Inactivation Of Fecal Coliforms Research Articles

Evaluating the aeration efficiency of hydraulic flume on photo-oxidative disinfection of wastewater

Photosensitized oxidation has been considered to offer better disinfection mechanism under natural sunlight and the efficiency of its inactivation pathway depends on the concentration of dissolving oxygen, the solar irradiance, and the reactive nature of the liquid. This study aimed to evaluate the hydraulic mixer's aeration performance during photo-oxidation treatment. A hydraulic jump was created to aerate the sewage prior to its passage into a reactor, and the amount of dissolved oxygen generated was measured. The effect of mixing intensity on sunlight inactivation of faecal coliforms in a reactor was investigated for 60 min using velocity gradients of 520 s−1, 640 s−1, 720 s−1 and 960 s−1 produced under flow rates of 3 L min−1, 5 L min−1 and 7 L min−1 and 10 L min−1 respectively. The photo-oxidation kinetics of faecal coliform contained in settled and raw sewage samples were also studied under two dark control tests (static and dynamic tests) and a light test. The system achieved a 2.0–2.34 log reduction of faecal coliforms and dissolved oxygen was within the range of 1.9 mg L−1 - 3.0 mg L−1. In the dynamic control test, the inactivation rate constant of bacteria indicated a reduction of 1.11 log (92%) for settled sewage and 1.0 log (90%) for raw sewage. The coliform inactivation rate constant, due to the combined effect of turbulent mixing speed and dark inactivation rate constant, was 2.3 h−1, and the solar irradiance inactivation rate constant was 2.4 h−1. These results have demonstrated that induced aeration is an economically friendly approach to enhance wastewater treatment in developing nations with long sunshine hours.

Combined process of chemically enhanced sedimentation and rapid filtration for urban wastewater treatment for potable reuse

ABSTRACT The objective of this study is to propose a new post-treatment of effluents from Upflow Anaerobic Sludge Blanket (UASB) using rapid filtration, aiming at the production of water for potable reuse. The final quality of the effluent produced by the treatment using gravel, sand, clinoptilolite and activated carbon associated with disinfection was evaluated by physical chemical analysis, heavy metals and persistent organic contaminants. Experiments were carried out in jar test, filter operation time, evaluation of the efficiency using peracetic acid and free chlorine as disinfectant and all results were statistically analysed. The best conditions were those using 20 mg/L of ferric chloride and natural pH of the effluent (≈ 7.0), which resulted in less reagent consumption. The use of intermediate fund discharges made it possible to obtain approximately 91% of recovered water efficiency. The effluent treated under these conditions showed DOC <2.0 mg/L, COD <1.0 mg/L, BOD <1.0 mg/L, turbidity <1.0 NTU, TSS <1.0 mg/L, ammonia <0.1 mg/L, total phosphorus <0.1 mg/L and surfactants <0.1 mg/L. The disinfection process with free chlorine and PAA allowed the total inactivation of faecal coliforms and total coliforms. The treatment using rapid filtration with disinfection by chlorine reached the appropriate level for urban, environmental, industrial and indirect potable water reuse.

Study of the performance of a cylindrical flow-through electro-Fenton reactor using different arrangements of carbon felt electrodes: effect of key operating parameters.

In this work, a cylindrical flow-through electro-Fenton reactor containing graphite felt electrodes and an Fe(II) loaded resin was evaluated for the production of the Fenton reaction mixture and for the degradation of amoxicillin (AMX) and fecal coliforms containing aqueous solutions. First, the influence of several factors such as treatment time, current intensity, flow rate, and electrode position was investigated for the electrogeneration of H2O2 and the energetic consumption by means of a factorial design methodology using a 24 factorial matrix. Electric current and treatment time were found to be the pivotal parameters influencing the H2O2 production with contributions of 40.2 and 26.9%, respectively. The flow rate had low influence on the responses; however, 500mLmin-1 (with an average residence time of 1.09min obtained in the residence time distribution analysis) allowed to obtain a better performance due to the high mass transport to and from the electrodes. As expected, polarization was also found to play an important role, since for the cathode-to-anode flow direction, lower H2O2 concentrations were observed when compared with the anode-to-cathode flow arrangement, indicating that part of the H2O2 produced in the cathode was destroyed at the anode. A fluorescence study of hydroxyl radical production, on the other hand, showed that higher yields were obtained using an anode-to-cathode flow direction (up to 3.88µM), when compared with experiments carried out using a cathode-to-anode flow path (3.11µM). The removal of a commercial formulation of the antibiotic AMX was evaluated in terms of total organic carbon, achieving up to 57.9% and 38.63% of pollutant mineralization using synthetic and real sanitary wastewater spiked, respectively. Finally, the efficiency of the process on the inactivation of fecal coliforms in sanitary wastewater samples was assessed, reducing 90% of the bacteria after 5min of electrolysis.

