) (m2/s) for beads of 1 mm in diameter and slight diffusion restrictions were observed (n = 0.85). Experimental results showed a correlation (p < 0.05) between the respirometric peak and the standard BOD test. The biosensor response was representative of BOD.

Preparation of Biofilm Electrode with Xanthomonas sp. and Carbon Nanotubes and the Application to Rapid Biochemical Oxygen Demand Analysis in High‐Salt Condition

A Xanthomonas sp. was isolated from the sludge on the drain outlet of a pharmaceutical factory. Then, the bacterium and carbon nanotubes (CNTs) were co-attached to an oxygen electrode for rapid analysis of biochemical oxygen demand (BOD). The response current was linear with BOD values in the range 10 to 300 mg/L for standard BOD solution with a response time of 35 seconds (R = 0.9994) and 20 to 580 mg/L for pharmaceutical wastewater with a response time < or =200 seconds (R = 0.9985), which means that this modified electrode might be used for online BOD analysis of pharmaceutical wastewater. Further studies revealed that the modified electrode can be used for BOD measurement in a high-salt condition. Also, the bacterium/CNTs biofilm can maintain its activity and good performance, even after being sealed and stored at 4 degrees C for 50 days.

Online Biochemical Oxygen Demand Monitoring for Wastewater Process Control-Full-Scale Studies at Los Angeles Glendale Wastewater Plant, California

The main objective of this investigation is to determine whether or not it would be feasible to use the measured values of biochemical oxygen demand (BOD) of wastewater obtained by an online instrument at the Los Angeles/Glendale Water Reclamation Plant (California) for controlling its activated sludge process. This investigation is part of a project to develop online BOD monitoring for process control in the City of Los Angeles wastewater treatment plants. Tests studied the Siepmann und Teutscher GmbH (ISCO-STIP Inc., Lincoln, Nebraska) BIOX-1010, which uses a bioreactor containing a culture of microbes from the wastewater to measure soluble BOD in 2 minutes. This rapid approximation to the operation of secondary treatment allows anticipation of system response. Calibration measurements allow the operators to find a conversion factor for the instrument's microprocessor to compute values of BOD that agree well with the standard 5-day BOD (BOD5) measurement, despite the differences in the details of the two testing methods. This instrument has recently been used at other wastewater treatment plants, at a number of airports in Europe and the United States to monitor runway runoff, and is also being used on waste streams at an increasing number of food processing plants. A comparison was made between the plant influent BOD values obtained by the BIOX-1010 online monitor from the end of August, 2000, to late January, 2001, and the individual and average values obtained for the same period using the standard BOD5, 20 degrees C test, to determine the effectiveness of the Biox-1010 to identify shock loads and their duration. Individual BOD estimates and averages over periods of overly high biological loads (shock loads) were compared, and the instrument readings were evaluated for their effectiveness in detecting shock loads. The results were highly satisfactory, so the instrument was used to trigger a shock-load warning alarm since late September, 2000. This allowed flow diversion and temporary storage to prevent process upsets.

Redox Coupling to Microbial Respiration: an Evaluation of Secondary Mediators as Binary Mixtures with Ferricyanide

MICREDOX is a rapid microbial-based assay, which was originally developed at Lincoln Technology to monitor biochemical oxygen demand (BOD).[1] The assay is characterized by high levels of biocatalyst (microorganisms) and redox mediator; these facilitate a fast reaction in which the microbial oxidation of an organic substrate is coupled with the reduction of the mediator. Previous efforts toward optimizing this assay have principally been directed at the selection and performance of different bacterial strains, either singly[2] or as a consortium.[3] Here we report the effect of adding a second mediator to the assay by comparing the coulombic responses and the substrate stoichiometric conversion efficiencies. Escherichia coli and half-strength standard BOD substrate (75 mg glucose L−1, 75 mg glutamic acid L−1; GGA) were incubated for one hour at 37°C in the absence of oxygen with an excess of redox mediator, potassium hexacyanoferrate(iii) (HCF), either individually or as a binary mixture that included a secondary mediator. Secondary redox mediators investigated were p-benzoquinone (BQ), 2,6-dichlorophenolindophenol (DPIP), menadione (MD), neutral red (NR), N,N′-tetramethyl-1,4-phenylenediamine (N-TMPD), phenazine ethosulphate (PES), and 2,3,5,6-tetramethyl-1,4-phenylenediamine (TMPD). When HCF was supplemented with TMPD or PES the stoichiometric conversion efficiency for the oxidation of the GGA by E. coli increased, whereas when supplemented with N-TMPD, MD, DCIP, or BQ the conversion efficiency decreased. No effect was evident when NR was used as the supplement.

