Optimisation of process parameters for bioreduction of azo dyes using Bacillus firmus under batch anaerobic condition

A new dye decolourising bacterial strain was isolated from textile wastewater and identified as Bacillus firmus. The study indicated that the bacterium could efficiently decolourise different azo dyes under static culture conditions. Characterisation of the efficiency of azo dye reduction by this isolate using both spectral and HPLC analysis was found to be a function of process parameters which include dye concentration, culture broth pH, incubation temperature, aeration as well as nitrogen source. For decolourisation, the optimal pH and temperature were 7–8 and 20–35°C respectively, while remarkable dye degradation was obtained within 18 h for dye concentrations below 100 mg L^?1. With the addition of yeast extract and under optimal conditions, dye reduction was enhanced and complete colour removal was achieved within 12 h. Colour removal was shown to be due to biodegradation rather than adsorption of dyes on bacterial cells. This study confirms the ability of the new dye‐degrading strain, Bacillus firmus, to decolourise and degrade different azo dyes and highlights its high biotechnology potential for the eco‐friendly treatment of textile wastewater when optimal conditions are applied.     

Non‐steroidal anti‐inflammatory pharmaceutical wastewater treatment using a two‐chambered microbial fuel cell

The two‐chambered microbial fuel cell (MFC) was designed and used for studying the efficiency of the real wastewater treatment from a non‐steroidal anti‐inflammatory pharmaceutical plant as well as from synthetic wastewater containing diclofenac sodium (DS). The removal of the contaminants was expressed regarding chemical oxygen demand (COD) removal, as measured by spectrophotometry experiments. Moreover, the effect of two different types of the cathode on current characteristics and COD removal was investigated. This research showed that the Pt‐coated Ti cathode could lead to higher efficiency of both power density and COD removal. In this case, the results indicated that the maximum power density (P_max) was 20.5 and 6.5 W/m³ and the maximum COD removal was 93 and 78% for MFCs using real and synthetic wastewater, respectively.     

Removal and accumulation of Cu, Ni and Zn in horizontal subsurface flow constructed wetlands: Contribution of vegetation and filling medium

This study investigated the accumulation and removal of Cu, Ni and Zn in two horizontal subsurface flow constructed wetlands for domestic wastewater treatment, which differ by shape, presence of macrophytes and water depth. Between March and December 2007, the three metals were measured in the influent and effluents of the two systems. Average percentage removal rates were extremely low for Cu (3% and 9% in the two beds) and higher for Zn and Ni (between 25 and 35%). Under higher Zn influent concentrations, it was found to be between 78-87%, which is in agreement with other literature data.During the peak standing crop season (August), biomasses of the different parts of Phragmites australis (stems, leaves and flowers, roots and rhizomes) were analysed in terms of weight and heavy metal concentration in order to assess heavy metal distribution among the tissues. It was found that the plants contribute to total heavy metal removal to a lesser extent than the filling medium. Aboveground tissues remove 34% of Cu, 1.8% of Ni and 6.2% of Zn % and, once harvested, their disposal does not appear to pose a problem for the environment. If heavy metals are present at high concentrations in the horizontal subsurface flow bed influent, over time, their accumulation in the filling medium could necessitate special care in the bed's management to avoid release into the surrounding environment.     

Exploring bioaugmentation strategies for azo dye CI Reactive Violet 5 decolourization using bacterial mixture: dye response surface methodology

The use of response surface methodology based on statistical design of experiments is becoming increasingly widespread in several sciences such as analytical and environmental chemistry. In the present study, the decolourization and the degradation efficiency of CI Reactive Violet 5 (CIRV5) was studied using a novel bacterial consortium. CIRV5 (1000 p.p.m.) biodegradation was investigated under shaking condition in mineral salt medium solution (MSM) at a 7.5 pH and a 25°C temperature. The degradation pathways were also predicted, using UV‐visible spectroscopy analysis. Under optimal conditions, the bacterial consortium was able to decolourize the dye completely (>99%) within 8 h. The colour and chemical oxygen demand (COD) removal were 99.29 and 94.93%, respectively. Polymerase chain reaction (PCR) technique was utilized to detect the adhesin genes ‘icaA’ and ‘icaD.’ Our results showed that Staphylococcus aureus had a high decolourization capacity. Phytotoxicity study using Triticum turgidum ssp durum showed the no toxicity of the produced products.     

