Denitrification of wastewater containing high nitrate and calcium concentrations

Design and applications of Ti nano-electrode for denitrification of groundwater

In the present study, a Ti-nano-electrode was fabricated for electrochemical denitrification. Response surface methodology (RSM) was utilized for the optimization of the factors that influence the production of Ti nano-electrodes. Box-Behnken design was applied to develop mathematical models for predicting the best electrochemical nitrate removal geometry. Parameters interacting together can be identified in this typical electrochemical removal process. A correlation coefficient R² > 0.90 for the mathematical model was predicted to be a high correlation between observed and predicted values. The optimal NH₄F concentration, oxidation time and oxidation voltage for preparation of Ti nano-electrode in the present experiment are 0.03 wt%, 34.61 min and 6.31 V, respectively. In this case, the increase in the nitrate reduction efficiency was more d (105%) than that from an untreated electrode, and energy consumption was 4.45 × 10^-4 kWh.

Segregating metabolic processes into different microbial cells accelerates the consumption of inhibitory substrates

Different microbial cell types typically specialize at performing different metabolic processes. A canonical example is substrate cross-feeding, where one cell type consumes a primary substrate into an intermediate and another cell type consumes the intermediate. While substrate cross-feeding is widely observed, its consequences on ecosystem processes is often unclear. How does substrate cross-feeding affect the rate or extent of substrate consumption? We hypothesized that substrate cross-feeding eliminates competition between different enzymes and reduces the accumulation of growth-inhibiting intermediates, thus accelerating substrate consumption. We tested this hypothesis using isogenic mutants of the bacterium Pseudomonas stutzeri that either completely consume nitrate to dinitrogen gas or cross-feed the intermediate nitrite. We demonstrate that nitrite cross-feeding eliminates inter-enzyme competition and, in turn, reduces nitrite accumulation. We further demonstrate that nitrite cross-feeding accelerates substrate consumption, but only when nitrite has growth-inhibiting effects. Knowledge about inter-enzyme competition and the inhibitory effects of intermediates could therefore be important for deciding how to best segregate different metabolic processes into different microbial cell types to optimize a desired biotransformation.

Catalytic reduction of nitrate in secondary effluent of wastewater treatment plants by Fe(0) and Pd-Cu/γ-Al2O3

Total nitrogen, in which NO3(-) is dominant in the effluent of most wastewater treatment plants, cannot meet the requirements of the Chinese wastewater discharge standard (<15 mg/L), making nitrate (NO3(-)) elimination attract considerable attention. In this study, reductant iron (Fe(0)) and γ-Al2O3 supported palladium-copper bimetallic catalysts (Pd-Cu/γ-Al2O3) were innovatively used for the chemical catalytic reduction of nitrate in wastewater. A series of specific operational conditions (such as mass ratio of Pd:Cu, catalyst amounts, reaction time and pH of solution) were optimized for nitrate reduction in the artificial solution, and then the selected optimal conditions were further applied for investigating the nitrate elimination of secondary effluent of a wastewater treatment plant in Beijing, China. Results indicated that a better catalytic performance (74% of nitrate removal and 62% of N2 selectivity) could be obtained under the optimal condition: 5 g/L Fe(0), 3:1 mass ratio (Pd:Cu), 4 g/L catalyst, 2 h reaction time and pH 5.1. It is noteworthy to point out that nitrogen gas (N2) predominated in the byproducts without another system to treat ammonium and nitrite. Therefore, the chemical catalytic reduction combining Fe(0) with Pd-Cu/γ-Al2O3 could be regarded as a better alternative for nitrate removal in wastewater treatment.

Removal Efficiency of Faecal Indicator Organisms, Nutrients and Heavy Metals from a Peri-Urban Wastewater Treatment Plant in Thohoyandou, Limpopo Province, South Africa

