These processes are usually divided into anaerobic and aerobic processes. Aerobic wastewater treatment processes include treatments such as activated sludge process, oxidation ditches, trickling filters, lagoon-based treatments, and aerobic digestion. Diffused aeration systems may be used to maximize oxygen transfer and minimize odors as the wastewater is treated. Aeration provides oxygen to the helpful bacteria and other organisms as they decompose organic substances in the wastewater.
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A time-honored example of an aerobic treatment method is the activated sludge process. This is a proven biological wastewater treatment widely used for the secondary treatment of both domestic and industrial wastewater. It is well suited for treating waste streams high in organic or biodegradable content and is often used to treat municipal sewage , wastewater generated by pulp and paper mills or food-related industries such as meat processing, and industrial waste streams containing carbon molecules.
Air is gently blown into a spirally wound membrane in a tank, with air on one side of the membrane and mixed liquor on the other. Nitrification-denitrification is achieved by a biofilm that forms on the membrane.
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The result is an effluent suitable for irrigation or release into the environment. By contrast, anaerobic treatment uses bacteria to help organic material deteriorate in an oxygen-free environment. Lagoons and septic tanks may use anaerobic processes. The best-known anaerobic treatment is anaerobic digestion, which is used for treating food and beverage manufacturing effluents, as well as municipal wastewater, chemical effluent, and agricultural waste. The type of biological treatment selected for wastewater treatment, whether aerobic or anaerobic, depends on a wide range of factors, including compliance with environmental regulations on discharge quality.
Biological treatments are often supplemented with treatments including chlorination and carbon filtration, as well as technologies like reverse osmosis and ultrafiltration. High concentrations of these constituents make the possible discharge of tannery wastewaters into water bodies problematic, as they cause eutrophication and other adverse environmental effects Leta et al.
Table 1 shows great variability in the quality of the influent. Great variability was observed with respect to the influent, depending on the type of hides and skins and the region from which they came, at the time of the sampling Lefebvre et al. Therefore, the biodegradability of the influent was found to be low, according to the criteria of Ahn et al. However, BOD 5 is a controversial parameter, when it is applied to tannery wastewater, since it contains many inhibitors of BOD 5 Ates et al. However, no phosphorus deficiency could be identified and this ratio is close to that of domestic wastewater Lefebvre et al.
Many conventional processes were carried out to treat wastewater from tannery industry such as biological process Vijayaraghvan and Murthy, ; Wiemann et al. Biological treatment methods: Biological treatment of wastewater is evaluated as a good treatment method for industrial effluents. Treatment of wastes with bacteria involves the stabilization of waste by decomposing them into harmless inorganic solids either by aerobic or anaerobic process.
In aerobic process, the decomposition rate is more rapid than the anaerobic process and it is not accompanied by unpleasant odours, whereas in anaerobic process, longer detention period is required and gives unpleasant odours. In general, ASP-based treatment is considered to be energy-intensive and expensive from an operation and maintenance point of view. On the other hand, anaerobic processes claim to offer several advantages, especially under tropical climatic conditions Rajamani et al.
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However, a comprehensive comparison of the relative merits of tannery wastewater treatment by these two processes with field data has not yet been performed. As such, it is imperative that experience and knowledge gained through the operation of full-scale treatment plants treating tannery effluents employing both ASP and UASB processes is properly utilized. High variability in the organic content reflected by COD concentration and salinity reflected by TDS concentration of the soak liquor might make the proper operation of a biological treatment plant uneasy, causing important disturbance in the equilibrium of the microbial community.
Yet, looking forward to applying the process at an industrial scale, a decision was taken not to artificially change the influent characteristics in order to make it more homogeneous. This choice resulted in frequent changes in the environmental conditions in the bioreactor. The results of some tannery wastewater treated by biological methods are given in Table 2. Aerobic biological treatment methods: Biodegradation of tannery wastewater using activated sludge process has been reported by many research workers Jawahar et al.
The performance of activated sludge process is affected by many factors. Various parameters of importance relating to growth of microorganisms and substrate utilization on which the operation of the reactor is based include mean cell residence time, Mixed Liquor Volatile Suspended Solids MLVSS concentration, hydraulic detention time, i. An ASP was used for the treatment of tannery wastewater. It was operated continuously for days. Settled tannery wastewater was used as influent to the aeration tank.
A reduction of Pathogens were not detected in the dried sludge. Complete elimination of fecal streptococci was observed in treated effluent. Around In treated effluent chromium level was 5. The AS system was fed for days with diluted unhairing effluent.
