Anaerobic treatment of the municipal wastewater under psychrophilic conditions

The article discusses possibilities of municipal wastewater treatment in various types of anaerobic reactors (UASB, UAF, AnSBR). The temperature during corresponding laboratory experiments varied between 9–23?°C. Real wastewater from WWTP Bratislava-Petr?alka and synthetic substrate were used in the experiments. The HRT values for reactors were found to be 10–46?h. Treatment of municipal wastewater with the AnSBR and UAF system has shown more positive results in laboratory scale studies then the UASB system. The mean removal efficiency of COD depended on the type of anaerobic reactor, temperature, used HRT and was found between 37–48% (UASB), 56–88% (AnSBR) and 46–90% (UAF).     

Comparison of startup and anaerobic wastewater treatment in UASB, hybrid and baffled reactor

An experimental study was carried out to compare the performance of selected anaerobic high rate reactors operated simultaneously at 37?°C. The three reactors, namely upflow anaerobic sludge bed reactor (UASB), hybrid of UASB reactor and anaerobic filter (anaerobic hybrid reactor – AHR) and anaerobic baffled reactor (ABR), were inoculated with the anaerobic digested sludge from municipal wastewater treatment plant and tested with synthetic wastewater. This wastewater contained sodium acetate and glucose with balanced nutrients and trace elements (COD 6000?mg?·?l^?1). Organic loading rate (B _v ) was increased gradually from an initial 0.5?kg?·?m^?3?·?d^?1 to 15?kg?·?m^?3?·?d^?1 in all the reactors. From the comparison of the reactors' performance, the lowest biomass wash-out resulted from ABR. In the UASB, significant biomass wash-out was observed at the B _v 6?kg?·?m^?3?·?d^?1, and in the AHR at the B _v 12?kg?·?m^?3?·?d^?1. The demand of sodium bicarbonate for pH maintenance in ABR was two times higher as for UASB and AHR. The efficiency of COD removal was comparable for all three reactors – 80–90%. A faster biomass granulation was observed in the ABR than in the other two reactors. This fact is explained by the kinetic selection of filamentous bacteria of the Methanotrix sp. under a high (over 1.5?g?·?l^?1) acetate concentration.     

Biotechnological process for sulphide removal with sulphur reclamation

A new biotechnological process for sulphide removal is proposed. The process is based on the oxidation of sulphide into elemental sulphur, which can be removed by sedimentation. In this study it was found that elemental sulphur and sulphate are the main oxidation products of the biological sulphide oxidation. The settling characteristics become worse as the sulphide concentration increases, due to polysulphide formation. The start-up phase of this biological system is very short; Only four days are needed to reduce the sulphide concentration of 100 to 2 mg/l at a HRT (Residence time) of 22 minutes. Also some environmental factors were evaluated. The optimal pH is situated in the pH-range 8.0–8.5. Significantly lower conversion rates are found at pH = 6.5 to 7.5 and pH = 9.0, while at pH = 9.5 the sulphide oxidation capacity of the system detoriates. The process temperature was 20°C, although the optimal temperature is situated in the range 25–35°C. No substrate inhibition of sulphide was found at sulphide concentrations up to 100 mg/l.     

Comparison of RNA- and DNA-based bacterial communities in a lab-scale methane-degrading biocover

Methanotrophs must become established and active in a landfill biocover for successful methane oxidation. A lab-scale biocover with a soil mixture was operated for removal of methane and nonmethane volatile organic compounds, such as dimethyl sulfide (DMS), benzene (B), and toluene (T). The methane elimination capacity was 211?±?40 g?m^?2 d^?1 at inlet loads of 330–516 g?m^?2 d^?1. DMS, B, and T were completely removed at the bottom layer (40–50 cm) with inlet loads of 221.6?±?92.2, 99.6?±?19.5, and 23.4?±?4.9 mg m^?2 d^?1, respectively. The bacterial community was examined based on DNA and RNA using ribosomal tag pyrosequencing. Interestingly, methanotrophs comprised 80 % of the active community (RNA) while 29 % of the counterpart (DNA). Types I and II methanotrophs equally contributed to methane oxidation, and Methylobacter, Methylocaldum, and Methylocystis were dominant in both communities. The DNA vs. RNA comparison suggests that DNA-based analysis alone can lead to a significant underestimation of active members.     

