Simultaneous nitrogen and carbon removal in a single chamber microbial fuel cell with a rotating biocathode

In this study, a single chamber microbial fuel cell (MFC) with a rotating biocathode is developed to simultaneously remove chemical oxygen demand (COD) and nitrogen accompanying current production. Under continuous regime with a feeding COD/N ratio of 5:1, removal efficiencies of total organic carbon (TOC) and total nitrogen (TN) were 85.7 ± 7.4% and 91.5 ± 7.2%, respectively, and a maximum power output of 585 mW m^?3 was yielded. In the batch tests, TN removal efficiencies for closed/open circuit were 82.1 ± 0.5% and 59.4 ± 3.3%, respectively. Cyclic voltammetry measurements demonstrated that the biocathode could efficiently catalyze nitrate reduction reaction. Autotrophic denitrification facilitated nitrogen removal using the electrode as electron donor. 16S rRNA-denaturing gradient gel electrophoresis (DGGE) was employed for community fingerprinting. At the biocathode the bacteria involved in nitrogen cycle predominated, of which the denitrifying bacteria were closely similar to Acidovorax sp. and/or Delftia sp. They were affiliated with the family Comamondaceae. The combination of rotating biological contactors with MFCs derives a promising opportunity for wastewater treatment with a low cost and high quality effluent.     

A pilot scale two-stage anaerobic digester treating food waste leachate (FWL): Performance and microbial structure analysis using pyrosequencing

Food waste leachate (FWL) from the food waste recycling facilities in Korea is a serious environmental problem. Much research was done on anaerobic digestion of FWL in a lab-scale; however, there is little information on a large scale anaerobic digestion system (ADS). In this study, a two-phase ADS in a pilot scale was operated using FWL and the ADS performance and microbial structure dynamics using pyrosequencing were investigated. The ADS was operated for 136 days using FWL containing a high concentration of volatile fatty acid (12,435 ± 2203 mg/L), exhibiting volatile acid (VS) removal efficiency of 74–89% and CH₄ yield of 0.39–0.85 Nm³/kg of reduced VS. The microbial structure at 76, 101, and 132 days indicated the methanogen population shift from acetoclastic methanogens (Methanosarcina and Methanosaeta) to hydrogenotrophic methanogens (Methanobacterium and Methanoculleus). The bacterial community also shifted to the taxa syntrophically related with hydrogenotrophic methanogens (Clostridia). The statistical analysis revealed the positive correlation of VS removal efficiency with Methanosarcina, but the negative correlation with Methanobacterium. The results presented here suggest that acetoclastic methanogens and their associated bacteria were more efficient for VS removal in the pilot scale ADS system, providing useful information for FWL treatment in a large scale ADS.     

Nitrogen transformation in the hybrid bioreactor landfill

The hybrid bioreactor landfill was promising in solid waste management. In the work, the nitrogen removal and nitrogen transformation in hybrid bioreactor landfill with sequencing of facultative anaerobic and aerobic conditions was explored. The result showed that the combination of facultative anaerobic and aerobic conditions in the hybrid bioreactor landfill was indeed effective in eliminating ammonia both from the leachate and the refuse thoroughly. About 72% of nitrogen was reduced from the landfilled fresh refuse through the operation of 357 days. At the end of the experiment, the concentrations of COD, ammonia, nitrate and TN in the leachate decreased to 399.2 mg l^?1, 20.6 mg N l^?1, 3.7 mg N l^?1 and 25.3 mg N l^?1, respectively.     

Application of polyethylene glycol immobilized Clostridium sp. LS2 for continuous hydrogen production from palm oil mill effluent in upflow anaerobic sludge blanket reactor

A novel polyethylene glycol (PEG) gel was fabricated and used as a carrier to immobilize Clostridium sp. LS2 for continuous hydrogen production in an upflow anaerobic sludge blanket (UASB) reactor. Palm oil mill effluent (POME) was used as the substrate carbon source. The optimal amount of PEG-immobilized cells for anaerobic hydrogen production was 12% (w/v) in the UASB reactor. The UASB reactor containing immobilized cells was operated at varying hydraulic retention times (HRT) that ranged from 24 to 6 h at 3.3 g chemical oxygen demand (COD)/L/h organic loading rate (OLR), or at OLRs that ranged from 1.6 to 6.6 at 12 h HRT. The best volumetric hydrogen production rate of 336 mL H₂/L/h (or 15.0 mmol/L/h) with a hydrogen yield of 0.35 L H₂/g COD_removed was obtained at a HRT of 12 h and an OLR of 5.0 g COD/L/h. The average hydrogen content of biogas and COD reduction were 52% and 62%, respectively. The major soluble metabolites during hydrogen fermentation were butyric acid followed by acetic acid. It is concluded that the PEG-immobilized cell system developed in this work has great potential for continuous hydrogen production from real wastewater (POME) using the UASB reactor.     

