Ecotoxicological evaluation of three tertiary wastewater treatment techniques via meta-analysis and feeding bioassays using Gammarus fossarum

Advanced treatment techniques, like ozone, activated carbon and TiO₂ in combination with UV, are proposed to improve removal efficiency of micropollutants during wastewater treatment. In a meta-analysis of peer-reviewed literature, we found significantly reduced overall ecotoxicity of municipal wastewaters treated with either ozone (n = 667) or activated carbon (=113), while TiO₂ and UV was not yet assessed. As comparative investigations regarding the detoxification potential of these advanced treatment techniques in municipal wastewater are scarce, we assessed them in four separate Gammarus-feeding trials with 20 replicates per treatment. These bioassays indicate that ozone concentrations of approximately 0.8 mg ozone/mg DOC may produce toxic transformation products. However, referred effects are removed if higher ozone concentrations are used (1.3 mg ozone/mg DOC). Moreover, the application of 1 g TiO₂/l and ambient UV consistently reduced ecotoxicity. Although activated carbon may remove besides micropollutants also nutrients, which seemed to mask its detoxification potential, this treatment technique reduced the ecotoxicity of the wastewater following its amendment with nutrients. Hence, all three advanced treatment techniques are suitable to reduce the ecotoxicity of municipal wastewater mediated by micropollutants and may hence help to meet the requirements of the European Water Framework Directive.     

A novel route for the synthesis of processable conducting poly(m-aminophenol)

Polymerization of m-aminophenol (mAP) in aqueous NaOH solution was done chemically by using ammonium persulfate (APS) as an oxidative initiator. The product poly(m-aminophenol) (PmAP) was found to be highly soluble in aqueous sodium hydroxide, dimethyl sulfoxide (DMSO) and N,N-dimethyl formamide (DMF). From the intrinsic viscosity measurement, the optimum condition for the polymerization was established with 0.6 M NaOH medium with the ratio of monomer to oxidant as 1:1.5 (mol:mol). The polymer was characterized by FTIR and ¹H NMR spectroscopy, elemental (CHNS) and thermogravimetric (TGA) analyses. From the spectroscopic analysis the structure of the polymer was found to resemble that of hydroxy polyaniline as the polymer contains free –OH groups attached to o/m position in the phenyl ring. The elemental analysis of the polymer also confirmed the same. From TGA study, the polymer was found to be thermally stable. A freestanding film of poly(m-aminophenol) was cast in DMSO solution followed by solvent removal and drying of the film at 100 °C for 7–8 h in an oven. A dc conductivity of 4.8 × 10⁻⁴ S cm⁻¹ was obtained for the synthesized polymer film after doping with H₂SO₄ solution.     

Failure Analysis of a Dissolved Air Flotation Treatment Plant in a Dairy Industry

Environmental pollution in Nigeria presents an urgent need to assess wastewater treatment facilities in various industries. This article presents an assessment of dissolved air flotation (DAF) operation in a dairy industry. The industry was visited, wastewater treatment facilities were assessed (based only on efficacy to remove selected environmental health-related pollutants) and measurements of essential design and characterization parameters were taken. The study revealed that the averages of flow rate, biochemical oxygen demand at 5 days (BOD₅), chemical oxygen demand (COD), suspended solids (SS) and total solids (TS) of the influent wastewater into the plant (DAF) were 3.45 L/s, 1652.37, 3304.67, 2333.82, and 4396.10 mg/L compared to effluent quality of 560.37, 1127.33, 172.33, and 1866.67 mg/L for BOD₅, COD, SS, and TS, respectively. The pH of the wastewater is being adjusted by addition of lime before the effluent equalization tank and individual efficacies of the system were 66.09, 65.89, 65.89, 57.54, 8.68, and 94.49% for BOD₅, COD, SS, TS, DS, and total nitrogen, respectively, with overall efficacy of 38.10%. It was concluded that failure (lower overall efficacy) of the system can be attributed to setting of lime in the oversized equalization tank (50 m³ instead of 16.82 m³ per 8 h shift), the lack of application of standardized engineering code and practices (provision of underground tank in the process, lack of complete coagulation processes, coagulation and flocculation units), lack of adequate aeration unit and lack of reliable systems for automatically adjusting dosage of coagulant and flocculant. Although, DAF unit is the centerpiece of a DAF-based system design, there are several other supporting systems important to optimal DAF operation. These observations, coupled with the analysis in this report, demonstrate that the facilities necessary to minimize continuous environmental pollution are lacking. Pollution will become an increasing problem unless pollution preventing codes and standards are developed; incorporated into government regulations and the regulations are enforced.     