Decolorization of Reactive Red 159 by a consortium of photosynthetic bacteria using an anaerobic sequencing batch reactor (AnSBR)

This experiment aimed to decolorize Reactive Red 159 using a high potential of a consortium of purple nonsulfur bacteria (PNSB) with an application of response surface methodology through a central composite design in open system. The three factors of hydraulic retention time (HRT), sludge retention time (SRT) and dye concentration were applied to the design. The decolorization was operated in an anaerobic sequencing batch reactor until the system reached to a pseudosteady state for 30?cycles in each experiment. The optimal condition was 6,500?mg/L of Reactive Red 159 concentration with 20 days of SRT and 8 days of HRT, achieving dye effluent of 142.62?±?5.35?mg/L, decolorization rate of 264.54?±?7.13?mg/L/h and decolorization efficiency of 97.68?±?0.74%. The results revealed that PNSB efficiently decolorized the high concentration of Reactive Red 159 and they were a high potential of microorganisms for dyes contaminated wastewater treatment.     

Polyhydroxyalkanoate production using waste vegetable oil and filtered digestate liquor of chicken manure

Abstract

The production of polyhydroxyalkanoates (PHA) using digestate of chicken manure combined with waste sunflower oil as no-cost feedstocks in a multi-stage process was investigated. Using Cupriavidus necator H16 in combined culture media, a maximum PHA accumulation of 4.6?±?0.2?g/L at 75.1?±?1.4% of cell dry matter and a residual cell matter yield of 1.5?±?0.1?g/L were obtained after 96?hr of cultivation (30?°C, 160?rpm, pH 7.0) in flask-based experiments. Manure was acidogenically fermented in a continuous stirring tank reactor in fed-batch mode. The bioreactor was operated at varying organic loading rates (OLR) and hydraulic retention times (HRT) ranging from 1–4?g volatile solids (VS)/L/d and 4–8?days, respectively. Optimal operation was observed at an OLR of 4?g VS/L/d and an HRT of 4?days. Analysis showed the presence of significant amounts of ammonia, potassium, magnesium, calcium, and trace elements, i.e. Fe, Cu, Ni, Mn, Co, Zn, Cr in the digestate. The micro-filtered digestate was utilized as a complex culture media base while waste oil served as an additional carbon source and supplemented for effective PHA production. The total volatile fatty acid content of digestate greatly affected the growth performance of the PHA-producing microorganism Cupriavidus necator H16.     

Domestic wastewater treatment using multi-electrode continuous flow MFCs with a separator electrode assembly design

Treatment of domestic wastewater using microbial fuel cells (MFCs) will require reactors with multiple electrodes, but this presents unique challenges under continuous flow conditions due to large changes in the chemical oxygen demand (COD) concentration within the reactor. Domestic wastewater treatment was examined using a single-chamber MFC (130 mL) with multiple graphite fiber brush anodes wired together and a single air cathode (cathode specific area of 27 m²/m³). In fed-batch operation, where the COD concentration was spatially uniform in the reactor but changed over time, the maximum current density was 148?±?8 mA/m² (1,000 Ω), the maximum power density was 120 mW/m², and the overall COD removal was >90 %. However, in continuous flow operation (8 h hydraulic retention time, HRT), there was a 57 % change in the COD concentration across the reactor (influent versus effluent) and the current density was only 20?±?13 mA/m². Two approaches were used to increase performance under continuous flow conditions. First, the anodes were separately wired to the cathode, which increased the current density to 55?±?15 mA/m². Second, two MFCs were hydraulically connected in series (each with half the original HRT) to avoid large changes in COD among the anodes in the same reactor. The second approach improved current density to 73?±?13 mA/m². These results show that current generation from wastewaters in MFCs with multiple anodes, under continuous flow conditions, can be improved using multiple reactors in series, as this minimizes changes in COD in each reactor.     

Continuous fill intermittent decant type sequencing batch reactor application to upgrade the UASB treated sewage

The performance of continuous flow intermittent decant type sequencing batch (CFID) reactor treating the effluent of an UASB reactor treating domestic wastewater and operated at 8 h hydraulic retention time (HRT) was investigated. The CFID was operated at three different HRTs (22, 8 and 6 h) and three different dissolved oxygen (DO) patterns (<0.5, 2.5–3.5 and 3.5–4.5 mg/L). The highest effluent quality was observed at the 8 h HRT and 2.5–3.5 mg/L DO concentration. At this operational condition, the average BOD, TSS, ammonia nitrogen and fecal coliform removal efficiencies were 83, 90, 74 and 99 %, respectively. The CFID is a promising post-treatment option for existing UASB systems, with a final effluent quality that comply with receiving water and effluent reuse criteria.     

