Boosted sono-oxidative catalytic degradation of Brilliant green dye by magnetic MgFe2O4 catalyst: Degradation mechanism, assessment of bio-toxicity and cost analysis.

The magnetic MgFe2O4 nanoparticles (NPs) were fabricated via a facile co-precipitation technique and was comprehensively characterized by XRD, FTIR, SEM, EDX and VSM. The prepared NPs were used as catalyst in presence of ultrasound (US) irradiation to activate persulfate (PS) for generation of sulfate radicals (SO4·-) for boosted degradation of toxic Brilliant Green (BG) dye. Preliminary experiments revealed that highest BG dye degradation efficiency of 91.63% was achieved at MgFe2O4 catalyst dose of 1.0 g/L, PS dose of 300 mg/L, and initial dye concentration of 70 ppm within 15 min of US irradiation. However, only US, US in presence of PS oxidation and US in presence of MgFe2O4 catalyst have shown 20.2%, 83.6% and 45.0% of BG dye removal, respectively. Furthermore, response surface methodology (RSM) based central composite design (CCD) was executed to investigate the effect of interaction between independent variables such as MgFe2O4 catalyst dose (0.5-1.5 g/L), PS dose (150-350 mg/L), initial BG dye concentration (50-150 ppm) and US irradiation time (4-12 min). The RSM based quadratic model was used to predict the experimental data, and the prediction accuracy was confirmed by analysis of variance (R2 = 0.98). The established RSM model has predicted the optimum experimental conditions as MgFe2O4 catalyst dose of 0.75 g/L, PS dose of 300 mg/L, initial dye concentration of 75 ppm and sonication time of 10 min. Subsequently, the treatment cost analysis was performed for all thirty experimental runs of CCD, and the RSM predicted response was found to be evidently optimum as this has delivered best economic condition (140 $/kg of BG removed) with respect to relative dye removal (%). COD removal and residual sulfate analysis have demonstrated satisfactory reduction of COD (90.31%) as well as sulfate ions (42.87 ppm) in the dye solution after treatment. Results of degradation pathway analysis portrayed the transformation of BG molecule (M/Z ratio 385) into simpler fractions with M/Z ratio of 193, 161, 73, and 61. Moreover, the toxicity analysis revealed that sono-catalytically activated PS system has efficiently reduced the toxicity level of BG dye from 93.9% to 5.13%.

Sediment porewater extraction and analysis combining filter tube samplers and capillary electrophoresis.

Careful extraction and analysis of porewater from sediment cores are critical for the investigation of small-scale biogeochemical processes. Firstly, small sample volumes and high spatial resolution are required. Secondly, several chemical species in the anaerobic porewater are sensitive to oxidation when brought in contact with ambient air. Here we present the combination of a special sampling technique and an analytical method for the porewater extraction of a varved sediment core from Lake Baldegg in central Switzerland, using MicroRhizon samplers and a portable capillary electrophoresis (CE) instrument. MicroRhizon filter tubes of 1 mm diameter and 20 mm length are suitable for fast retrieval of particle-free porewater samples directly from the sediment core. Since the time-span between sampling and analysis is less than 20 seconds, oxygen-sensitive Fe(ii) can be analyzed in one go together with Na(+), K(+), Ca(2+), Mg(2+), NH4(+), and Mn(ii) without splitting, acidification or dilution of the sample. The major inorganic cations and anions of the sediment porewater can be determined in less than 15 minutes. Detection limits are in the sub-micromolar concentration range. The capillary electrophoresis instrument used in this study requires sample volumes of only 20 µL. These remarkable small sample volumes allow the minimization of disturbance of the sediment cores and a high spatial resolution of the sediment profile, even in sediments with low water content. The equipment is inexpensive, easy to handle, fully portable and therefore suitable for environmental on-site applications.

A strategy for urban outdoor production of high-concentration algal biomass for green biorefining.

The present study was to investigate the feasibility of carrying out effective microalgae cultivation and high-rate tertiary wastewater treatment simultaneously in a vertical sequencing batch photobioreactor with small areal footprint, suitable for sustainable urban microalgae production. For 15 consecutive days, Chlorella sorokiniana was cultivated in synthetic wastewater under various trophic conditions. A cycle of 12-h heterotrophic: 12-h mixotrophic condition produced 0.98 g l(-1) d(-1) of algal biomass in tandem with a 94.7% removal of 254.4 mg l(-1) C-acetate, a 100% removal of 84.7 mg l(-1) N-NH4 and a removal of 15.0 mg l(-1) P-PO4. The cells were harvested via cost-effective chitosan flocculation with multiple dosing (3 times) applying established chitosan:cell ratio (1:300 w/w) and pH control (6.3-6.8). Reproducible flocculation efficiencies of greater than 99% and high-concentration algal broths (>20% solids) were achieved.