Bioleaching of heavy metals from wastewater sludge by ferrous iron oxidizing bacteria

Experiments on bacterial leaching of heavy metals from aerobically stabilized surplus activated sludge at the Bortnichi aeration plant in Kiev have been conducted with addition of FeSO₄ ? 7H₂O as a stimulant of iron-oxidizing bacteria. The mechanism of heavy metal leaching involving the ferrous iron oxidation by bacteria with subsequent formation of Fe(OH)₃ was confirmed. This process is accompanied by the reduction of pH level of wastewater sludge that results in leaching of heavy metals.     

On‐site wastewater treatment using reactive filter media

The aim of this study is to reduce the phosphate concentration in treated wastewater using a small amount of the reactive filter media, Filtralite P. Biologically treated wastewater was passed through a filter with 215 g of Filtralite P. In the laboratory, the phosphate removal efficiency was 51% at a flow speed of 0.87 m/h. Under real conditions, in an experimental stand filled with 0.5 m³ of Filtralite P, the phosphate removal efficiency was 85% and the removal efficiency of total suspended solids was 57% after a 5‐month period. The residual phosphate concentration in the filtrate from the experimental stand was 1 mg/L of PO₄‐P after the 5‐month period. The experimental filtration plant was buried in the ground, and it did not freeze and worked well under winter conditions. The results of this study can be useful in the design and development of tertiary wastewater treatment plants in view of their sustainability potential.     

Characterisation of the impact of coagulation and anaerobic bio-treatment on the removal of chromophores from molasses wastewater

The performance of a coagulation sequence using aluminium chlorohydrate (ACH) and a low MW polydiallyldimethylammonium chloride (polyDADMAC), and ferric chloride, for decolourising a high-strength industrial molasses wastewater was compared at bench scale. At their optimum dosages, ACH/polyDADMAC gave higher colour removal than FeCl₃ (45% cf. 28%), whereas COD reduction was similar (∼30%), indicating preferential removal of melanoidins (a major contributor to the colour) by ACH/polyDADMAC. Size exclusion chromatography and fluorescence excitation-emission matrix spectrometry suggested that chromophoric Fe-organic complexes were formed during FeCl₃ treatment of the molasses wastewater, which appeared to compromise decolourisation efficiency. Anaerobic bio-treatment of the wastewater enhanced the coagulation efficiency markedly, with FeCl₃ achieving 94% colour and 96% COD removal, while ACH/polyDADMAC gave 70% and 56% removal, respectively. The improved decolourisation was attributed to the decrease in low MW organics (<500 Da) and biopolymers by the biological treatment, leading to reduced competition with melanoidins for interaction with coagulant/flocculant. For both the wastewater and the biologically treated wastewater, ACH/polyDADMAC treatment gave flocs with markedly better settling properties compared with FeCl₃.     

化学生物絮凝工艺去除城市污水中重金属的研究

采用化学生物絮凝工艺处理上海市的低浓度城市污水，考察了对污水中重金属的去除效果，探讨了化学生物絮凝工艺反应的实质。平行对比试验结果显示：化学生物絮凝工艺中存在着化学和生物的协同作用，是一种深度集成的污水强化一级处理工艺。在相同的加药量下，该工艺在减少絮凝产物中铝含量的同时，可去除部分有害重金属元素且效果优于化学强化一级处理工艺。对铝的去除率比单一的化学絮凝工艺提高了106％；在重金属元素去除方面，对铬和锰的去除率提高了10％～15％，对镍元素的吸附量也有一定的提高。但是该工艺在处理高浓度污水时，处理效果会受到重金属浓度的制约。     

The fate of heavy metals in wastewater stabilization ponds

The distribution of toxic heavy metals was studied throughout the process of treatment of domestic wastewater by stabilization ponds. The concentrations and distribution of free and bound zinc, cadmium, lead and copper through the various stages of a treatment plant were analyzed by Anodic Stripping Voltammetry (ASV). Only a slight decrease in the total metals concentration was observed during the various stages of the wastewater treatment plant. However, the distribution among dissolved (free and chelated) and particulate fractions did change towards solubilization of most of the particulate fraction. Within the soluble fraction a significant decrease in the free cations occurred due to a proteinaceous chelating agent(s) released by the microbial population in the ponds. A similar phenomenon was found in simulated laboratory experiments which were carried out with a Chlorella strain isolated from the stabilization ponds.     