Removal of Cu(II) ions by biosorption onto powdered waste sludge (PWS) prior to biological treatment in an activated sludge unit: A statistical design approach

Biological treatment of synthetic wastewater containing Cu(II) ions was realized in an activated sludge unit with pre-adsorption of Cu(II) onto powdered waste sludge (PWS). Box-Behnken experimental design method was used to investigate Cu(II), chemical oxygen demand (COD) and toxicity removal performance of the activated sludge unit under different operating conditions. The independent variables were the solids retention time (SRT, 5–30 d), hydraulic residence time (HRT, 5–25 h), feed Cu(II) concentration (0–50 mg L^?1) and PWS loading rate (0–4 g h^?1) while percent Cu(II), COD, toxicity (TOX) removals and the sludge volume index (SVI) were the objective functions. The data were correlated with a quadratic response function (R² = 0.99). Cu(II), COD and toxicity removals increased with increasing PWS loading rate and SRT while decreasing with the increasing feed Cu(II) concentration and HRT. Optimum conditions resulting in maximum Cu(II), COD, toxicity removals and SVI values were found to be SRT of 30 d, HRT 15 h, PWS loading rate 3 g h^?1 and feed Cu(II) concentration of less than 30 mg L^?1.     

Application of anaerobic–aerobic sequential treatment system to real textile wastewater for color and COD removal

A sequential anaerobic packed column reactor and an activated sludge unit was operated continuously for treatment of a textile industry wastewater, in Izmir, Turkey. Metal sponges were used as support material in anaerobic unit and pre-activated textile dyestuff biodegrading PDW facultative anaerobic bacterial culture was immobilized on the support particles. Effects of hydraulic retention times in anaerobic unit (θ_H anaerobic = 12–72 h) and initial COD concentration (COD₀ = 3000 ± 200 mg/L and 800 ± 100 mg/L) at θ_H anaerobic = 24 h on color and COD removal performance of the system were investigated. The results indicated that over 85% decolorization and about 90% COD removal efficiency can be obtained up to θ_H anaerobic = 48 h but higher retention times causes decreasing in decolorization efficiency. Operating the system with real wastewater without adding any nutrients at θ_H anaerobic = 24 h resulted in over 60% improvement in color removal in studied wastewater compared to existing treatment plant.     

Microfiltration membrane performance in two-chamber microbial fuel cells

Proton exchange membranes (PEMs) are typically used in two-chamber microbial fuel cells (MFCs) to separate the anode and cathode chambers while allowing protons to pass between the chambers. However, PEMs such as Nafion are not cost-effective. To reduce the cost of MFCs, we examined the performances of cellulose acetate microfiltration membranes in a two-chamber microbial fuel cell using acetate. The internal resistance, the maximum power density and the coulombic efficiency (CE) of the microfiltration membrane MFC (MMMFC) were 263 Ω, 0.831 ± 0.016 W/m² and 38.5 ± 3.5%, respectively, in a fed-batch mode, while the corresponding values of the MFC using a PEM were 267 Ω, 0.872 ± 0.021 W/m² and 74.7 ± 4.6%, respectively. We further used the MMMFC for poultry wastewater treatment. The maximum power density of 0.746 ± 0.024 W/m² and CE of 35.3 ± 3.2% were achieved when the poultry wastewater containing 566 mg/L COD was used, removing 81.6 ± 6.6% of the COD. These results demonstrate microfiltration membranes, compared with PEMs, have a similar internal resistance and reduce pH gradient across the membrane. They parallel PEMs in maximum power density, while CE is much lower due to the oxygen and substrate diffusion. The MMMFC was effective for poultry wastewater treatment with high COD removal.     

