Comparison studies of adsorption properties of MgO nanoparticles and ZnO–MgO nanocomposites for linezolid antibiotic removal from aqueous solution using response surface methodology

In this investigation, the adsorption measure of linezolid antibiotic onto MgO nanoparticles and ZnO–MgO nanocomposites were performed. The adsorbents were characterized by different techniques such as XRD, SEM, TEM and BET. The parameters influence such as the pH, adsorbent dosage and temperature was tested and evaluated by Box–Behnken Design combined with response surface methodology. Performing adsorption tests at optimal conditions set as 0.5 g L⁻¹ of adsorbent, pH 10 and 308 K make admit to obtain high adsorption turnover (123.45 and 140.28 mg g⁻¹ for MgO nanoparticles and ZnO–MgO nanocomposites, respectively). A good compromise between predicted and experimental data in this research was observed. The experimental equilibrium data fitting to Langmuir, Freundlich, Tempkin and Dubinin–Radushkevich models indicate that the Langmuir model is a best model for evaluation of adsorption behavior. Kinetic evaluation of experimental data indicated that the adsorption operations followed well pseudo-second-order models. The adsorption capacity of ZnO–MgO nanocomposites is higher than MgO nanoparticles that because of the ZnO–MgO nanocomposites have high specific surface area.     

Pb(II) adsorption from aqueous solutions by raw and treated biomass of maize stover – A comparative study

The potential to remove Pb(II) ion from wastewater treatment systems using raw and treated maize stover through adsorption was investigated in batch experiments. To achieve this, batch mode experiments were conducted choosing specific parameters such as pH (2–8), dosage concentration (2–30 g L⁻¹), contact time (5–180 min), temperature (20–45 °C) and metal ion concentrations (10–50 mg L⁻¹). Adsorption was pH-dependent showing a maximum at pH value 5. The equilibrium sorption capacities of raw and treated maize stover were 19.65 and 27.10 mg g⁻¹, respectively. The adsorption data fitted well to the Langmuir isotherm model. Kinetic studies revealed that the adsorption process followed pseudo-second-order model. The calculated thermodynamic parameters showed that the adsorption of Pb(II) was spontaneous and exothermic in nature. Consequently, this study demonstrated that both raw and treated maize stover could be used as adsorbents for the treatment of Pb(II) from industrial wastewaters.     

Evaluating the efficacy of alumina/carbon nanotube hybrid adsorbents in removing Azo Reactive Red 198 and Blue 19 dyes from aqueous solutions

Concerning the high volume of wastewater containing dye in Iran and its adverse effects, it is necessary to develop scientific solutions for treating these wastewaters. The aim of this study was to evaluate the efficiency of the alumina-coated multi-walled carbon nanotubes in removing the Reactive Red 198 (RR 198) and Blue 19 (RB 19) dyes. Synthetic samples including dye with different concentrations were prepared. These samples were put in contact with different contents of alumina/multi-walled carbon nanotubes, in different pH values, in different contact times, different temperatures and the presence of sodium sulfate or sodium carbonate. The optimum pH, dye concentration and temperature for removal of the two dyes was 3, 50 mg l⁻¹ and 25 °C, respectively. The optimum adsorbent dose for removal the RR 198 dye was 0.5 g l⁻¹ and for Blue 19 was 0.4 g l⁻¹. The optimum contact time for RR 198 was 150 min and RB 19 was 180 min. In this condition, maximum removal efficiency for RR 198 and RB 19 was 91.54% and 93.51%, respectively. The adsorption study was analyzed kinetically, and the results revealed that the adsorption fitted a pseudo-second order kinetic model. According to these results alumina/multi-walled carbon nanotubes can effectively remove RR 198 and RB 19 from aqueous solutions.     

Removal mechanism of trace oxytetracycline by aerobic sludge

To investigate the mechanism of removal of selected pharmaceuticals in activated sludge systems, laboratory-scale batch experiments were conducted to assess the adsorption and degradation behavior of trace oxytetracycline (OTC). The adsorption equilibrium of OTC was observed in 30 min and the adsorption process could be well described by a pseudo-second-order model with a rate of 0.362 L μg^?1 min^?1. The OTC adsorption rate decreased with increasing temperature and could be fitted by the Freundlich isotherm. The linear partition coefficients (K_d) were 1.19, 0.999, and 0.841 L g^?1 at temperatures of 15, 20, and 25 °C, respectively. Thermodynamic analysis revealed that the adsorption of OTC onto the inactivated sludge was spontaneous (ΔG = ?16.7 to ?17.0 kJ mol^?1), enthalpy-driven (ΔH = ?24.9 kJ mol^?1), entropy-retarded (ΔS = ?27.4 J (mol K)^?1), and predominantly a physical adsorption.     