Continuous biohydrogen production from fruit wastewater at low pH conditions

Biohydrogen production from a simulated fruit wastewater (soluble COD = 3.17 ± 0.10 g L^?1) was carried out in a continuous stirred tank reactor (CSTR) of 2 L operational volume without biomass inoculation, heat pre-treatment or pH adjustment, resulting in a low operational pH (3.75 ± 0.09). The hydraulic retention time (HRT) varied from 15 to 5 h. A strong negative correlation (p < 0.01) between the biogas production rate and the HRT was observed. Biogas production rates were higher at 30 °C than at 25 °C (p < 0.01), when the CSTR was operated under the same HRT. The biogas hydrogen content was estimated as high as 55.8 ± 2.3 % and 55.4 ± 2.5 % at 25 and 30 °C, respectively. The main fermentation end products were acetic and butyric acids, followed by ethanol. Significant differences (p < 0.01) during the operation of the CSTR at 25 or 30 °C were identified for butyric acid at almost all HRTs examined. Simulation of the acidogenesis process in the CSTR (based on COD and carbon balances) indicated the possible metabolic compounds produced at 25 and 30 °C reactions and provided an adequate fit of the experimental data.     

Immobilization and characterization of lipase from an indigenous Bacillus aryabhattai SE3-PB isolated from lipid-rich wastewater

Abstract

Extracellular lipase from an indigenous Bacillus aryabhattai SE3-PB was immobilized in alginate beads by entrapment method. After optimization of immobilization conditions, maximum immobilization efficiencies of 77%?±?1.53% and 75.99%?±?3.49% were recorded at optimum concentrations of 2% (w/v) sodium alginate and 0.2?M calcium chloride, respectively, for the entrapped enzyme. Biochemical properties of both free and immobilized lipase revealed no change in the optimum temperature and pH of both enzyme preparations, with maximum activity attained at 60?°C and 9.5, respectively. In comparison to free lipase, the immobilized enzyme exhibited improved stability over the studied pH range (8.5–9.5) and temperature (55–65?°C) when incubated for 3?h. Furthermore, the immobilized lipase showed enhanced enzyme-substrate affinity and higher catalytic efficiency when compared to soluble enzyme. The entrapped enzyme was also found to be more stable, retaining 61.51% and 49.44% of its original activity after being stored for 30 days at 4?°C and 25?°C, respectively. In addition, the insolubilized enzyme exhibited good reusability with 18.46% relative activity after being repeatedly used for six times. These findings suggest the efficient and sustainable use of the developed immobilized lipase for various biotechnological applications.     

Process contribution evaluation for COD removal and energy production from molasses wastewater in a BioH<Subscript>2</Subscript>–BioCH<Subscript>4</Subscript>–MFC-integrated system

In this study, a three-stage-integrated process using the hydrogenic process (BioH₂), methanogenic process (BioCH₄), and a microbial fuel cell (MFC) was operated using molasses wastewater. The contribution of individual processes to chemical oxygen demand (COD) removal and energy production was evaluated. The three-stage integration system was operated at molasses of 20 g-COD L^?1, and each process achieved hydrogen production rate of 1.1 ± 0.24 L-H₂ L^?1 day^?1, methane production rate of 311 ± 18.94 mL-CH₄ L^?1 day^?1, and production rate per electrode surface area of 10.8 ± 1.4 g m^?2 day^?1. The three-stage integration system generated energy production of 32.32 kJ g-COD^?1 and achieved COD removal of 98 %. The contribution of BioH₂, BioCH₄, and the MFC reactor was 20.8, 72.2, and, 7.0 % of the total COD removal, and 18.7, 81.2, and 0.16 % of the total energy production, respectively. The continuous stirred-tank reactor BioH₂ at HRT of 1 day, up-flow anaerobic sludge blanket BioCH₄ at HRT of 2 days, and MFC reactor at HRT of 3 days were decided in 1:2:3 ratios of working volume under hydraulic retention time consideration. This integration system can be applied to various configurations depending on target wastewater inputs, and it is expected to enhance energy recovery and reduce environmental impact of the final effluent.     

