Reactors R1 Research Articles

Dominance of Candidatus saccharibacteria in SBRs achieving partial denitrification: effects of sludge acclimating methods on microbial communities and nitrite accumulation.

Partial denitrification (NO3−-N → NO2−-N) was combined with anaerobic ammonium oxidation (ANAMMOX) to achieve nitrogen removal with a low C/N ratio and low energy consumption. Three different acclimation conditions, namely, R1 (sequencing batch reactor (SBR) under anoxic conditions), R2 (SBR under alternating anoxic/aerobic conditions), and R3 (SBR under low-intensity aeration), were investigated using glucose as an electron donor to achieve continuous accumulation of nitrite during a 120 d run. Subsequently, the denitrification performance and microbial community structure of the sludge were investigated. The results showed that the acclimatized sludge in reactors R2 and R3 achieved better partial denitrification performance than the sludge in R1 due to the presence of dissolved oxygen as a result of aeration. Notably, the R3 reactor had the optimal conditions for nitrite accumulation. The high-throughput sequencing analysis indicated that the dominant bacteria in R2 and R3 were Candidatus saccharibacteria with a relative abundance of 45.44% and 34.96%, respectively. This was the first time that Candidatus saccharibacteria was reported as the dominant bacteria in denitrifying sludge. The microbial diversity of the R1 reactor was much greater than that of R2 and R3, indicating that a larger proportion of denitrifying bacteria were present in the R2 and R3 reactors. In addition, the batch experiments showed that the higher the initial pH, the higher the nitrite accumulation rate was.

A Study on VS Removal Efficiency and Methane Emission in Combined Anaerobic Digestion of Livestock Manure and Food Waste

Livestock manure treatments have become a more serious problem because massive environmental pollutions such as green and red tides caused by non-point pollution sources from livestock manures have emerged as a serious social issue. In addition, more food wastes are being produced due to population growth and increased income level. Since the London Convention has banned the ocean dumping of wastes, some other waste treatment methods for land disposal had to be developed and applied. At the same time, researches have been conducted to develop alternative energy sources from various types of wastes. As a result, anaerobic digestion as a waste treatment method has become an attractive solution. In this study has three objectives: first, to identify the physical properties of the mixture of livestock wastewater and food waste when combining food waste treatment with the conventional livestock manure treatment based on anaerobic mesophilic digestion; second, to find the ideal ratio of waste mixture that could maximize the collection efficiency of methane (CH4) from the anaerobic digestion process; and third, to promote CH4 production by comparing the biodegradability. As a result of comparing the reactors R1, R2, and R3, each containing a mixture of food waste and livestock manure at the ratio of 5:5, 7:3, and 3:7, respectively, R2 showed the optimum treatment efficiencies for the removal of Total Solids (TS) and Volatile Solids (VS), CH4 production, and biodegradability.

A comparative study of macrophytes influence on performance of hybrid vermifilter for dairy wastewater treatment

Population increase and speedy urbanization are two major driving factors for scarcity of water in present time. To fulfil such water demand, reuse of industrial wastewater is necessary after essential purification. Vermifilter coupled with macrophyte filter is one of the promising technology for the treatment of organics and nutrient rich wastewater. In the present study, various macrophytes have been planted in vermifilter to study their effect on pollutants removal efficiency. Four sets of reactors R1, R2, R3 and R4 were designed and each set of reactor consisted of two units: vertical flow (VF) and horizontal flow (HF) unit. R1, R2 and R3 were planted with Canna indica, Saccharum spontaneum and Typha angustifolia, respectively, whereas R4 was without any macrophyte. Earthworm Eisenia fetida was inserted in all the four reactors. VF units of all hybrid vermifilter were loaded with synthetic dairy wastewater at hydraulic loading rate (HLR) of 0.6 m d−1. Effluents were collected at the bottom of the VF unit and channelled to the HF unit. Final effluent was collected at the end of the HF unit. The order of average percentage removal of COD was R1 (82.8%) > R3 (78.9%) > R2 (75.5%) > R4 (69.4%). Organics and nutrients were targeted to remove in the filter as these pollutants make major fraction in real dairy wastewater compare to antibiotics and other emerging contaminants. Presence of very few kind and low amount of antibiotics in dairy wastewater like lincomycin, chlortetracycline, etc. have been reported in literature.