Reduction of pH by homolactic fermentation as indicator of fecal coliform inactivation in wastewater

The purpose of this research was to evaluate the capability of lactic acid bacteria (LAB) to remove pathogens present in domestic wastewater, generated in the eco-touristic circuit Lomas de Lucumo (Lima, Peru). The pH decrease was used as an indicator of the elimination of fecal coliform bacteria in the treated water. Experiments included 36 treatments, which consisted of different mixtures of sugar molasses and a lactic acid bacteria inoculum (B-Lac) in proportions of 0, 1, 3, 5, 7 and 10% (v/v) and wastewater in a fixed proportion of 200 ml, under a completely randomized design (CRD) with factorial arrangement 6x6. The pH values on the third day were evaluated using an Analysis of Variance (ANOVA) followed by Tukey´s range test for mean differences (p &lt; 0.05). The different treatments were analyzed in a first stage for 9 days, after which the best three were selected for a second evaluation: T16 (3% molasses and 5% B-Lac), T22 (5% molasses and 5% B-Lac) and T33 (10% molasses and 3% B-Lac); results show that the interaction effect between the two variables is significant. Finally, treatment T16 was selected as the most efficient, reaching a pH of 4.08 in a short time (3 days) that assured the complete removal of fecal coliform bacteria (9.65x105 MPN/100 ml) in the wastewater.

Mechanisms of potassium permanganate pretreatment improving anaerobic fermentation performance of waste activated sludge

Potassium permanganate (KMnO4), one typical strong oxidant, is used extensively in various applications. However, its impact on anaerobic fermentation of waste activated sludge is unknown. This paper therefore aims to investigate its effect on generation of short-chain fatty acids (SCFAs) and qualities of fermentation liquor and fermented solid sludge. Experimental results showed that when KMnO4 increased from 0 to 0.1 g/TSS, the highest SCFAs production enhanced from 33.9 to 251.8 mg COD/g VSS. The mechanism analysis revealed that KMnO4 addition increased the disintegration of sludge cells and the degradation of substantial recalcitrant organics in sludge such as humus and lignocellulose, thereby provided more substances for SCFAs generation. Ultraviolet absorption spectroscopy analysis showed that KMnO4 addition destroyed unsaturated conjugated bonds and decreased organics aromaticity, thereby promoting humus and lignocellulose degradation. GC/MS analyses showed that several micro-molecular substances (e.g., acid-like, alkane-like, and alcohol-like organics) were generated from KMnO4 pretreated humus and lignocellulose, and some of them were demonstrated to serve as substrates to produce SCFAs. The enzyme activity and model-based analyses showed that although KMnO4 restrained all the microorganisms to some extends, the activities of SCFAs generators were much higher than those of SCFAs consumers. In addition, the sludge mixture was separated into liquid and solid fraction after anaerobic fermentation, and the components in fermentation liquid and solid sludge were tested. It was found that the addition of KMnO4 effectively reduced the categories and total detected frequency of refractory organic pollutants in fermentation liquid, which improved the quality of the produced SCFAs. KMnO4 addition also increased the inactivation of fecal coliforms and degradation of emerging contaminants in fermented sludge, which were helpful to its final disposal.

