Influence of water electrolysis on hydrolysis and methanogenesis stages of anaerobic digestion at room temperature: Kinetic and metabolic analysis.

Batch cultures were performed to study hydrolysis and methanogenesis in the presence of an electric field at room temperature (i.e., 23 °C). Kinetic and metabolic analyses using RuO2/Ti electrodes were carried out in short reaction times to avoid biofilm formation, allowing the evaluation of the effect of O2 and H2 produced on anaerobic digestion during the imposition of three electric fields: 1.21, 1.45, and 1.64 V/cm. Results highlighted that at 1.21 V/cm, the electrolysis produced 0.0753 mg O2/L·min, where facultative microorganisms consumed 21 % oxygen, enhancing the hydrolysis phase by 52 %. Additionally, methane production was noticeably improved with an activity of 0.89 ± 0.02 g COD-CH4/g VSS·d, meaning 39 % higher than the control. The imposition of an electric field showed promising results since the methanogenic activity at room temperature was very close to the activities observed in conventional reactors at 35 °C.

How does a low-magnitude electric field influence anaerobic digestion in wastewater treatment? A review.

Anaerobic digestion (AD) is a physio-biochemical process widely used for treating industrial or municipal wastewater with concomitant methane production. Several technologies have been tested to improve AD's efficiency, like pretreatments and co-digestion, among others. Recently the imposition of a low-magnitude electric field (LMEF) has been applied at the AD to improve methane yield. Despite the positive results of imputing an electric field, many gaps are not understood yet. Therefore, this review focuses on the biochemical aspects of AD and electric field for a better understanding of the effect of the LMEF on the metabolisms of the AD during wastewater treatment and its application in methane production enhancement.

Influence of metronidazole on activated sludge activity.

Metronidazole is potentially carcinogenic to humans and it has been detected in wastewaters. The Wastewater Treatment Plants using biological processes have been highly impacted by the emergent compounds of recalcitrant type, and the knowledge about that issue is quite relevant. Therefore, this paper was focused on how metronidazole influences the kinetics and metabolic behaviour of nitrification and heterotrophic activity on activated sludge in batch cultures. Eight concentrations of metronidazole in the range of 5-100 mg/L were evaluated, in the presence of 2109 ± 129 mg VSS/L. The increment of initial metronidazole concentration caused a decline on COD and ammonium removal efficiencies, nitrate production yields, as well as in the substrate-specific consumption rates. Metronidazole (MDZ) had a greater impact on heterotrophic activity than nitrifying activity; also, it had a greater inhibitory effect on nitrite oxidation than ammonium oxidation. The activated sludge was not able to biotransform metronidazole; however, the azole compound significantly affected the physiology of it. The inhibition of ammonium oxidation was non-competitive (qmax = 120 mg NH4+-N consumed/gVSS-d, and Ki = 41.5 mg MDZ/L) and the initial metronidazole concentration that inhibited 50% of nitrifying activity (IC50) was 43 mg MDZ/L.

Copper removal from wastewater by a chitosan-based biodegradable composite.

This work demonstrates that a biodegradable chitosan-based biocomposite packed in mini-reactors successfully removes copper ions from aqueous solutions. The chitosan is obtained by deacetylation of biological chitin, which is extracted from shrimp wastes by lactic acid fermentation. The polysaccharide is embedded in a biodegradable prepolymer matrix before extrusion to produce porous cylindrical pellets of 2 × 80 mm. The highest copper ion removal is 62.5 mg Cu2+ per g of the biodegradable adsorbent. Additionally, the adsorption capacity of the material, below its saturation, allows several cycles of reuse with a hydraulic retention time reduction of 1 h. This chitosan-based material is advantageous when compared with other approaches using non-biodegradable materials or costly commercial adsorbents for removing heavy metal ions in wastewater effluents as well as a filter component in water purification devices.

Sulfide and ammonium oxidation, acetate mineralization by denitrification in a multipurpose UASB reactor.

The physiological and kinetic behavior of a denitrifying granular sludge exposed to different sulfide loading rates (55-295 mg/L d) were evaluated in a UASB reactor fed with acetate, ammonium and nitrate. At any sulfide loading rates, the consumption efficiencies of sulfide, acetate and ammonium were above 95%, while nitrate consumption efficiencies were around 62-72%. At the highest sulfide loading rate the ammonium was used as electron donor for N(2) production. The increase of sulfide loading rate also affected the fate of sulfide oxidation, since elemental sulfur was the main end product instead of sulfate. However, the lithotrophic denitrifying kinetic was not affected. FISH oligonucleotide probes for Thiobacillus denitrificans, Thiomiscropira denitrificans, genus Paracoccus and Pseudomonas spp. were used to follow the microbial ecology. The results of this work have shown that four pollutants could simultaneously be removed, namely, sulfide, ammonium, acetate and nitrate under well defined denitrifying conditions.