Analyzing the uncorrected error of dilution water demand for the dilution biochemical oxygen demand method.

Dilution water demand (DWD) can cause a positive error when the dilution biochemical oxygen demand (BOD) method is used. Dilution water demand may be attributed to oxidation of organic impurities in the dilution water and nitrification of ammonia added as a nutrient. To minimize the error associated with these sources, the standard BOD method requires that DWD be less than 0.2 mg/L in 5 days and does not allow correction for DWD when calculating test results. This study derives a set of theoretical equations to analyze the uncorrected errors with and without seeding. The authors concluded that DWD can be completely corrected if seeded dilution water is used for the sample dilution. When seeding individual bottles, the uncorrected error approaches 8.3 to approximately 8.8% at a 5-day depletion of 2 mg/L for a typical secondary effluent. Tests without seeding show an almost 1% higher uncorrected error than seeded tests. The analysis also suggests that these errors can be effectively reduced to less than 3% when the 5-day depletion approaches 6 mg/L. even for 5-day biochemical oxygen demand concentrations exceeding I x 10(4) mg/L. Further analysis indicates that, if not inhibited, the ammonium added to dilution water as a nutrient may contribute additional error due to nitrification.

MICREDOX ®—development of a ferricyanide-mediated rapid biochemical oxygen demand method using an immobilised Proteus vulgaris biocomponent

Biochemical oxygen demand (BOD) is an international regulatory environmental index for monitoring organic pollutants in wastewater and the current legislated standard test for BOD monitoring requires 5 days to complete (BOD 5 test). We are developing a rapid microbial technique, MICREDOX ®, for measuring BOD by eliminating oxygen and, instead, quantifying an equivalent biochemical co-substrate demand, the co-substrate being a redox mediator. Elevated concentrations of Proteus vulgaris, either as free cells or immobilised in Lentikat ® disks, were incubated with an excess of redox mediator (potassium hexacyanoferrate(III)) and organic substrate for 1 h at 37 °C without oxygen. The addition of substrate increased the catabolic activity of the microorganisms and the accumulation of reduced mediator, which was subsequently re-oxidised at a working electrode generating a current quantifiable by a coulometric transducer. The recorded currents were converted to their BOD 5 equivalent with the only assumption being a fixed conversion of substrate and known stoichiometry. Measurements are reported both for the BOD 5 calibration standard solution (150 mg l −1 glucose, 150 mg l −1 glutamic acid) and for filtered effluent sampled from a wastewater treatment plant. The inclusion of a highly soluble mediator in place of oxygen facilitated a high ferricyanide concentration in the incubation, which in turn permitted increased concentrations of microorganisms to be used. This substantially reduced the incubation time, from 5 days to 1 h, for the biological oxidation of substrates equivalent to those observed using the standard BOD 5 test. Stoichiometric conversion efficiencies for the oxidation of the standard substrate by P. vulgaris were typically 60% for free cells and 35–50% for immobilised cells.

A SIMPLE, MULTIPLE SIMULTANEOUS SPECTROPHOTOMETRIC METHOD FOR BOD DETERMINATION USING DCIP AS THE REDOX COLOR INDICATOR

ABSTRACT Especially in the analysis of environmental samples, it is necessary to perform rapid, simple and multiple analyses because it highly desirable to determine the results quickly as well as to analyze numerous samples simultaneously. We use 2,6-dichlorophenolindophenol (DCIP) as a redox color indicator for the Biochemical Oxygen Demand (BOD) determination in this report. The absorbance of DCIP decreases due to the metabolism of organic substances in aqueous samples by Pseudomonas fluoresens biovar V. Our technique using a microplate reader is able to measure 96 samples simultaneously. Thus real samples, blanks, standards and replicates can be determined concurrently, ensuring the accuracy of this method. The process requires approximately 20 min per determination, compared with 5 days for the standard BOD method. This method gives a linear response (r 2 = 0.943) to OECD synthetic sewage samples from 50 to 430 mg L −1.