Study on Rapid Start-up of Anammox Process under the Influence of Magnetic Field

In order to study the rapid start-up technology of the anaerobic ammonium oxidation process, a comparison test of no magnetic field and magnetic field was performed in two identical ASBR reactors R1 and R2 respectively. The results show that both reactors can successfully start Anammox. The R2 start-up period (75d) of the applied magnetic field is shortened by 15% compared with the unloaded magnetic field R1 start-up period (90d); the R2 ammonia-nitrogen removal rate is 97% higher than that of 95% of R1. The quantitative relationship analysis between NH4+-N, NO2--N and NO3--N shows that the change of R2 ratio is closer to the theoretical value, which can better improve the activity of microbial enzymes and accelerate the enrichment of ammonia oxidizing bacteria in the reactor. It is beneficial to nitrogen removal and R2 can quickly start the anaerobic ammonium oxidation process.

Characteristics of aerobic granules treating phenol and ammonium at different cycle time and up flow liquid velocity

Synthetic wastewater containing phenol (400 mg L−1), thiocyanate (SCN−) (100 mg L−1) and ammonia-nitrogen (NH4+-N) (100 mg L−1) was treated in the three aerobic granular reactors at different cycle time of 6 h (R1), 12 h (R2) and 24 h (R3) with organic loading rate (OLR) of 2.03, 1.02, and 0.51 kg COD m−3 day−1, respectively. Reactor performance was analyzed in terms of granule characteristics and organics and nitrogen removals. Granule size, biomass concentration and extracellular polymeric substances (EPS) in sludge were inversely related to cycle time. In R1, mean biomass size and volatile suspended solids (VSS) were 1334.24 ± 30.56 μm and 4.31 ± 0.40 g L−1, as compared to 97.93 ± 4.21 μm size and 2.28 ± 0.13 g L−1 VSS in R3. Sludge EPS in R1 was two-fold more than R3. The ratio of protein (PN) to polysaccharide (PS) content in sludge increased with an increase in loading. Pollutant removal performance was independent of cycle time with 94–96% removal of COD (chemical oxygen demand) and 99% removals of phenol, SCN−, and NH4+-N. In reactors R1 and R3, nitrification was complete to nitrate, and in R2, 40% of influent NH4+-N was converted to nitrite. Up flow liquid velocity of 2.5 m h−1 was appropriate for better granulation and can serve as a selection pressure for granulation.

Characterization of the Microbial Communities in Rumen Fluid Inoculated Reactors for the Biogas Digestion of Wheat Straw

The present study investigated the effect of rumen fluid (RF) concentration on the methane production through anaerobic digestion of wheat straw in batch mode, and compared the microbial communities in RF and RF inoculated reactors by 16S rRNA genes sequencing. Six levels of RF concentration including 1%, 5%, 10%, 15%, 20% and 25% (v/v) were used in reactors R1, R5, R10, R15, R20 and R25 respectively. The results revealed that lower than or equal to 5% RF concentrations resulted in reactor acidification and low methane production. The highest methane yield of 106 mL CH4 g VS−1 was achieved in R10, whereas higher RF concentrations than 10% could not improve the methane production significantly. Methanosarcina barkeri was abundant in the well-working reactors, and Methanobacterium was dominant in the poor-working reactors, implying the archaeal communities in reactors had changed greatly from the Methanobrevibacter-dominated RF. Although the relative abundance of Clostridium and Ruminococcus were greatly different between RF and reactors, the Bacteroidetes and Firmicutes communities were dominant in all the tested samples. The results indicated that the in vitro anaerobic conditions had altered the rumen methanogenic communities significantly and the facultative acetoclastic Methanosarcina was important for the methane production in the RF seeded reactors.

HYDROGEN PRODUCTION AND PERFORMANCE OF ANAEROBIC FIXED-BED REACTORS USING THREE SUPPORT ARRANGEMENTS FROM CASSAVA STARCH WASTEWATER

Fixed-bed reactors are good alternatives for hydrogen production due of their simple construction and increase in retention cellular. In this work, upflow anaerobic fixed-bed reactors using three support arrangements: recycled low-density polyethylene scraps (R1), recycled low-density polyethylene cylinders (R3) and bamboo stems (R2 and R4) were tested using cassava starch wastewater as the substrate. In reactors R1 and R2 the pH initial was adjusted for 6.0, with hydraulic retention time (HRT) of 4 h and organic load rate (OLR) of 9.5 g/L.d. Assays R3 and R4 were conducted in pH initial of 4.5, HRT of 4 h and OLR of 13.5 g/L.d. The hydrogen production was favored by bamboo stems arrangement and adjustment of the pH for 6.0 (248 mLH2/d.L). The reactor with polyethylene cylinders (229 mLH2/d.L), at pH 4.5, obtained better performance than polyethylene scraps (175 mLH2/d.L) at pH 6.0, due to maintenance of higher porosities in bed. Great concentrations of butanol and ethanol were verified in the reactors with bamboo stems, principally, in pH initial of 4.5, leading to decrease in hydrogen production due to occurrence of solventogenesis.