Biosorption of zinc(II) on rapeseed waste: Equilibrium studies and thermogravimetric investigations

The removal of heavy metals from aqueous effluents so as to avoid their toxic, bioaccumulation and biomagnification effects to humans and environment is usually realized by means of physical, chemical treatment, and biological processes. The aim of this study is to evaluate the potential of rapeseed waste from biodiesel production as a biosorbent for Zn(II) ions.The ability of the rapeseed waste for Zn(II) biosorption exhibited a maximum at pH 4.5–5. The removal efficiency of Zn(II) from solution with an initial concentration of 72 mg L⁻¹ varied from 39% to 89% for an increase of the rapeseed waste dose from 2 to 30 g L⁻¹. The amount of Zn(II) retained on the tested rapeseed increased with increasing metal ion concentration, but the Zn(II) sorption percentage decreased. The equilibrium data are fitted to the Langmuir isotherm better than to the Freundlich isotherm. The kinetics of Zn(II) biosorption process follows a pseudo-second order model. The thermal stability of the rapeseed before and after Zn(II) biosorption was studied by thermogravimetric analysis. It was found that the zinc loaded rapeseed exhibits a better initial thermal stability than the original rapeseed, presumably due to the cross linking generated by the intermolecular complexation of Zn(II) ions. In both cases, the thermal decomposition takes place according to some reassembling kinetic models, in two phases with order n reactions. The results of this study strongly suggest the possibility to use rapeseed as an effective biosorbent for Zn(II) ions removal from aqueous effluents (municipal/industrial wastewaters).     

Rotating biological contactors for wastewater treatment – A review

Rotating biological contactors (RBCs) for wastewater treatment began in the 1970s. Removal of organic matter has been targeted within organic loading rates of up to 120 g m⁻² d⁻¹ with an optimum at around 15 g m⁻² d⁻¹ for combined BOD and ammonia removal. Full nitrification is achievable under appropriate process conditions with oxidation rates of up to 6 g m⁻² d⁻¹ reported for municipal wastewater. The RBC process has been adapted for denitrification with reported removal rates of up to 14 g m⁻² d⁻¹ with nitrogen rich wastewaters. Different media types can be used to improve organic/nitrogen loading rates through selecting for different bacterial groups. The RBC has been applied with only limited success for enhanced biological phosphorus removal and attained up to 70% total phosphorus removal. Compared to other biofilm processes, RBCs had 35% lower energy costs than trickling filters but higher demand than wetland systems. However, the land footprint for the same treatment is lower than these alternatives. The RBC process has been used for removal of priority pollutants such as pharmaceuticals and personal care products. The RBC system has been shown to eliminate 99% of faecal coliforms and the majority of other wastewater pathogens. Novel RBC reactors include systems for energy generation such as algae, methane production and microbial fuel cells for direct current generation. Issues such as scale up remain challenging for the future application of RBC technology and topics such as phosphorus removal and denitrification still require further research. High volumetric removal rate, solids retention, low footprint, hydraulic residence times are characteristics of RBCs. The RBC is therefore an ideal candidate for hybrid processes for upgrading works maximising efficiency of existing infrastructure and minimising energy consumption for nutrient removal. This review will provide a link between disciplines and discuss recent developments in RBC research and comparison of recent process designs are provided (Section 2). The microbial features of the RBC biofilm are highlighted (Section 3) and topics such as biological nitrogen removal and priority pollutant remediation are discussed (Sections 4 Biological nutrient removal in RBCs, 5 Priority pollutant remediation in RBCs). Developments in kinetics and modelling are highlighted (Section 6) and future research themes are mentioned.     