Wastewater treatment facilities are known sources of fresh water pollution. This study was carried out from January to June 2014 to assess the reduction efficiency of some selected contaminants in the Thohoyandou wastewater treatment plant (WWTP). The pH and electrical conductivity of the effluent fell within the South African wastewater discharge guidelines. The WWTP showed the chemical oxygen demand reduction efficiency required by the Department of Water Affairs (DWA) guidelines of 75 mg/L for the months of April and June, although it was below this standard in March and May. Free chlorine concentration varied between 0.26–0.96 mg/L and exceeded the DWA guideline value of 0.25 mg/L. The concentration of nitrate-nitrogen (NO₃⁻ N) in the influent and effluent varied between 0.499–2.31 mg/L and 7.545–19.413 mg/L, respectively. The concentration of NO₃⁻ N in the effluent complied with DWA effluent discharge standard of 15 mg/L, except in April and May. Phosphate concentrations in the influent and effluent were in the ranges of 0.552–42.646 mg/L and 1.572–32.554 mg/L, respectively. The WWTP showed reduction efficiencies of E. coli and Enterococci during some sampling periods but the level found in the effluent exceeded the recommended guideline value of 1000 cfu/100 mL for faecal indicator organisms in wastewater effluents. Consistent removal efficiencies were observed for Al (32–74%), Fe (7–32%) and Zn (24–94%) in most of the sampling months. In conclusion, the Thohoyandou WWTP is inefficient in treating wastewater to the acceptable quality before discharge.

Metagenomic insights into Cr(VI) effect on microbial communities and functional genes of an expanded granular sludge bed reactor treating high-nitrate wastewater

In this study, a lab-scale expanded granular sludge bed reactor was continuously operated to treat high-nitrate wastewater containing different concentrations of hexavalent chromium (Cr(VI)). Nearly complete nitrate removal was achieved even at 120 mg/L influent Cr(VI). Pyrosequencing of 16S rRNA gene showed that Cr(VI) decreased the biodiversity of the bacterial community and potential denitrifiers. Proteobacteria dominated in the bioreactor, and Betaproteobacteria had increased abundance after Cr(VI) feeding. Thauera and Halomonas were the two predominant genera in the bioreactor fed with Cr(VI), demonstrating opposite responses to the Cr(VI) stress. Metagenomic analysis indicated that Cr(VI) feeding posed no obvious effect on the overall function of the bacterial community, but altered the abundance of specific denitrifying genes, which was evidenced by quantitative real time PCR. This study revealed that Halomonas mainly contributed to the denitrification under no or low Cr(VI) stress, while Thauera played a more important role under high Cr(VI) stress.

Nitrate levels modulate the abundance of Paracoccus sp. in a biofilm community

Conditions required to enhance a particular species efficient in degradative capabilities is very useful in wastewater treatment processes. Paracoccus sp. is known to efficiently reduce nitrogen oxides (NOx) due to the branched denitrification pathway. Individual-based simulations showed that the relative fitness of Paracoccus sp. to Pseudomonas sp. increased significantly with nitrate levels above 5 mM. Spatial structure of the biofilm showed substantially less nitrite levels in the areas of Paracoccus sp. dominance. The simulation was validated in a laboratory reactor harboring biofilm community by fluorescent in situ hybridization, which showed that increasing nitrate levels enhanced the abundance of Paracoccus sp. Different levels of NOx did not display any significant effect on biofilm formation of Paracoccus sp., unlike several other bacteria. This study shows that the attribute of Paracoccus sp. to tolerate and efficiently reduce NOx is conferring a fitness payoff to the organism at high concentrations of nitrate in a multispecies biofilm community.

Advanced nitrogen removal from wastewater by combining anammox with partial denitrification

The anammox (anaerobic ammonium oxidation) process has attracted much attention for its cost-saving. However, excess nitrate is usually produced which should be further treated. In this study, an innovative process combined anammox with partial denitrification (nitrate→nitrite) was proposed for advanced nitrogen removal in two sequencing batch reactors (SBRs). The nitrate produced in anammox-SBR (ASBR) was fed into partial denitrification-SBR (DSBR), in which the nitrate was reduced to nitrite, and then removed by backflow of the nitrite to ASBR for secondary anammox process. Results showed that ∼80% nitrate in the effluent of previous anammox was converted to nitrite in DSBR. And the maximum nitrogen removal efficiency (NRE) of 94.06% was obtained with total nitrogen (TN) in the effluent of 10.98 mg/L in average. It indicated that desired effluent quality could be achieved, and the advanced nitrogen removal performance was attributed to the successful achievement of partial denitrification.