Equilibrium chemical modelling of heavy metals in activated sludge

A chemical speciation distribution model of heavy metals, previously developed by Nelson et al. (J. Wat. Pollut. Control Fed. 53, 1323, 1981), was applied to cadmium in activated sludge from a full-scale wastewater treatment plant. In the model, cadmium adsorption to bacterial solids was quantified by the determination of conditional formation constants based on TOC. Adsorption of cadmium strongly pH-dependent. Soluble cadmium speciation was dominated by the free cadmium ion below pH 6, by cadmium-organic ligand complexation at pH 6 and 7 and by inorganic species at pH 8 and 9. Cadmium adsorbed by bacterial solids increased greatly with pH from near 30% at pH 4 to near 90% at pH 9. Cadmium speciation and distribution was also modelled in an indifferent electrolyte suspension of bacterial solids and in activated sludge using adsorption constants from the indifferent electrolyte medium.     

Pilot scale study on the ex situ electrokinetic removal of heavy metals from municipal wastewater sludges

In order to remove toxic heavy metals from municipal wastewater sludges, the ex situ electrokinetic technique was studied at pilot scale. This study focused on the feasibility of the electrokinetic removal of heavy metals from sludge and the effectiveness of this technique on the variations of abiotic (physicochemical) and biotic (intracellular and extracellular) speciations of heavy metals using several analytical methods. Even though the sludge used was taken from a municipal wastewater treatment plant, the sludge contained relatively high concentrations of target metal contaminants (Cd = 6.8 mg/kg, Cr = 115.6 mg/kg, Cu = 338.7 mg/kg, and Pb = 62.8 mg/kg). The removal efficiencies of heavy metals were significantly dependent on their speciations in the sludge matrices. The electrokinetic removal efficiencies of abiotic heavy metals exceeded 70% for the mobile and weakly bound fractions, such as, the exchangeable and carbonate fractions and were lower than 35% for the strongly bound fractions, such as, the organic/sulfide and residual fractions. In the case of the biotic heavy metals, the removal efficiencies of the extracellular fractions were slightly higher than those of the intracellular fractions.     

Role of physicochemical factors on bacterial attachment in textile fibrous media

One of the possible approaches to remove the Pseudomonas bacteria from surface water by using textile fibrous media has been studied in this article. The attachment of Pseudomonas bacteria inside textile fibrous media was studied using laboratory column experiment which led to the understanding of the physiochemical interaction between textile surface and the bacteria. Colloid‐filtration theory was used to investigate the effects of various physicochemical factors like pH, ionic strength (M) and mass (g) of the porous media on bacterial attachment. The quantitative assessment of bacterial attachment on the textile surface media was carried out by determining the collision efficiency. The physicochemical factors mentioned above were optimized to obtain maximum collision efficiency so as to achieve maximum bacterial attachment on the textile media surface. Bacterial attachment is found to be directly related to the ionic strength of the suspending medium and the mass of the textile media. A significant improvement in collision efficiency is observed when the ionic strength of the suspended medium is increased. Maximum collision efficiency is achieved at high level of ionic strength and medium level of pH with high level of mass of the textile media.     

Nitrogen removal in artificial wetlands

This report describes investigations which have demonstrated the exceptional utility of artificial wetlands for the removal of nitrate from secondary wastewater effluents at relatively high application rates. The artificial wetlands (14 in number) were plastic-lined excavations containing emergent vegetation growing in gravel. Without supplemental additions of carbon, total nitrogen removal efficiency was low ( 25%) in both vegetated and unvegetated beds. When methanol was added to supplement the carbon supply and stimulate bacterial denitrification, the removal efficiency was extremely high (95% removal of total nitrogen at a wastewater application rate of 16.8 cm day⁻¹). Since methanol is a relatively expensive form of carbon, we tested the feasibility of using plant biomass, mulched and applied to the surface of marsh beds, as an alternate source of carbon. At a wastewater application rate of 8.4 cm day⁻¹, the mean total nitrogen removal efficiency for the mulch-amended beds was 86%. When the application rate was higher (16.8 cm day⁻¹) the mean total nitrogen removal efficiency was lower, 60% in the mulch-amended beds.By using plant biomass as a substitute for methanol, the energy savings for a treatment facility serving a small community (3785 m³ day⁻¹ or 1 mgd) would amount to the equivalent of 731 day⁻¹ of methanol. As the cost of fossil fuel increases, energy cost will become a predominant factor in the selection of small (0.5–5 mgd) wastewater treatment systems. However, in many cases where natural wetlands are either geographically unavailable or protected from wastewater discharge by environmental, legal, or aesthetic restraints, artificial wetlands offer a viable alternative for energy-effective treatment of municipal and agricultural wastewater effluents.     