A low power DC/DC booster circuit designed for microbial fuel cells

A DC/DC booster circuit was fabricated and tested for use with microbial fuel cells (MFCs) to increase the typical operational voltage (100–300 mV) to a maximum power of >3 V. In steady state, the low power DC/DC voltage booster circuit was sustainable, i.e., powered by the MFCs alone, but required an external power source to start (but not needed to maintain) the oscillator. The operating principle and function of each part of the circuit is described. A procedure for determining the optimal set of values for each component in the circuit was established. The performance of the circuit was demonstrated using three Shewanella oneidensis MR-1 based MFCs connected in parallel. The power consumption of the booster circuit was less than 20 μW, which was less than the output from the three MFCs. After the output capacitor was charged to 5 V, the booster circuit can be powered by the MFCs alone. Under normal operation, the MFCs were able to power the booster circuit and a light emitting diode.     

Isolation,identification of sludge-lysing strain and its utilization in thermophilic aerobic digestion for waste activated sludge

A strain of sludge-lysing bacteria was isolated from waste activated sludge (WAS) in this study. The result of 16S rRNA gene analysis demonstrated that it was a species of new genus Brevibacillus (named Brevibacillus sp. KH3). The strain could release the protease with molecule weight of about 40 kDa which could enhance the efficiency of sludge thermophilic aerobic digestion. During the sterilized sludge digestion experiment inoculated with Brevibacillus sp. KH3, the maximum protease activity was 0.41 U/ml at pH 8 and 50 °C, and maximum TSS removal ratio achieved 32.8% after 120 h digestion at pH 8 and 50 °C. In the case of un-sterilized sludge digestion inoculated with Brevibacillus sp. KH3, TSS removal ratio in inoculated-group was 54.8%, increasing at 11.86% compared with un-inoculation (46.2%). The result demonstrated that inoculation of Brevibacillus sp. KH3 could help to degrade the EPS and promote the collapse of cells and inhibit the growth of certain kinds of microorganisms. It indicated that Brevibacillus sp. KH3 strain had a high potential to enhance WAS-degradation efficiency in thermophilic aerobic digestion.     

Spatial and temporal changes in the microbial community in an anaerobic swine waste treatment lagoon

Microorganisms are central to both the beneficial (organic degradation, nutrient removal, biogas production) and detrimental (odor production, pathogen contamination) effects of swine waste storage systems. In this study, both quantitative (real-time polymerase chain reaction) and qualitative (denaturing gradient gel electrophoresis, cloning, sequence analysis) molecular analyses were used to track spatial and temporal changes in the microbial community of swine slurry from a 0.4 ha anaerobic lagoon. The lagoon, located in a region of western Kentucky which has a humid, subtropical environment, was sampled on a monthly basis (n = 10) over a period of one year at four different depths (top, 51 cm from the top, 152 cm from the top, and bottom >198 cm). The concentration and diversity of Bacteroides sp. was seasonal (up to 90% decrease between March and June). Hespellia sp. and other clostridial species, on the other hand, were endemic in the slurry (concentrations up to 1.0 × 10⁷ cells mL^?1 slurry) regardless of time of the year or lagoon depth. Results suggest that there were seasonal effects on the microbial community in the swine lagoon, while the effect of depth was not as pronounced. Seasonal changes in the microbial community in stored wastes may be (directly or indirectly) correlated with changes in malodor emissions from lagoons.     

Effect of sewage sludge treatment and additional aerobic post-stabilization revealed by infrared spectroscopy and multivariate data analysis

Sewage sludge samples representing different stages during waste water and sewage sludge treatment were collected at four Austrian municipal waste water treatment plants. Changes of sludge composition are reflected by a specific infrared spectroscopic pattern. Anaerobically digested sludge was subjected to aeration in lab-scale reactors in order to find out if post-aeration after anaerobic digestion provides enhanced organic matter degradation and stabilization. Spectral data were evaluated by means of multivariate statistics. Similar spectral characteristics of sludge degradation stages were visualized by principal component analysis. The effect of additional aerobic treatment of anaerobically stabilized sludge was revealed by discriminant analysis that distinguishes additionally aerated sludge from all the other degradation stages of sludge because of changes in the spectral pattern by increasing stabilization. Based on partial least squares regression (PLSR) a correlation coefficient of R² = 0.91 was found between spectral characteristics and the chemical oxygen demand (COD).     

