Biotransformation of micropollutants in moving bed biofilm reactors under heterotrophic and autotrophic conditions.

We investigated the transformation of four pharmaceuticals (Diclofenac, Naproxen, Ibuprofen and Carbamazepine) in a moving bed biofilm reactor subjected to different COD/N ratios in four experimental phases. The shift from medium to high range COD/N ratio (i.e., 5:1 to 100:1) intensified the competition between heterotrophs and nitrifying communities, leading to a transition from co-existence of heterotrophic and autotrophic conditions with high COD removal and nitrification rate in phase I to dominant heterotrophic conditions in phase II. At lower range COD/N ratios (i.e., 1:2 and 1:8) in phase III and IV, autotrophic conditions prevailed, resulting in increased nitrification rates and high abundance of amoA gene in the biofilm. Such shifts in the operating condition were accompanied by notable changes in the biofilm concentrations, composition and abundance of microbial populations as well as biodiversity in the biofilms, which collectively affected the degradation rates of the pharmaceuticals. We observed higher kinetic rates per unit of biofilm concentration under autotrophic conditions compared to heterotrophic conditions for all compounds except Naproxen, indicating the importance of nitrification in the transformation of such compounds. The results also revealed a positive relationship between biodiversity and biomass-normalized kinetic rates of most compounds.

Biodegradation of organophosphorus pesticides in moving bed biofilm reactors: Analysis of microbial community and biodegradation pathways.

We investigated the performance of a lab-scale moving bed biofilm reactor (MBBR) with respect to general bioconversion processes and biotransformation of two commonly used organophosphorus pesticides, Chlorpyrifos (CHL) and Malathion (MAL). The reactor was operated for 300 days under different organic loads by changing hydraulic retention time (HRT). The decrease in organic load resulted in the formation of a thinner biofilm and the growth of more biomass in the bulk, which greatly shifted bioconversion processes. The low organic loading supported more nitrification in the reactor, but an opposite trend was observed for denitrification, which was enhanced at higher organic loading where the formation of anoxic zones in the thick biofilm was favored. 70% and 55% removal corresponding to 210 and 165 µg/m2/d occurred for MAL and CHL, respectively, at an HRT of 3 h and progressively increased with higher HRTs. Phylogenetic analysis revealed a shift in composition and abundance of taxa throughout the reactor operation where lower loading rate supported the growth of a more diverse and evenly distributed community. The analysis also highlighted the dominance of heterotrophic communities such as Flavobacterium and Acinetobacter johnsonii, which could be involved in the biotransformation of CHL and MAL through co-metabolism.

Synergy of combined free nitrous acid and Fenton technology in enhancing anaerobic digestion of actual sewage waste activated sludge.

In this study, actual swage waste activated sludge in batch reactors was employed to assess the synergistic effect of free nitrous acid and Fenton pre-treatments on enhancing methane production in the anaerobic digestion process. In addition to methane enhancement, the mechanisms driving the enhancement were also investigated via measuring enzymes activity and solubilisation of organic matter. This study revealed that the combined pre-treatments solubilised organic matter significantly more than the bioreactors pre-treated with individual FNA and Fenton. For understanding the influence of pre-treatments on solubilisation of organic matter, soluble protein, soluble polysaccharide and soluble chemical oxygen demand (SCOD) were measured before and after the treatments and it was shown that they respectively increased by 973%, 33% and 353% after the treatments. Protease and cellulase activity, as the key constituents of the microbial community in activated sludge, decreased considerably after the combined pre-treatments 42% and 32% respectively, which resulted in considerable methane enhancement. The results corroborate the synergy of the combined FNA and Fenton pre-treatment in degrading the organic and microbial constituents in waste activated sludge, paving the way for the big-scale implementation of these technologies.

Fe3 O4 @GO on silica sand as an efficient and economical adsorbent; Typical application for removal of phenol and 2,4-dichlorophenol from water samples.

