Adsorption of phosphorus onto nanoscale zero-valent iron/activated carbon: removal mechanisms, thermodynamics, and interferences

This study investigated removal mechanisms, thermodynamics, and interferences of phosphorus adsorption onto nanoscale zero-valent iron (nZVI)/activated carbon composite. Activated carbon was successfully used as support for nZVI particles to overcome shortcomings of using nZVI include its tendency to aggregate and separation difficulties. A comprehensive characterization was done for the composite particles, which revealed a high specific surface area of 72.66 m2/g and an average particle size of 37 nm. Several adsorption isotherms and kinetic models have been applied to understand the removal mechanisms. Adsorption isotherm is best fitted by Freundlich and Langmuir models, which indicates that the estimated maximum phosphorus adsorption capacity is 53.76 mg/g at pH 4. Adsorption kinetics showed that the chemisorption process behaved according to a pseudo-second-order model. An adsorption mechanism study conducted using the intra-particle diffusion and Boyd kinetic models indicated that the adsorption rate is limited by surface diffusion. A thermodynamic study showed that phosphorus removal efficiency increased as the solution temperature increased from 15 to 37 °C. Finally, the results of an interference study showed that the presence of Ni2+, Cu2+, Ca2+, Na+ cations, nitrate ions (), and sodium acetate improves removal efficiency, while the presence of sulfate ions () and urea reduces removal efficiency.

The Effect of Fe(II), Fe(III), Al(III), Ca(II) and Mg(II) on Electrocoagulation of As(V)

The interaction between metal chlorides and electrocoagulation was tested. Precipitation of As(V) was found to be optimal at pH 4.9 using FeCl2, 2.6 for FeCl3, 3.8 using AlCl3, 11.6 using CaCl2 and 8.6 using MgCl2. As(V) removal through electrocoagulation went down as initial pH (pHi) of the solution increased. Addition of FeCl2 increased removal of As(V) at all pHi but was not able to achieve full removal at pHi 7. FeCl3 had a similar effect but a lower Fe(III) concentration of 30 mg/L was not sufficient for full removal at pHi 5 either. AlCl3 addition reduced removal efficiency at pHi 3 but removed all or most As(V) through precipitation at pHi 5 and 7, with complete removal followed through electrocoagulation. The addition of CaCl2 and MgCl2 resulted in nearly identical behavior. Addition of either at pHi 3 had no influence, but at pHi 5 and 7 caused complete removal to take place.

Assessment of Domestic Wastewaters as Potential Growth Media for Chlorella vulgaris and Haematococcus pluvialis

Domestic wastewater contains chemical compounds that can be used as nutrients for microalgae. Removing these chemical compounds from wastewater by microalgae might help in reducing the operation cost of wastewater management while minimizing the cultivation cost for large-scale microalgae metabolite production. In this study, domestic wastewater collected from Indah Water Konsortium (IWK), Kuala Lumpur, Malaysia, was assessed as growth media for two types of microalgae, namely Chlorella vulgaris and Haematococcus pluvialis. The biomass growth and nutrient removal efficiency of total nitrogen (TN), total phosphorus (TP), and total ammonia (TAN) in different concentrations of diluted wastewater were measured. The results showed that biomass concentration (0.227 g/L), biomass productivity (0.029 g/L/day), and specific growth rate (0,284 d-1) yielded by C. vulgaris in 14 days of 80% wastewater were comparable to those microalgae grew in standard Bold’s Basal medium (BBM). Besides, C. vulgaris grew in 50% wastewater to remove TN, TP, and TAN with the highest removal efficiency (>88%). For H. pluvialis, the biomass concentration in all wastewater concentrations was lower than BBM. The removal efficiencies of TN and TP were lower than 55%, but more than 80% for removal efficiency of TAN in 50% and 80% wastewater. Hence, C. vulgaris has better growth performance and nutrient removal efficiency than H. pluvialis. These findings indicated that IWK domestic wastewater could be used as growth media for microalgae, especially C. vulgaris.