Isolation and bioelectrochemical characterization of novel fungal sources with oxidasic activity applied in situ for the cathodic oxygen reduction in microbial fuel cells

Brazilian filamentous fungi Rhizopus sp. (SIS-31), Aspergillus sp. (SIS-18) and Penicillium sp. (SIS-21), sources of oxidases were isolated from Caatinga's soils and applied during the in situ cathodic oxygen reduction in fuel cells. All strains were cultivated in submerged cultures using an optimized saline medium enriched with 10 g L⁻¹ of glucose, 3.0 g L⁻¹ of peptone and 0.0005 g L⁻¹ of CuSO₄ as enzyme inducer. Parameters of oxidase activity, glucose consumption and microbial growth were evaluated. In-cell experiments evaluated by chronoamperometry were performed and two different electrode compositions were also compared. Maximum current densities of 125.7, 98.7 and 11.5 μA cm⁻² were observed before 24 h and coulombic efficiencies of 56.5, 46.5 and 23.8% were obtained for SIS-31, SIS-21 and SIS-18, respectively. Conversely, maximum power outputs of 328.73, 288.80 and 197.77 mW m⁻³ were observed for SIS-18, SIS-21 and SIS-31, respectively. This work provides the primary experimental evidences that fungi isolated from the Caatinga region in Brazil can serve as efficient biocatalysts during the oxygen reduction in air-cathodes to improve electricity generation in MFCs.     

Granular activated carbon single-chamber microbial fuel cells (GAC-SCMFCs): A design suitable for large-scale wastewater treatment processes

As an emerging biotechnology capable of removing contaminants and producing electricity, microbial fuel cells (MFCs) hold a promising future in wastewater treatment. However, several main problems, including the high internal resistance (R_in), low power output, expensive material, and complicated configuration have severely hindered the large-scale application of MFCs. The study targeted these challenges by developing a novel MFC system, granular activated carbon single-chamber MFC, termed as GAC-SCMFC. The batch tests showed that GAC was a good substitute for carbon cloth and GAC-SCMFCs generated high and stable power outputs compared with the traditional two-chamber MFCs (2CMFCs). Critical operational parameters (i.e. wastewater substrate concentrations, GAC amount, electrode distance) affecting the performance of GAC-SCMFCs were examined at different levels. The results showed that the R_in gradually decreased from 60 Ω to 45 Ω and the power output increased from 0.2 W/m³ to 1.2 W/m³ when the substrate concentrations increased from 100 mg/L to 850 mg/L. However, at high concentrations of 1000–1500 mg/L, the power output leveled off. The R_in of MFCs decreased 50% when the electrode distance was reduced from 7.5 cm to 1 cm. The highest power was achieved at the electrode distance of 2 cm. The power generation increased with more GAC being added in MFCs due to the higher amount of biomass attached. Finally, the multi-anode GAC-SCMFCs were developed to effectively collect the electrons generated in the GAC bed. The results showed that the current was split among the multiple anodes, and the cathode was the limiting factor in the power production of GAC-SCMFCs.     

Characterization of aerobic granular sludge at various organic loading rates

Aerobic granular sludge was cultivated from activated sludge with two types of supports, namely bivalve shell carrier (BSC) and anaerobic granules (ANG). Granules were characterized at different organic loading rates (OLRs) ranging from 2.5 to 15 kg COD/m³ d and these granules were observed to withstand high OLRs. The physico-chemical characteristics of the aerobic granules were better than those of seed sludge. The granule formation with ANG support was found to be similar to that of non-support cultivation, i.e. formation from activated sludge only. By contrast, BSC support showed better performance in terms of faster settleability, compactness and especially resistance against organic shock loading. It also enabled self-cleaning effect by removing biofilm attached on the reactor wall during the start-up phase resulting rapid granulation process.     