Arsenic phytoremediation by Phragmites australis: green technology

The authors report arsenic phytoremediation by the common reed, Phragmites australis (P. australis). The plants for this study were collected from five sampling sites in the Chelpo contaminated area of Khorasan Province in Northeast Iran. P. australis was found to be a hyper‐accumulator plant. Because of the potential for this plant to be used as an agent to remove arsenic from a polluted environment, P. australis has a considerable enrichment factor. Thus, in the P. australis accumulation model following the order of root>rhizome>stem>leaves, the examination of P. australis for the phytoremediation process indicates that this species can cope with arsenic remediation from certain polluted soils.     

Heavy metal removal in anaerobic semi-continuous stirred tank reactors by a consortium of sulfate-reducing bacteria

Removal of heavy metals by an enriched consortium of sulfate-reducing bacteria (SRB) was evaluated through the abundance of SRB, sulfate reduction, sulfide production and heavy metal precipitation. Five parallel anaerobic semi-continuous stirred tank reactors (CSTR, V = 2 L) (referred as R1-R5) were fed with synthetic wastewater containing mixtures of Cu²⁺, Zn²⁺, Ni²⁺, and Cr⁶⁺ in the concentrations of 30, 60, 90, 120, and 150 mg L⁻¹ of each metal and operated with a hydraulic retention time of 20 days for 12 weeks. The loading rates of each metal in R1-R5 were 1.5, 3, 4.5, 6, and 7.5 mg L⁻¹ d⁻¹, respectively. The results showed that there was no inhibition of SRB growth and that heavy metal removal efficiencies of 94-100% for Cu²⁺, Zn²⁺, Ni²⁺, and Cr⁶⁺ were achieved in R1-R3 throughout the experiment and in R4 during the first 8 weeks. The toxic effect of heavy metals on the SRB consortium was revealed in R5, in which no SRB could survive and almost no heavy metal precipitation was detected after four weeks of operation.     

Precipitation of heavy metals from wastewater using simulated flue gas: Sequent additions of fly ash, lime and carbon dioxide

Lime is a preferred precipitant for the removal of heavy metals from industrial wastewater due to its relatively low cost. To reduce heavy metal concentration to an acceptable level for discharge, in this work, fly ash was added as a seed material to enhance lime precipitation and the suspension was exposed to CO₂ gas. The fly ash-lime-carbonation treatment increased the particle size of the precipitate and significantly improved sedimentation of sludge and the efficiency of heavy metal removal. The residual concentrations of chromium, copper, lead and zinc in effluents can be reduced to (mg L⁻¹) 0.08, 0.14, 0.03 and 0.45, respectively. Examination of the precipitates by XRD and thermal analysis techniques showed that calcium-heavy metal double hydroxides and carbonates were present. The precipitate agglomerated and hardened naturally, facilitating disposal without the need for additional solidification/stabilization measures prior to landfill. It is suggested that fly ash, lime and CO₂, captured directly from flue gas, may have potential as a method for wastewater treatment. This method could allow the ex-situ sequestration of CO₂, particularly where flue-gas derived CO₂ is available near wastewater treatment facilities.     

Improve effluent water quality at Abu‐Rawash wastewater treatment plant with the application of coagulants

This research investigated a process to improve the Abu‐Rawash WWTP effluent water quality with the application of aluminum chloride (AlCl₃); in turn, this improvement will lead to improve water quality at the El‐Rahawy drain and in the Rosetta branch of the Nile River. Sewage samples were collected from the effluent of the grit removal chamber. Jar tests were performed to estimate the coagulant dosage required to obtain acceptable treatment. To prove the efficiency of the AlCl₃ in wastewater treatment, a comparison was conducted between AlCl₃ and other common coagulants used in wastewater treatment which include ferrous sulfate (FeSO₄), ferric sulfate (Fe₂(SO₄)₃) and ferric chloride (FeCl₃). Results showed AlCl₃ was more cost‐effective and efficient in wastewater treatment than these three iron‐based coagulants. A paired‐sample t‐test was also performed to rank the performance of the various coagulants tested. The t‐test has also confirmed that the AlCl₃ has the highest performance over those coagulants.     