Predicting fecal coliform inactivation in a mixotrophic algal wastewater treatment system

Our previous reports have detailed the development of a pilot-scale algal wastewater treatment system (A-WWTS) utilizing a mixotrophic strain, Galdieria sulphuraria. This A-WWTS has consistently achieved discharge standards for organics and nutrients in a single step, concurrently reducing coliform bacteria to undetectable levels. Here, we present an approach to predict i) the fate of fecal coliform in this A-WWTS; and, ii) the fed-batch processing time required for a desired inactivation level. Specifically, a process model was developed to predict fecal coliform reduction under the synergistic effect of temperature, pH, and sunlight in terms of their individual first order inactivation rates. First-order temperature dependent inactivation rate at 20°C (k20) was established as 0.05h−1 with a temperature coefficient (θ) of 1.08. Inactivation coefficient due to the combined effects of sunlight was established as 0.647m2/MJ. The proposed approach was validated with experimental data from five scenarios; the quality of predictions of log removals spanning over five orders of magnitude (r2=0.947; n=12) was comparable to or better than those reported previously in inactivation studies. Utility value of this approach in forecasting fed-batch processing time under field conditions is illustrated.

Factors contributing to bacteria inactivation in the Galdieria sulphuraria-based wastewater treatment system

Our previous pilot scale studies showed concurrent removals of biochemical oxygen demand and nutrients, and inactivation of pathogens in urban wastewaters by an extremophilic alga, Galdieria sulphuraria. The current work evaluated the following as potential factors contributing to the observed pathogen inactivation, using E. coli as a surrogate: bacterial toxicity of algal metabolites, culture pH and temperature, sunlight, dissolved oxygen and adsorption to algal biomass. Microtox toxicity results implied that algal metabolites were free of bacterial toxicants as the toxicity in the reactor decreased from 38.8% to zero in 4 days. Low cultivation pH of 4 was identified as the primary factor influencing E. coli reductions. At neutral pH, under sunlight, E. coli were reduced to undetectable levels in 24 h. But, in the presence of live algal biomass and sunlight, E. coli were reduced to undetectable levels within 12 h. We attribute this accelerated reduction of E. coli to the synergistic effect of sunlight and elevated dissolved oxygen levels generated by biomass in the reactor. Temperatures below 45 °C and adsorption of bacteria to algal biomass did not appear to cause inactivation of E. coli. Simulation of pilot-scale conditions confirmed that the synergistic effects of pH, sunlight, algal biomass, and dissolved oxygen contributed to the superior fecal coliform inactivation observed in the algal wastewater treatment system.

Coupling Extracts of Plant Coagulants With Solar Disinfection Showed a Complete Inactivation of Faecal Coliforms

The small treated volume of water in polyethylene terephthalate (PET) bottles used in solar water disinfection (SODIS), and incomplete inactivation of bacteria at high water turbidity of ≥30 nephelometric turbidity units (NTU) are the major drawbacks of solar water treatment techniques. To address these problems, field experiments are conducted to inactivate faecal coliforms under natural sunlight. To assess the efficacy of large volumes, 3, 5, and 10‐L transparent plastic containers are used along with standard PET bottles (2 L) as SODIS reactors. To reduce the turbidity of the water, extracts of natural coagulants from tubers of Maerua subcordata and seeds of Moringa stenopetala are used. The results revealed that the turbidity of water and volume of containers affect the efficiency of SODIS, where the highest bacterial inactivation is observed at 10 NTU and a 0.5‐L PET bottle. However, the combined water treatment experiments of coagulation with extracts of either M. subcordata or M. stenopetala followed by SODIS on turbid water (150 NTU) showed 100% reduction of faecal coliforms with 4 h of exposure. This research demonstrates that a 10‐L container filled with water can be treated combining plant extracts with SODIS. The technology can be used for provision of safe and adequate drinking water for rural communities in developing countries.

