A review of imperative technologies for wastewater treatment I: oxidation technologies at ambient conditions

Nowadays, due to the increasing presence of molecules, refractory to the microorganisms in the wastewater streams, the conventional biological methods cannot be used for complete treatment of the effluent and hence, introduction of newer technologies to degrade these refractory molecules into smaller molecules, which can be further oxidized by biological methods, has become imperative. The present work aims at highlighting five different oxidation processes operating at ambient conditions viz. cavitation, photocatalytic oxidation, Fenton's chemistry (belonging to the class of advanced oxidation processes) and ozonation, use of hydrogen peroxide (belonging to the class of chemical oxidation technologies). The work highlights the basics of these individual processes including the optimum operating parameters and the reactor design aspects with a complete overview of the various applications to wastewater treatment in the recent years. In the next article of this two article series on imperative technologies, hybrid methods (basically combination of the oxidation processes) will be discussed and the current work forms a useful foundation for the work focusing on hybrid technologies

On the behaviour, mechanistic modelling and interaction of biochar and crop fertilizers in aqueous solutions

Although the benefits of applying biochar for the purposes of soil conditioning and crop productivity enhancement have been demonstrated, relatively few studies have elaborated on its causal mechanisms, especially on the biochar-fertilizer interaction. Thus, in the present study, the ex-situ adsorptive potential of base activated biochar (BAB) towards plant nutrient immobilization and removal from aqueous solutions was investigated. Napier grass (Pennisetum purpureum) was utilized as the precursor to prepare slow vacuum pyrolysed char and its affinity towards adsorption of urea was examined at various process conditions. Low sorption temperatures, moderate agitation speeds and high initial concentration were seen to favour greater urea uptake by BAB. The sorption was exothermic, physical, spontaneous and had a pseudo-second order kinetic fit. Both surface and intra-particle diffusion governed the removal and immobilization of urea. Furthermore, process mass transfer was limited by film diffusion of urea to the external surface of the BAB. Equilibrium studies suggested that Dubinin-Radushkevich is the most appropriate model to describe the urea-BAB behaviour with maximum uptake, estimated to be 1115 mg·g−1. Through such ex-situ analysis, it could be possible to have prior knowledge, quantification and differentiation of the potential of chars manufactured from various feedstocks. This could then be used as an effective screening step in designing appropriate biochar-fertilizer systems for soil conditioning and help reduce the time and effort spent otherwise in long-term field studies

Vacuum pyrolysed biochar for soil amendment

Biochar, a highly carbonaceous charred organic material obtained from biomass conversion can be deliberately applied as a conditioner/ amender in order to improve soil quality and associated environmental services. Napier grass (Pennisetum purpureum), a lignocellulosic biomass, can potentially be used to produce biochar. The aim of the present work is to manufacture, comprehensively characterize, and apply biochar obtained from the vacuum pyrolysis and investigate its potential for soil amendment. Biochar produced from Napier grass was characterized for its pH, electrical conductivity, soil water retention capacity, surface acidity and/or basicity, elemental composition, Infrared spectra, X-ray diffraction spectra, surface area, porosity, soil-water relation and morphological properties. Experiments on the methylene blue adsorption of the biochar indicated an equilibrium uptake capacity of 35 mg.g−1 and showed good agreement with the Langmuir-Freundlich model. Kinetic studies revealed Lagergren pseudo-first-order fit with intra-particle diffusion appearing to be one of the rate controlling mechanisms. Pot trials with Cicer grown in neutral and acidic soil amended with biochar validated that biochar augmented plant growth in terms of enhanced biomass weight and number of seed germinations. The entire investigation revealed that the properties of the produced biochar are in line with those necessary for it to act as a suitable agent for soil amendment

Quantification of the energy required for the destruction of Balanus amphitrite larva by ultrasonic treatment