Full-scale demonstration of step feed concept for improving an anaerobic/anoxic/aerobic nutrient removal process.

A small wastewater treatment plant (WWTP) failed to meet effluent requirements of the first-A discharge standard in China, with the anaerobic/anoxic/oxic (A/A/O) process treating municipal and partial industrial wastewater. Thus an A/O step feed process (Anoxic/oxic/anoxic/oxic/anoxic/oxic) with floating plastic carriers in aerobic units was proposed to improve nutrient removal within the existing WWTP. Four main reform strategies were applied: (1) the original influent was divided into three streams which led into corresponding anoxic units; (2) floating plastic carriers were placed in the second and third oxic units; (3) nitrified liquid recycling was omitted; (4) channel shapes and sizes were adjusted between adjacent units to prevent backflow. After these modifications were implemented, the total nitrogen and phosphorus concentrations in the effluent were reduced from 20.8 to 14.2mg/L, and from 1.89 to 0.57 mg/L, respectively. Moreover, annual electricity consumption in the WWTP was reduced by 245 MWh as a result of these modifications.

Assessment of the formation of inorganic oxidation by-products during the electrocatalytic treatment of ammonium from landfill leachates.

This work investigates the formation of oxidation by-products during the electrochemical removal of ammonium using BDD electrodes from wastewaters containing chlorides. The influence of the initial chloride concentration has been experimentally analyzed first, working with model solutions with variable ammonium concentration and second, with municipal landfill leachates. Two different levels of chloride concentration were studied, i) low chloride concentrations ranging between 0 and 2000 mg/L and, ii) high chloride concentrations ranging between 5000 and 20,000 mg/L. Ammonium removal took place mainly via indirect oxidation leading to the formation of nitrogen gas and nitrate as the main oxidation products; at high chloride concentration the formation of nitrogen gas and the rate of ammonium removal were both favored. However, chloride was also oxidized during the electrochemical treatment leading to the formation of free chlorine responsible of the ammonium oxidation, together with undesirable products such as chloramines, chlorate and perchlorate. Chloramines appeared during the treatment but they reached a maximum and then started decreasing, being totally removed when high chloride concentrations were used. With regard to the formation of chlorate and perchlorate once again the concentration of chloride exerted a strong influence on the formation kinetics of the oxidation by-products and whereas at low chloride concentrations, chlorate appeared like an intermediate compound leading to the formation of perchlorate, at high chloride concentrations chlorate formation was delayed significantly and perchlorate was not detected during the experimental time. Thus this work contributes first to the knowledge of the potential hazards of applying the electro-oxidation technology as an environmental technology to deal with ammonium oxidation under the presence of chloride and second it reports efficient conditions that minimize or even avoid the formation of undesirable by-products.

Screening of novel low-cost adsorbents from agricultural residues to remove ammonia nitrogen from aqueous solution.

Most studies on ammonia adsorption from aqueous solution have been focused on mineral materials. However, a series of batch experiments were performed in this study to screen novel adsorbent materials from 80 agricultural residues, and to investigate the adsorption characteristics of six screened samples. The results showed that the ammonia adsorption efficiencies of 11 agricultural residues were comparable to those of minerals. The equilibrium data fitted well with both the Langmuir and Freundlich models, and the theoretical maximum monolayer adsorption capacities of strawberry leaves and stems, Boston ivy leaves and stems, southern magnolia leaves and poplar leaves were 6.71, 4.62, 6.07, 5.01, 6.22 and 6.25mg/g, respectively at 30 degrees C. The adsorptions reached equilibrium at about 18 h, and the kinetics were well described by the Logistic model. In conclusion, these agricultural residues could be used as adsorbent materials for ammonia removal.

Recycle use of magnesium ammonium phosphate to remove ammonium nitrogen from rare-earth wastewater.

This paper presents a recycle MAP process (magnesium ammonium phosphate) to remove NH4-N from a typical rare-earth wastewater. The optimum conditions for the MAP precipitation and recycle use of the MAP with a newly-designed process were investigated in laboratory. The results showed that the pH value and dosages of P (phosphate) and Mg reagents have a significant influence on NH4-N removal, with a maximum removal efficiency of 99.4% at the conditions of pH=9 and Mg:N:P molar ratio=1.2:1:1.2. In the process of recycle use of the MAP, adding some HCl to dissolve MAP decomposition residues could effectively enhance NH4-N removal. The NH4-N removal efficiency reached 99.6% by adding an HCl amount of H+:OH- molar ratio=0.8 into the reused MAP decomposition residues, whereas the NH4-N removal efficiency without addition of HCl was only 96.4%. Moreover, the residual PO4-P from the end of reaction was recovered and the optimum recovery efficiency was achieved at a Mg:P molar ratio=6 and pH=10. Under these optimum conditions, the residual NH4-N and PO4-P concentrations in the treated wastewater, through 6 times of the recycling, were less than 15 mg/L and 1 mg/L, respectively. On the basis of this, an economic evaluation of the recycling MAP was made, and this recycle process could save 48.6% cost used in the chemicals for treating per cubic meter of the rare-earth wastewater, compared to the conventional MAP process.