Disinfection ability of hibiscus seeds in water treatment

The disinfecting ability of hibiscus seed proteins against Escherichia coli, total coliforms and faecal coliforms in water treatment was investigated. Hibiscus seeds are widely available as a primary source of protein in tropical countries. Using varying doses of extracts, partial inactivation of faecal coliforms and E. coli was achieved. Hibiscus sabdariffa crude extract (SCE) achieved 67% faecal coliform inactivation whereas Hibiscus cannabinus (kenaf) crude extract (KCE) achieved 57% using dosages of 200 mg/l. Additionally, E. coli were observed to be more sensitive to KCE than SCE, with maximum inactivations of 65% and 60%, respectively. Furthermore, complete bacterial regrowth was witnessed with the extracts after 72 h storage time. However, purified sabdariffa protein (PSP) and purified kenaf protein (PKP) showed complete (100%) bacterial inactivation post-treatment, using a dose of 1·48 mg/l. Additionally, PSP and PKP achieved 92% and 90% turbidity removal, respectively, from a value of 11·9 NTU. Therefore, the use of PSP and PKP in water treatment could improve access to clean water in developing countries.

The inactivation of fecal coliform using Fe3O4@Cu nanocomposite in real wastewater: emphasizing on synergic effect and inactivation mechanisms

The inactivation of fecal coliform using Fe3O4@Cu nanocomposite in real wastewater: emphasizing on synergic effect and inactivation mechanisms

Stabilisation and dewatering of primary sludge using ferrate(VI) pre-treatment followed by freeze-thaw in simulated drainage beds

This study evaluated the ability of potassium ferrate(VI) and freeze-thaw to stabilise and dewater primary sludge. Potassium ferrate(VI) additions of 0.5 and 5.0 g/L were used as a pre-treatment prior to freeze-thaw. Samples were frozen at −10, −20 and −30 °C, and were kept frozen for 1, 8 and 15 days. The samples were subsequently thawed at room temperature in a setup which allowed meltwater to be separated from the sludge cake via gravity drainage. The meltwater was characterised in terms of fecal coliform, soluble chemical oxygen demand (COD), soluble proteins, soluble carbohydrates, pH and turbidity. The sludge cake was characterised in terms of fecal coliform, total solids (TS) and volatile solids (VS). Freeze-thaw with gravity meltwater drainage reduced the sludge volume by up to 79%. After being frozen for only 1 day, the concentrations of fecal coliform in many of the primary sludge samples were reduced to <1000 MPN/g dry solids (DS), representing >3-log inactivation in some cases. However, pre-treatment of the primary sludge with ≤5.0 g/L potassium ferrate(VI) resulted in significant increases in soluble proteins, soluble carbohydrates, and sCOD, and reduced the effectiveness of stand-alone freeze-thaw. Follow-up experiments using higher doses ranging from 5.1 to 24.9 g/L of potassium ferrate(VI) demonstrated that >5-log inactivation of fecal coliform in raw primary sludge can be achieved within 15 min using 15 g/L of potassium ferrate(VI), and the resulting concentration of fecal coliform in the sludge was 1023 MPN/g DS. Pre-treatment with 22.0 g/L of potassium ferrate(VI), followed by freeze-thaw, with only 3 days frozen, reduced the concentration of fecal coliform to below the detection limit in the meltwater and the sludge cake. This demonstrates that potassium ferrate(VI) and freeze-thaw offers the flexibility to adjust the ferrate(VI) dose to meet treatment requirements for land application, and can be used as a stand-alone sludge treatment technology for primary sludge that achieves both treatment and dewatering.

Assessing iron and aluminum-based coagulants for odour and pathogen reductions in sludge digesters and enhanced digestate dewaterability

Anaerobic digestion (AD) is an effective way of recovering energy and nutrients from organic waste. However, several issues including the production of corrosive, highly odorous and toxic volatile sulfur compounds (VSCs) in digester biogas, and long digestion times to achieve sufficient pathogen reductions can limit its wider adoption. In this study, Kemira™ PIX-311 (ferric chloride), PAX XL-6 (aluminum chloride hydroxide sulfate), and PAX XL-19 (polyaluminum chlorohydrate) were added to the digester feeds to evaluate the effects on digester stability, organic removal, VSCs formation in digester headspace, pathogen removal and sludge dewaterability. After preliminary dose trials, two different doses of PIX-311, PAX XL-19, and a 1:1 mixture of PIX-311 and PAX XL-19 were selected. PAX XL-6 was removed from further study as dosing significantly increased VSC levels and the PAX XL-6 dosed digester exhibited signs of instability. During the total operation period of 100days, addition of PIX-311, PAX XL-19, a combination of PIX-311, PAX XL-19 at concentrations of 4000 and 4500mg/kg total solids (TS) to digester feed did not lead to process instability. Biogas yields of all metal added digesters were similar to that of the control (no metal addition) digester. PIX-311 achieved up to a 93% reduction in biogas VSCs, 82% better fecal coliform inactivation and exhibited improved dewaterability over the control digester. The PAX XL-19 dosed digester showed modest reductions in biogas VSC concentrations, pathogen levels and improved dewaterability versus the control. Metal addition can be an effective way to control odours from VSCs, pathogens and to improve dewaterability during AD.