Synthesis and Performance of PAFS Coagulant Derived from Aluminium Dross

Polymerised aluminium ferric sulphate (PAFS) was prepared from aluminium dross as a coagulant in wastewater treatment. The effects of leaching time, leaching temperature, and sulfuric acid concentrations on the turbidity removal of the wastewater were investigated, and the optimum conditions were determined using response surface methodology. The results showed that the optimum PAFS preparation conditions were at a leaching time of 60 minutes, a leaching temperature of 65°C, and a sulfuric acid concentration of 1 mol/L. Furthermore, experiments were performed to investigate the effect of coagulant dosages using the PAFS prepared under the optimum leaching conditions, settling time and initial pH of the wastewater on the turbidity removal efficiency. As a result, it was found that the optimum coagulation conditions for PAFS coagulants were at a settling time of 15 minutes, coagulant dosage of 0.5g, and raw water pH 8. Under these optimum conditions, the turbidity removal efficiency of the wastewater was 91.45%. The purpose of this study was to investigate the possibility of aluminium dross utilisation as a coagulant agent for wastewater treatment. Therefore, it can be concluded that PAFS prepared by leaching metal oxides from aluminium dross is an effective wastewater coagulant.

Effect of tetracycline on nitrogen removal in Moving Bed Biofilm Reactor (MBBR) System

The effect of tetracycline (TC) on nitrogen removal in wastewater treatment plants has become a new problem. This study investigated the effects of TC on nitrogen removal using a Moving Bed Biofilm Reactor system. The results showed that there was no significant effect on nitrogen removal performance when the concentration of TC was 5 mg/L, and that the total nitrogen (TN) removal efficiency could reach 75–77%. However, when the concentration of TC increased to 10 mg/L, the denitrification performance was affected and the TN removal efficiency decreased to 58%. The abundance of denitrifying bacteria such as those in the genus Thauera decreased, and TC-resistant bacteria gradually became dominant. At a TC concentration of 10 mg/L, there were also increases and decreases, respectively, in the abundance of resistance and denitrification functional genes. The inhibitory effect of TC on denitrification was achieved mainly by the inhibition of nitrite-reducing bacteria.

Effect of Oxidizers on Sulphide Removal from Hair Dissolving Liming Wastewater in Tannery

Liming and unhairing is the conventional operation in the tannery where raw animal skins are treated with sodium sulphide and calcium hydroxide to remove keratin proteins e.g., hair and wool epidermis and to dissolve nonstructural proteins. The hair dissolving liming process discharges wastewater containing soluble sulphide. In acidification, the sulphide in wastewater generates toxic hydrogen sulphide, which has a negative impact on the environment. In this present study, the efficiency of hydrogen peroxide (H2O2) and sodium chlorite (NaClO2) oxidizers are compared to remove sulphide from the hair dissolving liming wastewater. The soluble sulphide in the raw liming wastewater was 3666 mg/L. At optimized dose and pH for H2O2 and NaClO2 soluble sulphide in the solution were 109.2 and 54.6 mg/L, respectively. The sulphide removal efficiency for H2O2and NaClO2 were 97.0% and 98.5%, respectively at an optimum pH (pH 7). Before and after treatment the physicochemical parameters of the liming wastewater were analysed by observing different water quality parameters viz: pH, TDS, EC and salinity. At optimized condition TDS and salinity removal efficiency was 47.2%, 52.3% and 8.1%, 11.2% for H2O2 and NaClO2, respectively. This simple and easy method would be effective for treating hair dissolving liming wastewater in reducing soluble sulphide discharge from the tanneries. Journal of Engineering Science 12(3), 2021, 67-72

Removal of Excessive Nitrogen and Phosphorus from Urban Wastewater Using Local Microalgal Bloom

The organic content from urban wastewater is treated with various conventional processes efficiently. However, for biological treatment of secondary effluent containing excessive inorganic nitrogen and phosphorus, microalgae can be used. In this study, algal strains have been collected from locally available natural blooms and cultured in a BG-11 medium. Spirulina sp., the blue-green algae, dominant over the other species within the natural bloom, is applied in ten different dosages (0.2-2.5 g/L) to the synthetic wastewater with a 3-day hydraulic retention time. The removal efficiency of nitrate, ammonia, and phosphate have been observed to be about 60%, 30%, and 54% respectively. The highest removal efficiency has been found at 2.5 g/L of microalgae dose. Linear forms of Langmuir and Freundlich isotherms have been used for biosorption modeling, and both isotherms fit well with R2>60% and NRMSE<11% in all cases. Additionally, the separation factor and the adsorption intensity represent the favorability of the biosorption process. Journal of Engineering Science 12(3), 2021, 19-27