Full-scale blending treatment of fresh MSWI leachate with municipal wastewater in a wastewater treatment plant

Fresh leachate, generated in municipal solid waste incineration (MSWI) plants, contains various pollutants with extremely high strength organics, which usually requires expensive and complex treatment processes. This study investigated the feasibility of blending treatment of MSWI leachate with municipal wastewater. Fresh MSWI leachate was pretreated by coagulation-flocculation with FeCl3 2 g/L and CaO 25 g/L, plate-and-frame filter press, followed by ammonia stripping at pH above 12. After that, blending treatment was carried out in a full-scale municipal wastewater treatment plant (WWTP) for approximately 3 months. Different operational modes consisting of different pretreated leachate and methanol addition levels were tested, and their performances were evaluated. Results showed that throughout the experimental period, monitored parameters in the WWTP effluent, including COD (<60 mg/L), BOD5 (<20 mg/L), ammonium (<8 mg/L), phosphorus (<1.5 mg/L) and heavy metals, generally complied with the Chinese sewage discharged standard. Under the experimental conditions, a certain amount of methanol was needed to fulfill TN removal. An estimation of the operation cost revealed that the expenditure of blending treatment was much lower than the total costs of respective treatment of MSWI leachate and municipal wastewater. The outcomes indicated that blending treatment could not only improve the treatability of the MSWI leachate, but also reduce the treatment cost of the two different wastewaters.

Nitrate removal by Fe0/Pd/Cu nano-composite in groundwater

Nitrate pollution in groundwater shows a great threat to the safety of drinking water. Chemical reduction by zero-valent iron is being considered as a promising technique for nitrate removal from contaminated groundwater. In this paper, Fe0/Pd/Cu nano-composites were prepared by the liquid-phase reduction method, and batch experiments of nitrate reduction by the prepared Fe0/Pd/Cu nano-composites under various operating conditions were carried out. It has been found that nano-Fe0/Pd/Cu composites processed dual functions: catalytic reduction and chemical reduction. The introduction of Pd and Cu not only improved nitrate removal rate, but also reduced the generation of ammonia. Nitrate removal rate was affected by the amount of Fe0/Pd/Cu, initial nitrate concentration, solution pH, dissolved oxygen (DO), reaction temperature, the presence of anions, and organic pollutant. Moreover, nitrate reduction by Fe0/Pd/Cu composites followed the pseudo-first-order reaction kinetics. The removal rate of nitrate and total nitrogen were about 85% and 40.8%, respectively, under the reaction condition of Fe-6.0%Pd-3.0%Cu amount of 0.25 g/L, pH value of 7.1, DO of 0.42 mg/L, and initial nitrate concentration of 100 mg/L. Compared with the previous studies with Fe0 alone or Fe-Cu, nano-Fe-6%Pd-3%Cu composites showed a better selectivity to N2.

The influence of slaughterhouse waste on fermentative H2 production from food waste: preliminary results

The aim of this study was to evaluate the influence of slaughterhouse waste (SHW; essentially the skin, fats, and meat waste of pork, poultry, and beef) in a fermentative co-digestion process for H2 production from pre-selected organic waste taken from a refectory (food waste [FW]). Batch tests under mesophilic conditions were conducted in stirred reactors filled with different proportions of FW and SHW. The addition of 60% and 70% SHW to a mixture of SHW and FW improved H2 production compared to that in FW only, reaching H2-production yields of 145 and 109 ml g VS 0(-1), respectively, which are 1.5-2 times higher than that obtained with FW alone. Although the SHW ensured a more stable fermentative process due to its high buffering capacity, a depletion of H2 production occurred when SHW fraction was higher than 70%. Above this percentage, the formation of foam and aggregated material created non-homogenous conditions of digestion. Additionally, the increasing amount of SHW in the reactors may lead to an accumulation of long chain fatty acids (LCFAs), which are potentially toxic for anaerobic microorganisms and may inhibit the normal evolution of the fermentative process.

Start-up and performance of a hybrid anoxic reactor for biological denitrification

This study was aimed at denitrification of wastewater using a hybrid anoxic reactor (HAR), which uses self immobilized microbial granules under fluidized condition. Granulation of the denitrifying biomass was studied in the HAR with methanol and acetate as carbon sources. It was observed that by the end of 15 day almost spherical granules with a settling velocity of 1.5 cm/s and a mean diameter of 0.5 mm were produced. By stepwise increment of the influent nitrate concentration, the removal rate reached 740 g NO3-N/m3 day with a removal efficiency of almost 100% at a hydraulic retention time of 6 h or higher. For complete denitrification, the ratio of the organic substrate required to amount of nitrate nitrogen removed was as low as 2.2 g COD/g NO3-N. The study was then extended to denitrifying a nitrified toxic industrial effluent. Denitrification was on par with the synthetic wastewater and efficiency of more than 95% was achieved.

