Biodegradability of tannin-containing wastewater from leather industry

Tannins occur commonly in the wastewaters from forestry, plant medicine, paper and leather industries. The treatment of this kind of wastewaters, including settling and biodegradation, is usually difficult because tannins are highly soluble in water and would inhibit the growth of microorganisms in activated sludge. The objective of this study is to investigate biodegradability of tannin-containing wastewaters, so as to characterize the pollution properties of such wastewaters and provide a reference for their biological treatment in wastewater treatment plants. The research was typified by using the wastewater collected from vegetable tanning process in leather industry. A model was developed to describe the activated sludge process, and the biodegradation kinetics of vegetable tanning wastewater (VET wastewater) was studied. It was found that the biodegradability of tannin-containing wastewater varies heavily with the content of tannins in wastewater. The biodegradation of VET wastewater with tannin content around 4,900 mg/l occurred inefficiently due to the inhibition of tannins to the activated sludge process, and only 34.7% of biodegradation extent was reached in 14 days of incubation. The optimal biodegradability of VET wastewater was observed when its tannin content was diluted to 490 mg/l, where the COD and tannin removals reached 51.3% and 45.1% respectively in 6 days. Hence, it is suggested that a proper control of tannin content is necessary to achieve an effective biodegradation of tannin-containing wastewaters in wastewater treatment plants.     

Effect of phenolic tar on the work of activated sludge

The effect of different phenolic tar concentrations on the work of activated sludge in petrochemical and synthetic wastewater was investigated. The concentrations of 440 and 300 mg/l of phenolic tar did not show a destructive effect on the activated sludge and its work. The highest concentration of phenolic tar (880 mg/l) reduced the efficiency of purification and changed the structure of the activated sludge.     

Effect of methyl alcohol and ethylene glycol on the work of activated sludge.

The effect of methyl alcohol and ethylene glycol on the work of activated sludge grown in synthetic wastewater was investigated. Wastewater carrying these compounds could be purified by the activated sludge method, providing the concentration of methyl alcohol and glycol did not exceed 5,000 mg/l and 1,000 mg/l, respectively. At these values reduced purification efficiency, increased volumetric index of the sludge and changes in the structure of the activated sludge flocs could be observed.     

Preliminary studies on continuous chromium(VI) biological removal from wastewater by anaerobic-aerobic activated sludge process

The long-term continuous chromium(VI) removal from synthetic wastewater affected by influent hexavalent chromium (Cr(VI)) and glucose concentrations were studied with an anaerobic-aerobic activated sludge process. It was observed that before activated sludge was acclimated, the chromium in the effluent increased immediately as the influent chromium increased. However, both Cr(VI) and total chromium (TCr) in the effluent significantly decreased after acclimation. In the acclimated activated sludge, the chromium removal efficiency was 100% Cr(VI) and 98.56% TCr at influent Cr(VI) levels of 20 mg/day, 100% Cr(VI) and 98.92% TCr at influent Cr(VI) levels of 40 mg/day, and 98.64% Cr(VI) and 97.16% TCr at influent Cr(VI) levels of 60 mg/day. The corresponding effluent Cr(VI) and TCr concentrations were 0 and 0.012 mg/l, 0 and 0.018 mg/l, and 0.034 mg/l and 0.071 mg/l, respectively. When the influent glucose increased from 1125 to 1500 mg/l at influent Cr(VI) dosage of 60 mg/day, the Cr(VI) and TCr removal efficiency with the acclimated activated sludge improved from 98.64% and 97.16% to 100% and 98.48%, respectively, and the chromium concentration in the effluent decreased from 0.034 mg/l of Cr(VI) and 0.071 mg/l of TCr to 0 (Cr(VI)) and 0.038 mg/l (TCr). The effluent COD and turbidity was around 40 mg/l and 0, respectively, after the activated sludge was acclimated. Further studies showed that after the activated sludge was acclimated, its specific dehydrogenases activity (SDA) and protein contents increased. The SDA and protein increased respectively 15% and 10% when influent Cr(VI) increased from 20 to 60 mg/day.     