In this research, the layer-by-layer coating of silica sand surface with monolayer of graphene oxide (GO) immobilized on magnetite nanoparticles (Fe3 O4 MNPs) sublayer was investigated as a novel, low-cost, effective, and green nanocomposite material for adsorption of phenol and 2,4-dichloro-phenol (DCP). Several characterization techniques such as FTIR spectroscopy, X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM) were used to confirm the successful synthesis of Fe3 O4 MNPs@GO on silica. The efficiency of Fe3 O4 MNPs@GO-coated silica (SiO2 ) for the removal of the target phenolic compounds from water samples was evaluated. The maximum removal of phenol (52%) and DCP (73%) was observed using 1.0 g adsorbent, initial concentration of 12.5 mg/dm3 (for phenol) and 15 mg/dm3 (for DCP), sample volume of 10 ml (for phenol) and 15 ml (for DCP), contact time of 20 min (for phenol) and 10 min (for DCP), and pH = 5. The adsorption isotherm models of Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich as well as kinetic and intraparticle diffusion models were also examined. Eventually, SiO2 /Fe3 O4 MNPs@GO was regenerated five times for removal of examined contaminants and their removal efficiency from the water inlet of a water treatment plant was assessed. PRACTITIONER POINTS: Immobilizing monolayer of GO nanosheets on silica sands surface for the first time has been achieved. GO monolayer anchors on silica sands through Fe3 O4 nanoparticles as sublayer without using very expensive tris(hydroxymethyl) aminomethane agent. Modified silica sands are introduced as a novel and economic pollutants adsorbent, which can be used in filter sands of water treatment industry. The SiO2 /Fe3 O4 MNPs@GO significantly reduces the amount of phenol and 2,4-dichloro-phenol (DCP) as model organic pollutants from water samples.

Stabilizing of poly(amidoamine) dendrimer on the surface of sand for the removal of nonylphenol from water: Batch and column studies.

In this work, a novel adsorbent with stabilizing of PAMAM dendrimer on the surface of sand was successfully synthesized and used to remove NP from water. The characterization of the adsorbent was performed by XRD, FTIR, TEM, and FE-SEM. Batch and column studies were conducted to evaluate the performance of the adsorbent. It was found that Freundlich isotherm and pseudo-second order models are perfectly stimulated the adsorption behavior and kinetic rate of NP uptake. In column study, first the effect of bed depth, flow rate and initial concentration of NP on the performance of the adsorbent were evaluated then the breakthrough curve for each condition was drawn. Finally, Thomas model constants to describe NP adsorption were calculated. As the result of the experiments, it might be concluded that in conventional water treatment plants which the removal of NP is negligible, the use of synthesized adsorbent as a filter media can be a promising way to selectively remove NP from water.

Improvement of anaerobic digestion of sewage mixed sludge using free nitrous acid and Fenton pre-treatment.

BACKGROUND: Recently, it has been indicated that free nitrous acid (FNA) and Fenton pre-treatment of waste activated sludge can enhance methane production in anaerobic digestion of waste activated sludge. In addition, it has been revealed that the substances used in these pre-treatments are both eco-friendly and economically attractive because not only are they produced in anaerobic digestion, but they are also low priced. Since primary sludge and waste activated sludge are mixed prior to anaerobic digestion in the majority of wastewater treatment plants, this study aims to assess the influence of combined FNA and Fenton on the anaerobic digestion of mixed sludge. RESULTS: According to this study's results, methane generation from anaerobic digestion of mixed sludge was enhanced when using FNA and Fenton pre-treatment, affirming the effectiveness of the individual and combined pre-treatments in anaerobic digestion of mixed sludge. The enhanced methane production was significant in combined pre-treatments (up to 72%), compared with FNA and Fenton pre-treatment alone (25% and 27%, respectively). This corroborates the positive synergistic effect of the combined pre-treatments on methane production. The enhanced methane can be attributed to augmented soluble fractions of organic matter in addition to increased readily biodegradable organic matter, caused by the pre-treatments. Additionally, the amount of chemical oxygen demand (COD) was assessed during anaerobic digestion, and it was revealed that COD decreased considerably when the pre-treatment strategies were combined. CONCLUSIONS: This study reveals that the pre-treatments are potentially applicable to full-scale wastewater treatment plants because a mixture of primary sludge and waste activated sludge was used for the pre-treatments. Additionally, combined FNA and Fenton pre-treatments prove more effective in enhancing methane production and organic removal than these pre-treatments alone. The enhanced methane production is important for two reasons: a higher amount of renewable energy could be generated from the enhanced methane production and the COD of digested sludge reduces in such a way that facilitates application of the sludge to agricultural lands and reduces sludge transport costs.