Studies on biodegradation of vegetable-based fat liquor-containing wastewater from tanneries

Fat liquoring, a post-tanning operation is carried out on tanned leather using oils, fats, or greases in emulsion form to make soft leathers and to improve the physical characteristics of the finished products during leather manufacturing. Around 10–15 % of un-exhausted fat liquor is discharged in the process water as wastewater. The major components of vegetable fat liquor are triacylglycerols, which primarily consist of glycerol molecules esterified with long chain fatty acids. The presence of fats, grease, and oils not only causes choking of wastewater conveyance mains but also interferes with the oxygen-transfer efficiency in aerobic treatment process. The aim of the present study is to assess the rate of biodegradability of vegetable-based fat liquor-containing wastewater generated from tanneries for various food to microbial (f/m) ratio, i.e., 0.35, 0.25, and 0.15 g biochemical oxygen demand (BOD₅)/g volatile suspended solids (VSSs) day. The f/m ratio and reaction time were investigated in detail in aerobic batch reactor to arrive at the optimum ratio needed for biodegradation of vegetable fat liquor. From the aerobic biodegradation studies, it was established that at an f/m ratio of 0.15 and a reaction time of 24 h, BOD₅ and chemical oxygen demand removals were 97.24 and 89.58 %, respectively. It was evident from Fourier transform infrared spectrometry and electrospray ionization–mass spectroscopy analysis that the triglycerides present in vegetable fat liquor were degraded effectively.     

Sustainable treatment of wastewaters resulted in the textile dyeing industry

Adsorption on fly-ash-based substrates is discussed as a possible alternative to the industrial processes used for the treatment of wastewaters resulted in the dyeing industry. Three samples, containing four dyes and one conditioner, were collected from the dyeing and rinsing baths in a textile company. Adsorption on fly ash was comparatively discussed with adsorption and photocatalysis, both on fly ash and a mixed suspension with TiO₂. The fly-ash crystalline substrates are characterized by X-ray diffraction (XRD) and morphology studies were done using atomic force microscopy. The wastewater, before and after treatment is characterized by quality indicators (pH, TDS, BOD₅, COD, TOC, color, and total chromium content). The studies allow to calculate the efficiency of the dyes removal process and the kinetic parameters, for the pseudo-second order mechanism. The results show that, in designing an industrial wastewater treatment process, the results obtained in the investigations on single-dye solutions must be completed with data specifically obtained on industrial wastewaters. The data also support the assumption of competitive adsorption, between the initial components and between these and the possible by-products resulted after photocatalysis.     

Sorption of Pb(II), Cr(III), Cu(II), As(III) to peat, and utilization of the sorption properties in industrial waste landfill hydraulic barrier layers