Decolorization of synthetic Methyl Orange wastewater by electrocoagulation with periodic reversal of electrodes and optimization by RSM

Treatment of Methyl Orange (MO), an azo dye, synthetic wastewater by electrocoagulation with periodic reversal of the electrodes (PREC) was examined. Response Surface Methodology (RSM) was used to optimize the influence of experimental conditions for color removal (CR), energy consumption (ENC), electrode consumption (ELC) and sludge production (SP) per kg MO removed (kg(MO_r)) with optimal conditions being found to be pH 7.4, solution conductivity (к) 9.4 mS cm⁻¹, cell voltage (U) 4.4 V, current density (j) 185 mA cm⁻², electrocoagulation time (T) 14 min, cycle of periodic reversal of electrodes (t) 15 s, inter-electrode distance (d) 3.5 cm and initial MO concentration of 125 mg L⁻¹. Under these conditions, 97 ± 2% color was removed and ENC, ELC and SP were 44 ± 3 kWh kg(MO_r)⁻¹, 4.1 ± 0.2 kg(Al) kg(MO_r)⁻¹ and 17.2 ± 0.9 kg(sludge) kg(MO_r)⁻¹, respectively. With the enhanced electrochemical efficiency resulting from the periodic electrode reversal, the coefficients of increased resistance and decreased current density between the two electrodes in the PREC setup were 2.48 × 10⁻⁴ Ω cm⁻² min⁻¹ and 0.29 mA cm⁻² min⁻¹, respectively, as compared to 7.72 × 10⁻⁴ Ω cm⁻² min⁻¹ and 0.79 mA cm⁻² min⁻¹ as measured for the traditional electrocoagulation process. The rate constant of decolorization was also enhanced by 20.4% from 0.152 min⁻¹ in the traditional electrocoagulation process to 0.183 min⁻¹ in the PREC process. These performance characteristics indicate that the PREC approach may be more promising in terms of practical application, as a cost-effective treatment, than conventional electrocoagulation for textile dye removals.     

Growing Carbon Nanotube on Aluminum Oxides: An Inherently Safe Approach for Environmental Applications

Using micron-sized Al₂O₃ particles as carriers to grow carbon nanotubes (CNTs) under 700°C atmosphere of methane and hydrogen after pre-planted catalysts of Fe–Ni nanoparticles, those composite CNTs (CCNTs) have demonstrated several unique properties compared to CNTs—medium specific surface area and zeta potential, high adsorption capacity for metal ions, high recovery rate by acids, low decomposition heat for exothermal reaction, and so on. The adsorption behaviours of Pb²⁺, Cu²⁺ and Cd²⁺ in aqueous solutions by CCNTs are in good agreement with the Langmuir adsorption isotherm and second order kinetic model with maximum individual adsorption capacities of 67.11, 26.59 and 8.89 mg g⁻¹. The individual and competitive adsorption behaviours indicated that the preference order of adsorption were Pb²⁺ > Cu²⁺ > Cd²⁺ for aluminum oxides, activated carbon, commercial CNTs, and CCNTs as well as other researchers’ CNTs. We suggest that future development of CNTs to combine with metals and/or other materials, such as TiO₂, should consider attached to carriers or surface in order to avoid concerns on environment, health and safety. Thus, growing CNTs on Al₂O₃ particles to form CCNTs is an inherently safe approach for many promising environmental applications.     

Evaluation of Abelmoschus esculentus (lady's finger) seed as a novel biosorbent for the removal of Acid Blue 113 dye from aqueous solutions

The use of a new biosorbent derived from Abelmoschus esculentus (A. esculentus) seed for the removal of Acid Blue 113 (AB113) in aqueous solutions was investigated in batch mode. Biosorption studies were carried out under varying operational parameters including initial pH, biosorbent dosage, contact time, initial dye concentration and temperature. The results indicated that the biosorption properties were strongly dependent on initial pH. Fourier transform infrared spectroscopy analysis revealed that hydroxyl, carboxylic and amide functional groups present on the biosorbent surface were involved in the dye removal process. Equilibrium data were best fitted by the Langmuir model. The maximum biosorption capacity was 169.9 ± 3.1 mg g⁻¹ at 25 °C and initial pH 5.5. The kinetic data were in good agreement with the pseudo-second-order kinetic model. The process was controlled by diffusion through boundary layer at the initial stage followed by intra-particle diffusion at the later stage. Thermodynamic evaluation showed that the process was endothermic and spontaneous. The present study suggests that A. esculentus seed with maximum biosorption capacity which compared well with values reported in the literature can be a potential biosorbent for AB113 dye removal.     