Biological Denitrification of High Nitrate Processing Wastewaters from Explosives Production Plant

Wastewater samples originating from an explosives production plant (3,000 mg N l(-1) nitrate, 4.8 mg l(-1) nitroglycerin, 1.9 mg l(-1) nitroglycol and 1,200 mg l(-1) chemical oxygen demand) were subjected to biological purification. An attempt to completely remove nitrate and to decrease the chemical oxygen demand was carried out under anaerobic conditions. A soil isolated microbial consortium capable of biodegrading various organic compounds and reduce nitrate to atmospheric nitrogen under anaerobic conditions was used. Complete removal of nitrates with simultaneous elimination of nitroglycerin and ethylene glycol dinitrate (nitroglycol) was achieved as a result of the conducted research. Specific nitrate reduction rate was estimated at 12.3 mg N g(-1) VSS h(-1). Toxicity of wastewater samples during the denitrification process was studied by measuring the activity of dehydrogenases in the activated sludge. Mutagenicity was determined by employing the Ames test. The maximum mutagenic activity did not exceed 0.5. The obtained results suggest that the studied wastewater samples did not exhibit mutagenic properties.

Denitrification capacity of a landfilled refuse in response to the variations of COD/NO3--N in the injected leachate

Effects of different chemical oxygen demand (COD) to nitrate concentration ratios in the injected leachate on the denitrification capacity of landfilled municipal solid waste were evaluated. Results showed that the 6-year-old refuse possessed high denitrification capacity. The nitrate reduction rate increased with the increasing COD concentration in the injected leachate. When the initial COD concentration increased to 6500 mg l(-1), nitrate reduction rate could reach up to 6.85 mg NO3--N l(-1) h(-1). At the initial biodegradable COD/NO3--N ratio lower than the stoichiometric ratio of heterotrophic denitrification, autotrophic bacteria was the dominant microbial communities for denitrification. With the increase of COD/NO3--N ratio, the primary functional denitrifier would shift from autotrophic Thiobacillus denitrificans to heterotrophic Azoarcus tolulyticus. These results suggested that the initial biodegradable COD/NO3--N ratio in the injected leachate should be adjusted to higher than 6.0 for rapid in situ denitrification of 500 mg NO3--Nl(-1).

Acetate and propionate impact on the methanogenesis of landfill leachate and the reduction of clogging components

Synthetic leachate with different initial concentrations of acetate (500-2500 mg HAc/L) and propionate (500-3500 mg HPr/L) was treated with active biomass acclimated to landfill leachate under anaerobic mesophilic conditions for 72 h. Methanogenesis was observed within all samples during the first 48 h. The greatest removal of acetate (80-100%) and propionate (15-35%) was achieved in tests with initial concentrations ranging from 1500 to 190 0mg HAc/L and from 1000 to 1800mgHPr/L. Concurrent with the removal of acids, pH increased between 0.3 and 0.45 units, to above the threshold pH for precipitation of CaCO(3). Therefore, some 50-70% of dissolved Ca(2+) was removed from solution. This study suggests that by using an equalization tank (prior to the anaerobic digester) to maintain the acetate and propionate concentrations to within their optimum range would help to alleviate clogging through the removal of dissolved Ca(2+) and maximizing CH(4) production.

Evaluation of natural zeolite as microorganism support medium in nitrifying batch reactors: influence of zeolite particle size

An evaluation of natural zeolite as a microorganism carrier in nitrifying reactors operated in batch mode was carried out. Specifically, the influence of zeolite particle sizes of 0.5, 1.0 and 2.0 mm in diameter on microorganism adherence to zeolite, ammonium adsorption capacity and the identification of microbial populations were assessed. The greatest amount of total biomass adhered was observed for a zeolite particle size of 1 mm (0.289 g) which was achieved on the 12th day of operation. The highest ammonium adsorption capacity was observed for a zeolite particle size of 0.5 mm, which was 64% and 31% higher than that observed for particle sizes of 1.0 and 2.0 mm, respectively. The maximum de-sorption values were also found for a zeolite particle size of 0.5 mm, although when equilibrium was reached the ammonium concentrations were similar to those observed for a zeolite particle size of 1.0 mm. It was also found that the experimental data on ammonium adsorption fitted very well to the Freundlich isotherm for the three particle sizes studied. Finally, the nitrifying reactors showed similar microbial populations independently of the particle size used as microorganism carrier. The dominant bacterial community was Gammaproteobacteria making up 80% of the total population found. Betaproteobacteria were also identified and made up 12% approx. of the total population. Ammonium Oxidant Betaproteobacteria and Nitrobacter were also detected.