In this study, removal of suspended solids (SS) and turbidity from marble processing wastewaters by electrocoagulation (EC) process were investigated by using aluminium (Al) and iron (Fe) electrodes which were run in serial and parallel connection systems. To remove these pollutants from the marble processing wastewater, an EC reactor including monopolar electrodes (Al/Fe) in parallel and serial connection system, was utilized. Optimization of differential operation parameters such as pH, current density, and electrolysis time on SS and turbidity removal were determined in this way. EC process with monopolar Al electrodes in parallel and serial connections carried out at the optimum conditions where the pH value was 9, current density was approximately 15 A/m², and electrolysis time was 2 min resulted in 100% SS removal. Removal efficiencies of EC process for SS with monopolar Fe electrodes in parallel and serial connection were found to be 99.86% and 99.94%, respectively. Optimum parameters for monopolar Fe electrodes in both of the connection types were found to be for pH value as 8, for electrolysis time as 2 min. The optimum current density value for Fe electrodes used in serial and parallel connections was also obtained at 10 and 20 A/m², respectively. Based on the results obtained, it was found that EC process running with each type of the electrodes and the connections was highly effective for the removal of SS and turbidity from marble processing wastewaters, and that operating costs with monopolar Al electrodes in parallel connection were the cheapest than that of the serial connection and all the configurations for Fe electrode.     

Real-time control of oxic phase using pH (mV)-time profile in swine wastewater treatment

The feasibility of real-time control of the oxic phase using the pH (mV)-time profile in a sequencing batch reactor for swine wastewater treatment was evaluated, and the characteristics of the novel real-time control strategies were analyzed in two different concentrated wastewaters. The nitrogen break point (NBP) on the moving slope change (MSC) of the pH (mV) was designated as a real-time control point, and a pilot-scale sequencing batch reactor (18 m³) was designed to fulfill the objectives of the study. Successful real-time control using the developed control strategy was achieved despite the large variations in the influent strength and the loading rate per cycle. Indeed, complete and consistent removal of NH₄-N (100% removal) was achieved. There was a strong positive correlation (r² = 0.9789) between the loading rate and soluble total organic carbon (TOCs) removal, and a loading rate of 100 g/m³/cycle was found to be optimum for TOCs removal. Experimental data showed that the real-time control strategy using the MSC of the pH (mV)-time profile could be utilized successfully for the removal of nitrogen from swine wastewater. Furthermore, the pH (mV) was a more reliable real-time control parameter than the oxidation–reduction potential (ORP) for the control of the oxic phase. However, the nitrate knee point (NKP) appeared more consistently upon the completion of denitrification on the ORP-time profile than on the pH (mV)-time profile.     

The bio-activation of pozzolanic activity of circulating fluidized-bed fly ash by Paenibacilllus mucilaginosus

The present investigation reports an eco-friendly biotechnology applying Paenibacilllus mucilaginosus (P.m), a silicate solubilizing bacteria, to activate pozzolanic activity of CFA. The results show SiO₂ and Al₂O₃ dissolution rate of CFA treated by P.m and its Ca²⁺ absorption capacity in saturated Ca(OH)₂ solutions are increased compared to raw CFA indicating that pozzolanic reactivity of CFA is improved by P.m. One reason is destruction of the anhydrite coating layer of CFA particles surface through P.m erosion. Another reason is promotion of SiO₂ dissolution caused by deformation and destruction of Si-O-Si (Al) bonds by P.m. Carbonic anhydrase activity of P.m is one of the main factors involved in dissolution of SiO₂, which also induces CaCO₃ mineralization. The hardening characteristics and hydration products of CFA-15% lime system with different content of P.m further confirm the effects of P.m on pozzolanic activity of CFA. 40% P.m incorporation is conducive to promote CFA hydration, ettringite earlier formation and bio-mineralization, thereby improving the mechanical properties of hardened mortar. Incorporation of 40% P.m in cement blended with CFA results in that CFA content is increased by 5–20% and the 28d strength improved by 11.5–23.9 MPa. This is the first report of microbial activation of CFA pozzolanic activity.     