Biodegradation, decolourisation and detoxification of textile wastewater enhanced by advanced oxidation processes

Recently, an increasing application of so called advanced oxidation processes (AOPs) to industrial wastewater has been observed. In particular, an integrated approach of biological and chemical treatment of wastewater is advantageous conceptually. The subject of our study was synthetic wastewater, simulating effluents from knitting industry. The wastewater contained components that are very often used in Polish textile industry: an anionic detergent Awiwaz KG conc., a softening agent Tetrapol CLB and an anthraquinone dyestuff-Acid Blue 40, CI 2125. The toxicity of the detergents and the dye was determined in terms of effective concentration EC50 using mixed cultures of activated sludge as well as pure culture of luminescent bacteria Vibrio fischerii NRRLB-11177. The dye did not undergo biodegradation without AOPs pretreatment, therefore a degree of its removal (decolourisation) by the AOPs has been determined and its bio-sorption properties on the flocks of activated sludge have been studied. The dye adsorption onto flocks of activated sludge was described by Henry's isotherm. Our investigations focussed on the influence of various oxidants like O3, H2O2 and UV light on biodegradation of single components aqueous solution as well as of the whole textile wastewater. The results of kinetic measurements of the biodegradation (by means of acclimated activated sludge) was described by Monod type of kinetic equation. The experimental evidence of the positive effect of chemical oxidation pretreatment on the biodegradation of recalcitrant compounds was quantified by estimation of the kinetic parameters of the Monod equation. Due to the AOPs pretreatment a decrease of the Monod constant and an increase of maximal specific growth rate was observed. The activity of degradative enzymes of activated sludge was assayed by the methods of 2-[4-iodophenyl]-3-[4-nitrophenyl]-5-phenyltetrazolium chloride test.     

Kinetic modeling of aerobic biodegradation of high oil and grease rendering wastewater

Batch scale activated sludge kinetic studies were undertaken for the treatment of pet food wastewater characterized by oil and grease concentrations of up to 21,500 mg/L, COD and BOD concentrations of 75,000 and 60,000 mg/L, respectively as well as effluent from the batch dissolved air flotation (DAF) system. The conducted kinetics studies showed that Haldane Model fit the substrates and biomass data better than Monod model in DAF-pretreated wastewater, while the modified hydrolysis Monod model better fit the raw wastewater kinetic data. For the DAF pretreated batches, Haldane Model kinetic coefficients k, K(S), Y and Ki values of 1.28-5.35 g COD/g VSS-d, 17,833-23,477 mg/L, 0.13-0.41 mg VSS/mg COD and 48,168 mg/L, respectively were obtained reflecting the slow biodegradation rate. Modified hydrolysis Monod model kinetic constants for the raw wastewater i.e., k, K(S), Y, and K(H) varied from 1-1.3 g COD/g VSS-d, 5580-5600 mg COD/l, 0.08-0.85 mg VSS/mg COD, and 0.21-0.66 d(-1), respectively.     

Biodegradation of naphthalene in the oil refinery wastewater by enriched activated sludge

The main purpose of this paper is to study naphthalene (NAP) biodegradation by acclimated activated sludge, employing the culture-enrichment method in a continuous flow bioreactor of the wastewater treatment process. The effects of various COD loadings and influent flow rates of an artificial wastewater containing 15 mg l⁻¹ NAP on the biodegradation rates of the activated sludge will be investigated, in order to determine the biodegradation kinetics and minimum mean cell residence time of the activated sludge. From the experimental results, it was found that the resulting enriched activated sludge follows the growth rate of the Monod type and can biodegrade those COD and NAP loadings in the influents efficiently, and its bio-treatment efficiency on NAPs increases with the decrease of influent flow rate. The sludge volume index (SVI) of the resulting enriched activated sludge meets the design value required by the convectional activated sludge process for the treatment of wastewater.     