Assessment of denitrifying bacterial composition in activated sludge

The abundance and structure of denitrifying bacterial community in different activated sludge samples were assessed, where the abundance of denitrifying functional genes showed nirS in the range of 10(4)-10(5), nosZ with 10(4)-10(6) and 16S rRNA gene in the range 10(9)-10(10) copy number per ml of sludge. The culturable approach revealed Pseudomonas sp. and Alcaligenes sp. to be numerically high, whereas culture independent method showed betaproteobacteria to dominate the sludge samples. Comamonas sp. and Pseudomonas fluorescens isolates showed efficient denitrification, while Pseudomonas mendocina, Pseudomonas stutzeri and Brevundimonas diminuta accumulated nitrite during denitrification. Numerically dominant RFLP OTUs of the nosZ gene from the fertilizer factory sludge samples clustered with the known isolates of betaproteobacteria. The data also suggests the presence of different truncated denitrifiers with high numbers in sludge habitat.

Biological removal of nitrate by an oil reservoir culture capable of autotrophic and heterotrophic activities: kinetic evaluation and modeling of heterotrophic process

Kinetics of heterotrophic denitrification was investigated using an oil reservoir culture with the ability to function under both autotrophic and heterotrophic conditions. In the batch system nitrate at concentrations up to 30 mM did not influence the kinetics but with 50mM slower growth and removal rates were observed. A kinetic model, representing the denitrification as reduction of nitrate to nitrite, and subsequent reduction of nitrite to nitrous oxides and nitrogen gas was developed. The value of various kinetic coefficients, including maximum specific growth rate, saturation constant, yield and activation energy for nitrate and nitrite reductions were determined by fitting the experimental data into the developed model. In continuous bioreactors operated with 10 or 30 mM nitrate, complete removal of nitrate (no residual nitrite) and linear dependency between nitrate loading and removal rates were observed for loading rates up to 0.21 and 0.58 mM h(-1), respectively. The highest removal rates of 0.31 and 0.94 mM h(-1) observed at loading rates of 0.42 mM h(-1) and 1.26 mM h(-1), with corresponding removal percentages of nitrate and total nitrogen being 75.4, 54.4%, and 74.4 and 17.9%, respectively. Developed kinetic model predicted the performance of the continuous bioreactors with accuracy.

Design and monitoring of horizontal subsurface-flow constructed wetlands for treating nursery leachates

Nursery leachates usually contain high concentrations of nitrates, phosphorus and potassium, so discharging them into the environment often causes pollution. Single-stage or two-stage horizontal subsurface flow constructed wetlands (HSSCW) filled with different substrates were designed to evaluate the effect and evolution over time of the removal of nitrogen and other nutrients contained in nursery leachates. The addition of sodium acetate to achieve a C:NO(3)(-)-N ratio of 3:1 was sufficient to reach complete denitrification in all HSSCW. The removal rate of nitrate was high throughout the operation period (over 98%). Nevertheless, the removal rate of ammonium decreased about halfway through the operation. Removal of the COD was enhanced by the use of two-stage HSSCW. In general, the substrates and the number of stages of the wetlands did not affect the removal of nitrogen, total phosphorus and potassium.

The effect of calcium on the treatment of fresh leachate in an expanded granular sludge bed bioreactor

This research investigated the calcium effect on the anaerobic treatment of fresh leachate in an expanded granular sludge bed (EGSB) bioreactor under mesophilic conditions. The observations show that the bioreactor, inoculated with anaerobic granular sludge, can be started up only in about 40 days for the treatment of calcium-containing fresh leachate with chemical oxygen demand (COD) removal efficiency above 90% and organic loading rate up to 72.84 kg COD/m(3) day. The calcium accumulation onto the granules was monotonically related to the calcium concentration, accounting for 17-18 wt.% of Ca in the suspended solid in the form of calcium carbonate, phosphates/phosphonates and carboxylates. The mineral formation significantly increased the granule settling velocity (by ∼ 50%) and the suspended solid concentration (by ∼ 100%). However, the effect of calcium precipitation on the specific methanogenic activity and the CH(4) production rate was complex, first positive during the start-up but later on negative.

