Partial nitritation of landfill leachate with varying influent composition under intermittent aeration conditions

The start-up and operation of a partial nitritation sequencing batch reactor for the treatment of landfill leachate were carried out on intermittent aeration mode. Partial nitrite accumulation was established in 15 days after the mode was changed from continuous aeration to intermittent aeration. Despite the varying influent composition, partial nitritation could be maintained by adjusting the hydraulic retention time (HRT) and the air flow rate. An increase in the air flow rate together with a decrease in air off duration can improve the partial nitritation capacity and eventually result in the development of granular sludge with fine diameters. A nitrogen loading rate of 0.71 ± 0.14 kg/m³/d and a COD removal rate of 2.21 ± 0.13 kg/m³/d were achieved under the conditions of an air flow rate of 19.36 ± 1.71 m³ air/m³/h and an air on/off duration of 1.5 min/0.7 min. When the ratio of total air flux (TAF) to the influent loading rate (ILR) was controlled at the range of 163–256 m³ air/kg COD, a stable effluent NO₃^?–N/NO_x^?–N (NO₂^?–N plus NO₃^?–N) ratio below 13% was achieved. Interestingly, the effluent pH was found to be a good indicator of the effluent NO₂^?–N/NH₄⁺–N ratio, which is an essential parameter for a subsequent anaerobic ammonium oxidation (Anammox) reactor.     

Modeling of a sequencing batch reactor treating municipal wastewater using multi-layer perceptron and radial basis function artificial neural networks

A sequencing batch reactor was modeled using multi-layer perceptron and radial basis function artificial neural networks (MLPANN and RBFANN). Then, the effects of influent concentration (IC), filling time (FT), reaction time (RT), aeration intensity (AI), SRT and MLVSS concentration were examined on the effluent concentrations of TSS, TP, COD and NH₄⁺-N. The results showed that the optimal removal efficiencies would be obtained at FT of 1 h, RT of 6 h, aeration intensity of 0.88 m³/min and SRT of 30 days. In addition, COD and TSS removal efficiencies decreased and TP and NH₄⁺-N removal efficiencies did not change significantly with increases of influent concentration. The TSS, TP, COD and NH₄⁺-N removal efficiencies were 86%, 79%, 94% and 93%, respectively. The training procedures of all contaminants were highly collaborated for both RBFANN and MLPANN models. The results of training and testing data sets showed an almost perfect match between the experimental and the simulated effluent of TSS, TP, COD and NH₄⁺-N. The results indicated that with low experimental values of input data to train ANNs the MLPANN models compared to RBFANN models are more precise due to their higher coefficient of determination (R²) and lower root mean squared errors (RMSE) values.     

On–off control of aeration time in the simultaneous removal of ammonia and manganese using a biological aerated filter system

The biological aerated filter (BAF) system, a new alternative in drinking water treatment, was designed to remove NH₄⁺–N and Mn²⁺ simultaneously. This study aimed to control the aeration time in the BAF system for simultaneous NH₄⁺–N and Mn²⁺ removal to achieve the Malaysian effluent quality regulation for drinking water. The experiment was conducted under four strategies of S1, S2, S3 and S4. The results demonstrated that acceptable levels of NH₄⁺–N and Mn²⁺ were achieved over a 6 h aeration period (S1), producing effluent concentrations of 0.7 mg/L (93.2% removal) and 0.08 mg/L (79.6% removal), respectively. At the initial treatment of S1 and S2, the dissolved oxygen (DO) level rapidly increased until it reached a saturated concentration (6.8 mg/L DO) after 2 h period. Automatic on–off aeration time to maintain 3 mg/L DO set point (S4) resulted with a good effluent quality of NH₄⁺–N and Mn²⁺ compared with the 2 mg/L DO set point (S3) which did not meet the regulated standard limits. Through the automatic on–off aeration time, the saturated and excessive DO levels in the BAF system can be avoided consequently reduce the wastage of energy and electrical consumption for simultaneous NH₄⁺–N and Mn²⁺ removal from drinking water treatment.     

Continuous nitrifying granular sludge bioreactor: Influence of aeration and ammonium loading rate

Granulation of nitrifying bacteria was investigated in a continuous bubble column bioreactor. Then, the combined effect of aeration and ammonium loading rates on dissolved oxygen (DO) concentration as well as nitrification process was evaluated in the system using an experimental design technique. After 120 days, stable nitrifying granules with average diameter of 1.4 mm and settling velocities of 55 m/h were obtained. The influence of increasing ammonium loading rate (ALR) was found to be more significant than decreasing aeration rate on the reduction of DO concentration inside the nitrifying bioreactor. The system could handle the ALR values of 0.48–1.92 gNH₄⁺-N/L d with the ammonium removal efficiency from 65% to nearly 100% at the tested airflow rates of 2.5 and 4.5 L/min. At the low aeration, the complete ammonium conversion to nitrate was replaced with nitrite when the ALR increased to 1.44 gNH₄⁺-N/L d. At the high aeration, however, almost complete nitrification was achieved except the high ALR in which the nitrite accumulation was observed up to 38%. The study demonstrated that the continuous bioreactor had a considerable performance for obtaining stable nitrifying granules to have nitrite accumulation under control with changing the ratio of aeration rate and ALR.     