Application of struvite precipitation as a pretreatment in treating swine wastewater

In this study, the effect of the pretreatment of NH₄-N by struvite precipitation on biological nitrogen removal was investigated in treating swine wastewater. Evaluation was mainly focused on nitrification which occurred in the activated sludge system after struvite precipitation. Laboratory experiments were performed at four different hydraulic retention times (HRT), i.e., 48, 32, 24 and 16 h. Results of the long-term operation of systems showed that the struvite precipitation used as the pretreatment of raw swine wastewater enhanced the nitrification performance in activated sludge system by reducing the applied loading rates of NH₄-N and TCOD in all operating conditions. The reduction of the applied NH₄-N loading rate kept the levels of free ammonia (FA) concentration in biological reactors low and it prevented nitrite accumulation. In addition, the struvite precipitation elicited the biological denitrification reaction and PO₄-P removal by increasing the ratios of carbon-to-nitrogen and carbon-to-phosphorus of wastewater after struvite precipitation. The struvite precipitation also enhanced the biological TCOD removal performance by reducing the toxic effect of FA. Triplicate INT-dehydrogenase tests clearly showed that FA inhibited the degradation of organic matter in activated sludge system. Finally, the struvite precipitation contributed to high TCOD, T-N and PO₄-P removals of 83, 90, and 97% by facilitating biological reaction at a short HRT of 16 h.     

Phenol utilisation by fungi isolated from activated sludge

The paper presents the efficiency of phenol removal (concentrations from 500 to 2000 mg/l) by fungi isolated from activated sludge purifying wastewater with high phenol concentration. Five fungal strains were isolated and identified. All isolated strains appeared to be Moniliales from the class of Fungi Imperfecti (Candida sp., Monosporium sp., Trichosporon sp.) Stationary cultures of the individual strains and their mixtures were maintained in Czapek medium containing phenol in concentration from 500 to 2000 mg/l. All isolated strains (except one) were capable of utilising phenol up to a concentration of 1500 mg/l. Depending on investigated strain, phenol in concentration of 500 mg/l was decomposed during 4-25 days, 750 mg/l during 4-14 days. After 20 days, a phenol decline of 1000 mg/l was observed. After 16 days, the phenol decline was 1500 mg/l. Higher phenol concentrations (1500 mg/l) were utilised only by a mixture of two strains. The investigated fungal strains showed good efficiency of phenol removal from high phenol concentration in wastewater and they may be proposed for use in the process of purifying wastewater of this type.     

Degradation of fluoranthene by a newly isolated strain of <Emphasis Type="Italic">Herbaspirillum chlorophenolicum</Emphasis> from activated sludge

A fluoranthene-degrading bacterial strain FA1 was isolated from activated sludge and identified as Herbaspirillum chlorophenolicum, a newfound bacterial species that can grow well on fluoranthene as sole carbon and energy source. The kinetic characteristic of strain FA1 was tested in the aqueous model system (AMS) and the effects of nonionic surfactants on fluoranthene biodegradation in the AMS were then investigated. Tween 80 exhibited the best solubilization capacity for fluoranthene among three surfactants and its bioavailability decreased with an increase in its concentration and its degradation kinetics fit well with the first-order of power index model. The biotransformation of fluoranthene was greatly improved by Tween 80, and 58.5% fluoranthene degradation was obtained as Tween 80 was 100 mg/l. However, the bioavailability of fluoranthene decreased gradually with the increase of Tween 80 concentration. Bioremediation tests for fluoranthene in soil–water system were designed further to examine the degrading ability of strain FA1 with the presence of indigenous flora or not. The measurements showed that in the presence of indigenous flora, the optimum 30-day fluoranthene degradation in soil–water system reached 77.4%. Evidently, strain FA1 seems both efficient and high-effective and deserves further exploration on the enhanced bioremediation technologies for the treatment of fluoranthene-polluted soil.     