Ferrrate(VI) and freeze-thaw treatment for oxidation of hormones and inactivation of fecal coliforms in sludge.

This study examined the individual and combined effects of potassium ferrate(VI) additions and freeze-thaw conditioning for the treatment and dewatering of wastewater sludge in cold climates, with particular focus on the inactivation of fecal coliforms and oxidation of estrogens, androgens, and progestogens. The first phase of the study evaluated the effects of potassium ferrate(VI) pre-treatment followed by freeze-thaw at -20 °C using a low (0.5 g/L) and high (5.0 g/L) dose of potassium ferrate(VI). The results showed that pre-treatment of anaerobically digested sludge with 5 g/L of potassium ferrate(VI) reduced the concentration of fecal coliforms in the sludge cake to below 100 MPN/g DS. The second phase evaluated the ability of ferrate(VI) to oxidise selected hormones in sludge. Anaerobically digested sludge samples were spiked with 10 different hormones: estrone (E1), 17α-estradiol, 17β-estradiol (E2), estriol (E3), 17α-ethinylestradiol (EE2), equilin, mestranol, testosterone, norethindrone and norgestrel in two groups of low (3-75 ng/mL) and high (12-300 ng/L) concentration ranges of hormones. The samples were treated with either 0.5 or 1.0 g/L of potassium ferrate(VI), and hormone concentrations were measured again after treatment. Potassium ferrate(VI) additions as low as 1.0 g/L reduced the concentration of estrogens in sludge. Potassium ferrate(VI) additions of 0.5 and 1.0 g/L were less effective at reducing the concentrations of androgens and progestogens. Increasing ferrate(VI) dose would likely result in more substantial decreases in the concentrations of fecal coliforms and hormones. The results of this study indicate that the combined use of freeze-thaw and ferrate(VI) has the potential to provide a complete sludge treatment solution in cold regions.

Sunlight inactivation of faecal coliforms in domestic wastewater

The relationship between sunlight effect, algal biomass and faecal coliform inactivation in wastewater pond treatment systems is still not clearly understood. Increased pH and dissolved oxygen concentration in treatment ponds results in an increased destruction of faecal coliforms. Increased algal growth however results in a decreased destruction of faecal coliforms due to light attenuation. Algae also releases variable amounts and types of organic matter at various rates and quantities depending on environmental conditions and this can either aid or retard faecal bacteria destruction. We investigated the effect of algal density on faecal coliform destruction under field conditions in sunlight and darkness and how this can be affected by light intensity. In darkness, increased inactivation of faecal coliform occurred with increasing algal density. Rates of decay of faecal coliforms were much faster in sunlight than in darkness even in the absence of algae. In sunlight, rates of decay of faecal coliforms increased with increasing algal density up to a chlorophyll-a concentration of 1.3±0.1 mg/L after which rates of decay decreased. Increased decay rates of faecal coliforms occurred with increasing light intensity or light input. With decreased light input of 20% of 213 W/m2, the optimum algal density for maximum faecal coliform decay decreased to a value which is 6–7 times the value of that under normal insolation of 213 W/m2. It is recommended that in future studies relating to the assessment of performance and estimation of rate of Escherichia coli or faecal coliform inactivation, one of the parameters that need to be reported as well is the insolation.

