Recycle of Alum recovered from water treatment sludge in chemically enhanced primary treatment

An investigation was made to study the feasibility of recovering the Alum from coagulation sludges and reusing it in chemically enhanced primary treatment (CEPT) process to make the CEPT more cost-effective and recover the resource (Alum) efficiently. The optimum condition and efficiency of the acidification method for Alum recovery from coagulation sludge were investigated in the test. The results show that when the recovery rate of Alum reaches its highest level, 84.5%, the reduction rate of sludge is 35.5%. It turns out that the capability of recovered coagulant to remove turbidity, UV(254) and COD are 96%, 46% and 53%, respectively. The results prove that the recovered coagulants could be used in CEPT and the efficiency of recovered coagulant to remove pollutants is similar to that of fresh coagulant. Although some substances will be enriched during recycle, they have little effect on the quality of treated wastewater. The experiments verify that it would be an advisable and cost-effective way to recover Alum from coagulation sludges in water treatment and chemical wastewater treatment, and it could be then recycled to CEPT as well as reduce sludge volume.     

Pretreatment of wastewater: optimal coagulant selection using Partial Order Scaling Analysis (POSA)

Jar-test is a well-known tool for chemical selection for physical-chemical wastewater treatment. Jar test results show the treatment efficiency in terms of suspended matter and organic matter removal. However, in spite of having all these results, coagulant selection is not an easy task because one coagulant can remove efficiently the suspended solids but at the same time increase the conductivity. This makes the final selection of coagulants very dependent on the relative importance assigned to each measured parameter. In this paper, the use of Partial Order Scaling Analysis (POSA) and multi-criteria decision analysis is proposed to help the selection of the coagulant and its concentration in a sequencing batch reactor (SBR). Therefore, starting from the parameters fixed by the jar-test results, these techniques will allow to weight these parameters, according to the judgments of wastewater experts, and to establish priorities among coagulants. An evaluation of two commonly used coagulation/flocculation aids (Alum and Ferric Chloride) was conducted and based on jar tests and POSA model, Ferric Chloride (100 ppm) was the best choice. The results obtained show that POSA and multi-criteria techniques are useful tools to select the optimal chemicals for the physical-technical treatment.     

Combined advanced oxidation and biological treatment of tannery effluent

During leather processing in tanneries, considerable amount of wastes with organic and inorganic pollutants are generated. For removal of these pollutants and recovery of water, biological treatment methods and reverse osmosis (RO) based membrane technologies are adopted. While recovering water from treated tannery effluent using RO membranes, presence of residual organics, dye molecules, and other impurities in the effluent have been reported as the major drawback which leads to membrane fouling and failure. In this study, an attempt was made to improve the quality of the treated tannery effluent by subjecting the secondary treated tannery effluent by ozonation alone and ozonation of primary and secondary treated tannery effluent followed by aerobic biological Sequential Batch Reactor (SBR). Maximum color reduction of 98% at pH value of 12 with ozonation alone was observed for secondary treated tannery effluent. Ozonation of secondary treated tannery effluent followed by further biological treatment in aerobic SBR increased the chemical oxygen demand (COD) removal rate and resulted in COD values less than 300 mg/L. In case of primary treated tannery effluent, maximum COD reduction of 64% was achieved in SBR.     

Removal of sulfide, sulfate and sulfite ions by electro coagulation

The removal of various species of sulfur from beamhouse of tannery wastewater and also from synthetic samples was studied by electro-flotation technique. Consumable anodes of iron and aluminum and insoluble anode of titanium were tested as anodes. It was found that iron and aluminum anodes were effective for the removal of suspended solids, sulfide, sulfite and sulfate. Progress of simultaneous coagulation of suspended solids during electro-flotation was measured using particle size analysis. Coagulation was found to be essential for effective flotation of suspended solids. Metal ions generated in situ by electrolytic oxidation of anode were found to react with dissolved sulfide ions. Metal sulfides thus formed as colloidal suspension were coagulated and floated simultaneously by hydrogen bubbles generated from cathode. Simultaneous occurrence of precipitation, coagulation and flotation was observed during electro-flotation. X-ray diffraction studies were conducted to identify the nature of sulfide phase formed during electrolytic precipitation. The effect of pH, current density and initial concentration of pollutants was studied and the results are discussed. The removal of sulfite and sulfate ions is explained by zeta-potential measurements.     