Modelling salinity inhibition effects during biodegradation of perchlorate

AIMS: To determine the mathematical kinetic rates and mechanisms of acclimated perchlorate (ClO)-reducing microbial cultures by incorporating a term to relate the inhibitory effect of high salinity during biological reduction of concentrated perchlorate solutions. METHODS AND RESULTS: Salt toxicity associated with the biodegradation of concentrated perchlorate (200, 500, 1100, 1700 and 2400 mg l(-1) as ClO) was investigated using two microbial cultures isolated from a domestic wastewater treatment plant [return activated sludge (RAS) and anaerobic digester sludge (ADS)]. Experiments were performed in wastewaters containing various sodium chloride concentrations, ranging from 0% to 4.0% (w/v) NaCl (ionic strength: 0.14-0.82 mol l(-1), total dissolved solids: 5.3-42.6 g l(-1)) at near-neutral values of pH (6.7-7.8). Perchlorate biodegradation was stimulated through stepwise acclimation to high salinity. The ADS culture was capable of reducing perchlorate at salinities up to 4% NaCl, while the RAS culture exhibited complete inhibition of perchlorate degradation at 4% NaCl, probably resulting from either a toxic effect or enzyme inactivation of the perchlorate-reducing microbes. Further, a kinetic growth model was developed based on experimental data in order to express an inhibition function to relate specific growth rate and salinity. CONCLUSIONS: Biological reduction of concentrated perchlorate wastewaters using either acclimated RAS or ADS cultures is feasible up to 3% or 4% NaCl, respectively. In addition, the kinetic model including a salinity inhibition term should be effective in many practical applications such as improving reactor design and management, furthering the understanding of high salinity inhibition, and enhancing bioremediation under high salinity loading conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: Applications of these findings in water treatment practice where ion exchange or membrane technologies are used to remove perchlorate from water can have the potential to increase the overall attractiveness of these processes by eliminating the need to dispose of a concentrated perchlorate solution.     

Methanogenic toxicity in anaerobic digesters treating municipal wastewater

In upflow anaerobic sludge blanket (UASB) digesters treating raw sewage at low temperatures, the sludge progressively lost methanogenic activity, indicating the possibility of methanogenic activity inhibition caused by wastewater constituents. To check this fact, batch and semi-continuous methanogenic toxicity assays were carried out with raw and centrifuged sewage. Permanent methanogenic toxicity on anaerobic sludge of approximately 50% was found when the sludge exposure to wastewater was renewed in a semi-continuous way. A stronger methanogenic inhibition of about 70-100% was observed when an active anaerobic sludge was exposed to mixed liquor from the UASB digester treating municipal wastewater. Suspended solids removal from sewage slightly reduced methanogenic toxicity. Effective concentration of municipal wastewater that caused a 50% reduction in methanogenic activity was estimated to be in the range of 150-200 mg CODl(-1). As methanogenic inhibition appeared to be related to remaining COD, higher methanogenic toxicity in digesters operating with low conversion efficiency will be expected.     

Empirical model for the autotrophic biodegradation of thiocyanate in an activated sludge reactor

AIMS: The aim of this investigation was to develop an empirical model for the autotrophic biodegradation of thiocyanate using an activated sludge reactor. METHODS AND RESULTS: The methods used for this purpose included the use of a laboratory scale activated sludge reactor unit using thiocyante feed concentrations from 200 to 550 mg x l(-1). Reactor effluent concentrations of <1 mg x l(-1) thiocyanate were consistently achieved for the entire duration of the investigation at a hydraulic retention time of 8 h, solids (biomass) retention of 18 h and biomass (dry weight) concentrations ranging from 2 to 4 g x l(-1). A biomass specific degradation rate factor was used to relate thiocyanate degradation in the reactor to the prevailing biomass and thiocyanate feed concentrations. A maximum biomass specific degradation rate of 16 mg(-1) x g(-1) x h(-1) (mg thiocyanate consumed per gram biomass per hour) was achieved at a thiocyanate feed concentration of 550 mg x l(-1). The overall yield coefficient was found to be 0.086 (biomass dry weight produced per mass of thiocyanate consumed). CONCLUSION: Using the results generated by this investigation, an empirical model was developed, based on thiocyanate feed concentration and reactor biomass concentration, to calculate the required absolute hydraulic retention time at which a single-stage continuously stirred tank activated sludge reactor could be operated in order to achieve an effluent concentration of <1 mg x l(-1). The use of an empirical model rather than a mechanistic-based kinetic model was proposed due to the low prevailing thiocyanate concentrations in the reactor. SIGNIFICANCE AND IMPACT OF THE STUDY: These results represent the first empirical model, based on a comprehensive data set, that could be used for the design of thiocyanate-degrading activated sludge systems.     