Biodegradability enhancement of purified terephthalic acid wastewater by coagulation-flocculation process as pretreatment

In this work, the coagulation-flocculation process was used as pretreatment for purified terephthalic acid (PTA) wastewater with the objective of improving its overall biodegradability. PTA production generates wastewaters with toxicants p-xylene [1,4-dimethyl-benzene (C8H10)], a major raw material used in the production process, along with some of the intermediates, viz., p-toluic acid, benzoic acid, 4-carboxybenzaldehyde, phthalic acid and terephthalic acid. These compounds affect the bio-oxidation process of wastewater treatment; hence removal of these constituents is necessary, prior to conventional aerobic treatment. This paper addresses the application of coagulation-flocculation process using chemical coagulants, viz., aluminium sulphate (alum), polyaluminium chloride (PAC), ferrous sulphate and ferric chloride in combination with anionic polyelectrolyte. Polyaluminium chloride (PAC) in conjunction with lime and polyelectrolyte removed about 63.1% chemical oxygen demand (COD) and 45.2% biochemical oxygen demand (BOD) from PTA wastewater. Coagulation-flocculation process coupled with aerobic bio-oxidation treatment of PTA wastewater achieved, COD & BOD removals of 97.4% and 99.4%, respectively. The biodegradability enhancement evaluated in terms of the BOD5/COD ratio, increased from 0.45 to 0.67 at the optimum conditions. The results obtained from these studies indicate that the coagulation-flocculation process could be a suitable pretreatment method in reducing toxicity of PTA wastewater whilst enhancing biodegradability for aerobic biological treatment scheme.     

Adsorption of organic pollutants from coking and papermaking wastewaters by bottom ash

Bottom ash, a power plant waste, was used to remove the organic pollutants in coking wastewater and papermaking wastewater. Particular attention was paid on the effect of bottom ash particle size and dosage on the removal of chemical oxygen demand (COD). UV-vis spectra, fluorescence excitation-emission matrix (FEEM) spectra, Fourier transform infrared (FTIR) spectra, and scanning electron microscopic (SEM) photographs were investigated to characterize the wastewaters and bottom ash. The results show that the COD removal efficiencies increase with decreasing particle sizes of bottom ash, and the COD removal efficiency for coking wastewater is much higher than that for papermaking wastewater due to its high percentage of particle organic carbon (POC). Different trends of COD removal efficiency with bottom ash dosage are also observed for coking and papermaking wastewaters because of their various POC concentrations. Significant variations are observed in the FEEM spectra of wastewaters after treatment by bottom ash. New excitation-emission peaks are found in FEEM spectra, and the fluorescence intensities of the peaks decrease. A new transmittance band in the region of 1400-1420 cm(-1) is observed in FTIR spectra of bottom ash after adsorption. The SEM photographs reveal that the surface of bottom ash particles varies evidently after adsorption.     

Effect of Reactivity of Quick Lime on the Properties of Hydrated Lime Sorbent for SO2 Removal

The hydration of quick lime and the sulfation of hydrated lime were carried out for verification of relationship between the reactivity of quick lime and the properties of hydrated lime as a sorbent. The effect of reactivity of quick lime was investigated with the change of calcination temperature and time. Results obtained showed that the temperature rise during the hydration of quick limes varied from 31 to 69°C with the variation of calcination temperature and time. The specific surface area and the sulfation ability of hydrated lime prepared by hydration of quick lime showed a proportional relationship with the reactivity of quick lime. The hydrated lime which was prepared by hydration of quick lime calcined at 1100°C had the highest reactivity and showed 41.53 m²/g of the speci¯c surface area, 0.16 cm³/g of the pore volume and 87% of the removal effciency for SO₂ removal.     

Ecotoxicity tests in the environmental analysis of wastewater treatment plants: case study in Portugal

A global evaluation of wastewaters should include ecotoxicological tests to complement the chemical characterization, with advantages especially in the case of complex wastewaters. A European project developed in Tranc?o River Basin (Portugal), integrated the ecotoxicological and physicochemical studies of wastewater samples from two municipal sewer networks and respective wastewater treatment plants. Wastewater samples were analysed for physicochemical parameters, ecotoxicological acute and chronic tests performed and the potential for endocrine disruption evaluated. Organic load parameters and total suspended solids showed significant correlations with Microtox and ThamnoToxKit test results. Data analysis showed that treated treatment plant effluent samples are associated with less organic contamination and less toxicity in ThamnoToxKit test. Chronic toxicity test and endocrine disruption assay of treatment plant effluent samples indicated that, in a long term, potential population effects could arise in the receiving waters. A test battery to monitor this type of wastewaters is proposed, including tests with a bacterium, an alga and a crustacean. In a screening phase the most sensitive test, Microtox, can be used. The use of an ecotoxicological approach can have added value to hazard and risk assessment of discharges to the receiving waters and can contribute to the environmental management of the treatment plant.     