pH effects on growth and lipid accumulation of the biofuel microalgae Nannochloropsis salina and invading organisms

Biofuels derived from non-crop sources, such as microalgae, offer their own advantages and limitations. Despite high growth rates and lipid accumulation, microalgae cultivation still requires more energy than it produces. Furthermore, invading organisms can lower efficiency of algae production. Simple environmental changes might be able to increase algae productivity while minimizing undesired organisms like competitive algae or predatory algae grazers. Microalgae are susceptible to pH changes. In many production systems, pH is kept below 8 by CO₂ addition. Here, we uncouple the effects of pH and CO₂ input, by using chemical pH buffers and investigate how pH influences Nannochloropsis salina growth and lipid accumulation as well as invading organisms. We used a wide range of pH levels (5, 6, 7, 8, 9, and 10). N. salina showed highest growth rates at pH 8 and 9 (0.19?±?0.008 and 0.19?±?0.011, respectively; mean ± SD). Maximum cell densities in these treatments were reached around 21 days into the experiment (95.6?×?10⁶?±?9?×?10⁶ cells mL^?1 for pH 8 and 92.8?×?10⁶?±?24?×?10⁶ cells mL^?1 for pH 9). Lipid accumulation of unbuffered controls were 21.8?±?5.8 % fatty acid methyl esters content by mass, and we were unable to trigger additional significant lipid accumulation by manipulating pH levels at the beginning of stationary phase. Ciliates (grazing predators) occurred in significant higher densities at pH 6 (56.9?±?39.6?×?10⁴ organisms mL^?1) than higher pH treatments (0.1–6.8?×?10⁴ organisms mL^?1). Furthermore, the addition of buffers themselves seemed to negatively impact diatoms (algal competitors). They were more abundant in an unbuffered control (12.7?±?5.1?×?10⁴ organisms mL^?1) than any of the pH treatments (3.6–4.7?×?10⁴ organisms mL^?1). In general, pH values of 8 to 9 might be most conducive to increasing algae production and minimizing invading organisms. CO₂ addition seems more valuable to algae as an inorganic carbon source and not as an essential mechanism to reduce pH.     

Thermodynamics of the slow–fast transition in bacteriophage T2L

We have measured the thermodynamic parameters of the slow-fast tail-fiber reorientation transition on T2L bateriophage. Proportions of the virus in each form were determined from peak-height measurements in sedimention-velocity runs and from average diffusion coefficients obtained by quasielastic laser light scattering. Computer simulation of sedimentation confirmed that there were no undetected intermediates in the transition, which was analyzed as a two-state process. Van't Hoff-type plots of the apparent equilibrium constant and of the pH midpoint of the transition as function of reciprocal temperature led to the following estimates of the thermodynamic parameters for the transition at pH 6.0 and 20°C: ΔH° = ?139 ± 18Kcal mol^?1, ΔS° = ?247 ± 46 cal K^?1 mol^?1, and ΔG° = ?66 ± 22 kcal mol^?1. Per mole of protons taken up in the transition, the analogous quantities were ?15.9 ± 1.7 kcal mol^?1, ?26.3 ± 2.2 cal K^?1 mol^?1, and ?8.22 ± 1.8 kcal mol^?1. The net number of protons taken up was about 8.5 ± 1.5. The large values of the thermodynamic functions are consistent with a highly cooperative reaction and with multiple interactions between the fibres and the remainder of the phage. The negative entropy of the transition is probably due to immobilization of the fibres.     

Remediation of Explosive-Contaminated Soils: Alkaline Hydrolysis and Subcritical Water Degradation

Alkaline hydrolysis and subcritical water degradation were investigated as ex-situ remediation processes to treat explosive-contaminated soils from military training sites in South Korea. The addition of NaOH solution to the contaminated soils resulted in rapid degradation of the explosives. The degradation of explosives via alkaline hydrolysis was greatly enhanced at pH ≥12. Estimated pseudo-first-order rate constants for the alkaline hydrolysis of 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in contaminated soil at pH 13 were (9.6?±?0.1)×10^?2, (2.2?±?0.1)×10^?1, and (1.7?±?0.2)×10^?2 min^?1, respectively. In the case of subcritical water degradation, the three explosives were completely removed at 200–300°C due to oxidation at high temperatures and pressures. The degradation rate increased as temperature increased. The pseudo-first-order rate constants for DNT, TNT, and RDX at 300°C were (9.4?±?0.8)×10^?2, (22.8?±?0.3)×10^?2, and (16.4?±?1.0)×10^?2, respectively. When the soil-to-water ratio was more than 1:5, the extent of alkaline hydrolysis and subcritical water degradation was significantly inhibited.     