Ultrasonic treatment, a relatively less explored technology in water disinfection, was used to quantify the energy required for the destruction of larvae of barnacle Balanus amphitrite, which is a major marine fouling and a potential invasive organism. Since the power used and treatment time for disinfection are economically, and practically, the most important parameters, the energy required to pulverize the larvae into pieces ≤30 μm was determined as a function of the acoustic power density. The present investigation suggests that an ultrasonic system operating at 20 kHz and 0.0975 W/cm3 can effectively pulverize barnacle larvae having length (~440 μm) and breadth (~350 μm) within 45 seconds using 0.1 mJ/larva of pulverization energy. It was also observed that following pulverization of the larvae, the bacterial abundance increased and the rate of release of bacteria was dependent on power level and treatment time, which in turn decided the pulverization rate and hence the rate of release of bacteria

Rheological properties of concentrated distillery spent wash and some metal corrosion studies

185-193Spent wash generated by the alcohol distilleries is a major source of ground water pollution. Various treatment strategies, which include aerobic, anaerobic digestion, thermal treatment and incineration have been adopted with reasonable success. For the rigorous engineering analysis of any of these processes, the information regarding the physico-chemical properties of this eflluent such as density, surface tension and viscosity are essential. The rheological properties of concentrated distillery wastes at room temperature and elevated temperatures were measured. The rheological properties have been correlated to solid concentration of the waste in the dissolved and suspended state at room temperature. For highly concentrated wastes (viz. 50 % and 60 % by weight of solid concentration) the variation in rheological properties with temperature were also studied. A rheological model has been used to explain the observed results. The Bingham model was found suitable to explain the rheological properties of the concentrated distillery wastes at ambient temperature and elevated temperatures. 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Oscillating bubble concentration and its size distribution using acoustic emission spectra

New method has been proposed for the estimation of size and number density distribution of oscillating bubbles in a sonochemical reactor using acoustic emission spectra measurements. Bubble size distribution has been determined using Minnaert's equation [M. Minnaert, On musical air bubbles and sound of running water, Philanthr. Mag. 16 (1933) 235], i.e., size of oscillating bubble is inversely related to the frequency of its volume oscillations. Decomposition of the pressure signal measured by the hydrophone in frequency domain of FFT spectrum and then inverse FFT reconstruction of the signal at each frequency level has been carried out to get the information about each of the bubble/cavity oscillation event. The number mean radius of the bubble size is calculated to be in the range of 50-80 μm and it was not found to vary much with the spatial distribution of acoustic field strength of the ultrasound processor used in the work. However, the number density of the oscillating bubbles and the nature of the distribution were found to vary in different horizontal planes away from the driving transducer surface in the ultrasonic bath. A separate set of experiments on erosion assessment studies were carried out using a thin aluminium foil, revealing a phenomena of active region of oscillating bubbles at antinodal points of the stationary waves, identical to the information provided by the acoustic emission spectra at the same location in the ultrasonic bath

Hydrodynamics of Liquid-Liquid Flows in Micro Channels and Its Influence on Transport Properties: A Review

Hydrodynamics plays a major role in transport of heat and mass transfer in microchannels. This includes flow patterns and flow regimes in which the micro-channels are operated. The flow patterns have a major impact the transport properties. Another important aspect is the pressure drop in micro-channels. In the present review, the experimental and Computational Fluid Dynamics (CFD) studies covering all the above aspects have been covered. The effect of geometrical parameters like shape of channel, channel size, material of construction of channels; operating parameters like flow velocity, flow ratio and fluid properties have been presented and analyzed. Experimental and analytical work of different pressure drop models has also been presented. All the literature related to influence of flow patterns on transport properties like volumetric mass transfer coefficients (VMTC) and heat transfer coefficients (HTC) have been presented and analyzed. It is found that most works in Liquid-Liquid Extraction (LLE) systems have been carried out in slug flow and T-junctions. Models for coupled systems of flow and mass transfer have been presented and works carried out for different coupled systems have been listed. CFD simulations match experimental results within 20% deviations in quantitative and qualitative predictions of flow phenomena for most research articles referred in this review. There is a disparity in prediction of a generalized regime map and a generalized regime map for prediction of flow patterns for various systems would need the help of Artificial Intelligence