Optimization of phosphorus removal from secondary effluent using simplex method in Tianjin, China

Enhanced concentrations of phosphorus entering the aquatic systems have been linked with eutrophication and its associated problems. Jar tests were applied to a secondary effluent in order to determine optimal conditions for coagulation. The coagulants studied were ferric sulfate [Fe2(SO4)3], aluminum sulfate [Al2(SO4)3.18H2O] and polyaluminum chloride (PAC). The experiments were carried out using simplex research technique to determine the optimum conditions of these coagulants for phosphorus removal. For each coagulant examined, 18-25 experiments were carried out until a maximum removal was observed through the experimental procession. Increases of greater than 30% were found for the removal efficiencies of these three coagulants over the course of the experiments. Good removal efficiencies averaging at least 87.25% were obtained through the simplex procession. The orthophosphate removal efficiency was higher than that of total phosphorus for each coagulant. The maximum removal efficiency of total phosphorus obtained from the optimization procedures for ferric sulfate, aluminum sulfate and polyaluminum chloride was 87.3, 95.6 and 94.0%, respectively, and the minimum total phosphorus residual was 0.35, 0.12 and 0.16 mg/L, respectively.     

Utilization of moringa oleifera and nanofiltration membrane to treat palm oil mill effluent (POME)

The palm oil mill effluent imposes environmental issues because of natural and supplement substance. This waste has a significant amount of biological oxygen demand, total suspended solids, chemical oxygen demand, and turbidity. Moringa oleifera seeds′ performance analysis as natural coagulants during the pretreatment stage of palm oil mill effluent before it is filtered through commercial nanofiltration membrane is the focus of the current study. The untreated palm oil mill effluent has 2,410 mg/L biological oxygen demand, 3,900 mg/L chemical oxygen demand, 865 NTU turbidity, 41,900 mg/L total suspended solids, and 4.61 pH. The significant reduction occurred in the feed parameters viz., 91.7 % for biological oxygen demand, 83.0 % for chemical oxygen demand, 67.7 % for total dissolved solids, and 72.8 % for turbidity after the pretreatment; however, the pH increased to 4.88. Design expert® was used to design the experiments and optimize the palm oil mill effluent pretreatment process via a one-factor experimental design. The optimized solution has a 0.994 desirability index. Finally, it was concluded that with ever-tightening environmental standards, moringa oleifera could provide a cheap, green, and potential natural alternative to the existing coagulants employed to treat the palm oil mill effluent.     

Studies of a membrane aerated bioreactor for wastewater treatment

This study was undertaken specifically to collect engineering and process performance information on the behaviour of a membrane supported bio-film in a well-characterised bioreactor. A novel membrane aerated bioreactor has been tested in the laboratory on synthetic sewage, and also piloted for the treatment of primary effluent at a local municipal wastewater treatment plant. The reactor's design employs gas-permeable, hollow-fibre membranes that are submerged in the wastewater. Air is blown through the inside of the fibres. Aeration costs for such a reactor are likely to be lower than conventional systems because gas compression is not required. Thick bio-films grow on the outside of the fibres and effectively treat the wastewater. The bio-films grown in this manner are capable of biological oxygen demand (BOD) removal, nitrification, denitrification, and simultaneous sludge digestion. The character of the bio-film is very different from conventional bio-films grown on inert surfaces, since in this case the bio-film receives its oxygen and the wastewater components from different directions. In pilot studies, a reactor having a hydraulic residence time of 6.5 h and equipped with no sedimentation tank achieved 70–75% BOD and nitrogen removal, and produced an effluent containing less than 30 mg/l total suspended solids.     

Application of multicriteria decision analysis to jar-test results for chemicals selection in the physical-chemical treatment of textile wastewater

Jar-test is a well-known tool for chemicals selection for physical-chemical wastewater treatment. Jar-test results show the treatment efficiency in terms of suspended matter and organic matter removal. However, in spite of having all these results, coagulant selection is not an easy task because one coagulant can remove efficiently the suspended solids but at the same time increase the conductivity or increase considerably the sludge production containing chemicals and toxic dyes. This makes the final selection of coagulants very dependent on the relative importance assigned to each measured parameter. In this paper, the use of multicriteria decision analysis (MCDA) is proposed to help on the selection of the coagulant and its concentration in the physical-chemical wastewater treatment, since textile wastewater contains hazardous substances. Therefore, starting from the parameters fixed by the jar-test results, these techniques will allow to weight these parameters, according to the judgements of wastewater experts, and to establish priorities among coagulants. Two well-known MCDA techniques have been used: analytic hierarchic process (AHP) and preference ranking organization method for enrichment evaluations (PROMETHEEs) and their results were compared. The method proposed has been applied to the particular case of textile wastewaters. The results obtained show that MCDA techniques are useful tools to select the chemicals for the physical-technical treatment.     