Sorption of phenolics and carboxylic acids on polybenzimidazole

The sorption of phenolics and carboxylic acids on the new ion-exchange resin polybenzimidazole (PBI) has been measured using aqueous solutions of the sorbates and compared with the sorption on another weak-base resin, poly(4-vinyl pyridine) (PVP). The phenolics used include phenol, p-cresol, p-chlorophenol and m-aminophenol, while the carboxylic acids chosen are formic, acetic, propionic and butyric acids. For aminophenol and phenol, the equilibrium sorption capacities of PBI and PVP are comparable, while for more acidic p-cresol and p-chlorophenol, PVP has significantly higher equilibrium sorption than PBI. On the other hand, for carboxylic acids at low concentrations, PBI exhibits considerably higher sorption capacity than PVP, the difference being more pronounced for acids with smaller acidity. At low concentrations, formic acid has several-fold higher sorption than phenol on PBI, which thus offers a simple method for separation of formic acid from phenol in dilute solutions. PBI has fast sorption kinetics for both phenols and carboxylic acids and a fast rate of stripping and regeneration with dilute NaOH, being much superior to PVP in both these respects.     

Scale up of 2,4-dichlorophenol removal from aqueous solutions using Brassica napus hairy roots

Chlorophenols are harmful pollutants, frequently found in the effluents of several industries. For this reason, many environmental friendly technologies are being explored for their removal from industrial wastewaters. The aim of the present work was to study the scale up of 2,4-dichlorophenol (2,4-DCP) removal from synthetic wastewater, using Brassica napus hairy roots and H₂O₂ in a discontinuous stirred tank reactor. We have analyzed some operational conditions, because the scale up of such process was poorly studied. High removal efficiencies were obtained (98%) in a short time (30 min). When roots were re-used for six consecutive cycles, 2,4-DCP removal efficiency decreased from 98 to 86%, in the last cycle. After the removal process, the solutions obtained from the reactor were assessed for their toxicity using an acute test with Lactuca sativa L. seeds. Results suggested that the treated solution was less toxic than the parent solution, because neither inhibition of lettuce germination nor effects in root and hypocotyl lengths were observed. Therefore, we provide evidence that Brassica napus hairy roots could be effectively used to detoxify solutions containing 2,4-DCP and they have considerable potential for a large scale removal of this pollutant. Thus, this study could help to design a method for continuous and safe treatment of effluents containing chlorophenols.     

Removal of nitroimidazole antibiotics from aqueous solution by adsorption/bioadsorption on activated carbon

The objective of the present study was to analyse the behaviour of activated carbon with different chemical and textural properties in nitroimidazole adsorption, also assessing the combined use of microorganisms and activated carbon in the removal of these compounds from waters and the influence of the chemical nature of the solution (pH and ionic strength) on the adsorption process. Results indicate that the adsorption of nitroimidazoles is largely determined by activated carbon chemical properties. Application of the Langmuir equation to the adsorption isotherms showed an elevated adsorption capacity (X_m = 1.04–2.04 mmol/g) for all contaminants studied. Solution pH and electrolyte concentration did not have a major effect on the adsorption of these compounds on activated carbon, confirming that the principal interactions involved in the adsorption of these compounds are non-electrostatic. Nitroimidazoles are not degraded by microorganisms used in the biological stage of a wastewater treatment plant. However, the presence of microorganisms during nitroimidazole adsorption increased their adsorption on the activated carbon, although it weakened interactions between the adsorbate and carbon surface. In dynamic regime, the adsorptive capacity of activated carbon was markedly higher in surface water and groundwater than in urban wastewaters.     