Improving biogas production from continuous co-digestion of oily wastewater and waste-activated sludge by hydrodynamic cavitation pre-treatment.

Hydrodynamic cavitation (HC) was evaluated as a pretreatment for synthetic oily wastewater (OWW) to be co-digested with waste-activated sludge (WAS). The main objective of the present research was the enhancement of biogas production by the application of HC pretreatment. HC was applied to the OWW, and the OWW and WAS were added to a 50 L continuous digestion reactor. As a control system, an identical digestion reactor was set up for co-digestion of the WAS and the OWW without pretreatment. The reactors were initially filled with inoculum and the hydraulic retention time (HRT) was set to 22 d. The HRT was gradually reduced to 19, 16, and finally 13 d, but the substrate quality was kept constant. The loading rate, accordingly, increased from 0.86 to 1.46 g TVS/(L d). The biogas volume was recorded online and its quality was analyzed regularly. The HC improved biogas production up to 43% at 22 d of HRT. Reducing the HRT decreased biogas production from the main reactor while that of the control reactor was more or less constant. HC also increased the biogas methane content; the methane concentration of the main reactor was about 3% higher than the methane concentration of the control reactor. The main reactor experienced no clogging or accumulation of fatty materials.

An integrated methodology for establishing industrial effluent limits in developing countries: Iran as a case study.

BACKGROUND: Environmental policies should be developed in a contextual decision-making process regarding local environmental concerns emphasizing the economic, technical, social and institutional considerations. Establishing emission limit levels, especially in the industrial sector, is one of the most problematic environmental issues in developing countries, for which it is essential to include several criteria that reflect their country-specific constraints and capacities. Since Best Available Technology (BAT) is acknowledged to be the reference element for sustainable development and a basis for Emissions Limit Values (ELVs), the objective of this study is to present a reliable methodology for establishing ELVs thresholds with an emphasis on the BAT concept for national regulation at the sector level. METHODS: A hybrid fuzzy multiple-criteria decision-making (FMCDM) process, consisting of the Analytic Hierarchy Process (AHP) and fuzzy Technique for Order of Preference by Similarity to Ideal Solution (fuzzy TOPSIS) method, is structured to aggregate the different criteria and rank different ELV alternatives in this complicated evaluation. In order to use the most profound knowledge and judgment of a professional expert team, this qualitative assessment highlights the importance of supportive information. RESULTS: The results obtained indicate that experts have considered the country-specific information as a reliable reference in their decisions. Among different key evaluation criteria in effluent standard setting, the highest experts' priority is "Environmental protection". For both the conventional and toxic pollutants, the influence of all other criteria namely "Economic feasibility", "Technology viability" and "Institutional capacity", as constraining criteria in developing countries, have not reduced the responsibility towards the environmental objectives. In ELVs ranking, experts have made their decisions with respect to the specific characteristics of each pollutant and the existing capacities and constraints of the country, without emphasizing on any specific reference. CONCLUSIONS: This systematic and transparent approach has resulted in defensible country-specific ELVs for the Iron and Steel industry, which can be developed for other sectors. As the main conclusion, this paper demonstrates that FMCDM is a robust tool for this comprehensive assessment especially regarding the data availability limitations in developing countries.

Hydrodynamic cavitation as a novel approach for pretreatment of oily wastewater for anaerobic co-digestion with waste activated sludge.

Application of hydrodynamic cavitation (HC) was investigated with the objective of biogas production enhancement from co-digestion of oily wastewater (OWW) and waste activated sludge (WAS). Initially, the effect of HC on the OWW was evaluated in terms of energy consumption and turbidity increase. Then, several mixtures of OWW (with and without HC pretreatment) and WAS with the same concentration of total volatile solid were prepared as a substrate for co-digestion. Following, several batch co-digestion trials were conducted. To compare the biogas production, a number of digestion trials were also conducted with a mono substrate (OWW or WAS alone). The best operating condition of HC was achieved in the shortest retention time (7.5 min) with the application of 3mm diameter orifice and maximum pump rotational speed. Biogas production from all co-digestion reactors was higher than the WAS mono substrate reactors. Moreover, biogas production had a direct relationship with OWW ratio and no major inhibition was observed in any of the reactors. The biogas production was also enhanced by HC pretreatment and almost all of the reactors with HC pretreatment had higher reaction rates than the reactors without pretreatment.