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Biomass evaluations through oxygen utilization coefficients show that the specific oxygen uptake rate decreased from 1. The reduction of biomass activity could be attributable to the inorganic compound content ammonia and chloride in the unhairing effluent Vidal et al. Mazumder et al.
In this reactor, the sample was treated under suspended growth and then hybrid system with 20 g L -1 of 5 mm tyre tube beads in batch mode. The continuous study was made under suspended growth and hybrid system with g L -1 of beads. The maximum COD removal was The overall removal rate ranged from 0. Salinity of tannery wastewater makes it difficult to be treated by conventional biological treatment. Salt tolerant microbes can adapt to these saline conditions and degrade the organics in saline wastewater.
Tannery saline wastewater obtained from a Common Effluent Treatment Plant CETP near Chennai southern India was treated with pure and mixed consortia of four salt tolerant bacterial strains viz. Salt inhibition effects on COD removal rate were noted. Comparative analysis was made by treating the tannery saline wastewater with activated sludge obtained from CETP and with natural habitat microbes present in raw tannery saline wastewater.
The COD removal results for tannery saline waste stream by natural habitat strains as well as activated tannery sludge proved they were not suitable and that specialized consortia salt tolerant were needed for efficient treatment. The identified salt tolerant bacterial consortia is considered as a suitable working culture for efficient biodegradation of tannery saline wastewater.
The pre denitrification-nitrification process found to be efficient for simultaneous removal of nitrogen and organic substrates from tannery wastewaters. Normally chromium III will not cause process inhibition during performance operations. A pilot wastewater treatment plant consisting of a pre denitrification-nitrification process was constructed and operated for 6 months. The average effluent ammonium nitrogen ranged from 8. The average values of denitrification and nitrification rates determined by nitrate and ammonium uptake rates NUR and AUR were 8. A study on the biological nitrogen removal from tannery wastewaters without a preliminary chemical-physical phase or an external carbon source for denitrification were carried out by Szpyrkowicz et al.
Experiments were carried out over a 6 month period in a pilot plant of the modified Ludzack-Ettinger configuration. The COD utilization coefficient was No inhibition of the process was induced by Cr or by S 2- present in the raw wastewaters. A negative effect on the denitrification rate resulted from a high ratio between the quantity of oxygen returned with the mixed liquor and the inlet COD.
Hypersaline wastewater i. The characterization of the soak liquor showed that this effluent is biodegradable, though not easily and highly variable, depending on the origin and the nature of the hides. A lab-scale SBR was used to treat this soak liquor seeded with halophilic bacteria and the performance of the system were evaluated under different operating conditions with changes in hydraulic retention time, organic loading rate and salt concentration.
The changes in salinity appeared to affect the removal of organic matter more than the changes in hydraulic retention time or organic loading rate. Despite the variations in the characteristics of the soak liquor, the reactor achieved proper removal of organic matter , once the acclimation of the microorganisms was achieved.
The organisms responsible for nitrogen removal appeared to be the most sensitive to the modifications of these parameters Lefebvre et al. The wastewater, produced after the oxidation of sulfide compounds coming from the beam house section of a tannery, contained average COD and ammonium concentrations of and 90 mg L -1 , respectively. Goltara et al.
The MSBR was operated for a period of days, with no sludge removal during the whole period of operation. The biomass concentration inside the reactor varied considerably, with maximum values close to 10 g L -1 at the end of operation. An important accumulation of organic matter in the reactor was noticed, although the COD effluent was not affected due to the permeation through the membrane.
The feasibility of treating tannery wastewater containing chromium, an inhibiting compound, was studied by Farabegoli et al. The maximum chromium concentration tolerated by microorganisms is determined through aerobic and anoxic batch experiments and the biomass inhibition process is analyzed in a lab scale sequential batch reactor at higher chromium concentrations. It was observed that the chromium addition had less influence on the denitrification bacteria than on the nitrification bacteria.
In addition, it was observed that nitrification and denitrification rates, at the same chromium concentration, were higher in the SBR reactor than in batch experiments with unacclimated biomass. Experimental results confirm that sequencing batch reactors are able to produce a more resistant biomass, which acclimates quickly to inhibiting conditions. Thanigavel employed an inverse fluidized bed bioreactor for the treatment of tannery wastewater. A low density particle Polypropylene-Density, kg m -3 was used. From the result it was found the maximum COD removal of SBR coupled with respirometry is a cost-effective and a clear alternative to the conventional biological system for the treatment of tannery wastewater Ganesh et al.
The removal efficiencies are much higher than the continuous aerobic systems. Such enhanced performance with SBR over conventional activated sludge process is perhaps due to the enforced short-term unsteady state conditions, which facilitates the required metabolic conditions for treatment of wastewater. The removal of COD by degradation is stoichiometric with oxygen usage.