Comparison of CSTR and UASB reactor configuration for the treatment of sulfate rich wastewaters under acidifying conditions

The effects of lowering the operational pH from 6 to 5 on mesophilic (30 °C) sulfate reduction during the acidification of sucrose at an organic loading rate of 5 gCOD (l_reactor d)⁻¹ and at a COD/SO₄²⁻ ratio of 4 were evaluated in a CSTR and in a UASB reactor. The HRT was 24 h and 10 h, respectively. Acidification was complete in both reactors at pH 6 and the lowering of the operational pH to 5 did not affect the acidification efficiency in the CSTR but decreased the acidification efficiency of the UASB to 72%. The decrease to pH 5 caused an increase in the effluent butyrate and ethanol concentrations in both reactors. Lowering the pH from 6 to 5 caused a decrease in sulfate reduction efficiencies in both reactors, from 43% to 25% in the CSTR and from 95% to 34% in the UASB reactor. The acidification and sulfate reduction efficiencies at pH 5 could be increased to 94% and 67%, respectively, by increasing the HRT of the UASB reactor to 24 h.     

Activity of myrosinase from Sinapis alba seeds immobilized into Ca-polygalacturonate as a simplified model of soil-root interface mucigel

Ca-polygalacturonate is a demethoxylated component of pectins which are constitutive of plant root mucigel. In order to define the role of root mucigel in myrosinase immobilization and activity at root level, a myrosinase enzyme which had been isolated from Sinapis alba seeds was immobilized into Ca-polygalacturonate. The activity profile for the immobilized and free enzyme was evaluated using the pH-Stat method as a function of time, temperature, and pH. The Michaelis-Menten kinetic parameters change between the immobilized (V _max ?=?127?±?13 U mg^?1 protein; K _M ?=?6.28?±?0.09?mM) and free (V _max ?=?17?±?1 U mg^?1 protein; K _M ?=?0.96?±?0.01?mM) forms of myrosinase, probably due to conformational changes involving the active site as a consequence of enzyme immobilization. Immobilized enzyme activity evaluated as a function of different substrates gave the highest value with nasturtin, the glucosinolate that is typical of several brassicaceae plant roots containing the glucosinolate-myrosinase defensive system. No feedback regulation mechanism was found in the presence of an excess of enzymatic reaction products (i.e. allyl isothiocyanate or sulphate). The high enzyme immobilization yield into Ca-polygalacturonate and its activity preservation under different conditions suggest that the enzyme released by plants at root level could be entrapped in root mucigel in order to preserve its activity.     

Organics, sulfates and ammonia removal from acrylic fiber manufacturing wastewater using a combined Fenton-UASB (2 phase)-SBR system

A combined Fenton-UASB (2 phase)-SBR system was employed to treat acrylic fiber manufacturing wastewater. The Chemical Oxygen Demand (COD) removal and effluent Biochemical Oxygen Demand (BOD) to COD were 65.5% and 0.529%, respectively, with the optimal Fenton conditions: ferrous was 300 mg/L; hydrogen peroxide was 500 mg/L; pH was 3.0; reaction time was 2.0 h. In two-phase UASB reactor, mesophilic operation (35±0.5 °C) was performed with hydraulic retention time (HRT) varied between 28 and 40 h. The results showed that with the HRT not less than 38 h, COD and sulfate removal were 65% and 75%, respectively. The greatest sizes of granule formed in the sulfate-reducing and methane-producing phases were 5 and 2 mm, respectively. Sulfate-reducing bacteria (SRB) accounted for 35% in the sulfate-reducing phase while methane-producing archaea (MPA) accounted for 72% in the methane-producing phase. During the SBR process, shortcut nitrification was achieved by temperature control of 30 °C.     