The effect of mixing pharmaceutical and tannery wastewaters on the biodegradation characteristics of the effluents

This paper evaluated the effect of mixing the effluent of a pharmaceutical plant producing acetylsalicylic acid with tannery wastewater, on the biodegradation of the effluents. The evaluation involved the analysis of the oxygen uptake rate (OUR), profiles of each wastewater and the mixture by respirometry. Model calibration using the experimental OUR data identified major COD fractions and associated process kinetics for all samples analyzed. The tannery sample was a plain-settled effluent having a total COD of around 2200 mg/L with a readily biodegradable fraction of 15%. The same fraction was 57% in the pharmaceutical wastewater sample having a much stronger total COD content of 40,435 mg/L. Consequently, mixing of the pharmaceutical effluent with the tannery wastewater up to 38% of the total COD in the mixture increased the readily biodegradable COD fraction but had an inhibitory effect on the biodegradation kinetics. This effect was relatively lower on growth, but quite significant on the hydrolysis of the slowly biodegradable COD decreasing the maximum hydrolysis rate from 2.0 day(-1) to 1.2 day(-1). Model evaluation of the respirometric data, as performed in this study sets a workable protocol for the assessment of the compatibility of different wastewater mixtures for biological treatability.     

Application of nanofiltration for chromium concentration in the tannery wastewater

The article presents results of investigation concerning an influence of tannery wastewater composition on chromium(III) concentration in the wastewaters during the nanofiltration process (NF). The effectiveness of this process strongly depends on mutual relation between chloride and sulfate ions concentration in tannery wastewater. For this reason, the optimum composition of the tannery wastewater should consist chloride/sulfate ions ratio close to 1. Moreover, an influence of transmembrane pressure (TMP) and the "ageing" of chromium tannery wastewater on the efficiency of the process has been investigated. Optimal range of TMP equal to 14-16 bar has been assumed for the process. It is necessary to point out that the optimum transmembrane pressure can be changed in the case of the membranes with different permeation properties. "Ageing" of the tannery wastewater reduces only a little an efficiency of the process. Experimental results demonstrated that the NF process could be successfully used for the concentration of chromium in the tannery wastewater with high permeate flux, selectivity and performance stability.     

Optimization of coagulation-flocculation process for pulp and paper mill effluent by response surface methodological analysis

Coagulation-flocculation is a proven technique for the treatment of high suspended solids wastewater. In this study, the central composite face-centered design (CCFD) and response surface methodology (RSM) have been applied to optimize two most important operating variables: coagulant dosage and pH, in the coagulation-flocculation process of pulp and paper mill wastewater treatment. The treated wastewater with high total suspended solids (TSS) removal, low SVI (sludge volume index) and high water recovery are the main objectives to be achieved through the coagulation-flocculation process. The effect of interactions between coagulant dosage and pH on the TSS removal and SVI are significant, whereas there is no interaction between coagulant dosage and water recovery. Quadratic models have been developed for the response variables, i.e. TSS removal, SVI and water recovery based on the high coefficient of determination (R(2)) value of >0.99 obtained from the analysis of variances (ANOVA). The optimum conditions for coagulant dosage and pH are 1045mgL(-1) and 6.75, respectively, where 99% of TSS removal, SVI of 37mLg(-1) and 82% of water recovery can be obtained.     

Enhancement of bioseparation and dewaterability of domestic wastewater sludge by fungal treated dewatered sludge

A promising biological, sustainable, non-hazardous, safe and environmental friendly management and disposal technique of domestic wastewater sludge is global expectation. Fungal entrapped biosolids as a result of prior fungal treated raw wastewater sludge was recycled to evaluate its performance as inoculum for bioseparation/bioconversion of supplemented sludge in view of continuous as well as scale up wastewater sludge treatment. Encouraging results were achieved in bioseparation of suspended solids and in dewaterability/filterability of treated domestic wastewater sludge. Fungal entrapped biosolids offered 98% removal of total suspended solids (TSS) in supplemented sludge treatment at 6-day without nutrient (wheat flour, WF) supply. Consequently, 99% removal of turbidity and 87% removal of chemical oxygen demand (COD) were achieved in supernatant of treated sludge. The lowest value (1.75 x 10(12)m/kg) of specific resistance to filtration (SRF) was observed at 6-day after treatment, which was equivalent to the 70% decrease of SRF. The all results except SRF were not influenced further in treatments accompanied with WF supplementation. The present treatments offered significant (P相似文献   

Application of Doehlert matrix to determine the optimal conditions of electrochemical treatment of tannery effluents

The oxidation of organic and inorganic pollutants present in tannery effluents has been realised by electrochemical way. The influence of the electrochemical reactor parameters was carried out by the use of Doehlert matrix. The obtained results have shown that the current intensity and the electrolysis time were the main influent parameters on the removal ratio of chemical oxygen demand (COD), total organic carbon (TOC), electrochemical oxidation of trivalent chromium and sulphite ions.     