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.     

Evaluation of decentralized treatment of sewage employing bio-contact oxidation reactor integrated with filter bed

A bio-contact oxidation reactor integrated with filter bed (COR-FB) was developed for decentralized treatment of sewage, which consisted of a biofilm reactor and a gravitational filter bed. It has been investigated to treat municipal wastewater for reuse. The evaluation of COR-FB performance demonstrates that it produced good quality effluent regarding carbonaceous compound, nitrogenous compound, suspended solid and fecal coliform. The efficiencies of COD, NH₄⁺-N, TN, TP and turbidity removal were 90.7%, 81.4%, 64.6%, 60.1% and 96.7%, respectively. The residual geometric mean of fecal coliform counts in the final effluent of COR-FB was only 7.8 × 10³ MPN/10³ ml, corresponding to removal value of 3.8 log 10. However, TP removal indicates the necessity of an addition of a bagger and mud valve or an enhanced chemical phosphorus removal prior to treated water reuse. Microfauna communities were monitored in COR-FB, which was found to contain 5 genres and 19 species in the biofilm layer. Also, a simple kinetics model for COR-FB was developed based on the influent, effluent soluble COD concentration and the reaction time by regression simulation. In general, available data proved that COR-FB system can be recommended as a compact and cost-effective technology for decentralized treatment of sewage, especially for developing countries.     

An Experimental Study on Pyrolysis of Biomass

In this study, pyrolysis of sugarcane bagasse was performed in fixed bed tubular reactor under the conditions of nitrogen atmosphere, by varying temperature and different particle sizes. The effect of final pyrolysis temperature from 400 to 500°C and the nitrogen flow rate from 50 to 200 cc min⁻¹ on the pyrolysis product yields from sugarcane bagasse have been investigated. The Maximum bio-oil yield obtained is 24.12 wt% at the final pyrolysis temperature of 450°C, N₂ flow rate of 50 cc min⁻¹ and particle size of mesh number −8 + 12. The yield of bio-oil decreases with increase in temperature from 450 to 550°C and N₂ flow rate from 50 to 200 cc min⁻¹. The various characteristics of pyrolysis oil obtained under these conditions were identified on the basis of standard test methods. The empirical formula of pyrolysis oil with a heating value of 37.01 MJ Kg⁻¹ was established as CH_1.434 O_0.555 N_0.004. The results from the pyrolysis show the potential of sugarcane bagasse as an important source of liquid hydrocarbon fuel.     

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.     

Ion exchange membrane-assisted electro-activation of aqueous solutions: Effect of the operating parameters on solutions properties and system electric resistance

The properties of electro-activated (EA) aqueous solutions as well as the dynamics of their changes were considered in the current study using aqueous solutions of NaCl and NaHCO₃. The concentrations of the salt solutions were 0.5, 0.25, 0.125 and 0.05 M. The tests were performed at the DC current densities of 25, 37.5, and 50 Å/m². The electro-activation reactor consisted of three individual cells assembled together and separated by anion-exchange (AEM) and cation-exchange (CEM) membranes. During the experiments, four configurations of the membrane placements and solutions concentrations were studied. The obtained results showed the dynamics of the electro-activation process that allows obtaining electro-activated solutions with targeted properties such as pH and oxydo-reduction potential (ORP). It was possible to obtain electro-activated solutions at the anodic side (acid anolyte) with pH of 3.0, 3.5, and 4.0 and ORP of +1100 ± 15 mV when NaCl solution was used as electrolyte. Furthermore, several types of electro-activated solutions with high redox potential (ORP = +921 ± 12 mV) and neutral pH (6.48 ± 0.05) were obtained on the anode side when sodium carbonate was used. At the same time, two types of solutions, one with acid pH (2.14 ± 0.14) and the other one with alkaline pH (10.46 ± 0.03) with ORP = +689 ± 10 and 110 ± 21 mV, respectively, were obtained in the central compartment which considered as electro-activated solutions obtained by means of noncontact electro-activation.     