Kinetic properties of a commercial and a native inoculum for aerobic milk fat degradation

The aerobic fat biodegradation potential and growth characteristics of a commercial and a native inoculum (activated sludge from a dairy wastewater treatment pond), were evaluated. Batch tests were conducted with a medium based on butter oil, as the sole source of carbon, and mineral salts. Residual fat, biomass and CO(2) production were measured. Overall fat removal values were above 78% for both inocula. The growth kinetics of the commercial and native inocula followed Haldane and Monod models respectively. Both inocula showed a similar behaviour when butter oil concentration was under 360 mg/l; at higher values, the difference between the growth rates increased as a consequence of the inhibition exhibited by the commercial inoculum. The selection of an inoculum for bioaugmentation of bioreactors in the wastewater treatment requires a comprehensive knowledge of their degradation ability and tolerance to fluctuating compounds and of the operational conditions that will be utilized.     

Characterization and biological treatment of ceramic industry wastewater

Ceramic industry wastewaters not only contain high suspended and total solids but also significant amounts of dissolved organics resulting in high BOD or COD loads. Suspended solids can be removed from the wastewater by chemical precipitation. However, dissolved BOD/COD compounds can only be removed by biological or chemical oxidation. Effluent wastewater from chemical sedimentation stage of EGE CERAMIC industry was characterized and subjected to biological treatment in a laboratory scale activated sludge unit. Experiments were conducted at different hydraulic and solids retention times. The best results were obtained with Š_c=20 h of hydraulic and Š_c=20 days of solids retention times (sludge age) resulting in effluent COD concentration of 40 mg/l from a feed wastewater of 720 mg/l COD content. The suspended solids content of the activated sludge effluent was approximately 52 mg/l.     

Pollution control in pulp and paper industrial effluents using integrated chemical–biological treatment sequences

The main objective of the present study was to improve the quality of pulp and paper industrial wastewater of two local mills RAKTA and El-Ahlia, Alexandria, Egypt, and to bring their pollutant contents to safe discharge levels. Quality improvement was carried out using integrated chemical and biological treatment approaches after their optimization. Chemical treatment (alum, lime, and ferric chloride) was followed by oxidation using hydrogen peroxide and finally biological treatment using activated sludge (90 min for RAKTA and 60 min for El-Ahlia effluents). Chemical coagulation produced low-quality effluents, while pH adjustment during coagulation treatment did not enhance the quality of the effluents. Maximum removal of the tested pollutants was achieved using the integrated treatment and the pollutants recorded residual concentrations (RCs) of 34.67, 17.33, 0.13, and 0.43 mg/l and 15.0, 11.0, 0.0, and 0.13 mg/l for chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), tannin and lignin, and silica in RAKTA and El-Ahlia effluents, respectively, all of which were below their maximum permissible limits (MPLs) for the safe discharge into water courses. Specific oxygen uptake rate (SOUR) and sludge volume index (SVI) values reflect good conditions and healthy activated sludge. Based on the previous results, optimized conditions were applied as bench scale on the raw effluents of RAKTA and El-Ahlia via the batch chemical and the biological treatment sequences proposed. For RAKTA effluents, the sequence was as follows: (1) coagulation with 375 mg/l FeCl₃, (2) oxidation with 50 mg/l hydrogen peroxide, and (3) biological treatment using activated sludge with 2,000 mg/l initial concentration and 90 min hydraulic retention time (HRT), while for El-Ahlia raw effluents, the sequence was (1) coagulation with 250 mg/l FeCl₃, (2) oxidation with 45 mg/l hydrogen peroxide, and (3) biological treatment using activated sludge with 2,000 mg/l initial concentration and 60 min HRT. In conclusion, results confirmed that the application of the proposed sequential treatments removed almost all COD, BOD₅, high molecular weight compounds, and silica from RAKTA and El-Ahlia influents and produced high-quality effluents, thus achieving the main objective of this study.     