Studies of chromium removal from tannery wastewaters by algae biosorbents, Spirogyra condensata and Rhizoclonium hieroglyphicum

Chromium in the effluent is a major concern for tanning industry. Chemical precipitation methods are commonly employed for the removal of chromium but this leads to formation of chrome-bearing solid waste, plus it is uneconomical when the concentration of chromium in the effluent is low. Ion exchange and membrane separation methods are relatively expensive. In this study, two algae namely, Spirogyra condensata and Rhizoclonium hieroglyphicum have been employed to remove chromium from tannery effluent. The effect of pH and chromium concentration showed S. condensata to exhibit maximum uptake of about 14mg Cr(III)/g of algae at optimum pH of 5.0 whereas R. hieroglyphicum had 11.81mg of Cr(III)/g of algae at pH of 4.0. Langmuir and Freundlich models were applied. Increase of initial concentration of Cr resulted to a decrease in adsorption efficiency. Dilute sulphuric acid (0.1M) showed good desorption efficiency (>75%). Interference from cations negatively impacted on biosorption of chromium. Immobilized algae on Amberlite XAD-8 in a glass column, gave 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.     

Treatment of water-based printing ink wastewater by Fenton process combined with coagulation

Attempts were made in this study to examine the efficiency of Fenton process combined with coagulation for treatment of water-based printing ink wastewater. Parameters affecting the Fenton process, such as pH, dosages of Fenton reagents and the settling time, were determined by using jar test experiments. 86.4% of color and 92.4% of chemical oxygen demand (COD) could be removed at pH 4, 50mg/l H(2)O(2), 25mg/l FeSO(4) and 30min settling time. The coagulation using polyaluminium chloride (PAC) and ferrous sulfate (FeSO(4)) was beneficial to improve the Fenton process treated effluent in reducing the flocs settling time, enhancing color and COD removal. The overall color, COD and suspended solids (SS) removal reached 100%, 93.4% and 87.2% under selected conditions, respectively. Thus this study might offer an effective way for wastewater treatment of water-based ink manufacturer and printing corporation.     

Electrochemical treatment of tannery wastewater using DSA electrodes

In this work we studied the electrochemical treatment of a tannery wastewater using dimensionally stable anodes (DSA) containing tin, iridium, ruthenium, and titanium. The electrodes were prepared by thermal decomposition of the polymeric precursors. The electrolyses were performed under galvanostatic conditions, at room temperature. Effects of the oxide composition, current density, and effluent conductivity were investigated, and the current efficiency was calculated as a function of the time for the performed electrolyses. Results showed that all the studied electrodes led to a decrease in the content of both total phenolic compounds and total organic carbon (TOC), as well as lower absorbance in the UV-vis region. Toxicity tests using Daphnia similis demonstrated that the electrochemical treatment reduced the wastewater toxicity. The use of DSA type electrodes in the electrochemical treatment of tannery wastewater proved to be useful since it can promote a decrease in total phenolic compounds, TOC, absorbance, and toxicity.     

Enhancement of biogas generation during co-digestion of tannery solid wastes through optimization of mix proportions of substrates

Tanneries in India face the twin problems of managing process solid waste and treatment of effluent plant sludge. The present study covered (i) significance of optimization of mix proportions of substrates i.e., fleshings (F) and the primary sludge (PS) and secondary sludge (SS) generated during treatment of tannery wastewater (ii) residence time during co-digestion for enhancement of biogas generation and (iii) digestate analysis. Maximum biogas generation of 385 mL/g of VS_added was observed for the mix proportion of 1.00:2.70:0.30 (F:PS:SS) and a residence time of 45 days during co-digestion of tannery solid wastes. Biogas generation was enhanced by increasing the proportion of PS to SS. After digestion, secondary metabolites i.e., primary, secondary, and tertiary alcohols, amino acids, methane, and ammonia were observed from FT-IR analysis. The exothermic reaction was observed at around 175 °C and when C/N ratio of digestate was around 8.0.     