A study of low temperature inactivation of fecal coliforms in electrolyte solutions using hot air bubbles

A novel method to inactivate fecal coliforms in aqueous solutions, using a stream of hot air bubbles, without heating the solution above about 50°C was studied in this work. Initially, it was found that at high salt concentrations (e.g. 0.15 M NaCl), where bubble coalescence is inhibited, modest but consistent coliform inactivation rates were obtained for a range of fecal coliform contamination levels. That is, the coliform densities drop at a rate of 4% per min over the range 550–14,000 CFU/100 mL. More importantly, an analysis of the likely mechanisms involved in the inactivation process led to the use of lower level salt concentrations, targeted specifically at a reduction in the repulsive interaction forces between typical coliforms and hot air bubbles, rather than at bubble coalescence inhibition. The results obtained support the view that surface forces can strongly influence the coliform inactivation rate and that the addition of low concentrations of, for example, CaCl2, can increase inactivation levels by more than 1,000 times, without affecting bubble coalescence and bubble size.

A Review of the Mechanisms of Faecal Coliform Removal from Algal and Duckweed Waste Stabilization Pond Systems

The use of eco-technologies for wastewater treatment such as algal and duckweed-based pond systems is becoming popular in developing countries owing to its affordability and efficiency of pathogen removal in warm climates. The pathogen removal mechanisms of these treatment systems however is still not clearly understood and existing knowledge is also scattered in journals and books of different disciplines. The purpose of this paper is to provide a concise review of knowledge acquired in recent times on faecal coliform removal mechanisms in algal and duckweed ponds in a comparative way while identifying knowledge gaps that still exist. This review pays particular attention to little known removal mechanisms such as the role of algal biomass, attachment and sedimentation of faecal coliforms and the role of predation by macro-invertebrates and protozoans. Recent experiments showed that algal ponds, in comparison with duckweed ponds, are more efficient in faecal coliform removal due to the high pH and oxygenation that occur in the former and the rate of inactivation of faecal coliforms increases with increased algal biomass till a certain optimum concentration after which it decreases. This optimal algal concentration for maximum destruction of faecal coliforms can be affected by the quality and strength of the wastewater. Algae also appeared to have a destructive effect on faecal coliforms even in darkness, a phenomenon that may be the effect of toxic substances from the algae. Results also show that the role of invertebrates, particularly macro-invertebrates may be more important in duckweed pond systems. Removal of faecal coliforms through attachment and sedimentation in both duckweed and algal ponds appear to be dependent largely on concentrations of faecal coliforms present and to some extent on suspended plant and particulate matter concentrations. Wide variations in removal efficiencies were however observed. We conclude that the wide variations in removal efficiencies can be addressed by standardizing operating conditions of treatment systems. Further work is necessary to identify the substances produced by algae which appeared to be toxic to faecal coliforms as well as establishing the relative importance of predation by protozoans and macro-invertebrates in the removal of faecal coliforms.

Disinfection of an advanced primary effluent using peracetic acid or ultraviolet radiation for its reuse in public services.

The disinfection of a continuous flow of an effluent from an advanced primary treatment (coagulation-flocculation-sedimentation) with or without posterior filtration, using either peracetic acid (PAA) or ultraviolet (UV) radiation was studied. We aimed to obtain bacteriological quality to comply with the microbiological standard established in the Mexican regulations for treated wastewater reuse (NOM-003-SEMARNAT-1997), i.e., less than 240 MPN (most probable number) FC/100 mL. The concentrations of PAA were 10, 15, and 20 mg/L, with contact times of 10, and 15 min. Fecal coliforms (FC) inactivation ranged from 0.93 up to 6.4 log units, and in all cases it reached the limits set by the mentioned regulation. Water quality influenced the PAA disinfection effectiveness. An efficiency of 91% was achieved for the unfiltered effluent, as compared to 99% when wastewater was filtered. UV radiation was applied to wastewater flows of 21, 30 and 39 L/min, with dosages from 1 to 6 mJ/cm². This treatment did not achieve the bacteriological quality required for treated wastewater reuse, since the best inactivation of FC was 1.62 log units, for a flow of 21 L/min of filtered wastewater and a UV dosage of 5.6 mJ/cm².