Mechanism study of nitrate reduction by nano zero valent iron

This study investigates the fate of nitrogen species during nitrate reduction by nano-scale zero valent iron (NZVI) and related reaction mechanisms. The NZVI used for the experiments was prepared by chemical reduction without a stabilizing agent. NZVI has great ability to reduce nitrate. However, the question of what end-product results from nitrate reduction by NZVI has sparked controversy. Establishing nitrogen mass balance by quantitative analysis of aqueous phase and gas-phase nitrogen species, this study clearly determines that nitrate was converted to ammonium ion followed by ammonia stripping under a strong alkaline condition, which leads to a decrease in the total aqueous nitrogen amount. Moreover, some of the major reactions, which consisted of nitrate reduction, ammonia production, and ammonia stripping were modelled by pseudo first-order kinetics. According to the model estimation results, additional reaction mechanisms would exist in an early stage of reaction. This might be due to the adsorption and desorption reaction which could be explained by the core-shell structure model.

CO2 mineralization induced by fungal nitrate assimilation

Formation of CaCO3 induced by fungal physiological activities is a potential way to sequestrate atmospheric CO2 in ecosystem. Alternaria sp. is a saprophytic fungus isolated from a forest soil. We examined the precipitation of CaCO3 induced by the fungus in response to different levels of Ca(NO3)2 or CaCl2 in agar media, and the biogenesis of CaCO3 was verified by low δ13C value. The formed CaCO3 was identified as calcite by X-ray diffraction analysis. Square, rectangular and rhombic CaCO3 crystals and amorphous calcium carbonate were observed around mycelia at higher levels of Ca(NO3)2. Acidification occurred in media at low concentrations (0 and 0.0002 M) of Ca(NO3)2, and no CaCO3 formed in these media. The quantities of CaCO3 formed in media increased with increasing concentrations of Ca(NO3)2 and were significantly correlated to fungal biomass, pH value and nitrite concentrations. No CaCO3 was formed in media with CaCl2 at all levels. These results collectively indicated that the formation of CaCO3 can be induced by the fungal assimilation of nitrate. The study also revealed that biogenic crystal of CaCO3 tended to grow on a silicon nucleus and the amorphous calcium carbonate (ACC) was the transient stage of CaCO3 crystal.

Nitrogen and carbon removal from Fenton-treated leachate by denitrification and biofiltration

Treatment of a Fenton-treated leachate was carried out by denitrification of nitrate using an upflow anaerobic sludge blanket (UASB) biofilm reactor and subsequent biofiltration of the residual COD using a biological aerated filter (BAF). Methanol was selected as the optimal external carbon source because of its good performance, low cost and simple operability. Central composite design (CCD) and response surface methodology (RSM) were used to evaluate the effect of three factors namely hydraulic retention time (HRT), nitrogen concentration and COD/N (C/N) ratio on denitrification performance. Process optimization matched well with the model prediction and allowed 94% reduction of COD and up to 98% removal of total nitrogen (TN). The 21-day biofiltration experiments in a BAF showed that an effluent with COD concentration below 100 mg/L and TN concentration less than 40 mg/L was achieved. Our results indicated that the combination process of UASB-biofilter/BAF is effective for nitrate and residual carbon removal.

Treatment of nitrate contaminated water using an electrochemical method

Treatment of nitrate contaminated water which is unsuitable for biological removal using an electrochemical method with Fe as a cathode and Ti/IrO(2)-Pt as an anode in an undivided cell was studied. In the absence and presence of 0.50 g/L NaCl, the nitrate-N decreased from 100.0 to 7.2 and 12.9 mg/L in 180 min, respectively, and no ammonia and nitrite by-products were detected in the presence of NaCl. The nitrate reduction rate increased with increasing current density, with the nitrate reduction rate constant k(1) increasing from 0.008 min(-1) (10 mA/cm(2)) to 0.016 min(-1) (60 mA/cm(2)) but decreasing slightly with increasing NaCl concentration. High temperature favoured nitrate reduction and the reaction followed first order kinetics. The combination of the Fe cathode and Ti/IrO(2)-Pt anode was suitable for nitrate reduction between initial pH values 3.0 and 11.0. e.g. k(1)=0.010 min(-1) (initial pH 3.0) and k(1)=0.013 min(-1) (initial pH 11.0). Moreover, the surface of all used cathodes appeared rougher than unused electrodes, which may have increased the nitrate reduction rate (4-6%).