Upgrading of Florence wastewater treatment plant: co-digestion and nitrogen autotrophic removal.

In recent years a completely autotrophic nitrogen removal process based on Anammox biomass has been tested in a few European countries in order to treat anaerobic supernatant and to increase the COD/N ratio in municipal wastewater. This work reports experimental results on a possible technical solution to upgrade the S. Colombano treatment plant which treats wastewater from the Florentine urban area. The idea is to use 50% of the volume of the anaerobic digester in order to treat external sewage sludge (as septic tank sludge) together with waste activated sludge and to treat the resulting effluent on a SHARON-ANAMMOX process in order to remove nitrogen from the anaerobic supernatant. Anaerobic co-digestion, tested in a 200 L pilot plant, enables low cost treatment of septic tank sludge and increases biogas production; however, it also increases the nitrogen load re-circulated to the WWTP, where nitrogen removal efficiency is already low (<50%), due to the low COD/N ratio, which limits predenitrification efficiency. Experimental results from a SHARON process tested in a lab-scale pilot plant show that nitrite oxidising bacteria are washed-out and steady nitrite production can be achieved at retention times in the range 1 - 1.5 days, at 35 degrees C. In a lab-scale SBR reactor, coupled with a nitration bioreactor, maximum specific nitrogen removal rate under nitrite-limiting conditions (with doubling time equal to about 26 days at 35 degrees C) was equal to 0.22 kgN/kgSSV/d, about 44 times the rate measured in inoculum Anammox sludge. Finally, a cost analysis of the proposed upgrade is reported.

Ammonium removal by modified zeolite from municipal wastewater.

Ammonium removal by modified zeolite, H-form and Na-form zeolite, were examined by batch-type methods. The adsorption of ammonium on modified zeolite was exothermic process. The saturation adsorption capacity of ammonium on H-form and Na-form zeolite were 21.23 and 41.15 mg/g, respectively. After ten times adsorption-desorption-readsorption cycles the standard deviations of H-form and Na-form zeolite were 6.34% and 6.59%. The zeolite adsorption process has proved cost effective and practical in reducing ammonium by H-form and Na-form zeolite in municipal wastewater from concentration 27.68 mg/L to 2.80 mg/L and 5.91 mg/L.

Nitrogen removal from sludge digester liquids by nitrification/denitrification or partial nitritation/anammox: environmental and economical considerations.

In wastewater treatment plants with anaerobic sludge digestion, 15-20% of the nitrogen load is recirculated to the main stream with the return liquors from dewatering. Separate treatment of this ammonium-rich digester supernatant significantly reduces the nitrogen load of the activated sludge system. Two biological applications are considered for nitrogen elimination: (i) classical autotrophic nitrification/heterotrophic denitrification and (ii) partial nitritation/autotrophic anaerobic ammonium oxidation (anammox). With both applications 85-90% nitrogen removal can be achieved, but there are considerable differences in terms of sustainability and costs. The final gaseous products for heterotrophic denitrification are generally not measured and are assumed to be nitrogen gas (N2). However, significant nitrous oxide (N2O) production can occur at elevated nitrite concentrations in the reactor. Denitrification via nitrite instead of nitrate has been promoted in recent years in order to reduce the oxygen and the organic carbon requirements. Obviously this "achievement" turns out to be rather disadvantageous from an overall environmental point of view. On the other hand no unfavorable intermediates are emitted during anaerobic ammonium oxidation. A cost estimate for both applications demonstrates that partial nitritation/anammox is also more economical than classical nitrification/denitrification. Therefore autotrophic nitrogen elimination should be used in future to treat ammonium-rich sludge liquors.

Assessment of magnesium ammonium phosphate precipitation for the treatment of leather tanning industry wastewaters.

Magnesium ammonium phosphate (MAP) precipitation has a potential for ammonium removal from industrial wastewaters. Application basis of this recent method of treatment has not been fully determined. In this study application of MAP precipitation to leather tanning wastewaters has been experimentally evaluated. Five alternative places of MAP precipitation in leather tanning wastewater treatment scheme tested were; instead of plain settling, after plain settling, after polyelectrolyte added plain settling, within the chemical precipitation and after biological treatment. Among these alternatives MAP application instead of plain settling and within the chemical precipitation were found to be most favourable and efficient by reducing the nitrogen load to the level of nutrient requirement in the biological stage. pH 9.0-9.5 and stoichiometric magnesium and phosphate doses were determined to be optimum conditions for MAP precipitation.