Biogas from slaughter house waste and optimization of the process

To assess the potential of biogas generation by anaerobic digestion from slaughter house waste (undigested stomach content) and to determine the optimum conditions for biogas generation from the substrate, different proportions of substrate were used in six batch reactors R1, R2, R3, R4, R5 and R6. The reactors were operated with initial volatile solid concentrations of 34.00, 50.80, 67.20, 51.60, 48.10 and 63.36 g/l and corresponding specific gas production obtained was 0.258, 0.200, 0.160, 0.270, 0.201 and 0.170 l/g respectively. The volatile solids (VS) destruction efficiency was 31.71%, 29.15%, 28.26%, 32.29%, 30.56 and 29.08% as well as chemical oxygen demand (COD) reduction achieved in the test reactors were 40.31%, 44.44%, 49.40%, 53.24%, 48.55% and 51.26% in R1, R2, R3, R4, R5 and R6 respectively. Methane yield in different reactors varied from 72% to 76%. The optimum mix for generation of biogas from the substrate was 75% slaughter waste mixed with 25% cow dung.Bangladesh J. Sci. Ind. Res. 51(3), 203-214, 2016

Start-up of granule-based denitrifying reactors with multiple magnesium supplementation strategies

In the present work, the effect of Mg2+ supplementation on the start-up of a denitrification process and the granulation of denitrifying sludge was investigated in three upflow anaerobic sludge blanket (UASB) reactors. The reactors R1 and R2 were continuously and intermittently, respectively, supplied with 50 mg L−1 Mg2+, whereas R0 was used as the control. The nitrogen loading rate (NLR) and organic loading rate (OLR) gradually increased, and extremely high values were obtained (36.0 kgN m−3 d−1 and 216.0 kgCOD m−3 d−1, respectively). Granulation occurred in R1 first, but the reactor capacities were comparable. Suffering from starvation, the R0–R2 performances were comparable. At the end of the experiment, the average diameter of the granules in R0, R1, and R2 were 1.67, 1.72 and 1.68 mm, respectively, and the settling velocities of the granules in R1 and R2 were 1.14-fold the speed of R0. The specific denitrifying activity (SDA) of the sludge from the reactors supplied with Mg2+ was greater than the reactor without Mg2+. Intermittent Mg2+ supplementation was identified as the best choice to be utilized to cultivate denitrifying granules, which was consistent with kinetic analysis.

Microalgal process for treatment of high conductivity concentrates from inland desalination

Desalination concentrate contains high levels of dissolved ions such as alkalinity, sulfate, and synthetic chemicals. Microalgal species that have ability to grow in the presence of these ions can be used to treat concentrates. A natural indigenous microalgal consortium originally grown in the concentrate of an evaporation pond was selected, cultured, and seeded in the growth medium for treatment of concentrates. Fed-batch experiments were performed with five different conductivities of concentrates in five reactors, with duplicates. Supernatants or leachates from anaerobic digested sludges were supplied as nutrients. Energy was supplied by sunlight during regularly scheduled office hours. Artificial light was supplied as energy during the weekend and all holiday hours. Environmental air was supplied as carbon during the office hours, weekend, and holidays. Water quality from treated concentrate in reactor R1 at 20 d of treatment was sufficiently pure to be given to sheep. Overall mass conductivity reductions from concentrate and supernatant or leachate were 54.7, 53.4, 45.8, 37.3, and 40.4% at 110 d for reactors R1–R5, respectively. These reductions depend on the initial conductivity of concentrate. Mass reduction percentage is inversely proportional to initial mass conductivity, with a variation of the coefficients “a” and “b” as a second-order of polynomial function of the treatment time.