A new flat sheet membrane bioreactor hybrid system for advanced treatment of effluent, reverse osmosis pretreatment and fouling mitigation.

This paper introduces a new hybrid electro membrane bioreactor (HEMBR) for reverse osmosis (RO) pretreatment and advanced treatment of effluent by simultaneously integrating electrical coagulation (EC) with a membrane bioreactor (MBR) and its performance was compared with conventional MBR. Experimental results and their statistical analysis showed removal efficiency for suspended solids (SS) of almost 100% for both reactors. HEMBR removal of chemical oxygen demand (COD) improved by 4% and membrane fouling was alleviated according to transmembrane pressure (TMP). The average silt density index (SDI) of HEMBR permeate samples was slightly better indicating less RO membrane fouling. Moreover, based on the SVI comparison of two reactor biomass samples, HEMBR showed better settling characteristics which improved the dewaterability and filterability of the sludge. Analysis the change of membrane surfaces and the cake layer formed over them through field emission scanning electron microscopy (FESEM) and X-ray fluorescence spectrometer (XRF) were also discussed.

Evaluation of membrane bioreactor for advanced treatment of industrial wastewater and reverse osmosis pretreatment.

The evaluation of a membrane bioreactor (MBR) for pretreatment of reverse osmosis (RO) in order to reuse and reclamation of industrial town wastewater treatment plant was investigated in this study. Performance of MBR effluent through water quality in term of parameters such as chemical oxygen demand (COD), total suspended solids (TSS), total nitrogen (TN) and total coliform (TC) were measured. Also Silt density index (SDI) was used as indicator for RO feed water. The results of this study demonstrated that MBR produce a high quality permeate water. Approximately 75%, 98%, 74% and 99.9% removal of COD, TSS, TN and TC were recorded, respectively. Also SDI of the permeate effluent from membrane was below 3 for most of the times. It means that pilot yield a high quality treated effluent from the membrane module which can be used as RO feed water.

Comparison of COD removal from pharmaceutical wastewater by electrocoagulation, photoelectrocoagulation, peroxi-electrocoagulation and peroxi-photoelectrocoagulation processes.

This work makes a comparison between electrocoagulation (EC), photoelectrocoagulation, peroxi-electrocoagulation and peroxi-photoelectrocoagulation processes to investigate the removal of chemical oxygen demand (COD) from pharmaceutical wastewater. The effects of operational parameters such as initial pH, current density, applied voltage, amount of hydrogen peroxide and electrolysis time on COD removal efficiency were investigated and the optimum operating range for each of these operating variables was experimentally determined. In electrocoagulation process, the optimum values of pH and voltage were determined to be 7 and 40 V, respectively. Desired pH and hydrogen peroxide concentration in the Fenton-based processes were found to be 3 and 300 mg/L, respectively. The amounts of COD, pH, electrical conductivity, temperature and total dissolved solids (TDS) were on-line monitored. Results indicated that under the optimum operating range for each process, the COD removal efficiency was in order of peroxi-electrocoagulation > peroxi-photoelectrocoagulation > photoelectrocoagulation>electrocoagulation. Finally, a kinetic study was carried out using the linear pseudo-second-order model and results showed that the pseudo-second-order equation provided the best correlation for the COD removal rate.

Simultaneous nitrification-denitrification and phosphorus removal in a fixed bed sequencing batch reactor (FBSBR).