Integrated Sono-Fenton ultrafiltration process for 4-chlorophenol removal from aqueous effluents: assessment of operational parameters (Part 1)

Advanced oxidation processes (AOPs) and membrane separation processes are successfully used in the final stages of wastewater treatment for recycling and reuse purposes. This research proposes a new two stage process including in the first step a homogeneous Sono-Fenton process (as an AOP), coupled with ultrafiltration (UF), as a cleaner and safer alternative for advanced wastewater treatment, designed specially to enhance the removal of priority organic pollutants which are difficult to eliminate by means of conventional treatments. The aim of this study is to analyze experimentally the performances of an integrated ultrasonication-UF process for the removal of 4-chlorophenol (4CP) (as a model-pollutant for priority organic compounds from wastewaters), both from the removal efficiency (expressed as phenolic concentration and chemical oxygen demand reduction) and the energy consumption point of view. The most important factors with influence on both stages of the proposed process, such as acoustic amplitude, power density, and operating mode for the Sono-Fenton process and pressure, time, operating mode, and cleaning operations for the UF stage, were assessed in this paper (Part 1). The experimental results indicate that the process can be applied for such aqueous effluents, in laboratory scale equipments and represent the basis for modeling the process steps and scale-up of different process arrangements (Cailean et al. (2014): “Integrated Sono-Fenton UF Process for 4CP Removal from Aqueous Effluents: Process Modeling and Simulation (Part 2)”), with the purpose to analyze and control such a process, under various conditions and to understand better its advantages and disadvantages.     

Heavy metal removal from simulated wastewater using electrochemical technology: optimization of copper electrodeposition in a membraneless fluidized bed electrode

Heavy metal removal from industrial wastewaters has been intensively studied, since it is well known that they can cause severe problems to human health and aquatic life, even at very low concentrations. In this work, it was demonstrated that electrodeposition in fluidized bed electrode (FBE) can be efficiently employed to remove metal ions from solution, avoid contamination, and recover the metal. Copper electrodeposition from diluted solutions was efficiently performed using a membraneless FBE. The average current efficiency (ACE), average energy consumption (AEC), and space–time yield (AY) was optimized taking into account the operational and process variables. It was noted that for all response variables studied, the raise of supporting electrolyte concentration (C _s) contributed to improvements in the process. The operational conditions current (I) and bed expansion (E) determined the values of CE, Y, and EC under activated control, but the initial copper concentration (C ₀) determined how long the electrodeposition process will work under activated or mass transfer control, thus affecting the average values of CE, Y, and EC. Considering C ₀ of 500 mg L^?1, copper can be optimally recovered with ACE >60 %, AY >38 kg h^?1 m^?3, and AEC <4.0 kWh kg^?1 by applying the lowest I and the highest levels of E and C _s. It was concluded that the electrochemical technology using a membraneless FBE reactor is economically competitive and be applied for the treatment of wastewaters contaminated with copper or other metals.     

Separative recovery with lime of phosphate and fluoride from an acidic effluent containing H3PO4, HF and/or H2SiF6