The influences of temperature, salt and calcium concentration on the performance of anaerobic ammonium oxidation (anammox) process

Efficient biological nitrogen removal from high salinity wastewater has been focused recently. The present study comparatively investigated the effects of temperature, salinity and calcium concentration on the performance of anaerobic ammonium oxidation (anammox) processes using anammox granular sludge to treat synthetic wastewater. Four upflow anaerobic sludge blanket reactors were operated in parallel at ambient temperatures evolving from 25 to 9°C (reactor R1) and thermostatic room temperatures of 35±2°C (reactors R2, R3 and R4). The results demonstrated that low ambient temperature and high sodium levels impair the nitrogen removal performance of anammox granular sludge. The anaerobic ammonium-oxidizing bacteria gradually adapted to a salt concentration of 15gL−1 at low ambient temperature, and a nitrogen removal rate of 1.34±0.12kgNm−3d−1 was achieved. A nitrogen removal rate of 1.90±0.01kgNm−3d−1 in R4 was achieved at a salt concentration of 15gL−1. Moreover, 152mgL−1 calcium relieved the high salinity inhibition of anaerobic ammonium-oxidizing bacteria. Furthermore, the fractal dimension and permeability of anammox granules were also investigated with settling experiment, which indicated that the anammox granules were porous and permeable.

O uso da cavitação hidrodinâmica aplicado ao tratamento de água

A cavitação hidrodinâmica se apresenta como um processo oxidativo avançado (POA), permitindo integrar-se aos processos de tratamento de água para consumo humano. Esta pesquisa teve como objetivo investigar os efeitos de diferentes reatores de cavitação hidrodinâmica para tratar água contaminada com esgoto doméstico, avaliando a contaminação microbiológica e os parâmetros físico-químicos. Foram construídos três modelos de reatores com diferentes rotores (R1, R2 e R3). Os resultados obtidos nos reatores R1, R2 e R3 mostraram redução nas concentrações dos parâmetros químicos em todas as amostras, particularmente nitritos, nitratos, bicarbonatos e dureza total, ao passo que a contaminação microbiológica teve inativação completa dos microrganismos estudados (coliformes totais e Escherichia coli).

Source separation increases methane yields for waste-to-energy applications in the personal care product industry

Abstract High-carbon industrial wastewaters are attractive for anaerobic biological waste-to-energy treatment approaches. However, some waste streams, such as those from the personal care product industry (PCP), also can contain inhibitory compounds that impair biogas production (methane; CH4), reducing potential energy recovery. Here we show how source separation of PCP wastes can increase gross CH4 production by shunting inhibitory streams around the methanogenic treatment step. Methane production was compared between shampoo and hair colorant liquid wastes as sources for waste-to-energy applications. Methane yields were five times greater for comparable COD shampoo versus colorant wastes in batch reactors (∼250 versus ∼50 ml CH4/mg COD), suggesting colorant waste constituents impair methanogenesis, although anaerobic treatment reduced the toxicity of both wastes (i.e., Daphnia magna IC50 tolerance values increased from 0.23 ± 0.07 and 0.17 ± 0.04%v/v to 38.0 ± 2.0 and 15.3 ± 8.9%v/v, respectively). To understand methanogenesis inhibition, the colorant waste was separated into sub-streams associated with different production operations and assayed individually, and CH4 production almost tripled when dye and oxidant levels were reduced. To explain CH4 yields, qPCR was used to quantify eubacteria and five methanogen groups among reactors. Colorant-fed units always had lower microbial abundances than shampoo-fed units, but Methanosarcinaceae levels were especially low in the low CH4 reactors. Further, these acetoclasts and hydrogenotrophic Methanobacteriales significantly correlated with CH4 yields across all reactors (r2 = 0.46, p = 0.02 and r2 = 0.68, p = 0.003, respectively). Waste-to-energy opportunities clearly exist for PCP wastes, although source separation is required to maximise gross CH4 yields.