Pretreatment of municipal landfill leachate by a combined process

Biodegradability enhancement of landfill leachate using air stripping followed by coagulation/ultrafiltration (UF) processes was introduced. The air stripping process obtained a removal efficiency of 88.6% for ammonia nitrogen (NH₄–N) at air-to-liquid ratio of 3500 (pH 11) for stripping 18 h. The single coagulation process increased BOD/COD ratio by 0.089 with the FeCl₃ dosage of 570 mg l^?1 at pH 7.0, and the single UF process increased the BOD/COD ratio to 0.311 from 0.049. However, the combined process of coagulation/UF increased the BOD/COD ratio from 0.049 to 0.43, and the final biological oxygen demand (BOD), chemical oxygen demand (COD), NH₄–N and colour of leachate were 1223.6 mg l^?1, 2845.5 mg l^?1, 145.1 mg l^?1 and 2056.8, respectively, when 3 kDa molecular weight cut-off (MWCO) membrane was used at the operating pressure 0.7 MPa. In ultrafiltration process, the average solution flux (J_V), concentration multiple (M_C) and retention rate (R) for COD was 107.3 l m^?2 h^?1, 6.3% and 84.2%, respectively.     

Application of Modified Carbon Anodes in Microbial Fuel Cells

The effect of different carbon anodes was examined in a new design of single chambered microbial fuel cell (SCMFC). The new cell design used a low-cost hydrophilic membrane to replace costly proton exchange membranes and carbon felt and a range of carbon and modified carbon anodes were investigated. The fuel for the SCMFC was brewery wastewater which was diluted with domestic wastewater and the presented microflora acts as a source of electro-active bacteria. The membrane acts as a separator between the anode chamber and an air cathode and allows the transfer of ions based on the wastewater's natural conductivity. The air cathode was carbon black (Ketjen Black EC 300J) which was deposited (1 mg cm⁻² concentration) directly onto the surface of the separator (one side of the membrane). Steady state polarization demonstrated maximum power densities of up to 30 mW m⁻² and a steady state power density of 20 mW cm⁻² at a current density of 110 mA m⁻² was achieved. The best performing anodes were made from carbon modified with quinone/quinoid groups. With unmodified graphite felt (the control anode material) as anode, the maximal power density obtained was 9.5 mW m⁻².     

Biosorption of Co(II) ions from aqueous solution using Chrysanthemum indicum: Kinetics,equilibrium and thermodynamics

The present study investigates the adsorption potential of Chrysanthemum indicum flower in its raw (CIF-R) and biochar (CIF-BC) form for the removal of cobalt ions from aqueous solution. The adsorbents were characterized for their surface area using BET analysis, surface morphology and elemental composition with SEM-EDAX and for the presence of functional groups by FTIR analysis. Batch adsorption experiments were carried out to evaluate the effect of process parameters, viz. pH, adsorbent dosage, initial metal ion concentration, contact time, stirring speed, presence of interfering ions and temperature on the adsorption of Co(II) ion using both the adsorbents. The optimum conditions for maximum removal of Co(II) ion was ascertained to be pH 5 for both adsorbents, adsorbent dose of 4 g/L and 3 g/L, equilibrium time of 60 min and 45 min, respectively, for CIF-R and CIF-BC. The maximum adsorption capacity of CIF-R and CIF-BC was found to be 14.84 mg/g and 45.44 mg/g, respectively, for the removal of Co(II) ion. The mechanism of adsorption was studied using different models of adsorption kinetics, isotherms and thermodynamics. It was inferred that Co(II) adsorption on both CIF-R and CIF-BC followed pseudo-second order kinetics and Langmuir isotherm model with the process being spontaneous and endothermic in nature.     

Biofiltration of gas-phase hexane and toluene mixture under intermittent loading conditions

This paper reports the performance of a compost biofilter subjected to periodic intermittent loads of gas-phase hexane and toluene. The biofilter was operated for 10 h per day, at different empty bed residence times (4, 2 and 1.3 min), and at different inlet concentrations of hexane and toluene, varying between 2 and 3.8 g m^?3, respectively. Steady-state removal efficiency profiles, reaching more than 90% for both the pollutants, was observed after 44 days of operation. Periodic operation of the compost biofilter was characterized by an adsorption step, followed by biological conversion of the pollutants by the microorganisms inherent to the compost. After resuming daily biofilter operation, the required times for biochemical reaction to dominate the initial adsorption step was observed to be 2.5 and 1 h, respectively, for toluene and hexane. The maximum elimination capacity due to the biological step was found to be 61.6 g m^?3 h^?1. The results from this study showed the effectiveness of the biofilter to handle mixtures of gas-phase pollutants, subjected to regular intermittent operations, thus proving their worthiness for industrial use.     