Measurement of oxygen uptake rates and corresponding COD uptake rates showed that a 12 h operating cycle was optimum for tannery wastewater. A plot of OUR values provided a good indication of the biological activity in the reactor. At a h SBR cycle with a loading rate of 1. These removal efficiencies were much higher than the conventional aerobic systems. It was observed that with the exception of high organic load at the initial feed the oxygen transfer capacity was in excess of the OUR and aerobic condition was generally maintained.
Simultaneous nitrification-denitrification was observed in the SBR during the feed period as proved by mass balance Ganesh et al. Anaerobic biological treatments: The combination of the UASB with an aerobic post-treatment enhanced the performance of the overall wastewater treatment process and the COD removal efficiency. However, for effective operation, the system had to be operated at very low OLRs, which affects the economic viability of such a process.
The anaerobic digestion of tannery soak liquor was studied by using a UASB. Banu and Kaliappan made an attempt to treat the tannery wastewater by using hybrid upflow anaerobic sludge blanket reactors. The advantage of this reactor is both the fixed film and upflow sludge blanket treatment. The reactor was operated for days at two different hydraulic retention times viz. The average concentration of COD and tannin in the influent tannery wastewater used were mg L -1 and mg L -1 , respectively. The reactor performed to its maximum at an organic loading rate of 2. They also found that increase in OLR beyond 2.
The retention of the active methanogenic biomass in the form of biofilm supported by a carrier has been developed to treat tannery wastewater ensures with minimum particle washout independent of the HRT. The bio film colonisation on two types of micro carriers was compared. Porous polyurethane foam material was found to be more suitable than Raschig rings as a micro carrier in the UAFBR reactor.
Both SEM and TEM techniques were used to study the morphology of the bio film, the location of bacteria in the bio film and species diversity and community structure. In an Upflow Anaerobic Fixed Biofilm Reactor UAFBR , which retains a high concentration of accumulated biomass the effects of major process variables such as hydraulic retention time, organic loading rate and temperature on chemical oxygen demand removal and methane yield performances of the reactor were evaluated.
This aids the conversion of COD and results in a reduction in effluent suspended solids. The COD removal and methane yield is higher than the values reported previously Song et al. A long-term study was conducted to identify the process of biological sulfate reduction in anaerobic two-stage pilot plants treating tannery wastewater.
Influence of quality and quantity of wastewater on sulfate removal in both stages of the pilot plant was simultaneously tested. In the first stage, desulfurization increased with higher feed flow but the desulfurization then decreased in the second stage. The concentration of sulfate in the influent had a significant influence on the desulfurization in both stages of the pilot plants.
Operational parameters were adjusted in order to restrict the biological sulfate reduction to the first stage. Compared to pH 5 or 6 in the influent, a pH of 7 most increased biological sulfate reduction in the first stage. No significant influence on COD removal or volume of gas was observed. For three pilot plants operated parallel to each other, no significant difference in desulfurization was noticed Genschow et al.
Rajasimman et al. The gas production was in the range of L for the given organic load. Wetlands: Wetlands planted with Typha latifolia proved to be tolerant to high organic loadings and to interruptions in feed during biological treatment of tannery wastewater under long-term operation. The systems were subject to three hydraulic loadings, 18, 8 and 6 cm d -1 and to periods of interruption in the feed.
The relationship between the substrate, plant development and removal efficiency, especially of organic matter , was investigated. The three different substrates were adequate for the establishment of T. Bench scale membrane bio-reactors were operated to investigate the treatment efficiency of tannery wastewater with high organic and nitrogen contents and the optimum operating conditions. Under these conditions, the effluent COD and Total Nitrogen were and 54 mg L -1 , respectively, which satisfied the effluent limits for the tannery wastewater.
It was also observed that supplementation of phosphorus to maintain COD: P ratio of is needed to achieve the best performance Chung et al. Munz et al. The addition of powdered PAC to analyze improvements in effluent quality and in the filtration process, improvements in COD removal are found to be low, but not negligible and greater than the PAC adsorption effect alone.
The results refer to a pilot plant monitoring stretched over a period of days: without PAC, with a PAC concentration of 1. The sludge residence time and hydraulic retention time were maintained between 30 and 90 days and 50 and h, respectively. No effects were observed on the nitrification processes. The filtration process was evaluated in terms of sludge filterability, fouling rate and fouling reversibility. The fouling rate decreased with an increasing PAC concentration and showed complete reversibility both in presence and in absence of PAC.