Unhairing effluents treated by an activated sludge system

Leather tannery effluents are a source of severe environmental impacts. In particular, the unhairing stage, belonging to beamhouse processes, generates a significantly toxic, alkaline wastewater with high concentrations of organic matter, sulphides, suspended solids and salts. The objective of this work was to evaluate the biodegradability and toxicity of diluted unhairing wastewater after being treated by an activated sludge (AS) system. The biomass activity of the AS was also evaluated. The AS system was fed for 180 days with diluted unhairing effluent. The operation strategy increased the organic load rate (OLR) from 0.23 to 2.98 g COD/l per day while the HRT was variable until operation day 113, when the HRT was near 1.1 days. Results show that when the organic load rate was lower than 2 g COD/l per day, the biological oxygen demand (BOD5) efficiency was 99%, whereas the chemical oxygen demand (COD) was around 80%. The reactor operation was stable until 2 g COD/l per day. For higher values, the system was less efficient (COD and BOD5 removal rate lower than 40%) and the relation of food/micro-organisms (F/M) was higher than 0.15. Biomass evaluations through oxygen utilisation coefficients show that the specific oxygen uptake rate (SOUR) decreased from 1.11 to 0.083 g O2/g MLVSS per day, in the same way the endogenous oxygen coefficient decreased from 0.77 to 0.058 per day. The reduction of biomass activity (measured as oxygen respiration) could be attributable to the inorganic compound content (ammonia and chloride) in the unhairing effluent. Also, the bioassays with Daphnia magna and Daphnia pulex showed that with these compounds, only between 24 and 31% of the toxicity of the aerobic-treated effluent can be removed. On the other hand, ultrafiltration (UF) analysis indicated that a COD fraction is recalcitrant to the aerobic treatment, principally those above 10,000 Da (around 55% of total unhairing influent COD).     

Integrated treatment scheme for rubber thread wastewater: sulfide precipitation and biological processes

In this study, acidic latex wastewater containing high average zinc and acetic contents of 816mgL(-1) and 20,862mgCODL(-1), respectively, was treated successfully by a series of chemical and biological processes without any addition of acid or base for pH adjustment. Total dissolved solids of the treated effluent increased by only 1.1-fold on average for sulfide precipitation as compared to 2.8-fold for the hydroxide strategy. The oxidation-reduction potential (ORP) value of 0mV was used successfully as an indicator for optimum sulfide addition which consistently provided an appreciable reduction in effluent concentrations to less than 1 and 2mgL(-1) for zinc and residual sulfide, respectively. The anaerobic filter was very stable in handling the chemically treated wastewater up to the organic loading rate of 11.8gCODL(-1)day(-1) with an average efficiency of 92%. Methane production and biomass yield were 0.32L(gCOD(removed))(-1) and 0.014gVSS (gCOD(removed))(-1), respectively. For the activated sludge process, the optimum sludge age and hydraulic retention time were 30 and 0.8 days, respectively, which are equivalent to the organic loading rates of 2.50gCODL(-1)day(-1) or 2.13gBODL(-1)day(-1). Under these optimum conditions, average removal efficiencies for COD and BOD were 96.6 and 99.4%. Average soluble COD, BOD and suspended solids in the effluent were 71, 11 and 38mgL(-1), respectively. This integrated treatment scheme was proven to be an effective approach for highly polluted and toxic rubber thread wastewater.     

Removal of chromium(III) from tannery wastewater using activated carbon from sugar industrial waste

Chromium is commonly found in huge quantities in tannery wastewaters. For this reason, the removal and recovery of the chromium content of tannery wastewaters is crucial for environmental protection and economic reasons. Removal and recovery of chromium were carried out by using low-cost potential adsorbents. For this purpose three types of activated carbon; C1, the waste generated from sugar industry as waste products and the others (C2, C3) are commercial granular activated carbon, were used. The adsorption process and extent of adsorption are dependent on the physical and chemical characteristics of the adsorbent, adsorbate and experimental condition. The effect of pH, particle size and different adsorbent on the adsorption isotherm of Cr(III) was studied in batch system. The sorption data fitted well with Langmuir adsorption model. The efficiencies of activated carbon for the removal of Cr(III) were found to be 98.86, 98.6 and 93 % for C1, C2 and C3, respectively. The order of selectivity is C1>C2>C3 for removal of Cr(III) from tannery wastewater. Carbon "C1" of the highest surface area (520.66 m(2)/g) and calcium content (333.3 mg/l) has the highest adsorptive capacity for removal of Cr(III). The results revealed that the trivalent chromium is significantly adsorbed on activated carbon collected from sugar industry as waste products and the method could be used economically as an efficient technique for removal of Cr(III) and purification of tannery wastewaters.