Low-dose irradiation by electron beam for the treatment of high-SOx flue gas on a semi-pilot scale—Consideration of by-product quality and approach to clean technology

Attention has been focused on the treatment of lignite-fired flue gas in order to use lignite in an environmentally friendly way – (i) low-CO₂ emission, (ii) production of a valuable by-product, (iii) no discharge of wastewater, (iv) direct removal of SO₃ (strong toxicity), and (v) treatment of high SO₂ concentration. Based on these criteria, electron beam irradiation with ammonia injection was tested on a semi-pilot scale: 800 Nm³ h^?1 flow rate, 5500 ppm SO₂, 70 ppm NO_x, 22% flue gas moisture, and 75–80 °C at the reactor outlet.As an energy-saving measure, a low dose (5 kGy) of irradiation was applied: the problem lay in the by-product quality. It is considered that (NH₄)₂SO₃ and NH₄HSO₃ produced by thermal reactions are oxidized to form (NH₄)₂SO₄ (fertilizer) by an electron beam. However, not all reactions were complete because the by-product contained small amounts of H₂SO₄ and NH₂SO₃NH₄ (herbicide), so a vegetable pot test was performed to study the by-product quality: no adverse effect was observed. It is inferred from the pot test that slightly acidic soil may protect vegetables from disease and a small amount of NH₂SO₃NH₄ probably affects woody species and not herbaceous species.It is concluded that the electron beam system is noted as a multi-component pollution control process (removal of NO_x, SO₃, SO₂ and dioxins) and this system will contribute to environmentally friendly use of lignite as well as agricultural productivity via fertilizer supply.     

Calorimetric behaviors of N2H4 by DSC and superCRC

The objective of this study is to obtain information about the thermal decomposition behaviors of hydrazine (N₂H₄) caused by metals, using differential scanning calorimeter (DSC) and SuperCRC. The DSC measurements revealed that the exothermic reactions of N₂H₄ were caused by the reaction conditions such as the type of cells; the T_DSC with a gold pan is 485.2 K and that with a glass capillary is 620.5 K. Besides, the activation energy of the thermal decomposition of N₂H₄, calculated from the Kissinger and Ozawa methods, were found to be about 38±2 kJ mol⁻¹ in the gold pan and 141±8 kJ mol⁻¹ in the glass capillary. Moreover, a heat flow profile was observed with SuperCRC during the mixing of N₂H₄ and the metal ion solution at 298 K. The maximum heat flow was related to the metal ion oxidative characters. The higher oxidative characters would provide a faster acceleration for the exothermic behavior than the lower oxidative ions. Based on this study, Mn(VII) and Cr(VI) were considered to exhibit strongly oxidative characteristics during mixing with N₂H₄.     

Disintegration of waste activated sludge by different applications of Fenton process

Oxidative disintegration of municipal waste activated sludge (WAS) using conventional Fenton (Fe²⁺ + H₂O₂, CFP) and Fenton type (Fe⁰ + H₂O₂, FTP) processes was investigated and compared in terms of the efficiency of sludge disintegration and enhancement of anaerobic biodegradability. The influences of different operational variables namely sludge pH, initial concentration of Fe²⁺ or Fe⁰, and H₂O₂ were studied in detail. The optimum conditions have been found as catalyst iron dosage = 4 g/kg TS, H₂O₂ dosage = 40 g/kg TS and pH = 3 within 1 h oxidation period for both CFP and FTP. Kinetics studies were performed under optimal conditions. It was determined that the sludge disintegration was happened in two stages by both processes: rapid and subsequent slow disintegration stages and rapid sludge disintegration stage can be described by a zero-order kinetic model. The effects of oxidative sludge disintegration under the optimum conditions on anaerobic digestion were experienced with biochemical methane potential (BMP) assay in batch anaerobic reactors. Total methane production in the CFP and FTP pre-treated reactors increased by 26.9% and 38.0%, relative to the untreated reactor (digested the raw WAS). Furthermore, the total chemical oxygen demand reductions in the pre-treated reactors were improved as well.     

Artificial neural network modelling of As(III) removal from water by novel hybrid material

The present study reported a method for removal of As(III) from water solution by a novel hybrid material (Ce-HAHCl). The hybrid material was synthesized by sol–gel method and was characterized by XRD, FTIR, SEM–EDS and TGA–DTA. Batch adsorption experiments were conducted as a function of different variables like adsorbent dose, pH, contact time, agitation speed, initial concentration and temperature. The experimental studies revealed that maximum removal percentage is 98.85 at optimum condition: pH = 5.0, agitation speed = 180 rpm, temperature = 60 °C and contact time = 80 min using 9 g L⁻¹ of adsorbent dose for initial As(III) concentration of 10 mg L⁻¹. Using adsorbent dose of 10 g L⁻¹, the maximum removal percentage remains same with initial As(III) concentration of 25 mg L⁻¹ (or 50 mg L⁻¹). The maximum adsorption capacity of the material is found to be 182.6 mg g⁻¹. Subsequently, the experimental results are used for developing a valid model based on back propagation (BP) learning algorithm with artificial neural networking (BP-ANN) for prediction of removal efficiency. The adequacy of the model (BP-ANN) is checked by value of the absolute relative percentage error (0.293) and correlation coefficient (R² = 0.975). Comparison of experimental and predictive model results show that the model can predict the adsorption efficiency with acceptable accuracy.     