Effect of Media Packing Density on the Performance of Anaerobic Hybrid Reactors for the Treatment of Complex Phenolic Wastewater

AbstractThe effect of media packing on the performance of anaerobic hybrid reactors (combining upflow anaerobic sludge blanket reactors and anaerobic filters) was examined for the treatment of simulated coal wastewater at four hydraulic retention times (HRTs) under mesophilic (27±5°C) conditions. PVC rings were used as filter media; they were maintained at varying packing densities in three experimental reactors (R1, R2, and R3) at 34.29, 24.29, and 14.13 kg m−3. Synthetic coal wastewater with an average chemical oxygen demand of 2,240 mg L−1 and concentration of phenolics of 752 mg L−1 was used as substrate. During the four-month operation, the HRT was shortened from 0.66 to 0.33 days. The removal of phenolics was favored in Reactors R1 (98−92%) and R2 (96–86%) more than R3 (94−82%) with the reduction of HRT. Biomass concentration of Reactors R1 and R2 increased from 42 to 69.7 and 64.7 g VSS L−1 with an increase in the density of the packing media. Microbial biomass distribution revealed the lowest ...

A generic stoichiometric equation for microalgae–microorganism nexus by using clarified domestic wastewater as growth medium

Stoichiometric equations for microalgae–microorganism nexus culture were established by using 18 sets of experimental data from the literature where clarified domestic wastewater (CDWW) was used as a growth media. The best correlations between observed and calculated coefficients in the equations were 0.908, 0.878, 0.838, and 0.849 for reactors R1, R2, R3, and the sum of three reactors, respectively. Then, each stoichiometric equation was generalized to quantitatively describe the reactions in each set of data for 18 different experimental conditions. By analysis, the most and second most sensitive limiting parameters were identified from the 18 stoichiometric equations. The formulas and equations were further upgraded to a generic form for a general organic growth medium (CaHbOcNdPf). Microalgae–microorganism nexus was established by using the developed coefficients to depict the limited and balanced reactions. The study showed that nitrogen and phosphorus are required as additives in CDWW in order to gain a balanced microalgae–microorganism nexus for a higher yield of microalgae and microorganisms. For a balanced microalgae–microorganism nexus, the optimal nutritional molar ratio of C, N, and P in the CDWW growth medium was found to be 53:15:1.

Biological treatment of wastewater containing an azo dye using mixed culture in alternating anaerobic/aerobic sequencing batch reactors

The performance of one stage anaerobic/aerobic processes for the biological treatment of synthetic wastewaters containing Acid Red 18 was studied. In addition, a method for evaluating dye mineralization using lumped parameters was investigated. The selected initial dye concentrations were 0, 35, 70, 140, and 280 mg/L, in reactors R1 ∼ R5, respectively. This study showed that average COD removal was not lower than 85% while the remaining COD originated from Acid Red 18 and its degradation products. The majority of the dye removal occurred in the anaerobic phases and the aerobic phase contributions were insignificant. The kinetics data of dye removal showed that the increase in initial dye concentration (35 ∼ 280 mg/L) caused a decrease in first-order kinetic rate constants (0.0593 ∼ 0.0384/h). The overall mineralization of AR 18 dye was at least 44, 35, 13, and 0% in R2 ∼ R5, respectively. Increase in initial dye concentrations had no significant effect on sludge characteristics.

Two-Stage vs Single-Stage Thermophilic Anaerobic Digestion: Comparison of Energy Production and Biodegradation Efficiencies

Two-stage anaerobic digestion (AD) for integrated biohydrogen and biomethane production from organic materials has been reported to promise higher process efficiency and energy recoveries as compared to traditional one-stage AD. This work presents a comparison between two-stage (reactors R1 and R2) and one-stage (reactor R3) AD systems, fed with identical organic substrates and loading rates, focusing the attention on chemical and microbiological aspects. Contrary to previous experiences, no significant differences in overall energy recovery were found for the two-stage and one-stage AD systems. However, an accumulation in R2 of undegraded intermediate metabolites (volatile fatty acids, ketones, amines, amino acids, and phenols) was observed by GC-MS. These compounds were thought to be both cause and effect of this partial inefficiency of the two-stage system, as confirmed also by the less diverse, and thereby less efficient, population of fermentative bacteria observed (by PCR-DGGE) in R2. The extreme environment of R1 (low pH and high metabolites concentrations) probably acted as selector of metabolic pathways, favoring H(2)-producing bacteria able to degrade such a wide variability of intermediate metabolites while limiting other strains. Therefore, if two-stage AD may potentially lead to higher energy recoveries, further efforts should be directed to ensure process efficiency and stability.