Biological nutrient removal (BNR) was investigated in a fixed bed sequencing batch reactor (FBSBR) in which instead of activated sludge polypropylene carriers were used. The FBSBR performance on carbon and nitrogen removal at different loading rates was significant. COD, TN, and phosphorus removal efficiencies were at range of 90-96%, 60-88%, and 76-90% respectively while these values at SBR reactor were 85-95%, 38-60%, and 20-79% respectively. These results show that the simultaneous nitrification-denitrification (SND) is significantly higher than conventional SBR reactor. The higher total phosphorus (TP) removal in FBSBR correlates with oxygen gradient in biofilm layer. The influence of fixed media on biomass production yield was assessed by monitoring the MLSS concentrations versus COD removal for both reactors and results revealed that the sludge production yield (Y(obs)) is significantly less in FBSBR reactors compared with SBR reactor. The FBSBR was more efficient in SND and phosphorus removal. Moreover, it produced less excess sludge but higher in nutrient content and stabilization ratio (less VSS/TSS ratio).

Comparative cancer risk assessment of THMs in drinking water from well water sources and surface water sources.

This research evaluates the lifetime cancer risks from trihalomethanes in Tehran's drinking water. The Trihalomethanes were measured in seven different water districts. Sixty-three samples were taken from tap water across the city for 7 months. The samples were analyzed for trihalomethanes using US EPA method 524.2. The average concentration of total trihalomethanes in different districts were between 0.81 and 9.0 µg/L, and the highest concentrations were detected in district 2 at 19.5 µg/L. Total lifetime cancer risks assessment from exposure to trihalomethanes in drinking water (ingestion, inhalation, and skin routes) were performed for people living in different districts in Tehran. The lifetime cancer risk was 7.19 × 10(-5) in district 2 (a more affluent neighborhood) where mostly surface water sources is used to supply drinking water and 9.38 × 10(-6) in district 7 (a less affluent neighborhood) which is mainly supplied with well water sources. Based on the population data, the total expected lifetime cancer cases from exposure to trihalomethanes are 104, 108, 81, 81, 41, 27, and three for districts 1 through 7, respectively. The average lifetime cancer risk was 4.33 × 10(-5) which means a total of 606 lifetime cancer cases for the entire province of Tehran. The highest risk from THMs seems to be from the inhalation route followed by ingestion and dermal contacts.

Optimizing aeration rates for minimizing membrane fouling and its effect on sludge characteristics in a moving bed membrane bioreactor.

In MBR processes, sufficient aeration is necessary to maintain sustainable flux and to retard membrane fouling. Membrane permeability, sludge characteristics, nutrient removal and biomass growth at various air flow rates in the membrane and moving bed biofilm reactor (MBBR) compartments were studied in a pilot plant. The highest nitrogen and phosphorous removal rates were found at MBBR aeration rates of 151 and 85 L h(-1) and a specific aeration demand per membrane area (SAD(m)) of 1.2 and 0.4 m(air)(3) m(-2) h(-1), respectively. A linear correlation was found between the amount of attached biofilm and the nutrient removal rate. The aeration rate in the MBBR compartment and SAD(m) significantly influenced the sludge characteristics and membrane permeability. The optimum combination of the aeration rate in the MBBR compartment and SAD(m) were 151 L h(-1) and 0.8-1.2 m(air)(3) m(membrane)(-2) h(-1), respectively.

Fluoride removal from industrial wastewater using electrocoagulation and its adsorption kinetics.

Electrocoagulation (EC) process using aluminum electrodes is proposed for removing fluoride from treated industrial wastewater originated from steel industry. Effects of different operating conditions such as temperature, pH, voltage, hydraulic retention time (HRT) and number of aluminum plates between anode and cathode plates on removal efficiency are investigated. Experimental results showed that by increasing HRT, removal efficiency increases but after 5 min changes are negligible. Therefore, the total HRT required is only 5 min. The more HRT, the more electrical current is needed in order to achieve to constant voltage and temperature in system. In addition, it is found that pH value decreases from 6.91 to 4.6 during first 10 min but it increases up to 9.5 during 50 min. After treatment, the fluoride concentration was reduced from initial 4.0-6.0 mg/L to lower than 0.5 mg/L. The pH of the influent is found as a very important variable which affects fluoride removal significantly. The optimal range for the influent is 6.0-7.0 at which not only effective defluoridation can be achieved, but also no pH readjustment is needed after treatment. Moreover, increasing number of aluminum plates between anode and cathode plates in bipolar system does not significantly affect fluoride removal. Finally, the kinetic analysis is done for the system which indicates that the adsorption system obeys the second-order kinetic model.