Relationship between microbial activity and microbial community structure in six full-scale anaerobic digesters

High activity levels and balanced anaerobic microbial communities are necessary to attain proper anaerobic digestion performance. Therefore, this work was focused on the kinetic performance and the microbial community structure of six full-scale anaerobic digesters and one lab-scale co-digester. Hydrolytic (0.6–3.5 g COD g^?1 VSS d^?1) and methanogenic (0.01–0.84 g COD g^?1 VSS d^?1) activities depended on the type of biomass, whereas no significant differences were observed among the acidogenic activities (1.5–2.2 g COD g^?1 VSS d^?1). In most cases, the higher the hydrolytic and the methanogenic activity, the higher the Bacteroidetes and Archaea percentages, respectively, in the biomasses. Hydrogenotrophic methanogenic activity was always higher than acetoclastic methanogenic activity, and the highest values were achieved in those biomasses with lower percentages of Methanosaeta. In sum, the combination of molecular tools with activity tests seems to be essential for a better characterization of anaerobic biomasses.     

Thermophilic treatment of bulk drug pharmaceutical industrial wastewaters by using hybrid up flow anaerobic sludge blanket reactor

The hybrid up flow anaerobic sludge blanket reactor was evaluated for efficacy in reduction of chemical oxygen demand (COD) and biochemical oxygen demand (BOD) of bulk drug pharmaceutical wastewater under different operational conditions. The start-up of the reactor feed came entirely with glucose, applied at an organic loading rate (OLR) 1 kg COD/m³ d. Then the reactor was studied at different OLRs ranging from 2 to 11 kg COD/m³ d with pharmaceutical wastewater. The optimum OLR was found to be 9 kg COD/m³ d, where we found 65–75% COD and 80–94% of BOD reduction with biogas production containing 60–70% of methane and specific methanogenic activity was 320 ml CH₄/g-VSS d. By the characterization studies of effluent using GC–MS, the hazardous compounds like phenol, l,2-methoxy phenol, 2,4,6-trichloro phenol, dibutyl phthalate, 1-bromo naphthalene, carbamazepine and antipyrine were present. After the treatment, these compounds degraded almost completely except carbamazepine. Thermophilic methanothrix and methanosaetae like bacteria are present in the granular sludge.     

Distribution of anammox bacteria in domestic WWTPs and their enrichments evaluated by real-time quantitative PCR

Enrichment of anaerobic ammonium oxidation (anammox) bacteria using five activated sludges in three domestic wastewater treatment plants (WWTPs) were processed in a short term of 70 days and evaluated by real-time quantitative PCR (RTQ-PCR). Before the enrichment, building phylogenetic trees of Planctomycetes phylum in four reactors of sequencing batch reactor (SBR), anoxic and oxic reactors of anaerobic–anoxic–oxic (A2O) process, and rotating biological contactor (RBC) revealed six groups of distantly relative genera of Planctomyces, Pirellula, Gemmata, Isophaera, Candidatus and putative anammox bacteria. All clones of Candidatus sp. were affiliated with anammox bacteria and the majority of anammox clones were related to Planctomycete KSU-1 (AB057453). The discovery of anammox bacteria in raw activated sludges provided a partial rationale for the utilization of activated sludge as a seeding source of the anammox process. To verify the activity of anammox bacteria in the activated sludges, enrichment cultivations were conducted using SBRs. The enrichment of anammox bacteria resulted in the significant anammox activity of three samples. Quantification of 16S rRNA gene of anammox bacteria using RTQ-PCR showed the highest concentration of anammox bacteria of 2.48 ± 0.22 × 10⁹ copies of 16S rRNA gene/mg-volatile suspended solids (VSS), which was the same order of magnitude as that of the referential granular anammox sludge, 6.23 ± 0.59 × 10⁹ copies of 16S rRNA gene/mg-VSS, taken from an anammox upflow anaerobic sludge blanket (UASB) reactor. The doubling time of anammox bacteria enriched in this study was 1.18 days. The growth yield of anammox bacteria enriched in this study was 4.75 ± 0.57 × 10⁶ copies of 16S rRNA gene/mg of ammonium- and nitrite-nitrogen, which was similar to 4.50 ± 0.61 × 10⁶ copies of 16S rRNA gene/mg of ammonium- and nitrite-nitrogen for the referential anammox sludge. Substrate uptake rates of three successful enrichments at the end of the enrichment were comparable to those of granular and suspended anammox sludges. Rapid enrichment of anammox bacteria using activated sludge could offer an alternative method for obtaining a large volume of seeding anammox sludge.     