Effect of carbon sources on the removal of 1,1,2-Trichloroethane and 1,1,2,2-Tetrachloroethane in UASB reactor

The effect of two carbon sources namely sodium acetate and ethanol was studied in bench-scale Upflow Anaerobic Sludge Blanket (UASB) reactors for the removal of chlorinated ethanes i.e., 1,1,2-Trichloroethane (TCA) and 1,1,2,2-Tetrachloroethane (TeCA) contained in the simulated wastewaters. The Hydraulic Retention Time (HRT) was maintained as 24 hours in all the reactors. The granular biomass in the test reactors R2 and R3 were acclimated to 40 mg/L of TCA and 20 mg/L of TeCA, respectively. The effluent TCA and TeCA concentrations were 0.03 mg/L and 0.18 mg/L, respectively, at the end of acclimation phase. Sodium acetate and ethanol both were found to be suitable as the primary substrates in the biodegradation of TCA and TeCA. However, lower concentrations of the toxic pollutants (TCA and TeCA) were obtained in the effluents with the use of sodium acetate. The COD removal efficiency in the test reactors (R2 and R3) varied in the range of 95 % to 98.2 % accompanied by the formation of 1,2-Dichloroethane (DCA) as the major intermediate.

Effect of shock and mixed loading on the performance of SND based sequencing batch reactors (SBR) degrading nitrophenols

The effect of nitrophenolic shock loads on the performance of three lab scale SBRs was studied using a synthetic feed. Nitrophenols were biotransformed by Simultaneous heterotrophic Nitrification and aerobic Denitrification (SND) using a specially designed single sludge biomass containing Thiosphaera pantotropha. Reactors R1, R2 and R3 were fed with 200mg/L concentration of 4-nitrophenol (4-NP), 2,4-dinitrophenol (2,4-DNP), and 2,4,6-trinitrophenol (2,4,6-TNP) whereas reactor R was used as a background control. Three nitrophenolic shock loadings of 400, 600 and 800mg/Ld were administrated by increasing the influent nitrophenolic concentration while keeping the hydraulic retention time as 48h. The shocks were given continuously for a period of 4 days before switching back to normal nitrophenolic loading (200mg/Ld). The reactors were allowed to recover to normal performance level before administrating the next nitrophenolic shock load. The study showed that a nitrophenolic shock load, as high as 600mg/Ld was completely degraded by the 4-NP & 2,4-DNP bioreactors while almost half degraded by the 2,4,6-TNP bioreactor without affecting the reactor’s performance irreversibly. After resuming the normal nitrophenolic loading, it took almost 8–10 days for the reactors to recover from the shock effect. The study was further extended to evaluate the maximum possible mixed nitrophenolic loading (4-NP:2,4-DNP:2,4,6-TNP 1:1:1) to which a reactor (R3) containing 2,4,6-TNP acclimated single sludge biomass can be exposed without hampering the reactor performance irreversibly. The reactor was able to achieve pseudo-steady-state at a mixed nitrophenolic loading of 300mg/Ld with more than 90% removal of all the three nitrophenols, but could remove half of the mixed nitrophenolic loading of 600mg/Ld.

Evaluation of substrate removal kinetics for UASB reactors treating chlorinated ethanes

Lack of focus on the treatment of wastewaters bearing potentially hazardous pollutants like 1,1,2 trichloroethane and 1,1,2,2 tetrachloroethane in anaerobic reactors has provided an impetus to undertake this study. The objective of this exercise was to quantify the behavior of upflow anaerobic sludge blanket reactors and predict their performance based on the overall organic substrate removal. The reactors (wastewater-bearing TCA (R2), and wastewater-bearing TeCA (R3)) were operated at different hydraulic retention times (HRTs), i.e., 36, 30, 24, 18, and 12 h corresponding to food-to-mass ratios varying in the range of 0.2–0.7 mg chemical oxygen demand (COD) mg−1 volatile suspended solids day−1. The process kinetics of substrate utilization was evaluated on the basis of experimental results, by applying three mathematical models namely first order, Grau second order, and Michaelis-Menten type kinetics. The results showed that the lowering of HRT below 24 h resulted in reduced COD removal efficiencies and higher effluent pollutant concentrations in the reactors. The Grau second-order model was successfully applied to obtain the substrate utilization kinetics with high value of R 2 (>0.95). The Grau second-order substrate removal constant (K 2) was calculated as 1.12 and 7.53 day−1 for reactors R2 and R3, respectively. This study demonstrated the suitability of Grau second-order kinetic model over other models, for predicting the performance of reactors R2 and R3, in treating wastewaters containing chlorinated ethanes under different organic and hydraulic loading conditions.