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.     

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.     

Optimizing the preparation parameters of mesoporous nanocrystalline titania and its photocatalytic activity in water: Physical properties and growth mechanisms

Titania nanomaterial with an anatase structure and 5.6 nm crystallite size and 280.7 m² g⁻¹ specific surface areas had been successfully prepared by sol–gel/hydrothermal route. The effect of pH as a type of autoclave and calcination was studied. Crystallite size and phase composition of the prepared samples were identified. X-ray diffraction analyses showed the presence of anatase with little or no rutile phases. The crystallite size of the prepared TiO₂ with acidic catalyst was both smaller than that prepared with basic catalyst, and was increasing after acidic calcinations by a factor 4–5. Basic calcinations produced a specific increase of 1.5. Rutile ratio and the particle size were increased after calcination at 500 °C. However, TiO₂ powder synthesized using a basic catalyst persisted the anatase phase and a loosely aggregation of particles. Anatase TiO₂ as prepared with acidic catalyst in Teflon lined stainless steel autoclave demonstrated the highest photocatalytic activity for degradation of 2,6-dichlorophenol-indophenol under ultraviolet irradiation with t_½ 0.8 min.     

Effects of high ammonia loads on nitrogen mass balance and treatment performance of a biotrickling filter

A biotrickling filter packed with coal slag as packing medium was continuously used for more than 9 months under high ammonia loading rates of up to 140 g/m³/h. Nitrogen mass balance and microbial community analysis were conducted to evaluate the inhibitory effects of high ammonia concentration and metabolic by-products on the rates of nitrification. Ammonia removal efficiency reached above 99% at an empty bed retention time of as low as 8 s when inlet concentrations were below 350 ppm. The maximum and critical elimination capacities of the biotrickling filter were 118 g/m³/h and 108.1 g/m³/h, respectively. Kinetics analysis results showed that less than 2.5 s was required for the biotrickling filter with pH control to treat ammonia at concentrations of up to 500 ppm in compliance with the Taiwan EPA standard (outlet NH₃ < 1 ppm). Results of mass balance and microbial community analysis indicated that complete removal was mainly contributed by the activities of autotrophic ammonia oxidizing bacteria and not by physical absorption or adsorption at low loading rates. However, at high inlet loadings, ammonium became the dominant by-product due to inhibitory effects of high ammonia concentration on the bacterial community.     

An explosion of a tank car carrying waste hydrogen peroxide

On the Metropolitan Expressway in Tokyo, a tank car exploded because it was carrying hydrogen peroxide (H₂O₂) in a compartment in which copper chloride (CuCl₂) remained. Although the main cause of the accident was trivial, the background on the accident suggested that an induction period in the reaction led to a mistake. This report describes the experimental investigation of the catalytic ability of CuCl₂, and comparing it with two other copper(II) compounds (nitrate: Cu(NO₃)₂; and copper sulfate: CuSO₄) and three iron(III) compounds (chloride: FeCl₃; nitrate: Fe(NO₃)₃; and sulfate: Fe₂(SO₄)₃).The experiments were performed using a reaction calorimeter. During the experiments at 35 °C, 2×10⁻⁵ mol of copper compounds slowly reacted with H₂O₂ and generated a precipitate. The iron compounds allowed the hydrogen peroxide to violently decompose. A 1×10⁻⁴ mol solution of CuCl₂, however, produced a violent decomposition at 35 °C. At 15 °C, a moderate heat release occurred.Based on these results, the concentration and temperature dependence of the catalytic ability of CuCl₂ were postulated to contribute to the induction period observed in the accident.     

Preparation of iodine doped titanium dioxide to photodegrade aqueous bisphenol A under visible light

Highly photoactive iodine-doped titanium dioxide (I-doped TiO₂) photocatalysts were synthesized to degrade aqueous bisphenol A (BPA) under irradiation by visible light and sunlight. The band gap energies of TiO₂ and I-doped TiO₂ (I/Ti mole ratio = 0.5%) were 3.01 and 3.04, and the BPA photodegradation rate constants were 1.61, and 5.11 h⁻¹, respectively. The most probable reaction mechanism was proposed to involve IO₄⁻ and IO₃⁻ as electron acceptors that generate an inductive effect, increasing the photocatalytic efficiency of TiO₂. Results indicated that I-doped TiO₂ not only acted favorably as a photocatalyst, but also exhibited considerable mineralization effects. In addition, a recycling test after ten experiments demonstrated the stability and reusability of the photocatalyst.     

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).