Rate of change of bod for milk in natural sea water

As part of a project to determine the fate of contaminated milk in the marine environment (Elliott et al ., 2001), the Biochemical Oxygen Demand (BOD) of unprocessed natural milk in sea water was followed in standard BOD bottles and in an open system. The best estimate for the BOD was ¨ 170,000 r mg - l m 1 although measurable effects could still be seen with dilutions up to one in a million. If incubated in the light, simulating summer conditions, the algae produced oxygen and offset some of the loss through bacterial degradation thereby reducing any slump in oxygen. There was also a "nutrient effect" where the presence of milk increased the oxygen production at low concentrations in sea water. In an open system akin to a slick being dispersed, the change in BOD was exponential after an initial activation period. The length of this activation period was greater in more concentrated mixtures of milk and sea water. These results have been utilised in a model to determine the best strategy for disposing of contaminated milk (Elliott et al ., 2001).

Ferricyanide mediated biochemical oxygen demand – development of a rapid biochemical oxygen demand assay

The use of an artificial electron acceptor in microbial respiration was investigated with a view to developing a rapid assay for biochemical oxygen demand (BOD). The use of ferricyanide resulted in a significant increase in the rate of the biochemical reaction and allowed for biodegradative conversion efficiencies similar to the 5-day BOD assay to be achieved in 1 h. The extent and rate of the ferricyanide mediated microbial reaction was determined by monitoring the concentration of the microbially produced ferrocyanide during or after incubation of microorganisms in the presence of ferricyanide and organic substrate. Spectrophotometry, potentiometry and amperometry using microelectrodes were evaluated as detection methods, with the latter providing the most convenient, stable and reproducible results. Experimental parameters investigated included incubation time, incubation temperature, microbial concentration, ferricyanide concentration and substrate concentration. In all cases, the results obtained were analogous to that expected in conventional aerobic microbial oxidation of organic material, with the major difference being the considerable increase in rate. The microorganisms used in this study were Escherichia coli and Pseudomonas putida. Results showed that while E. coli could successfully catabolise a standard BOD solution containing glucose and glutamic acid, its use for other substrates was limited. Preliminary investigations into the use of P. putida, however, showed significantly improved performance and demonstrated the promise of this approach for rapid BOD determinations.

Biodegradability and microbial toxicity of aircraft fuel system icing inhibitors

In a pollution prevention and chemical substitution effort, the U.S. Air Force and Navy formed a joint initiative to find safer, more environmentally acceptable jet fuel system icing inhibitors (FSII) for military aircraft. Standard biochemical oxygen demand (BOD) analysis and variations of the BOD procedure were used as simple screening tools to evaluate the potential for aquatic biodegradation and microbial toxicity of proposed FSIIs. This laboratory evaluation of biological properties allows prediction of the biotreatability of the chemicals in wastewater treatment plants, and their potential application as biocides at higher concentrations. The current FSII, diethylene glycol monomethyl ether (DiEGME) was evaluated along with two new candidate compounds, dipropylene glycol and glycerol formal. At a low concentration (3.5 mg/L), DiEGME exerted a BOD5 of about 27% of theoretical oxygen demand. Test concentrations of ≥7 mg/L had decreasing oxygen consumption rate and extent, typical of a material with potential aquatic microbial toxicity. Dipropylene glycol began to moderately degrade only after more than 3 weeks exposure to microorganisms obtained from raw sewage. Glycerol formal showed no signs of biodegradation during a 5-week test period. In a simple microbial toxicity test DiEGME was most toxic, dipropylene glycol was moderately toxic, and glycerol formal showed little toxicity. At low concentrations (7 mg/L), none of the chemicals significantly inhibited microbial activity (P=0.34). ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 383–390, 1999