Effects of preservation procedures of rumen inoculum on in vitro microbial diversity and fermentation

Sheep rumen contents were used as inoculum for an in vitro semi-continuous incubation system to study whether preservation method affects microbial fermentation pattern. Rumen fluid was filtered and either used immediately as inoculum (CTL) or dispensed into 110 mm × 16 mm tubes, that were stored refrigerated at 6 °C for 4 h (REF) or frozen at ?20 °C (FRZ), frozen in liquid N (FLN) or added with 0.04 glycerol and frozen in liquid N (FGL) for 48 h. Frozen inocula were thawed at 39 °C for 2 min before use (16 ml per bottle). Two 24 h incubations with four bottles per treatment were completed. The microbial utilisation of added glycerol after thawing in FGL increased total gas production (P<0.05) and 24 h volatile fatty acid (VFA) production (P<0.05), and also increased propionate and butyrate proportions at the expense of acetate. The other freezing inocula (i.e., FLN and FRZ) reduced the rate of gas production (as ml/g dry matter per hour), compared with CTL in the first 2 and 4 h of incubation (P<0.05), but this was compensated by increased fermentation at 8 and 12 h, respectively. Differences in gas production did not manifest a different VFA pattern at either 6 or 24 h incubation. Bacterial diversity was slightly affected by the preservation process, and the similarity index between untreated inocula and the 24 h incubated CTL samples was 0.690–0.724. Similarity between bacterial communities in FRZ and FLN with that in CTL after incubation was 0.678. The freezing preservation method of rumen inocula for subsequent in vitro gas production studies does not affect microbial fermentation pattern or bacterial biodiversity, provided that processing is rapid enough by using a high surface to volume ratio. Freezing in liquid N is more appropriate than at ?20 °C.     

Improvement of sludge anaerobic degradability by combined electro-flotation and electro-oxidation treatment

Recently, bioenergy recovery from sludge biomass has attracted increasing attention due to the high demand for renewable energy resources. In order to enhance methane production from sludge biomass, electrochemical treatment can be used as a novel and efficient pretreatment for the hydrolysis of sludge biomass. In this study, a combined electro-flotation and electro-oxidation pretreatment was employed to improve the anaerobic degradability of sludge biomass. Electro-flotation was efficient in separating flocs in the mixed liquor and led to a sludge volume reduction greater than 60% after 10 min of operation at a current density of 4.72 mA cm⁻². Electro-oxidation using IrO₂/Ti anode was performed to improve the anaerobic degradability of sludge and resulted in a 30% increase in COD solubilization after 30 min of operation at current density of 9.45 mA cm⁻². The factors affecting electro-oxidation, i.e. the gap width between anode and cathode, current density and applied voltage, were investigated to optimize the operating conditions. A biochemical methane potential assay demonstrated that the anaerobic biodegradability of sludge was enhanced by combined electro-flotation and electro-oxidation pretreatment.     

Urine nitrification with a synthetic microbial community

During long-term extra-terrestrial missions, food is limited and waste is generated. By recycling valuable nutrients from this waste via regenerative life support systems, food can be produced in space. Astronauts’ urine can, for instance, be nitrified by micro-organisms into a liquid nitrate fertilizer for plant growth in space. Due to stringent conditions in space, microbial communities need to be be defined (gnotobiotic); therefore, synthetic rather than mixed microbial communities are preferred. For urine nitrification, synthetic communities face challenges, such as from salinity, ureolysis, and organics.In this study, a synthetic microbial community containing an AOB (Nitrosomonas europaea), NOB (Nitrobacter winogradskyi), and three ureolytic heterotrophs (Pseudomonas fluorescens, Acidovorax delafieldii, and Delftia acidovorans) was compiled and evaluated for these challenges. In reactor 1, salt adaptation of the ammonium-fed AOB and NOB co-culture was possible up to 45 mS cm⁻¹, which resembled undiluted nitrified urine, while maintaining a 44 ± 10 mg NH₄⁺–N L⁻¹ d⁻¹ removal rate. In reactor 2, the nitrifiers and ureolytic heterotrophs were fed with urine and achieved a 15 ± 6 mg NO₃⁻–N L⁻¹ d⁻¹ production rate for 1% and 10% synthetic and fresh real urine, respectively. Batch activity tests with this community using fresh real urine even reached 29 ± 3 mg N L⁻¹ d⁻¹. Organics removal in the reactor (69 ± 15%) should be optimized to generate a nitrate fertilizer for future space applications.