The role that tannins play in terms of biodegradability did not appear to be significant in tannery wastewater treatment. The methodology has established the preliminary use of respirometry to examine the biodegradability of a selection of commercial products; the subsequent analysis, by means of spectrophotometric reading and RP-IPC Reverse-Phase Ion-Pair liquid chromatography, estimates the concentrations of natural tannins and naphthalenesulfonic tanning agents in the influent and effluent samples.
The titrimetric tests that were aimed at evaluating the levels of inhibition on the nitrifying biomass samples did not allow a direct inhibiting effect to be associated with the concentration levels of the tannin in the effluent. Nonetheless, the reduced specific growth rates of ammonium and nitrite oxidising bacteria imply that a strong environmental pressure is present, if not necessarily due to the concentration of tannins, due to the wastewater as a whole Munz et al. Moreover, full nitrification could be established during the subsequent aerobic degradation and the remaining ammonia is completely removed.
The biological treatment of the tannery wastewater substreams beamhouse BH, pre-tanning steps and tan-yard wastewater TY, tanning and wet-finishing process steps and the application of an oxidative treatment by ozone, followed by a second aerobic treatment were investigated. It can be stated that the combined oxidative and biological treatment of BH and TY was effective and ensures the meeting of given COD and ammonia-limits for the direct discharge of this special industrial wastewater into rivers Jochimsen et al.
Degradation of leather industry wastewater by aerobic treatment incorporating Thiobacillus ferrooxidans, Fenton's reagents and combined treatment was studied by Mandal et al. The sole treatment by Fenton's oxidation involving the introduction of 6 g FeSO 4 and g H 2 O 2 in a liter of wastewater at pH of 3. They observed a decrease in photo absorption of the Fenton's reagent treated samples, as compared to the blanks, at , and nm wave lengths. This may be the key factor for stimulating the biodegradation by Thiobacillus ferrooxidans. Seawater-induced flocculation of alkaline tannery wastewater can increase the removal efficiency of organic compounds, such as particulate, colloids, colored compound and other dissolved organic compounds.
Flocculation through the use of seawater was used as the primary treatment in the onsite tannery wastewater treatment plant. Evaluation of the potential biological treatment was performed by the activated sludge system of suspended micro-organisms using seawater flocculated tannery wastewater. The pH adjustment of the influent wastewater and PO 4 -P addition after seawater flocculation were the most important operational parameters to enhance the removal efficiency of COD in the activated sludge process.
Experimental results demonstrated that seawater flocculation was more effective than the comparable ferric salt flocculation in enhancing the biological treatment during the days of operation Ryu et al. The ozonation of biologically pre-treated tannery wastewater and the influence of the applied specific ozone consumption onto a subsequent biological treatment were investigated by Jochimsen et al.
From their study it was found that the partial oxidation of COD is favorable for subsequent biodegradation, whereas further mineralization reduces the effectivity of biological oxidation. Biological degradation, carried out in a sequencing batch biofilm reactor, with chemical oxidation, performed by ozone is an innovative tannery wastewater process. Furthermore, it is proved that the combined process is characterized by a very low sludge production.
The combined treatment at the laboratory scale with and without ozonation were compared resulting to be very satisfactory only in the latter instance where recorded COD, NH 4 -N and TSS average removals were 97, 98 and In fact, the measured specific sludge production resulted unexpectedly much lower than the value reported for conventional biological systems Di Iaconi et al. High sulfide concentration present in treated wastewater may render aerobic biological treatment unsuitable.
Hence, it became essential to include sulfide removal unit operation preceeding aerobic biological unit. Among the techniques available oxidation of sulfide by air using activated carbon as catalyst gained importance for its removal of COD, BOD and TOC in addition to elimination of sulfide in wastewater. Thus post anaerobic treatment of wastewater was required to meet discharging standard.
Coagulation considerably reduced the concentration of sulfide and improved the anaerobic treatability lead to a reduction in waste disposal costs for tannery industries. Coagulation at pH 7. Incorporation of coagulation prior to digestion resulted in an increased capacity of the digesters and improved digestion performance. An anaerobic digestion was carried out on initial samples and supernatants from the coagulation at a hydraulic retention time of 10 days with a loading rate of 0.
A methane yield of 0. The combined system provided a residual COD of less than mg L -1 and a residual sulfide of less than mg L The results also demonstrated that a sulfide concentration in excess of mg L -1 completely inhibited methane production Song et al. Chromium removal: The tannery wastewater with increasing chromium concentrations, caused by poor waste water management with an average value in the influent was around 2. Investigations are focused on identification of the factors affecting the process performance Banas et al.