Species Trials of Short Rotation Woody Crops on Two Wastewater Application Sites in North Carolina,USA

Forty-two Populus spp. clones, Eucalyptus benthamii, and seven tree species native to North Carolina were evaluated for survival and height growth through the establishment phase at two municipal wastewater application sites. Groundwater was monitored at each site to determine if establishment of the species trials resulted in exceedances of nutrient mitigation requirements. At the Gibson Wastewater Treatment Facility, 26 Populus clones had 100 % survival, with mean height growths ranging between 152 to 260 cm, and basal diameters ranging between 11.4 and 28.8 mm. Green ash, planted in 2011 and 2012, had high survivorship (>95 %) with first year mean height growth of 30?±?28 cm (2012) and second year mean height growth of 101?±?52 cm (2011). Basal diameter for green ash was 33.3?±?12.6 mm. E. benthamii had moderate survivorship (>77 %) and first year mean height growth of 47?±?27 cm. At the Jacksonville Wastewater Treatment Facility, green ash and bald cypress had high survivorship (>96 %), first year mean height growths of 14?±?25 cm and 27?±?16 cm, and basal diameters of 13.1?±?3.9 mm and 11.6?±?4.8 mm, respectively. Survivorship for 12 Populus clones ranged from 50 and 94 % with mean first year height growths between 58 to 121 cm, and basal diameters between 6.8 and 12.5 mm. E. benthamii had low survivorship (43 %) with mean first year height growths of 17?±?17 cm and basal diameters of 12.0?±?7.7 mm. Groundwater concentrations of NO₃?+?NO₂ and N-NH₄ remained below regulatory requirements at both sites with one exceedance in February 2012 in Jacksonville, NC. The results show that some Populus clones are excellent candidates for woody biomass production on municipal wastewater application fields. Native green ash and bald cypress are also good candidates, but these trees may require longer rotations than Populus to achieve similar biomass yields.     

Distribution and change of microbial activity in combined UASB and AFB reactors for wastewater treatment

A thermophilic upflow anaerobic sludge blanket (UASB) reactor was combined with a mesophilic aerobic fluidized bed (AFB) reactor for treatment of a medium strength wastewater with 2,700?mg COD?l^?1. The COD removal efficiency reached 75% with a removal rate of 0.2 g COD?l^?1 h^?1 at an overall hydraulic retention time 14 hours. The distribution of microbial activity and its change with hydraulic retention time in the two reactors were investigated by measuring ATP concentration in the reactors and specific ATP content of the biomass. In the UASB reactor, the difference in specific ATP was significant between the sludge bed and blanket solution (0.02?mg ATP g VS^?1 versus 0.85?mg ATP g VS^?1) even though the ATP concentrations in these two zones were similar. A great pH gradient up to 4 was developed along the UASB reactor. Since a high ATP or biological activity in the blanket solution could only be maintained in a narrow pH range from 6.5 to 7.5, the sludge granules showed a high pH tolerance and buffering capacity up to pH 11. The suspended biomass in AFB reactor had a higher specific ATP than the biomass fixed in polyurethane carriers (1.6?mg ATP g VS^?1 versus 1.1?mg ATP g VS^?1), which implies a starvation status of the immobilized cells due to mass transfer limitation. The aerobes had to work under starvation conditions in this polishing reactor. The anaerobic biomass brought into AFB reactor contributed to an increase in suspended solids, but not the COD removal because of its fast deactivation under aerobic conditions. A second order kinetic model was proposed for ATP decline of the anaerobes. The results on distribution of microbial activity in the two reactors as well as its change with hydraulic retention time lead to further performance improvement of the combined anaerobic/aerobic reactor system.     

Effect of influent pH and alkalinity on the removal of chlorophenols in sequential anaerobic–aerobic reactors

This study was carried out to determine the effect of influent pH and alkalinity on the performance of sequential UASB and RBC reactors for the removal of 2-CP and 2,4-DCP from two different simulated wastewaters. The performance of methanogens at low (<6.0) to high (>8.0) pH values and at sufficiently high alkalinity (1500–3500 mg/l as CaCO₃) is described in this paper. Sequential reactors were capable of handling wastewaters with influent pH, 5.5–8.5. However, with influent pH 7.0 ± 0.1 UASB reactor showed best performance for 2-CP (99%) and 2,4-DCP (88%) removals. Increase in alkalinity/COD ratio in the influent (>1.1) caused gradual decrease in the chlorophenol removal in UASB reactors. The UASB reactors could not tolerate wastewater with higher alkalinity/COD ratio (2.6) and showed significant deterioration of its performance in terms of chlorophenols removal achieving only 74.7% 2-CP and 60% 2,4-DCP removals, respectively.