Removal of toluene vapour from air stream using a biofilter packed with polyurethane foam

Biodegradation of toluene vapour was investigated for 168 days in a polyurethane packed biofilter inoculated with a mixed microbial population. Biofilter consisted of five square cross-section modular units each of size 0.16 m × 0.16 m × 0.20 m and filled with the polyurethane foam cubes up to a height of 0.15 m. Inlet concentration of toluene was varied from 0.04 to 2.5 g m^?3 and the volumetric flow rate of toluene loaded air from 0.06 to 0.90 m³ h^?1.Depending upon initial loading rates, removal efficiency ranging from 68.2 to 99.9% and elimination capacity ranging from 10.85 to 90.48 g h^?1 m^?3 were observed during steady state operations. More than 90% removal efficiency was observed up to an inlet loading rate of 76.3 g h^?1 m^?3. High carbon recovery (>90%) indicated effective biodegradation in the bed. Low variation of pH (7.2–8.8) and pressure drop (45.8–76.3 Pa) was observed. The stability of the biomass was evident from the fast response of the biofilter to shutdown and restartup.     

Kinetics of nitrate reductive denitrification by nanoscale zero-valent iron

Nanoscale zero-valent iron (Fe⁰) was synthesized for nitrate denitrification. The reduction efficiency of nitrate decreased quickly with increasing initial pH value, increased considerably with the increasing dosage of nanoscale Fe⁰, and did not vary much with initial nitrate concentrations changing from 20 to 50 mg l^?1 when the excessive amount of nanoscale Fe⁰ was utilized. With reductive denitrification of nitrate by nanoscale Fe⁰, the removal rate of nitrate reached 96.4% in 30 min with nanoscale Fe⁰ dosage of 1.0 g l^?1 and pH_in 6.7, and more than 85% of the nitrate was transformed into ammonia. Kinetics analysis in batch studies demonstrates that the denitrification of nitrate by nanoscale Fe⁰ involves reaction on the metal surface, which fits well the pseudo-first order reaction with respect to nitrate concentration. The observed reaction rate constant of reductive denitrification of nitrate was determined to be 0.086 min^?1 with a nanoscale Fe⁰ dosage of 1.0 g l^?1 and pH_in 6.7. Fast and highly effective denitrification can be achieved by nanoscale Fe⁰ compared with commercial Fe⁰ powder, this is due to the extremely high surface area and high reactivity for nanoscale Fe⁰, which can enhance the denitrification efficiencies remarkably.     

Optimization of Innovative Ethanol Production from Wheat by Response Surface Methodology

A soft wheat variety has been tested as the raw material for fuel ethanol production via a novel processing route. The bran stream produced by the break section of a Buhler mill was used as the sole nutrient source in solid-state fermentation for the production of hydrolytic enzymes by two fungal strains, Aspergillus awamori and Aspergillus oryzae. Co-fermentation of the two fungi was largely problematic because of a significant difference between their growth rates. A mixture of the two enzyme solutions produced by separate cultivation of the two strains was effective for simultaneous starch and protein hydrolyses. Response surface methodology was used to design ethanol production trials using the flour hydrolysate as the only nutrient source by Saccharomyces cerevisiae. In a medium containing 150 g l⁻¹ glucose and 310 mg l⁻¹ free amino nitrogen, ethanol yield on glucose reached 50.7%, i.e., 99.2% of the theoretical conversion ratio, in 72 h. The yield of CO₂ from glucose was approximated as slightly higher than its theoretical yield due possibly to the availability of O₂ in the early fermentation stage. The overall production of 2-methyl-1-butanol, 1-propanol, 2-methyl-1-propanol and 3-methyl-butanol in all trials of yeast fermentation remained below 1000 ppm. Mass balance calculation concluded conversion ratios of 29.61% (w/w) ethanol and 23.74% (w/w) CO₂ from the wheat.     