Solar disinfection: an approach for low-cost household water treatment technology in Southwestern Ethiopia

Disinfection of contaminated water using solar radiation (SODIS) is known to inactivate bacteria. Its inactivation efficiency depends on local conditions where the disinfection is made. This study was aiming to test the efficiency of solar disinfection using different water parameters as low-cost household water treatment technology. Inactivation of microbes was tested using fecal coliform as test organism. The SODIS experiment was carried out at turbidity 2NTU, pH 7, and various water temperature (38.1°C, 41.8°C, 45.6°Cand 51.1°C) and solar intensities, using clear and black plastic bottles filled to different depths. The results show that the rate of microbial inactivation in relation to depth of water, turbidity, container type, intensity of light and color of container was statistically significant (p < 0.05). However, bottle placement, exposure and water pH were unrelated to microbial inactivation. Bacterial re-growth was not observed after solar disinfection. By adjusting the parameters, complete and irreversible fecal coliform inactivation was achieved within an exposure time of less than four hours in the areas where the solar irradiance is about 3.99 kW/m2 and above. Our results indicate that application of SODIS could play a significant role in the provision of safe water in rural communities of developing countries where there is ample sunshine, specifically in sub-Saharan African countries.

Self assembly of nanostructured hexagonal cobalt dendrites: an efficient anti-coliform agent

Highly crystalline self assemblies of three dimensional cobalt nanostructures are successfully synthesized by an electrochemical method without any template and surfactants. The cobalt nanostructures obtained by using two precursors, cobalt chloride (CoCl2) and cobalt acetate [(CH3–COO)2Co], shows similar dendritic structure, but with different hierarchical architecture. The architecture of cobalt dendrites (Co-DNDs) prepared by using CoCl2 consists of a long central trunk with hierarchical nanostructures of well aligned dendrites of length in the range 15–20 μm and sub branch is in the range 100–200 nm, while Co-DNDs prepared by using (CH3–COO)2Co additionally shows unique feature of hexagonal nanopoles orthogonal to main trunk. Well defined and highly crystalline Co-DNDs were obtained within thirty seconds at 15 V. Architecture of such well aligned and highly crystalline Co-DNDs with hexagonal fixtures within 30 seconds reaction is hitherto unattempted. The as-synthesized Co-DNDs showed an efficient antibacterial activity against model organisms, Bacillus subtilis NCIM 2063, Escherichia coli NCIM 2931, and fecal coliforms in a sewage waste. The inactivation of bacterial growth is due to the generation of reactive oxygen species (ROS) mediated rupture of cell membrane. An inactivation of fecal coliforms in the sewage wastewater is significant in eradicating water-borne diseases. This is an economical approach as compared to conventional and expensive metal nanoparticles like silver and gold.

Limits of UV disinfection: UV/electrolysis hybrid technology as a promising alternative for direct reuse of biologically treated wastewater

Although UV irradiation represents an energy efficient disinfection method, bacterial regrowth in UV irradiated secondary effluents is a serious problem for their direct reuse (e.g., for domestic or irrigation purposes). The decrease of the lethal UV fluence caused by coverings (scaling and biofouling) on quartz sleeves of UV lamps and/or fluctuating specific water parameters (suspended solids, transmittance or turbidity) results in a reversible inactivation of faecal coliforms ( Escherichia coli ). The reactivation of E. coli is increased with rising light intensity (≥470 Lux) and rising temperature (≥20 °C). The supplementation of UV disinfection with an electrolysis compartment ensures a reliable, sustained bacterial reduction and prevents reactivation of E. coli in UV irradiated (H = 138–140 J m−2) wastewater at a concentration of total oxidants of 0.5 mg L−1. The electric charge input of 0.012 Ah L−1 was lowest on MOX (mixed oxide) electrodes compared to particle BDD (boron-doped diamond) and thin film BDD electrodes. The formation of organic by-products (adsorbable organically bound halogens, trihalomethanes) ranged from marginal to moderate. In contrast to BDD electrodes, no chlorite, chlorate and perchlorate were observed on MOX electrodes. The energy consumption of the UV/electrolysis hybrid reactor was 0.17 kWh m−3.