Chromium in tannery sludge causes serious environmental problems and is toxic to organisms and it was efficiently leached by the acidophilic sulfur-oxidizing Acidithiobacillus thiooxidans. The results showed that the pH of sludge mixture inoculated with the indigenous A. The naturally occurring microbes have enough potential to mitigate the excessive contamination of their surroundings and can be used to reduce the metal concentrations in aqueous solutions in a specific time frame.
Microbes are isolated, keeping the natural selection in the view, from the tannery effluent since microbes present in the effluent exposed to the various types of stresses and metal stress is one of them.eczefunviomet.tk
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Investigations include the exposure of higher concentrations of Cr VI 1. The short termed study 72 h of biosorption showed significant reduction of metal in the media especially in the higher concentrations with a value from 1. A Gram-positive, chromium Cr resistant bacterial strain from effluent of tanneries, grown in media containing potassium dichromate concentration up to 80 mg mL -1 has the reducing capability Cr VI. The influencing factors are pH of the medium, concentration of Cr and the amount of the inoculum. Bacterial strains Acinetobacter sp.
Algae namely, Spirogyra condensata and Rhizoclonium hieroglyphicum were employed to remove chromium from tannery effluent. The effect of pH and chromium concentration show that S. Increase of initial concentration of Cr resulted to a decrease in adsorption efficiency. Dilute sulph uric acid 0. Interference from cations negatively impacted on biosorption of chromium. Immobilized algae on Amberlite XAD-8 in a glass column, gives better recovery of chromium in tannery effluent compared to a batch method with unimmobilized algae.
Fourier transform infra red FT-IR analysis of the two algae revealed the presence of carboxyl groups as possible binding sites Onyancha et al. Srivastava and Thakur evaluated the potential of Aspergillus sp. Aspergillus sp. The tannery effluent carrying hazardous Cr VI species due to the oxidation of Cr III species is found to pollute the soil and the ground water. Biosorption of the Cr VI onto the cell surface of Trichoderma fungal species in aerobic condition.
Batch experiments were conducted with various initial concentrations of chromium ions to obtain the sorption capacity and isotherms. The results obtained at pH 5. It was found that the sorption isotherms of fungi for Cr VI appeared to fit Freundlich models. Best results for sorption were obtained at 5.
Biological wastes sawdust, rice husk, coir pith and charcoal and a naturally occurring mineral vermiculite were successfully used to reduce the Cr concentrations in tannery effluent. Batch and column experiments were performed and the adsorption capacities of the substrates were also evaluated using isotherm tests and computing distribution co-efficient. The biosorbent and mineral vermiculite in columns were found very effective in removing Cr from tannery effluent.
This review article examines the extent of pollution created by tanneries and the different biological processes available for the treatment and disposal of tannery wastewater. The advanced methods like membrane filtration, oxidation by ozone are being field trials. Biological treatment methods appear to be a better choice for the removal of color and organic content; however, some of the questions are yet to be answered on its process efficiency. This is because of the lack of information on various aspects such as desirable influent COD, optimal level of volatile fatty acid s VFA concentration in the reactor, the reliable estimates of the bio kinetic constants and their dependence on the substrate levels.
In the field of wastewater treatment, it is generally accepted that anaerobic treatment is less energy-intensive and, hence, preferable to aerobic treatment. This review shows that the anaerobic treatment facility is superior in most respects for the treatment of tannery wastewater. The application of combined process of physical or chemical with biological process to treat tannery wastewater would give satisfactory results compared to individual treatment processes.
Ahn, D. Chang and T. Yoon, Dyestuff wastewater treatment using chemical oxidation, physical adsorption and fixed bed biofilm process. Process Biochem. Kurt and M. Gonullu, An investigation on the tannery wastewater by electrocoagulation. Orhon and O. Tunay, Characterization of tannery wastewater for pretreatment-selected case studies. Water Sci. Banas, J. Plaza, W.
Styka and J. Trela, SBR technology used for advanced combined municipal and tannery wastewater treatment with high receiving water standards.
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Kaliappan, Treatment of tannery wastewater using hybrid upflow anaerobic sludge blanket reactor. Rangel and P. Castro, Evaluation of different substrates to support the growth of Typha latifolia in constructed wetlands treating tannery wastewater over long-term operation. Choi, S. Lee and J. Cho, Health A. Lopez, R. Ramadori, A. Di Pinto and R. Passino, Combined chemical and biological degradation of tannery wastewater by a periodic submerged filter. Water Res.
Industrial Water Pollution Control. McGraw-Hill, Singapore. Farabegoli, G. Carucci, M. Majone and E. Rolle,