Environmentally friendly hide unhairing: Enzymatic-oxidative unhairing as an alternative to use of lime and sodium sulfide

Various studies have been conducted to develop technologies that minimize the environmental concerns associated with the leather industry. The use of enzymes and oxidizing products during the unhairing step reduces pollution by tanneries as well as process time. In this study, were used an enzymatic extract produced by a strain of Bacillus subtilis – BLBc 11 – and hydrogen peroxide to conduct enzymatic-oxidative unhairing as an alternative to the conventional process (lime and sodium sulfide). Tests for enzymatic-oxidative unhairing were performed by applying crude enzymatic extract at concentrations of 100 U g⁻¹ and 300 U g⁻¹ of hide and hydrogen peroxide at concentrations of 4% and 8%. Tests were conducted comparing the proposed unhairing method, the conventional unhairing and purely enzymatic unhairing, performed with crud enzymatic extract produced by strain BLBc 11. The results showed that the proposed enzymatic-oxidative unhairing method can be used as an alternative to lime and sodium sulfide.     

Removal of H2S by co-immobilized bacteria and fungi biocatalysts in a bio-trickling filter

Biological control of odor gases has gained more attention in recent years. In this study, removal performance of a vertical bio-trickling filter inoculated with bacteria and fungi was studied. Bacteria and fungi were isolated from activated sludge in a sewage treatment plant. By adopting “three step immobilization method”, the bio-trickling filter could degrade pollutant immediately once hydrogen sulfide (H₂S) passed. The optimal empty bed resident time was 20 s. The optimal elimination capacity was about 60 g H₂S m^?3 h^?1 with removal efficiency of 95%. And the maximum elimination capacity was 170 g H₂S m^?3 h^?1. Pressure drop was ranged between 5 and 15 mm H₂O per bed over the whole operation. Removal efficiency was not affected obviously after terminating nutrient supply. The bio-trickling filter could recover back after shut down H₂S gaseous and liquid supplies simultaneously. Microbial community structure in the bio-trickling filter was not changed significantly.Combining bacteria and fungi would be a better choice for inoculation into a bio-trickling filter because of the quickly degradation of H₂S and rapid recovery under shut-down experiment. This is the first study attempting to combine bacteria and fungi for removal of H₂S in a bio-trickling filter.     

Use of advance oxidation process to improve the biodegradability of olive oil mill effluents

In this study, recalcitrant total phenol (TPh) and organic matter removal were investigated at olive mill wastewater (OMW) in sequential Coagulation and Fenton system. This study focused on different operational parameters such as pH, H₂O₂, and Fe²⁺ dosages, and [Fe²⁺]/[H₂O₂] ratios. The optimum conditions were determined as; pH = 3; [Fe²⁺] = 2.5 g/L; [Fe²⁺]/[H₂O₂] = 2.5. A higher treatment efficiency was achieved at sequential Coagulation and Fenton system (COD, 65.5%) and TPh, 87.2%), compared to coagulation process (COD, 51.4%; total organic carbon (TOC), 38.6% and total nitrogen (TN) 52.1%). This study demonstrated that the Coagulation and Fenton process has a potential for efficient removal of phenolic pollutants from wastewater.     

Fate of trace tetracycline with resistant bacteria and resistance genes in an improved AAO wastewater treatment plant

The fate of trace tetracycline, tetracycline resistant bacteria (TRB) and tetracycline resistant genes (TRGs) in an improved anaerobic-anoxic-oxic (AAO) wastewater treatment plant (WWTP) was investigated in this study. Quantitative real-time polymerase chain reaction (qPCR) and conventional heterotrophic plate count method were used to measure eight tet genes (tetA, tetB, tetC, tetE, tetM, tetO, tetS and tetX) and TRB, respectively. The TRB percent of total heterotrophic bacteria (THB) is about 1.31–24.1% in WWTP influent. Tet gene abundance in the WWTP varied greatly among the gene types. The concentrations of TRGs in effluent samples ranged from 7.11 × 10⁻⁹ to 1.53 × 10⁻⁴ copies/copy 16S rRNA gene. TRB and THB, tetM and tetO, tetE and tetX, but not the others, showed a significant correlation with each other (p < 0.01). The relationships between ribosomal protection protein genes, enzymatic modification gene and corresponding concentrations of antibiotics were found to be considerably significant (R² = 0.898, p < 0.01 for ribosomal protection protein genes and R² = 0.872, p < 0.05 for enzymatic modification gene).