Fluoride content and flow-rate of fertilizer plant wastewater from phosphoric acid and/or triple superphosphate (TSP) production lead to the discharge of several thousand tons of fluoride (F⁻) per year and even more for phosphate (PO₄³⁻). Since sustainability is an important environmental concern, the removal methods should allow phosphorus and fluoride to be recycled as a sustainable products for use as raw materials either in agricultural or industrial applications. In the present work, separative recovery with lime of these two target species was investigated. A preliminary speciation study, carried out on the crude effluent, showed that two forms of fluoride: HF and H₂SiF₆ are present in a highly acidic medium (pH  2). Evidence that fluoride is present under both free (HF) and combined (H₂SiF₆) forms, in the phosphate-containing effluent, was provided by comparing potentiometric titration curves of a crude wastewater sample and synthetic acid mixtures containing H₃PO₄, HF and H₂SiF₆. In a second step synthetic effluent containing mixtures of the following acids: HF, H₂SiF₆ and H₃PO₄, were treated with lime. The behaviour of these compounds under lime treatment was analysed. The data showed that fluoride has a beneficial effect on phosphate removal. Moreover, by acting on the precipitation pH, a “selective” recovery of fluoride and phosphate ions was possible either from phosphoric acid/hydrofluoric acid or phosphoric acid/hexafluorosilicic acid mixtures. Indeed, the first stage of the separative recovery, led to a fluoride removal efficiency of 97–98% from phosphoric acid/hydrofluoric acid mixture. It was of 93–95% from phosphoric acid/hexafluorosilicic acid mixture. During the second stage, the phosphate precipitation reached 99.8% from both acidic mixtures whereas it did not exceed 82% from a solution containing H₃PO₄ alone. The XRD and IR analyses showed that during lime treatment, a H₂SiF₆ hydrolysis occurred, instead of CaSiF₆ solid formation, leading to CaF₂ precipitate. Calcium fluoride and calcium phosphate based-by-products resulting from the two-step treatment process can be used as raw materials in several industrial sectors, such as ceramic and phosphate fertilizer industries.     

Aqueous two-phase systems: a new approach for the determination of p-aminophenol

A new method has been developed for the spectrophotometric determination of p-aminophenol (PAP) in water, paracetamol formulations and human urine samples with a recovery rate between 94.9 and 101%. This method exploits an aqueous two-phase system (ATPS) liquid-liquid extraction technique with the reaction of PAP, sodium nitroprusside and hydroxylamine hydrochloride in pH 12.0, which produces the [Fe₂(CN)₁₀]¹⁰⁻ anion complex that spontaneously concentrates in the top phase of the ATPS (K[Fe₂(CN)₁₀]¹⁰⁻=97.7). The ATPS does not require an organic solvent, which is a safer and cleaner liquid-liquid extraction technique for the determination of PAP. The linear range of detection was from 5.00 to 500 μg kg⁻¹ (R ≥ 0.9990; n = 8) with a coefficient of variation of 2.11% (n = 5). The method exhibited a detection limit of 2.40 μg kg⁻¹ and a quantification limit of 8.00 μg kg⁻¹. The ATPS method showed a recovery that ranged between 96.4 and 103% for the determination of PAP in natural water and wastewater samples, which was in excellent agreement with the results of the standard 4-aminoantipyrine method that was performed on the same samples.     

Biological treatment of wastewaters from a dye manufacturing company using a trickling filter

The aim of this work was to assess the effectiveness of a biological trickling filter for the treatment of wastewaters produced by a company manufacturing organic dyes and varnishes. The combined wastewater effluent was fed to a pilot-scale trickling filter in two feeding modes, continuously and as a sequencing batch reactor (SBR). The biodegradability of the diluted wastewaters that were subjected to physicochemical treatment, using Ca(OH)(2) and FeSO(4), was initially studied using a continuously operated trickling filter. The system efficiency ranged up to 60-70% for a hydraulic loading of 1.1 m(3)/m(2)day and up to 80-85% for a hydraulic loading 0.6 m(3)/m(2)day. A stable chemical oxygen demand (COD) removal efficiency of 60-70% was achieved even in the case of undiluted wastewater at a hydraulic loading of 1.1 m(3)/m(2)day. The effectiveness of biological treatment of a mixture of the company's main wastewater streams was also examined. The microorganisms developed in the trickling filter were able to efficiently remove COD levels up to 36,000 mg/L, under aerobic conditions at pH values between 5.5 and 8.0. Depending on the operating conditions of the system, about 30-60% of the total COD removal was attributed to air stripping caused by the air supply at the bottom of the filter, whereas the rest of the COD was clearly removed through biological action. The proposed biological treatment process based on a trickling filter, which was operated either continuously or even better in an SBR mode, appears as a promising pretreatment step for coping with dye manufacturing wastewaters in terms of removing a significant portion of the organic content.