Colour removal from magnesium bisulphite pulp and paper mill effluent using lignite adsorption and salt coagulation
Creators: name: Yuliani, Galuh
Publisher: name: Monash University
Year: 2017
Subjects: Uncategorized

description: The removal of colour, organics and phosphorus from pulp and paper mill effluent and the development of colour of the wastewater were investigated. These contaminants are considered to be the most important due to their resistance over common treatment applied by the mill. Two approaches, adsorption and coagulation, were chosen for investigation of the removal of colour, organics and phosphorus from aqueous discharges of a bisulphite pulp and paper mill. Additionally, the colour generation induced by UV irradiation of the treated effluents was investigated. This study was carried out to explore the possibility of UV-induced colour development of the effluent over the long term and to characterize the colour producing species from the wastewater. Cheap and highly abundant brown coal (or lignite) was utilized as adsorbent for colour, phosphorus, and organics from the industrial effluent. Knowledge on the mechanism of brown coal adsorption, selectivity, the effect of pre-treatment and physical properties of brown coal is crucial for the future application of brown coal in the water industry. The mechanism of brown coal adsorption was investigated using various brown coal samples differing in physical and chemical composition and two model dye solutions, cationic (safranin) and anionic (alizarin red) dyes. The capacities of some brown coals (Loy Yang high Na and Yallourn) were higher than commercial coal-based activated carbon. However, the adsorption capacities of all brown coal samples for an anionic dye were very low, less than 3% of that for activated carbon. This result reveals the potential of brown coal to remove positively charged contaminants from aqueous solutions and suggests cation-exchange as the major mechanism involved. Effects of brown coal pre-treatment, drying and washing, were investigated. The equilibrium adsorption data were analysed using the two most popular adsorption isotherms, Langmuir and Freundlich. The Langmuir isotherm fitted most adsorption data of brown coal better than the Freundlich isotherm, supporting the concept of monolayer adsorption and the role of chemical adsorption in the mechanism. When applied to actual wastewater from a magnesium bisulphite pulp and paper mill, brown coal exhibited multi-component adsorption of colour, organics and phosphorus from the solution. Brown coal showed an ability to remove phosphorus from the wastewater, which could not be achieved with activated carbon; yet brown coal had significantly lower adsorption capacities for colour and organics than did activated carbon. This can be explained by the nature of organics and colour that carried negative charge in the wastewater as indicated by the zeta potential analysis. Another powerful technique for organic removal, coagulation, was then chosen to significantly reduce colour and organics content of the effluent. Coagulation using trivalent salts was selected to efficiently remove colour, organics and total phosphorus in the treated and untreated wastewater solution. Selectivity of salt-induced coagulation was achieved and showed the following trend of removal efficiency: colour ~ total phosphorus &gt; TOC. The removal of colour and total phosphorus from concentrated pulp mill effluents were above 90%. The coagulation method was proven to be superior for the remediation of both treated and untreated effluent from pulp and paper industry. However, a small amount of colour and organics still persisted in the wastewater which may lead to colour development after treatment at the collecting discharge point. The Photometric Dispersion Analyzer (PDA) and Focused Beam Reflectance Measurement (FBRM) techniques were utilised to study the coagulation kinetics of the wastewater upon addition of salt. The involvement of fast aggregation and adsorption in the coagulation mechanism were revealed. The high critical coagulation concentration (CCC) and the significant role of trivalent salts in the coagulation process indicated the involvement of complexation reactions prior to coagulation. In coagulation, pH was also found to be a dominant factor affecting efficiency. The UV-induced colour generation of the effluent from pulp and paper industry was studied using UV-irradiation at 302 nm and 254 nm. Lignin derived compounds were suspected to be responsible for colour growth of pulp and paper wastewater. Three model compounds, lignosulfonic acid, humic acid and vanillin, were selected and studied as comparison. The yellowing rate of the wastewater solution was found to be similar to that of the model lignosulfonic acid solution supporting the occurrence of lignin compounds in the wastewater. The yellowing rate of humic acid was lower than the wastewater solution, but the yellowing rate for vanillin was significantly higher than that of the wastewater solution. The irradiation products were analysed using High Performance Liquid Chromatography (HPLC), UV spectroscopy, Electrospray Mass Spectrometry (ES-MS), Proton Nuclear Magnetic Resonance (1H-NMR) and Fourier Transform Infrared Spectroscopy (FTIR). The mechanism of wastewater yellowing upon irradiation was suspected to mimic the mechanism of photo-yellowing of paper. The result also suggested that UV-induced chemical reactions may be important in the aqueous discharge of pulp and paper mill effluent that could potentially enhance its colour.