The risks from airborne asbestos in the urban environment

The objective of this full‐scale study is to determine the treatment performance of the activated sludge process for treating low strength municipal wastewater. The plant is located in Painesville, Ohio, and discharges its treated effluent into Grand River. The average plant wastewater flow was 3.43 MGD (million gallons per day). The plant performance was evaluated for a 12‐month period in 1989. The low strength municipal wastewater contained 104 mg/L TSS (total suspended solids), 105 mg/L BOD (biochemical oxygen demand), 17.76 mg/L TKN (total kjeldahl nitrogen), 9.66 mg/L NH₃‐N, and 3.90 mg/L P (phosphorus). The treatment performance after various degrees of treatment is as follows: primary treatment: 30% BOD and 54% TSS removal, secondary treatment: 97% BOD and 87% TSS removal, and tertiary treatment: 98% BOD and 98% TSS removal. The primary effluent contained 73 mg/L BOD and 48 mg/L TSS; the secondary effluent contained 3 mg/L BOD and 13 mg/L TSS; and the final effluent contained 2 mg/L BOD and 2 mg/L TSS. The effluent contained 0.22 mg/L NH₃‐N and 0.49 mg/L P, which were far below the US EPA standard of 10 mg/L BOD, 10 mg/L TSS, 1 mg/L NH₃‐N, and 1 mg/L P.     

Removal of phenolic compounds from raw industrial wastewater by Achromobacter sp. isolated from a hydrocarbon‐contaminated area

The discharge of raw industrial wastewaters, specifically coking wastewater, represents a severe environmental problem. In this work, a phenol‐degrading aerobic strain isolated from a hydrocarbon contaminated site, Achromobacter sp. C‐1, was tested for degrading raw coking wastewater to explore its potential for use in biological treatment. Initially, phenol degradation was reached after 24 h of inoculation in synthetic wastewater [600 mg/L of phenol]. The maximum specific degradation rate was 0.436 h^–1 found in the concentration 300 mg/L. In a raw industrial wastewater containing a mixture of phenols as carbon source [phenol 370 mg/L, m‐cresol 100 mg/L and o‐cresol 60 mg/L], 90% biodegradation of a mixture of phenols was achieved after 80 h of inoculation. Following the biodegradation process to remove the colour from the wastewater, polishing was performed by activated carbon adsorption, resulting in a clear wastewater (without colour and contaminants) ready for industrial reuse purposes. These results provided useful information about use of the phenol‐degrading bacteria for bioaugmentation in industrial wastewater treatment improving the quality of final wastewater. The quality of the resulting wastewater was confirmed by mass spectrometry analysis. This work shows the biodegradation process could be a cost‐effective and promising solution for the treatment and reuse of phenolic wastewater.      

Effect of plant species on water quality at the outlet of a sludge treatment wetland

Sludge treatment wetlands are mainly used to reduce the volume of activated sludge, and the pollutants at the outlet are generally returned to the wastewater treatment plant. However, in cases where sludges are produced far from treatment plants not only must the sludge be treated, but the discharge of pollutants into the surrounding environment must also be limited. The aim of this study was to evaluate the efficiency of different plant species in optimising pollutant removal in a decentralised sludge treatment wetland. In addition, a new system design was assessed, in which the wetland was not completely drained, and a saturated layer was created using an overflow. The experimental setup consisted of 16 mesocosms in total, planted with monocultures of Phragmites australis, Typha angustifolia and Scirpus fluviatilis, and unplanted controls, each in four replicates.The experiment was conducted during the third summer of operation after setup. The system was fed with highly concentrated fish farm sludge at a load of 30 kg of total solids m⁻² yr⁻¹. Results showed that such wetlands were highly efficient, with removal rates between 94% and 99% for most pollutants. Planted systems generally outperformed the unplanted control, with a significantly lower mass of pollutants at the outlet of the sludge treatment wetland planted with Phragmites, followed by those with Typha and then Scirpus. The distinct influence of plant species on pollution removal was explained by the sequestration of nitrogen and phosphorus in plant tissues and by the rhizosphere effect, which enhance the biodegradation of organic matter, allowed the nitrification process and created redox conditions favourable to the sorption of phosphorus. Filtration and evapotranspiration rates played a major role in limiting the discharge of pollutants, and the impact was enhanced by the fact that the sludge treatment wetland was not completely drained.