Simultaneous oxidation of ammonium, p-cresol and sulfide using a nitrifying sludge in a multipurpose bioreactor: a novel alternative.

A nitrifying continuous stirred tank reactor was used as multipurpose bioreactor and it was operated for 325 days at 220 mg NH(4)(+)-N/Ld, 89 mg p-cresol-C /Ld and 36-76 mg S(2-)/Ld. The bioreactor was fed in sequential way, firstly with ammonium, achieving a consumption efficiency of 89%, with a nitrate yield of 0.99. Afterward, p-cresol was fed, achieving ammonium and p-cresol consumption efficiencies of 95% and 100%, respectively. The nitrate yield was higher and no aromatic intermediaries from p-cresol were detected. Finally sulfide was fed and the consumption efficiencies for all substrates were of 100%, being nitrate, HCO(3)(-) and sulfate the end products. The kinetic results showed that biological sulfide consumption was 13-fold faster than the chemical oxidation. This is the first time that a nitrifying reactor can be used for multiple purposes and also for the simultaneous removal of ammonium, sulfide and p-cresol in one step.

The behavior of nitrifying sludge in presence of sulfur compounds using a floating biofilm reactor.

The tolerance, kinetic and oxidizing capability of a nitrifying sludge exposed to different initial concentrations of sulfide (1.7 to 18mg/L) was evaluated in batch experiments. A nitrifying sludge fed with ammonium and thiosulfate and produced in steady state conditions was used as inoculum. Sulfide induced a significant effect either on ammonium consumption rates or nitrite accumulation. In spite of the nitrifying kinetic was affected, the ammonium consumption efficiencies were close to 100%, with nitrate production yields around 1.0. The IC(50) value for ammonium oxidizing-process was 13mg/L of sulfide. Sulfide was oxidized in two steps: first sulfide was oxidized to elemental sulfur and afterward into sulfate. FISH oligonucleotide probes for Thiobacillusdenitrificans, Nitrosomonas spp., and Nitrobacter spp. were used in order to know if these bacteria were part of the microbial ecology. The obtained results showed that under nitrifying conditions are possible to carry out simultaneously two biological processes, nitrification and sulfur oxidation.

Effect of initial sulfide concentration on sulfide and phenol oxidation under denitrifying conditions.

The objective of this work was to evaluate the effect of the initial sulfide concentration on the kinetics and metabolism of phenol and sulfide in batch bioassays using nitrate as electron acceptor. Complete oxidation of sulfide (20 mg L(-1) of S(2-)) and phenol (19.6 mg L(-1)) was linked to nitrate reduction when nitrate was supplemented at stoichiometric concentrations. At 32 mg L(-1) of sulfide, oxidation of sulfide and phenol by the organo-lithoautotrophic microbial culture was sequential; first sulfide was rapidly oxidized to elemental sulfur and afterwards to sulfate; phenol oxidation started once sulfate production reached a maximum. When the initial sulfide concentration was increased from 20 to 26 and finally to 32 mg L(-1), sulfide oxidation was inhibited. In contrast phenol consumption by the denitrifying culture was not affected. These results indicated that sulfide affected strongly the sulfide oxidation rate and nitrate reduction.

Chemolithotrophic denitrification with elemental sulfur for groundwater treatment.

Denitrification for the treatment of nitrates in wastewater typically relies on organic electron donating substrates. However, for groundwater treatment, inorganic compounds such as elemental sulfur (S0) are being considered as alternative electron donors in order to overcome concerns that residual organics can cause biofouling. In this study, a packed-bed bioreactor supplied with S0:limestone granules (1:1, v/v) was started up utilizing a chemolithotrophic denitrifying enrichment culture in the form of biofilm granules that was pre-cultivated on thiosulfate. The granular enrichment culture enabled a rapid start-up of the bioreactor. A nearly complete removal of nitrate (7.3 mM) was NO3- attained by the bioreactor at nitrate loading rates of up to 21.6 mmol/(L(reactor)d). With lower influent concentrations (1.3 mM nitrate) comparable to those found in contaminated groundwater, high nitrate loads of 18.1 mmol/(L(reactor)d) were achieved with an average nitrate removal efficiency of 95.9%. The recovery of nitrogen as benign N2 gas was nearly stoichiometric. The concentration of undesirable products from S0-based denitrification such as nitrite and sulfide were low. Comparison of bioreactor results with batch kinetic studies revealed that denitrification rates were dependent on the surface area of the added S0. The surface area normalized denitrification rate was determined to be 26.4 mmol /(m2 S0 d).