The characteristics and application of sludge-fly ash ceramic particles (SFCP) as novel filter media

Novel filter media-sludge-fly ash ceramic particles (SFCP) were prepared using dewatered sludge, fly ash and clay with a mass ratio of 1:1:1. Compared with commercial ceramic particles (CCP), SFCP had higher total porosity, larger total surface area and lower bulk and apparent density. Tests of heavy metal elements in lixivium proved that SFCP were safe for wastewater treatment. A lab-scale upflow anaerobic bioreactor was employed to ascertain the application of SFCP in denitrification process using acetate as carbon source. The results showed that SFCP reactor brought a relative superiority to CCP reactor in terms of total nitrogen (TN) removal at the optimum C/N ratio of 4.03 when volumetric loading rates (VLR) ranged from 0.33 to 3.69 kg TN (m(3)d)(-1). Therefore, SFCP application, as a novel process of treating wastes with wastes, provided a promising way in sludge and fly ash utilization.

The effect of nitrate and sulfate on mediator-less microbial fuel cells with high internal resistance

Microbial fuel cells (MFCs) simultaneously provide waste treatment while capturing energy in the form of electricity. Although these devices are being used in engineered and natural environments where nitrate or sulfate may inhibit power production, the effects of these electron acceptors have not been fully explored. This research investigated the effect of nitrate and sulfate on MFC power production when these chemicals are present at the anode. Nitrate decreased the maximum current and power density by 15 and 17%, respectively, when present at 20 mg/L, and sulfate caused the maximum current and power density to decrease by 4 and 7%, respectively (also at 20 mg/L). Stronger inhibition was observed at higher nitrate and sulfate concentrations, but power production persisted. Coulombic efficiency decreased as nitrate and sulfate levels increased, although this was not primarily due to the biochemical reduction of nitrate or sulfate; rather, it was probably because of the inhibition of exoelectrogens.

Denitrification of nitrate contaminated groundwater with a fiber-based biofilm reactor

A fiber-based biofilm reactor was developed using a laboratory-scale apparatus for treatment of nitrate-contaminated groundwater. Denitrification bacteria were inoculated by anaerobic sludge from a wastewater treatment plant. Nitrate removal efficiency, nitrite accumulation, COD and pH in the treated water were investigated under various conditions set by several parameters including hydraulic retention times (HRTs) (24, 20, 16, 12, 8, 4 and 2h), influent nitrate loading (around 50, 100 and 150 NO(3)(-)-N mg L(-1)), pH (5, 6, 7, 8, and 9) and ratios of carbon to nitrogen (C/N=3.00, 2.00, 1.50 1.25 and 1.00). The experimental results demonstrated that the optimum reaction parameters were pH 7-7.5,C/N=1.25 and HRT=8h, under which over 99% of NO(3)(-)-N was removed, almost no NO(2)(-)-N accumulated and COD was nearly zero in treated water when the concentration of NO(3)(-)-N was around 100.00 mg L(-1) in influent.

Effect of high nitrate concentration on PHB storage in sequencing batch reactor under anoxic conditions

The study investigated effect of high influent nitrate concentration on poly-beta-hydroxybutyrate, (PHB), storage in a sequencing batch reactor, (SBR), under anoxic conditions. Acetate was fed as pulse during anoxic phase, sustained with external nitrate feeding. SBR operation involved three runs at steady state with COD/N ratios of 3.84, 2.93 and 1.54 gCOD/gN, where external nitrate concentrations gradually increased from 50 mg N/l to 114 mg N/l and 226 mg N/l, in 1st, 2nd and 3rd runs, respectively. In 1st run, acetate was fully converted into PHB with the storage yield value of 0.57-0.59 gCOD/gCOD, calculated both in terms of PHB formation and NO(X) utilization, confirming storage was the sole substrate utilization mechanism. In the following runs, PHB formation was reduced and the storage yield based on PHB dropped down to 0.40 and 0.33 gCOD/gCOD with increasing influent nitrate concentrations, indicating that higher portions of acetate were diverted to simultaneous direct growth. The observations suggested that nitrite accumulation detected at low COD/N ratios was responsible for inhibition of PHB storage.