Biodegradation by activated sludge and toxicity of tetracycline into a semi-industrial membrane bioreactor

Much attention has been devoted recently to the fate of pharmaceutically active compounds such as tetracycline antibiotics in soil and water. Tetracycline (TC) biodegradability by activated sludge derived from membrane bioreactor (MBR) treating swine wastewater via CO₂-evolution was evaluated by means of modified Sturm test, which was also used to evaluate its toxicity on carbon degradation. The impact of tetracycline on a semi-industrial MBR process was also examined and confronted to lab-scale experiments. After tetracycline injection in the pilot, no disturbance was detected on the elimination of organic matters and ammonium (nitrification), reaching after injection 88% and 99% respectively; only denitrification was slightly affected. Confirming the ruggedness and the superiority of membrane bioreactors over conventional bioreactors, no toxicity was observed at the considered level of TC in the pilot (20 mg TOC L⁻¹), while at lab-scale sodium benzoate biodegradation was completely inhibited from 10 mg TOC L⁻¹ TC. The origin of the activated sludge showed a significant impact on the performances, since the ultimate biodegradation was in the range −50% to −53% for TC concentrations in the range 10–20 mg TOC L⁻¹ with conventional bioreactor sludge and increased to 18% for 40 mg TOC L⁻¹ of TC with activated sludge derived from the MBR pilot. This confirmed the higher resistance of activated sludge arising from membrane bioreactor.     

Evaluation of methods to solubilize and analyze cell-associated ectoenzymes

A protocol for production, storage, and use of Shock 1 (Shk1) bioreporter cells for toxicity monitoring in wastewater treatment facilities was developed. Shk1 is a bioluminescent toxicity bioreporter for activated sludge previously constructed by the incorporation of lux genes into an activated sludge microorganism.

A number of factors affecting Shk1 growth and bioluminescence were examined including the growth medium, tetracycline concentration, storage conditions, and test media. Based on the results of these experiments, a toxicity testing protocol was developed that involved growth of cultures in nutrient broth with tetracycline, storage of cultures at 4 °C, cell activation by reinoculation into nutrient broth, and toxicity testing by cell injection into the test media. Effective use of this approach required standardized time intervals for cell growth, storage, activation and exposure in the test media.

Bioluminescence from Shk1 cells was measured in nutrient broth and influent wastewater and activated sludge mixed liquor from a municipal wastewater treatment plant. Using the Shk1 toxicity testing protocol, Zn EC₅₀ values for bioluminescence in nutrient broth, influent wastewater, and activated sludge mixed liquor were approximately 42, 7, and 32 mg/l, respectively. Zn concentrations as low as 1 mg/l could be detected in influent wastewater. The detection limit in influent wastewater is below the Zn concentrations typically reported to affect the activated sludge process.     

Fate and effects of methylene chloride in activated sludge.

Activated sludge obtained from a municipal wastewater treatment plant was acclimated to methylene chloride at concentrations between 1 and 100 mg/liter by continuous exposure to the compound for 9 to 11 days. Acclimated cultures were shown to mineralize methylene chloride to carbon dioxide and chloride. Rates of methylene chloride degradation were 0.14, 2.3, and 7.4 mg of CH2Cl2 consumed per h per g of mixed-liquor suspended solids for cultures incubated in the presence of 1, 10, and 100 mg/liter, respectively. Concentrations of methylene chloride between 10 and 1,000 mg/liter had no significant effect on O2 consumption or glucose metabolism by activated sludge. A hypothetical model was developed to examine the significance of volatilization and biodegradation for the removal of methylene chloride from an activated sludge reactor. Application of the model indicated that the rate of biodegradation was approximately 12 times greater than the rate of volatilization. Thus, biodegradation may be the predominant process determining the fate of methylene chloride in activated sludge systems continuously exposed to the compound.     

Improved treatment of tannery wastewater using Zoogloea ramigera and its extracellular polymer in an activated sludge process

Summary When Zoogloea ramigera and its extracellular polymer were daily added to the laboratory scale activated sludge reactor treating tannery wastewater, more than 15% of the COD concentration (COD; 151 mg/l) and 32% of the turbidity (NTU; 9.2) were removed compared with a controlled reactor (COD; 336 mg/l, NTU; 43.5) operated without any additions.